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Discussion Starter #1
Thought you electronics guys might like this ...

I'm not an electronics guru, just a tinkerer so i've probably overlooked something major, please lend some input if you spot anything :)


Take one failed Flux MIG Welder (dead motor speed controller and broken torch handle)

The massive transformer outputs ~26VAC RMS ... way too much, snip off and uncoil some of the thick secondary windings until you get down to ~11.5VAC RMS, noticed a -3V drop every 5 turns, yours may vary.

Feed that into the bridge rectifier(s). You will drop 1.4V going through a bridge rectifier (2x 0.7v) so you'll end up with a ~10.1V "DC" signal with heavy ripple, add your filter caps on the other end and you end up with vSmoothDC = (~1.4 x vRippleDC or about 14.14V DC), perfect to charging car batteries, testing amps lights, and radios, etc etc

In this case i'm using 2 35Amp bridge rectifiers in parallel to quickly buildup and jump a car battery, eventually i'll hookup all four, i'll be happy if it charges up a 8v "dead" battery in 5 minutes so you can start the car, that seems like a reasonable goal :D


Any thoughts? :werd:




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Thought you electronics guys might like this ...

I'm not an electronics guru, just a tinkerer so i've probably overlooked something major, please lend some input if you spot anything :)


Take one failed Flux MIG Welder (dead motor speed controller and broken torch handle)

The massive transformer outputs ~26VAC RMS ... way too much, snip off and uncoil some of the thick secondary windings until you get down to ~11.5VAC RMS, noticed a -3V drop every 5 turns, yours may vary.

Feed that into the bridge rectifier(s). You will drop 1.4V going through a bridge rectifier (2x 0.7v) so you'll end up with a ~10.1V "DC" signal with heavy ripple, add your filter caps on the other end and you end up with vSmoothDC = (~1.4 x vRippleDC or about 14.14V DC), perfect to charging car batteries, testing amps lights, and radios, etc etc

In this case i'm using 2 35Amp bridge rectifiers in parallel to quickly buildup and jump a car battery, eventually i'll hookup all four, i'll be happy if it charges up a 8v "dead" battery in 5 minutes so you can start the car, that seems like a reasonable goal :D


Any thoughts? :werd:




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I am not an electronic guy but I can offer you my opinion. This is a good idea to utilize the dead welder and build a massive power supply. Charging a battery is another matter. Battery does not like being charged this way and you have a good chance of overheating and busting the battery forever. Your charger is probably capable of putting out way more current than the battery can handle. And you can definitively leave out the caps; smoothing out ripple is not necessary for battery chargers because, first, the battery itself is a big cap, and secondly the ripple is believed to improve the charging process. What you need to do is to control the charging current either by adding resistance or regulating the voltage.
Stan
 

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Discussion Starter #3
You've got a point there, there's no current limiting at all. Rough estimates say this will put out 180amps absolute max coming off the transformer, lower of course when converting to DC

I'm looking at this like it's an alternator, they output 90-130amps in stock form right? 200 for the beefed up units. I don't see how that's any different than a standalone power supply feeding lets say 50amps.

I'll have to look up the 1C/5C etc charge rates on car batteries but I don't think the alternator cares it just puts out all it can and the battery just takes it in. You'd also think the current would naturally drop as the (vCharger-vBattery) difference approaches zero :dunno:


edit: and no fuse yet, probably going to add a 60amp circuit breaker to protect the BRs
 

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The alt CAN put out 200 amps, its not going to be putting that out all the time.
Charging with that many amps=boom. Either pieces of the battery are going to be embedded in your shop, or there's going to be a puddle of lead and plastic on the ground.
 

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The battery can easily handle 200A. It delivers 300A-450A every time you stat the car.
 

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The battery can easily handle 200A. It delivers 300A-450A every time you stat the car.
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You have a point here SHOZ but, DMX please remember to charge your battery 1, 2 maybe 5 seconds MAX... :)
Stan
 

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Most batteries can take as much as you can throw at them short of melting the internal busbars until they start gassing. I would think a dead car battery can easily take 100A for 5 minutes then start trickling down.

Gassing is the key, when you see this then you are putting in more amps than the battery can take.
 

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You've got a point there, there's no current limiting at all. Rough estimates say this will put out 180amps absolute max coming off the transformer, lower of course when converting to DC

I'm looking at this like it's an alternator, they output 90-130amps in stock form right? 200 for the beefed up units. I don't see how that's any different than a standalone power supply feeding lets say 50amps.

I'll have to look up the 1C/5C etc charge rates on car batteries but I don't think the alternator cares it just puts out all it can and the battery just takes it in. You'd also think the current would naturally drop as the (vCharger-vBattery) difference approaches zero :dunno:


edit: and no fuse yet, probably going to add a 60amp circuit breaker to protect the BRs
[/b]
I know of .1C charge being the usual rate. More than .3C you will need to control the process watching for temperature rise etc. The alternator does not put out all it can, there is a feedback circuit and by regulating the induction voltage the output is adjusted accordingly. If you want to add some regulation to your charger, look up the schematic on electronic webpages. Easy to build. I made mine long time ago, works nicely and I leave it overnight, never worry about overcharging.
Stan
 
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