Generating power from main engine vs generator

[valhalla360]

Originally Posted by John Holbrook

10-15k Genset - any installed name brand 7 - 10kva. If you want more battery charging power then add roughly $1500 per 100amps installed.

Large alternators make sense if you want to charge up the batteries fast at anchor or out sailing when you don't really need engine propulsion. Nothing to do with aircon. For aircon you probably do need a genset.

AGMs can be charged at 20-25% of their capacity so you would need at huge bank to untilize 300amps of charging. But Lithium and Firefly can be charged at rates near equal to their capacities. For me Lithium is expensive or complex. Fireflys look reasonable.

Why spend 5k on alternators - because the standard alternator is good for less than 100amps and I would have to put a smart regulator on it anyway. 2 x Balmar 200amp alternators $1,100 each, one Balmar regulator that handles both $700, 2nd alternator brackets from Yanmar $500? and cables, easy self and instal say $4k.

I guess I'm confused on what you are trying to accomplish:
- A 7kw generator is theoretically capable of generating 580amps @ 12v. Throttle it back to a more reasonable output and account for some conversion losses and it should be able to put out 300amps continuously via a large battery charger. (10kw even more). So your premise that the alternators are capable or drastically more output is false.
- You mentioned backup for solar, so again, why would you need massive amperage output when most of the time the solar array should be filling the battery bank. So what if you have to run 2 hrs instead of 1 hr once a month when you've had a few cloudy days in a row? Hardly worth spending thousands to avoid an extra hour of run time.
- If you are going to run an energy hog boat (and I'm not bothered by that), it quickly makes more sense to just run directly of a generator rather than build an elaborate storage system to try and store that energy for later use. In principal, you could do the same with large alternators and an inverter system.
- What loads are you running that you need 600+ amp-hrs per day? That's why I assumed you were running air/con or some other heavy load. Most people talk about 100-200amp-hrs per day, so even a single 200amp alternator or 2kw generator should do the job in a reasonable period of time.

It seems like you've decided you need a massive battery bank and you want to have backup that could charge it very quickly but you've never defined what you are running off the bank, so based on typical usage, it seems overkill.

[a64pilot]

Anyone click on his link and look at his boat?
I would assume logically his power demands would be several times what an average sailboat is, these guys may have massive refrigerators and freezers, several TV's etc.
Simply a matter of scale

[TheOffice]

But if you are running either AC or a watermaker doesn't that tilt the equation in favor of a generator?

[Pizzazz]

There should not be any doubt that a generator increases flexibility in electricity generation but it may not be worth it for smaller boats. The quoted analysis shows that the difference in efficiency is not so much gen/alt but if you are running the engine at optimal speeds/loads which is only logical. The typical use cases could be:

Sailboats with <25-30 HP engine, typically no room for a diesel gen, alternator could take a large share of available power which would allow relative efficiency this large alt is likely best.

Larger boats will have bigger engines thus relative inefficiency when generating power at idle so a generator becomes more practical and a necessity above a certain size.

[valhalla360]

Originally Posted by a64pilot

Anyone click on his link and look at his boat?
I would assume logically his power demands would be several times what an average sailboat is, these guys may have massive refrigerators and freezers, several TV's etc.
Simply a matter of scale

Yeah, I saw the boat but if that's the approach, it's like complaining about the fuel efficiency of your Rolls Royce... if he really is using 600-1000AH per day beyond what his solar system provides (only reason I can see for needing 300amps of continuous charging capability), it probably makes more sense to use a small battery bank and just power things directly off the generator.

[captstu]

I ran twin 200 amp alternators and twin 55 amp alternators on my twin Janmar three GM engines. There are issues beyond your economy to consider.

When maneuvering I had to disable the field card to the twin 200s because the on Yanmar were a bit overloaded and would not come up to speed quickly enough for maneuvering.

The cost of the alternators and the additional wiring was much less than the cost of the Gen set and a large battery charger.

