On the EA-40 two-part glue container, it mentions a temperature of 73°, but I've seen online videos where bowyers bring their heatbox temperature way higher.
What is the recommended heatbox temperature for laminated bows when using EA-40?
and also,
What is the recommended duration of heatbox cook time?
Thanks!
I still run 180 degrees, only because the snap disc I bought from Elmont who knows how long ago still works.
I leave the form in 4-5 hours. I reckon if I built over 3-4 bows per year I might look into the heat strips or at least an adjustable thermostat.
Thanks so much! You're awesome. I appreciate it. I'm curious about the heat strips too! Please keep me in the loop if you find any that work well.
Quote from: kennym on September 23, 2025, 08:28:51 PMI still run 180 degrees, only because the snap disc I bought from Elmont who knows how long ago still works.
I leave the form in 4-5 hours. I reckon if I built over 3-4 bows per year I might look into the heat strips or at least an adjustable thermostat.
Kenny,
Does yours have 300 watt bulbs? 4 for the limb box and 3 for the riser? I think the box I have was made from those plans and I'm wondering if I should stay with the 300 watt bulbs or could I drop some of the wattage down, I'm in need of some new bulbs and was just getting ready to hit the checkout button when I seen this post.
Dan
I use 3 200 watt bulbs. I have found that getting the surface temp to 130 and letting them cool in the box works well. I always mix more resin than hardener also.
I have 6 bulbs, usually unscrew a couple, think they are 150s , On curvy bows I unscrew the end ones to protect the hose from too much heat...
Quote from: kennym on September 25, 2025, 07:58:08 AMI have 6 bulbs, usually unscrew a couple, think they are 150s , On curvy bows I unscrew the end ones to protect the hose from too much heat...
Thanks, Good idea about the outside bulbs.
I use heat strips myself. 160 degrees for 30-40 minutes will cure the epoxy. Another 20 minutes for cool down.
Hot boxes take much longer to get that epoxy cured. I used a Xmas tree timer on mine and kept the box at 180 degrees for 5 hours... you need a thermostatic shut off to regulate temp on those hot boxes that shut the bulbs off when it hits 180.
I use heat strips too. For 1-pieces I was starting at 120 and going up 10 degrees every 30 minutes too 160. After reading kirkl post I tried limbs for 3-piece 30 minutes at 150 then another 30 at 160. Seemed to work well.
Where is people getting the heat strips from? I might build a setup for 2" width if I can find them.
Quote from: TC209X50 on October 03, 2025, 08:47:22 AMWhere is people getting the heat strips from? I might build a setup for 2" width if I can find them.
I really can't help with where to buy heat strips. I used to sell them years ago when everyone was using the silicone heat strips. But.... The damn things were not very dependable, and life expectancy was all over the place. The company I purchased them from replaced a few of them under warranty at first, but they finally discontinued the warranty.... It was a nightmare. I finally gave up on them and started messing around with building my own low voltage heat strips using various ideas and controllers with some success, but no longevity. Then I stumbled on to someone using stainless steel pressure strips and a battery charger. I've used that system very successfully for many years now. The down side has been the chargers only last for about 150 bows. I got over 200 bows out of one though... Now it's getting harder to find the right type of battery charger that will work for this application. The new electronic chargers won't put up with the abuse, and have a safety shut off. Using a battery charger with a voltage regulator is serious battery charger abuse, and the only last so long...
If this is something you are interested in using email me at kirk@bigfootbows.com and I can provide a detailed step by step instruction I wrote up on how to set this up.... Kirk
I wonder if there would be a way to do it with a voltage regulator and plug straight to the wall(without starting a fire or popping your breaker)? Any electricians on here????
Quote from: Watsonjay on October 06, 2025, 01:03:01 PMI wonder if there would be a way to do it with a voltage regulator and plug straight to the wall(without starting a fire or popping your breaker)? Any electricians on here????
Something like a Wall Wart power supply should be able to do it, assuming it is properly sized for the power requirements. It would also provide better control over the voltage and amperage to reduce risk of shock or fire, etc.
Many of the battery chargers used for charging the lithium ion batteries used in radio controlled aircraft offer a controllable constant voltage/amperage power supply intended to be used for hot wire cutting of foam. If properly sized for the power requirements this should also work.
Mark
I honestly can't see those small ac/dc power suppliers being powerful enough to heat up a 22 gage piece of stainless steel 6' long, much less two of them. My set up has a voltage regulator and requires 40-65 volts to the charger.
I was thinking more of a small buzz box welder might be the ticket.
Quote from: Kirkll on October 08, 2025, 10:26:51 AMI honestly can't see those small ac/dc power suppliers being powerful enough to heat up a 22 gage piece of stainless steel 6' long, much less two of them. My set up has a voltage regulator and requires 40-65 volts to the charger.
I was thinking more of a small buzz box welder might be the ticket.
Well, properly sizing your power supply is the big trick. I wasn't suggesting that a wall wart would be big enough, just that that is the sort of power supply that people could look for.
A small welder might work if it gives you what you need in terms of volts and amps. Lots of the small ones only have a 20% duty cycle rating, so you would have to watch that as well to avoid problems there.
