A Thought Worth Pursuing?

KE5YD

Hello, a NEW guy here..............so bear with me!

Here's my "penny" thought:

I have a K-Mart/Sears/Diehard battery charger...rating 10A/2A with 50A boost; typically $50 or so.

Seems to work quite well, with bulk/absorb..equalize..and float stages. Let me say, I have NO schematic, nor have

I opened the case yet. I was wondering if one could "break into" the circuitry at the "proper point" on the input stage

and use this THING as a charge controller?? Any experience in doing something like this by forum members? Your

thoughts...........

R. A.

Vic

Re: A Thought Worth Pursuing?

Hi Robert,

Well I may have a similar 12 V battery charger. It uses a real Transformer, and the only electronic part is a FWB Rectifier. The transformer limits the current, and has a thermal circuit breaker for over-current protection. If the one that you have (mine is a Schrauer (sp?)), has a similar setup then the answer is NO. As you would guess this is a bit heavy (the transformer), and the box is about 4.5" X 7" X 7" with a meter and a High current/Low current switch.

Mine cannot do an EQ because the Vout never really reaches 15.5 V. Possibly if you let it charge for days, the battery would get HOT enough for the Vout to reach a temperature compensated EQ voltage.

If your charger is more modern, and a switcher, perhaps it would be better suited to your idea. Although a packaged OEM Switching Power Supply (from some Surplus dealer) and a PWM controller might work better, and you might be able to use a real BTS on the battery.

Guessing done, Vic

Blackcherry04

Re: A Thought Worth Pursuing?

You can get a IOTA charger and crank it up to 15.5 v on the 12 volt and to 32 v on the 24 volt models and run them through a Xantrex C35 controller. That will give you the ability to have Bulk, Absorb and Float. It also gives you the ability to Equalize. I never tried a 48 V, I'd say they are the same, voltage output controlled with a 10 turn pot.

Cariboocoot

Re: A Thought Worth Pursuing?

He's talking about adapting the regulator circuitry in the charger he's got to function as a solar charge controller driven by PV's. I think.

The Catch 22 is: before you open it up and see what's inside you don't know what's inside or if it will work. So-called "smart" chargers that are meant to do "all types" of batteries in theory could, but don't be so sure that they actually do.

There would be no MPPT function of course; strictly PWM (if not V-reg only). As such you have to ask yourself if it's worth it over just buying a controller known to work correctly right from the start.

Caveat: most automotive chargers have very primitive regulatory circuits compared to a solar charge controller. They usually don't even have full-wave rectifying as it is not strictly needed. But one would expect the "smart" chargers to have something more to them. I can't say for sure, as the only one I ever tried failed on its first job and went back to the store, never to be bothered with again.

PNjunction

Re: A Thought Worth Pursuing?

KE5YD wrote: »

I have a K-Mart/Sears/Diehard battery charger...rating 10A/2A with 50A boost; typically $50 or so.
Seems to work quite well, with bulk/absorb..equalize..and float stages. Let me say, I have NO schematic, nor have...

Even if you could do this, have you actually tracked the charge algorithm with a voltmeter and ammeter to actually make sure it is doing things according to your battery chemistry properly?

For example, ALL four of my different Schumacher speed-chargers when set to AGM, will happily take agm's into 15.5+v equalize at the *start* of absorb and let them boil away for a few hours even when they don't need it. They are highly agressive, and really intended to bring badly abused batteries back to life enough to start the car.

For normal maintenance of charging AGM's, I purposely use the wrong setting, GEL to compensate and this actually tracks VERY well for agm! (Essentially the speedchargers are .5v high at most normally recommended settings). Even though I don't use gel's, if I did, I would never let my Schumachers touch them. It adds a lot of confusion to the marketplace to use this agressive work-around by using the gel settings for agm's with the speed-chargers unless you are trying to bring a battery back from the dead.

What makes it even more confusing is some battery manufacturers warning against this - and it would make sense on surface inspection of the product, but it is unknown if the other manufacturers ever really tested the charger, and not just made visual assumptions based on silkscreen labeling alone.

If you really want to get into this, then perhaps a power supply and a hobby-charger like a Hyperion, which can do up to about 20a of charge current, and allow you to custom set all the sla charge parameters would be interesting if you want to go that far. For more information and some really nice engineering, check out this setup (site and forum - see both!) from engineers and users that really pound their batteries daily:

http://www.wheelchairdriver.com/fast-charge-your-power-wheelchair.htm

There is an awful lot of good stuff that might spark a project build - even if you are not in a chair! Note that these guys mostly favor pure-lead agm's that can stand a lot of current, unless they go to a totally different chemistry like lifepo4.

But the biggest point here is that with automotive chargers, especially ones without any sort of voltage or charge algo specs at all, one MUST do a track with a voltmeter and ammeter at least once to make sure they aren't smarter than they need to be.

KE5YD

Re: A Thought Worth Pursuing?

Hello PN, Coot and Others,

I took the model #, searched I-net.....found wiring diagram? and user manual. Ok, so I decided to open-the-case for a peek. Things did not

look right?? Model # was correct? What could be wrong? Went to Sears "PartsDirect", model # was there, and what few parts they carried looked

much like the wiring diagram. Ok, but these were still not the parts that were in my charger. For anyone who wants to look, my model # is

Diehard #71222 . The xformer, case, meter, and switches look the same; but the rectification, control board?,heatsinking?,and how the fusing

and metering is setup looks to be different. The control board is a Schumacher Elec. 29-99001156 rev.4 date 11/29/2010; it contains a fairly long

multi-legged IC with the number on it of pcb 2144 06 ;... date? 10/26/11....the heatsink contains 4 SCRs [to-220] type devices that are connected

to the outer windings of the center-taped transformer secondary. The CT is positive and is connected thru 2-25 amp automotive type fuses in

parallel mounted on the control board. The metering is in the negative lead coming from the heatsink. The 2/10/50 amp business looks to be

done on the Xformer primary with switching.

Disclaimer: I am not an electronics tech!

I am not sure if the 4 SCRs make a fullwave bridge? I doubt it...since CT is used and the CT to each End voltage is 13.5....

I'm thinking that they are more than likely PWMed to set /control the output voltage. The charger will bring the battery voltage up to an

equalize/top-off of 16v momentarily then slowly drop back to a float of 13.5v and hold that.

That's how I see it? I was wondering if I could just feed the PV panels output into where the [AC converted DC] supply fed-in and utilize the

rest of the control circuitry? I don't know if it's possible/feasible and doing so may be "above my pay grade" technically. Hey! IT's a project...

R A

Cariboocoot

Re: A Thought Worth Pursuing?

Actually your description is not unexpected: it is quite standard on automotive chargers to change connections on the transformer primary to alter the current rating, and normal for the center tap of the secondary to go directly to one DC output (usually negative but not always).

The rest is the bells & whistles of rectification and regulation and who knows how good it is? Since the positive is taken direct from the transformer CT it is not full-wave rectified. Strictly speaking this wouldn't matter when fed by PV's because their output is DC anyway. But what does matter is that it relies on a certain "known" input from the transformer to make the regulating circuitry perform properly. Change the power source and it may not work right, or at all.

So it depends on if you want to sacrifice some equipment and time and money at analyze how it works to begin with and what will happen when you change things ... or just cut to the chase and buy a controller that works right to begin with.