The 20 on Mars running at sufficient speed to power my air-conditioner won't washer dryer were much quieter than the Jensen. After a day of sailing we started the engines to motor into the harbor and started the air conditioning cooling down the boat. There was no difficulty until we near the docks and we had to shut off the exciter to the larger alternators for docking.

The 900+ amp hour battery bank carried us through the docking. When we either plugged in or restart of the alternators.

The downside is the heavier alternator load accelerated to wear on the engines. At 5000 hours on each engine I had to put rings and some Pistons a new bearings in Both engines. Even with the cost of the major rebuild I believe the overall cost was lower for the engineers that the initial plus repair costs on an gen set over the same time.

We routinely ran the air-conditioning all night long on the battery bank and there was still sufficient power to go through our morning routine before starting the engines to charge them back up. Our eight large AGM batteries lasted about four years each under this punishment.

[S/V Alchemy]

Originally Posted by tanglewood

It's actually two alternators running in tandem. Both are Balmars, one 190A and the other 85A, so 275A theoretical max.

My boat is a big power boat, so very different from most here, but I don't think it really matters. I think the real key as that the generator is more efficient provided you have it reasonably well loaded - say above 30% - especially when powering AC loads. That can be applied at any scale, large to small. For lighter loads the main engine is better. Fortunately, as Paul L demonstrates, that's a good match for typical usage.

Nice post and I concur. But I have a sailboat with an oversized bank so I can operate in a relatively narrow SOC band, and I have about 600 watts of solar panels, a 300 watt wind generator and a couple of Honda 2000s to run power tools and for "emergency generating", should that be an issue. Emergencies don't presume A/C, although I have a heat pump type unit.

The upshot of all things, apart from stating the obvious differences between a big Nordhavn and a sailboat with two PTOs for a pair of externally regulated alternators, is that I can create my amps without a generator, but retain that option. If I need to motor, I can recharge or even equalize my bank at sea with little trouble. The main is not needed often, but when I motor out three miles to pump out waste tanks (say), I certainly don't hesitate to make a lot of power. For me, the added fuel burn and complexity and sheer heat of running a genset, even a modest one, is preferable. That said, I can't argue with your observations that the genset trumps the main in many instances. But there are many ways to achieve the same charging goals and to increase redundancy by having multiple charging sources. Takes work, however, to get it right.

[S/V Alchemy]

Originally Posted by TheOffice

But if you are running either AC or a watermaker doesn't that tilt the equation in favor of a generator?

Well, if you have a DC and an AC alternator (switched, of course), you can have an AC watermaker, which is quite efficient. Make water while you motor. When water is made, switch to charging batteries with the other alt.

[John Holbrook]

Originally Posted by valhalla360

I guess I'm confused on what you are trying to accomplish:
- A 7kw generator is theoretically capable of generating 580amps @ 12v. Throttle it back to a more reasonable output and account for some conversion losses and it should be able to put out 300amps continuously via a large battery charger. (10kw even more). So your premise that the alternators are capable or drastically more output is false.

No I didn't say battery chargers weren't capable of high output. Wanting to achieve, reduced costs, reduced space taken up, reduced weight, reduced maintenance and complexity. The cost of constant 300amps battery charger wouldn't be far of the cost of the alternators. Then there is the cost of the genset. Sure you could go for a smaller genset and save $1 or 2k.

Originally Posted by valhalla360

I guess I'm confused on what you are trying to accomplish:
- You mentioned backup for solar, so again, why would you need massive amperage output when most of the time the solar array should be filling the battery bank. So what if you have to run 2 hrs instead of 1 hr once a month when you've had a few cloudy days in a row? Hardly worth spending thousands to avoid an extra hour of run time.

