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Go Back   Madabout Kitcars Forum > Mad Build Area > Marlin Sportster, Cabrio, Berlinetta and Roadster builds

Marlin Sportster, Cabrio, Berlinetta and Roadster builds Enthused or Confused about your vintage Marlin build? Ask away here or show off your build.

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  #1  
Old 18th September 2016, 17:01
mcramsay mcramsay is offline
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Default Any electronic wizards around?

I have had major trouble getting my stack speedo to work correctly, and it's the last issue on my car to sort out, iva is booked for 19th of October so I have some time to sort it

Bit of background info, stack speedo with a 3 wire Hall effect sensor mounted on the drivers side inner cv joint picking up a bolt head glued on the joint.

I have had issues where the speedo has been counting pulses that don't exist( when calibrating the speedo you put it into calibration mode and you can watch it counting pulses. So after lots of testing and even sending the unit back for testing at the factory I have found the issue. All the wiring for the car runs in one loom to the rear, when in calibration mode with the wheels not spinning the Lp facet fuel pump is inducing a voltage causing the speedo to read haywire. With an oscilloscope on the trigger wire I can see a very noisy signal along with pulsing AC waves which will also affect the reading. I bypassed the signal wire for the speedo to move it away from the fuel pump wiring, this worked temporarily however I think I may be getting some AC induced into the 12v supply to the sensor which is then traveling back up the signal wire. All a bit complicated I know... Even more weird is that it takes around 5 mins of the fuel pump running to start affecting the speedo. If I unplug the pump the speedo instantly behaves normally.

So the easy answer is to move the fuel pump wiring away from the speedo wiring but I will have to take half the car apart to do so.

Is there anything I can put in line on the supply and signal wires on the speedo to remove any induced noise?
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Old 18th September 2016, 20:37
phil.coyle phil.coyle is offline
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Go to Maplin's and by a diode about 70pence tell them what voltage etc. that you want it for and make sure you ask which way the current travels through it, they usually are marked with a coloured band on the outlet end.
What a diode does is allows a current to flow in one direction only and stops any reversed spikes, ideal for rev counters picking up a feed from the coil or EFi injectors.
You can carefully crimp some wiring terminals on it and wire it in line, I don't recommend soldering.

On second thoughts buy a few, they come in handy.
p.s. I am not a wizard and if there are some leccy techy people about feel free to correct me.

Last edited by phil.coyle; 18th September 2016 at 20:41..
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  #3  
Old 19th September 2016, 18:01
NigelB NigelB is offline
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I had no end of trouble trying to use a hall effect sensor with wild, unstable and erratic readings. I moved the sensor all over the place.

No joy.

And then I decided to use the original sensor in the diff and it was perfect straight away. Just remember there are nine vanes on the sender so 1 wheel revolution equals 9 counts.

Stable as a rock, right from the word go!!

Worth a try...............??

Nigel
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Old 19th September 2016, 19:59
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peterux peterux is offline
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I had a similar issue of noise interference on the supply line to my speedo.
I built my car with an electronic Autometer speedo and the BMW sender in the diff (which is a reed switch)

Eventually, I solved the problem by adding a 47nF capacitor across the supply lines close to the speedo. After that I had absolutely no issues.

Full details here...
http://www.madabout-kitcars.com/foru...ghlight=speedo

Try something like this from Maplin....
http://www.maplin.co.uk/p/multilayer...apacitor-dt97f
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Old 19th September 2016, 21:46
Mike Mike is offline
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I must have been incredibly lucky!
Unlike you super smart electronic wiz kids (what is a 47nF across the supply lines?!), I am an electrical bimbo, but I followed Simon Gregory's lead and mounted a Hall effect sender to take a signal off the 3 prop shaft nuts at the back of the gearbox, and it worked straight out of the box.

