Can I usebattery charger as power supply to Foam cutter? - RC Groups
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Jul 19, 2012, 02:48 PM
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Can I usebattery charger as power supply to Foam cutter?

Hello guys,

I am completely new to this forum and this is my first question.
I new to this hobby and want to make my own aircraft from EPS foam.
I have dx5e radio and learning to fly on Phoenix RC Simulator V3.

I have ordered 50A Esc, 3750mah 50C 11.1v Battery, Imax b6 battery charger, C2850 1000kv 30A brushless motor....

I tried to cut EPS foam yesterday with exacto knife but it is big pain. So i think i will need to make my own foam cutter. I have heard guitar string is good solution.

I have a few questions:
- Which Guitar staring to use? (String E? or gauge 16? or any other alternative)
- What to use for power supply? (i have 12v 5a power supply, but can I use Battery Charger for precise voltage and current control, can i put it under niMh charging mode and fix charging current and voltage and use it to give power to foam cutter?)
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Jul 19, 2012, 03:40 PM
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Ward Hagaman's Avatar
In my early days I used .020" wire, speaker wire and alligator clips to my car battery. It worked! If the wire is cold, you can shorten span of wire, or use larger diameter wire.

Have fun!
Jul 19, 2012, 06:05 PM
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43851E's Avatar
I know there will be many replies to this age old question, but I can tell you that an "E" string that is 0.009" will do fine. You will want it to not cool down too much and still melt through during your cutting pass at a not too fast speed. Voltage & current regulation/control is not a bad thing, however using a light dimmer on 115Vac inputed into say a 12 volt output transformer will give you the control you need. I've seen one guy install a light dimmer into a 7 amp car battery charger box. You could attempt it on a bench with a "pig tail" however be sure to safely work around the 115Vac. He cuts 6" thick sections at about 12" in 20 seconds.

The guitar wire is a good choice. You want a wire with as much nickel as possible. Try a music store and buy .009, .010. 011 .012. They go for less than a dollar per string.

Also there are 2 types of light dimmers, one for motors and one just for lamps. Since you will be going into a transformer, I may elect for the slightly more expensive one (less than $10) that works w/ AC motors. The battery charger should have as big of a transformer as you can afford, say 20 amps. The ampmeter on the front panel can help you control your power also. So the solution is fairly low tech, however you will need a wire that acts like a nirachrome heater wire w/ alot of nickel (music wire) and a decent sized transformer and a way to adjust your power setting and monitor it.

Hope this helps, also there are many references to this question as many have done exactly what you're doing, so you potiently will have alot of reading to do. Also try youtube searching "DIY Foamcutter".

Jul 20, 2012, 12:20 AM
Registered User
I'm not familiar with Imax b6, but these smart chargers do monitor battery voltage before and during charge. Since your guitar wire doesn't generate any voltage, the charger will complain about "connection error", "battery undervolt" or something like that and refuse to output any power. On the other hand they may have a dedicated "power supply mode" just for these situations. I don't know if b6 has it, you will need to consult the manual for details.
Jul 20, 2012, 12:28 AM
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Underthetire's Avatar
And here is where those old model train transformers work quite well.
Jul 20, 2012, 04:28 AM
Registered User
If you look in the Foamies (Scratchbuilt) forum you'll find lots of information about making hot wire foam cutters.

Some chargers have a foam cutting mode but I don't know if yours is one of them (I use a variable power supply or an old brushed ESC/servo tester and 12V battery).

I've not had much luck with guitar strings, I find they tend to heat unevenly but if you want to try it a 9 or 10 thou E is apparently the one to use.

Jul 20, 2012, 09:33 AM
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43851E's Avatar
The B6 is flymsy enough, it's good for batteries only.
Jul 21, 2012, 07:35 PM
Twisted and Confused
flyonline's Avatar
I use my swallow charger on the NiXX settings as a cutter, much safer than transformers and the like as it has in built protection if the wire breaks, you get a short etc. It also means you can dial in the amount of amps you want and repeat it as many times as you like straight up if you write it down somewhere.

Occasionally I need to trick it by giving it a wiggle on the connector on the hot wire cos it gets stuck at a really low amperage, and mine does have a time limit (2min I think) that it will cut for before finishing the 'charge'.

Jul 22, 2012, 11:01 AM
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43851E's Avatar
You know something, I agree with you. Using low voltage is safer (personally), and the seemingly endless control with a computerized charger would be very versatile. I know the B6 charger is only a low power (120 watts?), so I would not recommend it. Mine failed after a year w/ the balancing input gone crazy, but it still works in {charge} mode only- no balancing.

Good fly'in
Jul 22, 2012, 07:30 PM
no points for speed
I've never done any cutting but I've done some research. I've heard that Rene wire is the best.
Michael Hancock said (on his podcast, that he prefers Rene wire and he is a very experienced scratch builder.
Jul 23, 2012, 05:11 AM
Twisted and Confused
flyonline's Avatar
Another cheap option is stainless fishing trace, somewhere between 25-50lb should sort you out. The thinner stuff cuts nicer and has less over burn particularly on the TE, but breaks more easily than the heavier stuff. I've been using 44lb stuff for ages and it's still going strong - just make sure you make up a system where you can really crank the tension up and let it off when not in use.

Mar 13, 2017, 12:21 PM
Registered User
see i used a battery charger to make a electric foam cutter but i failed to get the output.
what should i do?
Mar 13, 2017, 04:11 PM
B for Bruce
BMatthews's Avatar
I think you'd get better results with an automotive battery charger. The "smart" chargers will see a short circuit with no back voltage and cut out with an error code. Remember that in all the modes on the smart chargers they are looking for a continual rise in the pack voltage from a constant current being put out to the pack. Then they cut off when they see no further rise. So running a wire with a model airplane battery "smart" charger won't work at all.

But automotive chargers typically do not have such smarts built in. I would recomend one with at least two power levels. And preferrably three if you can find such a thing.

Another option is to use the automotive charger or other DC power supply as the power source and instead of using the wire size and length to control the power use a DC dimmer control. Here's an 8amp control for a whopping $2.

And since 12v isn't always enough voltage to drive longer wires here's a DC power supply that puts out 18v at 22amps. The shipping makes it a bit more expensive but it shows you that such things are out there. Shop around a little more for one that is cheaper when shipping is added on.
Mar 13, 2017, 05:27 PM
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wizard of odd's Avatar
Here are the details of my system, using similar components as described by Bruce: It uses the PSU, dimmer switch, a simple automotive fuse and a wattmeter. The wattmeter is not necessary, but it's handy to see how many amps/watts it takes to cut specific foam type using different types and diameter of wire. I use .013" (or around 30lb breaking strain) "Tooth proof" uncoated fishing wire trace on the cutting bow, which can be had from your local fishing shop for a modest sum.

PS: If you are in the USA, here's a reasonable option from a US vendor I found on searching Ebay. Way overkill, but the price is right.
Last edited by wizard of odd; Mar 13, 2017 at 07:11 PM.
Mar 14, 2017, 11:58 PM
Registered User
I use .015 control line braided flying wire available from Sig, Brodak or ebay. As for a power supply, I use an Astro Flight 110D nicad/nimh battery charger picked up from a swap meet for $10 or so. Most folks have given up on nicad chargers so these can be had for peanuts.

You can easily put the charger in test mode, which turns it into a variable power supply with precise voltage control, perfect for wire cutting.

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