Durofix Li-Ion screwdriver from CostCo, anyone?

Any old LiIon phone charger should do fine--typical phone cells run from 600 to 900mAHr.

Charging specs: IF 2.5v < v(cell) = 3.0v Charge current-limited at C/2 to 4.15v (max) top off at 4.15v until i(cell) drops to C/20.

Chargers are a dollar at the dollar store.

Cheers, James Arthur

Interesting, thanks. I looked at my Nokia 2115i charger. Says

3.7V/340mA. So you think I could just make a connector kludge and plug it into the drill?

Hmm, I doubt those little chargers would do the

Sure! What could happen? Blow up? Catch fire? Easy to find out ;-)

[snip]

LiIon charging is tricky, _usually_ done with controls within the cells.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
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 I love to cook with wine     Sometimes I even put it in the food

Yep, it should work fine. Worst-case it might take a little longer to charge your drill than the original charger. So build an adapter and you're good...go for it.

Cheers, James Arthur

Well, I just measured it. Sez 3.7V on the charger, open circuit it delivers 9.5V and with a 100ohm load 6.5V. I dunno ...

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Regards, Joerg

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I doubt the cell is that high-tech in this device. But yeah, I heard from one guy who experimented with Li-Ion that a cell went "exotherm", he couldn't extinguish it and he shoved it over to a somewhat safe place where nothing else could catch fire. IIRC it took 10mins to burn itself out.

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Regards, Joerg

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I think I have the same charger for an older analog Nokia. 9v output, but it had the standard switcher inside, a little mod and changed it to 5V for my Razr. Actually the switcher wasn?t doing squat, was just wired wrong to work with the nokia. An extra cap, ferrite bead and a mini usb connector, now it's nice and quiet. Charges my Razr and my Sansung Clip.

Cheers

Multi-cell protection electronics do cell-voltage leveling, but I haven't seen single-cell protection electronics ever play any charging role--they just open a MOSFET switch if the cell voltage gets too high, too low, for reverse applied voltage, and for short-circuits.

I've dissected many. If I still had abse I'd post a schematic.

Cellphone packs have a thermistor, but I'm not sure why they bother--the slow (C/2) chargers usually just ignore them.

The main danger is overvoltage, and resistive heating when a) fast-charging damaged cells that've gone hi-z or b) fast-charging sub 3-volt cells, which are also high-z.

C/2 is pretty gentle though, and I'll wager the phone charger's better, gentler, and safer than the one he lost.

Joerg, if you're worried, just measure the charger's open- circuit voltage and make sure it's less than 4.15v. If so, it's fine.

Cheers, James Arthur

Ouch!! No, that's not fine. Sounds like the phone controls the battery charge for that unit.

Score one for Jim:

Sorry. I've got something like 100 (really) chargers encompassing possibly 20 different designs, but I'd not seen that done.

I'd be happy to mail you one if you can't find another.

James Arthur

"Joerg" kirjoitti viestissä:4nyCl.5043$ snipped-for-privacy@flpi143.ffdc.sbc.com...

I think that charger is just simple current-limiting transformer and rectifier. Not even capacitor in there...

Here is charger specification for Nokia phones (for 2mm charge plug, but I think older version are similar):

(or Google "nokia 2 mm DC charging interface specification")

-EK

Yep, that's my experience as well.

In theory they're supposed to refuse to charge if the ambient temperature is too high or too low, although I suspect it really only matters if you're being more aggressive in your charging profile (e.g., C rate) so the cheap chargers don't bother.

---Joel

Thanks, Arthur. But I guess first I have to open the thing and re-trace the electronics if I can get to them. To see what's regulated up there if anything. Durofix doesn't sell separate chargers for those :-(

Doesn't anyone have the Durofix and could hang a meter on it? CostCo had oodles of them and shortly after Christmas the whole stash was sold, gone. I've asked in the neighborhood but all the responses were "No, but I want one of those!"

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Thanks, interesting. But that means there must be a voltage regulator in the device because else the Li-Ion could explode when 4.2V are exceeded at the end of charge.

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Do single cells always have that MOSFET and voltage sensing? Wow. I thought it's just the bare cell.

Yeah, I wish we didn't have overzealous AGs or that they had less power.

I'd have to build one, none of the chargers here seems to be regulated in any form.

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Regards, Joerg

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[snip] [snip]

You keep saying that, but you're wrong. Unscrupulous ISP's took the opportunity to save money by cutting all binary groups, then blaming AG's when complaints came in.

Grow up and spend $2.95/mo (or less) for a full-fledged news service.

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
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 I\'ll keep my guns, freedom, and money. You can keep the change.

Quote ""We are attacking this problem by working with Internet service providers to ensure they do not play host to this immoral business,"". Cuomo himself said that. You are old enough to know what "working with" means. Any questions?

Let's face it, most alt groups are dead anyhow. The one for home automation fell into an almost total coma. Not worth it anymore, not even $2.95. Sorry, but this AG did manage to toss the baby with the bathwater.

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Regards, Joerg

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I believe every virtually every cell used in a consumer product has those for protection, yes. Manufacturers generally won't sell bare cells to the public, for liability reasons.

Cell phone packs--by far the most common single-cell application I can think of--most definitely have them.

Those FETs are super-cheap as a result--nice to use in designs. The switch is usually a dual-n-ch low-side MOSFET, with the two FETs connected back-to-back.

Don't rely on the safety circuit for charge-termination. The overvoltage protection triggers at 4.35v or so, which protects against fire but wrecks the cell.

I collected scads of cellphone chargers to study their tiny little switchers. The bulk of them are just 4.20v

500mA current-mode flybacks. Charging is constant-voltage, constant-current, with a semi hi-z output that tapers the charge current as the cell voltage rises.

Anyway, I have about a hundred, and I've got one right here new in its dusty box with your name on it if needs be. I use the same one myself for charging all sorts of LiIon single cells.

Cheers, James Arthur

You might answer that question by measuring the battery terminals.

Most packs have 4-leads: two give access to the cell (via its protection circuits), and two go to a 10k thermistor.

3-lead packs usually tie one thermistor lead to (+) or (-).

If you find a pair of hot terminals, that's the LiIon cell. 10k ohms? That's the thermistor. Wanna be _really_ sure? Crack the pack open carefully and look inside, then re-seal.

Cheers, James Arthur

[...]

Interesting! Do you remember a part number? Always on the lookout for saving a penny in circuit designs ;-)

This could become even more interesting in linear amplifier applications since that means they temperature-track somewhat. They also must have a nice voltage supervisor chip in there. Might also be worth it because even the cheap (but good) NCP3xx series from ON-Semi is still 10-15c in quantities and sometimes that hurts in the BOM budget.

Thanks, I might contact you about it but I think now I've got it. If I provide 4.2V at, say, 150mA this should then charge the Li-Ion from any state to "topped off" if I leave it on there all day. Lowering the current towards max voltage would be easy, in the simplest form by a resistor.

The tough part is always to find a fitting connector but yesterday I found one that I'd have to snip off an existing wall wart.

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