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Old Aug 31, 2013, 03:59 PM
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Originally Posted by Wayne Giles View Post
L2F,

Thanks for endorsement.

I have a new version of the ESR meter which will shortly be available aimed at competition flyers and other user of large capacity high C rate packs.
It is re-dimensioned to use a higher measurement current pulse (25A) and produce a resolution of 0.01milliohms instead of 0.04milliohms in Cell Mode, with a resolution of 0.1milliohms in Pack Mode.

Will post more details when it is available, but the standard unit is still the best bet for an average flyer.

Wayne
Hi Wayne, Any update on when the new meter will be available?
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Old Sep 01, 2013, 11:17 PM
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Strange readings from ESR meter?

Wayne,

I recently encountered strange readings from my meter, I was hoping that you could shed some light on this.

I discharge one of my 2S lipos (5000 mah, 30C) at 30 A to 6.0 volts. pack temp increased to approx 40 deg C. I then tested the pack on the meter, one cell read very low 1.3 mohm. After successive pushing of the bottom, the resistance was dropping, it went to 0.36 mohm, then went to 40.05 mohm??!!

I tested on another pack (same type), when testing for resistance after a 30A discharge, the reading for the pack was at 400+ mohm, and each cell at 40+ mohm. When the pack cooled, readings were back to normal, approx 4 mohm per cell.

Does this have something to do with the meters resolution or something?

Appreciate any insight that you could provide.

Regards,
Mike.
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Old Sep 02, 2013, 02:01 AM
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Mike,

The reason for these wild readings is that the unit needs a minimum voltage of 6.6 - 6.8V supply from the lipo under test DURING THE LOAD PULSE.
The voltage of a discharged 2S pack will collapse to below this voltage level during the pulse so that the reading becomes meaningless.
The reason that it seems OK after the pack cooled would be because the voltage will have recovered to the point where it would remain >6.8V during the pulse.

Always read a pack when it is charged. Even if it is a 3S pack or larger so that you get a correct reading, it may be that you are looking at a discharged cell, so that the reading is still meaningless.

If the meter has the single cell modification, it is better to use an auxillary supply for testing smaller or partially discharged 2S packs which ensures valid readings.

Wayne
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Old Sep 02, 2013, 09:49 AM
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Originally Posted by Wayne Giles View Post
Mike,

The reason for these wild readings is that the unit needs a minimum voltage of 6.6 - 6.8V supply from the lipo under test DURING THE LOAD PULSE.
The voltage of a discharged 2S pack will collapse to below this voltage level during the pulse so that the reading becomes meaningless.
The reason that it seems OK after the pack cooled would be because the voltage will have recovered to the point where it would remain >6.8V during the pulse.

Always read a pack when it is charged. Even if it is a 3S pack or larger so that you get a correct reading, it may be that you are looking at a discharged cell, so that the reading is still meaningless.

If the meter has the single cell modification, it is better to use an auxillary supply for testing smaller or partially discharged 2S packs which ensures valid readings.

Wayne
Thanks Wayne!

This explains the behavior...

BTW, the meter can only measure resistance of pack up to 6000mah. If I was to measure resistance of a 7200 mah pack, how far off would the readings be?

Thanks again!!
Mike H
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Old Sep 02, 2013, 11:33 AM
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Originally Posted by mhavlena View Post
Thanks Wayne!

This explains the behavior...

BTW, the meter can only measure resistance of pack up to 6000mah. If I was to measure resistance of a 7200 mah pack, how far off would the readings be?

Thanks again!!
Mike H
No problem Mike to measure any capacity cell. The reading will still be accurate.
I should never really have put an upper limit on it. The current pulse is 16A which is not much for a 7200 cell ( but much larger than chargers use) but IR is largely independant of current anyway.
The limit you must not exceed is the 6 cell limit.

Wayne
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Old Sep 05, 2013, 02:53 PM
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Originally Posted by Ohmic View Post
Hi Wayne, Any update on when the new meter will be available?
Ohmic,

Sorry for delay in replying.
I have made a very small batch (3) of the Hi-Resolution version of the meter.
The price is 58.60 or $98.50 with postage costs as per standard unit on page at http://www.rcgroups.com/forums/showp...&postcount=249

It is a different version of the standard meter. I am not claiming it is better; just different and aimed at a specialist requirement of very high resolution at the expense of total range capability. Thus it will measure very low values more accurately but is only suitable for high capacity, high performance packs.
If you are not sure whether it is suitable for a particular application, PM me and I will try to help.
The last situation I want is a customer with one who wishes he had bought the standard unit.

Wayne
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Old Oct 16, 2013, 02:21 PM
Tim Lampe; Hobbico R&D
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Purchased and waiting for delivery of my new ESR meter (thanks Wayne!).

