Generator size

[seacolt]

I am in the market for a new generator for my 1976 46 c. I am struggling with the correct size to get. From what I understand I need to find the total amps and there is a formular ?. I have been able to get some of the amps but this is where I need help. I have two 1600 btu a/c's which I believe are 15 amps each ?. my fridge is 7 amps. my hot water heater is a sears kenmore and the only thing i can get off of it is 1650 watts I believe it is either 5 or 6 gallon heater, not sure of the amps. The other is my stove, three burner with oven princess model 1200. The only other stuff I have is light bulbs, 6 25 watt bulbs, and 8 florescent type not sure of watts. A 15 kw onan was in there. I am hoping to downsize some. reduce weight, fuel consumption and noise. I dont want to get one that is to small and regret it later. I was thinking a 12 kw but a friend told me a may be able to get down to a 8 or 10 kw... thanks for any input

 

[hattitude]

I have a 1980 46C also with a 15KW generator. I believe my salon AC uses 1500 watts and the stateroom AC (two air handlers) measures 2000 watts. I doubt that power panel is ever over the 3.5KW use. The other panel can get to 4000-4500 watts depending on how many galley fixtures I'm using... and the water heater kicks on. That would be a total of 7.5- 8.0 KW used at peak.

I would think that a 12KW is no sweat, a 10KW is definately doable with an eye on the power panel. I think an 8KW or 7.5KW is doable (kick off the water heater when cooking and that's an extra 1200 watts), but will need a hawk eye on the power usage.....

I've heard about having enough reserve power for motor start-up loads, but someone with more electrical knowledge than I have would better comment on that..

Bernie

 

[jim rosenthal]

Look on the Northern Lights and Westerbeke web sites. They should have formulas there to figure out what you need. Also, we had a thread on this not long ago for a forum member who posted a similar inquiry. You probably need a 10-12kW, no more than that. Forum members have posted good reviews on gensets made by Kohler, Northern Lights, and Westerbeke. Also Next Generation and Phasor have gotten favorable comments. The fit into your boat and service access are two of the most important points, because you won't service anything you can't get to. Also, a sound enclosure is important- make sure with any genset you buy that the hush hood can fit into your engine room.
PM me for comments about what I would avoid, fwiw.

 

[seacolt]

Yes I have heard good things about the northern lights. I'm pretty sure thats what i'm going with and the sound shield is a must due to the location. I am hoping the 10 kw will work... thanks

 

[StratPlan61]

I had a NL 12kw installed over the winter to replace one of my 20kw Kohler generators. Of course it is smaller, but it is super quiet and the sound shield comes off in panels allowing super maintenance access. I compared several, most seemed to be very good products. I alos liked the white paint - easy to track leaks, etc. Don't forget to consider whom your local dealer will be, availability of parts, etc. Remember, your warranty is only as good as your local dealer.

Bear'
1984 61' MY Strategic Plan

 

[dwaynec]

A previous owner of our boat replaced the 15kw Onan with a 9kw Onan. It works out ok for running the entire boat until the Admiral decides that she is going to cook. Since her style of cooking is to use at least two burners and the oven, the 9kw can't handle the load and the breaker on the genset trips. This causes two immediate problems. First the Admiral can't cook, and second I have to get into a nice warm engine compartment and reset the breaker.

Another problem I have with the 9kw Onan is that it is a 3600 rpm generator. Even with a sound shield, the thing is noisy. I am not sure if it is incorrectly mounted on the engine room floor or what, but the harmonics through the floor are nasty.

 

[Pascal]

if you have a twin 50amp system, your panel limits you to 12kw anyway...

i have a norpro 18, installed by the prev. owner and it's an overkill for the above reason. btw, its a great generator... reasonably priced, realiable, quiet, good sound box. i like the fact that it's self bleeding after changing filters (jsut turn the key to run the pump for a few minutes)

figure about 1800w for each ACs, that's 3600 plus the water heater 5000, your lights and misc... 6000, another 2000 if cooking, battery charger (you forgot that one)... you shoudl be around 10kw if cooking, running AC and charging batteries at night.

I woudl go with a 12kw...

 

[Brian Degulis]

What you need to know is not amps but watts or thousands of watts (KW) Amps x Volts = watts Also be sure to factor in start up loads like your AC units they can draw quite a bit more than name plate rating when the compressor is starting.