Mark
A lot of these newre battery chargers have a digital display and circuit boards with built in saftey controls that wont allow you to use them for heating up a stainless steel strip. It automatically trips a breaker well before you get any heat built up, and needs to be reset.
Trying to find the older style battery charger with manual controls is getting harder to find anymore. If someone comes up with a better solution i'm all ears. Kirk
As I already stated IM not an electrician. So using and adjustable voltage regulator plugged straight into wall then connected to heat strips wouldn't work? Assuming you need it on a big 40-60 amp breaker based off of what you guys are saying .Just trying to figure out a way to eliminate the battery charger/power supply that will burn out.
Good way to get your balls shocked off... :biglaugh: let me know how that works out for you...
Thats why I was asking :goldtooth:
Quote from: Watsonjay on October 11, 2025, 09:11:05 PMAs I already stated IM not an electrician. So using and adjustable voltage regulator plugged straight into wall then connected to heat strips wouldn't work? Assuming you need it on a big 40-60 amp breaker based off of what you guys are saying .Just trying to figure out a way to eliminate the battery charger/power supply that will burn out.
You need to convert from the AC of the wall outlet to DC out to the strips. The battery charger/power supply does this for you and insulates you from the mains power to prevent the electrocution Kirk mentions.
If you size the power supply correctly it will not burn out and will provide years of service.
Mark
Quote from: mmattockx on October 12, 2025, 07:03:45 PMQuote from: Watsonjay on October 11, 2025, 09:11:05 PMAs I already stated IM not an electrician. So using and adjustable voltage regulator plugged straight into wall then connected to heat strips wouldn't work? Assuming you need it on a big 40-60 amp breaker based off of what you guys are saying .Just trying to figure out a way to eliminate the battery charger/power supply that will burn out.
You need to convert from the AC of the wall outlet to DC out to the strips. The battery charger/power supply does this for you and insulates you from the mains power to prevent the electrocution Kirk mentions.
If you size the power supply correctly it will not burn out and will provide years of service.
Mark
IC thanks for the explanation. Now how to figure out what size power supply I need.
When I get back to the shop tomorrow I'll attach a link with my set up. I figure I get 200-300 bows out of a battery charger before it pukes..... So the cost per bow is about $1.50. I can live with that.... Kirk
Quote from: Kirkll on October 13, 2025, 01:24:49 AMWhen I get back to the shop tomorrow I'll attach a link with my set up. I figure I get 200-300 bows out of a battery charger before it pukes..... So the cost per bow is about $1.50. I can live with that.... Kirk
Seems like a good deal as long as you can keep finding the battery chargers.
Quote from: Kirkll on October 13, 2025, 01:24:49 AMWhen I get back to the shop tomorrow I'll attach a link with my set up. I figure I get 200-300 bows out of a battery charger before it pukes..... So the cost per bow is about $1.50. I can live with that.... Kirk
Have you ever measured the voltage and amps going out to the strips? If we know that then it would make shopping for a power supply much easier.
Mark
Nope.... The battery charger plugs into the 120 volt voltage regulator and has a 10 amp fuse. The voltage regulator has that fuse. I tried a smaller regulator with a 5 am fuse and it kept popping. So I know the battery charger is drawing over 5 amps.
The power going to the stainless steel strips changes with the amount of voltage the charger is getting. The AC voltage varies between 35-55 volts to keep the heat temp between 160-180. I have a heat probe thermometer with a high temp alarm that goes off at 185 degrees. I'll often crank the voltage up to 55 volts to bring the temp up quicker, then dial it back down a bit once the alarm goes off. Winter time and colder temps require a bit higher voltage too. When I'm doing a set of limbs I get the voltage setting dialed in on the first limb, and just leave it there for the second limb so they both cure at the same temp. The battery charger has a timer on it. I typically set the timer for an hour. The temp slowly comes up to 160 in the first 20-30 minutes and then cooks for 30 minutes.
I could get my volt meter out next lay up and check the DC voltage input if you like.
Kirk
Im liking that welder idea as you can usually set the voltage.
Quote from: Kirkll on October 13, 2025, 11:43:06 AMI could get my volt meter out next lay up and check the DC voltage input if you like.
Kirk
That would be very helpful. We can extrapolate the approximate amperage to the strips from the power the battery charger is drawing from there.
Mark
Quote from: mmattockx on October 14, 2025, 10:35:02 AMQuote from: Kirkll on October 13, 2025, 11:43:06 AMI could get my volt meter out next lay up and check the DC voltage input if you like.
Kirk
That would be very helpful. We can extrapolate the approximate amperage to the strips from the power the battery charger is drawing from there.
Mark
The battery charger is drawing power from an AC voltage regulator between 35-55 volts. I can measure the battery chargers DC output to the strips though.
I'm afraid using a small welder isn't going to work unless it's an inverter design with a built in voltage regulator. Even then, those welders are such high voltage designed for welding, I'm uncertain whether a std voltage regulator would handle it without blowing fuses. But.... My knowledge of AC/DC electricity is limited.
Kirk
Quote from: Kirkll on October 14, 2025, 11:55:25 AMQuote from: mmattockx on October 14, 2025, 10:35:02 AMQuote from: Kirkll on October 13, 2025, 11:43:06 AMI could get my volt meter out next lay up and check the DC voltage input if you like.
