Generator Output Question

[Offshore]

How many max amps does a 20KW generator put out for use ?
I realize I can only use 50Amps when plugged in dockside but how many Amps does the gen put out that I can use underway ?

 

[KnotYet]

At the full rated output, 20kW is 160 amps at 125V, 80 amps at 250V.

 

[Gdavid]

Approximately 80 amps for 240V loads, 160 amp for 120V loads or some combination there of using the following formula
20,000 W = 240V*Current1(amps@240) + 120V*Current2(amps@120).

In other words, quite a bit in terms of a boat but surprising little compared to household service.

 

[rgano]

At the full rated output, 20kW is 160 amps at 125V, 80 amps at 250V.

But you would not want to run it at that output for extended periods. I am sure there are wiser heads here than mine on this topic, but I like to run my little genny at about 50% load judging by the ammeter I have connected to it.

 

[KnotYet]

But you would not want to run it at that output for extended periods. I am sure there are wiser heads here than mine on this topic, but I like to run my little genny at about 50% load judging by the ammeter I have connected to it.

I would want the main breaker to permit full load but most boats under 60' or so
would be hard pressed to load their generator beyond half of that 20kW capacity.

Even my TIG welder only draws about 55 amps maximum at 240V.

 

[Don L]

I have to ask - why have a 20KW generator on boat that only has 50a shorepower service. Can the boats internal wiring etc even handle that 20KW.

 

[KnotYet]

I have to ask - why have a 20KW generator on boat that only has 50a shorepower service. Can the boats internal wiring etc even handle that 20KW.

Shore power will vary depending on where you dock, of course.
Slips for big boats may have more than 50 amp service and multiple connections.
I can see bigger boats with lots of LiPo batteries to charge using a healthy amount
of that 20kW to charge a low battery pack while running AC and laundry, etc.

 

[tiltrider1]

I have to ask - why have a 20KW generator on boat that only has 50a shorepower service. Can the boats internal wiring etc even handle that 20KW.

This is a real good question. Does the boat have a 50a 125v or does it have 50a 125/250v? 20kw would still be over kill for a 50a 125/250v set up that used on average 75% of the available power.

I have a 12kw gen on my 50a 125/250v set up. 12kw is 100 amps of 120, exactly what you get from shore. Since I have two 50a breakers I couldn't use more than 100 amps even if available.

a 20kw genset needs a draw of 80 amps at 125v just to be happy. My boat probably only averages 40 amps.

 

[Offshore]

I have 100 amp capability but only use one 50 amp cord at dockside as most of my things are dedicated to one side. I think the orig owner didn't want to lug out an extra 50 amp power cord all the time while traveling so I have to manage the power. Not a problem, just can't run everything at once.

 

[Don L]

Shore power will vary depending on where you dock, of course.
Slips for big boats may have more than 50 amp service and multiple connections.
I can see bigger boats with lots of LiPo batteries to charge using a healthy
amount of that 20kW to charge a low battery pack while running AC and laundry, etc.

I guess I can see that (I am a sailboat and have 2-30a plugs). But the OP says he knows he can only use 50a shore power. So guess just don't know what he has for different separate circuits that can be fed for that 20KW unit. A 20KW generator is a pretty $$$$$ so I would assume it had a reason to be installed.

BTW - everytime I see a post of yours the ex-submariner in me want to fire a couple of torpedoes

 

[O C Diver]

I have to ask - why have a 20KW generator on boat that only has 50a shorepower service. Can the boats internal wiring etc even handle that 20KW.

It's also become common for those size generators to have a hydraulic pump on the front for thrusters and sometimes stabilizers. It provides a constant flow / pressure rate when the main engine(s) are running near idle for docking, etc.

Ted

 

[twistedtree]

For a 55' to 60' boat, I think 20kw is actually pretty common. If you are at anchor and want to charge batteries, do laundry, make water, heat water, and run the oven it's pretty easy to load up a 20kw generator. In fact you can probably only do 2-3 of those things at the same time. HVAC loads alone can push the limits of a 50A 240V (12kw) shore connection.

