MAYCO's 1982 310 TD

[dadstoy]

10 volts on a battery probably means it is dead. You should probably pull it and have it tested.

The 12volt Side of Life (Part 1)

[mayco]

Dean, indeed the way my system is supposed to be working, as far as charging is concerned is the converter charges coach batteries only and the alternator will charge both the coach and the chassis batteries through the isolator. It was my understanding that the isolator will detect which needs the charge and both controlled through the internal voltage regulator. I have 12v coach batteries. Thanks for your input Dean, really nice schematic youve produced there.

Mike

[mayco]

Well I was wondering about that, Ill pull and have it tested tomorrow. This has happened now more than once so I guess there is a good possibility Ive murdered the defenseless thing. (Its only a year old)

[dadstoy]

Originally Posted by mayco

Dean, indeed the way my system is supposed to be working, as far as charging is concerned is the converter charges coach batteries only and the alternator will charge both the coach and the chassis batteries through the isolator. It was my understanding that the isolator will detect which needs the charge and both controlled through the internal voltage regulator. I have 12v coach batteries. Thanks for your input Dean, really nice schematic youve produced there.

Mike

My isolator/alternator combination uses a "Sense" wire off the alternator to tell the regulator built into the alternator whether to charge or not. This additional wire coming off the alternator is connected to one of the battery connections on the isolator.

Originally this wire was connected to the post for the chassis/engine battery. My coach batteries never seemed to get charged up when driving. I connected this sense wire to the coach post on the isolator. I figure that the chassis battery won't get run down much when on the road and dry camping but the coach batteries will. So I want the alternator to "sense" the charge needed on the coach batteries and keep outputting and charging until the coach batteries are charged up.

The forth small terminal on my isolator is coming from the ignition switch which is required to "excite" the isolator/alternator ? I think this is typical on the early GM gas engine setups (CS and CI alternators).

My dad had replaced the alternator a few times as evident by the shop receipts I have. It was dead again when I wanted to get the rig road worthy again. So I figured there was something wrong.

I replaced the alternator with a very expensive 200amp high output unit and installed the large 240amp isolator (with large fuse and large cable from alternator to isolator). I had to move the new windshield washer tank/pump to the other side of the firewall. My expensive alternator burned out quickly on the first trip to Burning Man.

I'm not sure what actually solved the problem, but all is working now and has been for a while. Here is what I did...

I replaced several wires from the isolator to the alternator and on the extra solenoid that is installed to prevent hard or inadvertent starting on the 454. I ran a new wire from the chassis post of the isolator to the engine battery. I also one day got under the chassis and removed the starter heat shield to look at the wiring connections. It was a fire waiting to happen. I put new connectors on all the wires to the starter and cleaned off as much oil as I could.

I replaced the burned out expensive 200amp high output alternator with a stock but rebuilt 130? amp alternator by a local starter/alternator shop. I learned my lesson once again on the "high performance" parts that make no difference on a motorhome!

[bkahler]

Originally Posted by mayco

If indeed the two systems are mistakenly tied together I also dont understand why the converter wouldn't be charging the chassis battery also. I dont have a clear understanding of this entire ignition/charging system. When I replaced the battery isolator under the hood, I referred to the Airstream manual to insure that the new isolator was installed the same as the original (or what was there).

The chassis battery seems to hold a good charge (12.4-12.5) when I use the disconnect but I havent taken the battery out to have it tested. It was under 10.0 the last time I had forgotten to use the disconnect but after a couple hours on the road it had charged back to about 12.43 and thats where it is at aprx right now. The alternator is putting out between 14.7 and over 15 depending on rpm.

A couple of days ago I turned on both my exhaust fans in the afternoon, chassis battery at 12.43 , and let them run till early the next morning. Plugged into shore power. Tested voltage and the chassis battery was down to under 10 volts. Coach batteries stayed charged, coverter doing its job. The only thing that I could come up with is that those exhaust fans had drained my chassis battery down, nothing else on over night. So thus my thinking that somewhere the two systems are tied together somewhere and the coach batteries are reveiving a charge from the converter and the chassis battery is not, duh! You would think it would if indeed they are somehow commingling.

