Power My Air Con unit.... Inverter Generator vs Inverter ?

I don't want to start a debate on generators here, there are a few interesting threads already on here with all the arguments for or against....

I am trying to power my 12500 - 15000 btu AC unit in my cabin cruiser... (I have no on board marine generator).

These are some options, as i see it. I could use a 3000w inverter (is this enough?) to run the AirCon while i am cruising, and use the shore power when docked. and install a 2 pole power switch and use inverter with remote switch, and possibly add a battery or two to run it for a few extra hours.

or I could use an inverter generator to run the AirConC (putting it on the swim platform only when stationary - see other threads for opinions on this!).

My main question is has anyone ever re-wired one of these inverter generators to use it purely as an inverter from the 12v DC battery? and , if so i'd be interested in finding out how it went.

It just seems crazy to buy a 3000w invertor... AND a 3000w Invertor Generator.

It would be great if the manufacturers put a 12 V input on them for just this reason, but i can't find any manufacturer that lets you use it as an inverter when its motor is not running.

Yes, i am too cheap to buy a marine Generator.

Thanks in advance for any advice or input. I'm not too sure how many amps/VA a 12500-15000 btu would typical draw?

Dave

Re: Power My Air Con unit.... Inverter Generator vs Inverter ?

10 -13 amps on compressor start up....i think run is 6 depending on the size of the fan.

Re: Power My Air Con unit.... Inverter Generator vs Inverter ?

A modern generator-inverter's alternator produces high voltage multi-phase AC power. The AC power is then converted to DC. The DC power is then converted back to AC by the inverter. A microprocessor controls the entire process, as well as the speed of the engine. I don't think at any point in this chain is there a 12 VDC injection point.

Re: Power My Air Con unit.... Inverter Generator vs Inverter ?

oops! said:

10 -13 amps on compressor start up....i think run is 6 depending on the size of the fan.

Click to expand...

I think OOPS might be a bit low on this, depending on unit manufacturer. I just checked the MarineAir and Webasto sites prior to posting, and they both indicated a start-up of 18-20 amps and a running draw of anywhere from 8-10 amps. This is based on 2.9KW of provided power...and that is for the 12K BTU. If you step up to the 15K BTU, your 3KW genny won't be sufficient. If you plan on running off of a separate generator, I would look into a 4 KW minimum (for the 12K) as the 3 KW would be at near max power output non-stop.

Webasto now makes a 110v/12v Reverse cycle heat/AC, but I have to assume that if you're too cheap to buy a marine generator, you would also be too cheap to buy a marine AC.

You can run your current AC off of an external generator, just make sure your power supply is isolated and secured. You'll also have to design a power input for the panel which controls the AC.

Re: Power My Air Con unit.... Inverter Generator vs Inverter ?

Fireman; based on 2.9kw...?? not sure what this means... 2900w/110v = 26 amp supply?

So with a 'ramp up' of 20 amps... 20a*110v = 2200w means a 3000w inverters 'surge' rating would cover this, then...
Running at 10a * 110v = 1100w

Same calculations for the inverter-genny, meaning i should be ok with a 3kw?
(i'll find out the exact BTU!)

i may have my ohms law mixed up, its been a while.

tx1961: yeah i know, i'm in the realms of wishful thinking; that i can find a unit to serve both purposes... but the technology would be pretty basic, would just need the engineers to add a few more connections and a couple of extra micro chips! the wiring diagram doesn't look too complicated, take a look... . http://hdgear.tv/images/catalog/product/docs/Honda_EU2000i_manual.pdf (page 55)

But you're right i'd void the guarantee and probably break it within minutes!

The real issue is a generator would only work when i'm stopped, and an inverter would only be good when cruising...
i'm guessing 2 x V8 running at cruising speed would easily produce the amps needed and not drain the 2 main batteries, as long as i kill the inverter/AC as soon as i stop/reduce rpm to idle??

Thanks for the input!

Re: Power My Air Con unit.... Inverter Generator vs Inverter ?

Just a word of advice, inverter generators are HORRIBLE at running electric motors. Inverters are nice for things that don't like voltage drops, whereas a conventional generator's voltage can be all over the place. That becomes important for an electric motor startup. A conventional generator might sag to 80 volts for a brief moment during startup, the electric motor doesn't car. An inverter generator will just cut the circuit.

(just got back from a weekend of camping. My 3000 watt inverter generator wasn't even close to powering the roof AC unit, but the 3500 watt standard model had no problem running both the fridge and the roof AC. The inverter would kick out instantly, whereas the standard one would sag way down, puff out a little black smoke and then throttle up while the roof AC was spinning up.)

As far as trying to use the inverter portion of an inverter generator without running it, don't do it... You will cook the inverter in minutes. The inverter engine also produces cooling air for the inverter. You could rig up some type of fan system, but it might be a challenge to make it effective enough.