Battery volts drop

[tpatodd]

Hi all-

First off... Happy New Year!

Car is running great. Even the battery when day driving.

This note is more-so out of curiosity. I rarely drive at night but recently I noticed that when I drive with my lights on the voltmeter drops quite significantly. Normal is 13-14v. Lights on drops it to 10v or less.

Even worse, lights on, fans on, drops it to 8-9v.

Is this normal?

Battery is ~12months old (Duralast 26R-DL). Even when the voltmeter drops all seems well. The lights are not fading or flickering.

Again, not doing much night driving so was interested it what others experience.

Thanks!!

tpatodd

[mikeinatlanta]

Sounds like corroded terminals or grounds to me.

[Bernica]

One of these might help on starting and charging readings....

Professional Battery Tester

[Jaydee]

Sounds like the alternator is not keeping up with the load.
JD

[Ron61]

That is not normal. when my fans and lights are on my voltage drops to about 12/13 volts. Check your terminals, have the battery load tested, and also check that your alternator is putting out a full charge. Running very long at less than 11 volts will cause the battery to discharge and leave you stranded.

Ron

[emm427]

Happy New Year to all as well ! ! First I would verify all your connections ( powers and grounds ) are clean and tight at the battery, starter and alternator . Then if you have a digital meter, start the car and verify voltage reads what the gauge is reading at the battery and the alternator, both with the lights off and then turn everything on. You might have a simple gauge gone bad, rare but is possible. A hour or so trouble shooting can save a lot of time running around to have parts tested that are still good. Good Luck !

[DanEC]

Assuming this isn't something that just started and it primarily drops at idle or very slow engine speed - then also look at your pulleys and make sure you don't have an underdrive pulley on your alternator. They are pretty common amongst the Mustang racers so one could have ended up on your engine.

[mln385]

Originally Posted by tpatodd

Hi all-

First off... Happy New Year!

Car is running great. Even the battery when day driving.

This note is more-so out of curiosity. I rarely drive at night but recently I noticed that when I drive with my lights on the voltmeter drops quite significantly. Normal is 13-14v. Lights on drops it to 10v or less.

Even worse, lights on, fans on, drops it to 8-9v.

Is this normal?

Battery is ~12months old (Duralast 26R-DL). Even when the voltmeter drops all seems well. The lights are not fading or flickering.

Again, not doing much night driving so was interested it what others experience.

Thanks!!

tpatodd

Your Alternator may be undersized for the loads, also Roush uses underdrive pulley's so this maybe it as well.

[twobjshelbys]

I'd suspect a grounding problem. Check where the battery ground is made and scrape the paint away underneath the strap. It could be the battery or alternator but any car parts store can check that for you. Check your grounds first.

[tpatodd]

Thanks all! I think it might partly be user error. My Smith Volt gauge actually bottoms out at 11v and the needle is staying above that (guessing ~12v) with everything on. Not sure why I was thinking it is 8-9v. Reading is fundamental.

I threw my fluke meter on it and it actually is staying right around 13v with everything on (even the amp for the ipod).

My guess was I never noticed this needle move since I rarely drive at night and that it is sensitive with a small range of motion.

I did find the ground wire on a rusted bolt under the frame so I will clean that off just to keep it in order.

Thanks for the input and sanity check!

[Kobura]

My car has the standard issue/stock voltage gauge and it shows a drop of about one and a half Volts when the electric fan kicks on. I have also found it to be a good indicator of operational turn signals and stop lights as the needle oscillates for turn signals and drops when I depress the brake pedal.

[allcarfan]

hate to rehash this thread, but it seemed appropriate. is this voltage drop normal?

I have a 140amp powermaster alternator in my new back draft vehicle. all grounds and power leads are good. I get 14.66volts at my battery. I flick on my heater and the volts drop to about 13.4. Turn on electric fans, lights, etc, and I drop to about 12.

[DWRAT]

Originally Posted by allcarfan

hate to rehash this thread, but it seemed appropriate. is this voltage drop normal?

I have a 140amp powermaster alternator in my new back draft vehicle. all grounds and power leads are good. I get 14.66volts at my battery. I flick on my heater and the volts drop to about 13.4. Turn on electric fans, lights, etc, and I drop to about 12.

I'm guessing your testing at idle, try it around 2,000 rpms.

[Gaz64]

Originally Posted by allcarfan

hate to rehash this thread, but it seemed appropriate. is this voltage drop normal?

I have a 140amp powermaster alternator in my new back draft vehicle. all grounds and power leads are good. I get 14.66volts at my battery. I flick on my heater and the volts drop to about 13.4. Turn on electric fans, lights, etc, and I drop to about 12.

The trouble with a lot of high output alternators is their output at idle is not as good as a factory 60-70 amp alternator.

[Cashburn]

Originally Posted by DWRAT

I'm guessing your testing at idle, try it around 2,000 rpms.

Excellent point.

[allcarfan]

Cruise at 2400rpms.....flick on heater..... appears to be 1.5v loss. Continued driving for 10 min...no change. Flick off heater....immediate 14.7v

[patrickt]

Originally Posted by allcarfan

Cruise at 2400rpms.....flick on heater..... appears to be 1.5v loss. Continued driving for 10 min...no change. Flick off heater....immediate 14.7v

Use the search function on this site to search for "inductive ammeter." I've posted here many times on it and provided pics of mine. That will let you easily diagnose exactly what each of your circuits is eating up, and what the alternator is putting out, without having to do any disconnecting or anything else -- you can't hurt anything with an inductive ammeter even if you tried. Once you know whether you're using too much, or not making enough, juice, then you can attack the problem. And these problems are invariably simple once you figure out what they are.

[patrickt]

Wait a minute -- this heater is a regular "coolant based" heater, like a Maradyne pictured below, right? It's not some funky resistance heat, all electrical, heater is it?

[allcarfan]

Coolant based heater.

I think when I go in for my 500 mile checkup, I will just have the shop take a look at everything. I don't like dealing with electrical gremlins.

[patrickt]

Originally Posted by allcarfan

Coolant based heater.

I think when I go in for my 500 mile checkup, I will just have the shop take a look at everything. I don't like dealing with electrical gremlins.

I understand. There is a fan, with a DC motor, in your heater that will normally draw about 5 to 7 amps -- that's it. Your headlights will draw ten or more. If your voltage drops significantly when you turn your heater switch on, but it does not do the same when you turn your headlights on, then you know there is something wrong on the heater circuit. Very easy for someone to diagnose -- maybe it's bad connections, a failing DC fan motor, something wrapped around the fins of the fan so it's holding the motor back, who knows. Try that test between the headlights and the heater, and if only the heater makes the voltage drop, then stick your head under the dash and see if you can look inside the heater and see if there's anything obviously wrong. If you can't see anything, then any shop or garage will easily be able to tell you what's wrong with it. But, sometimes getting the heaters out of these cars can be a bit of a nuisance.