Author Topic: Arc welder battery charger  (Read 12160 times)

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madlabs

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Arc welder battery charger
« on: May 08, 2009, 03:36:12 PM »
Hi All,


I'm going to try using an arc welder as a bettery charger as we have discussed elsewhere. I have a beefy 220V/50A variac to use to dial down the output, which is ~ 30V. My question is should I use the variac on the input to the welder or on the output? It seems that using it on the output would give me better resolution controlling the output voltage. The plan is to shoot for 13.8V or so to perform bulk charging. Any other tips or suggestions for this project would be great! I really can't afford to buy a "real" battery charger right now.


Batteries come today! My first battery bank. I'm in love already. :)


Jonathan

« Last Edit: May 08, 2009, 03:36:12 PM by (unknown) »

Flux

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Re: Arc welder battery charger
« Reply #1 on: May 08, 2009, 10:15:55 AM »
Not seen your discussion elsewhere so this is a guess. I assume this is an ac welder and you intend to add a rectifier.


My thoughts would be to use the variac on the input. With only 30v nominal ( very much current dependent) on the variac it would be fairly lossy and you would be pushing it to charge art anywhere near 50A.


You aren't going to get any precise voltage control as welding transformers are highly reactive and the open circuit volts will depend on output current. It will certainly be ok for bulk charging but you will need to monitor current and not just rely on a voltage setting. If the welder has a low enough current setting you can use it direct but the variac will let you use it if the current settings are too high.


Flux

« Last Edit: May 08, 2009, 10:15:55 AM by Flux »

scottsAI

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Re: Arc welder battery charger
« Reply #2 on: May 08, 2009, 11:04:27 AM »
Madlabs,


Depends on the Welder:

Welder with electronics, may shutdown on lower input voltage or go nuts. Use Variac on output.

Transformer only, input - lower currents.

At work shop has a DC welder, internally has an AC motor / DC generator...

Many types of welders.


Variac works with AC, if welder has DC output cant use Variac there!-)


Welders are time/current rated. Pushing lots of amps do not overheat welder.


BTW: most welders have a lossy transformer. Output voltage is high to help strike an arc, drops while welding. Source of transformer heating. Long term not a good battery charger. Toping off a battery once a while a cheap (not efficient) backup. Of course check out your unit, YMMV.


For my 8 golf cart batteries, bought a fork lift charger for $75, pushes 380amps @12v

Interesting idea to use a welder! A more useful toy.


Have fun,

Scott.

« Last Edit: May 08, 2009, 11:04:27 AM by scottsAI »

madlabs

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Re: Arc welder battery charger
« Reply #3 on: May 08, 2009, 11:34:27 AM »
The welder is old school style, no electronics. Yes, it is AC, and I have some fat hockey puck stud mount diodes on a huge heatsink. As far as amps out on the output side, I would expect that at the lower voltages it can handle more than 50 amps, after all that rating is for 220VAC, for 11,000 watts. The thing is huge, like 2 foot by 2 foot, and HEAVY. As the generator is rated for 4.5kW continous, I shouldn't be anywhere near the variac's smoke point. The welder is rated for 225A @ 25% duty cycle. So I would think it could push 100A at less than half voltage all day. Does that seem right? I have some 220V muffin fans I could use for cooling if need be.


Yeah, I know this is lossy and kludgy, but I have all the stuff. When I have some dough, I'll get a forklift battery charger.


Thanks for all the help!


Jonathan

« Last Edit: May 08, 2009, 11:34:27 AM by madlabs »

TomW

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Re: Arc welder battery charger
« Reply #4 on: May 08, 2009, 11:47:27 AM »
Jonathan;


It is always a good idea to have multitaskers in your gear inventory.


Anything that can do double duty saves on the purchase and maintaining another piece of kit.


Even if it doesn't do both perfectly.


Personal opinion, of course.


Tom

« Last Edit: May 08, 2009, 11:47:27 AM by TomW »

Flux

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Re: Arc welder battery charger
« Reply #5 on: May 08, 2009, 11:49:06 AM »
If you put the variac on the output side its rating will be 50A determined by the winding size and brush track. You can't divide the VA rating by the voltage to get its current rating. It will be ok up to 50A on the output side, if you want to exceed that put it on the input side. More logical to put it on the input side anyway and be done with it.


Should make a perfectly adequate battery charger.