Kirk
That would be very helpful. We can extrapolate the approximate amperage to the strips from the power the battery charger is drawing from there.
Mark
The battery charger is drawing power from an AC voltage regulator between 35-55 volts. I can measure the battery chargers DC output to the strips though.
I'm afraid using a small welder isn't going to work unless it's an inverter design with a built in voltage regulator. Even then, those welders are such high voltage designed for welding, I'm uncertain whether a std voltage regulator would handle it without blowing fuses. But.... My knowledge of AC/DC electricity is limited.
Kirk
Sounds like I may have to buy a couple of those battery chargers and save a couple as backup. Although as few of bows as I make one would probably last me a decade or two.
Here is a pretty detailed instruction write up i did some time ago.
Bow Press Heat Strips
This system for building laminated fiberglass bows is the best I've come up with in 15 years. But.... There are a few details in getting set up and operation that needs to be documented here.
First of all you will need 22 gage 304 stainless steel strips that are used both top and bottom in your form. I had mine cut to 1.5" and 1.75" widths and 72" lengths prior to shipping. You want these "Cut" not sheared too. You want enough length on these strips to have about 3" sticking out of each end of your form. I purchased enough strip material to have a pair for each bow form I use. I put the bottom strip in the form and attach it permanently and leave it there. Here is the link to my supplier:
https://www.stainlesssupply.com/order-metal-online/docs/g1c1045s1ss0p0/304-stainless-steel-sheet-4-finish.htm
........
Next you will need a fairly large battery charger that has manual settings. These are difficult to find now with all the electronic safety over ride models they have available now. The automatic ones with circuit boards will not work for what we are using this for. Look at the photo of the charger I use.
https://photos.app.goo.gl/SxemPLaXwT66Ad6B6
This one below will NOT work
https://www.amazon.com/Schumacher-SC1353-Wheeled-Battery-Charger/dp/B07BVFGVQ1/ref=sr_1_21?crid=2O3KDCXISAPSA&keywords=battery+charger+automotive&qid=1642610980&sprefix=battery+charger%2Caps%2C399&sr=8-21
This manual wheel type below is what you want.
https://www.amazon.com/Schumacher-Manual-Wheel-Charger-Engine/dp/B08PQ28NPB/ref=sr_1_27?crid=3G7TN835WBGWC&keywords=large+battery+charger&qid=1642611374&sprefix=large+battery+chargers%2Caps%2C195&sr=8-27
OK..... once you have your brand new battery charger, you need to tear it apart and rewire the cooling fan. There is a small fan that runs on 110 volts that needs its own power source. Why? Because the battery charger is going to run off of the voltage regulator at a reduced voltage..... That reduces the voltage to the cooling fan too, and slows it way down if it doesn't have its own power source, and..... it WILL over heat the fan and the charger, and eventually burn up.... Trust me on this one..... The only other option is to attach another fan to the battery charger body that blows cool air into it while its running. This is real important.
See the extra lamp cord I have plugged in to 110 and notice the battery charger plugs into the voltage regulator.
https://photos.app.goo.gl/T5qa6trSMqEaEx7J8
............
Next you need a voltage regulator. This will adjust the temperature of your heat strips. Get the "10 amp" version.... The 5 amp model will be popping fuses all the time. This is what you want.
https://www.amazon.com/LVYUAN-Variable-Transformer-Regulator-110V-120V/dp/B082KYKP9P/ref=sr_1_6?crid=3PF7ACKQJN850&keywords=voltage%2Bregulator%2B120v&qid=1642611136&sprefix=voltage%2Bregulator%2Caps%2C141&sr=8-6&th=1
https://photos.app.goo.gl/sKNmmsB6kfPizvtP9
The last item needed is an accurate thermometer. There are many different types of probe thermometers out there, but I like this one the best because it has a high temp alert built into it.... I can set the alarm for 180 degrees and if the strips get too hot it alerts me and I can turn down the voltage a bit.
Here is what I use. https://photos.app.goo.gl/ZyzWkz1hz3vHBVfs5
OK..... so now you have all your parts and pieces and equipment, and have a set of heat strips ready to go....You install one in the bottom of your form, wrap your bow laminations in a thin painters plastic , and put them directly on the heat strip. Then put the other heat strip directly on top of the limb and use zip ties to hold everything tight to the form. Take care to align the heat strips so they are the same length coming out of the form, and use a small clamp, or needle nose vise grips to clamp the two heat strips together on one end, and the battery charger clamps red on one strip, and black on the other. Be sure these two do not touch each other. I separate them with a scrap piece of wood lam.
Next is your air hose and button up your form. Then slip your temp probe in between the air hose and the top of the heat strip and give that hose about 20-25# of pressure. Check your lamination alignment and let it set 60 seconds before going up to 50-60#s of pressure.... No more than that is needed. I've laid up limbs completely using 25# before and they came out fine.... That was an ooops though... Recurve limbs need that extra pressure.
Now turn on the voltage regulator and adjust the voltage to about 40-45 volts. That is a good place to start for 2 -36" heat strips.... One piece bows with long heat strips will need more voltage, and going from 1.5" width to 1.75" width needs adjustment too. You will have to do some dry trials to establish the right settings. But what you want is the temp to slowly rise to 160 degrees in about 30 minutes and stay between 160-180 for another 20-30 minutes. I set my timer on the battery charger for one hour and its perfect every time once I have my voltage setting established. Btw.... Hot or cold temp in the shop can effect the setting a bit too.
The only other thing of note is to wait until the temp cools to 90 degrees before removing them from the form. You could easily lay up 3 sets of limbs per day with this set up.
Here are some of my bow forms I have set up.
https://photos.app.goo.gl/1ihdPa5SExkyBCma7
Kirk
Quote from: Watsonjay on October 14, 2025, 12:07:43 PMQuote from: Kirkll on October 14, 2025, 11:55:25 AMQuote from: mmattockx on October 14, 2025, 10:35:02 AMQuote from: Kirkll on October 13, 2025, 11:43:06 AMI could get my volt meter out next lay up and check the DC voltage input if you like.
Kirk
That would be very helpful. We can extrapolate the approximate amperage to the strips from the power the battery charger is drawing from there.
Mark
The battery charger is drawing power from an AC voltage regulator between 35-55 volts. I can measure the battery chargers DC output to the strips though.
I'm afraid using a small welder isn't going to work unless it's an inverter design with a built in voltage regulator. Even then, those welders are such high voltage designed for welding, I'm uncertain whether a std voltage regulator would handle it without blowing fuses. But.... My knowledge of AC/DC electricity is limited.
Kirk
Sounds like I may have to buy a couple of those battery chargers and save a couple as backup. Although as few of bows as I make one would probably last me a decade or two.
Even cranking out 50 bows a year or more, these chargers last 4-5 years. i'm on my 3rd charger now. That's why i never pursued it further. This is a pretty user friendly system that is safe, and the stainless steel strips are bullet proof. They sand easily if you get epoxy on them without distorting the surface....
The only thing i didn't mention with my build instructions is to purchase enough stainless steel to cover all your forms. I leave the bottom one in the form and screw my limb stop on top of it and leave 3" hanging out of the form on each end to attach the battery charger clamps on one end, and easily clamp the other end together with needle nose vise grips. Kirk
Quote from: mmattockx on October 14, 2025, 10:35:02 AMQuote from: Kirkll on October 13, 2025, 11:43:06 AMI could get my volt meter out next lay up and check the DC voltage input if you like.
Kirk
That would be very helpful. We can extrapolate the approximate amperage to the strips from the power the battery charger is drawing from there.
Mark
OK... i just laid up a couple sets of limbs and took some voltage readings with my multi meter. The settings on the charger has 3 settings 12V - 10amp, 12 volt-40 amp, and a 12 volt- 200amp used for starting vehicles. i run my heat strips on the low setting 12 volt-10 amp. Then i turn the AC voltage regulator knob powering the charger up to about 45 volts and the amperes gage on the carger hits 50 amps.
Using the voltage meter at the heat strips, it is only showing 2.43 DC volts. It takes about 20 minutes to hit 160-170 degrees. kirk
From Kirk's voltage reading we can determine what power supply can be used for heat strips.
I had asked a few years back if anyone using heat strips could tell me what voltage and current was applied to the strips but no one could tell anything other than "I set this to this and that to that" and off we go.
So, with 50 amps and 2.43 volts the results in 121.5 watts of power dissipated in the heat strips. That seems very reasonable to me; 120 watts is a lot of power and when concentrated in the strips will result in a lot of heat.
There are many power supplies that can be used. I would recommend a 300 watt power supply, but higher wattage cannot hurt. If you run 12 volts at 10 amps you get 120 watts.
A quick web search results in a bunch of 0-30 volt, 10 amp, supplies that will work for less than $100. A higher current supply might be more desirable. Look for a supply that has current and voltage that can be set. Any voltage and current combination that gives you 120 watts will work. W = V x A.
BTW Kirk, the way you are using the battery charger is probably why they don't last. Those chargers want to put out 6, 12 or even 24 volts. Running at full 50 amp current at such low voltage with other than 110 volts AC on the input is making the regulator circuitry do unnatural acts and something will fail.
I decided not to change to heat strips because I don't make that many bows and my easy bake oven works just fine.
Quote from: Cupcake on November 04, 2025, 07:50:31 PMFrom Kirk's voltage reading we can determine what power supply can be used for heat strips.
I had asked a few years back if anyone using heat strips could tell me what voltage and current was applied to the strips but no one could tell anything other than "I set this to this and that to that" and off we go.
So, with 50 amps and 2.43 volts the results in 121.5 watts of power dissipated in the heat strips. That seems very reasonable to me; 120 watts is a lot of power and when concentrated in the strips will result in a lot of heat.
There are many power supplies that can be used. I would recommend a 300 watt power supply, but higher wattage cannot hurt. If you run 12 volts at 10 amps you get 120 watts.
A quick web search results in a bunch of 0-30 volt, 10 amp, supplies that will work for less than $100. A higher current supply might be more desirable. Look for a supply that has current and voltage that can be set. Any voltage and current combination that gives you 120 watts will work. W = V x A.
