% Accuracy on Cellpro 4S

[rourkem]

When you plug a battery into the Cellpro 4S it estimates the percentage mAh left. You get one number at first, and then it tends to drop a little until it stabilize. It then slowly climbs as the battery charges. How accurate is that number?

I base my timed flights on the mAh put back into the battery as a percentage of advertised capacity. It occurs to me that the advertised capacity could be off and also that the capacity could decrease over time.

What do other folks do?

[zagiman]

I've always found it pretty close but, not pin point accurate. It doesn't show % of total mAh but, how much is left of the 80% of total capacity is used. So, if it reads 0% you have used 80% of the batteries full capacity.

That has been my experience. However, I just go by the mAh I put back in and just use the % capacity to get an idea when I first plug the battery in.

[astroflyer]

hmmmm....I don't think so. it bases capacity left on total capacity of the pack. 20 percent left means 20 percent left.

[zagiman]

Well, when I calculate what 80% of my pack is and then figure out the mAh based on the % it gives, it is pretty close to what the charger puts in.

If that was the case, then the % it gives is way off. I have seen it give around 20% to 25% or so and only put in about 1356mAh back in a 2200mAh battery.

[astroflyer]

I've seen nothing in either the cellpro 4s or 10s manuals indicating it bases the percentage left on the 80 percent rule. If that was how the metering was meant to operate, there'd be some discussion of that in the manuals.

no flame intended but I'm sticking with 20 percent being actually 20 percent.

a 2200 pack doesn't mean that you have 2200 you can actually use. even dead there is residual amperage. 25 percent of 2200 equals 550 plus your 1356 is 1906. with residual amperage and possible misrepresentation of the actual pack amperage, it's as close as those meters can get IMHO.

[zagiman]

80% of 2200 is 1760. 25% (taking the higher number since I can't remember exactly( of that is 440. 440 + 1356 = 1796. Yes I would have used more than I should have (not by much though). However, I never said the gauge was pin point accurate, which we both agree on. I have 2 of these chargers. One has older firmware and the other has much newer. Both, appear to indicate (to me anyway) that the gauge is % left of the 80% of capacity.

Edit: I just sent FMA question asking what it measures. If they come back and say that it measures total left of capacity, then the gauge isn't just a little off, it is a lot off.

[astroflyer]

your numbers are correct and similar to what my cellpro indicates with 2100 lipos. BUT the cellpro (as do I) knows you cannot get 2200 usable mah from a 2200 lipo. I can't tell you exactly how much is not usuable but guess it is in the area of 200 and perhaps even 300 mah.

the cellpro assumes dead or zero percent is 3 volts per cell or 9 volts on a three cell lipo. There are quite a few MAH left in a 2200 at 9 volts. If you don't believe that, just short one out at nine volts and see what happens. from nine volts to actually dead as in zero mah left is where the difference comes in. It's not usable for flight. but still usable when the manufacturer claims the pack is 2200 mah.....

Hope the cellpro folks respond to your email and maybe we can figure this out. meanwhile I still vote for 20 percent being 20 pecent.

IMHO if you consider your 2200 to be for practical purposes a 1900 to 2000 then the cellpro numbers are pretty accurate.

[rourkem]

Astro: based on the above, should we be timing flights to use 80% of the total advertised capacity, or 80% of the usable voltage?

Should I be trying to get to the point where my Cellpro ready 20% left when I go to charge, or less than 20%?

[astroflyer]

Time your flights so you see 20 percent indicated on the cellpro.

I fly my 2100 packs for a six minute flight and see right around 20 percent left indicated by the cellpro. I believe that to be correct and my current four batteries are almost through their third year of flying my 450, and still going strong. so if you see 20 percent or more on your cellpro after a flight, things are working for you and in fact that number is what I'd shoot for.

I too see 1200-1300 replaced during the charge. as zagiman points out, that doesn't indicate a 2200 pack, but I think my take on that explains it.

no disrespect meant to zagiman!

[zagiman]

Astro:
They did respond. Sorry for taking so long to report back as I went straight to the flying field afterwork and just got back. You are correct. It does report full capacity. I learned something from this as well, that a lipo isn't fully 2200mAh even though it is labelled as such. Never heard of some of it being unusable off the bat. I guess it was just pure coincidence that the numbers worked out the way they did to make it look that way.

BTW: No disrespect taken.


rourkem:
Time your flights as Astro says. As lipos age the usable capacity does diminish (I was under the impression they started at the advertised capicity) and you will need to shorten your flight times accordingly. A count down timer with an alarm will help you to ensure you do not over fly them and watching the mAh put back in will let you know when you need to start shortening up your flight times. mAh put back in will always be pretty close to pin point accurate as you are going to get. Where the fuel gauge is not quite as accurate.

[astroflyer]

Thanks for the info from FMA zagiman. Lots of stuff in this heli world that is kind of confusing.

thoroughly enjoyed our conversation and hope we'll chat again elsewhere on this great forum.

[E2C_Mech]

Hi,

When the voltage of a lipo cell is reading 3.1 volts, there is no capacity left and the fuel gauge will read 0% remaining. The Cellpro is +- 15% when a pack is first connected. You should wait approximately 3 minutes to obtain a more accurate reading. The closer the pack gets to full charge, the more accurate the reading will become. The fuel gage is intended to give you an idea where you pack is at after completion of a flight.

[joediamond]

That's correct. Per an email from FMA they stated that 0% is 3.1 volts per cell.

[let60]

I have a 4s and a couple of 2s1350mah FMA lipos. I use these in my esky FP and a small plank. I have put close to 1350 back in these cells several times. I have had them for about 1 1/2 years and they still work great. If I had to guess I would says they have around 200 charge cycles on them. They have some great batteries. My FP flys for over 20 minutes on these and I can recharge them in about 20 - 25 minutes on the #2 auto charge setting.