What voltage is too high?

What voltage is too high? - 02/18/08 11:31 PM

I think I'm having a charging system issue in my Li'l Red Express. It's measuring 14.8V - 15.0V at the battery. I've tried 3 different regulators (2 new), 2 different alternators (original and a 100A chrome that I had laying around) and 2 different batteries.

I have the ammeter bypassed (red and black tied together and insulated behind gauges) and I have a direct feed from the alternator to the starter relay battery post to minimize current running through the bulkhead connectors. Also, the headlights are on relays.

With the engine idling around 750RPM, I'm getting 14.8 - 15 at the alternator. The red field wire measures 14.4V and the light green measures between 8.8 - 9.2V. When I disconnect either field wire the alternator battery post measures about 12.4V.

I've check the voltages at the igition switch connector and they're all around 14.5V. Same on the bulkhead connector.

Is 15V too high, or should I just live with it? I always thought 13.8 - 14.1V was what I should be getting.

Any suggestions?

Thanks!

Posted By: 1_WILD_RT

Re: What voltage is too high? - 02/18/08 11:39 PM

13.8-14.2 is normal even 14.5 wouldn't be to bad...But your to high...Check the reading on the blue wire going to the voltage regulator, thats the referance signal for the regulator...also check the regulator ground, if you can get a voltage reading with a DVOM between the voltage regulator case & battery ground with the engine running then you have a ground problem...

Posted By: GoodysGotaCuda

Re: What voltage is too high? - 02/18/08 11:45 PM

Mine runs about 14.5v here. Have you done a voltage drop between the battery + post, to the v/r hot wire?

Posted By: bigslant6fan

Re: What voltage is too high? - 02/19/08 12:07 AM

did you know the VR automaticly increases voltage in cold weather?Heres specs from a 1977 CPD car sevice manual.-20F 14.9-15.9,80F 13.9-14.6,140F 13.3-13.9. page 8-208 If your doing this test in freezing weather,it sounds like your right on the money.many late model cars are near 15.5V,and great job on improving your wiring!

Posted By: dave571

Re: What voltage is too high? - 02/19/08 12:19 AM

I wouldn't be afraid to run 14.8 , but it is a tad high.

Looking at your voltage readngs, you see 14.5 in a lot of places, except at the battery.

What is likely going on, is that there is a voltage drop (resistance) between the ignition switch, and the voltage reg. The reg thinks it is regulating at 14.5, because that is what it is seeing. But in reality the voltage on the system is higher.

You can go digging through the 30 year old harness for the drop(or likely multiple drops of around .1 or .2 each). You may find them.
OR

What I normally do when I get a car like this, is I use the existing voltage supply/ign wire on the regulator to turn on a relay that is wired to direct battery voltage(straight to the positive terminal of the battery). Then the regulator sees actual system voltage, instead of the dropped down voltage through the harness.

Takes about half an hour to wire up, and cost less than 10 bucks.

Hope this helps

Posted By: 1_WILD_RT

Re: What voltage is too high? - 02/19/08 12:23 AM

Quote:

I wouldn't be afraid to run 14.8 , but it is a tad high.

Looking at your voltage readngs, you see 14.5 in a lot of places, except at the battery.

What is likely going on, is that there is a voltage drop (resistance) between the ignition switch, and the voltage reg. The reg thinks it is regulating at 14.5, because that is what it is seeing. But in reality the voltage on the system is higher.

You can go digging through the 30 year old harness for the drop(or likely multiple drops of around .1 or .2 each). You may find them.
OR

What I normally do when I get a car like this, is I use the existing voltage supply/ign wire on the regulator to turn on a relay that is wired to direct battery voltage(straight to the positive terminal of the battery). Then the regulator sees actual system voltage, instead of the dropped down voltage through the harness.

Takes about half an hour to wire up, and cost less than 10 bucks.

Hope this helps

Good shortcut..

Posted By: NotEnufGarage

Re: What voltage is too high? - 02/19/08 12:41 AM

Thanks.. I'll be heading out to find a relay shortly.

Posted By: 1_WILD_RT

Re: What voltage is too high? - 02/19/08 12:45 AM

Go see your local car stereo/alarm installer..

Standard Bosch ISO relay & connector...

Posted By: GoodysGotaCuda

Re: What voltage is too high? - 02/19/08 12:54 AM

Quote:

What I normally do when I get a car like this, is I use the existing voltage supply/ign wire on the regulator to turn on a relay that is wired to direct battery voltage(straight to the positive terminal of the battery). Then the regulator sees actual system voltage, instead of the dropped down voltage through the harness.

Thats exactly how my v/r is wired up as well.