BTW Kirk, the way you are using the battery charger is probably why they don't last. Those chargers want to put out 6, 12 or even 24 volts. Running at full 50 amp current at such low voltage with other than 110 volts AC on the input is making the regulator circuitry do unnatural acts and something will fail.
I decided not to change to heat strips because I don't make that many bows and my easy bake oven works just fine.
Wow! I haven't seen you post on an archery forum in years. I remember some interesting debates years ago on a different forum. How is life treating you?
I'd definitely be interested in exploring a different power supply to heat my stainless steel heat strips.... But how would you control the temp if you are not using a voltage regulator? Electricity isn't my strong suit.... Kirk
Quote from: Kirkll on November 06, 2025, 10:22:02 AMI'd definitely be interested in exploring a different power supply to heat my stainless steel heat strips.... But how would you control the temp if you are not using a voltage regulator? Electricity isn't my strong suit.... Kirk
The power supply has adjustable output for voltage and amperage, similar to a welding machine.
One question - where did you measure your 2.43V at in the system?
Mark
Quote from: mmattockx on November 06, 2025, 11:25:12 AMQuote from: Kirkll on November 06, 2025, 10:22:02 AMI'd definitely be interested in exploring a different power supply to heat my stainless steel heat strips.... But how would you control the temp if you are not using a voltage regulator? Electricity isn't my strong suit.... Kirk
The power supply has adjustable output for voltage and amperage, similar to a welding machine.
One question - where did you measure your 2.43V at in the system?
Mark
I measured the 2.4 volts at the connection leads at the ends of the heat strips, or the end of each battery charger cable.
Can you guys give me an idea of the type of DC power supply you are talking about than can be adjusted? Kirk
I found this adjustable DC power supply, but i'm uncertain this will work with the size of wires that come out of it.
https://www.temu.com/-heavy-duty-benchtop--power-supply-adjustable-0-60v-x-0-5a-precision-control-panel-with-4-digit-led-display--voltage-regulation---electronics-repair-industrial-use-compatible--outlet-115-equipment-userfriendly-interface-durable-construction-g-601099979287361.html?top_gallery_url=https%3A%2F%2Fimg.kwcdn.com%2Fproduct%2Ffancy%2F37e895b9-4b4b-4968-92ca-4a90a8d858b8.jpg&spec_gallery_id=3711575852&share_token=DZ0SiOuYI2rTbYJ-otzbm9Dd-S0KVTZiLr_6bAwxu0a_o2mrUB9KXKmM9UyI6-gUjyFhkRCJ6OWNWZd-v5uqFFiEsXAJaA_wFvE6ny1dge5rxQDHVo5qUFauT9HkacFb6XQ01kvW5P3zlsz5cMtBA9&_x_vst_scene=adg&_x_ads_sub_channel=shopping&_x_ns_prz_type=-1&_x_ns_sku_id=17594177788532&_x_ns_gid=601099979287361&_x_ads_channel=google&_x_gmc_account=5347809690&_x_login_type=Google&_x_ns_gg_lnk_type=adr&_x_ads_account=7917063364&_x_ads_set=22735289900&_x_ads_id=183380066124&_x_ads_creative_id=761133990177&_x_ns_source=g&_x_ns_gclid=Cj0KCQiAq7HIBhDoARIsAOATDxDBM3rKPvbsfaDCtVrgA1gFAZGedu7FJ7SykrG1QPvd-a4S7D4TUo4aAjWeEALw_wcB&_x_ns_placement=&_x_ns_match_type=&_x_ns_ad_position=&_x_ns_product_id=5347809690-17594177788532&_x_ns_target=&_x_ns_devicemodel=&_x_ns_wbraid=CkEKCQiAq7HIBhDZARIwAK4nT7bOM0So1pO013En8E1efvMPMOq5_-Z_1DC11UZrygRK196exjwHiFpUaFDSGgJrDA&_x_ns_gbraid=0AAAAAo4mICH_ZCgPZYfylRypVeNfq8tXx&_x_ns_targetid=pla-2410502723260&refer_page_name=kuiper&refer_page_id=13554_1762475468610_10hag2tqfm&refer_page_sn=13554&_x_sessn_id=o24v90sz25
I'm also concerned that hooking these up for the purpose of generating heat is basically shorting out the positive and negative leads, and will burn out the small 12-14 gage wires if it doesn't trigger a shut down or pop a breaker in the power supply.
Some of the battery chargers i tried to use that had digital readouts and a circuit board would shut down the charger when the circuit was complete touching positive and negative.
Quote from: Kirkll on November 06, 2025, 07:29:24 PMI measured the 2.4 volts at the connection leads at the ends of the heat strips, or the end of each battery charger cable.
Was the circuit connected? If it was, I think you were measuring the voltage drop across the strip, not the voltage the battery charger was putting into it. I am no electrical genius (I am a mechanical engineer...), so we are starting to get to the limits of my knowledge on the details.
