Is there a way to charge a battery pack manually?

[antillean]

I bought a 4200mah NIMH 6 cell pack for the RC Hummer I built last week, but the charger I got didn't work... So I got a replacement, and the replacement didn't work either. Someone suggested that it might not be detecting the dead battery (doesn't that defeat the purpose??). Can I plug in some power backwards, like 5v from my computer, and give it a "jump"?

 

[0roo0roo]

bench charger?

 

[antillean]

If I had a bench charger I wouldn't have a problem!

 

[tasmanian]

Buy a new battery pack.

 

[henryay]

Do not hook it to the computer's 5V supply. It'll destroy the battery. It needs a low constant current. The power supply will give it a HUGE amount of current.

 

[Colt45]

Originally posted by: antillean Can I plug in some power backwards, like 5v from my computer, and give it a "jump"?

backwards?

haha, i see this ending poorly

 

[Jeff7]

Do you have a voltmeter? Is the battery pack putting out any power? What kind of charger? Where was it bought from? Elaborate on "didn't work either."


Details!


And no, plugging it into your computer would likely not be a good idea. First, it's a 7.2v battery pack. 5v isn't the right charging voltage. Second, it might dump a lot of current through the battery - bad for the battery pack, and if the current is too high, it might not be good for the power supply.


PS - MS Dawn is now Rubycon.
Same repository of endless electro-mechanical knowledge, new name.

 

[soydios]

Get a cheap trickle charger from Radioshack. It outputs a few hundred milliamps at the specified voltage no matter what is connected to it. If you battery doesn't charge connected to one of those, then your battery is the problem.

 

[Analog]

Originally posted by: antillean
I bought a 4200mah NIMH 6 cell pack for the RC Hummer I built last week, but the charger I got didn't work... So I got a replacement, and the replacement didn't work either. Someone suggested that it might not be detecting the dead battery (doesn't that defeat the purpose??). Can I plug in some power backwards, like 5v from my computer, and give it a "jump"?

Nickel Metal Hydride batteries aren't like your car battery. They are highly sensitive to temperature while charging, and require an algorithm to charge properly. Why? Because they need to be monitored while charging. Look at Fig. 20 in this document:

http://data.energizer.com/PDFs...etalhydride_appman.pdf

If you overcharge the battery, then you risk damage to the cells. The amount of time based on the capacity of the battery is also critical. The charging efficiency of nickel metal hydride batteries is around 66% which means that you must put 150 amp hours into the battery for every 100 amp hours you get out of it.

You must not put more than C/10 (amp capacity charge) into the charging of the battery, this is to prevent overcharging.

If you can do this before hooking it up to the main charger, then you'll probably be okay. I would do it myself, since I have a current limiting power supply that is fully adjustable. If I only had a 5V computer supply - no way. Some of the more expensive chargers would probably not have an issue with this - they have a very robust algorithm, but it costs. HTH.

 

[Shawn]

Originally posted by: Colt45

Originally posted by: antillean Can I plug in some power backwards, like 5v from my computer, and give it a "jump"?

backwards?

haha, i see this ending poorly

"I tried hooking up this battery pack to my computer's power supply and it exploded and gave me 3rd degree burns. What should I do ATOT?"

 

[antillean]

Originally posted by: Colt45

Originally posted by: antillean Can I plug in some power backwards, like 5v from my computer, and give it a "jump"?

backwards?

haha, i see this ending poorly

You charge batteries by running a current through them backwards. I wasn't sure how the amps would work, whether you'd have to limit or no. I guess it wouldn't work



The battery puts out 1.4v. The charger apparently requires a higher voltage to detect the battery. Why they would design it like that is beyond me. I have to buy a trickle charger in order to use my fast charger-- WTF!?!?

 

[antillean]

http://www.scale4x4rc.org/foru...ead.php?t=13099&page=3

Those people piss me off. Only one guy even thought of the precharging thing, and all the others did was insult me for being a noob or whining about not being able to cancel the return replacement.

There are links to the items in that thread. MRC Super Brain 820 is the charger.

 

[antillean]

http://www2.towerhobbies.com/c...ti0001p?&I=LXNCR1&P=ML
http://www2.towerhobbies.com/c...ti0001p?&I=LXRPP7&P=ML

Notice how neither description says anything about having to charge the new battery before charging it. The support people at Tower Hobbies didn't know that either, and it's not in the instructions for the charger.

 

[antillean]

What if I connect a 4 cell AA (nimh) pack to it backwards? Will that charge it a little?

 

[Rubycon]

Do you have a DMM?

Measure the open voltage of the pack. It may even be open! If the pack has thermal protection it may be open. If it was drained too low a cell could've reversed. By all means check the pack with a volt-ohmmeter BEFORE trying to pump some voltage into it.

If you get that far, monitor current as well. Excessive charge rates will increase internal cell pressures and some venting methods are one shot (rupture disk basically) that can explode with the force of a small bullet hit squib (the thing Hollywood uses to give the effect of bullets hitting a subject like a car). Either way incorrect charging is dangerous.

 

[Jeff7]

Originally posted by: antillean

You charge batteries by running a current through them backwards. I wasn't sure how the amps would work, whether you'd have to limit or no. I guess it wouldn't work



The battery puts out 1.4v. The charger apparently requires a higher voltage to detect the battery. Why they would design it like that is beyond me. I have to buy a trickle charger in order to use my fast charger-- WTF!?!?

I think that once a NiMH cell drops to around .9V under load, it's considered "dead." Much less than that and I think you'd be risking damage.

It's possible that one cell in the pack is dead, and so reduces the voltage of all the cells in series. I've had some cheap Powerizer brand AA's from Thomas Distributing recently, and they died after less than 100 charge cycles, as in, they hold a voltage of about 1.2V, but then after only about a minute of a 0.1 amp load, they drop down to somewhere below 0.1V. Chinese crap, it seems. Meanwhile, some Japanese Sanyo-brand AA's that I bought years ago on clearance at Walmart are still working perfectly.

I'm looking forward to buying some Eneloop AA's, also made by Sanyo. They're NiMH's that are supposed to maintain 85% of their charge after a full year in storage.


And I see by the post before mine that our local expert has arrived.

 

[antillean]

I emailed the manufacturer of my charger, MRC, and the guy said to try jumping the NiMH pack with a 9v battery. I didn't want to risk damaging it though, so I bought a slow charger and NiCd battery combo at radioshack for $25 and tried to charge the NiMH pack--- it didn't take a charge. After a whole day it was still putting out 1.44v. I guess it's dead. I've been using the NiCd pack, until I get the NiMH one replaced. It's only 2000mah, but at least it charges in about 30 minutes (WOW).

In other news, I'm hooked on RCing forever. But I ran over dog poop so I had to leave my Humvee outside to dry-- I cleaned it with isopropyl but I don't want any dog doody residue stinking up my apartment.