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Old May 22, 2011, 07:23 PM
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Got my meter. Fast ship and nicely packed. It is great to check the IR of a cell, and then measure the pack so you know the connector resistance. IR was spot on compared to my CellPro measurements, but now I can check all my batteries without waiting 30 minutes for a charge cycle.

Great instrument!
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Old May 22, 2011, 07:50 PM
Southern Pride
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Haralson County GA. USA
Joined Oct 2004
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Quote:
but now I can check all my batteries without waiting 30 minutes for a charge cycle.
Powerlab 8 only takes 3 minutes and it does up to 8cell at once. .
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Old May 23, 2011, 03:45 PM
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Originally Posted by jj604 View Post
Wayne, I think you posted or emailed me at one time the process for calibrating the ESR meter. Do you have that handy and could post again? It's just that anything with linear circuitry in it says "calibrate me" occasionally.

Would prefer to do on both 16A and 1.6A ranges.

Thanks, John
John (+ any other meter owners),

Here is a simplified version of my calibration rig so anyone can check calibration of their meters.
I have attached the circuit which has two resistors in series; a 10milliohm one for calibrating the "Cell " mode and a 50milliohm one for checking the "Pack" mode.
It is first necessary to measure these resistors accurately. You will therefore need an accurate method of measuring both the current through the resistor and the voltage across it. I use 4Watt ceramic resistors and do not exceed 0.5W dissipation ie about 3A through them to avoid any temperature rise which might change the value.

It is most important to measure the volt drop across the resistor at exactly the same point both when calibrating the meter and measuring the resistor. At these very low resistance values the wire is significant.

To check the Cell mode there must be a voltage to measure the step change so an AA cell is connected in series with the signal from the 10m.ohm resistor, but in opposition to it so that the measuring cct. sees a voltage drop during the pulse load. The AA cell passes no current and the cell voltage does not matter. The search lead should be connected as shown and the operate button should produce a reading of 10 milliohms in cell mode.
To check the Pack mode a reading is taken with the 50 milliohm resistor in series and another reading with the resistor shorted out with a 6mm solid bullet. The difference between the two readings should be 50milliohms.

The resistors you use will not be exact so the accuracy of the calibration depends on how accurately you measure the resistors initially.

In my rig the 10 milliohm resistor is actually 10.08milliohms and the bigger resistor is 47milliohms nominal which I have measured at 43.7milliohms. This value is the difference with the resistor shorted out and not shorted out; the bullet connector + leads are just over 1 milliohm.

John: I'm sure you can work out that you can just use a 0.5ohm resistor on the 1.6A range and the comments about measuring points are less critical.

Anything not clear post or PM me.

Wayne
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Old May 23, 2011, 05:57 PM
Since 1952
Harry D's Avatar
Canada, AB, Edmonton
Joined Oct 2004
1,259 Posts
Thanks for that, Wayne. Great service as always. I'll have to try it, once I've digested and understood the procedure.

Question for you. Have you found that the meter goes out of calibration significantly, so that it should be recalibrated from time to time? I mean as a suggested or recommended procedure, as against just an interesting exercise.

Also, how much "error" should be apparent before it becomes advisable to make adjustments, and how does one actually go about doing that? In my own case, I'd be a bit reluctant to start fiddling with it unless I really need to, because of the possibility of messing things up. I have no doubt that your initial calibration was spot on, and probably much better than anything I would do.

Thanks again for the fine product and service.
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Old May 23, 2011, 06:43 PM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
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Thanks, Wayne. That's absolutely clear and straightforward. Need to get in some low value resistors!

