Generator size, making a change

[2savage]

My 12.5kw Westerbeke BTD is probably ruined due to the failure of the anti-syphon valve so I'm probably going to replace it.

The generator serves four main functions;

1) The main anchor windlass is 110 volt and needs plenty of power
2) My wife typically wants to run the A/C through the night as the master is often quite warm
3) The stove is electric and needs the generator
4) Topping up of house batteries when at anchor for days on end.

With these needs I am thinking a smaller generator that is run for longer may be better. I'm contemplating the 7.6kw BTD.

Input would be appreciated and if anyone knows if I can use the same engine mounts and soundproof box that would help too.

 

[DavidM]

What is your air conditioning capacity and what is its power draw. That will be your highest single (or multiple if you have them) load. Also are you comfortable with load sharing, ie not using the water heater, coffee maker or the microwave at the same time.

In general I think it is best to run a generator at a minimum of 50% and a maximum of 80% load. You usually can't do that if you size your generator to run all possible loads at once.

David

 

[cafesport]

Northern lights rates their Gennys at a .8 power factor. The 6 kw is equivalent to the one you are considering. I added a 6kw several years ago and the thing is a little beast. It can run our ac all night or 2 zones and a charger or 1 zone and the watermaker. NL recommends running no less than 25% load continuously so you’ll need to ad loads once your batteries get to absorption.

 

[mvweebles]

What is your air conditioning capacity and what is its power draw. That will be your highest single (or multiple if you have them) load.

Was thinking similarly. I see OP has a Seaton 50 so likely has 3+ A/C units. Suggest adding soft starts on all, especially if generator is downsized.

https://www.microair.net/collections/easystart-soft-starters

Peter

 

[2savage]

What is your air conditioning capacity and what is its power draw. That will be your highest single (or multiple if you have them) load. Also are you comfortable with load sharing, ie not using the water heater, coffee maker or the microwave at the same time.

In general I think it is best to run a generator at a minimum of 50% and a maximum of 80% load. You usually can't do that if you size your generator to run all possible loads at once.

David

Good questions. My inverter and twelve solar panels already provide additional power. I have four A//C units but rarely use more than two at a time.

 

[sunchaser]

Why not rebuild the 12.5.? Apparently it did fine until it sucked water.. With delivery delays for new ones rebuilds are a popular choice

 

[DavidM]

7-8 kW sounds about right in your situation. That would run all four A/Cs at the same time with little else. Two A/Cs would load it well and give you enough watts to run the hot water heater and microwave simultaneously or two similar loads.

David

 

[2savage]

Why not rebuild the 12.5.? Apparently it did fine until it sucked water.. With delivery delays for new ones rebuilds are a popular choice

There's a plethora of used generators available for around $4500. I wanted to go smaller anyway. And, the one being decommissioned should yield a few thousand in parts. The water pump for example is brand new and was $500.

 

[Jeff F]

Good questions. My inverter and twelve solar panels already provide additional power. I have four A//C units but rarely use more than two at a time.

What type of inverter do you have, and how big is your battery bank?

Modern inverters allow more flexibility in genset selection and can do a lot to manage the load.





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[2savage]

I have six trojan 6V in series. I think they are 435AH each. The inverter is Victron 3000.

 

[Jeff F]

This document might be of interest. I think 7-8 kW is adequate for your needs, and you could probably go smaller by using the powersharing features in the inverter/charger.

https://www.victronenergy.com/uploa...o-reduce-operating-cost-of-a-generator-EN.pdf



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[Alaskan Sea-Duction]

I just replaced my 8K Onan with a 9KW NL. Love it, but not cheap and regardless which brand you chose, you may have to wait several months to get it.

 

[Comodave]

I would definitely go smaller. Something like a 8 or 9kw. It is too difficult to load one as large as what you have now.

 

[twistedtree]

I have a bit of a contrary opinion, which is that you should stay with roughly the same size generator. I find it really nice to be able to charge batteries, heat water, make water, and do laundry all at the same time. With a 6-7kw gen I think you will be load managing a lot. By all means do the load analysis that DavidM suggested, but I think it's better to be a bit oversized rather than undersized.


