Running a Roof Air OTR on an inverter

Fred Mc · June 26, 2018, 11:23:40 AM

Just thinking out loud here..
My bus has 3 Group 31 start batteries .Is it possible to run a roof air(115V) OTR off an inverter with the stock alternator?

If so what size inverter would I need. Pure sine or modified?

Thanks

Fred

chessie4905 · June 26, 2018, 11:26:09 AM

Coach model, alternator amperage output and 12 or 24 volt system?

bevans6 · June 26, 2018, 01:14:14 PM

I run a 15Kbtu roof air over the road with a Magnum 4024 pure sine inverter and a Delco 50DN alternator. Works perfectly.

Brian

luvrbus · June 26, 2018, 02:18:29 PM

It's been done for a long time even before the sine wave inverters,I ran mine off a a Heart inverter for years,it does require enough alternator to keep the batteries replenished and a large battery bank is nice to have because it will die in a hurry at idle with a small battery bank

Fred Mc · June 26, 2018, 08:49:39 PM

Its a PD4106, 12v with a 50DN stock .alternator.

neoneddy · June 27, 2018, 08:21:56 AM

Looks like your alternator could be as stout as a 350 amp at 12v = 4,200 watts. So in stock form I don't think you should be pulling more than 3000 watts continuously, leaving 1200 left over for coach systems. My two ACs pull 2500-2700 watts together, it goes up and down with temp, that's about 80 degrees.

But yes, you'll be fine, the biggest issue is inverter power. I've found I need at least 2000 watts of inverter per AC unit. 3000 watts per unit gives good headroom for other items. I've heard some folks here running two units on a single 4000 watt inverter.

luvrbus · June 27, 2018, 08:33:14 AM

You won't get 350 amps from the older 50D Delco alternators it pushes one for 300 amp @ 12V and that is with the oil cooled version like on his 4106 and everything in #1 shape

windtrader · June 27, 2018, 10:28:07 AM

Don't your buses run? It's too hot, drive north! Too cold, drive south! Problems gone. lol

luvrbus · June 27, 2018, 10:55:14 AM

Quote from: windtrader on June 27, 2018, 10:28:07 AM
Don't your buses run? It's too hot, drive north! Too cold, drive south! Problems gone. lol

True but getting to point B from A can be a miserable drive often without heat or AC done that before

bevans6 · June 28, 2018, 04:45:57 AM

I spent a few weeks in New Orleans one August, a few years after Katrina. I figured my contribution to the rebuild would be to come down and spend as many tourist dollars as I could. Every day I checked the weather back home, in Toronto Canada. Every single day the weather was hotter in Toronto than it was in New Orleans, by a few degrees. Talking 95 to 100 degrees. That's what you find across the entire middle section of the continent, northern USA and Canada, from the Saskatchewan to around Quebec City - hot and humid summers. The only place it's different is on the coasts. Two nights ago it snowed not far from me in Nova Scotia, while Toronto has already had a week in the mid-high 90's.

Brian

luvrbus · June 28, 2018, 11:13:50 AM

We all become a pansy with all the modern day conveniences like the AC,Driving on I 40 and parts of route 66 made me stop and think how in world did the folks back in the 30's escaping the dust blow route 66 goes through terrible desert with extreme heat like Needles Ca for 1 place.
No AC, old cars breaking down,no truck stops,no Walmarts, no restaurants,no call boxes since 66 was fairly new, those were some tough folks is all I can say to make that journey, PS it was 116 there yesterday so I won't complain about my AC again

richard5933 · June 28, 2018, 11:35:48 AM

Quote from: luvrbus on June 28, 2018, 11:13:50 AM
We all become a pansy with all the modern day conveniences like the AC,Driving on I 40 and parts of route 66 made me stop and think how in world did the folks back in the 30's escaping the dust blow route 66 goes through terrible desert with extreme heat like Needles Ca for 1 place.
No AC, old cars breaking down,no truck stops,no Walmarts, no restaurants,no call boxes since 66 was fairly new, those were some tough folks is all I can say to make that journey, PS it was 116 there yesterday so I want complain about my AC again

My first car was a '56 Dodge. We joked that it had 4/60 air conditioning...4 windows down and drive 60mph. The car also had a working cowl vent and very effective vent windows.

I think that if cars (and buses) were designed in a way that permitted ventilation we could travel without a/c. The way our bus is set up (only two of eight side windows open) there would never be enough ventilation to be even close to comfortable.

chessie4905 · June 28, 2018, 11:36:28 AM

If you noticed, they hung canvas water bags over radiator. The water seeped out and evaporated off the fins of the radiators. Also those old engines had such low compression ratios that the combustion heat was less intense. You always saw them steaming out of radiators on hot days. The grapes of Wrath movie has good illustration of those hot crossings.

TomC · June 29, 2018, 01:58:48 PM

If you have a Diesel generator, just run the genset going down the road. Then you can have two roof airs running, use the microwave, have the refer running, etc without problems. The 50DN is just too expensive to risk burning out-plus you want to carry maybe an extra 600lbs of batteries? Good Luck, TomC

dtcerrato · July 03, 2018, 05:51:57 PM

How about dual residency? Summers (May through mid September) in the Alaska interior & winters (Oct through mid April) in N Central FL... That takes care of most of the air conditioning issue then there's the generator until we may add an inverter for otr A/C as an option. We're looking at the Magnum 2812 to run 1 roof top. Looking forward to the dual residency as soon as possible. Eventually if we get something built in AK we could fly for less $$$ than the road trip back & forth. If heat became nessessary it's because we decided to hibernate north for a winter! Yikes!