Lotus Elan

Quick way to check the voltage stabiliser

PostPost by: JonB » Sun Apr 15, 2018 8:58 am

Morning all

I have a failed coolant temperature gauge and was mucking around trying to test the connectivity. One of the Thing I tried was to hook up a light bulb between ground and the sender wire. The bulb started flashing. I take it this means my voltage controller is working (perhaps not to tolerance, but doing something). Is that right? If so, it's a really quick way to rule out the controller when the fuel / temperature gauges start acting up.

(The temperature gauge started reading something when the bulb was connected so there is no problem with it or the wiring. I ordered a new sender.)
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PostPost by: Chancer » Sun Apr 15, 2018 9:14 am

Yes, it proves that it is switching and if you use an analogue multimeter with a damped display you can get a better idea of the average voltage, the flash rate and duration of your test bulb does the same to an experienced eye.
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PostPost by: billwill » Sun Apr 15, 2018 7:10 pm

I can't think of any easy way to check the calibration of the stabilizer, other than use an oscilloscope to observer the pulse width of the flash then take that as a ratio of the full interval between flashes and multiply by the observed output voltage at the top square bit of the pulses.

Or get a big capacitor, put it across your test bulb then measure the voltage across the bulb.
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PostPost by: alan.barker » Mon Apr 16, 2018 7:37 am

Is the Fuel Gauge working :roll:
It's also feed from the Voltage Stabiliser
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PostPost by: JonB » Mon Apr 16, 2018 8:05 am

Yes it is.

However, it only ever registers just over 1/2 full when the tank is filled. There is something going on...
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PostPost by: JohnP » Mon Apr 16, 2018 8:25 am

You only really need to know when it is getting a bit empty.
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PostPost by: JonB » Mon Apr 16, 2018 9:02 am

JohnP wrote:You only really need to know when it is getting a bit empty.


That's true but you do need to be able to trust what it is saying when it is nearing empty.
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PostPost by: john.p.clegg » Mon Apr 16, 2018 9:11 am

JohnP wrote:You only really need to know when it is getting a bit empty.


Isn't there a red idiot light for that...

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PostPost by: JonB » Mon Apr 16, 2018 9:15 am

Doesn't work... :lol: ..or maybe I have never been truly empty?
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PostPost by: nigelrbfurness » Mon Apr 16, 2018 12:49 pm

Could be a fault with the tank sender or the gauge. Easiest to try another gauge, I would think.
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PostPost by: JonB » Mon Apr 16, 2018 12:52 pm

Ah.

Unwrapping the insulation from the loom in the boot and checking the wiring diagram reveals that the low fuel switch connection (on the right hand side of the sender) is actually connected to ground. The correct wire (black/brown) was tucked away under the insulation and cut short. I've reconnected it but testing the circuit (by grounding the sensor wire) does not give a light on the dash (it's on the speedometer in red), so I'll have to investigate further.

On the plus side, though, I found the boot light +ve wire (purple) in there, plus a spare ground and some 240v mains 2 core flex (!!) - dunno what that is for, yet. Speaker, perhaps.
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PostPost by: alan.barker » Mon Apr 16, 2018 5:14 pm

JonB wrote:Yes it is.

However, it only ever registers just over 1/2 full when the tank is filled. There is something going on...

If you have a reading on the Fuel Gauge then the Voltage Stabiliser is good :wink:
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PostPost by: JonB » Mon Apr 16, 2018 5:19 pm

It is definitely working, Alan, but is it working properly? I'm going to put a 'scope on it and work out the average voltage.
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PostPost by: john.p.clegg » Mon Apr 16, 2018 7:22 pm

as Chancer said ..... "if you use an analogue multimeter with a damped display you can get a better idea of the average voltage"

+1 the above...( do you need the damped display ? )

John :wink:
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PostPost by: Chancer » Mon Apr 16, 2018 8:23 pm

I would say yes, the only time Idid it was with a dirt cheap old analogue meter (all y decent ones are digital) and the needle swung up and down rapidly, fine if checking that a lamda sensor was switching but no use for judging an average voltage.

Maybe the cheapies these days have better damping, I think that the amount of damping needed for the bi-metallic regulator would make a meter too unresponsive for general use.
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