Gen Set Min. Size ?

[Tony B]

The Admiral will be*looking a trawler this morning. The GenSet is 3KW. Is that enough to power a 16K AC and a fridge?

*I dont have the AC specs or the fridge specs so I was just wondering in round figures if the 3KW was enough to keep the AC and fridge going. 3KW sounds kinda small.

*

 

[Tom.B]

It'll do. It's a bit small (mine is 3.5k) and it does fine. Not great, but adequate for my 35' trawler.

 

[hogrider46]

I have an old 16k AC that likes lots of power and my fridge is one of the apartment style 3 cu ft. units. My 3kw does fine. It will power the AC, Fridge, TV, and microwave at the same time (just barely). If i want to use the hot water tank i need to not use the microwave at the same time.

A 3kw gen output is about 26 amps. My system is 30 amps so some thinking is required not to pull over the max of the gen or shorepower as all electrical on the boat will surely pull over 30 amps

 

[Tony B]

Thanks guys, that is all I needed to know.

 

[sunchaser]

But what about the loads*from a microwave, coffee maker, TV, inverter charger, hair dryer etc? I'd say 3 is*too small unless you are very spartan with your plug ins.

 

[Woodsong]

I have a ridiculously large 8KW northern lights on our Monk that the previous owner installed. I wish it was smaller....literally- too big for our engine room and always in the way! Good thing is I can power up every system with never pondering power usage! If I could I'd go for a 5 or 6 KW. Best thing to do when looking at boats if you are worried about whether it will carry the load is ask the seller or broker and if you get serious about that particular boat, ask them to fire up the generator and switch the 110 system over to generator and see how it acts with everything powered up.

 

[Tony B]

sunchaser wrote:
But what about the loads*from a microwave, coffee maker, TV, inverter charger, hair dryer etc? I'd say 3 is*too small unless you are very spartan with your plug ins.

*I intend to move as much stuff over to 12V as possible. Also will add a propane stove/oven if it*doesn't come with one.*This wont appen right a way, but it is in the plan. When we start cruising I want to be as self sufficient as possible. Use gen to run AC/only. Now, just because this is in the plan, does not necessarily mean it will happen quite as planned, but that is the general idea.


-- Edited by Tony B on Thursday 21st of July 2011 10:21:58 AM

 

[Tom.B]

Then 3k is plenty.

 

[Marin]

Tony B wrote:
The Admiral will be*looking a trawler this morning. The GenSet is 3KW. Is that enough to power a 16K AC and a fridge?

*

*A good friend is the recently-retired head of engineering for Northern Lights/Lugger, aka Alaska Diesel Electric after a 30-plus year career with them.* When we bought our boat we talked with him about someday replacing the Onan 7.5 kw generator that was on the boat with a new Northern Lights, something we haven't yet had to do as the Onan continues to perform as advertised.* In response to "how much power should a new generator have" he said to add up all the AC power in terms of watts that could be required on our boat at any one time and get a generator sized to supply that.*

In our case, that would be the hot water heater, the battery smart charger, the big AC salt water washdown pump, the refrigerator (if we chose to run it on AC), the microwave, and a pad for things like tools (heat gun, drill, etc.).

 

[Per]

we have the 3.5KW genset (currently out of commission), but this was plenty for us and only needed to run it a few hours daily.
we are all AC: fridge, waterheater, stove/oven, icemaker.
but no watermaker or a/c...

how many watts is a waterheater?
seems to be the biggest energy user onboard our boat.

 

[Marin]

DavidM wrote:
Marin:

It is not necessary to run all of that stuff simultaneously.

*No it's not,*but since it's not 100 percent out of the realm of possibility the notion is to get a generator that will do everything*we could conceivably ever want it to do.* Including powering stuff*we might end up putting on the boat later.* Now if I wanted go into it knowing that*we will never be able to run all the boat's AC loads simulataneously, that's fine, and a smaller generator would suffice.

But*we don't choose to operate that way.**I want a piece of equipment that is capable of powering or generating electricity or digging a ditch at the absolute maximum capacity I might ever want it to run even if the chance of my demanding that kind of performance are almost nil.* Because I learned a long, long time ago, and sometimes the hard way, to never say never

And we have found ourselves at anchor running the hot water heater, the battery charger, a Makita heat gun on a high setting, an electric sander,*the microwave, and powering a rafted boat's battery charger*all at the same time.* That power demand was a one-time deal as I recall, but when we needed the power, we had it.


