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Forum Index : Electronics : Welder to charger conversion
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I've picked up a 2nd hand welder, little one, maybe 140 amps max. The plan is to convert it into a high current battery charger, so I can charge my battery bank with my petrol generator when the sun dont shine and the wind dont blow. My generator can supply 6kw, but I dont expect the charger to deliver that sort of power into my battery bank, I'm thinking more along the lines of 1.5 to 2kw, about 30 to 40 amps, into a 50 volt battery bank. If I get a few days of poor weather, I can connect up the generator to this charger, as well as the hot water system ( about 3.5kw ) for a hour or two to give everything a boost. The welder has a variable core, which might be handy for adjusting the charging current. So before I start on this project, I was wondering if anyone else has any experience with something like this? I was thinking of using several low current windings and bridge rectifiers in parallel instead of sourcing heavy copper wire and a dirty great bridge rectifier. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Might have had a real bit of luck with the welder. Just measured the AC output voltage and its 43 volts. Never measured a arc welders output before so dont know if thats typical, but if I bridge rectify that, I get 60 volts DC, perfect for charging a 48 volt battery bank. It also means I dont need to wreak a perfectly good little welder to make a charger, I can leave it as is, just add a bridge and a amp gauge. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Tinker Guru  Joined: 07/11/2007 Location: AustraliaPosts: 1904 |
Glenn the welders AC voltage you measured is most likely its arc striking voltage, This drops to a much lower value once a steady current flows, AC welders are purposely designed to do that. Years ago I built a 12V 40A power supply to charge car batteries quickly. It used the transformer from a medical shortwave machine where I removed all the secondary windings and wound a few turns of 8x4mm copper bar on instead. It was a lot of work, and the linear output stage has, I think, 6 high power transistors in parallel and they are on massive fan cooled heat sinks. I used 4 individual high current stud diodes on a heat sink arranged as a bridge rectifier and huge capacitors - salvaged from an old time computer power supply. It still works but is rarely used nowadays. Have fun with your project. IMO you might be better off to find a little stationary petrol motor and power a car alternator from it since your welder conversion idea already involves the noise of your generator running  Klaus |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Thanks Klaus I'll load down the welder output and see how much the AC drops. I do have a petrol motor driven car alternator, its come in handy on more than a few occasions, but its still only 12v and I need to charge a 48 volt battery bank. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Loaded the welder with a stove heating element. It was drawing about 200 watts, and output voltage remained at 43 volts, so thats good 
I have a couple of 50amp 600volt bridge rectifiers that I'll wire in parallel and fit to a heat sink. Might need a cooling fan as well. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Sparx Newbie  Joined: 16/06/2012 Location: AustraliaPosts: 1 |
G'day,in the distant past we used a 240v welder to charge the kraft trucks {24v} it was setup with a big diode bridge mounted to the handle, you adjusted the core for current and voltage control. most welders go 40+ open circiut,may be difficult to get 50v. |
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yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
Hi Glen, Your bargain welder will be rated on % duty cycle at max amps. The cheapies are usually 30%. you will get about 5 minutes flat out welding out of one before the power starts to roll off due to the windings overheating. A quality welder will be rated at 50% or 70% at max power and have a 100% duty cycle rating as well. If you can back the amps off a bit and still hold most of the voltage that would be great. With a fan it should run all day. Most welders I see put out between 32 and 37 volts flat out, once they are warmed up. What voltage you get when you dial the amps back ???? they are all different. I'm confused, no wait... maybe I'm not... |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Glenn I have used a 140 amp welder with success with bridge rectifiers totalling 200 amps, being a variable choke transformer you can adjust amps into your battery bank quite well as you know the volts when battery charging is tied to battery voltage not open circuit voltage with a light load, mine charged both 24 volt and 48 volts at around 60 amps 24 volt and 30 amps 48 volt. You just have to be careful with the top out voltage as it will climb to high when batteries are fully charged. Unfortunately mine went up in the shed fire so no pics. You do need to check the windings as if alum they heat up very quick on a consistent load copper is better. All the best Bob Foolin Around |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Thanks for the feedback guys. Yeah Yahoo adjusting the transformer ( its a slug that moves in and out between the primary and secondary, basically bypassing the flux from eaching the secondary ) did change the output voltage by a volt or two. I'll be adding a fan, there is a lot of space around the coils so a fan should help. Thats encouraging Bob. I think the next step is to connect up the rectifiers and battery bank to see how she performs before I spend too much time on it. Yep I'll be watching the battery voltage. This really is only a backup solution, so I dont mind monitoring it. Will give it a test tomorrow and post the results. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333 |
