I'd appreciate any comments on this approach. It's a long tale, so please bear with me....
Purchased the coach in 2010, shortly after had the chassis batteries die. Replaced them, and they died again not long after. System had the standard reese-neville alternator, echo-charger with house battery priority, etc. Some work with a meter and careful study of the echo charger manual revealed that if the house batteries were not up to snuff, the voltage would never rise enough to charge the chassis batteries. It seems that the quiescent load from the ECUs draw enough current, along with trying to charge the house batteries, that the solar couldn't keep up either.
so my first attempt at fixing this problem was to mount a Schumaker charger on the inside of the bed box to feed the chassis batteries when plugged in. Disconnected the echo charger. This worked for several years but the schumaker eventually died (probably from heat).
This all came to a head on the way back to NC from Indy. Around Greenville, at 4 or so PM in the summer, I noticed the battery voltage was VERY low - first alerted by some chattering relay issues and instrument dropouts. I fired up the generator and started killing all the 12v load I could. It came up a little and the erratic behavior stopped for a while. Then it started to rain.
Drove for a while with just parking lights and the wipers. The wipers would stop for minutes at a time. Thats when I noticed that they were the leading indicator of a voltage problem, and - I'd been seeing this in one way or another every time I used them since I bought the coach. Obviously the alternator was not up to snuff.
Daylight lasted until we got out of the cities and headed to eastern NC on 40 with almost no traffic. Wife drove in front lighting the way while I drove with just the marker lights on and managed to nurse it home. On several occasions I had to hold the boost switch down for minutes at a time to transfer some charge.
What follows is the long troubleshooting process and a bit of a re-design.
Weekend #1 - Got the coach back in its storage unit, and plugged in. Had to build a platform so I could lay over the motor to work. Got the old unit off - a Leece-Neville, and took it to a auto-electric place for a re-build. Also ordered a new serpentine belt.
Auto-electric guy calls me back and says for $90 more than re-building my 85A unit, I could get a 200A Delco. Sold!
Weekend #2 - Installed new alternator only to find it didn't fit at first glance. Turns out a J180 mount actually has TWO different sizes and no unique designator. L/N uses the big one and Delco the small one. Evidently the mounts on the CAT are adjustable for either. Returned alternator and asked for another before figuring this out.... Installed a new big-ass relay too so I don’t have to tap it with a dowel anymore to get it to tick over.
Weekend #3 - Picked up belt and alternator, went to storage unit and installed both after figuring out how to adjust the CAT bracket (pretty slick actually). Batteries too dead to turn the motor over. Charger on MH only charges the house batteries, trickle charger on the chassis batteries too small to get them to recover from the deep discharge (turns out it was dead too). Go back home. Strip the race car start cart and drag the mess back out to the storage unit. Charge chassis batteries on 15A for several hours, as well as hooked the house batteries up the the chassis batteries with jumper cables. Got the genny started, then the main diesel, but not enough juice left to get the Allison to shift. The new alternator is not working either - 0V at the isolator center lug.
Ordered two new chassis batteries from NAPA.
Weekend #4 - installed the chassis batteries, fired up the coach, and drove it about 20 minutes to my house, and plugged it in. On Monday, took it to auto-electric to troubleshoot new alternator.
Problem was that what they thought was a "sense" wire is actually the wire needed to get the Delco to self-excite when you use an isolator. Auto-electric charged the batteries and I drove it home - Higher voltage than it's had since I purchased it!
Weekend #5 - went to start the coach to drive it back to the storage unit, and it was completely dead. Hit the boost switch and a house battery blew up.
The chassis batteries wouldn't recover, so I ordered new chassis batteries, new golf cart batteries for the house side, and a new amp-l-start charge diverter so that the chassis batteries have more charging priority.
Weekend #6 - removed the battery tray to cleanup all the rust from the battery explosion and 17 years of use. Removal was a challenge. How they got the thing in escapes me. The assembly had two bolt heads rendering it wider than the compartment it was in that had to be sawzalled off. The slide couldn't be removed from the installed position and together they weighed 40 lbs. Several hours with a paintbrush and die grinder later, it's no longer rusty and the slide tray is removable. Added a sense line to the alternator.
Weekend #7 - installed the new charge diverter, installed the tray, cleaned up all the cable connections, and installed the house batteries first. On hookup, noticeable spark despite everything as disconnected as possible, breakers pulled, etc. Also, chassis battery connections show 12V..... hmmmmm. Spent several hours moving about filthy cables and probing with a couple of voltmeters. Nothing conclusive. Disconnected house batteries and installed chassis batteries. 12V appears on house battery connector.... More hmmmmm.
Figured the Isolator was fried. Disconnected house side of the isolator. Stray voltage disappears from everywhere it wasn't supposed to be. Ordered new isolator (turns out this was not the issue, but the old isolator was not rated for the new alternator's current, so it was going to need to be replaced anyway)
Fired up the diesel and got 13.5V to the chassis batteries with no sense line connected, 14.2 with the sense line. Instruments all have a "new normal"!
Installed new isolator, the Cole-Hersey with a fourth terminal. Was totally confused by several posts that tried to explain how to hook it up and why, including the manufacturer's instructions. finally figured it out:
The Delco 28SI can be excited via the "I" wire or self-excited via it's output cable. by putting 12V on the 4th lug of the isolator, 12 V is switched on to the center lug of the isolator and the alternator self-excites. It was here where I figured out what caused all my problems with the new alternator:
The "I" wire to the alternator is supposed to be ignition switched. It was not - it's hot all the time. Thus, when the Auto-electric guys hooked up the Delco alternator, current flowed from the chassis batteries through the alternator and the isolator and into the coach batteries, draining the chassis batteries to the basement in just a couple of days. the huge current draw caused by actuating the boost relay lit off the hydrogen in a house battery and that's why it blew up.
The original Leese-Neville never could get either of the batteries to full charge either, because it couldn't compensate for the voltage drop across the isolator. I believe it had a sense wire, but the output was always very low compared to this Delco. The LN would have been fine with a relay-type isolator setup.
I never could easily find a switched ignition signal in the rear harness. When I put in a 7-pin trailer connector years back I used a spare wire in the harness that comes out behind the right taillight for the breakaway battery charge circuit. That one runs from an automatic circuit breaker in the electrical bay That I added with the floodlight board. I tee'd off that signal to get the switched line for the alternator field. I would rather have used something else, but that was what I could easily access.
It's pretty amazing now. Alternator puts 15 into the isolator, so both the house and chassis batteries fully charge. with the AMP-L-Start instead of the Heart, the chassis batteries charge at a significant rate and then the house batteries, so I'll always have power to start either the diesel or the genset.
Here's the schematic I ended up with