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Tell tale dash lights


zhap135
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Am wiring up dash lights. Have some led telltales that work  (from CBS) indicators, beam and hazards work fine

So far so simple, the alt warning light, ( or the oil light and the brake fluid light) are not coming on when the ignition switch is on.

Alt Warning. Have traced the wire back and there is a circuit. My question I suppose is whether a straight forward circuit for this light is adequate, or is there something I'm missing

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You may find that the LED charge light wont go out when the engine starts. An LED doesnt put enough load to "excite"  the alternator circuit.

My heath robinson fix was to insert a small socket and bulb in the circuit but hidden under the dash.

Apologies in advance to any real leccies out there, who are either laughing  their socks off, or grinding their teeth.

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9 minutes ago, Bob Tucker said:

You may find that the LED charge light wont go out when the engine starts. An LED doesnt put enough load to "excite"  the alternator circuit.

My heath robinson fix was to insert a small socket and bulb in the circuit but hidden under the dash.

Apologies in advance to any real leccies out there, who are either laughing  their socks off, or grinding their teeth.

LOL, any bodge that works is a good bodge!. Thanks, will give this a try.

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27 minutes ago, nelmo said:

LEDs are polarity-sensitive so try just swapping the wires round. 

Thanks for that , I've got them all to a common earth and have tested each bulb individually, so don't think it's the polarity, but will have a look, thanks!

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Posted (edited)
39 minutes ago, IanS said:

Oil and handbrake/brake fluid lights need to be wired to live. the switches connect to earth.

Aaaaah, that makes sense, I see what you mean. I shall give that a go

[edit] Just to be clear, the Alt telltale lien from the aternator is not wired in that way , but is pos?

Edited by zhap135
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Posted (edited)

So another clarification, I'm not using a standard sierra FB or console. I just found in one of the ford forums a post that the alternator needs the console wired in to charge the battery as that is required to excite the field coils ( also touched on by Bob T above). This got me thinking, could this be connected to my issue, as I have pretty much replaced most of the wiring with new?

 

[edit] Looking at the old console, the lighting circs  seem to be just that , with no further componentry

I guess tomorrow I'll test the alternator and check that it is working and go from there

Edited by zhap135
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Rev most alternators fast enough and they will self excite.

This relies on residual magnetism in the rotating exciting iron pole pieces.

Typicaly engine needs to get to 1500 - 2000 RPM with 2.5 to 1 pully diameter  running the alternator at 3750 to 5000 RPM.

Once started alternators will self excite down to very low RPM.

New alternators might not self excite first time run and need the light for the first run only.

Forgot to add bulb is a usefull indicator of snapped drive belt.

Edited by IanS
missing bit of info
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1 hour ago, Pintogogo said:

I put a number plate lamp under bonnet in parallel with ignition light to excite alternator

Snap for that fix --- & I am an old school electrician ( retired 16 years ago from industrial work)

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10 hours ago, Pintogogo said:

I put a number plate lamp under bonnet in parallel with ignition light to excite alternator

Thanks PG, will have a look at that - any reason under the bonnet specifically rather than behind the dash?

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Posted (edited)
10 hours ago, IanS said:

Rev most alternators fast enough and they will self excite.

This relies on residual magnetism in the rotating exciting iron pole pieces.

Typicaly engine needs to get to 1500 - 2000 RPM with 2.5 to 1 pully diameter  running the alternator at 3750 to 5000 RPM.

Once started alternators will self excite down to very low RPM.

New alternators might not self excite first time run and need the light for the first run only.

Forgot to add bulb is a usefull indicator of snapped drive belt.

Thanks Ian - forgive me , I'm not an electrician or a mechanic by trade but am learning things as I go along

So the alternator does not charge necessarily at low revs or initially. when not charging the warning light is on. When the engine speeds enough for the alt and starts charging the warning light extinguishes? When this light is on it indicates that the polarity over the alternator is insufficient to charge the battery?

Edited by zhap135
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Correct, alternator light on battery not being charged.

In the old days this light was labled ignition or IGN. On old instalations using a dynamo it was common to see this glow at tickover. Dynamoes needed a longer shaft to include the comutator and so needed a bigger pully to prevent shaft whip due to over speed.

Adds a bit of history🙂

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50 minutes ago, IanS said:

Correct, alternator light on battery not being charged.

In the old days this light was labled ignition or IGN. On old instalations using a dynamo it was common to see this glow at tickover. Dynamoes needed a longer shaft to include the comutator and so needed a bigger pully to prevent shaft whip due to over speed.

Adds a bit of history🙂

Brilliant, love a bit of history me!

So my light not being on at all (with a sound connection and a tested light) when tried with either polarity might suggest a fundamental issue with teh Alt.

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