 

[High Wire]

My 8Kw Phasor gen uses a 25 hp Kubota D1105 diesel engine. Fairly typical of marine gen-sets. My old Westerbeke 8 Kw had a 21 hp Mitsubishi diesel. . Go ahead and run them at 100% if you need to. The only real problem is noise , fuel usage, and over heating if the heat exchanger isn’t kept clean.

 

[MOJO]

The correct answer is whatever the breaker on the generator output is rated for. I'd be a little surprised if it was more than a 60 amp double pole breaker, but it should be marked.

 

[ronobrien]

I would want the main breaker to permit full load but most boats under 60' or so
would be hard pressed to load their generator beyond half of that 20kW capacity.

Even my TIG welder only draws about 55 amps maximum at 240V.

Matching the breaker to max generator output is OK as long as the protected conductors are rated for that amperage load.

 

[Choices]

You want to run the genset at as close to fully loaded as possible.

Typically the big hits are the AC and battery charger. On my boat everything else is now DC.

The inrush from the AC can bring a fully loaded genset to it's knees and might crash it. This is bad cause many boats don't have circuit protection fast enough to protect the generator windings. As voltage goes down current goes up, but breakers fast enough to protect the windings are very special, so special super fast acting and accurate fuses are used instead. Overtime these get replaced by regular fuses not good enough to protect the generator.

So when loading allow starting current for the AC. On mine, it pegs the meter on start up for a brief second, and the genset hesitates for a second.

The Charger will tapper off with time.

Cause of this when I run my AC now, I turn everything on to load the genset down and allow the AC to cycle.

Otherwise you have a diesel running 1800rpm with a slight load, not good for long term health.

 

[Circumnavigator]

We installed two 9kW Northern Lights in Fintry; very rarely needed to run both of them. When we installed the gyro stabilizer (7.5kW) we upgraded one to a 12kW.


We never heated water electrically while not on shore power -- always off a heat exchanger with heat from the genset. A 9kW genset burns very roughly a gallon an hour. That's close to 200,000 BTUs. A significant fraction of that is waste which you can use to heat water or the boat.



And note that the poster above who never runs his generator more than 50% load is shortening its life. Generator diesels, in quality units, are sized to run at full load continuously and don't like extended running at part load.


Jim

 

[Darlin]

Fundamental electrical formula: Ohms Law amps x volts = watts.

 

[MYTraveler]

For a 55' to 60' boat, I think 20kw is actually pretty common. If you are at anchor and want to charge batteries, do laundry, make water, heat water, and run the oven it's pretty easy to load up a 20kw generator. In fact you can probably only do 2-3 of those things at the same time. HVAC loads alone can push the limits of a 50A 240V (12kw) shore connection.

That is mostly my experience, though we have never been unable to run everything we wanted. In that regard, because our genset is always running when we don't have shore power, I don't think we use much power to heat water, as opposed to keeping it hot. Also, we don't have an electric stove (it is gas), though the oven, 4 ACs, ice maker (not cocktail ice, but 600 pounds per day for fishing) washer and dryer (and probably some stuff I am forgetting) all run on 240. I have never worried about overloading since, during my initial Cummins captains briefing (the mains are QSM11's and the gensets are both Onan (Cummins), I was told that the genset power ratings (and I don't remember if they were 18kw or 20) were continuous, unlike the mains.

 

[Offshore]

Gen amps

My 3 AC units ( 12-18-24 ) will pull 50 amps by themselves.

 

[Simi 60]

For a 55' to 60' boat, I think 20kw is actually pretty common. If you are at anchor and want to charge batteries, do laundry, make water, heat water, and run the oven it's pretty easy to load up a 20kw generator. In fact you can probably only do 2-3 of those things at the same time. HVAC loads alone can push the limits of a 50A 240V (12kw) shore connection.

Our 60fter only has a 7.5kva strapped to a 21 hp Kubota
Wouldn't know what to do with a bigger Genset
But we have 2500w of solar

Washing machine used on sunny days - no Genset required
240v watermaker used on sunny days - no Genset required

And the 240v hot water system remains on 24/7 - the old one was definately a pick your time to turn on.
We changed the 180 litre to 25 litre and it only takes 10 minutes vs over an hour
Have never ran out of hot water.