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Electrical Discussion of preventative/corrective maintenance and other technical issues regarding your coach's electrical system.

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  #1  
Old 02-11-2010
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Turbokitty Turbokitty is offline
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Default Inverters...

Any commentary by some of you fine folk about running A/C units from an inverter? Sizing etc??
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  #2  
Old 02-11-2010
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While you technically 'can' do it, it's not a really good idea.

You would be placing a very heavy load on the inverter, and unlike a hair dryer or microwave, the AC unit will be running for an extended period of time.

Additionally, you are also placing a very heavy load on the alternator.

From my point of view, the issue is the fact that it is an extended time load. While technically the components can carry the load (assuming you buy the right inverter), you are going to reduce the life expectancy of the components.

Just my 2 cents...

-Robert
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Old 02-11-2010
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Ryan
You ask units? Maybe one could be with a 3,000 watt inverter two would require 2 inverters and a bigger alternator. We just run the generator run anything we need 3 ac's etc. Gen only uses about 1--1.5 gal fuel an hour. You can buy lots of fuel for what it would cost for bigger inverters and alternator.
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Old 02-11-2010
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Just the advice I was looking for Robert and Ed! Thanks.

What if... the invertor was well oversized? I understand Ohms law and losses associated within wiring, heat and circuitry efficiencies etc.

What I am ultimately trying to achieve (and build) is a very small watercooled diesel generator that will only generate 12 VDC at lets say... 300 amps maximum output. My desire is to have it set up for "auto start" based on battery voltage/demand. It would also be variable speed based on demand too. I am conversing with a friend/electrical/electronic engineer about the speed control which he says is "basic" on his end.

This generator would ultimately be extremely quite, fuel miserly and able to run at night without noise being an issue. This way, while "dry" camping I can automatically keep my batteries charged without having to generate 120V 60 cycles AC power only to then have to drop it back down to 12VDC. This generator would be able to basically stop, start and idle to keep things charged and then rev up as needed to cover additional loads.

I guess you get my desired effect? I would love to have a 12 or 24 VDC air conditioning unit as well as 2, 120VAC units. I would still have the regular diesel 120/240 VAC generator as well.

Any validity to my thoughts??? I know ONAN has this technology out there but hey... it would be fun to try one built on my own
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Old 02-11-2010
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Forgot one thing... I would operate this setup in conjunction with probably 8 T105 type batteries to act as a buffer and generated excess energy storage.
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  #6  
Old 02-11-2010
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Ryan,
There are newer systems that do just that. They adjust the engine speed and output based on demand. They use inverters to run everything. If you get it right you will be way ahead. The systems I read about also use the batteries to absorb the start-up load on AC units, etc. I would love to have such a system, but the cost is way high compared to maintaining the current generator.
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Old 02-11-2010
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Ryan,

You can already sort of achieve your desired results with your stock generator and an auto gen start (AGS), combined with an inverter.

I still think connecting a roof air unit to the inverter isn't a good idea, but there are folks out there who have done it and like it.

Anyway, if you were to go with such a configuration, here is how it could work:

Inverter is powered by your battery bank and alternator. Alternator will be providing 12v to keep batteries charged, and power the inverter while underway.

When engine is not running, inverter is using battery power. The AGS monitors the state of your battery bank. In my system (made by Xantrex), I can set parameters for the conditions which cause the generator to start. For example, if the battery voltage drops to 11.4v for 30 seconds, it will start. That would be caused by a high load device, such as your air conditioner, or a microwave. If the battery voltage drops to 11.6v for 10 minutes, it will start. That would be caused by dry camping, or if shore power fails.

The AGS will automatically turn the generator back OFF based on parameters you set as well. In my case, I have it set to normally shut off the generator once the battery charger has entered a float state, or after 4 hours. Whichever is shorter.
If the AGS was activated by the 11.4v for 30 seconds, the generator will shut back off after the load causing the drain is removed for 30 seconds.

So, it is possible to do what you are desiring, without building your own generator. I suppose you could also just install an AGS in the home-built generator.

-Robert
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Old 02-11-2010
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If you used the small "smart" generator instead of inverters and 3 tons of batteries you will be money ahead.
The entertainer coachs don't have inverters and all the expensive batteries,they just run the gennie.

Also,on my 95wb you could run one AC unit off the inverter,after about 3 hours the inverter would overheat and shut down.
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  #9  
Old 02-11-2010
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I think a 12 or 24 volt DC air conditioning unit would be a great advantage too. I know there would be larger gauge cabling involved but it would bypass the need for an inverter...
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  #10  
Old 02-11-2010
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I have had 1 electrician and 2 engineers tell me not to run the AC on inverter.

I used to run the AC on inverter while going down the road, but now I run the generator. The cost of replacing an alternator permaturely and/or AC unit, trumps the fuel savings of running the AC on inverter power. Besides, when the alternator is running, it decreases your fuel economy, therefore there is not as much savings as you might think.

I don't know how much extra HP an alternator needs when working, but your hydrolic fan uses about 50 hp (or .75 mpg) when it runs. There is no free ride. However, your idea of using a small aux generator to power the AC has merit.
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