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mcarthur · 22-08-2019, 23:50

Quote:

Originally Posted by Jim Cate

umm again! I think that 0.13 hp is actually around 0.1% of the rated output of your engine(s).

And BTW, on many engines, the same belt that drives the alternator drives the fresh water cooling pump... whatcha gonna do about that if you remove the alternator?

Well, according to the engine manufacturers consumption curve (

), at the rpm's we're talking about for 6kn (arbitrary speed I know), the engines are putting 13hp each to the prop.

The percentage of the total engine power isn't important since we're not at maximum throttle (almost ever, if ever

).

Oh yes, forgot about the fresh water pump! Thank you!

mcarthur · 23-08-2019, 00:02

Quote:

Originally Posted by Jim Cate

And BTW, on many engines, the same belt that drives the alternator drives the fresh water cooling pump... whatcha gonna do about that if you remove the alternator?

Phew, all safe for me - alternator is separate belt. Perkins M135 have gear-driven pumps.

**Dockhead** · 23-08-2019, 00:23

Quote:

Originally Posted by mcarthur

Well, according to the engine manufacturers consumption curve (

), at the rpm's we're talking about for 6kn (arbitrary speed I know), the engines are putting 13hp each to the prop.

The percentage of the total engine power isn't important since we're not at maximum throttle (almost ever, if ever

).

Oh yes, forgot about the fresh water pump! Thank you!

My numbers are WAGs, so you'll need to do your own research. But they should be in the ballpark, and I think you'd need an order of magnitude difference to those to even want to THINK about this.

Looking at the bigger picture, with a massive solar installation and no air con, I would keep this simple.

I would put school bus alternators on both main engines, with a Balmar Centerfielder regulator, sell on the generator, install a large bank of industrial LEAD batteries (although I'm a big fan of lithium), sized at 4x average daily consumption (which will give you usable 2 days consumption), a couple of ganged Victron Multipluses, and call it good. For all of the massive benefits of lithium, you don't really need those benefits with a massive solar installation, and industrial 2v cells in such an installation are extremely durable -- will last at least 10 years and probably more. Hybrid drive will bring you nothing worthwhile, and those Perkins beasts will outlive you. Go cruising instead of tinkering, and spend the $50 000 or $80 000 you save on women and booze.

My advice, maybe worth about what you paid for it

, but there it is.

tanglewood · 23-08-2019, 00:24

Just to be clear, the 100W parasitic load number is pulled out of thin air, so let's not get too hung up on how it factors in. If you are going to make a decision based on that, then just make it based on whatever you want to make up.

The only load from the alternator if it's not producing output will be the belt load and the fan load. Belts are high 90s efficiency (much higher than I thought), and who knows what the fan load is.

But I think this is an exercise in splitting hairs. If you want to do that, by all means go for it, and just make whatever decisions make you happy.

I think the real issue was summed up in the first response which is that you are saving nothing measurable, and eliminating redundancy in a very meaningful way.

There is no way I would get rid of both the generator and the alternators. I've had an off-grid house for going on 20 years now and it's 100% solar powered - except for when it's not. And then you need something, anything, to get charged back up again. No matter where you are, and how small your loads are, there will be times when solar doesn't meet your needs. What will you do then?

Compass790 · 23-08-2019, 00:41

Quote:

Originally Posted by mcarthur

Well, according to the engine manufacturers consumption curve (

), at the rpm's we're talking about for 6kn (arbitrary speed I know), the engines are putting 13hp each to the prop.

The percentage of the total engine power isn't important since we're not at maximum throttle (almost ever, if ever

).

Oh yes, forgot about the fresh water pump! Thank you!

Pretty easy to try out yr theory. Just take the alt belts off & run for as long as you care to see what your fuel savings will be. I dont know what the parasitic load of an alternator is but, as others have said, its not much. I would just leave the belts off & leave the alternators there & that will ensure you never have a problem with your solar or genset

tanglewood · 23-08-2019, 01:31

Quote:

Originally Posted by Compass790

Pretty easy to try out yr theory. Just take the alt belts off & run for as long as you care to see what your fuel savings will be. I dont know what the parasitic load of an alternator is but, as others have said, its not much. I would just leave the belts off & leave the alternators there & that will ensure you never have a problem with your solar or genset

Just consider the accuracy of your fuel burn measurements. Where I did my little gen vs alternator experiment, one of the things it revealed was the inaccuracy in the engine-reported fuel burn. There just wasn't enough precision in the measurements in many cases to tell what was really going on.

transmitterdan · 23-08-2019, 01:58

Many engines use the alternator to drive the tachometer. So if you remove the alternator will you then have no tach? You will likely need a different belt to run the cooling water pump.

