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Gauges reading high with electronic IVR.
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990V8 View Drop Down
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    Posted: Apr/25/2019 at 3:53am
In another thread, which I must finish off when I get the pictures from my camera, it was suggested that I replace the Instrument Voltage Regulator in my 63 Ambo with the electronic version, the LM7805.
Which I did.
Like this
 
In the event, my old IVR was good. Yes, I have a working IVR - for sale, $10,000 plus shipping haha.
 
Testing the old IVR it was interesting to watch the output on the DVM. Zero, then 4V then 5V then zero quite a long time then 4V etc etc.
In contrast, the electronic gives a steady 5.15V.
 
Now, the fuel and temp gauges are reading high. The fuel tells me I have a half tank when I know there was a quarter, and the temp is reading near the top whereas it always read near the middle. And I've done nothing at all this winter that would affect the cooling or running.
 
So I suppose I'm seeing the effect of 5V all the time instead of 5V intermittently.
 
I can correct the fuel with this calibrator that I've ordered
and I can put a ten-turn pot on the temp sender and wind the gauge back to the middle (after checking the radiator with a remote thermometer just to make sure) but I wondered whether anyone else had seen this difference in their gauges with the electronic IVR?
 
Ivor


Edited by 990V8 - Apr/25/2019 at 2:21pm
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Originally posted by 990V8 990V8 wrote:

Testing the old IVR it was interesting to watch the output on the DVM. Zero, then 4V then 5V then zero quite a long time then 4V etc etc.
In contrast, the electronic gives a steady 5.15V.


Something is awry here.  Typically the IVR pulses between 0 volt and 12 volts.  The time you have voltage divided by the total time, voltage+no voltage is the fraction of 12 volts that the gauges see.  That's why I'm a fan, and have said so, of the RTE solid state limiter rather than the LM7805 route.
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Originally posted by 6PakBee 6PakBee wrote:

Something is awry here.  Typically the IVR pulses between 0 volt and 12 volts.  The time you have voltage divided by the total time, voltage+no voltage is the fraction of 12 volts that the gauges see.  That's why I'm a fan, and have said so, of the RTE solid state limiter rather than the LM7805 route.
 
Oh. So the old IVR wasn't working properly after all?
 
In fact, the reason the gauges died was that the track on the PCB was fractured.
 
I have a couple more old-style (Lucas) IVRs, I'll have a look and see how they read. It may be that my DVM just isn't fast enough to 'see' the 12V.
 
Yes, I had noticed your post about the RTE, thankyou, but I can get the 7805 easily over here. not so the RTE. Sometimes, good enough has to be good enough.
 
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Originally posted by 990V8 990V8 wrote:

Originally posted by 6PakBee 6PakBee wrote:

Something is awry here.  Typically the IVR pulses between 0 volt and 12 volts.  The time you have voltage divided by the total time, voltage+no voltage is the fraction of 12 volts that the gauges see.  That's why I'm a fan, and have said so, of the RTE solid state limiter rather than the LM7805 route.

 
Oh. So the old IVR wasn't working properly after all?
 
In fact, the reason the gauges died was that the track on the PCB was fractured.
 
I have a couple more old-style (Lucas) IVRs, I'll have a look and see how they read. It may be that my DVM just isn't fast enough to 'see' the 12V.
 
Yes, I had noticed your post about the RTE, thankyou, but I can get the 7805 easily over here. not so the RTE. Sometimes, good enough has to be good enough.
 
Ivor


I bet there may be another break in the trace. I would follow along each trace to the gauges touching pin/pad locations to ohm and find where there may be a broken trace.

I have seen a few newer pin styles with loose pins, and cuts under where things mount with nuts or components being overly tightened.
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Originally posted by 6PakBee 6PakBee wrote:

Originally posted by 990V8 990V8 wrote:

Testing the old IVR it was interesting to watch the output on the DVM. Zero, then 4V then 5V then zero quite a long time then 4V etc etc.
In contrast, the electronic gives a steady 5.15V.


Something is awry here.  Typically the IVR pulses between 0 volt and 12 volts. ..
It is likely that the switching speed of the IVR is too fast for the DVM. It is averaging the voltage it sees over time. The display on the DVM simply can't catch up in time before the pulse disappears.  Nothing is awry IMO.
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Originally posted by 990V8 990V8 wrote:

Oh. So the old IVR wasn't working properly after all?
From your description, it sounds to me like it was working just fine.
 
Originally posted by 990V8 990V8 wrote:

Yes, I had noticed your post about the RTE, thankyou, but I can get the 7805 easily over here. not so the RTE. Sometimes, good enough has to be good enough.
Fix the bad track on the cluster PWB and you might find you don't need a new IVR. Chosing between RTE or 7805 may become moot.
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is your DVM "auto-ranging"?

very many -- most -- DVMs (digital volt meters) behave very poorly when voltages vary at slow rates, and intermittent regulators are one of the things a DVM can't really measure.

voltage is zero: the DVM tries it's 100V range, then 10V, then 1V, ... then the IVR goes ON: the DVM, on the 1V range, overloads then goes to 10V, then 100V, ... then the voltage goes off and...

if you can manually select it's range then it might be less misleading.

the old IVRs are make-or-break, on or off. i'd say it's impossible to read in between,and they usually fail open==off.

if you have an old analog pointer meter, though they are limited in what they do, have often poor accuracy, and often draw current from the thing they're measuring, they do have the advantage of being nicely behaved, because the sheer physicality of the D'Arsonval meter movement is grokkable.
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