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Old Jun 13, 2011, 10:10 AM
jrb
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Originally Posted by SteveM732 View Post

An average user trying to eek out a little more accuracy is simply going to calibrate the charger to match their multimeter and will have become the emperor with no clothes on.
Quite an analogy!

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Originally Posted by SteveM732 View Post

On the other hand, as kgfly said, 10mV error nothing so whatever makes you happy...
Missing a comma or something.

Isn't 10mV the same as 0.010 -- a 4 1/2 didgit meter?
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Old Jun 13, 2011, 10:30 AM
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Isn't 10mV the same as 0.010 -- a 4 1/2 didgit meter?
Is that a rhetorical question?
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Old Jun 13, 2011, 10:40 AM
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Not meant to be.

Wanted to be sure 1mV wasn't being implied; as one hundreth is required.
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Old Jun 13, 2011, 10:57 AM
Southern Pride
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Originally Posted by Patriek View Post
TY

'problem' is, I bought it overseas, and my vendor (one everyone is raving about) is non responsive.

I just don't fancy killing my expensive 6S packs because of a faulty charger
Undercharging LiPoly will not damage them,period. A cell charged to 4.15 is approx. at 95% stste of charge and for all intend and purposes should be considered fully charged.

Some chargers have a charge to 4.1 setting from the factory for LiPolys which is listed as Long Life or Longer Life. If more would use this setting they would have LiPolys which last much longer overall.

Instread of spending time worring about one or two cells being 4.21 -4.24 it would be best to drop the charge to point to say 4.16 so the highest cell(s) is 4.20 and the others are 4.16 or so.

I would not consider an iCharger or any other charger to be off until I had charged several LiPoly with the termination set at 1/10C and charged them at 1C rate several times.

Charging at greater than 1C and / or using a termination of 1/5 C or Fast or Faster charge does not let the charger spend as much time in the CV stage and thus many LiPolys will end up with greater inbalance (voltage spread).


Charles
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Old Jun 13, 2011, 11:07 AM
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Originally Posted by jrb View Post
Not meant to be.

Wanted to be sure 1mV wasn't being implied; as one hundreth is required.
I'm thinking you are referring to resolution where I was referring to accuracy.

Take the aforementioned VC97, when measuring a 4.2V battery cell it should have a 1mV resolution but ±(0.5%+3) accuracy, which works out to ±23mV. If measuring the total 25.2V of a 6S pack then it would have 10mV resolution and ±156mV accuracy. If the DMM is within these ranges the manufacturer considers it to be working fine, so why try to calibrate the iCharger's 10mV accuracy with the 23mV accuracy of the VC97?!
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Old Jun 13, 2011, 11:53 AM
jrb
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Yes, it’s true the accuracy of a system can never exceed its resolution.

Would appear the VC97 misses the iCharger’s requirement; and the HF CenTechs that are popular around here are not suitable:

Model VC97 - 3 3/4 Auto-range Digital Multimeter
Auto range (with manual range button)
3999 counts max.
DC voltage: 400mV/4V/40V/400V/1000V (± 0.5%)

Have you seen this thread Steve: http://www.rcgroups.com/forums/showthread.php?t=1453774 ?
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Old Jun 13, 2011, 01:12 PM
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For checking the cells, i use another product from Junsi - CellLog8.
I use it as simple voltmeter with mV resolution, so i probe each cell with it, in case i want to be sure.

I also use it for the intended purpose - measuring all cells by balance tab and logging voltage drops in flight, for checking weak cells.
When measuring 6S packs, it have about 5mV accurancy (it can be also calibrated).

Meaning i measure lets say 4.192V on each 6 cells when using only 1st channel, but when using all 6S channels, i get results from 4.189-4.194V.
I found it depends on the internal A/D converter resolution probably, because slightly different cell voltage across all cells makes the device "jump" to nearest value.

GREAT device for checking health of the pack and accurate.
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Old Jun 13, 2011, 02:10 PM
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Originally Posted by jrb View Post
I had not till just now. The input voltage indication between the chargers varies by ~1.2% which means either one is way off or the accuracy of the input voltage sensing is simply lower, possibly on purpose to cut costs since it's not something you usually need to be all that accurate. I don't think I can add anything to that thread that hasn't already been discussed.

