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Hi!

I have 2 HMI alternators on my engine, and I'd like to figure out the wiring, mainly because my tacho isn't registering any revs so it may be a dodgy connection to the alternator.

I've taken 2 photos, the first alternator has a red battery lead and a green/yellow wire plugged into the IND terminal. The second alternator has a brown battery lead, a black lead connected to the casing, and a blue/black wire connected at the W terminal, which I think is for the alternator. There is nothing in the IND terminal (is this correct?), however there is an unplugged brown wire hovering close to this terminal - I don't know if it should be plugged in or not.

 

I'll do some probing with the multimeter but basically I wanted to ask if anyone here can help me identify what is what.

 

To test the alternator signal, I probed the W terminal (on the 2nd alternator, where the blue/black wire is), and there is no voltage. However, on the first alternator, the W terminal shows 15-16V, but it is not connected to anything. Could I simply move the blue/black tacho wire to the W terminal on the other alternator that does seem to be producing a signal?

 

Thanks for any help!

Graham

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Did you have your multimeter on ac I think the whizzometer terminal is an AC signal. 

 

Do you have two charge lights ? Might be worth seeing if there is an ignition controlled +12 V on the brown lead and then touch it to earth to see if a charge light comes on if so then it could be the second alt isn't being excited and therefore no signal to the tach ?

 

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Not really enough info to be sure, but if we presume that the alternators are connected in parallel (as opposed to one for the domestic bank and one for engine battery) then a possible scenario is that the first alternator you mention is working correctly - but the tachometer isn’t connected to that one. The second alternator isn’t working and hence there is no signal on the W connector for the tachometer.

Why isn’t it working? Well many types of alternator require a connection via a warning light from the IND terminal to the battery. As the engine is started, the modest current flowing through the warning light into the alternator provides some magnetic field tomget the alternator to start generating power.

 

So yes moving the tachometer to the other alternator’s W connection should get the tachometer working. But I’d still be concerned that the second alternator wasn’t doing anything.

 

try tracing the wire that is hanging off. Where does it go? If to a light on the instrument panel I think we can be fairly sure it should be connected to the IND terminal.

 

My caveat on all this is that I don’t have sufficient knowledge to know whether that specific type of alternator requires a warning light to be connected for it to work. Some don’t. But then, why isn’t the second alternator’s W connection doing anything?

 

And to my untrained eye it looks very much like a Lucas A127 type alternator which does require the current from a warning light to get it going.

Edited by nicknorman

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Standard wiring for HMI Isuzu (and Engines Plus/Canaline) seems to be to use black/yellow for one charge indicator lamp and brown/yellow for the other. So it looks like the brown/yellow wire has fallen off the ind terminal in the second picture. The thick black wire is battery negative to the casing of the alternator; on some engines they fitted insulated return alternators, and the black wire would be attached to the B- terminal.

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I think I noticed that the first photo has a round feature with what may be threaded stud inside it marked W. W is frequently the alternator terminal. The regulator looks A127 ish but the drive end bracket does not so I can not be 100% sure this is correct. It has the main output lead connected and the warning lamp lead so this one does not drive a rev counter.

 

The second photo looks to be a similar type but the black and  blue wire APPEARS to be connected to the W terminal as far as the photo allows me to see. IF it is the W terminal this is the rev counter feed. The main charging lead is in place but I expect another one IF its a 9 diode machine, the warning lamp wire. The regulator shape and the blade terminal cutout in the case suggest it is. I suspect that brown and yellow wire is the warning lamp wire for that machine and would go onto the single 6mm blade in that case cutout. However I would expect that alternator to remain dead without warning lamp excitation unless you revved the engine to flat out and even then few energise. I would also expect the warning lamp to be oit all the time unless the  Br&Y cables shorting to metal and in that case it would be on all the time.

 

1st photo - Take the black and blue wire off & insulate it. Turn on the ignition & does a charge warning lamp now not work. If so it is probably the warning lamp wire. Now carefully short the terminal on the wire to clean metal. If the lamp comes on its definitely the warning lamp wire , if not its the rev counter wire. Repeat for the black & yellow wire that is in the cutout. I expect that one will behave as above and will prove to be the warning lamp wire. NOTE:- just in case its   an odd alternator take a bit of care with the shorting to metal, wipe the terminal across the metal and if you get massive sparks stop at once, its  alive wire , although the warning lamp current may cause a small spark.

