V and I for dual battery charger?

ejaf · #1 11-16-2002, 09:21 PM

Can anyone give me specs as far as what voltage and specs are necessary in order to charge 2 1.2 V 150 maH batteries in series.

Timing for the charge would be a plus as well.

A lot of good posts on the topic, and good advice, but I'm still at a loss. Probably will make an AC charger, but my "project" right now is to convert a 2AA charger that came with that MGA car from TRus (can't remember the name of it, I guess it didn't impress me).

Thanks in Advance.

ejaf · #2 11-17-2002, 03:14 PM

No one?

Azimov · #3 11-21-2002, 11:23 PM

Well, roughly off the top of my head you need a charger that supplies 3VDC at around 5-700mA and charge for 90 to 135seconds. Play with the charge time a bit, but don't exceed 135 seconds as you may over charge.

ejaf · #4 11-22-2002, 09:06 AM

Thanks...

Alot of posts mention varying numbers, but when I look up the specs for the cells in question, they are nowhere near in mA as compared to what thee chargers put out (fast charge specs for these sized cells mention ~ 100-150 mA).

The charger on the ZZ is putting out at least 700 mA and I have a Shen -Qi Wei charger that puts out over 1 Amp (ramps up from 700 mA to 1.2 mA...what's up with that?).

My other charger for my Panther is a contact amperage over 1 amp.

Namuna · #5 11-22-2002, 09:18 AM

As far as charging batteries goes, you set the V = to what the pack is...so the 2x1.2v in series = 2.4V...You SHOULDN'T mess with this setting.

You can 'play' with the settings as far as how much Current to pump to the batteries (mA). For instance, I put my Multimeter to the Bit Char-G charger and it was cranking out 2.0A...Now THAT'S fast charging!

So, in your case...The 'V' should be set for 2.4V, and the 'I' is up to you (For me, I'd crank 1.5A for 60 to 90 seconds...You can set either the current or time for more or less, depending on how daring you want to be)

Good luck.

Azimov · #6 11-22-2002, 09:44 AM

Yup, this is correct. I was posting off the top of my head and that may not be a good idea where this topic is concerned. VDC should be as exact as your charger will allow. Current can be played with as long as you keep the timing in mind.

This is flawed, please see the explanation below.

ejaf · #7 11-22-2002, 11:40 AM

Thanks, Namuna and Azimov (aka Isaac?)...

But now I am confused a little more...V out with the stock chargers are WAY over 1.2 V, so therein lies my confusion...

You are saying that I should set V = 2.4 since I will be setting the batteries up in series, and the higher the current, the quicker the charge (therefore careful of the timing), yet how are the stock chargers getting away with Voltage ~ 3.0 V (or slightly less, dependent on how new the batteries are)?

I WAS assuming that current was more important, and voltage wasn't as important (I have seen some threads on AC Converter charging specifying using 4.5 V, as well as some who have added a 3rd AAA battery to their controllers upping V to ~4.5).

Quote:

As far as charging batteries goes, you set the V = to what the pack is...so the 2x1.2v in series = 2.4V...You SHOULDN'T mess with this setting.

Namuna...are you saying that voltage should be >= sum(battery V) or = sum(battery V)

P.S. This forum is awesome...I feel like a kid again

Azimov · #8 11-22-2002, 02:27 PM

Look at it this way. The Motor Works clone from Wally World has two rechargeables in it rated at 2.4 volts in series. The stand alone charger has three batteries in it rated at 4.5VDC! And people wonder why they are so fast. Fact is, this 4.5VDC drops considerably when you charge the car, or put the source under load. And, if you aren't careful about how long you charge at a given level of current, you will fry the batteries in the car. Voltage is pressure. Combine the pressure with higher current for to long and fizzle-kablooey. Keep in mind that these specs are listed on open circuit. Put a multimeter on that battery pack and it reads 3.0VDC for two AA or AAA batteries in series. Now, hook it up to your car and check it again. You'll see that it has dropped considerably under load. But, let it sit there long enough and the car batteries fill up. Now, there is no load on the charger batteries and the VDC steadily rise back to the original 3.0. Now, you are starting to supply more VDC than the batteries can handle. That's why timing is so important. Let it get that far and your car batteries are toast. So, the voltage and current effect charge duration to keep the batteries nice and powerful, but not to long or they get fried. You time the charge by a formula dependant on current and battery capacitance. This flow of current drops the output of the VDC (like water rushing into a larger pipe, the pressure or VDC is reduced) but when the pipe gets full the pressure rises back to it's original state. So, you gotta turn off the spiggot before that happens.
And BTW, Issac spelled his name Asimov, not Azimov like I do. It's an homage to him as I idolize the man, but not an exact spelling. Sides, the correct spelling was taken the first time I tried logging in on e-bay and I used the same name here.

ejaf · #9 11-22-2002, 04:10 PM

Thanks...

I will try hook up the MM while the charging is underway, for my own curiosity. Where would be the best place for that measurement?

P.S. I love his books

Azimov · #10 11-22-2002, 04:59 PM

Right on the charger leads or the car battery poles. Doesn't matter at that point because the two are tied into a single circuit while connected. Might be hard to get in there though.

ejaf · #11 11-22-2002, 08:29 PM

Got it...thanks...I thought the same thing, "teeny weenie living space"