Products > Test Equipment
Brymen Crest and Min/Max Function VDC Capability
joeqsmith:
--- Quote from: bdunham7 on September 19, 2022, 05:19:04 pm ---
--- Quote from: joeqsmith on September 19, 2022, 04:36:28 pm ---If my cars go "click", I know the battery is dead. No need for anything too fancy. If it dies often, I would be looking for the current draw. I seem to get about six years out of them.
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And when that happens in an airport parking lot after 14 hours of security, customs, gate changes and mediocre premium seating in an airplane not of your choice, you may wish you'd been more proactive.
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What ever the circumstances are involving a dead battery, that would be my problem not yours but I appreciate the concern. I can tell you that I have never had a battery fail that was life changing... :-DD
--- Quote from: bdunham7 on September 19, 2022, 05:19:04 pm ---
--- Quote from: joeqsmith on September 19, 2022, 04:36:28 pm ---bdunham7's scope shot is nice. With a better scope, you should be able to see the compression stroke of each cylinder. We would expect them to be balanced. Maybe some monkey math applied to determine a weak cylinder. Certainly we could see if one was totally gone with a hole in it. :-DD
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Better scope? It's ancient but in some ways still unmatched, IMO. The Fluke 98 has that compression function as well, implemented in voltage or current configuration with a nice trace or 'relative compression' bars displayed. Voltage mode seems to not work very well with modern cars and I don't currently have an appropriate amp clamp. It's good enough to spot single burned exhaust valves on V8 engines that don't have very obvious running problems.
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Referring to the very low res.
splat2030:
The reason I like the multimeter cold cranking test is because it is not simply a battery load test, but rather a quick and easy whole starting system health check. Failing this test does not necessarily mean you have a bad battery, it could also indicate that the starter motor is beginning to fail. You would need to separately load test the battery to 1/2 CCA rating to determine if the problem is with the battery, because a starter motor won't typically put a large enough load on the battery to fully test it. The whole point of doing any of this testing is to identify a failing starter or battery so you can replace them before they are completely nonfunctional and result in a breakdown.
I like the suggestion of the Fluke 98 scope or the Fluke 27, but those meters are out of my budget. My vehicles service manual gives a minimum spec of 9.6 volts for a cold cranking test, so I would suggest that a true minimum reading of 7.12 volts is likely indicative of a developing problem with the starting system that has not yet manifested in any drivability issues. The regular min/max function on the Fluke meters needs a duration of 200ms to capture a voltage, so not using the peak function could allow you to show a passing result when in fact you failed the test. If the cold cranking test fails when monitoring voltage but the battery load tests properly, I would recommend retesting with an amp clamp to verify that the max current draw for the starter is in spec.
After all of this research into the Brymen meters I am leaning toward the BM789, but I still would like to confirm the accuracy of min/max and crest. I will try to contact Brymen to see if they can clarify the statement in the manual and give an update.
bdunham7:
--- Quote from: splat2030 on September 20, 2022, 03:05:22 am ---I like the suggestion of the Fluke 98 scope or the Fluke 27, but those meters are way out of my budget. My vehicles service manual gives a minimum spec of 9.6 volts for a cold cranking test, so I would suggest that a true minimum reading of 7.12 volts is likely indicative of a developing problem with the starting system (assuming it still cranks the engine over and functions at a basic level). The regular min/max function on the Fluke meters needs a duration of 200ms to capture a voltage, so not using the peak function could allow you to show a passing result when in fact you failed the test. If the battery loaded tested properly, I would recommend retesting with a clamp meter to verify that the max current draw for the starter is in spec.
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Fluke 27 can be had reasonably on ebay. There was a seller a while back with brand new units with case and HV probes for $140. I realize it is a bit primitive in some ways, but it has its good points like being very durable.
https://www.ebay.com/itm/155101904381
One of the reasons I put the scope shot up is to show that the 9.6 volt specification doesn't include that initial short current surge and resulting large voltage drop. My battery and starting system are in good condition, that's just what things look like on a scope vs the MIN/MAX feature of a DMM. The car sits a lot and the battery was a bit discharged, so a I took the opportunity to charge it, top off the water and retest it. Not much difference and still below 9.6 volts. That initial surge just what you get when you apply power to a DC motor at standstill when there's no back-EMF yet.
splat2030:
I was looking at the Fluke 27 II which is about $500 new, and the Fluke 98 scope which is about $1000 used. I hadn't really considered used just due to the potential of getting something that was knocked out of tolerance from to the way it was treated by the last owner. That Fluke 27 used for $70 doesn't look too bad, but something like the BM789 new for $175 seems like it would be much more useful due to the additional features. I am hoping I can just buy one multimeter that will meet all of my current and future needs, but I have also been debating back and forth whether I would be better served with both a cheap multimeter and a cheap scope like the Pico 2204a or the Hantek 6074BE rather than just a decent multimeter.
From what I recall my factory service manual recommends using a specific diagnostic tester that has a built in amp clamp for doing the cold cranking test, but also gives that minimum 9.6 volt spec. I'd be interested to see if the results you are showing to 8 volts for that instantaneous drop are typical across multiple different vehicles at different ages, or if your vehicle is an outlier.
bdunham7:
--- Quote from: splat2030 on September 20, 2022, 04:30:13 am ---I'd be interested to see if the results you are showing to 8 volts for that instantaneous drop are typical across multiple different vehicles at different ages, or if your vehicle is an outlier.
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I've tested many vehicles, and while they all have their unique characteristics, mine is not an outlier by any means. It actually is pretty undemanding of the battery--PM gear reduction starter motor, fairly puny battery cables. Probably less than 150A cranking current (not the initial surge) cold, less warm.
Edit: here is an entirely different car, also in known good condition and it only sat overnight
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