Help installing a new alternator onto an Isuzu engine

[Tasemu]

Hello!, I've been helping my friend install a new alternator onto his Isuzu engine. We are totally stumped on how to get this thing wired in. It is installed on the engine and the belt has been tensioned, however when we start the engine and rev it a bit the voltage on the batteries do not increase. I'm clueless about alternators and my friend has tried wiring it up as follows:

 

+ bolt terminal ----> +ve terminal on first leisure battery

W bolt terminal ----> -ve terminal on first leisure battery

AUX ----> he found a wire coming from the engine with a female spade connector which appears to connect to this, he tried with it connected and without it connected

 

This is surely looking very newbie to you guys right now, but we are out of ideas and would really really appreciate any help or advice as he has had no power since he bought the boat.

 

Cheers in advance for any and all help!

Edited January 22, 2020 by Tasemu

[Alan de Enfield]

18 minutes ago, Tasemu said:

Hello!, I've been helping my friend install a new alternator onto his Isuzu engine. We are totally stumped on how to get this thing wired in. It is installed on the engine and the belt has been tensioned, however when we start the engine and rev it a bit the voltage on the batteries do not increase. I'm clueless about alternators and my friend has tried wiring it up as follows:

 

+ bolt terminal ----> +ve terminal on first leisure battery

W bolt terminal ----> -ve terminal on first leisure battery

AUX ----> he found a wire coming from the engine with a female spade connector which appears to connect to this, he tried with it connected and without it connected

 

This is surely looking very newbie to you guys right now, but we are out of ideas and would really really appreciate any help or advice as he has had no power since he bought the boat.

 

Cheers in advance for any and all help!

You need to connect it thru' the ignition switch to get the 'little ignition light' working - it is this light that excites the alternator and once the alternator is generating the ignition light goes out.

 

Look for the D+ terminal.

 

From the internet :

 

If you disconnect the D+ wire from your alternator, your charging system will and will not charge depending on a few variables and circuit situations. Let's get some explanation on the functions of D+ first.

1. D+ is tapped to a small voltage through the battery light pre-energizing the field coil.
2. D+ provides earth to the battery light through the field coil thereby switching it on.
3. After the first few revs of the engine, D+ take over the excitation/energization of the field coils we have a voltage coming for the alternator side from excitor diodes. This voltage drowns the weak earth through the field coil that was switching the battery light on. Battery light therefore switches of, an indication that the system is charging.

So if D+ wire Is disconnected, The following will happen.

1. Battery light will not illuminate
2. Alternator will lose initial excitation.
3. Alternator will rely heavily on residual magnetism in the field coils.
4. After starting the engine, alternator most likely won't charge as residual magnetism is inadequate.
5. Once the engine is revved up, alternator starts charging as it begins to self excite from its own excitor diodes output.

So the short answer is, alternator won't charge at idle after starting the engine. However, after revving the engine up a bit, it'll start charging at all rpm ranges. I rest my case

Edited January 22, 2020 by Alan de Enfield

[Boater Sam]

17 minutes ago, Tasemu said:

Hello!, I've been helping my friend install a new alternator onto his Isuzu engine. We are totally stumped on how to get this thing wired in. It is installed on the engine and the belt has been tensioned, however when we start the engine and rev it a bit the voltage on the batteries do not increase. I'm clueless about alternators and my friend has tried wiring it up as follows:

 

+ bolt terminal ----> +ve terminal on first leisure battery

W bolt terminal ----> -ve terminal on first leisure battery

AUX ----> he found a wire coming from the engine with a female spade connector which appears to connect to this, he tried with it connected and without it connected

 

This is surely looking very newbie to you guys right now, but we are out of ideas and would really really appreciate any help or advice as he has had no power since he bought the boat.

 

Cheers in advance for any and all help!

Wrong, so very wrong.

 

+ Bolt to Battery + (Via isolator switch.)

W to rev counter

IND ( small tag in the socket of 3 with the spring clip ) to the ignition warning light. Whether this is the wire you found is another matter, check where it goes.

Body of alternator will be - battery connected via engine earth strap.

 

If that doesn't work, come back.

Sam.

[Jen-in-Wellies]

What is the alternator from? Is it a part supplied by Izuzu for that model engine, or one from elsewhere? Are there any part numbers? Either in the paperwork, or on the alternator.

Generally alternators are not good things to connect up by guesswork. It is possible to damage them in expensive ways when doing it wrong. Not saying that's happened, but it might.

 

Some possibilities. The three blade connectors between 9 and 10 o'clock look like a standard Lucas connector. You can get the plug for these. The two big blade connectors go to Battery +. The small blade go to the ignition warning light. The W stud at 4 o'clock goes to the tachometer for revs. I am not prepared to say this is right without more info on the alternator. I don't know where the Aux connector at 6 o'clock, or the + stud at 7 o'clock goes, or why there appear to be three + outputs, two on the Lucas socket and one stud.

 

Jen

Edited January 22, 2020 by Jen-in-Wellies

[Jen-in-Wellies]

4 minutes ago, Boater Sam said:

IND ( small tag in the socket of 3 with the spring clip ) to the ignition warning light. Whether this is the wire you found is another matter, check where it goes.

