t0m1980

t0m1980

Active Member
Afternoon all,

After some more of your expertise help if poss;

Just trying to find the the diode and resistor mentioned in this diagram..

2EA40E57-3634-4823-9289-2C36E99AF73F.png


So would this diode work?
https://www.autoelectricsupplies.co.uk/file_uploads/082101_spec.pdf

Also does anyone know what the resistor is?

Many thanks
 
mick 1986 said:
Without knowing the reason they are in the circuit, you can’t really guess at what value each will need to be.
Click to expand...

Do you know where or how I go about finding out that information?

Flossie said:
It's not the gubbins in the alternator is it?
Click to expand...

I have no idea, but what I have seen on line is some people suggesting it’s like an old fashion fuse holder, I found this in my parts catalog (my newest purchase.... wish I had it sooner), although it’s not crystal clear if that’s what I need?
1CE7975E-7891-4B65-A0B8-E9AA649B4C24.jpeg


I’m hoping google may be my friend today
 
t0m1980 said:
Do you know where or how I go about finding out that information?



I have no idea, but what I have seen on line is some people suggesting it’s like an old fashion fuse holder, I found this in my parts catalog (my newest purchase.... wish I had it sooner), although it’s not crystal clear if that’s what I need? View attachment 173364

I’m hoping google may be my friend today
Click to expand...

From what I could see last time I looked at the diagram, it wasn’t for the dim/dip circuit, but I wonder if it has something to do with it.

Best way to find out what it’s supposed to do is look at the circuit it’s on and see what it’s supposed to do.
 
Oh I just thought it was to protect the instrument panel, not that I know anything about electronics. It looks to go from the alternator to the battery light
512C64E2-F9F6-4945-8DCF-D5C3A5FAD3A8.jpeg
 
t0m1980 said:
Oh I just thought it was to protect the instrument panel, not that I know anything about electronics. It looks to go from the alternator to the battery light View attachment 173500
Click to expand...

I would think the resistor is to limit current through the charge light, and the diode will be to stop some sort of back feed, again to the charge light.
 
That sounds about right, hopefully they will let me know what they used, or even if it worked.

Could Flossie be on to something as technology has improved? there a way to test the cable?
 
It could possibly for stopping generated electricity from down winding motors or relays from backtracking a circuit.

When power is turned off to a fan motor for example the motor can then become a dynamo as it slows to a stop. Similarly a relay returning to rest can generate quite a strong pulse of power via its coils.
 
t0m1980 said:
Ok that sounds far too technical for me, I’m not going to lie. I’m thinking I maybe out of my depth with this......
Click to expand...
It’s easy if you think of electricity as water. As it’s pumped to a motor it turns the motor. As it’s switched off the motor still runs for a while as it slows to a stop. The motor is then a pump and tries pushing water back up the pipe risking damage to more sensitive equipment. One of your components is a one way valve and the other is a pressure release (to earth).
 
Oh by the way my series has neither and if I turn the engine off with the fan on full, the ignition light comes on until the fan motor comes to a halt.
It’s obviouslt generating enough power as a dynamo would to light the bulb up for a second or two.
Luckily very few components in a series can be called sensitive so no harm is done.

It’s the same if you fit a second battery and a split charge circuit. The large relay that switches the power on and off to your second battery should have a diode fitted so that when the electro magnet releases, the electricity generated by that magnet and coil inside the relay is sent to earth before it has chance to reach anything it can blow. Some of these relays can produce quite a lump of power even if it is only for a split second.
 
Bobsticle said:
Oh by the way my series has neither and if I turn the engine off with the fan on full, the ignition light comes on until the fan motor comes to a halt.
It’s obviouslt generating enough power as a dynamo would to light the bulb up for a second or two.
Luckily very few components in a series can be called sensitive so no harm is done.

It’s the same if you fit a second battery and a split charge circuit. The large relay that switches the power on and off to your second battery should have a diode fitted so that when the electro magnet releases, the electricity generated by that magnet and coil inside the relay is sent to earth before it has chance to reach anything it can blow. Some of these relays can produce quite a lump of power even if it is only for a split second.
Click to expand...

Thanks Bob, I have a little understanding of how it works, I was getting worried I wouldn't be able to find the correct diode, which again mystery has saved the day! But interestingly, I'm curious about what you have said about the split charge system as I will be running a split charge system and one of those twin alternator set up from Gwyn Lewis (although admittedly I haven't looked too much into it as yet, I'm just thinking for extras like a winch etc.), so are you saying I wouldn't need to bother with the diodes because they would run through a relay and would that be wired up to both alternators and then where do I stand with regards to the resistor in the diagram?

As I said I'm no electrician by any stretch of the imagination, but I can almost work out the whole diagram that mystery has kindly posted as it's very easy to read, in fact the only thing I don't understand as yet is why from the ignition switch there is a white and black which goes to orange and red and then to a yellow and black, why that isn't one wire is beyond me, but it maybe come obvious when I get that far in lol.
 
The diode sits in the charge indicator circuit to make it work basically and excite the field.

So the way it works is that the battery lamp gets 12V via the ignition, at the same time the alternators field has also been energised and this is the easiest route to ground (through the diode), so power goes in via ignition, through the lamp, through the diode, into the field, then to deck, then once the alt starts to generate itself then there is no flow as it's the same voltage as the battery, so power will not flow as there is no potential difference between the batt and the alternator, however they put a diode into the circuit because it is possible that the alternator voltage will be slightly higher at this point on the system than the feed to to ignition (impedance in connections etc.) and without the diode the lamp would possibly faintly glow as it then works the opposite way.

The resistor should be about the same resistance as the lamp (75Ohm's from memory... check that though) and is an alternative to the lamp, i.e. if the lamp blows, the alternator will still work - if the circuit went open, i.e. blown lamp and no resistor then there would be no way to excite the field. They do not directly connect without a resistor or the lamp would not light as it would bypass the lamp and go directly along the wire.
 
mick 1986 said:
I would think the resistor is to limit current through the charge light, and the diode will be to stop some sort of back feed, again to the charge light.
Click to expand...
Look at the circuit again... the circuit is sort of figure of 8 - with the lamp across the top of the 8 and the resistor in the middle of the 8 and the feeds are from the bottom of the 8 so the res and lamp are in parallel - thus it is a balancing circuit and incorporated redundancy.
 
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