Generator Alternator

[JLR]

This may be a silly question but does anyone know whether the OEM setup on our boats permits the gensets to charge the batteries. If the house or starting batteries are used to start the gensets, and if the gensets have alternators, do they charge the batteries, in turn?

 

[bostonhatteras]

Many things can happen after a boat leaves the factory, but I would imagine your genset only has an alternator large enough to charge its own starting battery. An alternator requires horsepower to run. The generator is producing electricity on the opposite end, therefore I believe any charging the Genset does will be through the battery chargers and not through its own Alternator. Smaller alternators, perhaps under 10k, often have permanent magnet alternators. These produce very little charging current. Some would say barely enough to get the job done. On my 8KW generator I replaced the permanent magnet alternator with a field charged alternator from a forklift. It still is only enough to charge its own starting battery. I would definitely think your generators only charge the batteries through the alternating current they produce, not direct current from the alternator, except for the small amount of starting battery charging mentioned above.

 

[Genesis]

Depends on how your boat is wired.

My 45C was wired with two DC banks; one for the generator and one engine, the other for the other engine and house loads.

This is not a good setup for a cruising boat but it works fine for a sportfishing vessel that will almost always have either the genset or mains up when away from the dock.

I added a combiner between the two so if the generator was running both banks would be topped off even if the AC charger was not switched on, although it normally would be.

Note that the alternator on the genset is quite small comparatively. A lot of people wire a separate starting battery for the genset (and this is not a bad idea at all, actually, as it can be a quite-small AGM battery in most cases) in which case none of this would apply.

Redundancy is a good thing.

 

[JLR]

Thanks. I always run with either one or both 20KW gensets on. The reason I am asking concerns an alternator rebuild question I had and have decided to opt for the repair rather than relying only on the charger or, as I learn, the alternators on the gensets or the other engine. Although I ran for over 100 hours from Florida to New York with this issue (as I now find out) I prefer not to have to worry about it when I take a family cruise.

 

[jim rosenthal]

Your generator set will only charge its own starting battery (and as Genesis pointed out, it should have its own starting battery) and supply current to the AC mains when it is running. However, if your battery charger is turned on, if (for example) you are at anchor, with your main engines off and your generator set running, with the battery charger turned on, it WILL charge all your batteries while it is running.

Most of our boats were wired by Hatteras in a fashion similar to what Genesis describes; the starting loads are split between the two banks, and in some boats the house loads are also split between the two banks. This has the potential to leave you with a boat that won't start on either engine, plus nothing to run your house loads. This is one of the reasons that a dedicated generator starting battery is desirable; if everything else is discharged to the point of uselessness, the generator can recharge your starting batteries enough to get you moving again.

Modern boats, especially trawlers, from which we could often learn something, are wired differently: there is a dedicated starting bank of starting-only batteries, used only to start the engines, and one engine's alternator charges that bank only. There is a dedicated house bank, of deep cycle batteries, which is big enough that it can also start the engines through a relay (which most Hatteras yachts already have), and that bank is charged by the other engine's alternator, usually using a smart regulator. Finally, there is a combiner, which will distribute and balance out the charging, also ensuring that if one bank is totally down it does not discharge the other bank. Also useful is a battery monitor which will let you keep track of the amount of charge left in each bank.

I had my boat rewired this way a few years ago and it has worked well so far. One of the biggest changes we made was using better voltage regulators, which make faster and better use of the alternators' output- so-called smart regulators. (what they are is multi-stage regulators with adjustable charging profiles) Most boats don't need bigger alternators, but they DO need better regulators. That made a big difference, too.

 

[kwerges]

The previous owner of our 58 YF had a 12v alternator added to our starboard engine that charges all of our house batteries when running. It is a slightly slower charge than the generator/battery charger combo, but allows us to not run the generator when we're cruising...

 

[saltshaker]

This may be a silly question but does anyone know whether the OEM setup on our boats permits the gensets to charge the batteries. If the house or starting batteries are used to start the gensets, and if the gensets have alternators, do they charge the batteries, in turn?

It depends on the set up. If yours is similar to mine, each generator is started by the same bank of batteries for that sides engines, IE starboard generator is started by the starboard battery bank, port generator by the port bank. Yours should be 24V same as the mains. OEM set up bypasses the generator charging circuit. The alternators on the mains are charging the batteries while under way and your charger will charge the batteries while the boat is at rest. Before you rebuild the alternator verify that it is connected to the batteries. My guess would be that it isn't and shouldn't be.

 

[JLR]

Jack - which alternators are you saying should not be connected to the batteries. I assume the engine main alternators are there to charge the batteries assuming the charger is not on underway?

 

[saltshaker]

Jack - which alternators are you saying should not be connected to the batteries. I assume the engine main alternators are there to charge the batteries assuming the charger is not on underway?

Generator alternators should not be used if your set up is like mine. When I bought my boat the engine surveyor noted that the alternators were bypassed. Checked with Hatteras and confirmed this is the OEM set up.