not to be trusted , battery meter

[ben goodfellow 1]

while flying the night, i used my mates battery meter the little black type that tells you the percentage and voltage remaining . i thought ill see what mine says and it was a different reading ,so tried 2 others .they were all different . the four different readings were 51% ,55% 66% and 83% so how can we trust them or what else can i use .. fly low

[Gary Manuel]

I generally trust the first reading I take after landing, when the battery is hot as it is whilst flying - with high internal resistance.

I don't think it's coincidence that your readings are increasing as the battery cools down and it's internal resistance drops and chemistry stabilises.

[ben goodfellow 1]

no these were all taken at the same time sevaeral times on each different meter and were all different.fly low

[John Olsen 1]

I only trust the meter to confirm that I have in fact picked the right battery, eg one that has been charged, not one that I used. So I expect to see either over 95% or under 50%. The flight time is short enough without starting with a partly charged battery.

John

[Phil Green]

Posted by Gary Manuel on 18/06/2014 23:30:24:

I generally trust the first reading I take after landing, when the battery is hot as it is whilst flying - with high internal resistance.

I don't think it's coincidence that your readings are increasing as the battery cools down and it's internal resistance drops and chemistry stabilises.

Gary, sorry but this is quite wrong.
Both NiMh and Lipo batteries have a negative temperature coefficient, as the cell temperature rises, the internal resistance falls.

Cheers
Phil

[iqon]

dont know if its true but have been told they are no good for testing nimh`s....

[john stones 1 - Moderator]

What type of battery are you checking Ben ? I carry 2 both read pretty much the same, I also just bought a 3rd to check lipo's percentage and balance, again all read the same

John

[Gary Manuel]

Posted by Phil Green on 19/06/2014 00:14:28:

Posted by Gary Manuel on 18/06/2014 23:30:24:

I generally trust the first reading I take after landing, when the battery is hot as it is whilst flying - with high internal resistance.

I don't think it's coincidence that your readings are increasing as the battery cools down and it's internal resistance drops and chemistry stabilises.

Gary, sorry but this is quite wrong.
Both NiMh and Lipo batteries have a negative temperature coefficient, as the cell temperature rises, the internal resistance falls.

Cheers
Phil

Quite right - my brain must have gone to sleep before me. Battery resistance is lower and chemical reaction faster at higher temperatures, which is why we see better performance with a warm battery.

The point I was trying to make was that the meter reading we are interested in is the one at the high temperature immediately after landing as these are the conditions that will dictate the remaining flight time.

The meter reading will change as the battery cools down and its chemistry settles from the shock of rapidly discharging.

Ben,

It would be interesting to see what readings are given on the different meters with a fully charged battery. Maybe they are set up for different types of battery (LiIon, LiFe, NiMh etc)?

I personally use a Fusion SmartGuard 2 meter and have found it to be very reliable on LiPo batteries, which is it's default type. I'm assuming that you were using LiPo for night flying.

Gary.

[john melia 1]

Has a battery checker specifically for LiFe batterys came out yet, i have a checker that does four different cell types, but on fully charging my life packs the checker only reads 66% with each cell being 3.3v

Charger says its full, checker says its 66%

[john stones 1 - Moderator]

G.T. power capacity controller

lipo,life, lilon,nimh, NiCad

John

[Allan Bennett]

I'm not a big fan of "cheap" stuff, but with HK prices so low I decided earlier this year to get a couple of their meters. One is a wattmeter that has a receiver lead as well as a power lead, and two scales, so that I can check the receiver and servos' current draw. The other is a simple voltage display that plugs into battery balance leads. Both of them work, but they're not very accurate when compared with a reasonable quality dvm and another mainstream brand wattmeter.

Estimating the % remaining in an LiFe battery from a voltage reading is not easy, for the discharge curve is very flat. So any manufacturing tolerances could make a mater highly inaccurate if displaying %.

[Peter Miller]

I have an old Hitec battery checker. The black one with an unused battery compartment. I use it in the workshop before going flying to see if I need to top up a battery.

It is interesting that this always reads low because if I put the battery on my cycler/charger there is always far more in the battery than the checker says. e.g. 800Mah NiMH, checker says 50% capaccity left and the cycler will show that I had 600Mah left.

I also have one of the gold colour Hitec checkers and that reads even lower than the black one. I don't bother to use it.

[YakMad]

That's interesting I have one of those Hitec Gold battery checkers it was reliable when new but started reading low after about a year, I now use a Hyperion battery checker which is the same as the Fusion SmartGuard, seems to be fairly accurate.

[Josip Vrandecic -Mes]

I've had problems with measurement, and since then, I control voltages from two meters..

Old green one is 35 years old ,made ​​in Slovenia and a new yellow, Made in China ...lol

Edited By Josip Vrandecic -Mes on 19/06/2014 11:40:08

[iqon]

Smart guard 2 does life / lipo / nimh, as said , not reliable on nimh...

