Diode reverse protection and current limiting.

How is the voltage varied? Why don't the rectifiers prevent back current flow?

It is varied by turning a beefy knob that probably switches transformer windings.

Second question is a good one, my guess is that there are capacitors and a big safety discharge resistor that play a role.

i

From what I can make of the manual, yes, voltage taps. However there is a type of magnetic amplifier which helps keep the voltage constant under load. This is a fairly complicated gadget. I'd be inclined to add an external 'box' to do what you want rather than tinker with it. A heat sinked diode should work fine re back flow. For constant current, maybe a big transistor - depends on the max current you want. You could use SCR's and a commutation circuit for more amps, but I'd look for an old GE SCR manual if you want to do that. Or. google for (scr commutating dc).

(page 2) shows a typical circuit.

Right.

That would be my own approach, as well.

Yep. I just added a beefy 140A diode on a beefy 1/4" by 2" by 6" copper bar, right to the + terminal, it works great (as it should). Had to tap that bar to 3/8-24 NF thread. In testing of this, the voltage drop varied from 0.78 to about 0.9v or so depending on (light) load. Could not find my heatsink paste, I need to buy some or find what I have.

So, I would say, my first problem of battery discharging through this power supply when it is turned off, has been SOLVED.

I would say 50A max (so that I do not exceed 15 amp single phase power draw to not blow my house breakers), but it should be adjustable by a pot.

I do have two big transistors, not sure if I could use them or not.

Do you mean something as pictured in Figure 6? What would be the point, to turn current on and off like that? Or are you suggesting high frequency switching? I would rather regulate it, that is my first, unstudied thought, than switch on and off? I apologize if my comment is off base.

The point is to handle large currents without large heat losses. SCRs were used for such tasks before large transistors or FETs were common. One use was as a speed control for a battery golf cart. Basically you fire the first SCR to turn the current on. At a certain point you fire another SCR across it with a capacitor in series. This shunts the first SCR which turns off and the capacitor then charges and turns the second SCR off. Then repeat.

A more modern design might have transistors cycling on and off to control the current with lower heat losses than remaining on. Basically this is a form of switch mode power supply, perhaps without the transformer and Schottky diodes.

As I say, it depends on how much current you want to use for electro plating. 50 A at 12 V drop (say) is mighty hot.

This is the kind of thing I just buy. I have a lot of gel cells I use for power in the field. I use

They have other smart chargers at

The problem with charging batteries is you can't sit there and watch the damn thing charge. Thus you need protection circuitry in the charger. I suppose you can spend you time designing such circuits. Generally I only build what doesn't exist off the shelf. I can tell you the Japlar Schauer I bought is a good product.

Getting back to your situation. Lead acid batteries tend to self limit. I don't have my Gates Energy book handy, but I think the limit is generally around 25% of capacity. This means your 100A charger is set up for a 400AH battery. I am presuming your battery isn't 400AH, so you really should current limit the power supply just to be on the safe side.

Seriously consider buying an off the shelf product.

A 100 amp contactor in series with the output would be the simplest way to go. Wire the coil across the transformer primary to turn it on, when the supply is on.

--
Service to my country? Been there, Done that, and I\'ve got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

OK, I see now. 50 A at 12V is not that much -- it is just 500 watts. Nothing that a 10 inch long heatsink could not handle. I have a heatsink with 2 transistors assembly, would be nice to try to make it into a variable voltage limited and current limited supply using them.

i

Hm, thanks. That's interesting. If you vouch for them, that means a lot to me. The "smart chargers" that I tried were basically all very poorly programmed, had a lot of software bugs, and would not charge my deep cycle batteries correctly and would "hang" while continuing to charge etc. (that is, they would continuously display 88% charge whereas the battery was at 15V or something).

My batteries are about 180 AH rated.

Yes, so this comes back to current limiting discussion.

So, let me ask you then, the charger that you are describing, charges all sorts of batteries well and does not hang or misbehave in any way?

I have a 1.5v smart trickle charger/battery maintainer, these ones work VERY well, but they charge too slowly when I need to charge a battery quickly.

Oddly enough, when I clicked on enlarge image, it showed a 24v charger, but I suppose it is their mistake and that's all.

i

Mike, I put in a diode yesterday, it works just fine. I just need to find heatsink paste, I misplaced it. Otherwise it is great.

i

--
What you\'ve described isn\'t a constant-current supply, but rather
one where the _average_ current into the bath can be controlled by
varying the duty cycle of the waveform into the tank.  Still, for
plating that should be adequate.

The controller can take the form of either a fixed cycle time,
variable-width pulse or a fixed-width pulse, variable cycle time
supply.

In either case the current into the bath would have to be measured
and then either the pulse width or the cycle time adjusted in order
to get the right number of electrons into and out of the bath in the
allotted time.

I\'d go the fixed pulse width, variable cycle time route myself
because it would be easier to figure out how long to wait to pump
another load of charge through the bath after I knew how much I\'d
just pumped through it than trying to figure out how much to pump
through it on the fly.

Google "pulse electroplating" (no quotes) for a lot of folks who
have already done it.

I believe this can be jumpered for 14 V or 28 V.

If you are thinking of any kind of switching regulator, and given that you have low voltage DC already, I would definitely avoid SCRs since they always drop quite a lot of voltage and are difficult to turn off. I would either use MOSFETs in a switching constant current source, or get a big heatsink with a fan, and build a linear regulator with either NPN bipolar transistors or MOSFETs. The switching regulator would be more intersting and more efficient, and an inductor to handle 50A DC could probably be scavenged / built up from some computer power supply parts.

Chris

Chris, you know me. I am basically looking to see what would it entail to make the cheapest/easiest solution to making a more versatile power supply out of this PP-1104B/G. If the power converter is lossy, I think that in the end it is not a huge consideration.

Is it true that a linear transistor based regulator is basically an extremely simple solution?

i

Chris, would I be able to make a linear voltage and current regulator with these transistors

I have two, conveniently mounted on a heatsink. Would be great to put them to some use. Ignore the for sale verbiage, whatever I sold was sold a long time ago. That heatsink also features a 150A current shunt and some SCRs, which I do not thinkI would need fora linear regulator.

i

One would give you up to 30 A assuming dissipation was not a limit. You need to drop enough voltage to make the regulation work, but not so much as to create excessive dissipation.

Actually one would give me 300A, not 30A. (I just double checked). My question is, are they a suitable type transistor for both voltage and current regulation with pots.

Ie can use them to I make a device to convert incoming 14VDC with no current limit, to a power source with voltage up to some limit below

14 VDC and with current up to some limit below 50A. (the limits being settable) i

I was going by the speciication on the auction document..

Seems doable.

15V is way too high. I don't know if that is dangerous, but it probably damaged the battery. The smart charger I bought uses a bi-color LED to indicate the charging.

Well, that is a serious battery. I would contact the company at the link I provided and see if you can agree on an acceptance criteria for whatever charger you determine fits your need.

I have charged a very narrow range of 12V batteries, 50AH to 70AH. Thus far, no problem. These are not deep discharge, but SLA.

My issue with home brew battery charging is the fecal matter can really hit the fan if you screw up. Nothing like burning down the house to save $50 on a commercial charger. When I was designing chargers, I'd run the charger in an environmental oven, just in case something bad happens.