What's left of a Solar #1002 battery charger.   Funny story, that.

(Keep reading.)

     Electronics      Reviews, Teardowns, & Guides


The simple battery charger is not so simple anymore. 

Every household has (or needs) one of these gadgets, but what do we really know about them?

What follows is a tale of mystery, puzzlement and consternation.

Oh, and I'll review the Solar #1002 battery charger while we're at it.

Caution:  Electronics repair can be dangerous.  Disclaimer.

A Quick Note

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In This Article

Meet the Solar #1002

The SCR Battery Charger

Fixin' It Real

All Op-Amped Up

Oh You've Gotta Be Kidding

The Good News


Meet The Solar #1002

The Solar 1002 is a compact, 1.5 amp battery charger and maintainer.  

I would like to show you a picture of what this battery charger looks like new, but I hacksawed apart the case to get at the circuit board.

I'll tell ya what:  in its original configuration, the Solar 1002 is a very handy size.  It's semi-splash-proof, I guess... and the danged AC cord is too short.

It's a good little charger, though. 

Until, as most chargers eventually do, it starts to malfunction.

And thus begins the "teardown" portion of this story.

The SCR Battery Charger

Because the manufacturer does not supply a schematic, I really don't know how this particular SCR circuit works.  It could be similar to one of the freely-available DIY battery charger circuits out there, but I'm not totally sure.   I haven't taken the time to try to reverse-engineer a schematic for it, but I guess I could always try that.  Some of you guys are electronics engineers, and you could probably do a lot better job at reverse engineering than I could.

Here's what I do know.  The SCR in this unit had a weird catalog number which-- through an exhaustive search-- cross-references to an NTE 5552

When I was gearing up to fix the Solar 1002, I therefore ordered a nice new NTE5552 (which you can get here or here.) 

The SCR in this charger-- which is equivalent to a 5552-- can handle some pretty serious voltage and current.  200 volts at 25 amps, peak. 

And lemme tell ya, that SCR gets HOT when it's being used in this battery charger circuit.

Fixin' It Real

The Solar 1002 has a small red LED that lets you know when the battery is charging.  At 1.5 amps, it's a relatively slow charger.  As the battery reaches some pre-determined voltage (probably about 13.5 volts give or take), the LED shuts off.  Actually it will usually blink a few times first.

Well, what happened was that the LED gradually started to work less and less often, on any battery.  Eventually it would not turn on at all.  And there was no output voltage.

"Somethin's kaput," I pronounced.

It was a few months ago that I decided to tear into it and really figure out what was wrong. 

Everyone loves to re-cap circuit boards, right?  So I threw a couple of Nippon Chemi-Cons in there (well, not threw, but...)

Charger didn't work, still.

Next up:  Hey, I see scorch marks around two of the resistors.  And they're bubbled!

So I replaced 'em.

Nope, that didn't fix it.

Um, OK.  Hmm... what's this over here?  Oh, that's the silicon-controlled rectifier.  Hey, don't these pass a lot of current?  I betcha that SCR toasted itself!

Eight bucks later... Nope, the charger still wasn't fixed.

I was really beginning not to like this battery charger. 

All Op-Amped Up

The battery charger was starting to run out of possibilities for part replacement.

Oh, wait a second.  The op amp!  Surely it must be the op amp!

I figured maybe the op-amp was toast.  (They do go bad, you know.)   I didn't feel like building an op-amp test circuit, because the time it would take for me to do that would be more than I'd spend just replacing the one that was in there.  What I did do, though, was solder an IC socket into the board, so I could swap out op-amps at will.  Yeah!!

Let's cut to the chase.  The new op-amp didn't fix it, either.

Hmm, this is getting to be rather peculiar, I thought.

Next up:  I desoldered the transistors and checked 'em.  They tested OK.

Next:  I began desoldering diodes and checking 'em.  They, too, tested OK.

