Too Much Voltage?

[superchargeddrt]

Hi Guys.

First, I just wanted to say that although my background is electronics I have no Idea what the high limit is for alternator output. Here's a little background on what we are working on. My friend has a 1988 318 powered Dodge D150 pickup. One Friday he got into the truck to go to our weekly cruise and it wouldn't start. I came over to help him out and after a few hours of troubleshooting I decided that it could be the pickup coil in the distributor. I disconnected the pickup wires and with a spark plug tester connected to the coil I shorted across the connector and removed it, when I did it produced a spark. He replaced the pickup and the truck started fine, but the next Friday it failed to start again ( new pickup bad?) Anyway he got ANOTHER pickup and the truck started fine. By this time he had had enough and he couldn't trust that it wouldn't fail again so he wanted to rip all of the computer garbage out. We removed the computer and rewired the entire truck. The computer in this truck controls the alternator and so I had to come up with a external regulator setup which is now a standard Chrysler electronic regulator and a very simple circuit. The center pin on the regulator goes to the battery and to one of the field connections on the alternator. The other pin on the regulator goes to the remaining alternator field. When we start the engine the alternator is charging but at 14.6 volts which I feel is excessive. I have checked for proper ground, sanding the paint away before mounting. I believe that the problem may be with the three words on the back of the regulator "MADE IN CHINA"!!!!!!!! Anyway I've heard that someone was making a regulator with a adjustment pot on the back of it. If any of you know where to get one of these or have any suggestions any input would be greatly appreciated.

Thanks
Glenn

 

[nm9stheham]

14.6 volts cold at 1500 RPM is pretty good; may be just a tidge high but nothing to worry about. Di you test this voltage at fast idel (1500 RPM) or low idle (700-800 rpm)? If this 14.6v is at low idle, re-test at 1500 rpm and see what you get.

 

[67Dart273]

Be sure you check WARM. VRs are "temperature compensated."

Be sure you allow enough run time for the battery to become normalized.

In rare cases the battery itself can cause this

In some cases the VR can be "out of spec"

But MOST of the time it is a bad ground or MORE probable,

"voltage drop" in the positive harness

=======================================

Ground. It matters not how well sanded the firewall and VR are. (Actually it does) But what DOES matter after the VR is mounted clean and tight, is whether the firewall is "actually" the "same as" the battery negative. Essentially you want a nice big bonding cable from the battery neg (or the block) to the firewall.
================

Voltage drop in the harness: The VR center pin is not only power to the VR, it is the voltage sensing. So the voltage the VR "sees" between the center pin and it's case (ground) MUST be "same as battery." Typically, "it is not."

As this voltage drop increases, providing less voltage to the VR, the VR "says to itself" "HEY the voltage is LOW let's kick it up"

So the VR regulates so the center pin is the set point...........13.8----14.2 ..........and because there is voltage drop in the harness, this equates to the V at the center pin PLUS the voltage drop = the V at the battery

IE if there is .5V drop in the harness and .3 drop in the ground, you ADD .8V to the charging voltages for perhaps 15V at 14.2

==========================

How to check?

EASY

Warm and charge the engine / battery get everything "normal." Recheck charging voltage to be sure the problem still exists

With engine running at good fast (cold) idle or to simulate low speed cruise, make the following test with all accessories off, and again with heater, lights etc on

Stab one meter probe into the battery NEG post. Stab the second probe into the flange of the VR. Be sure to "stab" through any pain, chrome, rust. With the meter on low DC volts, you are hoping to read VERY little voltage, the lower the better, and zero is perfect. More than .3V (three tenths of one volt) is too much

====================================

Harness drop. This can be done a bit different.

Access a point "same as" the VR voltage supply, "switched ignition." This can be the "key" side of the ballast, the blue field wire, etc

Turn the key to "run" with engine off. Hook one probe to battery POS post, the other to your switched ignition. As before you hope for a very low reading, and more than .3V is too much.

 

[superchargeddrt]

14.6 volts cold at 1500 RPM is pretty good; may be just a tidge high but nothing to worry about. Di you test this voltage at fast idel (1500 RPM) or low idle (700-800 rpm)? If this 14.6v is at low idle, re-test at 1500 rpm and see what you get.

