Hotwire Cutter Power Source/Supply

If you do not want to read this entire thread to learn how to use a low-voltage, “fixed-ouput” power supply/source for a hotwire cutter (e.g. a “manual” automobile battery charger), click the link below. The information posted there is condensed and updated with a link to DIY plans for building a simple low voltage, “variable output” power source/supply.



I use a battery charger on a 2 amp setting and plain ol’ bailing wire ($3) from northern equipment.  It works great!


You can splice in a light dimmer if you feel you really need it, but my setup does not.

Thanks for the reponse.  What is your voltage output at 2 amp (my lowest output is 2 amp – typo).  I’m assuming you are using 12 volt 2 amp output.

Can you use a dimmer switch in a 12 volt 6 amp circuit.  Seems like they’re made to use 120 volt ouput and lower amperage.

I’m a little nervous around electricity and my charger is basically brand new.  I’d feel better if I could vary the output so I could get the best cutting setting for my power source.  Don’t really want to buy a Variac with that charger just sitting there.  But I would like to make it more precise if I can dial it in with some cheap low voltage power source regulator from someplace like RadioShack.

From all of my reading, seems like NiChrome wire works well, very reliable.  It is fairly cheap and available in small quantities on eBay.  I figure somewhere between 22 to 28 guage would work.

If I could vary the power output from my charger, testing would be much easier witout risking destroying the charger.

12v 2amp is great.  You should try first and see what you think.  I used nichrome on a few blanks and gave the bailing wire a shot just tp see what it did.  The NiChorme breaks just as much as the cheap stuff unless you go with the really heavy stuff. The bailing wire worked just as well and was $3 for 60 ft.  No need to reinvent the wheel, I did 8 blanks for a total investment of $10. Just remeber to go slow it takes about 15 minutes per side on a 9-10ft blank.





















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I suppose it depend on how many blanks you are planning to make, higher volume = larger investment.  How many blanks do you need to make to get the cost of your Variac down to a buck a board (plus labor)… for me it was ten and I have enough wire for 20 more boards.    With wood, my blanks cost me about $30 bucks (plus an hour of labor) for an LB.  No need to do with more if you can do the same with less.  It’s a tough economy and from what I hear many independant board builders could use a little extra profit built into the price of their boards.

If you want to stick with the fixed output of the battery charger, the variable you have to work with is the resistance of the wire (and of course length of wire, but I'd assume that's relatively fixed). If you specify your desired length of wire, someone on here might be able to tell you what has worked for them off of a battery charger. Otherwise it's trial and error. Guitar strings, fishing leader wire, etc.



Modern dimmer switches require an alternating voltage to function properly.


Like I said higher volume = larger investment. If you are going to do 30 boards a day why not just buy a hot wire CNC and use no labor.  I’m not looking for a fight , I’m just offering an inexpensive option. Take it or leave it.

Don’t bother replying to this , I am done with this thread and won’t read it.


Many good responses, thanks.

Rather than try to address each post individually, I’ll just post one general answer/summary.

For now, I am just experimenting/playing.  I have a new battery charger I never use for anything.  And I’d like to keep costs low for something I’ve never tried.  I only plan to make a few boards and some smaller projects at the moment.

I was going to start with the smaller projects first to get some experience under my belt – foam core mountainboard decks.  Then I will move to a few surfboards – it has been 41 years since I made a surfboard.

To start, I will probably use wire length of 30-36 inches in a plywood bow, more or less.

I will be working with 3-lb/cf EPS.

Is there no easy way to vary the voltage/amperage coming out of the charger?

Thanks much to all for the helpful responses.  I am glad for any information you have to offer.



Don’t bail just yet.  I’m all about low tech solutions, using what you already have in the barn when starting.  As we used to say on the TX coast, if it ain’t broke don’t fix it.  We have plenty of farm supply stores out here in rural west KY.

Does bailing wire have a standard diameter/guage?


Please Gents,

Offer any information you have...




It would be easy to test some lengths of various wires you might have laying around. You should find that you don't need to vary the output of the charger, if you get the correct resistance in the wire. There might be some kind of rheostat you could use, but it might cost as much as a variac. Be careful if you decide to go building makeshift electrical devices!

The variac is, of course, the best solution. Then you can run whatever wire at whatever length and adjust power to suit.

If the search function was working you could find all sorts of info about charger/wire combos.


Yeah I have read many of them already.  None get super specific but they are all using different types and lengths of wire with different voltage/amperage ratings, so it’s hard to get any standard setup.  I figured I would have to experiment, was just hoping somebody knew of an inexpensive “RadioShack solution” to varying power output from a 12-volt, 6-amp battery charger.  I will probably just add a fuse to the bow circuit as a safety default if I can’t vary the power output.

BTW I like to use Google to search forums.  I usually get more specific results than when using the forum search engines. Just add:  to your search string.  It has allowed me to bypass the swaylock’s search feature crash.

Correction:  The total length of my wire will be 24-30 inches long.

My bad.

The variac is, of course, the best solution. Then you can run whatever wire at whatever length and adjust power to suit.

Well said!


Gotta use what I got…

One does what one must in this imperfect world.

One step at a time.

Hey get a variac and some stainless steel fishing leader,150 pound test leader works good.I ordered the small white variac online and it showed up on my doorstep in like 4 days,by then I had all of my hotwires built and my foam stocked and even some templates cut.



The variac is, of course, the best solution. Then you can run whatever wire at whatever length and adjust power to suit.

Well said!



I'm in San Marcos , Ca.....If you need help cutting a board let me know....

I have the full set up...Wire , Variac , two different hotwire jigs.....lots of rocker templates.....This is not child's can get burned......Please wear safety glasses.....Please listen to Pros like Surfding. A Variac is not a waste of money.