Can I (safely) run several NiMh battery packs in parallel?

From: Nick Toop (nick_at_cortexcontrollers.com)
Date: 09/28/04 

Date: Tue, 28 Sep 2004 11:37:52 +0000 (UTC)

Hi,

I have a portable application for which I require 12V at 1A for 3 or 4
hours.
12V 4000mAH NiMh packs are readily available.
However, I want to be able to recharge the system quickly i.e. in about
15mins.
I do not want to change the battery pack.

The data*** for the Maxim MAX712 or MAX713 appears to imply that the
fastest acceptable charge rate is 4C which for the above battery pack would
mean 1 hour

It occurs to me to use 4 x 12V 1000mAH NiMh packs with individual chargers
(15mins charging). There then appear to be 4 ways I might use them.

1) Run the 4 packs in parallel...this makes me feel uneasy..there might be
large current flows between the packs after (partial) charging
2) Put the 4 packs in series (48V) and use a smpsu to generate 12V.
3) Switch between the packs on a regular basis i.e. every 5 minutes
4) Use one pack but monitor its activity and switch to next best pack when
it starts failing etc: (a bit complicated at the end)

Obviously 1) is the simplest but is it likely to give problems?

 I am inclined to 2).

Is there a 5), 6)....? 

-- 
Regards,
  Nick Toop
Quantcast