Brian

 

[Jaxfishgyd]

We have a 9kw Kohler in our 43'. Can run everything "within reason", wife and granddaughters all trying to use blow dryers at the same time while using the microwave and grandson taking a hot shower can cause a circuit failure !!!
But it's no different than when we are on shore power.
ONLY time I ever had the genset main circuit breaker trip is when both A/C units were turned on at the same time main circuit panal control was moved to the Genset setting.

 

[Paul45c]

I am in the market for a new generator for my 1976 46 c. I am struggling with the correct size to get. From what I understand I need to find the total amps and there is a formular ?. I have been able to get some of the amps but this is where I need help. I have two 1600 btu a/c's which I believe are 15 amps each ?. my fridge is 7 amps. my hot water heater is a sears kenmore and the only thing i can get off of it is 1650 watts I believe it is either 5 or 6 gallon heater, not sure of the amps. The other is my stove, three burner with oven princess model 1200. The only other stuff I have is light bulbs, 6 25 watt bulbs, and 8 florescent type not sure of watts. A 15 kw onan was in there. I am hoping to downsize some. reduce weight, fuel consumption and noise. I dont want to get one that is to small and regret it later. I was thinking a 12 kw but a friend told me a may be able to get down to a 8 or 10 kw... thanks for any input

FYI, I've got a 1984 45c Ser II that has an 8kw Onan MDK. Everything appears to fit within the load limits of that 8kw when we're running. At the dock after a day of travelling, it wouldn't be enough. Both a/c's are running, partly because the engine room is heating up the boat some. Wifey is cooking. And somebody is taking a shower and that h/w heater is running at a good load. Then the main breaker on the power panel will trip, and that's the 240v/50a shore power main service breaker I'm talking about, not just the 30a you get from the genny.

But, then again, we usual travel pretty heavy with lots of people and we run in S Florida where that a/c load is always going to be with you. Depends on your usage.

If you're anywhere around an area with an ever-present hurricane threat like I am, I would think it would be a good idea to try to max out your generator capacity as much as possible. Having the boat in the backyard proved VERY handy when this area was out of power for ten days after Hurricane Wilma last year. Having it on the boat means I don't have to go through the pain of maintaining a separate genny for the house, and the boat needs one anyway. You can backfeed a genny's output to light up select circuits in the house if you want, or you do like we did and just go out to the boat for any of the creature comforts that need power.

 

[DickB]

Five or six years back, we downsized from a 15kw Onan to a 12.5 Yanmar. Still overkill. I rarely see the watt meter exceed 5,000. But in the NW, we rarely run the A/C. I think 8kw would be tight for you, but 10 would do the trick.

Dick

 

[captainwjm]

I've got an 8KW Westerbeke on my 46 Jefferson [original on the boat - '87 model]. It provides plenty of power for my 2 Cruisairs, 3 burner electric stove, house type refridgerator, etc. It also has a self priming function. I don't have a sound shield, and it is a bit noisy in the main saloon [we just have to turn the volumne up on the TV a bit]. A newer model with a sound shield shouldn't have this problem.

 

[Will]

Last January, I installed a 7.8 BTD Westerbeke (7.8 KW) with Sound Shield in my 1980 43’ DCFB. This is similar to the original 7.6 Onan in capacity which exceeds the shore power installation of dual 30 amp circuits (one for house, the other for AC). I chose this model primarily because in addition to the output requirements, installation needs presented limited options as far as physical size was concerned. Electrical loads include, a 1600 Watt Water heater, dual CruiseAir AC units, a Princess 3 burner stove with oven, refrigerator, a microwave, electric coffee maker, toaster, TV, DVD & VCR players, house lights and an automatic Freedom 30 Inverter/Charger. I know that it is possible to create an overload but it is unlikely to happen in normal service as long as reasonable awareness of electrical loads is maintained. It has never been an inconvenience. Sound levels are extremely low; about the level of an engine room blower inside the boat and with just the swishing sound of the exhaust water on the outside of the boat.
The problem with generators is that they hold up better if run under fairly heavy loads. It makes little sense to size a generator to meet maximum possible load requirements if normal service almost never requires such performance. For us, the above generator works out best since with AC running, our normal loads run between 3KW and 6KW.
We are extremely happy with the generator and its performance.
Will

