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Old Aug 19, 2011, 09:12 AM
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N2UMK's Avatar
Clifton, VA
Joined Mar 2003
86 Posts
High IR on 3rd cell of 3 cell xmitier lipo pack

Here is a screen shot of one of the 3 cell lipo xmitter packs where the 3rd cell is showing > 250mohms.
I just charged 3, 4Ah 6 cell packs in parallel and it displayed the 6 individual cells as normal (4.2, etc). Cell #3 read 4.1.

Before the PL8, I had 2 FMA 10S units that failed (they were refurbished units) within a day or two of receipt (May 2011). They were great about taking them back and crediting me. In the end I decided to get the PL8 instead.

If it is reading "incorretly" it's consitent on the 2 xmitter packs. Maybe there is some circuit in them. One 3 cell xmiter pack is a blue lipo and the orher is a zippy.

Thanks for your thoughts.
Pat
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Old Aug 19, 2011, 11:42 AM
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akschu's Avatar
USA, AK, Houston
Joined Aug 2005
789 Posts
Hey Wayne.

I have a 8s pack I accidentally ran to lvc because I thought it was charged and it wasn't. I would like to compare it to another identical 8s pack using the ESR meter, but the instructions say only up to 6s.

Can you provide a wiring diagram to test individual cells in larger packs?

Thanks,
schu
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Old Aug 19, 2011, 01:48 PM
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Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by akschu View Post
Hey Wayne.

I have a 8s pack I accidentally ran to lvc because I thought it was charged and it wasn't. I would like to compare it to another identical 8s pack using the ESR meter, but the instructions say only up to 6s.

Can you provide a wiring diagram to test individual cells in larger packs?

Thanks,
schu
Schu,

You can use the balance connector as the power connector as although the measuring pulse is 16A it is only present for a few milliseconds so it cannot cause any overheating or damage. Therefore you need to make up a power lead with two flying male pins which you can plug into any two positions in the balance connector. If you want to measure cell 3, for example, you can plug these two pins into positions 2 and 5 or 6 in the balance connector and the cell search lead into positions 3 and 4 and it should measure cell 3. Draw the schematic of the pack out in front of you and you will see the logic of it.
By moving the pins up the connector, ensuring that there is always only 6 cells max between the pins, you will be able to measure all the cells. To measure cell 1 and cell 8, you should use the the (-ve power connection + 1 pin) and the (+ve connection + 1 pin) respectively.
This means that the leads carrying the current are never the leads measuring the cell voltage so that the Kelvin principle of measurement is maintained. Thus the high voltage drop at the power connections into the balance connector will not be included in your measurements.
The overiding requirement is that you do not apply more than the voltage of 6 cells into the two power leads If you do you will damage the unit. Two customers have proved it so far!!

Wayne
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Old Aug 22, 2011, 11:37 AM
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akschu's Avatar
USA, AK, Houston
Joined Aug 2005
789 Posts
Right, that makes sense, I figured it would be something like that because just connecting the draw and measurement wires together would defeat the purpose of the 4-wire setup.

The pack flew the airplane fine so I figure I'm ok, just over discharged it once and was worried I cooked it. It's an expensive pack.

schu
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Old Sep 30, 2011, 02:04 PM
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Connexxion's Avatar
The Netherlands-Amsterdam
Joined Mar 2007
940 Posts
Wayne,

before I buy one of your IR meters,could you explain what amount of ohm is ok and when I should start looking for a new lipo pack?
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Old Sep 30, 2011, 02:53 PM
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Rugby, UK
Joined Feb 2007
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Quote:
Originally Posted by Connexxion View Post
Wayne,

before I buy one of your IR meters,could you explain what amount of ohm is ok and when I should start looking for a new lipo pack?
Mark Forsyth proposed that any lipo cell which which has an IR in milliohms at say 25deg.cent of less than 12000 divided by the cell capacity is a good cell with which I agree. ( see http://www.rcgroups.com/forums/showp...19&postcount=7)

Thus a 1000mAh cell should be <12 milliohms, a 3000mAh cell should be <4 milliohms, a 4000mAh cell should be <3milliohms etc.
We the can extend this to give a cell a Figure Of Merit ( FOM) which is equal to 12000 divided by (Cell IR x Cell capacity in mAh). A figure of >1 is good and vice versa. This gives you a much better guide to a lipo's performance than any quoted C rating.

