battery or alternator - Dezzy

Hope someone can help.

How do you diagnose a problem with the battery /alternator. I'm not sure if the problem is with my battery not holding the charge or if the alternator is not pumping enough charge in to the battery.

I have purchased an battery tester but I'm not sure what the readings should be. Can some one help a dimwit !!!

Basically - did a long run this weekend, when arrived at destination - the battery was dead. I did have the heater, lights, wipers etc on and the vehicle in question is a Renault Trafic Van.

battery or alternator - Peter D
Assuming this is not a connection problem, not forgetting any earth straps, the battery voltage when being charged by the alternator should be 13.8 to 14.2 volts. If you have this then turn on all the ligths and heater holt the engine at a couple of thousand rpm and make sure you still have at least 13.8 volts or so. If this drops to less than 13 then you have an alternator problem. Come back with the results. Regards Peter
battery or alternator - John S
Peter D is basically right on how to check this, but I'd expect rather higher voltages. A couple of newish cars I've checked recently give at least 14.4 volts with no electrical load, and maintain this even with headlights plus foglights on. Don't forget modern alternators are rated at 60A or more. Even my Minor with a dynamo holds 13. 6 - 13.8 v with the lights on.

These figures assume a well charged battery, and one problem you have is that a flat battery is going to be pulling a higher current than a charged one, and so depress the readings. It may be best to charge the battery overnight and then do the alternator voltage test. This wil also check the battery - if it won't start the car after a night on charge, then it's probably failed



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