Battery or alternator

[Fraser1989]

Hey guys,

I am wondering what you guys think about this. I was driving to work and normally my voltage is a solid 14.5V I noticed while driving to work it was around 11.2V when I got to work I let it sit and idle and it got up to around 12.0V. Then I tried reving it a little and the volts dropped more.

I am guessing that it is the alternator, however this summer my truck sat for a while and the battery drained 100% twice from sitting too long so I am wondering it the battery could be responsible?

What are your thoughts?

 

[RonD]

Alternator would be first stop because you are running off the battery if you rev engine and voltage drops, electrics need more power at higher rpms which is why voltage drops.

But battery may have hurt the alternator, just after starting voltage can be up around 14.5v-15.0v, that is the voltage regulator/alternator recharging the battery after being drained from starting engine, then after a few minutes voltage NEEDS to drop to 13.6volts, this maintains the battery voltage of 12.6volts without burning it out from over charging.

So if you were running at 14.5v constantly then either voltage regulator was at fault or battery was always under volt(below 12v) forcing alternator to be at max output all the time.
But I would expect a few no-starts(click, click, click) on a cold morning or if truck sat a few days, if battery was at fault.

Best thing is to test battery with volt meter while unhooked from truck.
Voltage should be 12.4v or higher
If voltage starts dropping just from voltage meter being hooked up then battery has a shorted Cell.
Hook battery back up and start engine.
Test battery voltage again, should be above 14v then slowly drop down to 13.6v
If voltage is lower than 12.4v with engine running alternator is not putting out any voltage, check all the connections(with engine off), if all look OK pull alternator and have it tested for free at local parts store.

 

[4x4junkie]

Normal alternator output voltage should be ~14.2-14.4 (slightly more if it's cold outside or if the engine is cold, slightly less if it's hot out).

Agreed, it sounds like your alt has quit.

Try charging your battery with a plug-in charger before you swap the alt though (disconnect the battery's cables also). If the battery charges up to ~14.4V on a charger and remains above 12.6V while off the charger the next day, the battery is fine (or at least it's not going to damage your alt). If the battery refuses to rest above 12 volts though upon sitting for some hours after charging it, then it definitely needs replaced.