If you dig through this thread and others on IR values you should get an idea of what are good IR values. Also have a look at a thread I started on C ratings at http://www.rcgroups.com/forums/showthread.php?t=1392662

Wayne
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Old Oct 01, 2011, 01:36 AM
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Joined Jul 2005
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Hello Wayne!

Have you got any more IR meters ready?
I am intrested in purchuasing one to Sweden.

Regards /Mattias
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Old Oct 01, 2011, 02:14 AM
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Rugby, UK
Joined Feb 2007
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Mattias,

I am in the process of updating them and will have new ones available in a few weeks. I will post on this thread when I have them.

Wayne
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Old Oct 01, 2011, 10:05 AM
Since 1952
Harry D's Avatar
Canada, AB, Edmonton
Joined Oct 2004
1,301 Posts
Hey, Wayne: you need to come up with a snappy name for this thing!

BTW, mine continues to be one of the most useful and informative devices I have.
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Old Oct 01, 2011, 12:43 PM
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Rugby, UK
Joined Feb 2007
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Harry,

Cheesy suggestions from here are "Oh-my Meter" or "Waynometer" (from son) or "Wayney's Wonder Meter"! (from daughter-in-law).
OK, we are out in the garden drinking -can you believe it is 29deg.C (86F) in October in UK! Turns out to be a record apparently.

Wayne
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Old Oct 01, 2011, 12:54 PM
It's all fun till Crunch!
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InSane Diego
Joined Jan 2002
1,968 Posts
Glad for your Super Balmy weather, same here it turms out, but I'm not in the garden drinking until the yard chores are dfone!

Please sign me up for one of the "Ohm-y Meter" or "WaynoMeter" or "Wayney's Wonder Meter"

Wayne Walker
alias Capt. Crunch

San Diego, CA USA
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Old Oct 01, 2011, 01:29 PM
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United Kingdom, Aviemore
Joined Feb 2005
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Internal Oh-my meter! thought you could only get those from a shop with no windows
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Old Oct 01, 2011, 02:26 PM
Since 1952
Harry D's Avatar
Canada, AB, Edmonton
Joined Oct 2004
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IRA - Internal Resistance Analyzer [Analyser]?

Maybe the somewhat confrontational aspects associated with another meaning of that acronym wouldn't be as significant in other parts of the world as they might be in yours...
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Old Oct 03, 2011, 04:59 AM
who dares wins
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London,England
Joined Apr 2005
1,850 Posts
My ‘Wayne ohm meter’ is indispensable.

I think it’s as important to have for electric flight as a watt meter.

A quick check of my packs on Friday night showed an unusually large pack IR on one of them, I then checked all the cells of the pack and they were fine. I stripped the heat shrink on both bullets and found that the solder on the second had failed, it was held together with the heat shrink only… but still able to take a charge. I re-soldered it ready for Saturday, IR now reading as expected (I let the pack sit for good order after soldering before taking a reading). That’s potentially a model saved, had I flown the pack as it was.

The meter also tells me that the Gens ace 25C packs I have are potentially better (not taking into account longevity as I don’t have enough cycles yet) performers than the TP 65C’s I have.

A friend flew my 8s Habu32 yesterday, pretty much full throttle all the way. The motor cut due to LVC (not something I’ve seen for years as I fly within the limits of my setups, but hey) which is not surprising with 80amps drawn on 25C 3800’s with only 20% remaining (thankfully It has a separate rx pack in // to the BEC). Using Wayne's meter on the packs after they’d returned to normal temperature quickly showed that surprisingly (for me) they hadn’t been damaged, giving me confidence to charge them and fly again.

Alex
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Old Oct 06, 2011, 09:22 AM
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Joined Jan 2010
272 Posts
IR from FMA PL8

So how close is the cell IR reading from the PL8 to this IR meter?
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