The only exception to this is if you have all your electric loads running through inverters, and those inverters can do power assist to supplement generator output. That provides a nice peak load shedding capability, and I think can allow you to run with a smaller generator than the peaks would otherwise demand. But that probably requires a lot of changes to your electrical system, and possibly larger inverters.

 

[High Wire]

How many full load amps does your windlass draw? Starting amps are typically 6 times running amps for only a couple of seconds. If it’s really 120v, 15-18 amps max? Guess you wouldn’t be cooking or running the water heater while pulling anchor. The 7.6 will handle that.
The 7.6 will handle one or two A/C units all night while battery charging and water heater too.
100% load on the generator is 63 amps @ 120 vac. 50-80% of that should give you long life.
Our biggest load time is the first hour of generator time. After that the water is hot, the cabins cooled down and cycling, the battery chargers tapered off from max and I’m looking for load or else time to shut down.

 

[OldDan1943]

Your Seaton is no doubt a 50 amp boat, and perhaps a 12kw boat so think real hard before you down size your gen. I came up with the term "30 amp dance". You dont want to learn that dance. LOL

 

[rslifkin]

Your Seaton is no doubt a 50 amp boat, and perhaps a 12kw boat so think real hard before you down size your gen. I came up with the term "30 amp dance". You dont want to learn that dance. LOL

As another perspective on this, my boat takes 50A shore power, so I've got 12kw at 120v to play with when plugged in. We've got a 6.5kw generator and I don't find it undersized. It won't run everything on the boat, but it doesn't need to. I'd be fine with up to about an 8k, but anything bigger would be too hard to load adequately. As is, the 6.5 can run all 3 A/Cs and still have headroom for the water heater and some battery charging. Or I can swap the A/Cs for all 3 stove burners while cooking. Realistically, I don't run A/C on generator power often. It's mostly used for heating water and cooking with some occasional battery charging.

 

[OldDan1943]

Ideally you want to run 3 burners, the oven and the water heater and 3 A/Cs while on the gen. An alternative would be, pipe the water heater exchanger to the main engine, turn off the breaker. This gives your the alternative of having the main engine heat the water when you are away from the dock. Now you have a few KW saved for other things.
If it were with me, I'd still go with a 12kw gen and never look back.

 

[Alaskan Sea-Duction]

I have a bit of a contrary opinion, which is that you should stay with roughly the same size generator. I find it really nice to be able to charge batteries, heat water, make water, and do laundry all at the same time. With a 6-7kw gen I think you will be load managing a lot. By all means do the load analysis that DavidM suggested, but I think it's better to be a bit oversized rather than undersized.


The only exception to this is if you have all your electric loads running through inverters, and those inverters can do power assist to supplement generator output. That provides a nice peak load shedding capability, and I think can allow you to run with a smaller generator than the peaks would otherwise demand. But that probably requires a lot of changes to your electrical system, and possibly larger inverters.

100% what he said.....

 

[sunchaser]

There's a plethora of used generators available for around $4500. I wanted to go smaller anyway. And, the one being decommissioned should yield a few thousand in parts. The water pump for example is brand new and was $500.

We have a 12.5 kWh unit and use most of its capacity frequently. It is nice to be able to charge, cook, use washer dryer, heat, cool etc without too much, but some, load monitoring. Again I suggest, get the 12.5 assessed for rebuild needs then you'll have some decision metrics.

Used gensets, be careful. They're used for a reason and quite possibly need a tear down sooner rather than later.

 

[mvweebles]

Used gensets, be careful. They're used for a reason and quite possibly need a tear down sooner rather than later.

I thought about a used generator in the 6kw range. I found a few smaller Fisher Pandas and some ofher scattered brands, but got nothing but chuckles if I asked 'anything like a used Northern Lights?" I decided that finding one was hard enough, but the install would be equally difficult. I just didn't want to search for a unicorn, then risk premature rebuild or finnecky operation. I decided new made sense for me (NL 6kw)

Peter

 

[OldDan1943]

Rumor has it, if you buy a Fisher-Panda, buy 2. Does that give you a hint?

