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.