I have used smaller style mig welders for chargers for a long time (albeit 24v) most of the smaller migs have several sets of windings that can be switched to give different voltage ranges. The latest charger i done was using a microwave oven transformer and remove the secondry winding and rewind it with heavy copper wire (2 in hand 1.6mm) about 21 turns gives close to 28v DC, at +/- 20 amp. The microwave oven transformers are a simple E-core with a bottom plate of laminations welded to the E-core, a quick pass with the angle grinder along the weld and the bottom comes off the E-core, allowing 100% access to the windings. Once all the new windings are installed, i just clamp the base back on and run a weld along it, all in all a few hours work once you have done one and worked out the proceedure. You can stack as many transformes as needed to get the current you want. I often put several sets of windings on the core, as there is plenty of room when using 24 volt (48 v might be different), a heavy winding for about 32 volts, this is used for the bulk charge, then when the voltage reaches 29-30VDC it then switches to a lighter winding of 28-29VDC as the current draw is lower. A 3rd winding of 0.5mm wire gives me a 15v output that is used to run the electronics to switch between windings and control the state of charge. The last one i built had taps in the main windings to suit 12 and 24 volt systems, a picaxe was used to read the battery voltage on startup and if greater than 15 volts, then it switched to 24V charging, if less the 15v it switched to 12v charging, and if less than 6v it was programmed to not switch to any charging as it was likely connected to the battery wrong. Some might argue you cant charge a dead flat battery with this system.....true, but the battery is normally shagged if its that flat anyway. Pete. Sometimes it just works |
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| VK4AYQ Guru Joined: 02/12/2009 Location: AustraliaPosts: 2539 |
Hi Pete Still making good use of those Pichandles, very clever. All the best Bob Foolin Around |
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Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1345 |
Hi Glenn, After reading this thread I remembered I've got a AC welder up in my shed I nicknamed R2D2 as well over a decade go I scored a 360 amp diode block on a massive heatsink and put that said diode block on the front of the welder so I may need to get the cobwebs off and give this a go. It is a choke one with a handle ontop for changing the amps out, it also has a high and low amp setting. It is ali wound so some further butchering may be needed to fit some fans. When I get a chance for some shed time (next joke) I'll drag it out and take a couple of pic's. Cheers Bryan |
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| yahoo2 Guru Joined: 05/04/2011 Location: AustraliaPosts: 1166 |
I lusted after the old Woods dialomatic manual charger for years and never found one at clearing sales, etc. The new Woods Dial-o-charge just doesn't have that "heath Robinson" feel about it... a vintage welder would be just the ticket (steam powered of course). I'm confused, no wait... maybe I'm not... |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
I have one of those Australian made Goodwell 140 amp stick welders, bought it new about forty years ago. They must have made millions of these, and they are more or less readily available secondhand in full working condition for typically fifty to a hundred dollars from Gray's and E-bay. http://res0.graysonline.com/handlers/imagehandlerxt=l&id=620 1337&s=n&index=0&ts=634364449592630000 The magnetic core and primary winding will supply 3Kw continuously, that is 240 volts/13 mains amps. It will run hot, but not dangerously so. The primary has exactly 240 turns. You can force 5Kw load for intermittent duty such as welding, but it will handle 3Kw all day continuously loaded. You can use the sliding shunt magnetic gap to limit the current, but that has a bad effect on the output voltage regulation. The shunt gap also buzzes annoyingly, removing it produces a silent transformer. If you remove the shunt magnetic gap completely, then you will have a very low cost 3Kw transformer primary plus core that will produce 1 volt rms per turn on the secondary with excellent voltage regulation. That translates to around 28 volts at a genuine 100+ continuous amps, not bad for fifty dollars. Cheers, Tony. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Did some testing with a bridge rectifier and my battery bank. The output is too low. With the battery bank floating at 56 volts, the welder was only supplying 1 amp. I shut down the solar charge controller and loaded the bank a little, then at 52 volts the welder was supplying 6 amps. So assuming a battery bank in need of charging, at around 48 volts, I would get about 10 to 15 amps. Thats OK if I could leave the welder/charger connected for several hours, but I need a fast charger, with 30 or so amps. So I'll have to modify the transformer. 
