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abomans
New User
Dec 6, 2014, 2:00 PM
Post #1 of 8
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Chevy Impala has hard starting. Checked the batteries and found low water in cells. Topped up with distilled and ran for a good 20min. Checked battery and got 12.6v with car off and 14.4 car running. Check ripple voltage using multimeter across battery terminals with car running and got 30VAC. With car off got 26VAC. Turned lights on with car off and got 0VAC. Suspecting bad alternator.
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 6, 2014, 2:13 PM
Post #2 of 8
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Re: A/C voltage high
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All those measurements you made and not one of them is going to tell you anything about the battery and definitely not telling you that you have a bad alternator.
You need to remove the battery and have it charged and tested.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
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Dec 6, 2014, 2:29 PM
Post #3 of 8
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Re: A/C voltage high
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?! Don't switch to AC voltages for checking. DC observations were fine.
Now - what is this and how old is this battery? Most (the ones I've been buying) you can't add water if you tried or easily and never check on those - totally maintenance free.
Whatever. Hard starting and found low battery water and just those volts are fine but what are then while cranking and need to poke both the side post bolt and if at all possible the eyelet only at battery is enough for right now.
I can't say much until you say year of this thing about other reasons but a low water in a battery suggests already it's been spitting acid and any battery terminals are NOT going to like that and if wet and dirty that will drain battery alone sometimes fast enough to discharge one that might test well.
For now - bad battery highly suspect by itself for amps or can't deliver the amps.
Now if you say this car pre dates GM side posts the voltage regulator isn't inside the alternator on most or many.
Gotta tell us more,
T
(edit) Actually have a DVOM at my feet and a 12v battery and checked what it said switched to AC volts and did just what you found - never did that before)
(This post was edited by Tom Greenleaf on Dec 6, 2014, 2:31 PM)
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Hammer Time
Ultimate Carjunky
/ Moderator
Dec 6, 2014, 2:30 PM
Post #4 of 8
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Re: A/C voltage high
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Get your battery tested first.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Discretesignals
Ultimate Carjunky
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Dec 6, 2014, 3:59 PM
Post #5 of 8
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Re: A/C voltage high
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I believe your ripple test is flawed. The only thing in the electrical system that could produce excessive AC voltage is an alternator with diode issues. You can't have 26 VAC when the car isn't running because the alternator isn't functioning. Something is wrong with your volt meter. 30VAC and the car wouldn't even run or you would have some major drive-ability issues. I agree you should have your battery checked out.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 6, 2014, 3:59 PM)
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abomans
New User
Dec 6, 2014, 5:08 PM
Post #6 of 8
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Re: A/C voltage high
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I thought multimeter was messed up. But, Greenleaf, you said your DVOM did the same thing? Where I work, one of the concrete mixers had electrical issues (no drum control, no chute control, radio not working) another driver suggested to that driver to shut off to reset. Then truck wouldn't start at all. Got it boosted and back to the yard. I load tested batteries for condition and everything was good. DVOM at alternator had same read-out as this problem.
(This post was edited by abomans on Dec 6, 2014, 5:20 PM)
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Tom Greenleaf
Ultimate Carjunky
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Dec 6, 2014, 10:15 PM
Post #7 of 8
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Re: A/C voltage high
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To clarify: I just turned dial to AC from DC on a 12v battery (gel cell but same DC) at my feet in house and got your readings not testing for AC current going thru a vehicle and it is TMK doing that inside alternators via diodes converting it before you should ever need to test inside and been a while but if/when those fail most you just toss alternator depending on cost of individual parts inside one.
There may be for some need for AC for some component in a vehicle but think it would be converted right at the item not running thru the vehicle?
I was just seeing what DVOM would read on the wrong range setting and it matched what you found that's all,
T
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Discretesignals
Ultimate Carjunky
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Dec 8, 2014, 5:46 PM
Post #8 of 8
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Re: A/C voltage high
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Ripple testing should be done at the output lug on the alternator with the engine running and all loads turned on. There is no set maximum reading for how much AC voltage is too much, but usually anything higher than 90mA(.09V) is too much.
The OP was probably reading 30mV and not 30V. 30VAC would probably kill all solid state devices or seriously wig out the PCM.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
(This post was edited by Discretesignals on Dec 8, 2014, 5:48 PM)
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