Dual Alternators on Single Engine

Pack Mule,
The bracketry looks skookum. There is a fly though and that is the fact that the alternator bracket is mounted to the boat meaning the engine wiggles around and the alternator does not. It may not be a problem though but normally the alternator should be mounted to the engine so the two vibrate as a unit. I have seen them mounted opposite sided to the original, mounted on the engine mount but still so they can vibrate WITH the engine.

If it is now many years old without any problem then you may have a good one.

C lectric said:

Pack Mule,
The bracketry looks skookum. There is a fly though and that is the fact that the alternator bracket is mounted to the boat meaning the engine wiggles around and the alternator does not. It may not be a problem though but normally the alternator should be mounted to the engine so the two vibrate as a unit. I have seen them mounted opposite sided to the original, mounted on the engine mount but still so they can vibrate WITH the engine.

If it is now many years old without any problem then you may have a good one.

Click to expand...

That type of mounting become less of an issue as the thinner belt become longer. Many alternators can be run in either direction. What's important in that application is to make sure the fan on the front is for the correct rotation.

Ted

MurrayM said:

Another tangent/rabbit hole on my quest for fast and efficient battery charging times. This article is rather long, but compelling to say the least; Marine high output alternator and second alternator discussion

Thoughts? Experience?

Click to expand...

Murray

How many amps are you wanting? I agree with others, maybe a single larger capacity unit would do fine and be easier and cheaper to install.

If you can find a larger amp capacity replacement that can be controlled by an external 3 stage regulator that will fit then I think you will be better off.
Keep in mind that a larger replacement can be turned down by the regulator yet that turned down output will continue for far longer than the Hitachi resulting in a faster recharge. I mean so the new alt. turned down max is also 80A but because the new alt is better built it can run hotter and keep up that output whereas the Hitachi will fall off fast as soon as it starts to get hot.

The crank side loading should be about the same as the current alt. once the new alt is turned down.

Maybe if you can post the specific Hitachi model and amp output [80A?] it would help.

Sorry about the lagard response time, but the day job keeps getting in the way of my life and there was a short lived house renovation emergency...carpenters should actually read blueprints

I don't have our specific model of alternator on hand (or the power curve) but it was the 80 amp upgrade offered by Yanmar for the 4JH2-UTE. The measurements I took last year were 5.25" for the crankshaft pulley and 3" for the water pump pulley, giving a pulley ratio of 1.75. I'm learning to really hate belt dust, so a serpentine belt kit is looking pretty good for that reason alone. The ones for our engine have a pulley ratio of 2:1.

The house bank is 450 Ah (four 6 volt golf cart batteries) and the general rule of thumb for wet cell batteries is to have an alternator 25% of Amp hour capacity (112-ish amps).

Using the example of a 124 amp Ample Power #4023 alternator Ample Power Alternators (found their power curves easily)

...at 1000 engine rpm the alternator would give 51 amps (cold) or 41 amps (hot)

120 Ah divided by 41 = 2.9 hours to bulk phase charge from 50% to 80%

...at our cruising speed of 2700 rpm the alt would give 121 amps (cold) or 102 amps (hot)

120 Ah divided by 102 = 80 minutes to bulk phase charge from 50% to 80%

I do have a Sterling Power 130 amp Alternator to Battery Charger which they claim speeds up charging times up to 5 times faster Sterling Power 12 volt, 130 amp Alternator to Battery Charger If their claims are to be believed that would mean 36 minutes at 1000 engine rpm. (I'd settle for an hour )

Again, the goal is to charge from around 50% to around 80% as fast as possible, and let wind or solar add to that while at anchor. Full charging would be on long traveling days or on shore power.

How much above low idle do you guys run your engines to charge your batteries? (We rarely have anyone at the same anchorages as us so we can't learn from watching others).

My head is starting to hurt...

If i must charge batts, i use the Gen, as she uses less fuel and puts out more.
What more could one ask

AS mentioned about, what I like so much about the solar panels is that they provide that slow charge that as the batteries get above 80% becomes inefficient by either the engine or genny.

With auto or non industrial based engines the first question should always be to the eng mfg to find out the HP that can be taken off the front of the crank.

All cars today have air cond and frequently good sized alts , so I would guess 15-20 HP , but checking is free.

Don't forget to take into account the acceptance rate of the batteries particularly with wet cells. As the amps go back in, the batteries heat up and the acceptance voltage decreases. Ample Power and Sterling both can do a good job of monitoring/controlling battery temperature which will definitely keep your batteries healthy longer.

Realizing the folly of gleaning scraps of info from here and there and the dire consequences of getting it wrong, I'll now retire to pour over Calder's book and have ordered these two books which should give me a good base from which to operate from Living on 12 Volts with Ample Power and Wiring 12 Volts for Ample Power

MurrayM said:

How much above low idle do you guys run your engines to charge your batteries? (We rarely have anyone at the same anchorages as us so we can't learn from watching others).