For valid comparisons from pack-to-pack, I understand it is paramount to be consistent with battery temperature. I understand the standard temp is 72F (71.6). To that, how do you bring your LiPos to this temp for testing?

Tim
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Old Oct 16, 2013, 02:38 PM
Tim Lampe; Hobbico R&D
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And thinking ahead...

The packs I am using are ThunderPower 5S 70C 1800mAh (comprised of one 2S pack and one 3S pack connected in series) and Genesis Power 5S 65C 1800mAh (configured the same).

Then, if the drive in my plane draws about 50A, then the measured cell IR I'm looking for is 4.3 (in the F.O.M. calculator, when I set the capacity to 1800 and the IR to 4.3 the Max Current comes out to 50).

Also, during a flight I draw only about 1100mAh from the pack (but it's right at 50A the duration).

From what I gather, 4.3 is extremely low. But if I'm drawing only 50A from an 1800mAh pack that's less than 30C anyway.

Tim
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Old Oct 16, 2013, 03:56 PM
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Originally Posted by KRProton View Post
Purchased and waiting for delivery of my new ESR meter (thanks Wayne!).

For valid comparisons from pack-to-pack, I understand it is paramount to be consistent with battery temperature. I understand the standard temp is 72F (71.6). To that, how do you bring your LiPos to this temp for testing?

Tim
Tim,

I used to use 25*C (77*F). as a standard temperature only on the basis that 25*C is usually the ambient temperature quoted in specifications of most electronic components. Mark Forsyth pointed out, very reasonably, that the average house or apartment emperature was more like 22*C which really means that is what his house is set to!!! I am forced to agree so we changed the measurement temperature to that value.
So the answer to your question is that you leave it to settle for 2 hours at least in that ambient. Being in the UK and having an outside workshop which generally runs well below that, I have converted a small drink cooler/ heater into a temperature controlled enclosure and set it go 22*C. Again I soak them for 2 hours before test.

Re your later post, I am away at present so don't have access to records but 4.2milliohms does not sound too low for a good 1800 cell at 22*C. I have seen a several 2200 cells at <3.5 milliohms which pro rata is about the same.

Remember that the Lipotool is just a guide and that if you preheat your lipos, the IR will be lower and you can then take more current without overstressing them.
This is within sensible limits of course.

Also be aware that some of the latest lipos claiming very high C ratings, really just have a higher temperature coefficient of their IR which means that you can take higher currents, but the downside is that they do not perform well at lower and moderate currents.

Wayne
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Old Oct 16, 2013, 04:13 PM
Tim Lampe; Hobbico R&D
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Superb and thanks then Wayne.

The setback thermostat in my home during the afternoon and evenings when we're home is set to 72F I believe (I keep bumping it up, but my wife - being the one who pays the bills (I balance the checkbook) - turns it back down to 72!)

So, I'll just get a good thermometer and find a room or area in the house that seems to stay around 72F (away from windows, air ducts, etc.) and "soak" the batteries there before taking readings.

Also, the batteries I'm most concerned with - the ones I use for F5D - use Castle Creations 4mm bullets. I'll convert your meter upon receipt to same, yes?

Tim
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Old Oct 16, 2013, 04:34 PM
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Originally Posted by Wayne Giles View Post
which really means that is what his house is set to!!!
Guilty.

My home 'thermostat' consists of my open windows and cool ocean breezes. Close proximity to the Pacific has its benefits!
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Old Oct 16, 2013, 05:47 PM
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Guilty.

My home 'thermostat' consists of my open windows and cool ocean breezes. Close proximity to the Pacific has its benefits!
yes it does!! where are you located?
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Old Oct 16, 2013, 05:56 PM
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South Bay. Just northwest of LB.
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Old Oct 19, 2013, 12:17 PM
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Just wanted to say thanks to Wayne for a terrific meter. I haven't used mine much yet, but I'm very impressed with how easy and quick it is to use.

Many thanks!


David
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Old Oct 21, 2013, 11:00 AM
Tim Lampe; Hobbico R&D
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Just asking for clarifications on a few things with my ESR meter;

To use the FOM (Figure of Merit) calculator, you read the resistance of each cell in your pack, then enter the single highest value (most resistance) in the calculator, right?

For consistency to compare all your packs (and to compare to packs those cataloged in the forum) readings should be taken at 72F (22C). This is a fine tool for finding my best and worst packs and comparing to others in the forum. However, the packs I am most concerned about the ones I use for racing I preheat. So then, to find real-world maximum discharge Amps (C-rating) for these packs, would it be prudent then to also take resistance readings at the temp at which I will be using these packs?

In other words, I assume the FOM calculator takes into account normal heating of packs, but what about pre heating?

Thank you.

Tim
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