Sizing a Genny based on requirements.

[JDCAVE]

I’m looking at a new Northern Lights Genset and I am trying to decide between the 5kw 673LD3G at 120 V and 42 amps or the 6kw 673L3G, 120V and 50 amps. The units have identical engines.

My shore power service is 30 amp. The second 30 amp inlet is disserviced.

I haven’t got a quote on the 6kw unit but I expect it will be about $500 USD more. Right now I’m leaning towards the 5kw. I don’t have a water maker and right now I’m not inclined to get one. However, I’m thinking about the loads at anchor: running the washer and dryer, possibly a push on battery charging. My existing Entec Genny is 4.2 kw and when I used it I had to be careful to do load shedding. Expected runtime will be 1-2 hours per day, depending on whether we do laundry or not. The boat is largely DC. The stove/oven is propane. Other loads are on the inverter and we have adequate solar panels.

Thoughts?

Jim

 

[Comodave]

Personally I would go with the 5kw unit. Doing a bit of power management isn’t that big of a deal IMO. But my major concern would be proper loading of the genset. If you can get by easily with the smaller unit then you will be loading it more and that is better for the genset.

 

[DavidM]

Personally I would go with the 5kw unit. Doing a bit of power management isn’t that big of a deal IMO. But my major concern would be proper loading of the genset. If you can get by easily with the smaller unit then you will be loading it more and that is better for the genset.

David

 

[rslifkin]

I just looked through the datasheets. They're the same engine, rated at the same HP. Units are the same weight, etc. Which means they might even have the same generator head (but if not, the 6kw one is a bit beefier). Engine wise, neither one will be better from a loading perspective. What's strange is that the half and full load fuel consumption is rated the same on both.



Other than the extra cost, I see no downside to the bigger unit. The smaller one is just a de-rated version (with possibly a less hefty gen head), so it won't save you any fuel or anything. In this case, there's no penalty for the extra power.

 

[koliver]

I don't know if you put in the old genset. If you know what the boat wiring consists of, that the shore power and the genset connect to. Whether you might need to rewire if you up the size of the genset.
I did a genset replacement a few years ago. My original was an Onan 4kw. My new one is a Westerbeke 4.8(or so)kw. The mechanic doing the replacement recommended against an increase to the available 6kw, as he thought the wiring wouldn't take the extra and my old 4kw could already handle all of the loads that the shore power could handle.

 

[caltexflanc]

If you had to screw around with load management on your old one, then you will with the 5kw too. I would go with the 6kw without hesitation, assuming extensive time is going to be spent away from the dock. I like being able to crank up the generator and run any and everything on the boat without a second thought.

I'm curious about one thing though: do you also have to engage in load management when on shore power? As you describe it, it's 3.6KW.

 

[High Wire]

You said the boat only has one 30A? 6Kw is unnecessary. You can't even load it close to 100 percent periodically to burn off some soot. That means using electric cube heaters as dummy loads. 5 Kw is plenty with no electric stove or air conditioning. 4-4.5 Kw would be better as long as its 3 cyl/1800 rpm IMHO.

 

[JDCAVE]

KOliver makes a good point about the wiring and the answer is, I don’t know. I suspect it too would need upgrading if I went to 6 kw...and possibly to even to 5 kw.

WRT load management, yes, I do have to do it while on shore power. In the winter time, we often go to dock at Granville island and we definitely use the Webasto to heat up the boat, at least first thing in the morning as electric space heaters and an electric hot water trip the breaker. We have a recently installed breaker inside the boat at the shore service inlet and that’s the one that is usually tripped. I’m not sure why the second shore power inlet was never connected to the panel, but the electrician I used determined it wasn’t connected, so we completely decommissioned it. Good thoughts on loading the Genny.

I will have a look at the wiring and determine the gauge. I don’t recall, off the top of my head.

I want to hear back from the marine group that is a local dealer and who will be doing the install. He was going to check with Northern Lights and get back to me, but I thought I’d ask around as well.

Jim

 

[FF]

The larger unit will be happier starting induction loads , so if air conditioning , water maker , scuba compressor is on the desirement list , go bigger.

