Battery capacity and Cellpro charger

[flyboy320]

After about a six minute run time on my Trex 450, when I hook up my battery (3s 2200mah) to the cellpro 4s, it will say battery level 25%. Now this battery is a 2200mah, so with a level of 25%, that should mean the charger should put in about 3/4 * 2200 = 1650. When the charge is done, and I check to see how much was put back in, it will at most be about 1100ma.

So what is this telling me? Is the battery getting old, and its capacity is getting low and the 25% level the charger is telling me is correct, so in effect its now about a 1460mah battery, or is the battery level of 25% wrong, and I should be able to discharge the battery further until I'm putting about 1650ma back in?

[astroflyer]

I think mainly it is telling you that these meters are just a reference..

I see similar numbers on similar packs and have seen such on some packs for almost two years so personally I wouldn't worry much about it. I also fly six minutes on a trex with almost identical numbers on the cellpro.

I personally don't go below the 25 percent indicated on the cellpro.

On a 2200 pack you'll never get anywhere near 2200 out of it even if you killed it totally. Long before the pack reached it's 2200 capacity the motor wouldn't even turn over. There is always residual capacity in any battery after it is "dead" so 2200 is not a reality in terms of real use.

I think with the cell pro, a longer time to put that much back into the pack is more an indication of an aging pack. When you first start using a battery it might take say 45 minutes to fully charge after 6 minutes. Later when you see it taking an hour or even more, then you could probably assume the pack is aging.

my .02 worth

[zagiman]

It takes a few minutes for it to become more accurate. It can take up to 3 minutes before it becomes something I would pay attention to. However, it is only an estimate but, it does get more accurate what the percenage left in the pack as the charge goes on. I've had mine say 20% right when I plugged it but, after 3 minutes or so is the percentage that I believe based on what it puts back in.

Again, it is only an estimate. Always, verify by calculating 80% of the pack and making the sure the mAh you put back in doesn't go above that number.

BTW: I fly about 5 minutes on my 2170s and that is about how much I put back in my packs as well.

[th3tick]

My 2 cents is this: don't pay too much attention to the %age shown. Base your info on the mAh you're putting back in, and obey the 80% rule. If you're only putting 1100mAh back in, then you should be able to fly longer. Aim for about 1760mAh back in, although it will always take more mAh to charge it than you discharged.

One note of caution: don't just do the math and do 6 minutes uses 1100, so that's 1760/(1100/6) = 9.6 minutes. Work your way up to 1760 gradually, say by adding 30s at a time.

Also note that older weaker cells may not give quite as many mAh as new, so you may get less than 1760 out of a pack. That's where a low-voltage alarm may be a good backup to a timer to let you know the pack has hit a voltage where you should stop. I usually go with 3.3V/cell plus another 0.5V margin on the warning to stop.

John

[George1234]

After about a six minute run time on my Trex 450, when I hook up my battery (3s 2200mah) to the cellpro 4s, it will say battery level 25%. Now this battery is a 2200mah, so with a level of 25%, that should mean the charger should put in about 3/4 * 2200 = 1650. When the charge is done, and I check to see how much was put back in, it will at most be about 1100ma.


I believe that the Cellpro is set up to read battery level above the 20% minimum. In other words, it will read 0%, but still has the 20% required. In your case that would mean 20% + 25% or 45%left at the beginning of the charge. That would be 990mah remaining, 1210 to full charge, sounds fairly close.

George

[Pinecone]

Exactly. I remember reading this somewhere, but even so, first time I hooked up a pack it got my attention. :)

[flyboy320]

I believe that the Cellpro is set up to read battery level above the 20% minimum. In other words, it will read 0%, but still has the 20% required. In your case that would mean 20% + 25% or 45%left at the beginning of the charge. That would be 990mah remaining, 1210 to full charge, sounds fairly close.

George

That would be interesting, and also make sence if true...I'll have to go digging :wink: