Generator sizing

[wildcard]

Yanmar also makes small diesel gensets....

[sailingdog]

The other problem is that generators are sized for resistive loads. Inductive loads, like that of large motors in the A/C unit, should be sized at twice their nominal wattage as a general rule of thumb. While a 2000-W generator is fine probably for 20-100W incandescent bulbs, it would have a lot of trouble working with a 1000W microwave oven for that reason, even though it says it seems to be rated for it—it isn't.

[sailaway21]

The only practical way I can see to operate the a/c using a smaller gen-set is through the use of a very large inverter, relying on the reserve capacity of the battery bank for "rock over" amperage.

That being said, has anyone considered changing the motor on the a/c unit to a 3-phase, say 204 volt, unit? There is technology out there, I'd start with Franklin Motor, to "trick" single phase 220 into acting like three phase. Mind you, the unit that Franklin makes to do this for submersible well pumps runs about a grand.

Grundfos, another pump manufacturer, has their own motor (everyone else uses Franklin) and it has a "soft-start" feature. It runs on 220 volts and the frequency is varied to slow and speed the motor.

Both of these are radical departures from capacitive start motors and quite specialized for the constraints of well casing installation. I would imagine the technology is available in some form for surface use.

While on the topic, why not switch the a/c motor to 220 volts, and power it direct off the gen-set? Amps, which are what count, would be halved as would starting amps. Most motors come pre-wired for either 110 or 220 volts and it would be rather simple to make an external voltage input switch on the unit. 220 at sea. 110 alongside. Of course you could just leave the motor wired for 220 and parallel the gen-set with shore power once alongside. The port authorities might want a "blast radius" diagram on file before your attempting this.

[ebs001]

Sailaway, we have been talking in amps but what really matters is watts. A EU2000 is good for approximately 1800 watts. Since power in watts equals amps times volts, halving one while doubling the other will not change the power. Bottom line, the A/C still won't start

[sailaway21]

Yes, I know that. But here's the rub. While the same motor will consume the same power, whether wired for 220 versus 110, it will turn over much more easily on 220 versus 110. Using the water flow illustration of electricity, we are much more efficient if we increase the diameter of the pipe, reducing the rate of flow, rather than forcing water through the smaller pipe at a higher rate. Amps effect our motor in a far more deliterious way than voltage. One of our resident ship's electricians will have to offer further explanation beyond that.

[Brezzin]

Ok, I think it safe to say I'm an electrical novice. Here's my problem, On my boat I have a 50 amp connector. I want to get a eu1000 or eu2000 generator simply to charge my batteries when on the hook or on the hard. The AC side of the generator only has ports for a 15amp home style plug. I've seen conversion pigtails for a 30amp plug but not 50. any thoughts on this?

[PBzeer]

Make your own pigtail, or have an electrician make one, probably cheaper than a Marinco.

[CharlieCobra]

Panda makes a 3.4KW diesel genset that I've seen in the Laz of a couple of Catalinas.