 

[JDCAVE]

No, I don’t have any loads like those. The two big loads most of the time are the Magnum 2800/125 and the water heater.

Jim

 

[jungpeter]

Hi Jim,

Don't forget, someday you'll have to sell the boat. Would a prospective owner (who may WANT a watermaker, for instance) turn away from the sale due to a perceived lack of AC power in the gen set? Or during sea trial, if the gen set kicks off should all the AC loads be applied simultaneously?

Underloading of a gen set is possible, but no more of a PIA than load shedding to accomodate an undersize unit. And I fall in the camp of running my gen set with little need to load shed-I'm lazy.

My vote's for the 6KW unit, given adequate wiring. And personally, I'd uprate it as well if you have questions about even a 5kw unit.

Regards,

Pete

 

[PaulGel]

If you have a watermaker then size it for that. Otherwise get some solar panels because the biggest issue with any battery bank is the last 10%.

 

[Tator]

Just installed the 6kw last fall to replace a 42 year old 7.5 Onan. Love it! My usual morning load is 45amps for hot water, coffee maker, fridge, chest freezer and 130amp DC charger. You don't want to run your genset at its maximum rate for normal continuous duty. With your solar panels, your battery charging needs are probably different from mine. However, I see no problem at running at a 50% load. Once you have the 5kw you can't add more power and with the 6kw you'll have a greater reserve if ever needed.

Tator

 

[Larry M]

... Once you have the 5kw you can't add more power and with the 6kw you'll have a greater reserve if ever needed.

Tator

We had a 5kw Northern Lights on our last boat but had wished we had a 6kw. We could run the inverter/charger and water heater with no problem. We then added a water maker and just couldn't run all three together. We have an 8 kw Northern Lights now but the 6kw would serve our purpose just fine.

 

[Shrew]

My shore power service is 30 amp. The second 30 amp inlet is disserviced.

You have a single 30amp shore power inlet pushing stove, oven, water heater, washer/dryer, battery charger, 120VAC outlets, fridge and pumps?

Since you have 2 x 30amp connections, my assumption is that 30amps services one side of the panel and the other 30 amps serviced the other side of the panel. That sure seems like a lot for a single 30amp.

User load balancing is not an assume solution.

That boat should have a 8K on it.

 

[Shrew]

That boat should have a 8K on it.

Actually, I take that back....

How many Heat/AC units??

 

[caltexflanc]

It's beginning to sound like the load management issues are due to the second 30 amp circuit being decommissioned. Any ideas on why? I'd guess the boat was originally set up for 7kw for a reason.

Underloading of generators is way over played on these forums. They can be hurt by running with no load for some periods of time. But running at 20% or even 10 for a few hours a day is just fine.

 

[MYTraveler]

If nothing on your boat is 220v, and if you only have one 30-amp leg, and if my math and understanding are correct, you can only pull 3600 watts (120 x 30), in which case you should go with the 5KW. But if you can pull more than 4kw, it seems to me you should go with the 6KW genset.

 

[caltexflanc]

If nothing on your boat is 220v, and if you only have one 30-amp leg, and if my math and understanding are correct, you can only pull 3600 watts (120 x 30), in which case you should go with the 5KW. But if you can pull more than 4kw, it seems to me you should go with the 6KW genset.

Since he has to do load management whether at the dock or on his 4kw generator, that says there is demand well north of 30 amps.

 

[MYTraveler]

Since he has to do load management whether at the dock or on his 4kw generator, that says there is demand well north of 30 amps.

Admittedly, I probably read too quickly, though I did not miss his need for load management. Still, if he has only one leg, at 120v and 30 amps, he cannot pull, from shore or genset, much more than 3600 watts and the 4KW may suffice. Note that if his aggregate draw on one leg exceeds 3600 watts, he will have to manage loads, at least until he shifts some of the draw to another leg.

 

[rslifkin]

Admittedly, I probably read too quickly, though I did not miss his need for load management. Still, if he has only one leg, at 120v and 30 amps, he cannot pull, from shore or genset, much more than 3600 watts and the 4KW may suffice. Note that if his aggregate draw on one leg exceeds 3600 watts, he will have to manage loads, at least until he shifts some of the draw to another leg.