There is approx 200 to 250 turns on the primary, and 35-45 on the secondary, so I'm going to guess this is a coil per volt transformer. I can remove a few turns from the primary to increase primary current, but not good practice, and will mean more heat to get rid of. Or I can add a few turns to the secondary, say to bring it up to 50vac, maybe. That would only be about 7 turns, which will fit easily. I dont have any wire thats the same size as the exiting secondary turns, so I'll have to see what I can dig up in the junk pile and wire several in hand to get the current capacity. These extra coils can also serve to provide a 10-12vdc supply for a cooling fan. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Bryan1 Guru Joined: 22/02/2006 Location: AustraliaPosts: 1345 |
Hi Glenn, Eh mate I do have some heavyduty enameled wire here and off memory it is about 8mm x 5mm, it came off some damaged spools and I scored a heap of 1.5-2 metre lengths. When I get my so called smart phone back from warranty I'll take a pic and if you can tell me the length you need I'll be happy to post some up to you. This wire was used by a company here (WIA off memory) that went off shore and the wire was used for heavyduty 3 phase welders so it would suit your application to a tee. Cheers Bryan |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Thanks for the offer Bryan but I jumped in already and wound on a few extra coils. The wire in the secondary is 4mm diameter, about 12mm square, aluminium wire. I had some 1.2mm enameled copper wire, thats 1.1mm square. I made a bundle of 8 wires, any more and it would have got to tight in the transformer. 8 wires gives 8.8mm square, which is probably as good as 12mm alu wire, at a guess. I could fit on 8 extra turns. Applied power and I was reading 52 volts AC. Thats it for tonight, tomorrow I'll test in on the battery bank and see how it goes. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
OK, tested the transformer with the extra turns and it was only good for about 500 watts at 50 volts. I needed to get more windings onto the secondary. So I made the decision to dedicate this thing to being a charger only, not a welder. I removed the variable core mechanism and unwound the 8 turns from earlier. This gives me a lot of extra space in the core for winding in additional turns. 
I glued in a piece of plastic to make sure the primary and secondary are well isolated from eachother, and some cardboard to the laminations to protect the coils. Then wound on 14 turns. 
Put it all together. Added a fan to keep things cool, the bridge rectifiers, and a 30amp fuse. 
Tested the output again, and it was supplying 1050 watts into the battery bank, which was already in a good state of charge, sitting at about 53 volts. I would expect this to rise to 1200 or more watts for a discharged battery. Now I feel I could get a lot more out of this transformer, I have space for more windings, but this will do for now. It is afterall just a backup to give a tired battery bank a bit of a boost while I'm heating the hot water tank. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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Madness Guru Joined: 08/10/2011 Location: AustraliaPosts: 2498 |
As previously mentioned you can use a MIG welder transformer also. A MIG welder is designed to supply constant a voltage which is selectable on the various winding taps, an arc welder is setup to supply constant current. MIG welders often come up on Ebay, some times large welders can go quite cheap if they are not working. They also have a rectifier in them, I think output voltage is around 30 to 45 volts DC. There are only 10 types of people in the world: those who understand binary, and those who don't. |
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| Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406 |
The voltages vary a bit, but my own MIG goes from 17.5vdc to 41.4vdc in 24 switched steps. It would make a wonderful high current 24v battery charger with switched output voltages of: 26.1v 27.2v 28.3v 29.4v Cheers, Tony. |
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