Also, I agree with the rest of posters who estimate there will be zero measurable fuel savings. If the alternators are drawing 2% of engine output then they are charging batteries. When batteries are full the alternators will draw much much less than 1% of engine power. Not enough to make a measurable difference in fuel consumption.

Try to think of other things to reduce fuel consumption like clean hull, optimum propellers, timing passages for best current, etc.

**GordMay** · 23-08-2019, 02:40

“Improving Alternator Efficiency Measurably Reduces Fuel Costs” ~by Mike Bradfield, MSME, Remy, Inc.
➥ http://www.delcoremy.com/documents/h...ite-paper.aspx

Fuss · 23-08-2019, 02:58

Quote:

Originally Posted by mcarthur

Question - any reason not to get rid of the propulsion engine alternators, and
Question - would I expect any fuel consumption benefit?

Our position is:

50' power cat
2 x 135hp NA diesels with original (old) mid-sized alternators
1 x 6.5kW diesel genset
a 12v house bank of SLA batteries
about 300w of solar
no aircon, biggest draw is fridge/freezer, radar and autopilot when underway

We're eventually changing to:

3+kW of solar
a 48v LiFEPO4 bank in preparation for hybridization (propulsion and house bank)
a DC-DC converter 48->12v

Since travel won't be in 100% darkness

, the solar will be the primary charging method for everyday living, replacing the alternators (when moving anywhere in daylight) and generator (at anchor).

(to the actual question!) But, since we're taking this in stages I think the first removal could be the two alternators - keeping the genset for now. Are there any reasons to keep the alternators?

As far as I can research using Dr Google, the alternators may be responsible for anything from 2-5+% of horse power from the main engines at cruising speed and some amount of torque. This is even if the batteries are fully charged (can anyone explain?). So by removing the two alternators, apart from not having to worry about two more belts, could I expect 2-5% better fuel consumption?

There have been some interesting posts which are inconclusive, but don't take into account large solar input (like Tanglewood's).

I've also got a sabre M135, (135 horse power) the original alternators are 70amp with internal regulator. They produce nearly no load and are only there to help maintain the start batteries. They would never have been having any impact on anything as they spend most of their time doing nothing. Before I replaced mine with a big externally regulated leece neville alternator, it used to go to about 12a after about 10 mins of engine run regardless of battery soc.
Taking them off won't produce a measurable result.

**Dockhead** · 23-08-2019, 04:04

Quote:

Originally Posted by GordMay

“Improving Alternator Efficiency Measurably Reduces Fuel Costs” ~by Mike Bradfield, MSME, Remy, Inc.
➥ http://www.delcoremy.com/documents/h...ite-paper.aspx

Indeed, but note that this is all about saving fuel from the process of the alternator generating power, not from the alternator spinning without a load. Two different things.

**GordMay** · 23-08-2019, 06:59

Quote:

Originally Posted by Dockhead

Indeed, but note that this is all about saving fuel from the process of the alternator generating power, not from the alternator spinning without a load. Two different things.

You, and the others, are right.
I'd guess you might save only about 1/4 to 1/3 HP by removing a typical alternator.

"Operating Efficiency of an Alternator"
➥ https://www.stamford-avk.com/sites/s...s/AGN182_B.pdf

barnakiel · 23-08-2019, 07:24

I would never get rid of alternators. Yes, plural.

I would kick out the genset. Get a fuel cell or something similar. Honda 10i, for emergency scenarios. Or do without.

Hence, keep them alternators. They are only 6 pounds each ...

Alts are prime method of recharging the starter battery. Alts + good regulators are prime way of charging the house banks FASSSSST. So why get rid of something that comes with every engine, weighs 'nothing' and is virtually maintenance free?

Cheers,
b.

steve77 · 23-08-2019, 07:53

Quote:

Originally Posted by Compass790

Pretty easy to try out yr theory. Just take the alt belts off & run for as long as you care to see what your fuel savings will be. I dont know what the parasitic load of an alternator is but, as others have said, its not much. I would just leave the belts off & leave the alternators there & that will ensure you never have a problem with your solar or genset

I really like this answer. Try it for yourself and see what the fuel saving actually is. Leave the alternators in place and if you need them for charging batteries you simply put the belts back on and you’re good to go.

Cheers!

Steve