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LiIon charger ct

I was given an electric drill that uses 12V lithium ion batteries because the charger didn't work and the batteries died and the owner lost interest. I hack sawed the transformer case open and found that the primary winding was open somewhere that I couldn't see, so I didn't try to repair it.

Also the charge adapter that the battery slides into has a burnt out resistor on the circuit board. It's a very simple circuit board, there are 4 diodes on the input side which I assume is a full wave bridge rectifier. After the rectifier there is a small series resistor (R1) powering an LED across the dc power lines coming out of the rectifier, and a larger resistor (R2) which got hot enough to char the circuit board near it as it was blowing up. I'm guessing it was over-voltaged, or maybe more likely the outputs were shorted together. The V+ output voltage passes through R2.

I don't have a schematic, and would like to repair the ct. board if I can choose a replacement resistor that doesn't unsafely charge the batteries. If I get a transformer with the same V and I ratings (14.5V

200mA) I'm wondering what value Resistor to replace R2 with.

I am including a picture.

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I read this, "Most consumer orientated lithium ion batteries charge to a

per cell. Charging beyond this causes stress to the cell and results in oxidation that reduces service life and capacity. It can also cause safety issues as well."

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Since the batteries are labeled "12V", if it uses the same LiIon technology the article is referring to, I assume it has 3 cells totaling

12.6V. The transformer was clearly labeled 14.5V 200mA.

Also from the web page, "Charging lithium ion batteries can be split into two main stages: Constant current charge: In the first stage of charging a li-ion battery or cell, the charge current is controlled..."

It seems like it might be a simple matter of trial and error, power the charge adapter attached to the battery, and find a value of R2 that leaves 12.6V on the output side, when the battery is fully charged. The adapter has no current regulation, other than the series R2. Is that a safe approach?

Would a 12V car trickle charger work safely, with a maximum charging current of 2A (based on the web page)? The transformer had a much lower current rating.

I'm surprised the charge circuit is so simple after reading this web page!

TIA, Mike

Reply to
Mike S
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Short answer...don't do anything until you figger out what you're doing. Are you sure that they're lithium? Is the picture showing EVERYTHING that is in the charger path? That ain't nearly enough stuff to charge a lithium battery.

The picture suggests that you have the typical symptom of what happens when a NiCd battery shorts and the crap unregulated charger melts trying to charge it.

Reply to
Mike

0 mV

!

A 14.5v transformer when rectified would give over 20v output. A resistor t hat will let the cells charge then drop the V_out to 12.6 when current fall s does not exist.

I suspect Mike may be correct that the battery is NiCd or NiMH. If you can verify that it is, they usually use 1.3Ah sub-C cells with a card case. Tho se typically have a 5hr charge time in power tools.

The burnt resistor & oc transformer both indicate a significant overload.

One plus with 12v & 14v tools is that if all else fails you can run them of f a car. Thick wire is necessary.

NT

Reply to
tabbypurr

The photo is NOT a LiIon charger, which would include an IC to control the voltage and current to the battery.

Perhaps it might be useful if you would disclose the maker and model number of the drill and charger? The battery type could then be easily researched.

It is possible to convert a NiCd or NiMH drill to operate from a LiIon battery. Is this what the former owner has done? If so, you will need a much better LiIon battery charger designed specifically to charge a LiIon battery.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
Santa Cruz CA 95060 http://802.11junk.com 
Skype: JeffLiebermann     AE6KS    831-336-2558
Reply to
Jeff Liebermann

Thanks to everyone who replied.

I screwed up assuming it was Lithium Ion, it is not.

Black & Decker FSB12 FireStorm 12-Volt 1.2-Amp Hour NiCad Battery

Reply to
Mike S

Battery failure leaves them with a residual value of zero. You could cobble a battery pack together from other dead packs, putting test-good cells together, but once one cell dies the others follow.

NT

Reply to
tabbypurr

I'm sorry if I wasn't clear, I don't know if the batteries work or not, the charge adapter ct. bd. had R2 blow up, and the transformer had a bad primary winding. The batteries may be good.

Reply to
Mike S

IIRC it was already been explained that those are most likely the result of bad batteries. You might be lucky & it was just caused by accidental shorting. Bodge-charge the battery pack (safely) & find out.

NT

Reply to
tabbypurr

l
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bble a battery pack together from other dead packs, putting test-good cells together, but once one cell dies the others follow.

I've seen that a few times in wall-wart battery chargers, and it's always b een from a shorted secondary rectifier. You could still have a bad battery though, either as the source of the problem or as a result of the shorted rectifier (classic chicken or egg scenario). An ohm meter will tell you wha t you need to know.

Reply to
John-Del

I was about to say... I don't do much electrical work any more, but an electric drill battery that is lithium ? I've never heard that. (then again, I'm just not in the business right now - just my 2 cents)

Reply to
bruce2bowser

I bought a new NiMH battery for my RC car.

7.2 volts 3500 mah. Would it do any harm to try to charge it with a small plug pack charger made for use with NICAD?
Reply to
Lucifer

I was given some battery packs from medical equipment. I used the good cells to power a pocket TV.

Reply to
Lucifer

No problem. Just unplug it when it's had it's charge time, NiCd chargers can't be counted on to shut off.

NT

Reply to
tabbypurr

Thanks.

Reply to
Lucifer

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