A question of voltage drop - Page 2 - Fiberglass RV


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Old 12-09-2012, 06:33 PM   #15
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On the car, I'm seeing an average of 12.5 volts to 12.9 volts. The question becomes - why the difference? and Is the difference normal?

Derek
Is this the voltage with the car running?
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Old 12-09-2012, 06:36 PM   #16
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Is this the voltage with the car running?
Yes.
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Old 12-09-2012, 06:41 PM   #17
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Is this the voltage with the car running?
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Originally Posted by glamourpets View Post
Yes.
OK, I'm up to speed. I'd be a little concerned, too. If you turn on the headlights or blower motor, does the voltage drop even more?

It may be that it has a smart charger circuit to minimize needless charging of a full battery and everything is fine, or it is not charging adequately.

If you discharged the battery a little with the lights or blower on, with the engine off, the voltage should kick up when the engine is started and the alternator recharges the battery.
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Old 12-09-2012, 06:43 PM   #18
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Sooooo the real question is "Why is my cars cigarette lighter output voltage reading low" correct?

Before answering here are a few points to consider:

1. If you plug the same gauge into the truck does it read higher? If not the gauge may be defective. I am not a fan of anything less than a "Voltminder" (voltminder.com) for accurately monitoring voltage at a plug connection.

2. You are saying "Cigarette Lighter". Most newer cars don't have a cigarette lighter but a "Power Outlet" or other similar name. These are not always the same as a cigarette lighter plug for 2 reasons: 1) They are not designed to withstand the heat generated by the end of a hot lighter element and, 2) As alternator voltage can spike up to well over 16 volts at startup, some (but not all) of these power outlets have the voltage limited/regulated/clamped to less than 13 volts to assure that you don't plug in an electronic device and damage it from over voltage. A look at your owners manual or a call to your dealer may provide more info on that possibility.
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Old 12-09-2012, 06:47 PM   #19
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.......... 2) As alternator voltage can spike up to well over 16 volts at startup, some (but not all) of these power outlets have the voltage limited/regulated/clamped to less than 13 volts to assure that you don't plug in an electronic device and damage it from over voltage. A look at your owners manual or a call to your dealer may provide more info on that possibility.
This makes sense.
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Old 12-09-2012, 06:48 PM   #20
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OK, I'm up to speed. I'd be a little concerned, too. If you turn on the headlights or blower motor, does the voltage drop even more?

It may be that it has a smart charger circuit to minimize needless charging of a full battery and everything is fine, or it is not charging adequately.

If you discharged the battery a little with the lights or blower on, with the engine off, the voltage should kick up when the engine is started and the alternator recharges the battery.
The more stuff you turn on, the lower it drops. The defroster, for example seems to drop the voltage about 0.3volts. A smart charger should see the drop and turn up the alternater output. I'm not seeing that.

Also, I know an alternator will produce more power at higher RPMs. At highway speed, voltage is still low.

Derek
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Old 12-09-2012, 06:56 PM   #21
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Have you tried a different meter?
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Old 12-09-2012, 07:03 PM   #22
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The more stuff you turn on, the lower it drops. The defroster, for example seems to drop the voltage about 0.3volts. A smart charger should see the drop and turn up the alternator output. I'm not seeing that.
That's puzzling. The way to know for sure would be to put an ammeter in series with the battery.

Quote:
Also, I know an alternator will produce more power at higher RPMs. At highway speed, voltage is still low.

Derek
More amps at higher rpms, but even at idle it should charge adequately. The alternator is sized to maintain charge even when idling for long periods like police, soccer moms, etc.
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Old 12-10-2012, 12:12 AM   #23
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Define "voltage gauge", and why are you measuring at a cigarette lighter? Get a good meter and check at the battery, running and not running. Personally, I stick to fluke meters.
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Old 12-10-2012, 07:09 AM   #24
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Originally Posted by Bob Miller View Post
Sooooo the real question is "Why is my cars cigarette lighter output voltage reading low" correct?

Before answering here are a few points to consider:

1. If you plug the same gauge into the truck does it read higher? If not the gauge may be defective. I am not a fan of anything less than a "Voltminder" (voltminder.com) for accurately monitoring voltage at a plug connection.