So, converter is working, alternator is working, looks like the battery combining solenoid is working, but the battery isolator? Even though I removed and replaced as the old one was, same type isolator but a little higher amp, dunno. At first glance at the wiring for the isolator I thought the alt post and battery #1 post should be reversed but I installed according to the manual and the one that was removed. Ill post pics of the isolator wiring/ old and new.

This may sound sort of off the wall but I'm wondering if your coach batteries are actually tied into the coach DC buss. I say that because your chassis battery acts just as I would expect after having powered two fans for as long as you indicated with out being charged at the same time.

Do this, disconnect the chassis batteries so that you know they are not jn the system. Now try the different positions of your disconnect switch and see what happens.

At some point I would repeat the above with your DC converter unplugged. The idea here is to see what does and doesn't work on the chassis battery.

There just has to be something obvious that we're just not seeing yet.

[mayco]

Originally Posted by bkahler

This may sound sort of off the wall but I'm wondering if your coach batteries are actually tied into the coach DC buss. I say that because your chassis battery acts just as I would expect after having powered two fans for as long as you indicated with out being charged at the same time.

Do this, disconnect the chassis batteries so that you know they are not jn the system. Now try the different positions of your disconnect switch and see what happens.

At some point I would repeat the above with your DC converter unplugged. The idea here is to see what does and doesn't work on the chassis battery.

There just has to be something obvious that we're just not seeing yet.

Brad, did you mean "disconnect the chassis batteries" or the "coach" batteries?
Take the coach batteries out of the equation to see if anything still works with just the chassis battery connected?

[bkahler]

Originally Posted by mayco

Well I was wondering about that, Ill pull and have it tested tomorrow. This has happened now more than once so I guess there is a good possibility Ive murdered the defenseless thing. (Its only a year old)

Yeah definitely have it tested. The good news is I've had batteries discharged that far and they recovered. Good quality batteries have a better chance of surviving.

[bkahler]

Originally Posted by mayco

Brad, did you mean "disconnect the chassis batteries" or the "coach" batteries?
Take the coach batteries out of the equation to see if anything still works with just the chassis battery connected?

Sorry, I meant the coach batteries. The thought is to see what circuits work with the chassis battery especially when the disconnect is ppen.

[Smartstream]

I'm certainly not an electrical guy but after reading the above especially Brad's last post why not disconnect the coach batteries and start turning things on to see if anything is connected to the chassis battery that shouldn't be? Kind of what Brad said but maybe a more direct route.

Sorry, I guess Brad beat me to it while I was typing.

[mayco]

Ok, thats what I thought you meant. Good idea.

Dean, Ive got the 3 post isolator. Im not exactly sure where the second wire on the battery "1" terminal and the battery "2" terminal go. I was assuming one goes up to the voltage gauge in the dash "1" terminal, and the one from the "2" terminal is a sensing wire. But Im not sure on either.........Ive obviously got some testing to do here.........thought this might be an easy one but like everything else on these rigs, budget 2 hrs and it will take 10.

[bkahler]

Originally Posted by Smartstream

I'm certainly not an electrical guy but after reading the above especially Brad's last post why not disconnect the coach batteries and start turning things on to see if anything is connected to the chassis battery that shouldn't be? Kind of what Brad said but maybe a more direct route.

Sorry, I guess Brad beat me to it while I was typing.

Dan, I've been stewing on the problem all day and it just sems more and more like the coach batteries aren't connected into the system like they should be. If they were being charged by the converter their voltage should be higher. Mike says they are 12.4 to 12.5 volts. That's just to low if they were connected to the converter.

Once Mike figures it out the answer will probably surprise all of us!

[PeterH-350LE]

Originally Posted by mayco

Old isolator
Attachment 244029

New isolator
Attachment 244030

Center terminal on both is alternator, left terminal coach batteries, right terminal "to engine battery through Chevrolet harness" (quote from manual) at a glance, I thought the wire on the right terminal and the wire on the center terminal should be flip flopped but as you can see from the pictures I installed as per the old isolator.


Sent from my iPhone using Airstream Forums

Identical Isolator wiring on my 310. I also was surprised to see the gauge of the alternator charging wire and the lack of size of the Motor Battery charging wire, but I did check all the voltages and it appears to be correct.

