Battery Charges

[hockeyhead019]

Hi guys,

Me and my dad rigged a charger and i have two 3000 NiMH packs at 7.2 v. I was wondering, what should i charge them at? The charger can go from 3 to 10 amps and i don't wanna fry my cells but i don't wanna wait hours to race. So can you guys help me out. Like what to charge them at, whether temp. is a factor and all that other stuff. Thanks for any advice.

[mark christopher]

what charger have you "rigged"

[josh_smaxx]

I dont like the sound 'charger we "rigged" but if tis all safe with a peak cut off ect the if its a stick oack, charge at 1c, it its a soldered side x side pack charge at 1.5c

c= capacity of the pack

[hockeyhead019]

okay heres the thing the charger we built doesn't have a peak detector so i have to manually time it so at 1c (7.2v) for a six cell stick how long should a 3000 take to charge?

[Chequered Flag Racing]

Originally Posted by hockeyhead019

okay heres the thing the charger we built doesn't have a peak detector so i have to manually time it so at 1c (7.2v) for a six cell stick how long should a 3000 take to charge?

3000mAh charged @ 3amps (1c) from 5.4v for the pack (0.9v per cell)

= 60 mins to full charge (estimate, give or take a few mins either way)

3.5 amps = 51mins
4 amps = 45mins
4.5 amps = 40mins
5 amps = 36mins

you could also monitor the charge temp and stop when the temp of a cell = 40 to 45c
or measure with a DVM and stop around 9.2v for the pack

all the above is for new cells but doubt the 3000's you have are new.
stick to the temp but the peak volts will be higher say 9.6v for old cells

[hockeyhead019]

hey thanks a lot man

but what if i wanted to go at 6 amps how long would it take? is that too much cuz i don't wanna fry them

thanks again

[Chequered Flag Racing]

Originally Posted by hockeyhead019

hey thanks a lot man

but what if i wanted to go at 6 amps how long would it take? is that too much cuz i don't wanna fry them

thanks again

5.5 amps = 32.7mins
6 amps = 30mins

if you don't want to fry them stop the charge @ 40 to 45c when a cell gets there.

do you eqaulise your cells?
if not it's more than likely 1 cell @ least will reach the above temp 1st due the to stored energy in it.

[hockeyhead019]

no i don't equalize them is there another way to do it besides buying an equalizing tray?

[josh_smaxx]

No not really, apart from discharge each cell to 0.9V individualy.

[hockeyhead019]

o ok thanks

[mark christopher]

you would be far better off buying a decent charger, a good one can be got cheap and it will be far safer and you will not have to sit watching it

[josh_smaxx]

Ye, how does £33 sound? It can be done

[hockeyhead019]

I'm fine with the one i built it works fine and i don't mind watching it i just check every couple minutes and read or something while it's charging. Did i mention that we made it so that it can charge two batteries at once and i think i used the wrong word when i said "rigged" it was more of a built from scratch but it works fine with everything you guys just told me. i already ran a cycle in each of my 3000 and they are fine.

Thanks for everything

[josh_smaxx]

Ok, if you say so if you start racing then you will need a 'proper' one though.