The man with one watch always knows exactly what time it is.
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Old Jun 13, 2011, 02:16 PM
jrb
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Thanks for checking.
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Old Jun 13, 2011, 06:06 PM
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I agree that end-user calibration of chargers should not be required. It is useful that it is possible. One of my older 1010B chargers was showing a difference between cells that bugged me so I recalibrated it using the VC97 to bring all cells into line.

Note In measurements there are three aspects to consider:

Accuracy = how close is the measurement to the real value
Precision = how repeatable is the measurement for the same input
Resolution = the smallest measurable change of the input

Usually people are concerned about two aspects with a LiPo charger:
(a) Imbalance between cells
(b) Cell over-voltage

A multimeter is very useful to help confirm any apparent imbalance between cells. Several measurements taken in close succession (e.g. measuring each cell voltage one after the other) are likely to be quite precise. Any lack of accuracy is unimportant since when considering imbalance, only the difference between cells matters.

Checking for over-voltage is subject to the accuracy and here the "emperor's new clothes" situation applies. In this case you should take the stated accuracy of the meter into account when interpreting the readings. For example, to be absolutely sure that a cell is not over 4.20V with the VC97 the reading should be less than 4.177. Now the cell could actually be anywhere in the range 4.154 to 4.200.

It gets more complex since to measure 4.2V you have to be on the 40V range where the resolution is lower (larger steps) than on the 4.0V range.

In the end, Charles' advice is the best. Configure your charger to charge to something less than 4.20V (I use 4.18V) and you probably don't have to worry about over-voltage.
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Old Jun 13, 2011, 06:43 PM
jrb
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Great reply kgfly!

I'm looking at my auto rangers to see what range is used for 4.2 volts too.
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Old Jun 13, 2011, 06:49 PM
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For checking the cells, i use another product from Junsi - CellLog8.
I use it as simple voltmeter with mV resolution, so i probe each cell with it, in case i want to be sure.
Yes indeed, the CL8 (or PL6) is a quick and easy way to check LiXx packs before/after/during flying or charging. Tests by various users have found them to be usefully accurate.

I also find it useful somtimes to compare measurements of the same pack across several devices to see how close they are to each other. For example I might compare a couple of chargers, the CL8 and one or two multimeters. If the results all fall within the expected resolution and accuracy of the devices then I feel pretty comfortable.

JRB - For best resolution when measuring cells I do it when they are discharged below 4.0V so that I can use the 4.0V range.
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Old Jun 13, 2011, 07:13 PM
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Hello. I purchased a new but used from another rcg member 206b.

I am charging 4s 5000 mostly in balance mode. At the end of every charge I get a termination with control error. Every pack does this. All right at the end.. 16.8v. I see the error mentioned in this thread but what is the resolution?

I have tried 8 packs. They charge fine on my B6AC.
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Old Jun 14, 2011, 12:11 AM
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Originally Posted by kgfly View Post
In the end, Charles' advice is the best. Configure your charger to charge to something less than 4.20V (I use 4.18V) and you probably don't have to worry about over-voltage.
True, but if you fix a 40mV imbalance by lowering end charge voltage, the pack might get beaten at the other end of the curve.

Fred
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Old Jun 14, 2011, 12:37 AM
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Originally Posted by holda29 View Post
Hi,
I have a problem with my 206B. I tried to charge 4s pack, which wasn't used for approx. one month. When I plugged-in a ballance connector, charger says Bal. error.
I thought the battery was dead, but I tried the same on Accucell 6 and everything worked just fine. Volt meter also confirmed, that this pack is good.
When I connected fully charged battery in LiPo monitor mode, cells 1 and 4 looks fine, but cell 3 shows 2,8 V and cell 2 shows nothing.
I tried to reset to factory defaults and upgrade firmware, but with no effect
It is my only 4s pack, but with 3s packs everything is working absolutelly fine.
Any suggestions?
This problem maybe was caused by the burnt of the balance socket, and you can check it yourself via referring the file bal err.

Junsi
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