Advice on battery found at thrift store..
rwgast_logicdesign
Posts: 1,464
So I was in Angel View and I saw a battery laying there, 9.6v 3400mAH NiMH, there was no price on it, when I asked the guy said I could have it for 99 cents! I searched the model number on Google, wanting to know what the battery was acually for, I've never seen a battery back like it, it looks like a video game cartridge with 7 terminals on the bottom. From what I can tell it has something to do with an IBM blade server, maybe a specialty UPS system.
The battery number is TP750-MC, here is a picture, maybe someone has experience with these
Anyways I figure for 99 cents I cant lose! If it works I have a nice battery for my sting ray! So I hooked it up to an LM117 wired as a constant current driver at 240mA, just a little under a 1/10c charge, I figured a slower trickle may be the best way to "restore" the cells if none are dead.
What I was wondering is what is the best way to test load? I want to make sure it still works at 3400mA, Maybe drawing 3.4A from it for 1 hour? Im just looking for a simple way to make sure this battery is actually better than my 2450mah pack, and has not been abused to the point where it has lost its capacity.
The battery number is TP750-MC, here is a picture, maybe someone has experience with these
Anyways I figure for 99 cents I cant lose! If it works I have a nice battery for my sting ray! So I hooked it up to an LM117 wired as a constant current driver at 240mA, just a little under a 1/10c charge, I figured a slower trickle may be the best way to "restore" the cells if none are dead.
What I was wondering is what is the best way to test load? I want to make sure it still works at 3400mA, Maybe drawing 3.4A from it for 1 hour? Im just looking for a simple way to make sure this battery is actually better than my 2450mah pack, and has not been abused to the point where it has lost its capacity.
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This is my google search:
"TP 750" battery nimh
Duane J
(It looks as if it was designed to fit in the Multibay and add to the capacity instead of as an replacement of the original)
The 750 series was introduced in 1993... Want to make any guess as to how old that battery pack is?
My guess s that it's pretty rotten by now.
Ok, operative word is *simple*. How about you get two 10 ohm, 10 watt wire-wound resistors. Charge both batteries. Connect each up to a 10 ohm load (will draw roughly 1 amp, which at 9.6V will be roughly 10 watts), and see which one goes flat first ie which resistor stops being hot soonest. Check maybe every half an hour. Time should be the ratio of 3400/2450.
If you don't have any 10 ohm resistors, when you buy some, buy a few 1 ohm 10 watt resistors too. 1 ohm and 10 ohm resistors are very handy for dummy loads and for measuring current. eg if you use a 1 ohm resistor, V=IR and I is 1, so V=R and so volts = amps. Handy.
You should soon get a decent curve.
(Ni-mh doesn't have as flat a discharge curve as Li-ions)
Well considering my battery looks like an after market version it may be a little newer, Im not counting on this thing working well... Im hoping it does though. I mean usually people don't donate broken items to angle view so im hoping the person new this thing worked first. Since it had 0 charge when I bought it I am going to assume this was donated with out being tested first and is most likely junk by now.... but it does not hurt to test the thing, it is a nice big battery for cheap.
I know leaving NiMH around completely discharged is bad for them but what about time in general? If you were to take care of a battery and then store it for 15 years would it be in the same condition it was when you stored it, or do the chemicals break down over time?
Or a donation to a good cause.......
FF
My very general understanding of batteries, is that for Nicads, they are most happy when you discharge them and leave them in that state. For Lead Acids, it is the opposite, they are most happy when you store them on a float charge. I don't know about NiMH. Wikipedia says that NiMH lose 20% of charge on the first day then 4% a day thereafter. So if that battery has been sitting in the store for more than a few months, chances are it is fully flat. And if the chemistry is the same as Nicad, it probably is happiest in that state.
Which is why I am still keeping my fingers crossed you can get some energy into this battery and then extract it.
(addit - Nicads grow whiskers which decrease the energy capacity. I don't think NiMH grow whiskers. The radio control people I talk to say the best thing you can do for Nicads and NiMH is to use them regularly. My smart NiMH charger has a mode which can rejuvenate cells by cycling 3-4 times. You may find it is worth trying that too)
But the rule of thumb is a battery has about 3 years of useful life. I don't know how alkaline batteries extend their unused shelf life, but they seem to get a bit more.
Buying used batteries? To me, it is a lot like buying used underwear.