2. You are saying "Cigarette Lighter". Most newer cars don't have a cigarette lighter but a "Power Outlet" or other similar name. These are not always the same as a cigarette lighter plug for 2 reasons: 1) They are not designed to withstand the heat generated by the end of a hot lighter element and, 2) As alternator voltage can spike up to well over 16 volts at startup, some (but not all) of these power outlets have the voltage limited/regulated/clamped to less than 13 volts to assure that you don't plug in an electronic device and damage it from over voltage. A look at your owners manual or a call to your dealer may provide more info on that possibility.
The gauge reads between 13.7 volts and 14.1 volts in the truck when the truck is running. The fluctuation is influenced by acessories turned on and engine RPM. This, to me, is normal. The car readings are significantly lower. Its the low readings that are of issue.

For what its worth, you cannot currently buy voltminders. If you click the buy it now button you can get more details.

Jared, if you would like to hide under the hood while I drive so we get better readings, I'm all for it. Just don't hold me responsible if you die during the process. A cigarette lighter gauge is imperfect, but it can give you readings on the go. Some fluctuations are normal. Battery charge, rpms, and acessories turned on have their influences.

If the alternator is failing, and only producing a portion of its rated capacity, that's a concern. If the alternator is ok but the voltage is filtered, that's good news. Anybody want to take bets on whether I arrive at xmas dinner by tow truck?

Derek
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Old 12-10-2012, 07:58 AM   #25
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Nearly any automotive garage has a "meter" they can use to test your alternator and battery in about 5 minutes.

It's got an amperage meter they put in series with the positive cable to your battery and a HUGE adjustable load so they can watch your alternator in action.

It might be $15 or so to have them tell you what's going on using science!!!
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Old 12-10-2012, 11:03 AM   #26
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Define "voltage gauge", and why are you measuring at a cigarette lighter? Get a good meter and check at the battery, running and not running. Personally, I stick to fluke meters.
Fluke meters are just a bit expensive. I might also add that they are named very ironically.
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Old 12-10-2012, 09:34 PM   #27
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Have you tried a different meter?
X2....

Or a different point of measuring your voltage other than the cigarette lighter?

Francesca
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Old 12-10-2012, 10:16 PM   #28
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Oh boy....

No load voltage of a fully charged 12V battery is 12.65V. Charging voltage is specified as 13.8V to 14.2V, with a tolerance to 13.4V on the low end and 14.5V on the high end. Too high voltage and some systems shut down and accessories get damaged. Extended use below 13.4V the battery will not charge correctly and fails early (1-2 years instead of 5-7 years).

Measuring at the power outlet will be after a couple fuse panels and, on some cars, through a control module. So after a half dozen or more connections there can be a significant voltage drop.

[soap box]
How are you checking voltage at the cigarette lighter? It's just a heater coil with a handle that gets hot after being plugged into a power outlet for a few moments.
[/soap box]

And why do you have to drive the car to test the charging system? Attach a good DVOM or volt meter to the battery (I just threw mine out this morning as it was reading .5V low), start the engine and rev it up for about 5-10 seconds before letting it idle. Read the voltage with everything turned off (door shut? dome light?) at idle then at about 2000 to 2500 RPM. Turn on your lights (high beams), a/c fan high (and the a/c), rear window defroster, radio about 50% volume on a strong signal, bum heaters and such if you have them. Read voltage at idle and at 2000 to 2500 RPM. Let the voltage stabilize at both speeds before making your reading.

Now a well designed system in good condition will be able to keep above 13.5V with all those loads on with the RPMs up. A great system can do it at idle. If you get below 13V at idle or 13.3 at higher RPM you will have issues. If you don't think those loads are realistic - So Florida in slow traffic on a cold night will have lights, a/c to keep the humid air from fogging the windows, rear defroster to keep that window clear, heated seats to keep warm while a/c is keeping windows clear, wipers to clear the condensation on the outside (or in a cruel twist when it stars raining). Worst was Missouri though - defroster got the inside of the windshield clear just in time for the condensation build up on the outside.

Back to your regularly scheduled program,

Jason
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