 

2nd photo - I cant see how the alternator energises and i cant see how it would produce any signal for the revcounter. Basically pull the brown and yellow wire up and repeat the warning lamp wire tests above BUT this time first put a voltmeter (20V DC) between the wire terminal and  clean metal. . With the ignition off it should read zero. Turn the ignition on and it should read battery voltage IF its the warning lamp wire. If it does repeat the tests above and if they confirm its the warning lamp wire connect it to the 6mm blade in the cutout.

 

That should allow that alternator to work and drive the revcounter. If not report back

 

 

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Just seen EEyor's post and it seems to agree. The first photo is probably the engine alternator (because the engine block is connected to battery negative so that means the alternator case is as well so this provides the negative connection. The second photo is probably of the domestic alternator and although the engine and domestic bank should have joined negatives so the same applies I expect someone did not realise this and provided the negative. Nothing  wrong with this at all except the alternators are usually striven from the engine alternator - for no good reason apart from the marniser's ease and some people's logic..

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Thank you all for your very helpful replies. I've finally got around to figuring this out.

Ditchcrawler: No I don't have a Sterling charge controller.

Jonathan, Nick, Eeyore, Tony: I have done some checks and can confirm that the brown/yellow wire from the alternator in photo 2 goes to the charge warning lamp, and the blue/black wire connects the W terminal on this alternator to the tacho. The black/yellow wire on the alternator in photo 1 goes to the other charge warning lamp. Neither of the charge lamps lit up during ignition so my first checks were the bulbs:

The bulb for the second alternator is ok but the connections had corroded so it was an open circuit. I've cleaned these connections and this is now working as it should.

The bulb for the first alternator is blown so I am looking for a replacement but I'm struggling to find any. What is this type of bulb called? (please see attached photo).

I'll report back if this improves things or uncovers another problem. I'll start the engine tonight to see if the tacho now works.

Also, there are small ceramic blocks wired in parallel with the lamps (see other attached photo). One of the connections has corroded and come off. Are these resistors?

 

Thanks for all your help,

Graham

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The ceramic block is indeed a resistor. It is 47 ohms, which is about the reistance of an alternator warning bulb, so it has probably been fitted to do the bulbs other job of energising the alternators coils so they can start charging. I don't know the bulb type in the other picture, but it looks very small and may not pass enough current to get the alternator energised, hence the low value resistor has been added. This is a common modification when people fit LED alternator warning indicators, for the same reason. If the rwisitor was needed before, then it will need replacing as well as the bulb. The wire may well have broken from vibration. It doesn't look well supported.

 

Jen

Edited by Jen-in-Wellies

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The ceramic blocks are wire wound resistors probably about 5 watts.  To get the alternator to power up when it starts it uses the warning light, but if the bulb is too low powered it won’t work.  Solution is to either use a brighter bulb or increase the current by putting a resistor in parallel.  The resistance value is not critical, and in your case a 47ohm resistor has been used.  47ohms at 12v is just over 3 Watts, so the resistor needs to be a bit chunky.  You can get them on eBay, look for ‘5w 47r’ 

 

Added Jen beat me, I’m getting slow at typing

Edited by Chewbacka
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That resistor is 5 watts 4.7 ohms, thats 4 point 7 ohms not 47.

The bulb is a slide in fitting, not easy to source. It was an early capless design. As a rule of thumb the bulb needs to be at least 2.2 watts to energise an alternator.

If less then a resistor such as you have wired across the bulb will pass sufficient current to energise the alternator. 4.7 ohms seems too low a value, it will pass too much current at 12v hence it will burn out. I would suggest the resistor needs to be 100 ohms with a low wattage bulb or LED in use or 68 ohms without a bulb. 5 watt will be ample but it will get warm, keep it away from wiring.

You could mount any 12v 2w bulb behind the lens to do the job, a miniature screw or capless or miniature bayonet, in a suitable holder.

Edited by Boater Sam
added more

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If no one here can help with the bulb type, take it to a local motor factors. If you can, find one with a knowledgeable staff member who can cope with you not being able to give them a car registration number. They should be able to help and get you a couple of spares for a few pennies.

Jen

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2 minutes ago, Boater Sam said:

That resistor is 5 watts 4.7 ohms, thats 4 point 7 ohms not 47.

The bulb is a slide in fitting, not easy to source. It was an early capless design. As a rule of thumb the bulb needs to be at least 2.2 watts to energise an alternator.