 

[hmason]

We have 2 Northern Lights generators; a 12kw and a 20kw. I recently had them both serviced by an authorized NL technician. I asked him about under loading issues. He said it will not hurt them and that it’s a myth that it will. I’m just the messenger here.

 

[Circumnavigator]

Fintry (see photo) had two 9kW NLs until we added the gyro, which takes 7kW, so we changed out one of the 9s for a 12. We never ran more than one genset at a time. The A/C is a 50,000 BTU chiller, electric stove, and oil fired heat. The one big factor is hot water. In our initial setup, in the morning with the inverter running the boat overnight, the battery charger, the electric hot water heater, and the cook all wanted power totaling more than 9kW. We solved that with a water heater that runs electric, but also has a heat exchanger for hot water from the running generator, so we never used electricity to heat water while cruising.


Morning Light has an 8kW NL, to run 4 A/C units. The stove is propane. I haven't yet run generator water to the heat exchanger in the electric water heater, but will -- but the 8kW is plenty.


So I would say that without a gyro, 8-9kW ought to be plenty for boats up to say 90 feet or so.



Jim

 

[Flatswing]

My 12.5kw Westerbeke BTD is probably ruined due to the failure of the anti-syphon valve so I'm probably going to replace it.

The generator serves four main functions;

1) The main anchor windlass is 110 volt and needs plenty of power
2) My wife typically wants to run the A/C through the night as the master is often quite warm
3) The stove is electric and needs the generator
4) Topping up of house batteries when at anchor for days on end.

With these needs I am thinking a smaller generator that is run for longer may be better. I'm contemplating the 7.6kw BTD.

Input would be appreciated and if anyone knows if I can use the same engine mounts and soundproof box that would help too.

I have the same generator-also on the way out per serial oil analyses & declining compression (though in my case, the needed Anti syphon was never installed). Every dealer and trusted mechanic I have spoken too indicates that the labor costs to remove, rebuild and re-install will likely approach the cost of new replacement. So, if you are having a pro do the repair, it's not cost effective (sadly, I don't have the skills or equipment for such a project).

I too was contemplating a smaller replacement, but as our friend and wise counsellor, Jim Healey pointed out, the loads you draw at the dock, running AC, stove, water heater, Battery chargers etc. will dictate what you need to replace with your new gen set unless you want to spend lots of time managing your loads. Simplest way seems to be turn everything on at the dock and see how many amps you are pulling. In my case, almost 50A on a 50A, 125/250v cord = 100A x 120v hence the 12.5 KW genset.

 

[rslifkin]

Simplest way seems to be turn everything on at the dock and see how many amps you are pulling. In my case, almost 50A on a 50A, 125/250v cord = 100A x 120v hence the 12.5 KW genset.

Just because you can turn on everything on the boat at the same time doesn't mean you actually ever do. Pay attention to what your worst-case actual loads are and see how that compares to the theoretical maximum.

 

[Capt Ray]

Our 2000 MS390 has a Kohler 8kw genset and it is LOUD.
When it comes time to replace this, the dB level will be just as important as the KW output in our discernment process. I'm surprised noise didn't make it into the other posts (unless I missed it!)

A new 600w solar and 540AH LiFePO4 bank has helped a lot. Hardly makes any noise at all. But the panels don't work very well at night.

 

[hmason]

Elon Musk will soon introduce Starlight panels that will work at night.

 

[catalinajack]

Our 2000 MS390 has a Kohler 8kw genset and it is LOUD.
When it comes time to replace this, the dB level will be just as important as the KW output in our discernment process. I'm surprised noise didn't make it into the other posts (unless I missed it!)

A new 600w solar and 540AH LiFePO4 bank has helped a lot. Hardly makes any noise at all. But the panels don't work very well at night.

It's the solar panels that make the difference for you, not the batteries. Last I knew solar panels charge flooded lead acid batteries.

 

[2savage]

if you are having a pro do the repair, it's not cost effective

There are a few things to consider here:

1) I have twelve solar panels.

2) The failed generator has had a few issues in the past that may have reduced its life (like raw water in the oil).

3) The parts from the removed generator have value.

I'm in favor of replacing it. I want to be able to run my generator frequently without worrying about the fuel consequences.