John
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Old May 24, 2011, 03:04 AM
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The Netherlands, LI, Venray
Joined Dec 2008
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Wayne,
what means cct
the drawing, what is about the resistance of the 3 dean connectors?
I will have say 6mOhm per dean connector = 18mOhm extra

If measured value is say 60mohm instead of 50mOhm how to adjust that in the meter?..ok you explained this already in answer to harold

What is the max voltage you can apply on the cell meter leads?
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Old May 24, 2011, 03:26 AM
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Rugby, UK
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Originally Posted by Harry D View Post
Question for you. Have you found that the meter goes out of calibration significantly, so that it should be recalibrated from time to time? I mean as a suggested or recommended procedure, as against just an interesting exercise.
Harry,

No, the meters do not go out of calibration, as the analogue part depends on a very stable voltage reference, an op amp and a ceramic resistor, none of which will show any significant drift. I only put the details on to humour John as he is now retired and and looking for something to do/ finding excuses not to go shopping!
I have just been and rechecked my prototype unit and it read the 10.08mohm resistor as 10.04mohm and the 43.7mohm as 43.5mohm, the difference being only 1 bit in each case which is a basic tolerance in any digital measurement.
BTW I thought I had a faulty unit last week on test as the 43.7mohm read about 65mohm but it turned out to be a dirty blade on the Deans connector, which looked slightly discoloured, but not that bad. I had to use a solvent to clean it. A connector at 20mohms with 60A through it equals 72Watts - frightening isn't it.

If anyone thinks their meter is out, please let me know as the most likely cause is akin to the above. There is a fine adjustment but if you move it the meter needs recalibrating on accurate equipment.

Wayne
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Old May 24, 2011, 06:30 AM
ancora imparo
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Melbourne, Australia
Joined Jul 2005
6,321 Posts
C'mon Wayne. I have a perfectly satisfactory wife who is tasked with that kind of comment. But you did get me thinking. I probably need THREE ESR meters so that if they don't agree I know which one is the inaccurate one.
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Originally Posted by Wayne Giles View Post
I only put the details on to humour John as he is now retired and and looking for something to do/ finding excuses not to go shopping!
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Old May 24, 2011, 11:04 AM
Since 1952
Harry D's Avatar
Canada, AB, Edmonton
Joined Oct 2004
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Originally Posted by Wayne Giles View Post
... the meters do not go out of calibration...
Thanks, Wayne. That's what I thought. I won't be messing with mine.
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Old May 25, 2011, 02:59 PM
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Rugby, UK
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Originally Posted by jaccies View Post
Wayne,
what means cct
the drawing, what is about the resistance of the 3 dean connectors?
I will have say 6mOhm per dean connector = 18mOhm extra

If measured value is say 60mohm instead of 50mOhm how to adjust that in the meter?..ok you explained this already in answer to harold

What is the max voltage you can apply on the cell meter leads?
The Deans connectors are only there as a convenient way to insert and remove the calibration equipment. Actually a Deans connector is only about 2 - 3 milliohms, but the unit will measure everything such as soldered joints, wire etc so the difference between the total cell resistances and the pack reading will be about 6 milliohms. It does not affect the calibration readings as the inputs to the meter are feeding differential amplifiers; ie the circuit reads the voltage between the two cell connections, not the voltage above 0V.
The cell meter leads will only read up to a maximum voltage of about 4.8V although higher voltages (up to 20V) will not cause any damage, but the meter cannot read them.

Wayne
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Old May 26, 2011, 03:06 AM
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The Netherlands, LI, Venray
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Originally Posted by Wayne Giles View Post
The Deans connectors are only there as a convenient way to insert and remove the calibration equipment. Actually a Deans connector is only about 2 - 3 milliohms, but the unit will measure everything such as soldered joints, wire etc so the difference between the total cell resistances and the pack reading will be about 6 milliohms. It does not affect the calibration readings as the inputs to the meter are feeding differential amplifiers; ie the circuit reads the voltage between the two cell connections, not the voltage above 0V.
The cell meter leads will only read up to a maximum voltage of about 4.8V although higher voltages (up to 20V) will not cause any damage, but the meter cannot read them.