[ben goodfellow 1]

they were 2s life rx packs of 1100mah. i use 2 and they were both doing the same readings ,its just an overlander meter but they are all probs made in the same place . one of the lads that was there had a fusion meter with a switch to load the pack and that was set on 6v and the green light came on so indicating full. also when i checked my pack before charging my little black meter said around 70 % after charging it and putting in 58mah it said 98%.very odd .. flylow

[John Privett]

I had one of the black ones that appear under a variety of different labels and do LiPos, LiFes, NiMHs etc. and display individual cell voltages on the press of a button.

The LCD display on mine failed after a while, but not before I had cause to doubt the accuracy of the thing. It would consistently tell me that my batteries were down to 14% (rarely any other figure!) after use, and the cell voltage for cell 2 in all my 3S LiPos was always lower than cells 1 and 3. When the display failed I was glad to lob it in the bin.

The replacement - a smaller, simpler HK one has yet to be put to any real use, but the cell voltages on the batteries I've checked, look a lot better than what the old meter used to show.

[john melia 1]

Posted by ben goodfellow 1 on 19/06/2014 18:05:15:

they were 2s life rx packs of 1100mah. i use 2 and they were both doing the same readings ,its just an overlander meter but they are all probs made in the same place . one of the lads that was there had a fusion meter with a switch to load the pack and that was set on 6v and the green light came on so indicating full. also when i checked my pack before charging my little black meter said around 70 % after charging it and putting in 58mah it said 98%.very odd .. flylow

Ben thats what my life rx packs do, after charging they read maybe 66% then if i put them back on charge the charger might get 15-20mah into them, and my checker will state 96%, sometimes over time this drops to 66% with individual cells reading 3.3v each. I also use two 2000mah life packs in my sbach.

Anyone know how to reliably figure out what the % of a life pack actually is

[john melia 1]

Ben is that the fusion 2 battery checker, it states in the specifications not to rely on the % indicator, for life A123 or P04 packs!

The original fusion is only for nicad and nimh.

[ben goodfellow 1]

John P Thats funny , i use 2 packs together as 10 s and very very regularly they read 14% when im done, infact ive just tried the ones from last night .bet you cant guess what % is in them. J M hopefully some one will suggest one that works accurately as that would be handy for us ...fly low

[John Privett]

Ben, John M,  the problem is that LiFe cells have a very flat discharge curve.

So the voltage drops a bit initially but then only drops very slightly until just before the battery is almost "empty" at which point it stops dropping faster. This makes it much more difficult to equate a voltage reading with a "%age full" figure. Any slight error in the voltage reading is going to have a big effect on the % figure.

LiPo cells, on the other hand, have a much steeper curve, so are easier to show a %age figure based on cell voltage.

Edited By John Privett on 19/06/2014 21:14:46

[Peter Beeney]

Ben,

I would consider that you are never going to be very successful trying to judge the state of charge using this type of meter on a LiFe receiver pack. Because of the voltage and discharge characteristic of the LiFe battery you’d require a meter designed specifically for the Life. The meter is only a crude voltmeter, after all, with the readout given as a percentage, and just how accurate are they?

The LiFe discharge curve is very flat after an initial little fall, so it’s always going to be difficult to gauge the remaining capacity. Using an expanded scale very accurate voltmeter might be the best chance, with a Full Scale Deflection, (FSD), of say 500 millivolts perhaps. But it’s quite easy to fool these things anyway if you really want to. One way might be like this. Discharge a pack until flat and then recharge for just 20% of capacity. This will raise the voltage enough, and also hold it up long enough, so that that the checker would indicate the pack was fully charged. But we actually know, of course, in reality that’s it’s only one fifth charged.

I believe a much better indicator of the remaining battery capacity is the on-board Hextronik led indicator. I’ve given these a good coat of looking at before and posted the findings in a thread long ago. You can definitely rely on this to tell you exactly where the battery is. The first green soon goes out, but after that it goes down the leds very slowly; I tested four ganged together and all the reds came on simultaneously. Extreme precision, to say the least! I used a variable voltage supply with an accurate voltmeter.

Another plan too is to test discharge your pack in the first instance, at say 0.25C; make note on the label what the capacity actually is, rather than what the label says it is, and repeat occasionally, say yearly. This will indicate any early signs of deterioration, and a change of more than 10% might require further investigation.

Safety is everything, models that crash because of a power failure, and this will be totally out of control, too, are a very unnecessary and avoidable misfortune!

PB

PS Sorry John, I'd not seen your post!

Edited By Peter Beeney on 19/06/2014 22:26:21

[iqon]

because you get a good reading all the way till its too late I have gone back to using sub c batteries, if nothing else peace of mind......

[john stones 1 - Moderator]

Posted by iqon on 19/06/2014 22:57:11:

because you get a good reading all the way till its too late I have gone back to using sub c batteries, if nothing else peace of mind......

Think you'll find nimh behave similar Iqon, they don't taper like nicads either

Of course I could be wrong

John

[Biggles' Elder Brother - Moderator]

Like John O, previous page, I tend to use these mainly as a final check that I'm not accidentily picking up a discharged battery thinking its full.

Having said that I have found them fairly reliable in that a 5000mAh supposidly say 30% left does indeed take about 3250-3500 mAh of charge. I certainly wouldn't trust them to the last percentage point - but intuitively I would say the one I use (a Fusion) is within 5% or so of being correct.

BEB