Using car battery in project - how to test a used one and how to charge it

[dxpwny]

I am working on a project that requires 12VDC and at least 20 Amps - for maybe 20 seconds, three times a day. The idea of using a used car battery occurred to me. If I look to buy a used one, how should I test it ?


If I go this route, would it be fine to trickle charge it continuously - maybe connecting a power supply set to about ~13 or 14 V ? Would it be ok to just put a diode in series with the + lead so as to prevent battery current from flowing back into the power supply ?

 

[srizbf]

I am working on a project that requires 12VDC and at least 20 Amps - for maybe 20 seconds, three times a day. The idea of using a used car battery occurred to me. If I look to buy a used one, how should I test it ?


If I go this route, would it be fine to trickle charge it continuously - maybe connecting a power supply set to about ~13 or 14 V ? Would it be ok to just put a diode in series with the + lead so as to prevent battery current from flowing back into the power supply ?

if it is lead-acid , check their electrolyte and the condition of the plates , with the help of a known service personnel.

 

[crutschow]

Most places that sell car batteries have a tester that will give an indication of the battery condition.