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starcruiser · 02-06-2016, 05:46

I'd like to have a small 5000 btu domestic window air conditioner on the boat.

My 2000 watt Kipor generator would easily, run it but it may not supply enough power for the startup surge.

However, my inverter can supply it...but would drain the batteries running it.

So, is it possible to start the air con off the inverter and a few seconds later flip the manual selector switch to the generator- which of course would already be running?

I see two possible concerns.

In the instant the switch is flipped from inverter to generator, the air con compressor may lose momentum and stall? Dunno.

The inverter and generator cycles will be out of sync and have a residual affect and clash during that split second changeover period. Dunno.

I don't want to buy smart changeover switches which will cost more than the air conditioner. Nor do I want add-on hard starter kits that would void the air con warranty.

Inverter split system air cons are easy to start and run but take more space, are costlier and must be installed by a licenced person.

Moontide · 02-06-2016, 07:32

How big is your battery charger? Enough just to keep running off inverter and use generator solely to charge at same time?

**newhaul** · 02-06-2016, 07:40

Most 5k ac units use about 550 watts to run so figure about 1200 watts to start. Your 2k watt Genny should have absolutely no issue with the start and running of your ac unit. As far as starting on inverter and switching No it most likely won't work . The electronics controlling the unit will see the switch off time as a power interruption thereby shutting the unit off.

**a64pilot** · 02-06-2016, 07:44

A Honda 2K will do it easily, it will run my 12,000 BTU on my 5th wheel and my 5,000 Webasto in my Sailboat, the Sailboat 5K it will start and run in Eco mode. I could even charge batteries and run the little AC
The 5th wheel worked it pretty hard.

It helps if you turn the fan on for a few seconds and let the fan spool up, then turn the AC on.

Boatguy30 · 02-06-2016, 07:50

Might need to ad a start capacitor as cheap window units probably have a cheap small capacitor. A marine air 6700 hatch mount will not start on a Honda 2000 without an ad on boost capacitor.

transmitterdan · 02-06-2016, 15:18

Quote:

Originally Posted by starcruiser

I'd like to have a small 5000 btu domestic window air conditioner on the boat.

My 2000 watt Kipor generator would easily, run it but it may not supply enough power for the startup surge.

However, my inverter can supply it...but would drain the batteries running it.

So, is it possible to start the air con off the inverter and a few seconds later flip the manual selector switch to the generator- which of course would already be running?

I see two possible concerns.

In the instant the switch is flipped from inverter to generator, the air con compressor may lose momentum and stall? Dunno.

The inverter and generator cycles will be out of sync and have a residual affect and clash during that split second changeover period. Dunno.

I don't want to buy smart changeover switches which will cost more than the air conditioner. Nor do I want add-on hard starter kits that would void the air con warranty.

Inverter split system air cons are easy to start and run but take more space, are costlier and must be installed by a licenced person.

No, this idea will not work. The generator and inverter will not be in sync with one another which will most likely stall the compressor. That is if you can switch fast enough which you probably can't.

One solution to this problem is to use a charger/inverter that is designed to run in sync with your generator. Mastervolt and Victron make inverters that can do this. They call it Power Assist. Then you can start bigger loads with the inverter handling the startup surge and leaving the generator to handle the running condition.

**tkeithlu** · 02-06-2016, 16:00

We've had the same problem with an inverter being able to run but not start an apartment sized refrigerator. We'd still have 12.8 volts in the house bank, but the inverter would be screaming at us at 3:00 AM. The answer was a 2 farad capacitor - they make them for autombile audio systems - you know, the annoying BOOM BOOM BOOM at the traffic light. They're cheap, as long as you don't mind the teenager graphics on the can. We mounted it across the DC intet to the inverter, since it was pulling down voltage on the surge start-ups, and it has worked fine. If I could get to the back of the refrigerator, I'd probably mount a "soft start" capacitor.

sailjumanji · 02-06-2016, 16:54

Quote:

Originally Posted by Boatguy30

Might need to ad a start capacitor as cheap window units probably have a cheap small capacitor. A marine air 6700 hatch mount will not start on a Honda 2000 without an ad on boost capacitor.

My 8k BTU and March pump will run with my Honda 2000. Start the Honda with OFF the eco mode, start the AC, and then switch the Honda to eco mode. Once ac running, the Honda on eco more is OK. When the compressor and pump kick on the eco mode can handle the changes in load.

Quote:

Originally Posted by transmitterdan

No, this idea will not work. The generator and inverter will not be in sync with one another which will most likely stall the compressor. That is if you can switch fast enough which you probably can't.

One solution to this problem is to use a charger/inverter that is designed to run in sync with your generator. Mastervolt and Victron make inverters that can do this. They call it Power Assist. Then you can start bigger loads with the inverter handling the startup surge and leaving the generator to handle the running condition.

starcruiser · 02-06-2016, 16:57

Thanks for the replies, which tend to confirm my negative suspicions about the idea.

I am prepared to spend about $500 on the new air conditioner---yes, they are much more pricey and small ones are hard to get here in Australia--but I don't want to go into the expense of changeover switches, more electronics and warranty-voiding modifications.

One manufacturer's technical department told be start-up current was 6-8 times rate current.

My inverter is 1500 amps, 3500 peak --BUT non-pure sinewave, so while I'd be happy to start --if it indeed does--a new air con off that, I'd be reluctant to keep it running.

Stu Jackson · 02-06-2016, 18:02

The reason you can't do it with the switch is that you can't have two AC sources working at the same time.

Ya think the capacitor will go boom boom? Don't try it.

Good luck, lots of good advice here.

SteveInMD · 02-06-2016, 18:13

With a good start capacitor your genset should handle the startup just fine.

smac999 · 02-06-2016, 21:36

if you had a pass through inverter it would switch automatically for you.

blackswan555 · 03-06-2016, 06:59

The "number" to be looking at/for on the compressor is LRA, Locked Rotor Amps, The amount of current it takes to start, It is on most motor rating plates or you should find it on net with motor serial number etc, Add the fan loads & you should get an idea of how close you should be,

Changeover switch, You could do as you suggested, either with manual switch or relay/contactor, The AC will not mind as long as it is quick, However running motors with non true sine wave inverters does shorten the life of some,,,,, Drastically from what I read,

New true sine wave inverter with gen assist would be probably you best

Tim