My head is starting to hurt...

Click to expand...

You can determine this while running engine and charging batts. Watch voltmeter for bank being charged. Slowly raise throttle and volts will rise as alt output increases with rpm. At some point further rpm increase will cause no further increase in volts. Regulator now is limiting output, not rpm. Raise rpm a touch beyond and you are good. Probably around 1000 to 1500 engine rpm.

Once charge state increases, you can throttle back engine. If you see volts start dropping, you throttled back too far.

Your original alternator can be modified with an external regulator with a control panel mounted at the helm. Adjust volts so you get a desired charge rate. It will charge much faster than the internal reg you have now. The internal one is really set up for just topping up a batt after a start, not the bulk charging you want.

Alternator in this set up will also make more heat than it used to, so you want to check on it and make sure it is not getting too hot. Higher engine rpms actually help in this case as the fans are more effective.

Most battery Mfg chose a 10% recharge rate for extended life of their batts.

Charge them harder/faster and do not be surprised they dont last as long.

Most cruisers will operate 50% to 85% full to reduce charge times , unless underway.

The Mfg estimate of charge cycles also expects charge to at least 100% ,
some are now suggesting 115% recharge for longest life.

Usually onlr solar or a power hose can do this.

We have dual alternators on both our engines but we also have agm batteries which can be charged at 3 to 5 times the rate of golf cart batteries.


Via iPhone.

MurrayM said:

Realizing the folly of gleaning scraps of info from here and there and the dire consequences of getting it wrong, I'll now retire to pour over Calder's book and have ordered these two books which should give me a good base from which to operate from Living on 12 Volts with Ample Power and Wiring 12 Volts for Ample Power

Click to expand...

Google Prestolite. One need not buy an expensive Leece Neville made likely on the same bench.

Dire consequences, not too likely as there are about 20 ways to do it right and within budget.

I'm afraid I never had any luck with Leece Neville alternators and our Broom 42 has a Perkins M90 (4236) 80 hp engine and we opted for 4x225 amp domestic batteries charged via a 110 amp Bosch alternator through an Adverc alternator controller with a 45 amp Bosch charging a 150 amp engine start battery. 440 amps of solar panels keep us autonomous providing we use the power sensibly, ie we only use the washing machine when we're on the move or in port.
The domestic battery system powers a 4 kw inverter for freezer, washing machine etc when not in port.
More importantly the engine has sufficient torque to cope with the extra alternator and still give us 8 knots economical cruising speed.
I'm all for comfort on board but on some boats it's beginning to get over the top.
KISS.

440AMPS of solar would cover a football field,

Perhaps its 440 WATTS of solar ????

Perhaps 30 amps when charging a 12v system.

Still grand for batt charging.

Okay...have gone through Calder's alternator sizing guidlines for a single alternator and this is what I come up with for our boat with its 1980's equipment aboard;

450Ah (house bank) + 16 amps (DC load while running) + 25% (to ensure alternator isn't running at full capacity) = 582.5

Calder recommends, for golf cart batteries, an alternator 25% of 582.5 which is 145.625, or a 140 amp alternator.

Next to consider will be pulley ratios (from serpentine pulley kit) to ensure alternator is not providing too many amps at our engines RPM's, as well as side loading on shafts. Once this is figured out, will move onto cooler battery location out of engine room and/or ventilating battery boxes, cables, and so much more...

Interesting stuff.

FF your perfectly correct, the solar panels on our boat are 440 watts NOT as I incorrectly stated amps. Apologies for the misleading typo.

Realized I was off (again...) with the math.

450 (Ah) divided by 4 = 112.5 + 16 amps (DC load while running) = 128.5 + 25% (to ensure alternator isn't running at full capacity) = 160...therefore according to my understanding of Calder's theory...a 160 amp alternator should be the "best" size as long as the pulley ratio puts it in the sweet spot at our engines rpm, and if the shafts & bearings can handle it.

The usual consideration is belt load.

At 150A or so dual belts are a must.

Murray

At the Seattle Boat Show I noticed a Beta Marine diesel of about 50 HP that had a very nice serpentine belt driving a 180 amp alternator. They may be worth approaching for advice and hints for the setup you are envisioning.

sunchaser said:

Murray

At the Seattle Boat Show I noticed a Beta Marine diesel of about 50 HP that had a very nice serpentine belt driving a 180 amp alternator. They may be worth approaching for advice and hints for the setup you are envisioning.

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Thanks for the tip. According to the US Beta Marine website they use Balmar serpentine pulley kits and alternators.

Still navel gazing this issue, when time permits, which means I'm probably a year away from making a decision. Thanks again.

FF said:

440AMPS of solar would cover a football field,

Perhaps its 440 WATTS of solar ????

Perhaps 30 amps when charging a 12v system.

Still grand for batt charging.

Click to expand...

Yep 440 AMPs would be about 18 large 300 Watt panels. That would be a small 5KW propulsion system.