How to take the alternator out of charging if all power is needed to run engine???

[wingssail]

It there another way to do it? Yes, of course, probably several ways but in my opinion, none are satisfactory and will result in "kluge" set up.

The right way is to take off the alternator, take it to an alternator shop, and remove the internal regulator which I assume it has. Then it will no longer "self excite".

Then buy an external regulator and install it. This will be a proper installation.

Some, such as the Balmar regulators, offer small engine mode with reduces the charge rate, an intelligent way to accomplish what OP is after. Also, with an external regulator the field wire can be switched, cutting off all excitement and stopping any charging load.

And to protect the alternator from overheating add an alternator temperature sensor which will reduce the output when needed to keep the alternator from exceeding safe temps.

[Nicholson58]

Originally Posted by roverhi

The real question is why an 80 amp alternator on a 16hp motor. You'd need huge battery amperage, 400 amp plus or exotic batteries to be able to use 80 amp output and then only for a short period before the regulator cuts back alternator output. Think you'd be better off with smaller alternator with an external multi-stage regulator. The external regulator would give you the ability to cut the field current. Assume you have a Hitachi internal regulator alternator which makes cutting the field impossible once it takes over.

Yup, external charge control is the best way. You can program the output to field limit. This can easily drop the output a great deal. Also, since it’s externally regulated, the field can be switched off if desired. Also, turn off the key and it’s totally dead but so will your engine instruments. There are many external controllers. We have Balmar. These also provide for better charging and battery maintenance than the internal regulators.

Our original monster alternator was too great a load on the 115 HP Westerbeke. We had frequent overheating in challenging seas. After the new Firefly big bank was installed, the alternator burned out. Turns out it wasn’t rated for continuous full load. The new batteries simulated that condition. We subsequently installed a new much smaller alternator and used the Balmar to reduce its output to 80%. This is comparable to our solar panels on a good day so big enough and the engine hardly knows it’s there.

[captstu]

My previous cat had twin 27 hp Yanmars. Each was fitted with a stock 55 amp and an added 200 amp alternator. The 55s were self excited.

Each 200 was excited with a Balmar 612 regulator.

The house bank was 1100 Ah and supported, via a 3 kw inverter, boat air conditioning, a Splendid w/d and a water maker.

The regulators were each set to a 1 minute start delay.

Each regulator was hooked to its respective “ignition” switch.

When charging or air conditioning, there was significant engine load, 600 rpm or more.

In normal operation, we shut off the ignition switches, relieving the engine load, when maneuvering, fo example when anchoring.

[capnorv]

Over the years I have found it very useful too what the poster wants. The benefit is great when say leaving an anchorage still on an incoming tide of three or four knots current to acquire beneficial seastate and currents for transit. My last three engines were wired with the alternator through the ignition switch. They were a Yanmar, Sole, and Perkins. In all cases I could just turn my key off when necessary. Granted, you lose instruments and stop start control, but turning switch back on will bring that back. When conditions become more favorable, you can turn key back on and charge the house.

[CarinaPDX]

Most of these posts are simply repeating the other thread, so I'm not sure there is much additional value. The simple answer is to have a switch on the regulated field lead (P or N, whichever is used) from inside the alternator. But this leaves unsolved the other issues: the alternator is too large for the engine, too large for a single belt, does not do a proper 3-step charge cycle, and can (at least in theory) run too long at high output and run too hot as a result. So do the right thing and invest in a good external regulator. There are many on the market, and some of them can have a shunt attached that can be used to sense current and limit the alternator accordingly. Others typically limit the duty cycle as a proxy for current. However it is done you should limit the alternator output down to something on the order of 60A, not the current 80A. And to reduce charge times there should be bulk and absorption charging, plus a lower float voltage to protect the batteries. External regulators typically have an ignition lead that signals the regulator to start, and can be used to shut off the alternator. Also, many external regulators have soft start capabilities, where they delay starting the alternator until the engine is running for a minute or so, and may also ramp up output as well. So do some research into external regulators and solve a host of problems at once.

Greg