voltage problems [Archive] - GrandAmGT.com Forum


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07-19-2008, 04:43 PM
i have a new deep cycle battery and a HO alt thats about 4 months old.

For the past week or so, when ever im at idle or anything under 1000rpms, my voltage drops from normal mid to high 14s down to high 12s (battery power). it never used to do this. the funny thing is, sometimes maybe 3 times outta the all the times i used my car this past week, it'll be normal again, as if it fixed itself. like today comign home from work (6 mile drive) it was fine until i got home it dropped again.

any ideas? voltage regulator on the way out or something? i checked my grounds for my amps and theyre all tight along with the battery connections; again theyre all good.

07-19-2008, 10:04 PM
yah, or a bad batt cable...shouldnt fluctuate that much

07-20-2008, 01:26 AM
i checked the connections at the alt and the batt, everything is tight. besides, the alt---> batt is less than a year old due to me doing the big 3. what could cause it to work fine here and there though? like it was raining tonight on the way home from somewhere, i had both lights on and my wipers and i didnt notice any problems at all....

but when i do have problems, i get a loud whine that varies with rpms which is from the alt i take it. but when i have no problems its like normal... i dont get it

07-20-2008, 02:23 PM
So when the voltage drops- you hear a loud whine? Sounds like the belt is slipping on the alternator. The alternator could be ready to go out.
Check the belt tension first. Then see if the alternator is stiff to turn.

07-20-2008, 02:34 PM
i looked at the belt and the pulley when the car was running and it's just fine. or could it be slipping only a little bit?

i suppose that could really be it, iv noticed this problem since i drove on the highway thru a pretty good rain storm a few weeks back. maybe its not slipping a lot, but just enough to cause problems

07-20-2008, 02:50 PM
Next time you hear the whine noise, look at the alternator pulley, see if the pulley and belt are moving at different speeds. It does not take much. Also I have seen alternators with a dead spot in them, causing them to lock up up occasionaly. Got to love the intermittent problems.
Good luck!

07-20-2008, 07:03 PM
the loud whine is usually the alt full fielding, or a bearing...not the belt prob

07-20-2008, 07:05 PM
so is it possibly im getting a short spiratically and that is causing the alt to run at full tilt? i only see a big difference at idle, as soon as i get the rpms over 1000 again its more or less fine. but ill be driving along and have to stop at a light or something and ill notice that its fine again...

07-20-2008, 07:32 PM
well the alternator will inherently produce more current due to the electromotive force when you rev the engine. at idle it relies on the power of the alternator and the regulator as well as the sensing voltage from the battery to the alt. if the voltage is low, the alt will full field(go full boogey) to get the battery charge, reaching max output, dimming everything else, pulling alot of power from the engine, and making a whining noise, because of the current produced, but if the sensing voltage is bad then itll do that all the time, it just wont need to produce as much voltage again because it already is due to the extra rpms it is turning. so you were either overcharging the battery and choking it on its own charge basically or you have full fielded the alt til it is nearing the end of its useful life. also if you have ANY corrosion whatsoever on the connection from the batt to the alt you need to get it cleaned...even .1 ohm of resistance is too much for a battery connection

07-20-2008, 07:39 PM
so is there anything i can fix? or do i just need a new alt

07-20-2008, 07:49 PM
i would take the alt off and take it to an alt/gen shop. not autozone or oreillys, a shop that specializes in alternators. they can test it to make sure it is ok. if its not that, then you may want to look at the belt and the tensioner, make sure it isnt bad, fluctuating too much. then its on to the connection from your batt to the alt, then your batt...

07-20-2008, 08:20 PM
damn i wish i knew how to do more of this kinda stuff.

i think what ill do is ill have him put in a new 105amp alt, and just buy another battery for my system. jake is running his setup like that and hes got more powa than i do, and he has no problems in the least.