Building a 500 cell NiMH battery pack, 15 Ah @120V?

[JazzMan]

I was toying around with what it would take to
build a 1.8 KWh (15A @ 120V for 1 hour) battery
pack. So far I'm at around 500 AA 3,000 mAh
batteries, but how to connect them up? I bet
that 5 x 100 cell series sets in a 5-wide parallel
array wouldn't work, where does one start with
something like this? I don't have a particular
project in mind, well, maybe, but this is more
of a mental workout.

JazzMan
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[gcd]

Hi,
Have you considered using a DC-DC converter or DC-AC inverter for your
application, may be a lot simpler.

Maybe even 10 sealed lead acids may be a better choice?

If you want to parallel stacks then you will need to isolate them from each
other using diodes or similar so one stack doesn't try to charge a weaker
one. As the load increase and the terminal voltage drops on the highest
voltage stack the others will eventually load share.

Also, you can load NiMH cells to about 2C. This will reduce capacity to
around 80% with reasonable terminal volts but would reduce the number of
stacks needed to be paralleled. However the downside is the cell dissipates
more power. You can load to higher than 2C but usually done in motor
applications such as Radio Control and the capcity decreases rather quickly
for higher loadings, check googgle for "discharge rates for NiMH".

Depending on your application Li-Ion or Li-Ion polymer may be a better
choice - higher power densities.

Good luck making a charger for that

of course no need to mention the safety aspects is there?

Cheers
Greg

 

[Pooh Bear]

I was toying around with what it would take to
build a 1.8 KWh (15A @ 120V for 1 hour) battery
pack. So far I'm at around 500 AA 3,000 mAh
batteries, but how to connect them up? I bet
that 5 x 100 cell series sets in a 5-wide parallel
array wouldn't work, where does one start with
something like this? I don't have a particular
project in mind, well, maybe, but this is more
of a mental workout.

Why AA ? Surely D cells would be simpler ?

Graham

 

[BobG]

This is what AC Propulsion uses for the TZero. They make packs the size
of cigar boxes out of em and have em everywhere.

 

[JazzMan]

Why AA ? Surely D cells would be simpler ?

Graham

I arbitrarily chose AA because those are commonly
available, though it appears not in the 3000mAh that
I originally thought. If I get serious about this I
will do calculations on price/mAh to get the best
value irrespective of size. I'm shooting for a pack
that weighs less than 60 lbs including charging. For
charging I was going to use a dedicated charger
circuit for each series of cells, implementing one
of the advanced charge strategies, along with
temp sensing for each series set.

JazzMan
--
**********************************************************
Please reply to jsavage"at"airmail.net.
Curse those darned bulk e-mailers!
**********************************************************
"Rats and roaches live by competition under the laws of
supply and demand. It is the privilege of human beings to
live under the laws of justice and mercy." - Wendell Berry
**********************************************************

 

[Jasen Betts]

I arbitrarily chose AA because those are commonly
available, though it appears not in the 3000mAh that
I originally thought.

I was kind of suprised when you wrote that, I'd just been to the battery
shop for new cells for the digital camera and they guy said that the
Sanyo 2500mAh cells he sold me were the highest capacity he also said
that cheap cells were crap but the Sanyo cells didn't strike me as being
expensive.

Bye.
Jasen