Flux

« Last Edit: May 08, 2009, 11:49:06 AM by Flux »

bob g

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Re: Arc welder battery charger
« Reply #6 on: May 08, 2009, 12:26:33 PM »
i think you will find your efficiency is going to be horrible at best

and even worse likely using the welder.


another alternative might be salvaging some transformers from some old ups's


i have to believe you could parallel a few match xformers and use your variac

just fine.


bob g

« Last Edit: May 08, 2009, 12:26:33 PM by bob g »
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madlabs

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Re: Arc welder battery charger
« Reply #7 on: May 08, 2009, 12:29:37 PM »
Ok, thanks for correcting me on the variac in terms of amps. Makes sense. Input side it is. I'll do a test in the next week or so, got a lot on the plate ATM. Nice to know it should work though.


And yeah, it's plain old cool to use the welder as both a welder and a charger. I'm the knid of hick that finds that very entertaining!


Jonathan

« Last Edit: May 08, 2009, 12:29:37 PM by madlabs »

scottsAI

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Re: Arc welder battery charger
« Reply #8 on: May 08, 2009, 04:16:01 PM »
Jonathan,


Last week studying how to use batteries as a welder!

Today learning about using a welder as a battery charger!

Full circle:-)

Options are great to have.


Have fun,

Scott.

« Last Edit: May 08, 2009, 04:16:01 PM by scottsAI »

dnix71

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Re: Arc welder battery charger
« Reply #9 on: May 08, 2009, 04:19:50 PM »
You need to watch the "duty cycle," too. You'll have magic smoke coming off that tranny within a couple of minutes unless you keep the load under whatever the continuous duty rating is.
« Last Edit: May 08, 2009, 04:19:50 PM by dnix71 »

nick1234

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Re: Arc welder battery charger
« Reply #10 on: May 08, 2009, 08:21:14 PM »
your 25% duty cycle is for home use open circuit voltage is about 35 volt when welding it goes down just a few volts 25% duty cycle is 1 minute weld 4to5 minute rest or use it longer and the unit turns OFF  then you have to wait longer for the welder to recycle reset. As you put a load on it voltage goes down no good for charger and is AC

go buy a charger cheaper than replacing batteries

thats my 2 cents

nick

« Last Edit: May 08, 2009, 08:21:14 PM by nick1234 »

Blimpman

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Re: Arc welder battery charger
« Reply #11 on: May 08, 2009, 08:49:30 PM »
I would have an amp meter before the batteries. You don't want to overcharge the batteries or exceed the batteries charging rate. Check with the battery dealer for the charging rate.
« Last Edit: May 08, 2009, 08:49:30 PM by Blimpman »

wooferhound

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Re: Arc welder battery charger
« Reply #12 on: May 09, 2009, 04:07:36 AM »
if you put the variac on the welder output, then it will need to handle 50 amps plus...
« Last Edit: May 09, 2009, 04:07:36 AM by wooferhound »

madlabs

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Re: Arc welder battery charger
« Reply #13 on: May 09, 2009, 07:08:57 AM »
Scott,


Where did you get a forklift charger for $75? Looking around all I see is much more expensive.


Thanks!


Jonathan

« Last Edit: May 09, 2009, 07:08:57 AM by madlabs »

madlabs

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Re: Arc welder battery charger
« Reply #14 on: May 09, 2009, 07:21:59 AM »
I'll have an ampmeter on the batteries for sure. I'll also keep an eye on the welder to make sure it isn't getting too hot. I would like to buy a real charger, but money is super tight for me. I'll dig through my stuff, I have a collection of old iron and may have a better xfrmr to use. But the welder would be handy and it's not buried in the shed. :-0
« Last Edit: May 09, 2009, 07:21:59 AM by madlabs »

scottsAI

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Re: Arc welder battery charger
« Reply #15 on: May 09, 2009, 06:20:15 PM »
Jonathan,


Like most great deals sort of fell into it.

Searching on eBay, for weeks.

Found a unit being sold locally (30 minutes away).

Unit has scratches / dents / rust, yet works, well used.

Several other units on ebay at the same time, they got the bids...

I was the only bidder.

Seller supplies batteries to local stores in the area, delivered it for $25. (heavy)

Bough 8 golf cart batteries from the guy months later. Delivered $57ea. (3yr ago)


Have fun,

Scott.

« Last Edit: May 09, 2009, 06:20:15 PM by scottsAI »