Portable Generator / AC

[sailorboy1]

Yeah, even my 3.5kw italian marvel POS generator could start and run my 16k unit even before it died when it could only be counted on supplying 2 kw

[WDR]

Originally Posted by a64pilot

LRA or locked rotor amps is the absolute max possible amps and is usually never reached, it’s also of extremely short duration so yes, a 30 amp shore power connection can handle it.
Some generators can handle surge much better than others, my little 3.5 generator has a 6 kw generator, so that it handles surge very well, what makes it a 3.5 generator is engine power, same generator on a bigger motor is a 5.5.
Then some generators are rated conservatively meaning they will actually make more, and some are rated on fantasy, they will never make rated power output.
I guess there hasn’t been any truth in advertising for along time now.
If your generator is actually a 3.5, then you won’t need a soft start, cause 3500W at 120V is 29 amps.

First and foremost; thanks for the air support. I am at a Navy marina and every time those jets fly over head it brings back the warm feelings I had when the Apache’s and A-10’s flew over our heads.

That was good info and I will update in a few days, hopefully, with my results using all the info provided here.

[transmitterdan]

The LRA at 62A will be a challenge for a 3.5kW generator head to handle. I predict the voltage drops so low that the air conditioner either will not start or it shuts down automatically due to low voltage. Either way it’s not likely to start.

There are two types of air conditioner add-ons in the market place. There is a thing called “soft-start” or some other trade name. These are all similar and utilize a capacitor, resistor and a relay to “help” the motor start. Supco is one brand.

Some of these are “smarter” than others. For these capacitor helper devices to work there is a specific optimal capacitor value that works for each motor. The “smart” ones have the ability to change the capacitor value using relays and a tiny control circuit. They “learn” the optimum capacitor value within 4-5 startups. I believe Dometic makes one of these so-called “smart” types.

There is also a more uncommon type that uses a variable voltage/frequency inverter to start motors. These are much more expensive but they work perfectly because they never draw high current from the generator.

[transmitterdan]

Originally Posted by transmitterdan

The LRA at 62A will be a challenge for a 3.5kW generator head to handle. I predict the voltage drops so low that the air conditioner either will not start or it shuts down automatically due to low voltage. Either way it’s not likely to start.

There are two types of air conditioner add-ons in the market place. There is a thing called “soft-start” or some other trade name. These are all similar and utilize a capacitor, resistor and a relay to “help” the motor start. Supco is one brand.

Some of these are “smarter” than others. For these capacitor helper devices to work there is a specific optimal capacitor value that works for each motor. The “smart” ones have the ability to change the capacitor value using relays and a tiny control circuit. They “learn” the optimum capacitor value within 4-5 startups. I believe Dometic makes one of these so-called “smart” types.

There is also a more uncommon type that uses a variable voltage/frequency inverter to start motors. These are much more expensive but they work perfectly because they never draw high current from the generator.

Another option is to use an inverter with a “power assist” or “generator boost” feature. Mastervolt and Victron are two popular brands of inverters that have the feature.

[mvweebles]

Gone with the Wynn's video comparing Easy Start relay with a Soft Start relay for marine AC. Momentary start-up with nothing: 55A. Soft Start: 52A. Easy Start 16A. About $300, and need one per A/C. Looks like the ticket.

https://www.youtube.com/watch?v=yjK1Gi_u6ss

[RickG]

We had a similar experience with the EasyStart. It works nicely.

Cheers, RickG

[WDR]

That update I promised.

I decided to forego the generator and all the problems that are associated. After reading this thread a few times, I just could not bring myself to bond the neutral to circumvent. Instead I chose to read a great deal more on marine electrical and as one might imagine, I am glad I did.

I have a 2200 amp battery bank and 600 watt solar panels already installed and working. I am going to just forget the air conditioner for now* and install a couple more solar panels and a wind generator and feed my 120 needs from a 2500 watt Inverter/Charger.

I won’t try and cut corners again in such critical systems. Not giving a rats a*# about my own safety is one thing. Knowing now that a McGuyver moment on my boat by me could kill all aboard (and others) either by electrocution or CO2, well now, that’s another.



* Yes I know it is easy for me to say I am no longer going to place such a priority on air conditioning, in December. Next July I am sure I will feel different.

[sailorboy1]

I think you are greatly over reacting to the neutral/ground thing, but hey it never brothers me what other people do on their boats.

If not for the air conditioning I don’t think I would even have a generator.

[CharlieJ]

Post #20:

Basically there should be one neutral-ground connection and it should at the "source", i.e. at the generator or at the panel. NEVER make the connection after a load.

This is not totally correct. The panel is not a source. The only sources on a boat are the secondary of an isolation transformer, the output from an inverter (or an inverter/charger when inverting) and the output from a genset. Any additional N>G bonds will cause AC leakage into the water column and trip a shore power pedestal residual current device (RCD).

[Sam8989]

I'm curious to hear the answer to this question. I've been researching this issue through highperformancehvac.com . For air conditioning on a cruising boat there are two major considerations - first, how often are you going to use it. And secondly, what does it cost.