Exciter coil - motorcycle

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judokezza
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Joined: Fri Nov 13, 2015 1:23 am

Exciter coil - motorcycle

Post by judokezza »

Hi everyone. I'm new to the forum and fairly inexperienced using my 4425a scope. I've just recorded some waveforms of the Exciter coil on a honda xr400 (uploaded to the waveform library). The Exciter coil is working find. I would like to understand the waveform better. Does anyone have any experience testing Exciter coils? The honda manual specify 100vdc peak voltage (measured with a DVM and peak voltage adapter attached). Thanks kez

ben.martins
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Joined: Tue May 16, 2017 1:02 pm

Re: Exciter coil - motorcycle

Post by ben.martins »

Hello Kez,

Welcome to the group and the start of your PicoScope journey.

For all those that would like to view the waveforms from the Honda you will need to add the model to your own library. To do this click on the 3 dotted button next to the model drop down box and then select Add. You will need to type it exactly the same as Kez has which from a little searching I believe is XR400R. You can scan through the whole Honda list but this should filter out the ones of interest.

Kez, I believe the issue lies with where you are reference the ground lead too. We have to be a little careful with the CDI systems but you should be OK with your 4425A. I need to look a bit closer at a wiring diagram when I get a second Kez and I'll update after.

Hope this is OK. If you need for urgent support please email into support@picotech.com.

Kind regards

Ben

ben.martins
Pico Staff Member
Pico Staff Member
Posts: 301
Joined: Tue May 16, 2017 1:02 pm

Re: Exciter coil - motorcycle

Post by ben.martins »

Hi Kez,

Apologies for the delay in getting back to you on this. I think I have what appears to be a common wiring diagram for this particular bike and also ties up with the wire colours you've added to the waveform in the library. I have to mention that bikes is not a well known area for me and if anything below is incorrect please tell me! I've done a little work with outboards that use a CDI ignition module and drawing my knowledge from that. It might be different for bikes.

Where the exciter coil comes from the main stator/alternator it appears to only be on a single phase. What makes it interesting is in the notes you have made, you mention the manual specifies 100V DC when using an adapter. If the adapter is used to rectify the signal into DC then this will of course be a peak voltage reading in just DC but if looking at it with just the scope the voltage will in fact be AC.

When connecting the scope though I imagine there is no adapter and you've purely measured across the phase using the black and the signal parts of the test lead. With the 4425A we can allow the measurement to float, where the USB ground and the BNC ground can have a difference of 30V. More on floating inputs can be found here - https://www.picoauto.com/library/traini ... ing-inputs. Any more than 30V will cause a common mode error. The only safe way to get a 100VAC signal into the scope is to use an active differential probe such as the TA057. Attenuators shouldn't be used here as they only attenuate the signal side from the probe and not the ground side.

When it comes to measuring we could treat this exciter coil in a similar way to a floating crankshaft sensor where we measure both sides of the sensor referenced to ground. If we were to then use a math channels to take one side away from the other we should be left with the correct amplitude. With everything referenced to chassis ground we shouldn't cause any problems. https://www.picoauto.com/library/automo ... g-running/.

In terms of amplitude, most stator checks on bikes will need to be run at idle and then at 5000RPM. This does vary with some saying 3000RPM so always check the manual. This will naturally cause an increase in the voltage which may be one of the reasons as to why you haven't got your peak voltage output.

I hope this helps.

Kind regards

Ben

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