battery resting at different voltage than cap in back?

[lawlyes2007 10+ year member]

My voltage up front is around 11.45 up front with the car off, and 12.45 at the cap in the back. How is this possible??

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[pentavolvo 10+ year member]

maybe a bag ground up front

 

[pentavolvo 10+ year member]

11.45 is way low for resting IMO even 12.45 aint great

 

[TurdFergueson2 5,000+ posts]

I had a similar issue when I used a cap. Then I got rid of it. Reading was always higher than the DMM.

 

[Lakota 5,000+ posts]

You must have a bad connection somewhere or one of the readings is off. The components in a cars electrical system are for the most part all ran in parallel (there are exceptions), so the voltage at every point should be very similar.

 

[audiolife 5,000+ posts]

if it were that low up front it would eventually lower the caps voltage...11.45 is a dead battery voltage unless you are measuring with the system on during a bump and IF your cap stays steady at 12.45 you either have a slow DMM, the meter in back is less sensitive or the esr of the cap is so great it isn't doing anything LOL

 

[lawlyes2007 10+ year member]

Well the cap sucks, the only reason I have it in there is because it came with my amp and I didnt know any better when I bought it. Im in the process of building a new box and the cap def wont be used. And im not sure why my batt is resting so low. Ill charge it tomorrow. The cap reading is wayyy higher than the dmm and I kno its not right. Reading like 18 or something but the dmm said 12.45 in the rear and 11.45 on the batt up front. EDIT: What should my batt be resting at fully charged? 13?

 

[audiolife 5,000+ posts]

does the car even start?

 

[lawlyes2007 10+ year member]

yea car starts fine.

 

[grassroots 10+ year member]

what are the checking the voltage with? a dmm or the lousy volt meters built into the terminals/cap?

edit: nm... read some more

 

[audiolife 5,000+ posts]

I would check the battery in the dmm at 11.45 v the battery is dead and if it starts it would at least be real weak

 

[lawlyes2007 10+ year member]

Well the car is kinda hard to start but it has always been kinda slow. It may be a lil harder but i guess i jus thought it was the cold weather. Anyone know why my battery could be loosing voltage from when it is fully charged? Im only running 500 watts.

 

[loopkiller 10+ year member]

Sounds like either your alt is too small or not working properly. Your battery is not fully charged for one reason or another. Here is a few things to test, but first, take out the cap to rule it out.

1) Voltage at battery with engine off, key off

2) Voltage at battery with engine off, key on acc

3) Voltage at battery with engine on, all loads off

4) Voltage at battery with engine on, all loads on (headlights, audio, interior lights, heat blower, etc)

Take those readings and post back. I will be able to help you more then.

 

[lawlyes2007 10+ year member]

My alt is a 120 I do believe since my car had the "upgraded" bose system.

 

[Cpyder 10+ year member]

Check the voltage right before and after the in line fuse. Somehow my old fuse was restricting voltage. F-ing weird.