For a power supply, this a random selection from Amazon from the search term 'adjustable DC power supply':
https://www.amazon.ca/Adjustable-Switching-Regulated-Adjustments-Jesverty/dp/B0B8S6CH3H/ref=sr_1_6?dib=eyJ2IjoiMSJ9.gKWaMKjwxG8J6PXy-I0Q8af0GvHG9xIDP0plsWaaL1SpJ_CDdJBb4sJQYIrQ1mQ80JCUaEPMr4t-pl3kbdcTVazbg9q4aE9gZpD1Z0WhB2Ky6cYo9KvWHfDvMWCNLD1tJ1qgNUwV6_UjW6TN9GUzE_8A9fM0MrZckuOHj9ROsowGknEwFbm0onvtp46SEoVaq1o20dw9jlY45EIPRz3L7szKvXo1_1gGR363xlP0xGVY4mkePKyNPVY-G99nFDbFURTcVtKiwAJ_iTvnD2_dxi2ips-w_p8zSJowaTl7ibQ.Jh4GEjQU-lPXWwH1phCA2OjqYL0dXQcS2zO_V6hf3Bs&dib_tag=se&keywords=adjustable%2Bdc%2Bpower%2Bsupply&qid=1762529173&sr=8-6&th=1
As for wire ratings, have a look at this chart: https://www.powerstream.com/Wire_Size.htm
12ga is rated for 41A continuous when not in a bundle (chassis rating).
Mark
Quote from: mmattockx on November 07, 2025, 10:33:58 AMQuote from: Kirkll on November 06, 2025, 07:29:24 PMI measured the 2.4 volts at the connection leads at the ends of the heat strips, or the end of each battery charger cable.
Was the circuit connected? If it was, I think you were measuring the voltage drop across the strip, not the voltage the battery charger was putting into it. I am no electrical genius (I am a mechanical engineer...), so we are starting to get to the limits of my knowledge on the details.
For a power supply, this a random selection from Amazon from the search term 'adjustable DC power supply':
https://www.amazon.ca/Adjustable-Switching-Regulated-Adjustments-Jesverty/dp/B0B8S6CH3H/ref=sr_1_6?dib=eyJ2IjoiMSJ9.gKWaMKjwxG8J6PXy-I0Q8af0GvHG9xIDP0plsWaaL1SpJ_CDdJBb4sJQYIrQ1mQ80JCUaEPMr4t-pl3kbdcTVazbg9q4aE9gZpD1Z0WhB2Ky6cYo9KvWHfDvMWCNLD1tJ1qgNUwV6_UjW6TN9GUzE_8A9fM0MrZckuOHj9ROsowGknEwFbm0onvtp46SEoVaq1o20dw9jlY45EIPRz3L7szKvXo1_1gGR363xlP0xGVY4mkePKyNPVY-G99nFDbFURTcVtKiwAJ_iTvnD2_dxi2ips-w_p8zSJowaTl7ibQ.Jh4GEjQU-lPXWwH1phCA2OjqYL0dXQcS2zO_V6hf3Bs&dib_tag=se&keywords=adjustable%2Bdc%2Bpower%2Bsupply&qid=1762529173&sr=8-6&th=1
As for wire ratings, have a look at this chart: https://www.powerstream.com/Wire_Size.htm
12ga is rated for 41A continuous when not in a bundle (chassis rating).
Mark
I posted a link above for a power supply that puts out 0-60 volts...
I just did another measurement on the positive negative battery charger cable ends without making the connection, and the reading was only 3.68 volts regulated to 45 volts AC input to the charger. So i was only loosing 1.2 volts once the circuit was connected.
I do not know how this all works. but i do know is these seriously heavy gage battery charger cables , probably 6 gage heat up when you connect the two heat strips together at the other end. When generating enough heat to bring 1.75" X 6' X 22 gage stainless steel up to 160-180 degrees, its heating up those battery charger wires too. I just can't see a small 12 gage copper wire coming from a power supply holding up well and not burning out.
What we need is an electrical engineer to explain exactly what is happening to create the heat, and how to best control it. I know there are much better heating element material out there. Nichrome material comes to mind.
Nichrome is a non-magnetic resistance alloy primarily composed of nickel and chromium, with iron often included. Its function is to generate heat when an electric current passes through it, making it ideal for heating elements in appliances. But... It isn't durable material..
Stainless steel is also a non magnetic material, with nickel and chromium.... But the stuff makes very durable heat strips. Kirk
Quote from: Kirkll on November 08, 2025, 09:01:20 PMI posted a link above for a power supply that puts out 0-60 volts...
Your link wouldn't open for me, Temu just kicked me out to their front page.
Quote from: Kirkll on November 08, 2025, 09:01:20 PMI just can't see a small 12 gage copper wire coming from a power supply holding up well and not burning out.
You will find wiring ratings are much higher than you think is wise. At least this has always been the case when I look at rating charts and see what the industry/code says they are good for. Most of the temp limit relates to the insulation and what it can take, not the wire itself.
Quote from: Kirkll on November 08, 2025, 09:01:20 PMWhat we need is an electrical engineer to explain exactly what is happening to create the heat, and how to best control it.
It is the resistance in your strips that is generating the heat. They are simply long, flat resistors the same as resistors used in any other circuit.
