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Old 03-09-2014
rangerstepside's Avatar
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battery gauge dipping

ok so here's the short of it. left work yesterday, and on my way out, i jumped a 67 vw bus. his started up and i disconnected and went to a parking spot to add some power steering fluid. when i stopped my gauge for batt. dipped down to 1/3 and the battery light came on. alternator is 1 day old. so working at a parts store i went in and tested the alternator and the battery. both tested good. went out and swapped out the battery and it fixed it. day after... it's back. same condition. battery is an optima yellow top. one thing i noticed today is that the battery is sizzling like it's hot from an over charge. but 2 things, my gauge goes low, not high. and the battery is not hot at all. it's a real quiet sizzle and you have to have your ear next to it to hear it. so what do you guys think? im guessing voltage regulator, which is in the alternator right? and can it be replaced by it's self? it runs and drives fine. only time it does it is at idle and it's only once or twice in a drive. motor only lugs a little when it dips and it dosent seem to hesitate at all when driving. i also noticed that my little connector on the back of the alternator is kinda loose due to the end of the retaining clip being broken, but i wiggled the hell out of it and the only time i can get it to do it is if i unplug it. which every time it does it the connector is plugged in.
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Old 11-10-2017
MaDMaXX's Avatar
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Well, kinda - that's what I have look at in more than a passing observation, from memory, it's looped right around the exit of the valve.
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Old 11-10-2017
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OK, first thing is you need a volt meter

sizzling is most likely a dirty battery cable, remove both and clean them with wire brush, battery terminals as well

Good battery has 12.3 to 12.8volts
12.8+ volts is new battery
12.3v is 5/6 year old battery

After start up battery voltage should show 14.4-14.9volts, under 15volts
Thats the voltage regulator ReCharging the battery after startup
After 5 minutes or so of driving/running battery should show 13.5-13.8volts, this keeps battery charged but doesn't "cook it"

After engine has been running for a bit do not shut it off but pop the hood and check battery voltage again
Should be 13.5-13.8v range still
Raise RPM, and hold steady at about 2,000, voltage should go up then come back down to same range even with higher RPM, thats voltage regulator work correctly
If voltage goes up and stays up with RPM then voltage regulator is stuck, broken

With engine still idling, turn on all lights, set heater fan to high
Check voltage at battery, should still be 13.5-13.8v range

If it is lower then alternator has 1 bad field

If you jump start another vehicle with your engine running then its a roll of the dice you will damage alternator, doesn't always happen but does happen

Best practice is to have your engine off/key off, even better is to have one of your battery cables disconnected.

This is the way vehicle electric system work:
Battery is used to start engine, then not used again
Alternator takes over once it is spinning fast enough, and makes 13.5 to 14.9volts, since battery is always under 13volts it is obviously not part of the system any longer.
But the higher voltage does keep it charged for next time you need to start engine.

Alternators can produce 60 to 100amps depending on the model, long term
Battery's can produce 200 to 400amps depending on the model, short term

Starter motors draw 75 to 125amps, depending on model

So if your engine is running, that means your Battery is OFF LINE..............
If you Jump start another vehicle that means Alternator has to produce ALL the AMPs instantly, at least until system voltage drops down to 12.X when battery can add amps.
So you full peg alternator to produce way more AMPs than it can, remember it is still providing at least 40amps to keep YOUR vehicle running, PLUS the AMPs to run electrics in the other vehicle when they turn that key on, maybe 20 more amps

Just saying your alternator doesn't even have a fighting chance to produce the AMPs needed to start any engine, yours or anyone elses
Thats what the battery is for, KEY OFF when jumping
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Old 11-10-2017
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Sorry Ron, this was my fault, the stupid mobile app replied to the similar thread instead of my revs dipping thread.
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Old 11-10-2017
Join Date: Jun 2005
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That little connector on the back of your alternator is your voltage regulator. I that is broken you need a new alternator. of its the plug you can probably repair
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Old 11-10-2017
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Minimum: Clean all connections from the battery to everything else. Use some dielectric paste on all connection.

Maximum: Replace all the cabling, use one size larger than OEM, replace positive wires and all grounding wires, run additional wires for the ground side of the battery to the a starter mounting bolt, and to the alternator. Use some dielectric paste on all connection.

When done if it is still happening check out the wiring for the gauge.

Last edited by Scrambler82; 11-10-2017 at 07:25 PM.
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