SCR Battery charger

[qrper]

Hola Gang!

In my junk box I have a 12 volt lead-acid battery charger. It's kinda of slick as it uses two SCRs and has just one transformer inside. Of course there's also a pcb with pieces parts on it. It will charge at a 25 amp rate. I don't recall the name of the thing right off hand. I do remember calling the company and asking for a schematic should the thing break. They refused saying to just return it for service.

I've googled the snot out of SCR battery chargers and while I've got many returns, the results usually just give a web site to purchase one.

So... how do these things work? Anyone know the whereabouts of a SCR battery charger schematic?

Would love to build one just to see if I could


mike

 

[ParkingLotLust]

Battery Charger 12v SLA

"scr battery charger circuit" on Yahoo.

 

[qrper]

WOW! Interesting...

This charger I have in the 'ol junk box uses two scrs. They are mounted on a rather large aluminum heat sink.

I've seen some battery chargers that use a SCR but mainly to signal the end of charge.

mike

 

[ccurtis]

An SCR has only a slightly higher voltage drop than a PN diode so SCRs are suited for high current recification. The turn on point of an SCR can be controlled to vary the output voltage to allow voltage regulation without the relatively heavy heatsinking requirements of series pass transistors.

I have seen high current DC bench power supplies with a controlled SCR bridge rectifier that served to preregulate the input voltage feeding a linear regulator. Doing this minimizes the power lost in the series pass transistors of the linear regulator.

 

[qrper]

Well then with two scr's one would have a full cycle going into the battery?

this schematic Battery Charger 12v SLA shown above only shows one scr and thus is a half wave rectifier.

There must be a reason why this kind of battery charger is not seen very much in consumer devices.

mike

 

[ccurtis]

Well then with two scr's one would have a full cycle going into the battery?

this schematic Battery Charger 12v SLA shown above only shows one scr and thus is a half wave rectifier.

There must be a reason why this kind of battery charger is not seen very much in consumer devices.

mike

Yes, if your transformer is center-tapped then two SCRs can give full-wave rectification. Most consumer battery chargers I remember (it's been a while since I looked at one) don't give 25 amp continuous charge, and are not regulated. That last one I actually took apart had a selenium rectifier in it and relied on a hefty transformer to provide a fairly constant voltage. It had no filter capacitor, at all. It had a cheap voltmeter and a current meter on it.

 

[Andrew Leigh]

Hi

I have a very nice one (have used it for 12 years now) that has protection against pretty much all fault conditons, reverse polarity, short circuit etc. It also has a turbo switch to give very flat batteries a boost in order to start charging. The only problem is that the circuit is set to provide 4A. It starts in constant current mode and then switches to regulated voltage mode to avoid overcharging. It can float a battery indefinitely. Perhaps someone clever here will modify the output for you, I am not that bright.

Cheers
Andrew

 

[qrper]

The beasty thing i have in the junk box is not a consumer item. i think it may be from either a floor sweeper or maybe a electric wheel chair.

Life goes on, but I sure would like to know what makes it tick.



mike

 

[qrper]

dug up some more info


the charger is made by SBS---storage battery systems

it has two pic16c540 ics in it (as near as I can see the text, it's been painted over)

model hd212

 

[fernando_g]

An SCR battery charger,
Courtesy of General Electric's SCR manual, 5th edition, 1972

 

[qrper]

Interesting circuit!

This charger I have has no rectifier diodes in it, just two scrs mounted on a 6x6 inch aluminum sheet.

The pcb is quite busy with two PIC ICs mounted along with a power relay. There's at least 6 two pole connectors on the back that I have no idea what they are for.