replacing battery circuit: need help

daguuy · Post by **daguuy** » Sat Jan 28, 2006 4:12 pm

my batteries came in a clump of 7 huge 1.2v cells so i used a chisel to separate them into 2 sets of 3 and 4 cells and that went well, no broken batteries or anything (that would really suck, don't break batteries!) but when i tested it with my screen, nothing happened. my battery has a charging/regulating circuit between the batteries and the plug that bumps the peak voltage down to 8.4v (in case it goes higher when fully charged) and charges it. i think i damaged that circuit because when i tested it with some LEDs they were very dull. here's a pic:

by then i was hoping i didn't damage the cells because they're really good (4200 mah) so i put a battery plug on the other ond of the circuit (the battery end connected directly to the cells) and tested that with the same LEDs and they were nice and bright

(yes, those are LEDs, not a mini nuclear explosion

)
then i connected my screen to that side and the LCD loked like it was starting to turn on but didn't and the LEDs didn't turn on at all. it did theat every time i tried it so it either didn't blow the fuse or there's a timed fuse on the screen somewhere. then i tested the batteries with my multimeter and it said 9.2v so i think the screen thing's just a voltage issue. now here's what i plan to do and may need help with: since my 8.4v charging circuit is probably dead and 9.2v is too high, i want to remove a cell so it'll be a low enough voltage and get a NiMH RC car battery charger (for 6 cell batteries, like mine will be). will an RC car battery charger work with bigger 4200mah cells or is there a problem with that? also, are there 7.2v NiMH cargers that use a car adapter?

timmeh87 · Post by **timmeh87** » Sat Jan 28, 2006 9:50 pm

some parts of that dont make sense... as far as i know there is no circuit that
'bumps the peak voltage down to 8.4v", as nimh batteries, under load, will rarely develop more than that, and any hardware that can handle 8.4 should be able to handle 9.

now, if youre testing them with a multimeter, that dosent count. its always like .2v per cell higher than the voltage under load. which is what would really matter. right?

anyhow, you can charge any (matched) 6 cells with a 6 cell charger. unless its a timed charger, there should be no problem. of course, it might be a timed charger. and if it IS a timed one, then the time will probably be too short, and you can just run it through twice and risk slightly overcharging it.

daguuy · Post by **daguuy** » Sat Jan 28, 2006 9:51 pm

alright, thanks. i think i might have fixed the charging thing (dvd player battery came with a built in charger). there's 4 pins on it: bat- , bat+ , ntc- , and ntc+. i decided that it wasn't gonna get any deader than it was at the moment so i shorted some of those pins and when i shorted bat- with ntc+, it started working normally again

. the (possibly) bad thing is that even though the discharge is working properly, i havn't tested it to make sure the charger supplies 8.4v from the 12v input (it has a plug that can be 8.4v out and 12v in) so i'll test that tommarow

timmeh87 · Post by **timmeh87** » Sat Jan 28, 2006 11:44 pm

well bat +- is clearly where the batteries go, and ntc+- is likely where the load goes. shorting bat+ to ntc+ would make sense, as that would bypass the circuit (the -'s are common). shorting ntc+ to ground dosent make sense. ... it might work now, but thers a very good chance that it is not working properly. in general randomly shorting pins isnt cool. anyhow, good luck.

daguuy · Post by **daguuy** » Sat Jan 28, 2006 11:50 pm

yeah i tried bat+ to to ntc+ but it didn't do anything. i'll just have to see how it's working tomarrow...

daguuy · Post by **daguuy** » Sun Jan 29, 2006 8:34 pm

i detached the battries from the charger and tested the charger with a multimeter to see what voltage the charger was outputting and it said 19.3v! aren't 8.4v batteries supposed to charge with 8.4v? also does the voltage that chargers charge with vary a lot depending on if there's a battery hooked up to it? i need help

Post by **marshallh** » Sun Jan 29, 2006 8:35 pm

I'd guess your batteries might have come in two sets of 7 cells. (wired in parallel)
Since you wired them in series, the voltage makes sense. Or am I missing something here?

daguuy · Post by **daguuy** » Sun Jan 29, 2006 8:41 pm

ok here's the scoop:

1. i opened up my battery pack and there's 7 cells and a charger circuit

2. when separating the clump of 7 cells into 2 clumps of 4 and 3 cells, i think i may have damaged the charger because the output line was barly supplying enough power to light some LEDs

3. i shorted 2 pins on the charger and the output started working right again

4. i didn't know if the charging function was working though so i detached the batteries from the charger and put a multimeter in their place to see what voltage the charger was outputting from the normal 12v power supply and it said 19.3v

now i'm confused because either
a) that's too much
b) it's 19.3v with no load but 8.4v when attached to batteries
c) the 8.4v battery is supposed to charge with 19.3v
d) i'm screwed and need a new charger

Post by **marshallh** » Sun Jan 29, 2006 9:05 pm

Ok, I understand you now.

Everything is fine. Your 12v wall wart is NOT regulated. That means, it could be anywhere from 11-20v depending on your house wiring. Nothing to worry about there. (Most aren't regulated anyway)

However, when a load is applied the voltage will drop down. I'd guess the charger has a regulator in it.

An 8.4v battery does not charge with 8.4v. Usually it's a few volts higher.

daguuy · Post by **daguuy** » Sun Jan 29, 2006 9:17 pm

thanks! that's awsome, i thought i was gonna have to blow $20+ on a new charger, those things are expensive

daguuy · Post by **daguuy** » Thu Feb 02, 2006 7:40 pm

i was trying to test my screen and stuff with the battery and this time it's really pooping on me. i found out that the fix i did earlier was briefly bridging the battery - with the output - and that was working. then it stopped again and this time it won't do crap. i tried removing the charger and getting power straight from the batteries and it's not working

. any ideas? are there any problems like this that are known to happen to NiMH batteries? i know they're fully charged because i charged them earlier when it was working.

EDIT: ok this is wierd. i just made a handy dandy little LED test plug to see if the battery was working and it suddenly started working again. wierd.
EDIT2: dang it just stopped working again! this is insane, i hate this battery but would love it because high cpacity but it's just wierd! i think it's haunted....
EDIT3: i tested it with a multimeter when it was (unsuccessfully) powering a psone screen and it said 8.9v but not even the LEDs lit up. how do you test amps with a multimeter?
EDIT4

: i think it's not a problemwith the battery, but the screen (good thing it's the screen cause good batteries are usually expensive). my screen won't power on and i tried bypassing the fuse but that did nothing. that sucks but maybe it's fixable, it's probably just a wiring/shorting problem.