[Smartstream]

Brad I agree it's probably something stupid simple. As old as these rigs are and as many people have played with them over the years it could be anything.

On two occasions over the past several years I have had a dead chassis battery after being parked for a day or two. Something hung up but I have no idea what. Luckily what ever it was it hasn't happened in the last four or five years so I'm not losing sleep over it.

As to Mike's coach if the chassis battery is going down that fast I would think that after the coach batteries are disconnected, remove a clamp from the chassis battery and there should be a pretty good arc indicating something is drawing from that battery. I always refer to notes from Mr. Lucas regarding smoke and sparks.

[mayco]

Originally Posted by PeterH-Airstreamer

Identical Isolator wiring on my 310. I also was surprised to see the gauge of the alternator charging wire and the lack of size of the Motor Battery charging wire, but I did check all the voltages and it appears to be correct.

Glad you chimed in Peter because that wiring on the isolator was still bugging me. Like I said, at a glance the heavy gauge wire going to the ALT post looks like it should be on the chassis battery post and the smaller gauge wire on the chassis post looks like it should be on the ALT post. I double checked the manual and the drawing seemed to confirm the way its wired is correct, according to Airstream.

Mike

[PeterH-350LE]

Originally Posted by mayco

Glad you chimed in Peter because that wiring on the isolator was still bugging me. Like I said, at a glance the heavy gauge wire going to the ALT post looks like it should be on the chassis battery post and the smaller gauge wire on the chassis post looks like it should be on the ALT post. I double checked the manual and the drawing seemed to confirm the way its wired is correct, according to Airstream.

Mike

I doubt that the isolator wiring is your problem, but it's easy to check anyway. Engine not running, no voltage on center post and different voltages on batt post 1 and 2
I suspect the reason why we see that #6 charge wire is the engine harness of the early 80's GM's had an internal wire connection of the red #10 coming from the alternator to another red #10 or 12 that would feed a junction block in the engine compartment for things like heater fan Motor.
Responsible RV builders would eliminate that internal connection in the GM wiring harness to allow for multiple batteries, controlled by the Isolator.
So they added that #6 charge wire, separated from the GM loop. The #10 chassis bat charge wire appears to only travel a very short distance

[Kota]

Mike,

Haven't read the entire electrical saga but the wire from the isolator to the coach battery looks pretty light. It takes very little voltage drop to get the voltage at the battery below the threshold where the battery will accept a charge. You need to see better than 13 volts to accept a decent charge. Ideally about 14 for a good charge at the capacity of the alternator. A trickle charge at 12.8 volts won't do much good in a day of driving. I'd replace the wire with #8.

Check the voltage at the battery post. Not the connector. I've seen sneaky connections right up to the clamp on connector. The ground side can also be a culprit. Less then 1 volt can be the difference between charging an not. And that drop won't even create much heat.

[bkahler]

Originally Posted by Kota

Check the voltage at the battery post. Not the connector. I've seen sneaky connections right up to the clamp on connector. The ground side can also be a culprit. Less then 1 volt can be the difference between charging an not. And that drop won't even create much heat.

I literally spent days trying to figure out why a brand new chassis battery on the 310 read 12.6 volts but did not have enough power to open the steps or start the engine or anything. I cleaned the battery connection multiple times and all the other connections as well.

Turned out to be an internal problem within the clamp on battery cable connector at the battery. This was the style that uses a stud on the battery terminal and a ring connector on the cable. The problem was the stud was not making a good connection with the clamp it was embedded in. Surprised the heck out of me when I found that one.

Replaced the clamp and everything worked like a charm.

[mayco]

Here is what I have this morning;
With the coach unplugged from shore power, chassis bat at 12.4, coach bat at 12.8.
Disconnected coach batteries and tried about every 12v device...nothing. Chassis disconnect was in the on position. Same results in off position. Left coach batteries disconnected and plugged coach into shore power, all 12volt devices work.
Disconnected chassis battery snd took it in to have it tested. Results 12.33v, 741cca out of 800cca. A little low on voltage but I believe the battery is fine.