Because I can. Beacause the standard alternator only makes 80amps and doesn't have a smart regulator, because the engine if not properly loaded is at risk of glazing. Crickey you are worse than a wife:-)

[Bluebeard]

Can somebody please tell me how to see embedded links on the forum. Every time I
I click on a link I am redirected to this site

"http://go.redirectingat.com/?rdrflb=1"

which reads like this
"
If you’ve landed on this page, you may be wondering exactly what it’s all about.
We’re Skimlinks — a service that helps online publishers earn money.
When links in publishers’ content lead their users to click through and buy from an online retailer, we make sure they’re rewarded!
We aim to make our service seamless and unobtrusive, so your user experience should not be interrupted. If you’ve landed on this page and didn’t mean to, unfortunately you’ve most likely clicked on a broken link along the way. Links can be broken if they are badly formatted; if you spot any again, we’d advise reporting these to the site owner.
- Team Skimlinks"

I have trouble believing that every link is broken, but then I also thought that switching the underlining off was simple.

[valhalla360]

Originally Posted by John Holbrook

No I didn't say battery chargers weren't capable of high output. Wanting to achieve, reduced costs, reduced space taken up, reduced weight, reduced maintenance and complexity. The cost of constant 300amps battery charger wouldn't be far of the cost of the alternators. Then there is the cost of the genset. Sure you could go for a smaller genset and save $1 or 2k.



Because I can. Beacause the standard alternator only makes 80amps and doesn't have a smart regulator, because the engine if not properly loaded is at risk of glazing. Crickey you are worse than a wife:-)

snip from your prior post:
"Maybe. Most dedicated genset and battery charger costing 10-15k can charge the batteries at say 100amps.
"

Sure sounds like you were saying the generator would be limited to 100amps.

Randomly throwing out comments, some of which are flat out wrong only provides confusion. Why comment if it's just random statements with no coherent meaning or purpose?

Maybe your wife needs to step it up a bit to get you thinking more clearly.

[skipmac]

For me the question is not which method is more or less efficient. Even with a large difference in efficiency I look at usage, long term cost and wear on the system.

Use the main engine for charging on a regular basis. Wear this out and you're looking at min $10K or so to rebuild or buy used, $15-$25K for a new engine.

Wear out a generator $6-$10K max.

Whether one or the other burns 10% or 20% or 30% more fuel to charge is of minor consequence.

So install a big alternator and charge with the engine when motoring, charge with gennie when anchored OR, install more solar and use the gennie for an occasional top off.

[a64pilot]

Originally Posted by skipmac

Wear out a generator $6-$10K max.

Whether one or the other burns 10% or 20% or 30% more fuel to charge is of minor consequence.

I think I paid $5K or so for mine, in a sound shield, with muffler, fuel filter etc.
I'm assuming I can just replace the motor and generator for about $4K, that if I decide to not rebuild.
Mine is the Baby Nexgen though, would not even come close to powering a big Nordhaven, again just a difference in scale.

But I agree, the purpose of the generator is to save hours on the main engine

[skipmac]

Originally Posted by a64pilot

I think I paid $5K or so for mine, in a sound shield, with muffler, fuel filter etc.
I'm assuming I can just replace the motor and generator for about $4K, that if I decide to not rebuild.
Mine is the Baby Nexgen though, would not even come close to powering a big Nordhaven, again just a difference in scale.

But I agree, the purpose of the generator is to save hours on the main engine

Yes I was thinking about a small boat gen and even remembered you installed a Nexgen. So after using it for a year or so any comments, problems, like it or hate it or in between?

[a64pilot]

Not to try to thread drift too much, but it's fine. It is not a Northern Lights or other gen that is at least twice as expensive and heavy, but it will run fine all day or all night if you want it to. I think I have 500 or 600 hours on it.
I bought it as a Honda replacement, not trying to have full time generator, although I think it would work better for that than many think. Oil change interval is 100 hours though.
Tough little bugger from what I can tell, it's crankshaft is ball bearing, I can't imagine why, but it ought to last forever, the crank anyway. I assume rings will go first and unless I'm mistaken its wet sleeved, so a top end overhaul ought to be easy.
It may not be wet sleeved, I'm not sure.