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Speedometer problem from RFI or EMI.

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Old 04-05-2009, 01:58 PM
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Default Speedometer problem from RFI or EMI.

I just installed a cheap, 4-function electronic bike speedometer that mounts to the handlebars of my bike (I wanted to know how fast I was going). After setting up the meter and starting the engine, I found that electronic noise from the ignition system caused the new meter to malfunction by going into reset mode. As long as the engine was running, the meter would not work.

The fix was to install a small split ferrite bead on the sensor wire between the magnetic sensor and the meter (see photos). These things are made to suppress RFI (radio frequency interference) in electronic equipment. They are inexpensive and easy to install. I just happened to have a bunch handy, snapped one on, and solved the problem. Since I’m an amateur radio operator, a.k.a. HAM, I tend to accumulate such stuff.

If you have similar problems, but don’t have a split ferrite bead handy and don’t know a HAM, you might be able to find one at Radioshack or online. Buy from the following links:

Digi-Key - 240-2344-ND (Steward - 28A0434-0A2)

The link above is for Digi-Key Part Number240-2344-ND

0431164281

Beads


More info on RFI suppression can be found at …

Ferrite Beads
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Last edited by Earthman; 04-07-2009 at 08:03 PM.
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Old 04-05-2009, 02:13 PM
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Default Re: Speedometer problem from RFI or EMI.

thanks thats the problem im having.
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Old 04-06-2009, 01:17 AM
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Default Re: Speedometer problem from RFI or EMI.

Also the battery can vibrate off its terminals causing a reset. Some soft rubber packing helps it stay in place.
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Old 04-06-2009, 09:22 AM
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Default Re: Speedometer problem from RFI or EMI.

I prefer to fix the problem rather than adding a band aid, although the band aid works. If you replace your plug wire and boot with a good one it will solve the problem as well and it really should be done anyway since the stock plug wire and boot are pretty crappy.
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Old 04-06-2009, 09:16 PM
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Default Re: Speedometer problem from RFI or EMI.

I don't know if my meter has a plug wire and boot - it's all hardwired together. Replacing the stock light-gauge zip cord with coaxial microphone cable may help, but it only took about 10 sec. to put the split ferrite bead on, and it didn't cost me anything 'cause I already had the part.
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Old 04-07-2009, 10:24 AM
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Default Re: Speedometer problem from RFI or EMI.

Quote:
Originally Posted by Earthman View Post
I don't know if my meter has a plug wire and boot - it's all hardwired together. Replacing the stock light-gauge zip cord with coaxial microphone cable may help, but it only took about 10 sec. to put the split ferrite bead on, and it didn't cost me anything 'cause I already had the part.
I believe he is talking about the motor plug wire and boot, sick bike parts has some, worked great to fix the resetting of my speed o. I still get some interference from the cdi and kill switch being so close to the speed o. The speed o doesn't reset, but the mph tend to jump around, but not enough to not see how fast I'm going most times.
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Old 04-07-2009, 04:06 PM
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Default Re: Speedometer problem from RFI or EMI.

Thanks for clearing that up (I'm a newbie when it comes to these motors). I agree that a better plug wire and boot can make a difference. However, a ferrite bead will block RFI and EMI from entering the electronic device along external wires, which act like antennas. Try it, it may fix your intermittent problem.
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Old 04-07-2009, 07:32 PM
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Default Re: Speedometer problem from RFI or EMI.

You can go to a auto parts store and get a good 7mm coil wire with boots on both ends and cut in half and now you have two plug wires for your motor. I was having the same problem with my speedo and this solved my problem.
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