adding nicd cells to a car battery?

[monster]

hi

i have a load of rotten nicd cells lying around and my car battery is too week. past owner put a smaller battery in and its diesel. how can i do this? if i parallel nicds i need diodes, right. but the parallel strings would still need to be charged seperatly before the diodes, so i can't just charge it from the alternator anymore?

any ideas?

 

[liveforphysics]

Its an idea born of fail. NiCd doesn't parallel well, as the voltage is not linear with SOC.

If its a small 4 cylinder, get a $19 lawn tractor battery.

 

[jag]

I've contemplated using NiCd in my car before. As Luke said though not a good idea (in most cases at least).

Closely matched NiCd can be paralleled on the cell level, then put 10 in series.
Charged by a car alternator at 14.5V they will reach I believe 50-80% state of charge, but it will take a really long time.
Nickel chemistries are supposed to be charged constant current until a specific breakpoint, not constant voltage like car alternators provide.

i have a load of rotten nicd cells lying around and my car battery is too week.

Doesn't sound promising. Get a decent quality car starter battery. Since you mention you have a Diesel it has 2x compression and starter will need two times the current of a gas car with a similar engine. A car starting battery should last 5-10 years if kept charged and not let run dry.

 

[jag]

Of course, since you have the cells nothing prevents you from trying.
I would do the discharge curve and Ir of each cell. Pitch bad ones. Combine rest into 10sXp, where X gives you however many 100A's you need to crank your car. E.g. with my high rate size F Elegance NiCd I would need 2-3 in parallel to get 100A. That would start a gas car. Double or triple for Diesel.