Advice needed on charging current waveform

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Willyl
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Joined: Thu Dec 16, 2010 3:57 am

Advice needed on charging current waveform

Post by Willyl »

Thanks in advance for any input here,. This is a Triumph motorcycle with new alternator and reg/rec. it has a history of burning aftermarket alternators and we went with oem here. What I am concerned with is the way the charging current cycles up and down so far from +12 amps or so to 12 below zero

Iver
TwoWaves
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Re: Advice needed on charging current waveform

Post by Iver »

Can you post the waveform again. Right Click > Open With > Pico 6.

I did see your waveform and clearly it is spending half it's time charging and the other half discharging..

ben.martins
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Re: Advice needed on charging current waveform

Post by ben.martins »

Hello Willyl,

Thank you for your post. Motorbike alternators are something we have been asked about before in the past and how we test them PicoScope.

I'll be completely honest here and whilst I have spent sometime with these machines they were never something I ever had to deal with on a daily basis so my knowledge isn't great and some of it you will know already, so please forgive me if this is work you've already done.

If we begin by testing the current and voltage at the battery we will see the results after it has passed through the Regulator rectifier (R/R). This will look at current output as well as voltage after the rectification has taken place and can be done at idle with the headlights on. However, it is worth noting here that the peak output of the alternator is between 3000rpm and 5000rpm , I would test at both engine speeds. This should see the current output increase and the battery voltage decrease but then stabilise. It should sit somewhere between 13.5 and 15V approximately. It would be a worthwhile test here to also look at AC coupling the voltage signal to observe the ripple.

There is another test that can be carried out which looks directly at the stator. I’ve not carried out this test before but it would be interesting to see what type of signal you could potentially see and I’m also going to assume (which we should never do!) that there are 3 wires going to your stator. One technique involves measuring the AC voltage at the plug from the stator to the R/R. Please bear in mind that we will now be measuring in AC so couple the scope in the appropriate way. Ground each of your test leads at the battery negative and connect 3 channels each of the 3 phases. If you only have a 2 channel then look at two phases and then the third. One thing the mention here is the voltage output of the stator. Depending on what scope you have it may be to high for some of the earlier scopes and as it is AC voltage we can't use the attenuator to make it safe for the scope. All the auto scopes are protected of course but if you are unsure then the only safe way to measure this is using the active differential probe.

In terms of what you are looking for, this is where my experience is lacking as I'm not sure what you will see. I guess the most important thing to look for is uniformity in the waveform. If one looks completely off then it could be a phase issue but if they all look similar in terms of output then its back to the R/R.

You could also look at the current using the 20/60A clamp. If you have 3 and some break out leads to make life easier we can see all 3! If one is all we have to work with though then we can still get your clamp in to one of the 3 wires from the stator but this will allow you to see the max output from each phase. Not knowing the output I would maybe look to setup the scope and the clamp for 60A to start with and adjust if needed. Try the same test with idle speed and 5000rpm but with the headlights on this time so we’re making the stator work. The current output should, in theory, increase with load on the battery!

I'm not sure if this has helped at all and sorry this isn't more conclusive but I would be interested to see the results and happy to discuss further on what you find.

Kind regards

Ben

Iver
TwoWaves
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Re: Advice needed on charging current waveform

Post by Iver »

Let me throw in a curve ball. Are motorbikes using Smart Charge ?

Willyl
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Joined: Thu Dec 16, 2010 3:57 am

Re: Advice needed on charging current waveform

Post by Willyl »

Thanks all, I think what the problem was that I was on the negative cable as that was accessible. to regulate the voltage in this type of system the regulator dumps excess to ground thus the amperage fluctuation throught the ground lead. I will test again at the first oppertunity to confirm.
Ben, Thanks already familliar with those tests but you one that doesn't come up more very often in modern bike is ac clipping from and overloaded alternator The ac waveform goes flat on top and bottom when the load is greater than the output capability Again Thanks

ben.martins
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Re: Advice needed on charging current waveform

Post by ben.martins »

Hi Willyl,

Thank you for the update and the extra information, interesting to read about the AC clipping on an overloaded alternator.

Just to make you aware Willyl be careful with AC voltage on PicoScope. We see it with some inductive crank sensors which can cause problems when looking at additional signals. Sometimes the only safe way to measure these signals is with the active differential probe.

Look forward to seeing some captures if you get a chance. Thanks again and great to have your experience and knowledge with bikes here on the forum.

Have a good weekend

Kind regards

Ben

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Autonerdz
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Location: Washington State USA

Re: Advice needed on charging current waveform

Post by Autonerdz »

ben.martins wrote:
Fri Sep 06, 2019 4:44 pm

We see it with some inductive crank sensors which can cause problems when looking at additional signals.
This occurs when improperly hooked up to a floating ground VR sensor. Easy to create a no start condition with your scope. No active differential probe needed. Just hook up properly. What you don't want to do is put a channel across a floating style VR sensor.

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