Alternator field wire switch

[EdHouston]

I have just replaced the alternator on Moonlight Mile and have used an external regulator, what would be the effect of installing an on off switch on the field wire?

My thought process here is that when running the engine for extended periods the alternator could be turned off when the batteries are fully charged.

Any thoughts, I know by installing a 3 stage regulator this may be mute point but until I can justify the $300 cost I do not want to boil my batteries.

Ed
S/V Moonlight Mile

[RayNWanda]

 Ed, if the regulator is working properly, it should not boil your batteries. The problem with a "standard" type regulator is that it starts to taper off the charge rate earlier than optimum, resulting in longer charging times. The smart regulators back off in stages and sort of "force feed" a little more into the batteries before backing off another step. The smart regulators are programmable for the type of batteries they are feeding to optimise the charge curve for that type battery.

Check to see what the charging voltage is from the alternator. Your battery monitor should work well for this. Generally, you boil batteries with overvoltage. If the charge voltage looks OK- I would run it. If the voltage is high, there is a problem with the alt/ regulator. Adding a switch to the field wire just increases the chance of a problem. If the switch or a connection goes belly up- the alternator quits charging.

[Dale Tanski]

Ed,
Ray is spot on.  The only other thing I could add is if your start battery was weak shutting off the alternature would be just that little less load required to start the engine. 

Oh ya... one more... Just like in many of the newer cars today when you stomp on them the AC and alternator kick out to transfer as much power to the drive wheels as possible, you guys pull skiers much?

Good Sailing...   Dale

[RayNWanda]

According to Balmar's website, an alternator at full output will consume about 1 hp for every 25 amps of output. So at full output, it's going to eat about 4 hp.

When we were in high school, my buddies and I went water skiing on New Year's Day all four years. So yeah, we pull skiers year round down here- Nothing wrong with that, it's an advantage of living in a subtropical climate...

[SV THIRD DAY]

We do have an alternator field wire cut off on THIRD DAY, but it is installed to shut down the alternator for when we want to use the Ham Radio while motoring.  The alternator puts out a Horrible amount of noise, so the easy fix was to simply turn it off.

Bingo....a quick fix, but it is true, a properly working alt will not fry the batteries rather will give them a GREAT 100% float charge when making long motor runs, WHICH you WANT out cruising or your batties will not be happy....oh, I can tell you ALL about that!

Rich
San Blas, Nayarit Mexico

[Sta-Sea-Dawn]

Rich....San Blas, Nayarit Mexico......
Hey...off and on topic.....first it has been two years (Jan 2010) but....how long were you in San Blas.  My cursing goal is to stage there for a while.

I am not leaving for at least a year.  I sure would like to hear some lore. 

Now....I have a marine alternator that may or may not be working.  It is a one post...single wire.  I have it on the engine and I am going to check it again today.

Opinion....I have red somewhere that the higher amps put more pressure on he engine shaft.  It looks like the westerbeke 40, has a range of 40 to 100 amps.  I ma going to get the alternator checked if it does not work today for amperage and voltage is possible.  Thoughts or rebuild vs new?

[Sta-Sea-Dawn]

Rich.
I will check out San Blas, Mex. online.
It was a miss read, I am lookikg at San Blas Islands...Panama.

[barrylab]

The alternator doesn't directly put pressure on the crankshaft, but any alternator more than about 50 Amps will not be happy with the standard V-belt. Some uninformed owners try to stop the squeal by tightening the belt and therefore putting undo pressure on the crank. This can lead to a cracked crankshaft right at the first bearing. There are 3 solutions:

1. Get a smaller alternator

2. Live with the squeal when the battery is low and carry extra belts for when they break (also runs the fresh water pump)
- I used to do this, until the engine overheated when it broke!

3. Get a very expensive serpentine belt kit

As I'm doing an engine rebuild so I chose door number three this spring, and I'll let you know how well it works.
It has about 6 times the surface area of a normal v-belt, so it can handle the high output alternators pretty well I guess.
It comes with a new water pump (another item that will have trouble with an over tightened v-belt).
Here's what I bought: https://store.electromaax.com/index.php?route=product/product&path=38&product_id=113

[Bev & Billy on Sta-sea-dawn]

I am looking at a Leeche-Nevellie alternator.....how does your alternators hook up to your tachometers.  My old alternator that I think works has no way to hook up tach...it just has an out put lead to hook to battery.  Is there some other way to hook up Tach?

[barrylab]

The tachometer hooks directly to the field of the alternator. The unfiltered AC output has a frequency range the tach conditions to create a current to the meter. Basically it's a high pass filter that gives more current for higher frequency pulses.

There is an adjustment on the back of the tach to allow for different alternator outputs.

Westerbeke put out a service bulletin that might help:

http://www.westerbeke.com/ServiceBulletins/sb_148.pdf

[Bev & Billy on Sta-sea-dawn]

The tachometer hooks directly to the field of the alternator. The unfiltered AC output has a frequency range the tach conditions to create a current to the meter. Basically it's a high pass filter that gives more current for higher frequency pulses.

There is an adjustment on the back of the tach to allow for different alternator outputs.

Westerbeke put out a service bulletin that might help:

http://www.westerbeke.com/ServiceBulletins/sb_148.pdf

Thanks Barry...If I understand, the only terminal on the alternator that I hooked to the positive on the battery, I can also hook to the tach wire if I can find it...
I will read the bulletin

[Bev & Billy on Sta-sea-dawn]

Okay...I am a better sailor than an electrician.  I read the bulletin and it shows the tach connections and shows one wire coming off going to the alternator.  My alternator only has one connector on it and I hooked to the battery.  I will check Tuesday the 15/Jan. and make sure I have voltage coming out of the terminal and charging the battery.  I will attempt to connect this terminal to the tach once I figure out all the wires.

[S/V Deo Volente]

Not all Alternators have this connection, but all of them are capable of having it. If there is an alternator repair shop near you they can add a wire for the tach.