OK you stinkin' piece of silicon, time for the junk box.

That battery charger thought I was not going to spend another forty bucks (it was right about that!), so it just kept playing this to the hilt.

Oh You've Gotta Be Kidding

So I replaced about 70% of the components on the circuit board.  And I still couldn't get that red LED to go on, except when I shorted a couple of the pins on the NTE 5552.  That's kind of a dumb thing to do, I reckon, because I think the maximum gate voltage on that SCR is like 3 or 4 volts.  So there I was, putting about three times that voltage across there, because by that point I was like "Yeah, whatever, this is going in the junkbox anyway."

After way more work than was even worth doing on this thing, and after subjecting the 5552 SCR to treatment that probably should have zapped it, I had an epiphany.

You see, another battery charger quit working one day.

If you can afford to order anything you need when something breaks down, then by all means take advantage of that!  I've always had to scrounge.  I tend to have used stuff in various states of disrepair, simply because new equipment can be expensive.  Used stuff is cheap, but it's a trade-off, because it also has a lot more problems than new stuff.  

So I had to call into service another battery charger (old and used) to charge a battery (old and used) on a lawnmower (old and used) which wasn't working again (surprise!!).  

And that's when I saw it.

The battery clip on the second battery charger fell off in my hand.  No problem, I thought:  I'll just go into the junk box and salvage the clips off the Solar 1002, which was never gonna work anyway, because... well, I wasn't sure.  

So I soldered them on, wires and all.  And just to be sure... I checked the continuity.

No continuity.

Do you see where this is going?

Let me run that by you again.

The battery clips were connected to wires, which I snipped off the Solar 1002 that was in the junk box.  I attached those wires to another battery charger.  And yet, the meter was telling me there was no connection.  There was a break in the battery wires somewhere... such as, in the place where the wires connected to the clips.

Hey, wait a minute.

That Solar #1002 battery charger might not have been bad, after all.

So I swapped out some components that were probably OK.

But now it's in this awesome, made-from-junk project case, so it was totally worth it.

Aside from the way-too-short AC power plug that's not polarized, this is a pretty darned good charger.  Get yours here (in its original housing, not the made-from-junk project case.)

The Good News

The Solar 1002 was immediately rescued from the junk box.  After re-attaching the battery-clip wires (which I fixed) and making sure there was continuity, I was ready to test it. 

It worked!   There is a little variable resistor, VR1 on the circuit board, which you can turn with a Phillips head screwdriver. It sets the shutoff voltage for the charger.  I made sure it was shutting off somewhere between 13.5 and 13.8 volts, and it was good to go.

Know what, though?  It's entirely possible that there really were some things wrong with it before I replaced all those parts.  Remember those scorched and bubbled resistors?  And the electrolytics were from like 1999 or something, so it was about time to replace them anyway.

And the SCR:   it was worth it to have an SCR with a real part number, not some "house numbered" SCR which took hours to find a cross-reference.



That little battery charger is actually a good one.  Now that I've replaced about 70% of the components, broken apart the case, and backyard-engineered a whole new case from household junk, I'm actually glad I got that battery charger way back around the year 2000.

The Solar 1002 is still on the market.  And if you've read this article, you now know:   the thing that's most likely to go wrong with it could happen to any battery charger.  And it's also the easiest to fix! 

Therefore, I wholeheartedly encourage you to get one of these.   (Ideally I would order one of these, but there is something to be said for a compact, 1.5-amp battery maintainer.)

Maintaining batteries is not the average person's idea of "fun", but it's worth doing.  New batteries are expensive.  It's a lot smarter to spend forty bucks on a charger than to waste a $100 battery by lack of maintenance.

So that's about it.  Forty or fifty bucks, there are no surface-mount devices (Yesss!!!), and you can actually sort of repair this one yourself without a schematic.  That puts it in high esteem as far as I'm concerned, even though this battery charger spent about two months in my junk box.

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