-- Edited by Marin on Thursday 21st of July 2011 06:40:27 PM

 

[FlyWright]

Per wrote:

how many watts is a waterheater?
seems to be the biggest energy user onboard our boat.

*Mine is 1500 W.

http://www.defender.com/product.jsp?path=-1|51|10172|319679&id=10205

 

[FF]

"he said to add up all the AC power in terms of watts that could be required on our boat at any one time and get a generator sized to supply that."

Just the answer one would expect from a sales man.

MY way would be to create an AC system , not just plop in a huge unit.

Fuel consumption and service life depends on how well loaded the noisemaker is , the bigger the normal load the better.

The biggest question in sizing is how many air cond units are required to operate at once.

On small boats its usually only two , so a 3 or 4 KW unit will be fine.

Assuming a good following inverter that can supply the start boost for a second as the units cycle on.

Any loads over 4KW could be short term , like a microwave or house fridge, so the inverter would handle them,
or long term like a scuba compressor or HW heater , and those would be handled with automatic Load Shedding.

 

[cd30ketch]

So my 12kw gen set is over kill

 

[Marin]

cd30ketch wrote:
So my 12kw gen set is over kill

*If it's paid for, runs great, and powers what you need it to power, I don't believe it is

 

[Edelweiss]

Try getting*three teenage girls on board with their curling irons, blow dryers and each ironing their four sets of clothes for the day. . . Even my 7.5 kw gen set wasn't enough!!

 

[FF]

"So my 12kw gen set is over kill"

Depends ,

IF your boat has a total electric galley , range ,oven ,broiler and deep fat frier and an electric HW heater.

If there are missing , and you don't run 4 - 5 air cond , or a couple of scuba compressors, it very well could be over sized.

 

[jleonard]

Marin wrote:
And we have found ourselves at anchor running the hot water heater, the battery charger, a Makita heat gun on a high setting, an electric sander,*the microwave, and powering a rafted boat's battery charger*all at the same time.* That power demand was a one-time deal as I recall, but when we needed the power, we had it.

*

*I am glad I am not the only one who sands, runs power tools, and runs extension cords across a raft.

 

[bobofthenorth]

Oversized gensets tend to have shortened lives.* Consider that a 7500 watt noisemaker will supply roughly 2x the power that a 30 amp shore cord will and then govern yourself accordingly.* The notion that you should add up every possible load and then give yourself a fudge factor over that is silly IMHO but its not my boat.

 

[sunchaser]

Adequately*sized gensets DO NOT have a shortened life if run at 65 to75% load for a period of time and and then back to 30 to 40%. Ill maintained gensets DO HAVE a shortened life no matter what the load.

What determines adequate sized?*Marin stated it, All the potentially connected loads*including our plug in ricemaker, George Foreman grill, and*hairdryers.

 

[cd30ketch]

You do understand that oversived means it can out produce a smaller one? What your saying is that a generator that heavier constructed so that it can handle higher loads will go bad quicker by not producing its rated load thus running cooler etc. Please please someone explain this to stupid ole me.

 

[RickB]

cd30ketch wrote:You do understand that oversived means it can out produce a smaller one?

But what if the smaller one too big?

Is it still undersized or is the right size oversized?

 

[jleonard]

RickB wrote:
But what if the smaller one too big?

Is it still undersized or is the right size oversized?

Can you get around that if is *circumsized?

 

[cd30ketch]

Yikes

 

[FF]

When I installed an interior in our boat , at a mooring, I installed a 4KW OHNO.

It worked but with no cruising use for it , today I believe the battery powered tools would do as good a job.

They could be charged at home , or for the amount of actual drilling , cutting et all, the 85W solar could charge them easily.

This is because the tools are seldom (if ever ) used on a cont basis, drill a hole , cut some wood , sand for a better fit , min not hours of use.

The 1500W --$200 inverter could handle any tools that require more power than a 18V batt., like a few min of plainer time.


-- Edited by FF on Wednesday 3rd of August 2011 05:06:54 AM

 

[Per]

hmmm, me more confused now
lots of twisted tongue talk
i am guessing most trawlers smaller than 45 ft, really dont need more than 5kw gennys, even with a/c.
but if ya' gotta run a couple of large screen tv's while using the stow, the microwave, the hairdryer, the hot water heater, the coffeemaker, the fridge and the a/c comes on at the same time, ok at this point even the breakers at my house would fold..

 

[bobofthenorth]

Per wrote:
i am guessing most trawlers smaller than 45 ft, really dont need more than 5kw gennys, even with a/c.

You are guessing correctly, IMHO.* Less than that if they live comfortably on the dock on a 30 amp cord.