Had the coach plugged in over night, usually keep it plugged in, 3 stage converter.
As I had said in an earlier post, to test the problem earlier in the week, I had a chassis battery reading of about 12.4. Unplugged the coach from shore power in the late afternoon and let the two ceiling exhaust fans run over night. Next morning the chassis battery was discharged to under 10v. Had a similar problem over the 4th, we were boondocking and monitoring the coach batteries, running the generator to recharge as necessary. After 3 days went to start the coach and the chassis battery was dead. Coach batteries were low in the morning after running a ceiling vent over night. But the chassis battery wouldnt even start the generator. Got a jump start from another vehicle and it started right up.

So, with the chassis disconnect turned off the chassis battery holds a good charge. We have put about 3000 miles on the coach traveling since getting it road worthy. So its gotten put to use without this electrical hitch. I went ahead and ordered a new solenoid.

What to try next? I have gone through and cleaned battery connections and ground to frame as I have worked on the coach. Scratching me head here

Mike

[dadstoy]

Sounds like the coach battery system is fine.

And it is just the chassis/engine battery that discharges over night.

I would do two more tests on the coach battery system to see that it is working ok...

Standing batteries that are fully charged should read 12.5 across the posts and this is what you have.

Test 1: with shore power plugged in, you should see 13.6 - 13.65 across the posts on your coach battery, even if the battery is fully charged (higher like 14.5 if the converter is in full charge mode). You should see 12.5 across the posts on the chassis battery (since the converter should not be charging the chassis battery). Also verify that a 12v light in the coach is working.

Test 2: with shore power disconnected, you should see 12.5 across the coach battery and the chassis battery. Start engine. You should see 13.65 +/- or higher on your coach battery and the chassis battery since the alternator should be providing a charge...you may have to increase engine rpm above idle for alternator to provide a charge. Also verify that a 12v light in the coach is working.

The above should prove that the shorepower/converter sub-system is working...providing 13.65v to the 12v lights and to the coach battery. Will also prove that with shore power disconnected, the coach battery is providing 12.6v to the 12v lights. This will also prove that with shore power disconnected, the alternator/isolator is providing 13.65+v to both batteries.

In your last test I think you proved your chassis battery is not inadvertently connected to your coach battery system. The above test 1 should also help to prove this.

So sounds like the issue is your chassis battery discharges overnight. If something is draining your chassis battery, it should take more then one night to do so. Even though you have tested the chassis battery, do you have another engine battery you could swap in for a couple days to test with? When you had the chassis battery tested, did they do a "load" test on it?

What else is connected to the chassis battery that is draining it overnight? The wiring at my firewall is daunting and it would be very easy for something that should be connected to the coach battery bus on the firewall to get connected to the chassis battery bus on the firewall. My "bus"'s are simply stand alone posts that wires are connected to.

I have all 12v outlets at the dash as well as my stereo system connected to the coach battery system and not the chassis battery system. This is so these things do not discharge the chassis battery and leave me stranded. Make sure your refrigerator and CO detector are also connected to the coach battery and not the chassis battery.

Have you followed the chassis battery cable from the battery up to the starter (common setup at least on a gasser). Have you checked the connections at the starter? I was really surprised when I looked at mine!

Also check the battery cable feeding the starter on your GenSet. I have my GenSet connected to the chassis battery. Again this is to ensure I can start the GenSet if the coach batteries become discharged. Factory had run a long cable from the GenSet all the way to the starter and then of course there is a cable running from the chassis battery to the same starter post. I removed the GenSet cable from the starter and connected it much closer to the chassis battery.

Another test would be to disconnect the chassis battery cable going to the GenSet for a few days and see if your chassis battery still discharges overnight. If you have to disconnect this GenSet battery cable at a point where the cable will still be live, make sure it doesn't get grounded while disconnected.

[bkahler]

Dean's got it covered. There is definitely some obscure unknown load that is showing up on your chassis battery.

Are your steps wired to the chassis or coach battery?

What about your doorbell?

Not necessarily related to your problem but Dean brings up a good point about the genset being connected to the chassis battery and not the coach battery.

I'm not 100% certain but I seem to recall the genset on the 310 being connected to the coach battery. I'll have to look at that to verify.

Brad