Actually the idle was already on the high side 1500 or so. We didn't get a chance to lower it as this was the first start after a cam change, head replacement and a switch to carbs. Maybe it will be lower at a lower idle. Thanks for the resonse

 

[superchargeddrt]

Be sure you check WARM. VRs are "temperature compensated."

Be sure you allow enough run time for the battery to become normalized.

In rare cases the battery itself can cause this

In some cases the VR can be "out of spec"

But MOST of the time it is a bad ground or MORE probable,

"voltage drop" in the positive harness

=======================================

Ground. It matters not how well sanded the firewall and VR are. (Actually it does) But what DOES matter after the VR is mounted clean and tight, is whether the firewall is "actually" the "same as" the battery negative. Essentially you want a nice big bonding cable from the battery neg (or the block) to the firewall.
================

Voltage drop in the harness: The VR center pin is not only power to the VR, it is the voltage sensing. So the voltage the VR "sees" between the center pin and it's case (ground) MUST be "same as battery." Typically, "it is not."

As this voltage drop increases, providing less voltage to the VR, the VR "says to itself" "HEY the voltage is LOW let's kick it up"

So the VR regulates so the center pin is the set point...........13.8----14.2 ..........and because there is voltage drop in the harness, this equates to the V at the center pin PLUS the voltage drop = the V at the battery

IE if there is .5V drop in the harness and .3 drop in the ground, you ADD .8V to the charging voltages for perhaps 15V at 14.2

==========================

How to check?

EASY

Warm and charge the engine / battery get everything "normal." Recheck charging voltage to be sure the problem still exists

With engine running at good fast (cold) idle or to simulate low speed cruise, make the following test with all accessories off, and again with heater, lights etc on

Stab one meter probe into the battery NEG post. Stab the second probe into the flange of the VR. Be sure to "stab" through any pain, chrome, rust. With the meter on low DC volts, you are hoping to read VERY little voltage, the lower the better, and zero is perfect. More than .3V (three tenths of one volt) is too much

====================================

Harness drop. This can be done a bit different.

Access a point "same as" the VR voltage supply, "switched ignition." This can be the "key" side of the ballast, the blue field wire, etc

Turn the key to "run" with engine off. Hook one probe to battery POS post, the other to your switched ignition. As before you hope for a very low reading, and more than .3V is too much.

Wow as always a wealth of information! Thanks for taking the time to type all of that. We will do the voltage drop diagnostics and report back. Thanks Again

 

[superchargeddrt]

So my friend installed a new voltage regulator and achieved the same results (14.6 volts). After checking Optima's website I discovered that the maximum acceptable voltage from the charging system should be a maximum of 14.7 V. So at 14.6 V we are within optimize specifications. Additionally max external charger voltage is 15.0 V.

Thanks to all who provided input!

 

[garyfish340]

I have to add to something 67Dart273 said. Bad Ground. One night I jumped in my car to go to the store, and I could not believe how bright my headlights were. The next day I opened my trunk, and my battery was wet.( I think I also lost the headlights.) So I replaced the VR, with one from the same place I got the 1st one. A few weeks later the battery was cooked. Got this new Duster, and really didn't drive it much, but no matter how I cleaned the battery cables, they kept getting all this caked white corrosion. Than I noticed the same voltage regulator I had problems with in the Barracuda. I think some of the chrome plating on these VR's, are not actually chrome, but rather some sort of metallic ceramic coating. In both cases, I carefully took a grinder and cleaned off the coating by the attachment bolt holes, and the mounting spot, and bought a little braided ground strap from the tractor supply, put some dielectric grease on the mounting area, assembled everything with those washers that dig into metal, and the problem ceased to be. I guess if the VR isn't grounding really good, it can do some weird things.

 

[BillGrissom]

... I guess if the VR isn't grounding really good, it can do some weird things.

It requires the case to be grounded as a "voltage reference", ideally the same "0 V" as BATT-. It simply regulates the voltage from its case to the blue wire (BATT+ after key switch), keeping that at ~14 V. Any drops which make that different than the voltage across the battery will cause errors, usually the "running voltage too high" problem.