running stock otr ac unit

[reelnative]

the org ac unit in my bus was changed over to use 134a from the old r-12, if I keep this unit for ac while driving, is there more draw on the alternater and will I have to use the larger 8d batts or 2 sets of group 31s or could I get away with just one set of group 31s, I dont have any house bank set up yet and when I do Ill prob go 12 volt and just have 2 or 3 deep cycles for that

[Sean]

the org ac unit in my bus was changed over to use 134a from the old r-12, if I keep this unit for ac while driving, is there more draw on the alternater

Yes, it will nearly max the alternator out.

and will I have to use the larger 8d batts

Yes.

or 2 sets of group 31s or could I get away with just one set of group 31s,

I would not try to run the OTR A/C on just two group 31's.  The alternator will only keep up while you are at road speed; the big batteries are needed to buffer over the time when you are idling at stop lights, etc..  You should always use the fast idle whenever you are stopped long enough to engage the parking brake.

You have not told us how you plan to use your bus.  But you might seriously reconsider keeping the OTR air if you will be using it in a traditional motorhome application.  Lots of discussion on this in the archives; bottom line is that it takes up lots of room and weight, is very, very costly to maintain, and is only useful when rolling down the road, which for most motorhomes amounts to less than 10% of the time spent on board -- sometimes as little as 1-2%.  By contrast, electric air conditioning, such as RV roof airs or basement units, is generally less costly to maintain and can be used 100% of the time, whether driving or parked.  It, too, takes up space and weight, but you will need to have it anyway for when you are parked, whereas the bus air can be dispensed with.

I dont have any house bank set up yet and when I do Ill prob go 12 volt and just have 2 or 3 deep cycles for that

Again, I would strongly suggest you reconsider using a 12-volt house system.  Again, lots of discussion in the archive, or buy the April issue of BCM; I just did a complete write-up on 12 vs. 24 volts in that issue.

-Sean
http://OurOdyssey.BlogSpot.com

[reelnative]

ok now ive got more stupid questions for you, why does the stock ac take up so much power from the alternator and batts, is it from the fans that have to run? the compresser runs on blets from the engine right.

I was planning on installing 2 or 3  roof ac s for when parked and hooked up to shore power, if I get rid of the stock ac would I have to run a seperate gen to power the roof ac or a basement unit while in route also if I did go with the basement style is it better then the roof type. Thanks

[JackConrad]

OEM AC compressor is belt driven from the engine, but there is a huge electric motor on the condenser fan and another one on the evaporator fans that circulate the air through the bus. The motors are slightly larger than a stater motor.  Jack

[scanzel]

In my conversion I have two sets of electric motors for the otr air and heat and these motors draw alot of amps when running so you do need the big alternator to run them when they are running. I thought of removing the otr, but have decided to have it fixed. I have two roof tops but without the otr I would need to run the genarator while traveling to locations which in turn would add many hours to the generator. With you stating 3 roof tops what would happen if your generator failed, then you would have no air while traveling. You could add a  big battery bank and have it charge off of the alternator but you would probably only be able to run one roof air while traveling.

[bevans6]

The compressor itself is belt driven and takes perhaps 30 hp from the engine, at a guess.  The condenser fan is a 2hp 24 volt fan and takes close to 100 amps.  The evaporator fan, which is also the OTR heater fan, takes a little less, it's is fused at 80 amps from what I recall (manual is at home).  So it's the combination of the two fan motors which draws roughly 150 amps between them when the AC is on.  Add to that the drivers AC fan motors.

when I did the research, I looked at the benefits of stripping about 500 lbs out of the bus, not driving the compressor from the engine with it's power requirement, gaining the space in the condensor bay for a generator, vs having the AC recharged (mine had been converted but had a leak), getting the leak fixed (estimate $1,000) and estimated annual maintenance of about $1,000 a year.  I bought a roof-top 15K unit for $450, and put a little Yamaha generator in the old condenser bay.

Brian

[buswarrior]

Historical total load, compressor and electric, for these older coaches was somewhere 25 HP.

Which really doesn't matter.

Back then, I tried turning it on and off in revenue service, trying to feel a difference, the coach still climbed the mountain the same.

Can't feel it in your bum.

happy coaching!
buswarrior

[reelnative]

thanks for the replys guys,

jack knowing that your from my neck of the woods and know the kind of weather we have in the summer here would it be wise for me to keep the stock ac unit in the rig, its been changed over to the 134 so if I do have a leak or problem down the road it wont be a major job to find 134 to refill it,

[Sean]

I was planning on installing 2 or 3  roof ac s for when parked and hooked up to shore power, if I get rid of the stock ac would I have to run a seperate gen to power the roof ac or a basement unit while in route

Running a generator is one way to do it.  However, if you ditch the OEM road air, you will have a huge amount of electric power available from the alternator, which has a rated output of over 6,500 watts -- larger than some generators.  You can use a true sine wave inverter to run one, two, or even three roof air conditioners with this alternator.  A 2,500-watt inverter can run a single air, a 4,000-watt unit will easily run two, and a 5,000-watt unit will run three.  The alternator will power any of these without breaking a sweat.

