7.2v NiMh - charger says 8+volts FLAT wtf?

[SqueakyBum]

Seriously, this rockfighter came with a supposed 7.2V 1500Mah NiMh battery (which I believe is true)

- it's a 6 C-cell (configured 3cells x 2cells - standing vertically beside each other)

So, it's discharged. Plugged it into my Etronix Powerpal DC charger set for 7.2V NiMh - 1500Mah @1.5A (1C)

Charger does battery check and starts charging - I look at the screen and it's showing 8+ volts.....so I switched it off quick sharp, just in case something was Fecked.

Maybe I looked at it wrong or something but don't want to hook it up again to find out....what sort of pack could this be; if not a 7.2V?

Any advice?
The manual states that specifications can change without notice.....did they change the battery specifications?

Or did I just mis-read the display? It was the first time I tried charging a NiMh with it, I've used it a few times for LiPo and where the voltage of the LiPo shows as it charges is where I spotted the 8+volts. Hence my problem. Should I just go for it again and assume that because the charger didn't flag it as something other than what I told it to charge that i just read it wrong?

Advice please

[Charlie-III]

Chill.....take a deep breath....it's fine, you didn't mess anything up.

The 7.2 volts is a nominal voltage, the full charge is much higher which is what you are seeing.

Charge & have fun.

[SqueakyBum]

I'm with you all the way there mate, only thing is - the battery is discharged - fully. At least the truck thinks so.

That's why I freaked out LOL, I'll try it again and post back if I don't get my face blown off by it

[Charlie-III]

Originally Posted by SqueakyBum

I'm with you all the way there mate, only thing is - the battery is discharged - fully. At least the truck thinks so.

That's why I freaked out LOL, I'll try it again and post back if I don't get my face blown off by it

"Discharged" is NOT the same thing as "0" volts. When charging, the voltage can come up very fast, but not all the capacity is there yet.

Don't worry about your face.

[SqueakyBum]

Okay, Weird. just weird.

Regardless of what battery I plug in to charge, the display shows the voltage way over 8 volts. The 2100 Mah pack I'm now auto charging at max. 2.1A - (was) sitting steady at 8.83v - is that normal?

Sounds a bit high no matter what. this is the actual battery voltage, not the supplied voltage.
over 8.9v as I type now.....

how can it detect the correct voltage if it's way above what it should be?
The LiPo charge builds the current in the cells and I can watch it doing so; eventually getting to the desired voltage (8.4v), the NiMh on the other hand is off like a spanked horse into sillyville. don't get it.

It just doesn't ring true, despite everything.

Guess I'll have to assume the charger is more knowledgeable than me.

[SqueakyBum]

I know the discharged voltage isn't going to be zero LOL, just expected it to be less than 7.2v - yet it's straight into the 8+v range, I stopped the charger as it went past 9v.

Please forgive the newbie posts here, I actually know (or have learnt) a fair bit about batteries for the most part, I'm just new to charging them with proper equipment, I understand capacity/C ratings, charge rates (1C) nominal voltage, charged voltage etc. series and parallel - All the theoretical stuff. Just alarmed by the voltage not building gradually and embarrassed by the fact I've no idea what the fully charged 7.2V NiMh voltage should be.

The LiPos were no bother, self explanatory, yet I'm still a little unsure about the NiMhs.


So what is the normal fully charged voltage of a 7.2V NiMh then guys? please...it's like the one little bit of puzzle I missed and it's got me running scared from NiMh batteries I charged like about 100 times already, sheesh.

[Trubble]

Relax.......... settle down............

The voltage of a completely charged NiMh cell is in the 1.45-1.5 volts range. So for the charger to JUST MATCH the voltage of a fully charged pack, it'd hafta be darn near 9 volts. Now consider the charger still needs to have enough voltage to actually 'shove' electrons in, it actually needs to be above 9 volts.

And it's not unheard of to have voltages shoot up over 11 if you have a cell or two in the pack that are fixin' to check out. Of course by that time you'll see a mountain of false peaks and the pack won't tolerate even 1C charging.

Plug it in, and let it fly. Provided your charger's at all competent, your pack should charge just fine.

[SqueakyBum]

Originally Posted by Trubble

Plug it in, and let it fly. Provided your charger's at all competent, your pack should charge just fine.

LOL, yeah it's a decent charger (budget but competent).

I did some reading and found that this voltage rise is pretty normal.
Others asking the same questions elsewhere on the web.

So far as I can tell, if it goes to 10V or above for a 7.2V pack - it's on it's last legs.

Considering my 7.2V packs have been pumped silly on a cheapo Ansmann fast charger for a couple of years, I expect these old NiMhs I have are way past it anyway.

I'll plug the brand new one in and see how it goes.

Thanks to all for the kind words, will post back anything interesting I find.
(given that the pack is new I suppose it's worth sharing what the pack voltage goes up to during charging)

Little side note; I also read that if an old pack has leaked and given up, it may be possible to re-activate the cells by charging with a much higher voltage........ooft. don't think I ever want to be trying that trick!!!

[squatch71]

if a cell has leaked......don't charge it...you have bigger problems.

I'm with the rest...charge and enjoy........that is if your cells havn't leaked

[Charlie-III]

Cell's that are not happy "may" be able to be brought back. Keep checking the pack temp. If it gets "rather warm" (almost too hot to touch) then remove the bad cell.

I have brought back quite a few "rather old" NiCD & NiMH packs. Keep in mind, when things go wrong, they usually start fires!

I just want to make sure you know what you're getting into, YMMV........