Electrics a bit sketchy...

[mkIIIman089]

Hey guys, for quite a while now (before I got my tiny battery, so thats not it) I have noticed that at idle, my electrical system seems extremely weak. Symptoms:

idling with headlights on, apply brakes = entire car dims
idling with healights on brakes and reverse enguage = entire car dims more
idling no headlights, apply brakes and reverse = volts drop a bit

Now, I have no stereo and only 3 guages and a turbo timer adding to stress on the system. So thats not it.

Also you can visibly see on my N/A volt meter that the voltage goes from about 1/2 dash above 12 to a full dash below 12 with brake application.

When driving at any RPM the whole system operates perfectly fine at roughly 13V on my N/A volt meter. (probably not perfectly accurate)

What I have gotten it down to is what I believe is probably the alternator since it dogs the motor when the voltage drop hits as well.

Any input pertaining to my problem would be great! Thanks!

 

[GrimJack]

Put a test meter on the battery terminals when the car is running and post how many volts you have.

 

[Nick M]

If the alternator belt is tight, have it tested for amperage output.

And you could have had a weak battery replaced by your "tiny" battery, so yes, that could be it.

 

[GrimJack]

And you could have had a weak battery replaced by your "tiny" battery, so yes, that could be it.

Agreed!

 

[Suprastic]

souds like it could either be altenator, improper battery size, back ground connections, or a combination of all. Check/replace all as necessary and you should be good.

 

[mkIIIman089]

Well, the battery I have now replaced a brand new optima red top that was about 4 months old. The grounding thing I don't really know what I should be checking for all I can say for sure is that I just replaced the battery cable with a new OEM one about a month or so ago.

How should I check the output on the alternator? From what I found there is not really a benchmark on different RPM outputs.

 

[Nick M]

You take the car to a qualified shop and have amperage output tested. Your gauge isnt bad, they just arent dead on. Using a DVOM is also an easy check on the voltage. Running voltage of 13 is not enough. You should be at least 1 volt higher than shut off, which should be 12.6.

 

[mkIIIman089]

Okay, I went out (since I did find a way to test without the tool you spoke of Nick, it was in the TSRM) and started to check the voltage at the battery at idle at least (and the car was fully up to temp about an hour ago) since I only had myself to test. What I came up with was 13.95V with headlights on, and 13.98V with headlights off. I was unable to test further without 2 people but its a start, and within spec...

See TSRM specs here:
http://cygnusx1.net/supra/library/TSRM/ch/CH_04.html
http://cygnusx1.net/supra/library/TSRM/ch/CH_05.html

 

[bluemax]

Doesn't sound like you have a problem.
At idle, the motor isn't turning over fast enough to generate enough electrical power so the battery has to supply some. That's normal.
I believe most car electrical systems run at around 13.7 volts and the battery is normally around 12.5 volts.