A way to test this. With ignition on, there should be 12V measured between the connector wire and ground ( with the connector disconnected from the alternator). If so, carefully touch it to a grounded bit of bare metal, like a bolt head. The alternator warning light should come on. If this happens, it is the ignition warning light. If not, you may pop a fuse!

[Tony Brooks]

Its an A127 and the two large blades are used on vehicles so one blade charges the battery while the other feeds the loads. This forms a junction that on a  boat is often on the starter pos. It also reduces the current through each blade with high loads and a low battery. For marine use  they fitted the stud B+ connection so the large blades and the stud are the same. Use the stud, the blades are likely to overheat and cause a bit of voltdrop.

 

I think the aux is simply a blade riveted to the pos diode plate and on vehicles it was for a radio suppressor connection.

 

The small blade close to the two large ones is the warning lamp connection.

 

 

Edited January 22, 2020 by Tony Brooks

[Jen-in-Wellies]

More questions for the OP. Is this going to be the only alternator on the engine, or a second alternator to charge the leisure batteries? Some of what you say implies this, but it would be good to know for sure.

If it is a new second alternator, has there ever been a second alternator on this boat before?

If it is a second alternator, then the W terminal will be unconnected as the existing alternator should be providing the signal to the tacho. It will need a 12V supply, via a small warning light bulb, or a resistor, to the small blade terminal in the Lucas three blade socket. The Battery + connection goes to the B+ stud as @Tony Brooks says. If this is a replacement for a second alternator fitted in the past, then there should be a second ignition warning light and wire already there. If this is the first time a second alternator has been fitted, then there won't be and something will need to be installed. The alternator will not charge the batteries without this connection.

 

Jen

Edited January 22, 2020 by Jen-in-Wellies

[Mike Adams]

39 minutes ago, Boater Sam said:

+ Bolt to Battery + (Via isolator switch.)

W to rev counter

IND ( small tag in the socket of 3 with the spring clip ) to the ignition warning light. Whether this is the wire you found is another matter, check where it goes.

Body of alternator will be - battery connected via engine earth strap.

 

That's how mine is wired and it works!

[Tasemu]

44 minutes ago, Boater Sam said:

Wrong, so very wrong.

 

+ Bolt to Battery + (Via isolator switch.)

W to rev counter

IND ( small tag in the socket of 3 with the spring clip ) to the ignition warning light. Whether this is the wire you found is another matter, check where it goes.

Body of alternator will be - battery connected via engine earth strap.

 

If that doesn't work, come back.

Sam.

Is it ok if we dont have a rev counter? or is it required.

[nicknorman]

If no rev counter, leave W disconnected.

[Tasemu]

30 minutes ago, nicknorman said:

If no rev counter, leave W disconnected.

Just tried moving the female spade connected to the IND socket but no luck, after revving the engine we still get no voltage jump. Maybe the connector is wrong but it goes under the engine and is in conduit with 2 other cables, both with ring terminals.

[Alan de Enfield]

2 minutes ago, Tasemu said:

Just tried moving the female spade connected to the IND socket but no luck, after revving the engine we still get no voltage jump. Maybe the connector is wrong but it goes under the engine and is in conduit with 2 other cables, both with ring terminals.

Have you just connected up some 'random' wires without sorting out where they go ?

[Tasemu]

6 minutes ago, Alan de Enfield said:

Have you just connected up some 'random' wires without sorting out where they go ?

I've just been showing him this thread and trying to help, but yeah in this case we did, as there are no other cables in the engine bay at all that we could find that were disconnected, also the conduit ends where the replaced alternator needed to be installed. Not ideal i know. ?

[Tony Brooks]

Be aware that another design of alternator may well use ring terminals instead of blades. It would help if we knew what the other alternator was.

 

MY guess is that you have one large ring and one or two smaller rings. The large ring is all but certain B+ - the + stud.

 

AS Jen explained get the other two terminals   and in turn connect a voltmeter between each terminal and negative/clean metal on the engine. The meter should read zero. Then turn on the ignition. I bet on one blade you will then get 12V if so very carefully tough the ring to the alternator body. IF the warning lamp comes on then connect that wire to the smaller of the triple blades and it should then charge.

 

I expect the other ring will be for a revcounter wire if small even though you have no revcounter although wee can't be sure because some alternators, not this one, need a live feed as well. If its a large ring then its probably a negative.. If things don't work then connect it to a fixing bolt. Before actually doing that put a voltmeter between that wire and battery positive, If it is a negative the meter should read battery voltage.

 

 

[Sir Nibble]

7 hours ago, Boater Sam said:

Wrong, so very wrong.

 

+ Bolt to Battery + (Via isolator switch.)

W to rev counter

IND ( small tag in the socket of 3 with the spring clip ) to the ignition warning light. Whether this is the wire you found is another matter, check where it goes.

Body of alternator will be - battery connected via engine earth strap.

 

If that doesn't work, come back.

Sam.

This is the 100% correct answer to the question and I am at a loss as to what the purpose of subsequent advice is. Why cloud the issue? It's an ordinary flint axe nine diode alternator. 

As an aside, the only part available for this machine is the regulator because it's a Lucas part. Rectifiers can be made by modifying a Lucas one but the problem is the unavailability of slip rings. If anyone should need one l am importing some from of all places South Africa!