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Old 10-03-2016, 11:37 PM   #1
Join Date: Sep 2016
Location: Hesperia, CA
Posts: 126
Year: 2007
Coachwork: Thomas Saf-T-Liner
Chassis: HDX with lift
Engine: Mercedes MBE 920
Rated Cap: 22
Electrical Questions

Okay, so I got my 1982 Carpenter 7 row home. Yanked all the seats out, now I'm looking at the electrical system. For the record, I am a better mechanic than I am an electrician, but here's what I found:

A bank of 3 batteries, wired in parallel. Calling the manufacturer, I found they are 12v 700 amp starting (as opposed to deep cycle) batteries. So, am I right that I am getting 12 volts and 2100 amps of cranking power? (The engine starts up in, literally, less than a second, so it could be).

The other thing is, I had thought the air conditioner didn't work, but it turns out it does. I think the refrigerant is low, so it takes a bit to get going, but it eventually blows what is definitely refrigerated air. So, I am going to keep it, even though it's monstrously large with an underbody condenser bigger than the fuel tank and two evaporators inside, about 3feet long, each with two fans. I assume the A/C is why there is 2100 amps of battery power.

So, here's my question: Is that giant air conditioning system running on 12v DC? Or is there an AC inverter somewhere in there? If it's 12v DC, it would be easy to tap in to those wires to add some 12v appliances and sockets and what not.

The battery bank is all one, not separated into engine and coach, so I also assume I can't run the a/c too long without the engine running to charge them.

So...should I isolate two of the batterys and replace them with deep cycle to run the A/C and such in the coach? I am pretty sure one starting battery would be sufficient for the engine, and leaving the a/c on while parked would be nice.

Also, there was a wheelchair lift in the bus at one time, and I am putting in another. The way the batteries are wired, all three positives go into a conduit, and all three negatives go in to another conduit. Those conduits snake up to the engine compartment, back to the condenser, up thru the floor to the evaporators, etc. I'll chase all that down when necessary. But besides that there is a single cable coming off one of the positive terminals, which appears to run to where the wheelchair lift was wired in. No corresponding negative. Would that be right, that the lift would get positive from the battery, and just be grounded to the chassis? Or is there a missing wire somewhere?

Any advice, corrections or suggestions would be greatly appreciated. I'm going to ponder the whole thing for a couple days while I cut this wheelchair lift hatch back open (it's 1/8" steel welded to angle iron. Should be as much fun as grinding the heads off the 88 bolts holding the seats in)

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Old 10-04-2016, 12:23 AM   #2
Bus Nut
Join Date: Dec 2015
Location: Utah
Posts: 266
Year: 1990
Coachwork: BB
Chassis: TC2000
Engine: Cummins
Rated Cap: 25.999K

I dont know about the AC being 12 or inverted 120. There are pros and cons of having "house batteries" and "engine batteries" on the same circuit. As for your bolts, i found it easier to break them by over tightening them, that is IF they didn't come off easy.. A couple of them did get the grinding wheel, but that was before i realized how easy they break..
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Old 10-04-2016, 07:04 AM   #3
Bus Crazy
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Join Date: Nov 2010
Location: Andrews,Indiana
Posts: 2,353
Year: 1991
Coachwork: Bluebird
Chassis: AARE
Engine: 3116 Cat 250hp
Rated Cap: Just the two of us.
I doubt if your AC is electric, especially in 1982, more likely engine driven compressor. It would take serious battery power to run for any length of time with engine not running. My modern inverter AC will only run about 1/2 hour on a battery bank about that size.

Wheelchair lift probably grounded to chassis.
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Old 10-04-2016, 09:21 AM   #4
Join Date: Sep 2016
Location: Hesperia, CA
Posts: 126
Year: 2007
Coachwork: Thomas Saf-T-Liner
Chassis: HDX with lift
Engine: Mercedes MBE 920
Rated Cap: 22
Ah. Yes. It is compressor driven. Which means , I guess, the engine has to be running to get cooling. So a/c while parked is going to need a separate system altogether. House battery, generator, shore power, etc. Bummer
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