Depending on how the wiring, transfer switch and breakers are sized, it's possible that the gen can feed more than 30A to the panel even though the shore inlet only supplies 30A. No way to know without looking at the setup, however.

 

[MYTraveler]

Depending on how the wiring, transfer switch and breakers are sized, it's possible that the gen can feed more than 30A to the panel even though the shore inlet only supplies 30A. No way to know without looking at the setup, however.

I suppose anything is possible, particularly with a panel that has been modified from factory, but each leg should have its own breaker, so that a 30 amp leg is protected by a 30 amp breaker, even if their are 20 15-amp circuits drawing from that leg. If so, that breaker should prevent any more than an aggregate load of 3600 watts. And if that breaker is not in place, it should be added, and once added the 4kw genset will provide just as much power as a 5kw.

 

[Larry M]

Jim: Do you have a toaster or a washer dryer where you use the dryer occasionally? With the 6kw you don’t have to be as aware of the load sharing as much. Just thinking out loud here.

 

[Tator]

One important difference between the loads at dock versus at anchor is the need to charge up the battery bank at anchor. This alone can add 15-20 AC amps to the genset load that aren't usually needed when plugged into shore power.


Tator

 

[catalinajack]

I'm curious about your mechanic's concern about the wiring being inadequate for a larger generator. Did he determine the wire gauge before reaching that conclusion or did he just guess?

I don't know if you put in the old genset. If you know what the boat wiring consists of, that the shore power and the genset connect to. Whether you might need to rewire if you up the size of the genset.
I did a genset replacement a few years ago. My original was an Onan 4kw. My new one is a Westerbeke 4.8(or so)kw. The mechanic doing the replacement recommended against an increase to the available 6kw, as he thought the wiring wouldn't take the extra and my old 4kw could already handle all of the loads that the shore power could handle.

 

[catalinajack]

Adequacy of wiring has been questioned several times. Guessing is not acceptable. Determine the wire gauge of what exists. Then consult an ampacity chart. You will find your answer there.

KOliver makes a good point about the wiring and the answer is, I don’t know. I suspect it too would need upgrading if I went to 6 kw...and possibly to even to 5 kw.

WRT load management, yes, I do have to do it while on shore power. In the winter time, we often go to dock at Granville island and we definitely use the Webasto to heat up the boat, at least first thing in the morning as electric space heaters and an electric hot water trip the breaker. We have a recently installed breaker inside the boat at the shore service inlet and that’s the one that is usually tripped. I’m not sure why the second shore power inlet was never connected to the panel, but the electrician I used determined it wasn’t connected, so we completely decommissioned it. Good thoughts on loading the Genny.

I will have a look at the wiring and determine the gauge. I don’t recall, off the top of my head.

I want to hear back from the marine group that is a local dealer and who will be doing the install. He was going to check with Northern Lights and get back to me, but I thought I’d ask around as well.

Jim

 

[catalinajack]

"Getting solar" is not a viable solution for some folks not to mention added expense and complexity and lots of new wire runs.

If you have a watermaker then size it for that. Otherwise get some solar panels because the biggest issue with any battery bank is the last 10%.

 

[catalinajack]

Or, just increase alternator size and run the boat drive the boat for four or five hour to the next anchorage.

If you have a watermaker then size it for that. Otherwise get some solar panels because the biggest issue with any battery bank is the last 10%.

 

[FF]

Except for a bit of cost , and a hassle installing it oversized wiring has no downside.


Its frequently cheaper in the long term to simply buy a coil of heavier wire .

 

[caltexflanc]

Admittedly, I probably read too quickly, though I did not miss his need for load management. Still, if he has only one leg, at 120v and 30 amps, he cannot pull, from shore or genset, much more than 3600 watts and the 4KW may suffice. Note that if his aggregate draw on one leg exceeds 3600 watts, he will have to manage loads, at least until he shifts some of the draw to another leg.

He said he had to manage power at the dock as well. For some unknown reason a second 30 amp shore circuit was decommissioned.