Bill H. You were a lot of help last year on electrical problems. Perhaps you can help again. (See post from 6/8/2003)

I am having electrical charging issues with the chassis battery. I am assuming that the following item is an isolator and may have some impact on the charging circuit. On the front, behind the grill, is an electrical box with three “red” wires mounted to the posts. One comes from the alternator and mounts to the the “center” post. One wire goes to an auxiliary circuit breaker. One goes to either the battery or the remote starter relay (I never finished tracing that circuit).

This item has fins, indicating to me that it gives off heat and is more than just a junction. However, the wiring diagrams indicate that this is just a junction. How does it affect the charging circuit? How can I check it out as a problem?

I am having issues with the charging system and this appears to be the first item in the circuit right after the alternator. I am measuring 11.8 volts at the chassis battery, indicating that there is a problem with the charging system. I replaced the alternator a year ago, just before the June Rally last year. Obviously, it could be the alternator. I’m not 100% certain that the alternator has a built in regulator. Any comments or thoughts about the regulator being within the alternator?

This is on an ’84 on a P chassis, Chevy 6.2 L diesel, forward diesel. However, I suspect that the voltage control/ distribution are similar on all forward P chassis units.


[This message has been edited by Mike Cropper (edited July 04, 2004).]

The "finned box" you are looking at is the battery isolator. It allows both the coach battery and the chassis battery to be charged off the alternator but allows current to be drawn only from the coach battery when the alternator is not turning over. This eliminates draining the chassis battery when you are parked and using coach circuits.

There is a possibility that this isolator is on the fritz --- if you are not getting almost the same voltage (with the engine running)between ground and the center post(direct from alternator) and both of the side posts (to chassis and to coach batteries) then the isolator would be suspect.

But there is a more likely suspect and that is the connection of the chassis battery, the output from the isolator, and the ignition which can be found on the starter solenoid. This connection could be either loose or corroded or both. Crawl under & clean this connection.

Prayer often helps too.



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Gary & Edie
North Idaho Panhandle
28' P-30 454

Gary is right about cleaning contacts. Even if that is not a problem, you have built good Karma by cleaning them all. I like to put a star washer under the lug from the battery negative to the chassis ground, too. Then spray them with LPS 3 to prevent future corrosion.

Disclaimer: I am speaking from my gas Chevy experience with 10si or 12si alternators. Most of it will apply to your diesel, but I am not sure what alternator you have. If it has a two conductor push-on terminal on the alternator, it is a 10si or 12si, which are similar. If it has four terminals on the alternator, it is a CS121, CS130, or CS144. These appeared in the late 80's, but may have been retrofitted. If you can open MSWord, I can send you a picture of each from my files to be sure I am talking about the right alternators.

Let's trouble shoot by elimination. Go to your isolator, disconnect all three wires and bolt them together and tape them up. Fire up the engine and see what happens. If it charges now, the isolater, which you eliminated, was bad. If not, untape and unbolt them. Two of them will show 12 volts with a test light. The one that is not hot will be the one to the alternator. Mark it. Disconnect the positive cable on the chassis battery. The wire at the isolator that shows 12 volts with a test light is the one to the coach battery. Mark it, and the remaining one to the chassis battery, too. Tape up the terminal from the coach battery. Reconnect the connector on the positive post of the chassis battery. Connect the alternator wire to the wire that connects to the coach battery with a nut and bolt and tape it up. Start the engine and see what the voltage is now. If it is charging, something is likely wrong in the chassis battery wiring, the battery itself, or the isolator. If it is not charging, the alternator or its wiring are the suspects. You could also put an ammeter in the line between the contacts you removed. They are cheap at auto parts stores.

Now, another approach: Your alternator is either not charging or it is charging and something is dragging the voltage down. The quickest way to check if it is charging is to use an inductive ammeter. They are under ten dollars and are held against the wire to read the current going through it. A regular auto parts store ammeter can be temporarily connected between the alternator and isolator, too. Another way is to see if the voltage rises with rpm. At night, a voltage rise can be seen as slightly brighter lights as the engine revs above idle.

If something is dragging the alternator down, it could be a bad battery or a short to ground. A bad battery can be tested for free by many auto parts stores, or you can substitute a known good one. If you have a charger, with an ammeter, you can observe how it charges. A hydrometer will also tell you about your battery. Do you have one? Sears sells a good one with a thermometer for temperature compensation.

Now, a short to ground is a pain to chase. I had a problem once that was an internal short in the emergency start solenoid. I never really analyzed it, but removing it and bolting the wires together and taping them up got me on the road again.

Of course, you can remove the alternator and have it checked for free at many auto parts stores, too. It might be good practice to do it at home without time pressure. I carry a spare alternator, as so many of the rebuilts are poor, even though I always buy the lifetime warranty one.

Are you using a Gates belt? Some lesser brands are about 2mm narrower and ride too low in the pully and slip. Every temp employee at a chain auto parts store will swear their brand is made by Gates, so watch out. I know for a fact that Dayco is too narrow and they make a lot of house brands.