I think you would find a power supply would work much better than your battery charger, because you could up the input voltage to the strips a bit and then you would need less amperage to get the same temps. This would stress the wiring less and keep the heating down.
Mark
Your theory is good, but I'm uncertain how the power supply will react with a closed circuit for long periods of time. There are most likely ground fault saftey switches , breakers, or fuses built into these power supplies with digital readouts that shut things down before they generate enough heat.
The newer battery chargers have safety switches built into them, and kick off automatically way before the heat strips warmed up.
But I suppose there is only one way to find out. Buy one and see if it works. If not, send it back.
Quote from: Kirkll on November 09, 2025, 09:53:10 PMYour theory is good, but I'm uncertain how the power supply will react with a closed circuit for long periods of time.
They are designed for that sort of service. I have a battery charger I use for my radio controlled aircraft batteries. It has a mode specifically for powering a hot wire, for cutting foam. It will run that mode non-stop forever as long as you don't exceed its power ratings and overheat it. The power supplies should be the same thing.
Doing some more reading, it appears they act as I say above.
https://www.tek.com/en/blog/dc-bench-power-supply-fundamentals
https://www.ni.com/en/shop/electronic-test-instrumentation/power-supplies-and-loads/what-are-programmable-power-supplies/remote-sense-ripple-noise.html?srsltid=AfmBOoo8NVjFXfYXgoFkklEwTkN2jRY1c1OXiwx5fFZQIZDgoWOEZGYJ
They will power a load indefinitely as long as you stay within their power rating limits. Since they are DC output a resistive load is no issue.
Quote from: Kirkll on November 09, 2025, 09:53:10 PMBut I suppose there is only one way to find out. Buy one and see if it works. If not, send it back.
Most likely this is the answer.
Mark
This unit puts out 60 volts, 300 watts DC....
"https://www.amazon.com/Adjustments-Adjustable-Switching-Regulated-Quick-Charge/dp/B0D93S1Y7T/ref=sr_1_1_sspa?crid=1ZC8L0BISTNYH&dib=eyJ2IjoiMSJ9.r4MhqVAO4lyiREM4IKlg3l4UuiZojLBN_VSKEcL7-Tafb54mqVn9yrHooRmrHAYXn5rDRjNXtbFT9xdwvJzk155U2nVtdgfw2er5_S-XQXL5Zj36w-uQREbgj_hrR0_n_DlyGbkZUCzSk84VE9bf0NsvhQnVZJdi__noMg3PoU__0pcBCmRzfyRDWTDYZZ3O7_sNTdz6KnqkD5KUJr7LAuMtpg-okKK4Fs3ANKksxas.4qgVYpkS12Bq9F692HHU2yC5HSQ7lSru7pD0N-2ZcfM&dib_tag=se&keywords=60%2Bvolt%2BDC%2Bpower%2Bsupply&qid=1762792782&sprefix=60%2Bvolt%2Bdc%2Bpower%2Bsupply%2Caps%2C254&sr=8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1
But this is what concerns me.
"Short circuit alarm: In order to improve the safety of lab power supply and prolong its service life, we designed a short circuit alarm device for DC power supply. After the OCP function is turned on, if the load equipment is short-circuited in the working process, the variable power supply will automatically stop outputting and send a buzzer to remind the user, protecting the adjustable power supply and the load from being damaged. Bench power supply also has safety protection functions such as overvoltage, overcurrent, overtemperature and overload."
Isn't hooking up the positive and negative leads together with the heat strip between the leads a short circuit? Even if it doesn't turn off, keeping a constant voltage to reach temps needed for the heat strips may kick the unit off too with the other built in saftey features.
Quote from: Kirkll on November 10, 2025, 11:49:09 AMThis unit puts out 60 volts, 300 watts DC....
I think you want one of the 30V/10A supplies instead, that one only goes to 5A and that may not be enough.
For instance:
https://www.amazon.com/dp/B0DDPVDWPZ/ref=sspa_dk_detail_1?pd_rd_i=B0DDPVDWPZ&pd_rd_w=Mf0oy&content-id=amzn1.sym.7446a9d1-25fe-4460-b135-a60336bad2c9&pf_rd_p=7446a9d1-25fe-4460-b135-a60336bad2c9&pf_rd_r=7MTFR5P1RQK3J8E4FN5N&pd_rd_wg=IJ9PJ&pd_rd_r=2f5cc0db-2656-468d-a47c-77c2ee609cfc&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw&th=1
Quote from: Kirkll on November 10, 2025, 11:49:09 AMIsn't hooking up the positive and negative leads together with the heat strip between the leads a short circuit?
No, not if there is enough resistive load in the circuit. When operating in constant voltage mode the supply adjusts the current to keep the voltage constant at the desired setting. If you short the leads the resistance drops to near zero and the current has to spike super high to maintain the voltage output. This is what they are referring to.
Quote from: Kirkll on November 10, 2025, 11:49:09 AMEven if it doesn't turn off, keeping a constant voltage to reach temps needed for the heat strips may kick the unit off too with the other built in saftey features.
As long as you stay within the voltage/amperage/total power output limits the supply will run forever at that setting without issue.
EDIT - Just had a thought. Can you measure the resistance of the heat strips between where you attach the battery charger clamps?
