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Resistance wire

Submitted by michel_crowhurst on Sun, 15/04/2012
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Light Twins

Hi Guys,

Since getting my basket-case Navigator running last year I've been wondering why I've had random readings from my ammeter. I bunged meters across various points and even altered where it sits in the wiring, with no success. In the end I bypassed the ammeter completely. Then a guy at work said it sounded like a resistance wire problem, which I hadn't thought of.

I had to buy a new loom when rebuilding it, but there's no resistance wire in the new loom. Is there a way of simulating the resistance wire with a resistor?

Submitted by alan_dawes on Mon, 16/04/2012

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It's easier to get a replacement ammeter than faffing about replacing the shunt (which I assume you mean). Variable readings from an old Lucas ammeter are not necessarily caused by a poorly connected shunt anyway. Original and reproduction ammeters are plentiful on Fleabay etc at a reasonable price.

Cheers

Alan

Submitted by tony_ripley on Wed, 18/04/2012

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Hi,

Just to clarify, the resistance wire is not the ammeter shunt. The resistance wire runs from the light switch to frame earth down close to the battery. It comes into circuit when the ignition is on and the lights are off or on side lights. Remember that when the lights are off you have one set of coils from thealternator, when the lights are on you have both sets of coils. If the headlights are on you need all the amps you can get, with the sidelights on you need to load the system slightly so it does not blow the side lights.

If your loom has a normal wire where the circuit diagram shows a resistance wire then you will have problems.

What do you mean by random readings ?

When you turn the ignition on you may or may not get a reading on the ammeter depending on the status of the points, if they are closed you will see a discharge, if open you should see no movement.

With the ignition off turning the side lights on will show a small discharge. The head lights will show a large discharge. The brake lights and horn do not go via the ammeter so will show nothing.

Once the engine is running it is fairly normal for the meter to flap about wildly, this is more down to vibration than anything else.

Have you rewired according to the manual ? If so what do you have where the resistance wire is shown ?

Regards

Tony

Submitted by tony_ripley on Wed, 18/04/2012

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Hi,

Got itslightlywrong, the resistance wire is only in circuit when the lights are all off.

All off - one set of coils - resistance wire in circuit.

Side lights - one set of coils - no resistance wire.

Head lights - two sets of coils - no resistance wire.

Tony

Submitted by michel_crowhurst on Mon, 07/05/2012

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Hi Tony,

Many thanks for the information - I suspected the resistance wire was there to balance the circuits up under different loads.

However, your excellent explanation may not help me as I have messed around with the electrics somewhat! It's now 12V with Boyer ignition and a modern reg/rectifier, so running the alternator coils in series. I know - I'm a bad man! :)

In case it makes any sense though, the symptoms are as follows:

With ignition on there is a tiny -ve reading which I'd expect from the Boyer electronics. Lights show loads as expected. But, on starting, the reading goes up to about 4A for a couple of minutes, then slowly drops to about -1A. With lights on the reading drops to -4ish.

But putting a meter across the battery shows it is charging at about 15V, 0.5A with lights on. I've put 500 miles on it in this state and had no electrical troubles at all. I've actually bypassed the ammeter completely now.

Cheers,

Michel.

Submitted by tony_ripley on Tue, 08/05/2012

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Hi Michel,

Until recently I had an Electra with the same setup. Ignition on, small discharge. gently turn the engine over until the boyer sees that the engine is turning, higher discharge, maybe 4A.

Start the bike, you have been taking volts out of the battery so the charging system does what it should and shows a charge of 4A or so. This only lasts until the battery is up to voltage and then reduces.

It sound like it is all working OK. If you have been using the lights and it is still running then enjoy.

Regards

Tony

Submitted by michel_crowhurst on Fri, 29/06/2012

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Thanks Tony,

Sorry for the delay in coming back to you, but the head gasket blew, so I've not had a chance to play around with the electrics.

I'm glad I'm not the only one to have noticed this anomaly with the ammeter readings! :) I'm happy to keep it running as-is as I'm confident the battery is being charged, regardless of what the ammeter thinks.

Regards,

Michel.

 


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