There is one more thing here to consider:

The Delco alternator needs either an idiot light or a resistor in the wiring from the battery to terminal 1 of the regulator to get things going. Does your coach have a "charge" light? If it is burned out, charging will be affected or limited. If it does not have a charge light, it needs a resistance in the wiring of about 15 ohms in the harness.

On the push-on connector to your alternator, the big red wire should always be hot. The smaller brown wire on my 84 gasser is hot (but with a lower voltage) when the ignition is on. It needs either a lamp or a resistance of about 15 ohms in the circuit. If the nichrome resistance wire in your harness is open, I have a source.

I know I have told you how to build a clock when you asked me the time, but I am trying to cover all the bases here. When I was a tech writer, I always went out to a plane to try my stuff and find slipups, but I am operating from memory here, so if something is not clear or you hit a snag, holler.

PS, we just found out our dog likes tequila.



[This message has been edited by bill h (edited July 04, 2004).]

I should add here that I do not like isolators, as they rob .7 volt from the charging voltage. That is a built in characterstic of a silicon rectifier. One could go to a Schottky diode rectifier, but there is a simpler way, using a continuous duty solenoid. If anyone is a fiddler and is interested, I will try to explain it in text.

Update:

Thanks for the confirmation that this is only an isolator. Just an aside note, I started chasing this problem looking for bad contacts. With a unit that’s almost 20 years old (chassis is an ’82, coach is an ’84), I too am in the school that it never hurts to clean any and all contacts. Also, thank goodness I’m currently at home base, but about to hit the road for a trip.

Bill, thanks for the instructions on building the watch, it’s what I really wanted.

After the posting, the parts store was contacted and confirmed that the regulator is internal to the alternator. It is a Delco unit. It is the two wire plug in as you describe, therefore it is either 10si or 12si unit.

When I checked the voltage from ground to each post on the isolator (after reading Bill h’s old post), I got:
Center post (from alternator?) 10 volts that decreased to 9.4 volts
Bottom (Battery) 11.8 volts, same as at the battery
Auxiliary 13.38 volts.

After this reading, I decided to take the alternator in for a test. Unfortunately, the parts store was closing in 30 minutes when I called and I could not get there. Today, I’m heading there in a few minutes to test the alternator.

Prior to any testing, each contact on the isolator was disassembled; cleaned with a contact cleaner and wire brush; then reassembled. Even then, I had to contact only the wire connections and not the posts to get a reading on the VOM. After the check of the alternator, I’ll start with the great list from Bill.

Let’s assume for the moment that it is the isolator. How hard is it to find one? Here in the Cincinnati area, we have the national auto parts chain stores (A.k.a. Auto zone), the local chain used by almost all professional mechanics (KY motors) (because this local chain is so strong, NAPA has never been able to penetrate the market), Chevy parts, and finally a large RV parts store. Any thoughts on who might have the part? Any idea on how to specify it, i.e. how to know that I have the correct part?

I’ve had difficulty clearly determining the specifications for some of these electrical components. I do not see any marking on the front of the body. For instance, I have two inline circuit breakers (i.e. little black boxes) mounted next to the isolator with the “battery” terminal connected to the “top” terminal on the isolator. These two do not have any markings that indicate what they are, i.e. amperage rating, etc. (if the part information was pad printed on it, then surface rust would have wiped it out) Therefore I have no idea what amperage circuit breaker to get as a replacement part (again, keeping in mind good, clean contacts. These contacts are fairly pitted and I thought about replacing these parts just to have clean, full surface contacts.)

Thank you for your inputs.

Battery isolaters are common after-market accessories, and as far as I know, they don't vary in their electrical specifications.

You might try your local auto parts chain first, then go on to the RV store if they don't have it. "RV" in front of an accessory's name is a lot like "marine." It raises the price but usually does little else. One exception is marine alternators & carburetors.

Update (7/05/04 11:46 AM EST.)

The alternator was tested at auto parts store and determined not to be charging. New alternator (exchange under warranty) tested before leaving the store and determined to be OK.

Post installation of the rebuilt alternator, here is the situation:
• Voltage at Chassis battery: 13.5 +/- a little, pretty much as expected.
• Voltage at Chassis battery (with lights on, radio on, fan on, wipers on): 12.6 volts
• Voltage at all three posts on the isolator: 15 .3 +/- 0.3 volts.

After consulting Bill H.’s post from 10/12/02, it looks like these voltage readings at all three posts should be more in the 13 to 12.5 volt value (minus a half volt).

Question, does the higher output indicate an issue with the isolator? All other discussion concerned the low side.

Golly, Mike, those readings don't make sense to me. I am at a loss here.

I delayed replying in hope that someone else might come up with something.

Have you tried the other stuff I mentioned?

Bill,
I haven’t rechecked these specific readings. Since I last reported, I have driven Ol’ Bart over 2000 miles. During that time, the volt meter in the dash never varied much. It always indicated a little above mid-range. I checked the batteries (coach and chassis) a few times and had the correct voltage. Since it’s still here in the driveway, I’ll check the output at the three posts again and report back.