M920/916/915 Air Conditioner

My set-up is slightly different, I have starting batteries isolated from "house batteries", which are used for everything else, fuel burning heaters, inverter(s), genset starting etc, so that the engine starting operation is never effected by other electrical systems.
Using two batteries for starting is sufficient, since the reserve capacity is then not so important.
The charging of the house batteries is manually selected and monitored on a dedicated ammeter.

The charge rate on the m920/m916/m915 is 15 amp 24v and 85 amp 12v I think thats were he is coming from.

cranetruck said:

Please explain...I mean, how does the alternator know what's loading it down?

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OK, quick explation of the 915/916/920 electrical system: 4 batteries, 2 in parallel for 12V, the second 2 also in parallel for 12V, both battery banks in series for 24V. 24V is used for the starter motor, 12 volts for everything else. The alternator produces 12 volts at 100 amps to charge the first battery bank, and 24 volts at 10 amps to charge both battery banks. If you connect a 24 volt air conditioner that draws 20 amps, the draw would exceed the alternator's capacity and the second bank of batteries would be drained.

Thats a no brainer.....don't run a 24v AC unit

R Racing said:

Awe NDT , I took a new 200 amp unit and had it reworked without the transformer so it internally does 70 amp 24v and 130 amp 12V . then we use a battery equilizer to balance things out . I'll take pic's of that install shortly. It probably in the long run been cheaper to do a new 12V unit .But I have been collecting parts here and there along the way . The 24v ac uses 20 amps

Jamboly I'll snap a pic of the inside later today.

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I take it the Red Dot A/C unit you have is 24V only?

Jim

It is its from a Hmmv it wasn't designed for a m920, lol but were working it into it.

You guys need to look around for used units at truck and equipment salvages. I got my Red Dot off an asphault sealing truck that was getting parted out. I only paid $200 for the system and that included the compressor. Those rooftop units are also mounted alot on older tractors. I think I know where a few may be that are on tractors that where "sent out to pasture".

I guess what I'm trying to say is this.....don't make it harder than it needs to be trying to fit surplus HMMWV units and paying big bucks for them. There is no need in it.

I actually didn't pay a ton for my units ( bought 2 sets new) but the 24V side was another expence.

NDT said:

OK, quick explation of the 915/916/920 electrical system: 4 batteries, 2 in parallel for 12V, the second 2 also in parallel for 12V, both battery banks in series for 24V. 24V is used for the starter motor, 12 volts for everything else. The alternator produces 12 volts at 100 amps to charge the first battery bank, and 24 volts at 10 amps to charge both battery banks. If you connect a 24 volt air conditioner that draws 20 amps, the draw would exceed the alternator's capacity and the second bank of batteries would be drained.

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Got it. So it's the capacity of the alternator, regardless of the load.

I like this unit size the best AP AIR, INC - Part Details

Also like this one as well for over head ops. http://www.apairinc.com/detail.asp?Part=590-61010

Does anyone have one of the Red Dot A/C units for the M915a2 for sale?