Electrical issue

Neshkoro

Neshkoro

Senior Member
I have a strange request. The speedo in my Model A stopped working. I was considering replacing it with a GPS speedometer. I had one from another project. I powered it up from the Model A battery through a little pcb that increases to voltage from 6 to 12 volts. It doesn't work! I wired it up with a 9 volt battery and put it in my daily driver and it works as it should. I wired it up with the same 9 volt battery and it won't work in the Model A. Any thoughts? Is the A producing some sort of "dirty" signal from the points or the generator?
Might there be a workaround? I thought would be cool to have the GPS speedometer!
If you think i'm crazy to try to get this to work, just let me know. I'll just get the speedo fixed! If you have any ideas on how to make it work, Ill try that, too!
Thanks!
 
Neshkoro said:
I have a strange request. The speedo in my Model A stopped working. I was considering replacing it with a GPS speedometer. I had one from another project. I powered it up from the Model A battery through a little pcb that increases to voltage from 6 to 12 volts. It doesn't work! I wired it up with a 9 volt battery and put it in my daily driver and it works as it should. I wired it up with the same 9 volt battery and it won't work in the Model A. Any thoughts? Is the A producing some sort of "dirty" signal from the points or the generator?
Might there be a workaround? I thought would be cool to have the GPS speedometer!
If you think i'm crazy to try to get this to work, just let me know. I'll just get the speedo fixed! If you have any ideas on how to make it work, Ill try that, too!
Thanks!
Click to expand...
Just a quess but a ground to it?
 
When you say it doesn’t work do you mean that the unit doesn’t power up or that it is powered up but not reading the speed? If the latter, the generator could be causing interference. Maybe try coasting down a hill with the engine off and see if it reads then? That would at least rule out interference.
 
Does the GPS work outside the vehicle? You could try holding it in your hand with it connected to 9V battery and walk around in the yard. If it works, then have confirmed the GPS is working. Then install in the vehicle and try with 9V source. If it works then try connecting to 12V source. If the GPS is located in the dash, there is a lot of metal surrounding the unit and the signal may not penetrate all that metal without an external antenna. Ignition noise from spark plugs and no ignition wires that are RF suppressed could cause interference.
 
Neshkoro said:
I wired it up with a 9 volt battery and put it in my daily driver and it works as it should. I wired it up with the same 9 volt battery and it won't work in the Model A. Any thoughts?
Click to expand...

Was the Model A engine running? Or not?
 
The power coming from the model a generator is quite dirty and your boost converter may not like the unsteady voltage at the battery. Then again there are vendors out there that sell USB chargers for the A so they must be doing something different than what your converter is doing.
 
I'm aware that the A has positive ground, but thanks for reminding me! It seems that the power from then generator or the points is"dirty"! If I run the GPS speedo from a different power source, it works fine. i have two different GPS speedometers. One is 12 volts and the other is 5 volts USB. I will need to find a clean power source!
Thanks for your input! I appreciate it. If I find a solution, Ill let you folks know.
 
I ordered the noise filter. It was less than $10. I thought it was worth a shot. In the mean time I can't sit still so I was monkeying around and connected the speedometer directly to the battery. It worked, mostly! I was holding it in my hand and moved it around in the car
As soon as I got it near the original speedometer, it started acting up. It would work intermittently and then stop, and then start up again. Must be interference as you said!
 
I finally got the filter that I ordered as eagle suggested. I hooked it up as the diagram dictates. The GPS speedometer does work, sometimes! It'll work for a couple of minutes and then begin to act up for a few minutes. It goes in and out of working. Im about ready to hang it up. When I got the filter I temporarily hooked it up and it seemed to work correctly. It was hooked up to the chassis ground and the battery cable at the starter. This is the last thing to try.Im going to move the negative connection directly to the starter motor battery post. I hate to admit defeat!
 
That filter is the wrong polarity. You need one with positive ground connection and negative input and output.
 
I just assumed that if I hooked the positive to grond and the negative to the speedo, it would work!ll look for a reversed polarioty filter.
 
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