... I have two roof tops but without the otr I would need to run the genarator while traveling to locations which in turn would add many hours to the generator. With you stating 3 roof tops what would happen if your generator failed, then you would have no air while traveling. You could add a  big battery bank and have it charge off of the alternator but you would probably only be able to run one roof air while traveling.

See above. If you have both a generator and an inverter, then you do have a backup system.  You can run one, two, or three air conditioners depending on inverter size.  The size of the battery bank is nearly irrelevant when the alternator is running; even three roof airs use only about 4,700 watts, just 70% of the alternator's capacity.

This is not merely theoretical, BTW -- we do it all the time.  We never run the generator while traveling, and have no engine-driver air conditioning whatsoever.  We can easily run two of our four air conditioners on our 4kW inverter while driving.

also if I did go with the basement style is it better then the roof type. Thanks

That's a personal choice, and there are all manner of pros and cons on both sides.  Rather than repeat them all here, let me reiterate that this is a subject that has been discussed here many times, and a quick search will turn up several of those discussions.  I'd recommend you to read through them to get a feel for what the issues are.  For example:

http://www.busconversions.com/bbs/index.php?topic=12876.0
http://www.busconversions.com/bbs/index.php?topic=11544.0
http://www.busconversions.com/bbs/index.php?topic=1797.0

and many more.

-Sean
http://OurOdyssey.BlogSpot.com

[reelnative]

if I went the route of using the alt output to run an inverter for the roof airs whlie under way, will the alt put out enough power when at idle or is this were the larger batt bank will come into play as a buffer

[Sean]

if I went the route of using the alt output to run an inverter for the roof airs whlie under way, will the alt put out enough power when at idle or is this were the larger batt bank will come into play as a buffer

Depends on how many A/C's you are trying to run.

Remember the OTR system is designed to cool the entire bus, along with the body heat generated by 48 souls.  As such, the blowers for the cabin and condensers are enormous, drawing nearly 200 amps at full load (5kW).  With all these running, for sure you need the 8D batteries for those idle times.

Likewise, if you try to run three roof airs simultaneously, which would require a 5kW inverter, you'd be in a similar situation.  However, if you had only a 4kW inverter (more common) and ran only two A/C's, the alternator can just keep up with that at idle speed.

In any case, you will want to be connecting an inverter to a "house" battery bank, not the chassis batteries.  Unless you plan to always be plugged in or running a genny when parked, you're going to want a decent size set of house batteries anyway.  The alternator comes into play by bridging the house batteries over to the chassis system when the engine is running.

-Sean
http://OurOdyssey.BlogSpot.com

[bryanhes]

Sean,

What size alternator are you referring to? Mine is 225 Amp. So I should have a peak of 5400 watts correct?

I just need to give you a place to stay for a few weeks some food, wine and a hookup to help me put mine together  

Bryan

[Sean]

What size alternator are you referring to? Mine is 225 Amp. So I should have a peak of 5400 watts correct?

The MC-8 we've been discussing would have come with a Delco 50DN rated at 270 amps @ 28 volts, peak.  That's actually over 7,500 watts; I always de-rate this to 250 amps @ 26 volts, or 6,500 watts, just because I think that's closer to the practical limits of the device.

I'm not sure what the specs are on the alternator that came with the older GMCs.  225 amps @ 28 volts is 6,300 watts, but, again, I would de-rate it somewhat, especially if it is air cooled (the big 50DNs are oil cooled).  Call it 200 amps at 26 volts, which would be 5,200 watts.  Still respectable.

I just need to give you a place to stay for a few weeks some food, wine and a hookup to help me put mine together  

It will take more than that to bring me out of retirement 

If I'm in the neighborhood, though, I am happy to "consult" -- that's where I pontificate on how you should do things, without doing any actual work. 

-Sean
http://OurOdyssey.BlogSpot.com

[JohnEd]

One thing that hasn't been mentioned is that you will recover some heat load capacity when you delete the OEM OTR AC.  Subtract what your alternator puts out but it won't be 25-30 HP worth so you have a net gain.  And just what would we pay for a 30HP bump??

I'm just say'n

John

[Highway Yacht]

Would a 24v 5000w continuous power sine wave inverter connected to 2 group 31 house batteries operate 2 rooftop air units without any trouble while driving down the road for hours??? Also, don't you have to have a switch located somewhere to change the power over when connected to shore power??