What charger can I "hack" to charge 4 NiMh with?

[BatteryCharger]

What charger can I \"hack\" to charge 4 NiMh with?

I plan on building something that uses a battery pack made from 4 AA NiMh batteries. I really want some kind of charger that I can charge that with, and will cut off when it is done charging. What can I use? I'm thinking some kind of camcorder/cell phone charger...anybody know something that is 4.8v and has a charger like that?

 

[UK Owl]

Re: What charger can I

How fast do you wish to charge the batteries ?, if you will accept a long charge time e.g. 15 - 20 hours, then the charge rate used is unlikely to damage the cells by overcharging them.

In this instance a simple constant current circuit e.g. LM317, or even just a resistor and diode in series may offer the solution you need.

If you want a fast charge, then cutoff when the delta V shift is seen, you would be better getting a NiCD / NiMh charge controller chip and building your own PCB.

Commercial chargers fall into the following categories:

(based on chargers I have seen for sale)

1) constant current only, but you have to watch the time yourself carefully. These are very cheap.

2) timer and constant current, these are slightly more expensive and are what most chargers use. Some of the better ones contain temperature monitoring.

3) delta v measurement. These are the ones to get, but can be a lot more expensive. some also contain temperature measurement sensors to detect overcharging.

If you want a Delta V charger to pull apart, you may have to spend $30 or more for it!.

 

[FreeBSDboy]

Re: What charger can I

Might want to consider one of the maha universal charger/analyzers, like the 777 plus.

 

[lemlux]

Re: What charger can I \"hack\" to charge 4 NiMh with?

Use an R/C charger.

 

[Entropy]

Re: What charger can I

As mentioned above, it depends on how fast you want to charge it.

If you charge it at C/16 or slower, you can leave the batteries on the charger for a while without problems. Just don't leave them forever. In fact, many charge controllers will switch to C/16 or C/32 or so at the end of charge and then "trickle charge" indefinately.