Beginners Guide to Processing 18650 Cells | Cell Database


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Mistake busbars ?
#11
What you might be able to try is to take the Neg of both meters and connect them at the same point on one end. Then take the Pos of one and connect it to the same end and the Pos of the other and connect at the other end. This "may" give you a voltage difference. It's just that the two meters must have a common starting point. Connecting them completely at either end won't yield any differences as they can't show you the true load across the pack.

But, then again, if your buss bars large enough, they won't show any differences anyways as the voltage drop is too low, or non-existent. You could test your voltage drop across the buss bar by using it as a shunt type of connection. Put a load across the buss bar and see what the voltage drop is at either end that way. This would allow you to use your multimeter in .0001 mode instead of the .001 or .01. We don't care about full voltages, we care about the milli-volts or micro-volts.
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#12
Kind of did that with my multimeter ( common negative rail in the front and on the positive side on the cells in the back and front )
my meter is not sensitive enough (millivolts only) to detect a difference.

Microvolts... do you think that low is of any importance?
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#13
Depends on how often you pull on your pack that hard. Wear and tear is cumulative. So, there's not much difference between 1000 hits of .0001v, or 100 hits of .001v. It still kinda does the same thing, kinda. It's probably more like 2000 hits of .0001v is equal to 100 hits of .001v. Just theory at this point Tongue

Actually, I guess I mis-typed that. When the MM has no decimal reading, it is reading millivolts. Microvolts would be 5 decimals. So, really, what I meant/should of said was reading in decivolts (0.01V), centivolts (0.001V) or millivolts (0.0001V). Most MM's won't read in centivolts, though. You jump from decivolt to millivolt. The problem is when reading in millivolt mode, you can't go over a few thousand or the meter goes wonkers. Which is odd, cuz you'd think it should be able to read up to 9999 millivolts, or close to. At least read up to 5000mV or so.

Ok, I hope i didn't confuse anyone with my rambling set of corrections of myself Tongue
And please feel free to correct my corrections that may not be correct, or partially correct, or somewhat correct.
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#14
One correction on the corrections Smile  you are a digit off.

1,0 = 1 Volt
0,1 = 1 "Decivolt" or 100 millivolts
0,01 = 1 "Centivolt" or 10 millivolts
0,001 = 1 millivolt
...

i do not think decivolts and centivolts is a real thing Wink  at least not here.

So my MM is accurat up to 10 millivolts, as most "cheap" ones are...

Wear and tear cumulative ? makes sense... dont know...
It is never going to be easy to detect/messure, so it stays a theory i am afraid....
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#15
@wim: thanks for the correction on my correction that needed a little more correcting. Wink

Well, I wouldn't quite say deci/centi-volts aren't real. Most MM's are either xxxx, xx.xx, xxxx. Or, at least the few different ones I've used only show those 3. So we readily use, or have access at least, to all 3. On packs that are over 4 volts, I'm sure we all use the deci-volt mode as we only need to see the tenth of a volt. I'm not sure how far the MM will go in centi-volt mode. I know they have kick offs at certain voltages and I don't have a variable PS to test mine (yet).

Hrmm, actually, there are 5 settings. HV (High Voltage; not sure what it's range/max is), 200 (00.0), 20 (0.00), 2000m (000), and 200m (00.0 ?? I'm guessing this is fractional millivolts, or, pico-volts. it's sensitive enough that moving the wires slightly generates a voltage).

But we are really interested in the main 3. However, you could use the 2000m setting to detect voltage drift across the pack as it's that sensitive. I'm guessing you could use 200m as well, but you'd need to not move the wires afterwards to make sure you get an accurate reading.
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#16
Haha, I've been involved in electronics in one way or another(hobby/professional) for over 35 years and this is the first time I've heard decivolts and centivolts.
Sounds really weird.
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#17
Yeah, we actually don't use that "term", but we use the numbers, though Wink I think most ppl would say 10 millivolts instead of 1 centivolt, and 1 tenth volt rather than 1 decivolt.

When i was writing it up, I was basing it on the fact that mill is metric, so I went with metric on the other decimals. I guess some things just don't translate well Tongue
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#18
Yep, from Volt straight to millivolts... thats wat we do. Cool

Then you say:

Hrmm, actually, there are 5 settings. HV (High Voltage; not sure what it's range/max is), 200 (00.0), 20 (0.00), 2000m (000), and 200m (00.0 ?? I'm guessing this is fractional millivolts, or, pico-volts. it's sensitive enough that moving the wires slightly generates a voltage).

But what you realy want to say is : "Go and buy yourselve a decent multimeter" is it not? Big Grin Big Grin

My multimeter starts at 2V as a lowest setting, so you are probably right... Rolleyes
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#19
Well, mine are the "cheapo" harbor freight ones that we got as freebies with their coupons. However, the board model number on the casing is the same model number that's in the Lowe's electrical section that sells for >$30. So, just because the case is cheapo, doesn't mean the guts aren't Tongue Of course, I guess that could go the other way, too. Just cuz the outside piece is expensive, doesn't mean the innards are worth crap Wink

But I've checked my 3 MM's and calibrated them best I could. Fairly easy to do. It does everything I need it to do for now. I did have to buy a separate amp-meter, but I think most of would have to do that anyways if we wanted that feature.
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#20
Can get some decent meters for next to nothing these days.
Mine hurt, it cost me about $600 about 20 years ago... though it's still pretty decent even by today's standards, was better than the competing flagship Fluke of the time. (Autoranging 40,000 count and 0.06% basic accuracy (DCV)
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