diagnosing starter, battery and charging problems

[donald73d]

I recently read an article (which I can dig up if someone is interested) about doing diagnosis with an oscilloscope and a clamp-on probe. So I bought a Velleman hand held scope and ordered a clamp-on probe. The goal is to accurately measure the lowest cranking voltage and highest amp draw and see if they are within limits. In this case one needs the scope as peak or min/max meters are not good enough. Lastly see that the charge current settles down after a few minutes to almost nothing. I don't have any problems in this area right now with skidder, but want to learn a bit on using a scope for diagnosis. Other things to try are looking at the cranking voltage/current draw (with fuel relay pulled) and seeing if one or more cylinders look different, thus poorer compression. Looking at the alternator waveform output to see if 1 of the 6 diodes are gone. So if anyone has any ideas or tid bits to pass along in this area it would be appreciated.

 

[Tazza]

That actually sounds quite interesting.
I assume for cracking to find possible compression issues you watch the wave from the current draw from the starter to see when its under load if it changes as the pistons come up to the compression stroke? So in an ideal world, there would be a waveform with 4 equal current spikes for every 2 revolutions.
For this test, i think you would need to have the fuel turned off so you can crank a bit longer and get a better reading. Modern engines start up pretty fast, so seeing the difference in the waves could be harder.
Do keep us informed, i'd like to see how this would go in a real world situation.

 

[Wirenut2266]

Alright.....I have to be honest here. Why would anyone purchase a "scope" for working one a DC circuit much less on a Bobcat? I have used many an oscilloscope, only for AC circuits for true waveform troubleshooting, and DC only for serious circuit board diagnostics. That said: If a diode goes bad on a alternator, there goes my dc output, hence no charging. No scope needed for that. As far as amp draw....Why do we need to know draw on a starter motor, etc. Check the draw when it is 90 deg. outdoor compared to 15 deg. yes they will be dramatically different, but this is normal. So why do we need this scope???? Seriously, I don't mean to be rude just a little confused. If you tossed that kind of money in a scope and probe, dude put the $$$ in your Bobcat. I have used my Fluke 87 for years, can troubleshoot with the best of em, that meter is even overkill for most fellas that can't use it to it's full potential. Dumb question, but I must ask: Why are you concerned about voltage/amp draw on your machine if no error codes come up? Bruce

 

[1awert1]

Alright.....I have to be honest here. Why would anyone purchase a "scope" for working one a DC circuit much less on a Bobcat? I have used many an oscilloscope, only for AC circuits for true waveform troubleshooting, and DC only for serious circuit board diagnostics. That said: If a diode goes bad on a alternator, there goes my dc output, hence no charging. No scope needed for that. As far as amp draw....Why do we need to know draw on a starter motor, etc. Check the draw when it is 90 deg. outdoor compared to 15 deg. yes they will be dramatically different, but this is normal. So why do we need this scope???? Seriously, I don't mean to be rude just a little confused. If you tossed that kind of money in a scope and probe, dude put the $$$ in your Bobcat. I have used my Fluke 87 for years, can troubleshoot with the best of em, that meter is even overkill for most fellas that can't use it to it's full potential. Dumb question, but I must ask: Why are you concerned about voltage/amp draw on your machine if no error codes come up? Bruce

I have worked in the electronic test area for years, (retired now) i have not used a scope since the 1980's.... but some ppl are just curious....he must have the time and money...or insane........

 

[donald73d]

I have worked in the electronic test area for years, (retired now) i have not used a scope since the 1980's.... but some ppl are just curious....he must have the time and money...or insane........

I did not fully explain the reasons. See this article http://motorage.search-autoparts.com/motorage/Technical/Startingcharging-system-scope-analysis/ArticleStandard/Article/detail/714436 According to the author the scope is the only instrument that can show the cranking voltage properly along with the max current draw of the starter. One can now purchase a decent hand held LCD scope for $100. Its not some expensive thing you need to roll around on a cart. Add a current probe and you can run some tests that only can be run with a scope. I believe if 1 of 6 diodes is broken in the diode bridge for the alternator, the output voltage will not be much lower and is hard to detect without a scope.

 

[Wirenut2266]

I did not fully explain the reasons. See this article http://motorage.search-autoparts.com/motorage/Technical/Startingcharging-system-scope-analysis/ArticleStandard/Article/detail/714436 According to the author the scope is the only instrument that can show the cranking voltage properly along with the max current draw of the starter. One can now purchase a decent hand held LCD scope for $100. Its not some expensive thing you need to roll around on a cart. Add a current probe and you can run some tests that only can be run with a scope. I believe if 1 of 6 diodes is broken in the diode bridge for the alternator, the output voltage will not be much lower and is hard to detect without a scope.

