Diode reverse protection and current limiting.

I agree that it should be possible. Because they are Darlingtons, they will probably need to drop a minimum of more than 1 Volt (maybe even 2V) whereas a MOSFET can work with much less voltage dropped across it, so theoretically could give more efficiency, especially in a switching circuit. On the other hand, if you already have these darlington transistors, and if you can get rid of all that heat, then they should work in a linear regulator. You might want to consider "fold-back current limiting", which means that you apply a current limit which is say 50A at

14.5V, but the current limit might drop to only 10A when the output voltage is near 0V. The advantage of this setup is that the output transistors will be less likely to melt if the output ever gets short circuited. (There is more voltage dropped across the pass transistors when the output is short-circuited, compared to normal operation. Since power dissipation is the product of voltage dropped across the transistor multiplied by the current, it is useful to drop the current limit when the transistor has lots of voltage across it.) I think there is something about this in the book "The Art of Electronics" which I recommend highly.

If you make a switching regulator, then you would need an inductor, a current sense resistor, and two capacitors that could handle the required current. (50 Amps ripple in the capacitors will make them hot if they are not designed for it, and 50 Amps DC will saturate the core of an inductor if it is not designed for it. Old computer power supplies, especially bigger ones than you would find in a PC e.g. old minicomputers, would be a source for these parts.) Apart from that you would need some MOSFETs, these are pretty small and cheap for 50 Amps, and probably some diodes and control circuitry. It should not need much heatsinking because it would be efficient.

Whichever system you use, it might be a good idea to put a relay / contactor and fuse or circuit breaker between the battery and the charger. You could connect the contactor to a comparator circuit which would disconnect the charger from the battery in the event that something in the charger fails resulting in wrong voltage or current. This could also prevent discharging when the charger is switched off.

Chris

Well, a timer is a start, but for lead acid, a constant float is good. Just off the top of my head you need these protections:

1) undervoltage. My charger refuses to charge anything under 4V. I don't know where they got that limit 2) overvoltage 3) current limiting 4) reverse current

Your diode takes care of reverse current. I suppose your power supply will take care of overvoltage. However, the smart charger I have is multi-stage. I believe it is current feed up to a point, then goes to voltage float.

Gates Energy published a book on charging lead acid. I can't find Gates Energy on the web unfortunately.

I think that getting rid of 200 watts of heat on that heatsink is a no brainer.

Chris, I have AoE, so if you can refer me to some particular page or chapter, that's all I need to get started. I am looking for something simple that I could use to drive motors, charge batteries, electroplate etc.

Agreed on this, I will start with a fused circuit.

i

What is a constant float?

I would rather avoid that.

yes

yes

Yep.

Yes, it is CV by nature.

I would be interested in anything on this matter. I think that battery capacity is a necessary input to a proper charging algorithm, and it is missing on all those "smart chargers".

i

[snip]

P 316 in 2nd ed.

[snip]

Chris, thanks, I looked at it and it is very straightforward. Thank you.

i

A float charge is basically put 13.8V on the battery and let it draw what it wants.

The smart chargers that do a current dump followed by float are matched to the size of the battery. That is one of the reason the chargers are given a range.

you do like industrial sized machines!

For battery chargers current limiting is often done by using SCRs in the rectifier.

--

Bye.
   Jasen

apart from the heatsinking, yes.

Bye. Jasen