Main engine as generator, which capable alternator?

[andre26]

Hey everyone, I need your help to not lose this season.

So, I have a 56 feet sailboat, which used to have a 6kwh Genset (Dynamica Emi-60), which died, but the boat has a Yanmar 110 hp main engine (4jh3-HTE), and given that I don't have enough money for a new Genset I'd like to buy a big alternator and use that on the engine as genset.

My need is to be able to charge the batteries while also producing water, I have an old watermaker which requires 3kwh, so ideally the alternator needs to produce at least I'd say 4kwh without having to spin the engine to too high RPMs, it would be great to be around 2000 RPMs or less.

i have as batteries 8x 95Ah 12v lead acid AGM Tudor, 2s series so 24v, the boat runs at 220v

Can you guide me on which alternator to buy and what I should do to mount it properly?

Thank you very much

[Pizzazz]

It is difficult to do what you are asking. Alternators are not very efficient, 55-60% at 12V, increasing to 70-75% at 24V. This means, in order to produce 4kWh reliably, you need to remove around 3kWh of heat in addition to the heat from the engine from the engine compartment. This is not impossible but it is hard to do. Also, you will be drawing around 7kWh of power from the engine or 10 hp.

Look for example at the Delco Remy 55si alternator, 24V, ~250A max. It will reliably produce around 4 kWh from 2,500 rpm's onwards. You have to keep the temperature below 230F - this means a ducted fan routed outside the engine compartment. Do you really want to spend $3,500 on this? Plus, the concern that drawing 10 hp sideways from the shaft will lead to bearing problems soon or later. It is really not a long-term solution.

[Rumpi]

Whatever 28V 200A+ truck alternator the used parts store has on offer will work. Mounting it is a different problem you probably need a different pulley to keep the engine rpms low. In the end it isn't going to be a cheaper solution unless you have significant diy capabilities.

What happened to your generator? The Yanmar L100N air cooled engine that powers it costs ~1300€ new, buy one and swap out the proprietary parts from the old one (exhaust, water pump, fuel lines). The electrical generator can be repaired by a shop specializing in electric motors, or they sell you a new equivalent. The governor is a simple centrifugal one, it can be ordered new.

[skipperpete]

As Pizazzz pointed out, it’s not as easy as it seems, from an installation point of view I’m not even sure if it can be done on a 4jH3 because of the fluid damper on the front of the crankshaft. You can fit a pulley inside the damper easily enough but the amount of power you can extract from it decreases rapidly as the overhang increases and with a double row pulley, the overhang is substantial. Yanmar refers to the front of the crankshaft as the power takeoff and gives a complete description of what can and cannot be done as far as loading up that end of the crank in the installation manual…. You might even need to get the optional keyed pulley, even though the pto stub has a keyway , often the pulleys did not. Mackboring in the US sells the twin row alternator pulley in aluminium. I’m sure you realize that the alternator needs to be engine mounted not hull mounted ( unless you install a jackshaft) so this requires a lot of careful thought…. One option is to extend the engine mounting bracket, another is to make a plate that bridges the 2 front engine mounts and held by the adjusting nuts.