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Altenator Terminals Question

Biggles
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alan_fincher Veteran II

alan_fincher

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Hi

 

Can someone tell me what the 'W' terminal is for please. I know what the other 2 are for 'B+' & 'D+'. If it is the warning / charge light how is it wired up ?

 

Biggles

It can be used to drive a rev counter (tachometer).

 

I've no idea why the chosen letter is "W" though.....

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alan_fincher Veteran II

alan_fincher

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Your learned friend is wrong

Actually if you don's assume it means the charge warning light, he could just be right.....

 

W TERMINAL

 

A seperate (sic) low voltage output terminal on the alternator which is used to operate a tach or RPM warning light.

Edited by alan_fincher
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RobinJ Experienced

RobinJ

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Your learned friend is wrong

This confuses me, I think because some of the old car manuals labelled it W.

On the alternator the warning light connection should be labelled I or D and the connection for the tacho W or T.

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Sir Nibble Veteran II

Sir Nibble

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W is an ac output from one of the three phases W P and R. Most Japanese units use P, only Delco use R. It could also be marked S or STA. Some alternators have another terminal connecting to the neutral point between the phases, N, or C if you're Italian. Some very old alternators (10/11AC) used this terminal to operate a hot wire device to turn off the warning light. More recently, for many years Japanese alternators were +ve regulated with vibrating contact regulators and had a relay powered again, from ac to operate the warning light.

What was the question again?

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Biggles Veteran

Biggles

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W is an ac output from one of the three phases W P and R. Most Japanese units use P, only Delco use R. It could also be marked S or STA. Some alternators have another terminal connecting to the neutral point between the phases, N, or C if you're Italian. Some very old alternators (10/11AC) used this terminal to operate a hot wire device to turn off the warning light. More recently, for many years Japanese alternators were +ve regulated with vibrating contact regulators and had a relay powered again, from ac to operate the warning light.

What was the question again?

 

 

OK Thanks chaps

 

Seems it is not a warning light terminal, this then brings on 2 more questions.

 

1. If it is a rev counter how can it be accurate as the input pulley will vary model to model and won't show a true engine speed, although it will show a alternator RPM.

 

2. How does the warning light wire up, and what makes it go out. Currently I have no red light on my NB

 

Biggles

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alan_fincher Veteran II

alan_fincher

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1. If it is a rev counter how can it be accurate as the input pulley will vary model to model and won't show a true engine speed, although it will show a alternator RPM.

I believe the tachometer has to be calibrated for your particular engine. Ive not done this, but I'd expect some kind of potentiometer adjustment on it.

 

The next question, which I don't know the answer to, is how do you know your engine is turning at (say) 1000rpm, when you adjust the tachometer to say 1000rpm.

 

Somebody, please ?

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Timleech Veteran II

Timleech

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I believe the tachometer has to be calibrated for your particular engine. Ive not done this, but I'd expect some kind of potentiometer adjustment on it.

 

The next question, which I don't know the answer to, is how do you know your engine is turning at (say) 1000rpm, when you adjust the tachometer to say 1000rpm.

 

Somebody, please ?

 

You check it with another tachometer :D

 

It would normally be done in the factory or marinisers workshop where they should have the proper gear, but there are fairly simple hand-held tachos available in various forms.

 

Tim

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Biggles Veteran

Biggles

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Well the RPM is no problem as I have a hand held lazer tacho, just need to find out how to calibrate it if I ever decide to for a tacho

 

So more importantly how do I get a warning light set up on my NB?

 

Biggles

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Keeping Up Veteran II

Keeping UpDonate to Canal World

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Well the RPM is no problem as I have a hand held lazer tacho, just need to find out how to calibrate it if I ever decide to for a tacho

 

So more importantly how do I get a warning light set up on my NB?

 

Biggles

Normally the "ignition" switch feeds one end of the lamp, and the other end of the lamp goes to D+. It's as simple as that.

 

When you switch on, the current flows through the lamp (which therefore lights up) and that's what starts the alternator going. The alternator springs into life and produces volts, some of which it feeds internally to its D+ terminal so it stays energised. This means there's the same number of volts on both sides of the lamp, so it goes out.

 

Are you saying yours is working at the moment without a lamp?

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RobinJ Experienced

RobinJ

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You check it with another tachometer :D

Some do have a twiddly pot, some (digital) have a set of switches (some don't seem to have any adjustment).

Fiddle Factor = (Crank size/Alternator size)*(Alternator poles/2)

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Sir Nibble Veteran II

Sir Nibble

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I believe the tachometer has to be calibrated for your particular engine. Ive not done this, but I'd expect some kind of potentiometer adjustment on it.

 

The next question, which I don't know the answer to, is how do you know your engine is turning at (say) 1000rpm, when you adjust the tachometer to say 1000rpm.

 

Somebody, please ?

The tacho comes with a little instruction sheet and a formula to do a little mathematics with the engine and alternator pulley sizes. You compare the result with a little table which indicates a compination of positions for little switches on the back of the tacho. Fine adjustment is by a small potentiometer and the instructions say to set it against the governed no load speed of the engine, I prefer to use a hand held tacho for that bit.

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Biggles Veteran

Biggles

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Normally the "ignition" switch feeds one end of the lamp, and the other end of the lamp goes to D+. It's as simple as that.

 

When you switch on, the current flows through the lamp (which therefore lights up) and that's what starts the alternator going. The alternator springs into life and produces volts, some of which it feeds internally to its D+ terminal so it stays energised. This means there's the same number of volts on both sides of the lamp, so it goes out.

 

Are you saying yours is working at the moment without a lamp?

 

 

Yep I have no warning lamp at all. So it is a simple as that a light in from the ignition energizing line , no negative, no relays. So I assume a buzzer could be put in there too to warn that the key was still on as I have a pull to stop on my NB.

 

If it is that simple no wunder I couldn't work it out. I had all sorts of complicated ideas.

 

Biggles

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