Mark
Hi Kirk, yes it has been a long time. I have still been shooting and occasionally building bows. I just got back from the Gene Foster Rendezvous at the Fresno Field Archers range. I have retired and keep my interests in motorcycles, archery, etc. Since I built a CNC router a few years back I am getting into that a lot.
Did I ever tell you that I am an electrical engineer? Back to the power supply. A few photos would help a lot.
I think I understand that you have measured 2.43 volts from one end of your heat strip to the other; on the positive and negative leads where they connect. With no heat strip connected the voltage was higher, 3.xxV, because in this case no voltage is dropped in the cables from the charger to the strips because no current is flowing. With the strips in place and 50 amps of current flowing there will be voltage drop in the wires since they too have resistance. To drop 1.2 volts at 50 amps requires only 0.024 ohms which is in line with what heavy wire resistance would be if it is several feet long.
To get the power needed to heat the strips the V x I needs to be about 120 watts, according to your original data. If you use 12 volts it takes 10 amps to get this power - that is why I think a 300 watt power supply will work. Using lower current means that you can use smaller wires as well. It seems a 30 volt, 10 amp supply should do the trick.
Can you photograph how and where you measured the 2.43V drop in your strips? A photo of the battery charger gauges in operation will also help. Lastly, can you measure the resistance of the heat strips from one end to the other? On paper, you should get 0.0486 ohms with the 2.43V and 50A in the strips. Measure the resistance with no power applied. You may not be able to measure this low of resistance with most volt meters. Before trying to read the resistance of the strips connect the two meter leads together and read their resistance and subtract it from the reading you get across the strips.
I have been interested in the SS heat strip and power supply method for years but do not build enough bows to warrant it out for my use but I would like to help bowyers make a better setup.
Kirk, it just occurred to me that we can test my theory with your setup.
Set the current on your charger to 10 amps and adjust the AC so that the voltage at the strips is 12 volts and then see if the strips get to the temperature profile you like. If this works it will demonstrate the a power supply will work.
Kevin
Wait, don't do as I suggested in the previous post - that will not work. I think I have the correct answer in my head but need to noodle on it for a bit.
Repeating the measurements of your existing setup just to make sure we have the right data with a few photos will help.
In order to get a higher voltage to work for the heat strip a higher resistivity material needs to be used. The most prevalent materials in SS all have about 9 x 10-8 ohms per m2/m. If we wanted to use 12 volts to run the heat strips the material would have to be about 6x higher in resistivity.
I calculate about 0.2 ohms resistance for the SS from Kirk's data. If you run 12 volts through this strip it would dissipate 7200 watts and require 600 amps.
To get 120 watts at 12 volts requires 1.2 ohms. One could place 0.5 ohms resistors at each end that bolt to the strip and their temperature would be put into the strip, albeit at the ends, so it is not likely to heat evenly down the strip.
Nichrome has more than 10x the resistivity of the SS so that is why it works so well.
Now that I have spent a bit more time on this problem and did a bit of math and see that we need a higher resistance material I conclude that with SS strips you need very high current and low voltage. To use a higher voltage and lower current requires a higher resistance. V = I x R
Quote from: Cupcake on November 11, 2025, 11:37:07 AMDid I ever tell you that I am an electrical engineer?
Excellent news, you're far more qualified than I am to sort this out.
Mark
"Now that I have spent a bit more time on this problem and did a bit of math and see that we need a higher resistance material I conclude that with SS strips you need very high current and low voltage. To use a higher voltage and lower current requires a higher resistance. V = I x R"
Kind of like what you get from a battery charger? :biglaugh:
Hey Kevin.... I'm not laughing at you, i've just got a warped sense of humor. I know you said that using a batter charger with a voltage regulator is making the machine do unnatural, things and its the reason they only last so long. That "Unnatural" thing is heating up 6-12' of 22 gage SS to 160-180 degrees.
But not all battery chargers will do this.... The newer models with digital readouts and a circuit board have saftey shut off switches that will not let the charger run as the heat builds up.
All these DC power supply units available have overvoltage, overcurrent, overtemperature, and overload saftey switches built into them. This being the case, i just don't see them working for me. Kirk
Kirk, there is likely a power supply that will do what you need but it is likely a very specialized type and would be expensive.
Digital gizmos these days can be a pain in the neck with all of their safety interlocks. Over the years I have used high current linear power supplies that would do this. There may be some available from surplus sellers. I am thinking of a particular HP model that could supply 60 amps of current with the ability to manually set voltage and current limits.
Sometimes a problem that appears easy to solve is not at all.
Well i appreciate all the thought and time you've put into this Kevin. I think for now i'll just stick with my battery charger system until someone comes up with a solution. These chargers that work are not that expensive, and pay for themselves in time saved alone...
Besides that, i don't cook my forms to death in a hot box, and they just stay in the form vise while in use. Much less form handling.
Using heat strips will spoil ya rotten. You can build a bow complete ready to finish in 2 days easily. With that being said, i still never string my bows until the epoxy has cured overnight. But you can lay up the limbs, mount them on the riser block, profile them, and get tip overlays on the first day. Its all down hill from there...
Kirk