 

[seacolt]

Pascal, what do you mean twin 50amp system. I have a seperate pannel for my A/C ? . Does that mean I have to go with a 12 kw ? thanks

 

[luckydave215]

I've been thinking my 20kw Onan's are overkill, but maybe not. It hasn't been warm enough to run the air conditioners (4) yet, so I really haven't checked. If I have all 5 fridges, the stove, air conditioning, bait tank, lighting loads, water heater, water maker, battery chargers, and bridge loads running at the same time, 20 kw might be a bit thin.
However, most of the time, I'm using <10 amps at 220v, so a small unit to replace one of the 20kw gens sounds tempting. I guess I'll wait until low load running kills one of the Onan's Cummins first................

 

[Norm Mayer]

I agree with Will. I have a 44' Tricabin with all the usual loads, and a 10kw Westerbeke that has never had a problem delivering all the power needed, even with water heater, oven, stove, crock pots, 2 16kbtu ACs, and all the rest, running at the same time. I even added a 30 amp outlet on the side of my boat so I can run my buddies boat with one air and the other usual stuff.
If I ever had to replace my genny it would be no more than a 8kbtu unit. FWIW

 

[Genesis]

I put an 8kw in my 45C and it was all I needed. While it was POSSIBLE to trip it the only way I ever did so was to attempt to use the STOVE while both ACs were on along with significant other loads (e.g. water heater, etc)

Even then - no guarantees it would trip - it all depended on what was cycled on at what time. But yes, it was possible.

Nonetheless I used the stove (btw the OVEN alone would NOT trip it even with both AC units up) rarely enough that I saw this as not a material issue.

Five years of ownership and I can count on the fingers of one hand and have a couple left over the number of times I managed to open the genset breaker.

Don't get crazy about generator size. Besides the cost and size diesels really don't like to run for extended periods of time at very low loads - they tend to glaze cylinder walls and/or the rings don't seat right, and then you start having problems.

The only two issues I had with the Kohler was a bad injector and the big cable connector at the rear of the electrical box got loose a couple of times. The latter would allow the genset to start but it would immediately shut down due to lack of proper excitation voltage (protective circuit trip.) Not a big deal. The injector was simple to change (had a needle stick open) but getting the part took two weeks in the middle of the summer, which got me pretty angry as the unit was unusable until it came in.....

 

[jim rosenthal]

I think the ideal setup for a big boat would be one small set and one large one. (although this is not what you asked) For boats the size that most of us have, there used to be things called cruising alternators- 3-5kw alternators driven off one of the main engines that would run the stuff you wanted to keep going, but you didn't need the genset for. For example, keeping the fridge cold, etc...that kind of thing.
It's true that gensets don't take kindly to being run at light loads. This is probably the result of the fact that they have to run at a constant rpm- the load up with unburned fuel or partly burned fuel at light loads. A cruising alternator would be perfect, but I have yet to see one marketed by a company that stuck around for any length of time. If anyone knows of one, I would like to be made aware of it.

 

[Genesis]

I think the solution that these days is a fairly decent-sized inverter and a big 12V or 24V alternator. Balmer makes some big ones and you could put one on each engine for 300-400A of total output and from that draw 3kw of 120V via an inverter with the battery bank serving as a buffer.

I suspect that would be quite workable if you wanted to do such a thing. The big bug-a-boo is air conditioning - down here in Florida its a must for most of the year.

 

[seacolt]

I agree, Inverter works great for the small stuff. Last year I had a 1500 watt mastervolt inverter installed. I was 1st looking at a larger inverter but the electroics guy I used talked me into a 1500 watt. His idear is that 3000 watt would need a big battery to keep up with demands and I would need the genny for the major stuff. I'm not sure I like the way he set mine up. It runs of my starboard starting bank (the 8d's). I think I should get a seperate battery for the inverter. However I am ok with the 1500 size, it runs my frigde and other small stuff. Even up here in New England we like to run our A/C, It gets quite muggy here in the summer months, I also like the fact that it keeps the humidity out of the cabin, and the reverse cycle warm air works well when it gets chilly. I'm leaning to the 10 kw northern lights.