running stock otr ac unit

[philiptompkjns]

While my bus expericance in non-existant, let me throw in my RV experiances here.


The Dash air is adequate to keep the 2 people up front happy in the summer sun, I would close off the doors to the bathroom and rear bedroom while driving.

With more than 2 people neither the dash air or heat would keep everyone on board happy, I just had to run the gen. and 2-3 roof airs or propane heater for anyone sitting out of direct blast of the front dash vents.

From this experience I'm going to set the bus up to to run the front a/c from the inverter and use that for OTR, and close off the rear of the bus while driving.  If there are many people on board (just a few times a year) I'll just run th gen..... In my case saving the factory OTR A/C would probably save less than 40 hours of generator run time a year.... not worth the $1k maintenance bill.

[Sean]

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???

Yes.  The power is not coming from the batteries, it is coming from the alternator.

Also, don't you have to have a switch located somewhere to change the power over when connected to shore power??

Generally, this is part of the inverter.  If it is not, then, yes, you would need to have a transfer switch.

-Sean
http://OurOdyssey.BlogSpot.com

[reelnative]

  sean you wrote             .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.


now does the power from the alt run thru the batts then thru the inverter, or is there a way to hook the inverter right to the alt, the reasion I ask is someone asked if a set of group31 batts would be big enought to do this and you answered that the batt size didnt matter, and I was under the impression that the inverter was hooked to the batts and they were used as a buffer, sorry if im sounding confusing but that kind of happens to me after 3 crown and cokes


your quote

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.

[JohnEd]

Reel,

Hydraulics is used to explain DC circuit analysis and operation.  Think of your bats as big tanks that are plumed to the generator(pump) and the inverter(water wheel).  The current flow can come from the "tank" OR the pump and drive the wheel.  Tanks are high and provide water by gravity.  As they are tied to the same "pipe", the water can be supplied by the tank OR the pump OR they can both act together to provide the flow.   If the pump has the capacity to meet the flow needs then the water will fill the tanks  AND drive the wheel.  When the wheel needs more flow than the pump can provide then the tanks starts to help.  If the pump quits and the wheel continues to demand water to do its work then the system will only run as long as there is water in the tank.   The pump is your generator, the tank is your bat and the water wheel is your AC.  At the end of the pipe is your converter and that is really connected to your AC unit.

The AC compressor mounted on the engine is usually a multi ton capacity affair.  The single evaporator unit in the drivers area will rarely be able to extract all the "COOL" that the compressor can create.  You can add a evaporator in the rear of your coach and run it with its own thermostat to keep the rear cool under way.  If your compressor happens to not be large enuf then a quick trip to the wrecking yard will turn up one of those biggie 10 cubic inch plus compressors for cheap.  The same goes for heating.  Install a aux heater back there with a thermo and fan and you will have comfy passengers for free.  Your AC won't be free as your engine running on fuel will make the COOL but it will cost a small fraction of what an OTR AC system will cost to operate and repairing an OTR is out of sight.

now does the power from the alt run thru the bats   This question got me going.

HTH

John

[bevans6]

No.  the batteries are in parallel with the load so no power that goes to the inverter flows through the batteries.  Each will draw power according to it's need, or internal resistance.  The alternator has the ability to produce 250 amps or whatever, the "capacity", but it doesn't produce it unless there is a load to draw upon it.

The reason battery size has impact to the decision to run larger inverters powered by the alternator is that the alternator requires a certain rpm in order to produce power, there is a curve you can look up.  At idle, the alternator produces little power, comparatively speaking.  The batteries must have the capacity to supply the inverter at such times, which in stop and go traffic could easily be 60%  - 80% of the time for quite a while.  Think of a traffic jam on an interstate.  So you need to size the batteries such that they can not only supply such a load for a reasonably design time,, but also so they will not be damaged by supplying such a load in the first place.

Brian

[Sean]

Well said, John and Brian.

And the curve Brian mentioned can be found here:
http://www.delcoremy.com/alt50dngear.aspx

Because of the nature of alternator output, which is actually a fluctuating waveform, and the danger to the alternator of having no load whatsoever, batteries are always required.  Beyond starting needs, the size of the chassis batteries depends on how much load they will have to carry, and for how long, during those periods of time when the load exceeds the alternator output.

-Sean
http://OurOdyssey.BlogSpot.com