electrical question

drbobj67 · Nov 27, 2006

I'll describe the situation. I was putting some air in my tires with a compressor that plugs into the cig lighter while the car was idling. I noticed that the idle speed seems to fluctuate slightly, like it was changing the idle rate faster and slower slightly in a somewhat rythmic cycle or the car would run smooth and then slightly rough. As it did that I noticed that the dome light would become slightly brighter and the compressor would speed up, then the light would dim slightly and the compressor would slow down. the cycle would repeat itself every second or two. I also notice when sitting at the drivers seat I would notice the needle for the alt guage would move with the same rhythm

Anyone have any ideas on what to check? Perhaps a loose ground somewhere. Could it be the alt is going bad? the alt does keep the battery charge though

jikelly · Nov 27, 2006

Could be your alternator is going out, or it could be things fluctuating to the beat if you have a high powered stereo with amps and stuff.

You can get the charging system checked at AutoZone or one of them other parts stores.

drbobj67 · Nov 27, 2006

My stereo is not hooked up right now so that would not be the issue. I have a meter that I could probably use to check the alt, if I remember right I checked it . But it's easy enough to get it checked at Kragen or someplace like that. Napa is the closest but I think they can only bench test it.

Nemesis67 · Nov 27, 2006

Could possibly be your voltage regulator. But does this problem occur without the compressor plugged in? If it doesn't then I would consider this normal operation. Due to the fact that you are running a compressor off of a power source that is only suppose to heat up a small lighter, which puts a considerable load on the circuit and the whole electrical system.

drbobj67 · Nov 27, 2006

I know for sure that I have seen the alt needle move without the compressor plugged in. Later I'll have to check the dome light without the compressor. I don't think I have a voltage regulator unless it is the same thing that I've seen refered to as the selonoid or starter motor relay.

drbobj67 · Nov 27, 2006

sorry double post

Nemesis67 · Nov 27, 2006

Well if you have a 67, then you most likely have one. The voltage regulator (alternator regulator), I believe is installed on the left front side of the engine compartment. It should be square in shape and silver in color. At least mine was in my 67 FB.

bnickel · Nov 27, 2006

sounds like normal operation to me. the alternator will not constantly charge the battery otherwise the battery would get overcharged,, it will cycle on and off just like an ac compressor does. i wouldn't worry about it at all. BTW, that's one of the reasons they call it an alternator, because it alternates on and off when charging the battery.

drbobj67 · Nov 27, 2006

found the VR

Nemesis67 said:
Well if you have a 67, then you most likely have one. The voltage regulator (alternator regulator), I believe is installed on the left front side of the engine compartment. It should be square in shape and silver in color. At least mine was in my 67 FB.

WTF sure enough I do have a voltage regulator. it was in the left front engine compartment attached to the back of the bracet that holds the radiator hidden by the radiator overflow container. I always figured that I should have one but never saw it before since it was hidden behind the overflow container.
Thanks for the info.

Is there a way to test the VR or do you just replace it

drbobj67 · Nov 27, 2006

bnickel said:
sounds like normal operation to me. the alternator will not constantly charge the battery otherwise the battery would get overcharged,, it will cycle on and off just like an ac compressor does. i wouldn't worry about it at all. BTW, that's one of the reasons they call it an alternator, because it alternates on and off when charging the battery.

I was wondering if the alternator cycling on and off would change the idle of the engine? Does anyone know what is the frequency that the alternator normally cycles on and off. Is it a second or less or a few seconds or more. I realize that this is probably trivial information but it helps me to understand more about how things work.

bnickel · Nov 27, 2006

drbobj67 said:
I was wondering if the alternator cycling on and off would change the idle of the engine? Does anyone know what is the frequency that the alternator normally cycles on and off. Is it a second or less or a few seconds or more. I realize that this is probably trivial information but it helps me to understand more about how things work.

it depends on what the load on the electrical system is. but yes it can affect the idle and it can cycle pretty quickly. ever hooked up a set of jumper cables to really dead battery? notice the idle speed drop considerably? same principle here, when the alternator is charging the idle speed will drop when the alternator cycles off the idle speed will go back up. as long as the system charging don't worry about it. if at some time you need to replace the alternator you should also reaplce the voltage regulator at the same time just like the starter and the solenoid should be replaced in pairs the alternator and regulator should be changed in pairs also.

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