batt readings on safcII

[atlpd3147]

I've been trying to determine what voltage numbers I should be seeing.. Im trying to find someone with a safcII installed in their car to see what volt readings they see on the monitor window when batt is selected.
I get 14.3volts when the car 1st comes on then if I turn on my head lights the reading goes all the way down to 12.3 or 12.5. Is that normal? I don't think it is the battery cause I just purchased a brand new battery tonight. Alternator belt is tight and I don't think its that. The altternator is also new. Probably only 2 weeks old. I have a vpc and safcII combo..
Anyone please advise what u think the problem is. Thanks!

 

[Ckanderson]

the headlights do take a significant amount of power but im not sure 12.3 is acceptable...

 

[Supra5MGTE]

sounds like somin ain't right. 12.4Vish is a Full battery. but when "charging" you need to be 1V over that. So 13.5V is as low as you'd want for Voltage when the car is running. If you're getting that much voltage drop from headlights sounds to me like the Battery could be going. It also might be some corroded connections/cables. Or Alternator not keeping up with load. Really have to start checking things with a Voltmeter at the battery itself to get a accurate reading from the SOURCE.

 

[drunk_medic]

My Turbo Timer has a battery voltage reading mode, but I wouldn't use it as a concrete troubleshooting tool. Get after the problem with a multimeter/voltmeter.
Many times, problems in an electrical system come down to poor grounding or charging [alt]. Cleaning your battery posts/terminals and chassis grounding point, and checking alternator output are important.

You will also want your power/ground wires going to the SAFC to have really good splices for best reading capability.

 

[atlpd3147]

Well the alternator is new. And the battery is brand new. Just got it today. So I don't thinks its either one of those things. How would I check the voltage output of the alternator? Sorry for that newbie question..

 

[IHI-RHC7]

The alt is probably fine, Shawndude has had great success running new power and grounds to the headlights to fix a similar problem.

 

[Supra5MGTE]

put your + probe of your voltmeter on the Alternator Output post and the - probe on the battery - post. see what you get. then put the + probe on the + of the battery. see how much of a difference there is.

 

[atlpd3147]

Ok kool I'll try that as soon as I get back home tonight. I assume I need to do this when the car is running.. And just by chance what voltage readings should I be looking for as far as normal readings and abnormal readings.. Might as well know what to expect.

 

[gixxer750]

if you do need a better/bigger alternator.... advance auto sells one for an Mr2 that is an upgrade to 100 amps...

 

[Ckanderson]

^you shouldent need to put a better alternator on...

 

[atlpd3147]

I agree no need to buy the mr2 alternator.

 

[atlpd3147]

Tested the readings a few minutes ago.
1st off the car was still cold when I took the 1st set of readings.
Start the car and get 14.58 from alternator post and neg post on the battery (headlights off)
From the +post on battery to -post on battery (headlights off) and I got 14.32
Then I turned on the headlights and 13.8 from the + and - posts on the battery and 13.5 from the alternator to the -post on the battery. But to be honest I think thise readings would have been lower. The car hadn't gotten to normal operating temps yet and the idle hadn't settled down to normal post warmup readings.
I had to run to work so I wasn't able to do the testing when the car was nice and warm. Well what do u guys think. Btw I looked at the batt numbers on the safcII and I saw 13.1v when the lights were on after I did the readings with the headlights on.

 

[atlpd3147]

Bump...... Anyone?

 

[mkiii222]

I would have to say grounding issues. Redo the battery - to chassis ground with some 4 gauge(the copper wire from Home Depot is fine for this and is way cheaper than audio shop wire) and double check the headlight wiring and replace where needed(it is almost 20 years old after all).

 

[IHI-RHC7]

The reason that audio wire is better is because power travels around the surface area of wire, not the core. So the more strands, the better. Welding cable is by far the best.

 

[atlpd3147]

Well I guess I fixed the issue.
I just came back from the auto parts store after picking up a new battery terminal for the positive side on the battery and I just redid the ground wire that connects to the chassis and tranny housing and the drop in voltage is gone. I tested it bu turning on the head lights when the car was running and the volts dropped from 14.2v to 14.1 volts on the batt reading on the safcII monitor page.
Im not sure which one actually cured the voltage drop cuz the other battery terminal wasn't bad its probably a few months old. Im thinking it was the tranny to body ground wire. That was the orginal wire. Oh well thanks for your suggestions. Someone reply with regards to the tranny to body ground. How important is that ground wire?

 

[atlpd3147]

During my rebuild last year I replaced the battery to chassis ground the back of the head to body ground with 4 guage wire.

 

[atlpd3147]

Update again.. Freaking car went back to those wacky readings. I swear I need to ignite this car with a flamable liquid!

 

[atlpd3147]

Bump

 

[IHI-RHC7]

Do the lights dim? or does the number just go down a tad?