If less then a resistor such as you have wired across the bulb will pass sufficient current to energise the alternator. 4.7 ohms seems too low a value, it will pass too much current at 12v hence it will burn out. I would suggest the resistor needs to be 100 ohms with a low wattage bulb or LED in use.

Well spotted. In my defense, I was trying to zoom the picture on my phone! I've used two 15 ohm 5W resistors in series to give 30 ohm in parallel to an LED succesfully, which lead me to see 47R, not 4R7.

 

Jen

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Er, but it does say 47RJ. To be precise, it says "47RJ CY 1W" - which may mean it is rated at 1 watt, not the 5 watts suggested by Boater Sam?

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The code printed on the side of the resistor is 47RJ.  I take this to mean it’s 47 ohms.

added - the J is the tolerance which is 5%

 

as to the bulb, is anything printed on the metal plates on the side?

 

added - I was curious about the bulb and it looks like a T5.5 base which you can get on eBay, 

https://www.ebay.co.uk/itm/T5-5-12V-100ma-Slide-Bulb-x-2/321583551934?hash=item4adfdf95be:g:vtgAAOSwuMFUY82q

 

or

https://www.ebay.co.uk/itm/2x-LAMP-6020-Filament-lamp-telephone-T5-5-12V-100mA-Bulb-T1-3-4-4-8mm/192225689025?hash=item2cc18b3dc1:g:mi0AAOSwDrNZTHte

Edited by Chewbacka

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Sorry,  you are all correct, I'm upside down, it is 47 ohms. Still a bit low value in by opinion.

The bulb looks like a telephone indicator slide wedge bulb but they are all 24v.

Edited by Boater Sam
added more

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For the sake of less knowledgeable members reading this thread.

 

Often on such resistors an R takes the place of a decimal point and R means in effect "Ohms" so 47R = 47 ohms. 4R7 would mean 4.7 ohms.

  • Greenie 1

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30 minutes ago, Boater Sam said:

Sorry,  you are all correct, I'm upside down, it is 47 ohms. Still a bit low value in by opinion.

The bulb looks like a telephone indicator slide wedge bulb but they are all 24v.

The bulbs I linked to on eBay are 12v, though most with that base are 24v or higher.

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Great, thanks for all the replies!

I've ordered a couple of the new bulbs from ebay, and got a couple of new 68 ohm resistors from work.

If my calculations are correct:

New bulb is 12V, 100mA, so consumes 1.2W, and the 68-ohm resistor will consume 2.1W, giving a total power consumption of 3.3W which hopefully is enough for energising the alternator.

The old (blown) bulb says 12V, 2W, so with the 47-ohm resistor this gives a total of 5W.

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Leave your 47 ohm resistors in. They are sound or your batteries would be flat.Start messing with the values and you may run into problems with cutting in speed. They carry no current at all once the lamp is out so have an easy life. If it ain't broke, don't fix it.

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9 minutes ago, Sir Nibble said:

Leave your 47 ohm resistors in. They are sound or your batteries would be flat.Start messing with the values and you may run into problems with cutting in speed. They carry no current at all once the lamp is out so have an easy life. If it ain't broke, don't fix it.

But it is broke!

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There is a wire off the D+ on one of the alternators, that doesn't warrant new resistors, there's bulbs blown, that doesn't warrant new resistors either. There may be one blown but there is no evidence that this might be the case and it's not very likely.

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7 minutes ago, Sir Nibble said:

There is a wire off the D+ on one of the alternators, that doesn't warrant new resistors, there's bulbs blown, that doesn't warrant new resistors either. There may be one blown but there is no evidence that this might be the case and it's not very likely.

Did you see the picture of the corroded resistor with the lead detached at the casing? A new resistor is definitely required.

0EB749E4-AAF2-4BFE-9911-A3B77C68C45A.png.780ef7c90b4a8412b9f2a17e08a6729c.png

Edited by nicknorman

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2 minutes ago, nicknorman said:

Did you see the picture of the corroded resistor with the lead detached at the casing? A new resistor is definitely required.

 Not if the alternator is energising to the questioner's satisfaction its not - once the new bulb is fitted. However I think the OP said the new bulb will be of a lower wattage so a resister may still be needed at that point.

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27 minutes ago, nicknorman said:

Did you see the picture of the corroded resistor with the lead detached at the casing? A new resistor is definitely required.

0EB749E4-AAF2-4BFE-9911-A3B77C68C45A.png.780ef7c90b4a8412b9f2a17e08a6729c.png

HA! No. I stand corrected. I would still replace it like for like though.

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