Except its to my starter relay since my batt is in the trunk.Alt output feeds directly to the batt back there

Posted By: NotEnufGarage

Re: What voltage is too high? - 02/19/08 01:00 AM

Quote:

did you know the VR automaticly increases voltage in cold weather?Heres specs from a 1977 CPD car sevice manual.-20F 14.9-15.9,80F 13.9-14.6,140F 13.3-13.9. page 8-208 If your doing this test in freezing weather,it sounds like your right on the money.many late model cars are near 15.5V,and great job on improving your wiring!

It's about 60F out here.

Posted By: dave571

Re: What voltage is too high? - 02/19/08 02:23 AM

Quote:

Good shortcut..

Thanks.

I was feeling really smart the day I figured that one out

Posted By: NotEnufGarage

Re: What voltage is too high? - 02/21/08 06:38 PM

Quote:

Quote:

Good shortcut..

Thanks.

I was feeling really smart the day I figured that one out

Is this what you mean?

Attached picture 4212891-alt-relay.JPG

Posted By: NotEnufGarage

Re: What voltage is too high? - 02/21/08 09:05 PM

I think this is what I really want, right?

Ignition triggers relay which passes battery voltage to regulator and red field wire on Alternator.

Attached picture 4213223-alt2-relay.JPG

Posted By: JonC

Re: What voltage is too high? - 02/22/08 01:31 AM

Too bad you bypassed the ammeter unless it was bad. It would be nice to know the current involved then you would have a lot more info on what is going on. I would rather have an ammeter than a voltmeter. A voltmeter only tells you if it is producing voltage. An ammeter will tell you if it is acutually being used. Realistacly both meters are important

Posted By: 1_WILD_RT

Re: What voltage is too high? - 02/22/08 01:56 AM

Yeah but Chrysler didn't have the good sense to put a shunt style gauge in these cars all the power actually had to pass through the firewall twice & through the ammeter which caused alot of electrical problems & a few fires...Besides vary few people actually watched & understood the ammeter the best system is a voltmeter & an idiot light..

Posted By: Sinitro

Re: What voltage is too high? - 02/22/08 03:26 AM

The amp guage, wiring harness & bulkhead connections can/will pose some issues with age...
But the basic premise is when Mopar invented their electrical systems it wasn't designed to handle loads up to 125 Amps..

Maybe up to 60-70 Amps but not double...
A beefy subwoofer amplifier can draw 100 Amps, Then next add...
Electric fuel pump..
Electric fans..
MSD box..

Turn ON the lites..

Nuff said..

Posted By: dave571

Re: What voltage is too high? - 02/22/08 06:37 AM

The second one would be right with the 70 and up style reg.

Then the reg sees actual battery voltage when the key is on. not the reduced voltage through the bulkhead etc.

The red wire on the alt doesn't have to be from the same source. It only has to be a positve voltage source, that is on with the key. It doesn't need to be as exact..

The green wire is the ground, and that is how the field output is controlled (on the ground side for 70 up)
The voltage on the positive side of the field connections is not crucial. It needs voltage, but the ground is applied to increase alt output. It will simply ground less or more as needed with a lower or higher voltage positive source

The point of the mod, is Only that the regulator knows what the actual voltage is, when controlling the ground side. Not to improve the positive connection to the alt itself.

Posted By: NotEnufGarage

Re: What voltage is too high? - 02/22/08 07:33 AM

Quote:

Too bad you bypassed the ammeter unless it was bad. It would be nice to know the current involved then you would have a lot more info on what is going on. I would rather have an ammeter than a voltmeter. A voltmeter only tells you if it is producing voltage. An ammeter will tell you if it is acutually being used. Realistacly both meters are important

That's pretty much the first mod I make to all my Mopars, along with adding headlight relays, which make the ammeter read incorrectly, anyway. I like bright headlights, a good stereo and I'd rather not risk a dash fire.

Posted By: Exit1965

Re: What voltage is too high? - 09/01/08 12:35 AM

I was considering doing the relay mod mentioned, then did a quick measurement. With the key in the ON position, I get 12.66 volts across the battery terminals, and 12.60 volts from the IGN side of the (electronic, pre 70) voltage regulator to ground (neg bat terminal). Is the .06 drop anything to worry about, e.g. would it adversely affect charging?

Posted By: Anonymous

Re: What voltage is too high? - 09/01/08 12:45 AM

Quote:

I was considering doing the relay mod mentioned, then did a quick measurement. With the key in the ON position, I get 12.66 volts across the battery terminals, and 12.60 volts from the IGN side of the (electronic, pre 70) voltage regulator to ground (neg bat terminal). Is the .06 drop anything to worry about, e.g. would it adversely affect charging?

no. thats very small