Wayne
thanks , Wayne , that i can say i understand the explanation for 100% i have to say no , i am not an elecrial engineer , only i try to think logical
when i see 3 dean connectors in the circuit .
and the abbreviation CCT what does that mean ?
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Old May 26, 2011, 03:13 AM
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Originally Posted by jaccies View Post
thanks , Wayne , that i can say i understand the explanation for 100% i have to say no , i am not an elecrial engineer , only i try to think logical
when i see 3 dean connectors in the circuit .
and the abbreviation CCT what does that mean ?
Jaccies,
Sorry about using abreviations; we all do it without thinking, - it is short for "circuit"

Wayne
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Old Jun 13, 2011, 09:53 AM
who dares wins
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London,England
Joined Apr 2005
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Iíve got two packs for one of my EDF jets.

I was about to connect one of the packs and noticed that the bullet-wire joint felt a little wobbly. (The leads are too long with little room for them in the fuse, they are cramped. I will shorten them)

Using your IR meter I quickly confirmed my suspicion. The cells IRís were normal on both 4s packs, one packs total IR was about 19 mohms, the other was about 40! Time to re-solder! Glad I didnít just fly and deal with it later. I have the IR meter in my flight box ready.
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Old Jun 13, 2011, 02:44 PM
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Originally Posted by like2fly! View Post
Iíve got two packs for one of my EDF jets.

I was about to connect one of the packs and noticed that the bullet-wire joint felt a little wobbly. (The leads are too long with little room for them in the fuse, they are cramped. I will shorten them)

Using your IR meter I quickly confirmed my suspicion. The cells IRís were normal on both 4s packs, one packs total IR was about 19 mohms, the other was about 40! Time to re-solder! Glad I didnít just fly and deal with it later. I have the IR meter in my flight box ready.
Glad to hear it is useful. Although intended to measure cells and packs, I found a "Deans" with a contact resistance of 35milliohms a week or so ago which turned out to be just a smear of dirt on one blade!
The meter also sorted a problem with a club members' ducted fan model which kept surging for no apparent reason. Cell voltages all looked OK but it turned out that 2 cells were about 6 milliohms and one was 38milliohms!

Wayne
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Old Jun 18, 2011, 06:52 PM
Needs to do 52 legs !!
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Verenigd Koninkrijk, Fareham
Joined Aug 2008
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Hello Wayne,

Lucky to find this great thread thanks to a post from Wim on the dutch forums. Very good of him and of you for creating this device and the amazing support. Was a great read so far!

A little bit of background on myself and what i spend my time with. Ever heard of the FAI class F5B ? It's some crazy people who insist on pulling way to many amps out of those poor little lipo's for short periods at a time and making our planes go from 100 to 300kph in less then 3 second while going strait up. It's addicting, what can i say. We regularly pull around 100C for about 2 seconds out of around 500 grams worth of Lipo. We generally only discharge the pack down to ~50% charge state. To throw in some more typical numbers, 5KW is about where most competitors are at now, on 5S 3300mah that would be around 300A at 16.5V under load or 3.3V/cell.

I think you can already see how important it is for us to have good cells, make sure out packs are in good health and possibly controll the temperature of the pack. I say that last thing a bit hesitantly as i have been avoiding flying in cold weather (sub 5 deg C) and generally don't bother preheating the packs when i do fly. This means i get less power on the first climb but then the power seems to be very constant for the other remaining 10-12 climbs. In the past this effect was much worse and it would take nearly 5 climbs for the power to level out.

In terms of wear on the packs. I have had no trouble abusing packs like this for more then one flying season and usualy when a new generation comes out the next year, the old ones get moved to the dust collection area anyway. But i do fear that we might get a bit less power nearer the end of the year and an injection of a fresh pack into the mix can have some ''unexpected'' results where suddenly more power is to hand. This is where people run out of their energy allowance as we fly with a total energy limiting device (1750W.min).

Many people have the SM Unilog with a 400A sensor in use and it has a nice 16hz recording feature with some spare slots;
http://www.sm-modellbau.de/

I was wondering about maybe seeing if we could somehow connect your unit to a Unilog and run a pack through on a ''tester unit'' to simulate a flight and see how the pack temperature really effects the IR of the pack.

Would love to hear your thoughts on the above and in general. Also i am probably wanting to buy a unit from you.

Kind regards, Joe
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