Don: I don't want to start a pissin match here. A 6-diode bridge as far as I know is for 3-phase power in, singe phase DC out. All bridges I have seen for basic ac/dc conversion is a 4-diode. Hense one goes, screws alternator output immediately. Bruce

 

[BobCat]

Don: I don't want to start a pissin match here. A 6-diode bridge as far as I know is for 3-phase power in, singe phase DC out. All bridges I have seen for basic ac/dc conversion is a 4-diode. Hense one goes, screws alternator output immediately. Bruce

Seems like a whole lot of unnecessary over thinking. Shunt meter and a multimeter is all ya need. Probably could take the battery down to your local auto parts store to have it checked out if ya don't want to buy a shunt meter and I would imagine most everybody has a multimeter. IMHO.

 

[donald73d]

Don: I don't want to start a pissin match here. A 6-diode bridge as far as I know is for 3-phase power in, singe phase DC out. All bridges I have seen for basic ac/dc conversion is a 4-diode. Hense one goes, screws alternator output immediately. Bruce

For normal AC conversion to DC, 4 diodes are what is needed as its single phase. But alternators in cars, etc are almost always 3 phase needing 6 diodes. The 3 phase could be for the lowest ripple or its more efficient. Or both. The paragraph below seems to indicate its for the lowest ripple. I am not doing this specific to my Bobcat. It will help with any vehicle with a battery, starter and alternator. Just trying to gain a little more knowledge. From the WIKIPEDIA Alternators are used in modern automobiles to charge the battery and to power the electrical system when its engine is running. Until the 1960s, automobiles used DC dynamo generators with commutators. With the availability of affordable silicon diode rectifiers, alternators were used instead. Alternators have several advantages over direct-current generators. They are lighter, cheaper and more rugged. They use slip rings providing greatly extended brush life over a commutator. The brushes in an alternator carry only excitation current, a small fraction of the current carried by the brushes of a DC generator, which carry the generator's entire output. A set of rectifiers (diode bridge) is required to convert AC to DC. To provide direct current with low ripple, a three-phase winding is used and the pole-pieces of the rotor are shaped (claw-pole) to produce a waveform similar to a square wave instead of a sinusoid.

 

[BobCat]

For normal AC conversion to DC, 4 diodes are what is needed as its single phase. But alternators in cars, etc are almost always 3 phase needing 6 diodes. The 3 phase could be for the lowest ripple or its more efficient. Or both. The paragraph below seems to indicate its for the lowest ripple. I am not doing this specific to my Bobcat. It will help with any vehicle with a battery, starter and alternator. Just trying to gain a little more knowledge. From the WIKIPEDIA Alternators are used in modern automobiles to charge the battery and to power the electrical system when its engine is running. Until the 1960s, automobiles used DC dynamo generators with commutators. With the availability of affordable silicon diode rectifiers, alternators were used instead. Alternators have several advantages over direct-current generators. They are lighter, cheaper and more rugged. They use slip rings providing greatly extended brush life over a commutator. The brushes in an alternator carry only excitation current, a small fraction of the current carried by the brushes of a DC generator, which carry the generator's entire output. A set of rectifiers (diode bridge) is required to convert AC to DC. To provide direct current with low ripple, a three-phase winding is used and the pole-pieces of the rotor are shaped (claw-pole) to produce a waveform similar to a square wave instead of a sinusoid.

Impressive! Way to deep for me.

 

[Wirenut2266]

Impressive! Way to deep for me.

Don: I'll give ya props. You obviously know your sheet. I'll have have to take your word on the 6-bridge diode circuit in automobiles, etc. I have not tore into a newer alt. in quite some time. The old girls I have taken apart are always 4-diode bridge. So yes, in theory, if one of six diodes goes there is no way to really know without a scope. As far as affecting charging, that is a good question. I guess a scope looking at output wave is one way, load test is only other test I know. Maybe a good graphic VOM can see an issue also. O'kay, now I have a headache and must end this conversation, Bruce...... Good luck to ya!

 

[skidsteer.ca]

Don: I'll give ya props. You obviously know your sheet. I'll have have to take your word on the 6-bridge diode circuit in automobiles, etc. I have not tore into a newer alt. in quite some time. The old girls I have taken apart are always 4-diode bridge. So yes, in theory, if one of six diodes goes there is no way to really know without a scope. As far as affecting charging, that is a good question. I guess a scope looking at output wave is one way, load test is only other test I know. Maybe a good graphic VOM can see an issue also. O'kay, now I have a headache and must end this conversation, Bruce...... Good luck to ya!

Nothing wrong with higher learning!
Far too many people don't know anything about how electricity works.
Ken