So glad it did as I would not have had a clue how to deal with your issues: I marvel at your knowledge.
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Old 19th September 2016, 22:18
phil.coyle phil.coyle is offline
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Quick, jot it down in your note book for future reference, just in case some other poor unfortunate has the same problem.

And remember, Knowledge is Power,
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Old 24th September 2016, 18:03
mcramsay mcramsay is offline
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Cheers for the replies, sadly the 5 series diff does not have a speed sensor on the diff so I have to make what I have work!
I bought some capacitors that were mentioned above and I am going to try one of these tomorrow, wiring wise do I put the capacitor across the signal input into the speedo and ground?
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Old 24th September 2016, 19:55
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MartinClan MartinClan is offline
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Capacitor should go between the power feed to the speedo and ground. As close to the speedo as possible.
The problem is that the power feed picks up noise from the rest of the cars systems. The capacitor helps to filter it out.

Cheers, Robin
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Old 24th September 2016, 20:12
mcramsay mcramsay is offline
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That is completely backwards to how I thought it would work. I thought it would have to be filtered out of the signal wire from the Hall effect into the speedo rather than the 12v supply to the speedo.

unless it's the power supply which plugs in just under the signal input on the back of the speedo which has been causing all the trouble all along.... And not the cable run...
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Old 24th September 2016, 20:13
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Quote:
Originally Posted by mcramsay View Post
Cheers for the replies, sadly the 5 series diff does not have a speed sensor on the diff so I have to make what I have work!
I bought some capacitors that were mentioned above and I am going to try one of these tomorrow, wiring wise do I put the capacitor across the signal input into the speedo and ground?
It on depends how the noise is getting to the input. Try it first across the supply and if that doesn't work put another across the signal input. I've sent you a bit more detail in a PM. Let us all know if it works.
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Old 25th September 2016, 17:18
mcramsay mcramsay is offline
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So I tried with the capacitors and no luck, when connected across the signal and ground they temporarily stopped the interference and then it all started again.

I then looked at running a new cable in the transmission tunnel, extremely difficult with the car on the floor and floors bolted in. Very frustrated at this point... Iva is only 3 weeks away.

And then I remembered I had an old acewell reed switch sender and Magnet left over from a previous project, this is a non powered sender only switching to ground. Took a punt and dug it out and it fitted in the same sender hole as the previous sender, stuck the magnet on and wired it up with the original troublesome wiring And hey presto it seems to work, sat with the electrics on for over and hour with the speedo in calibration mode, it counted pulses and it should and when in running mode the speedo sat at zero the whole time, previously with the Hall effect it would count around 50 pulses per second in calibration mode and when in running the needle was full scale. I need to do a full test but I think I have cured it. Car Is all back together and should be fully 100% finished for iva by Friday, then I can have two weeks off before it heads back to marlin it's test.
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Old 26th September 2016, 07:57
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peterux peterux is offline
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Quote:
Originally Posted by mcramsay View Post
So I tried with the capacitors and no luck, when connected across the signal and ground they temporarily stopped the interference and then it all started again.

I then looked at running a new cable in the transmission tunnel, extremely difficult with the car on the floor and floors bolted in. Very frustrated at this point... Iva is only 3 weeks away.

And then I remembered I had an old acewell reed switch sender and Magnet left over from a previous project, this is a non powered sender only switching to ground. Took a punt and dug it out and it fitted in the same sender hole as the previous sender, stuck the magnet on and wired it up with the original troublesome wiring And hey presto it seems to work, sat with the electrics on for over and hour with the speedo in calibration mode, it counted pulses and it should and when in running mode the speedo sat at zero the whole time, previously with the Hall effect it would count around 50 pulses per second in calibration mode and when in running the needle was full scale. I need to do a full test but I think I have cured it. Car Is all back together and should be fully 100% finished for iva by Friday, then I can have two weeks off before it heads back to marlin it's test.
Shame the capacitors didn't work but glad you got it fixed. Good luck with your IVA!!
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