Battery true % remaining

[CW.]

I've always calculated the percentage used from a battery by the mAh's I put back in.
So if I charge a 2200mAh battery and it takes 1,540mAh to put it back to 100%, that would mean it was 70% discharged leaving 30%/660mAh remaining.

A mate said that wasn't a true measure of the percentage remaining and I should use a battery checker, so I bought one. Well, if his reads 45%, mine will read 60% and to confuse things even further the new PL8 will say 35%

Should I be measuring voltage and not mAh's?

Please tell me the most accurate way to check the remaining percentage left in my batteries!

Chris.

[stanley1]

i do it your way and works for me, over time the capacity will drop though i guess so it wont always be the correct % i guess

[jamiem]

Mah used is the only true way of knowing what's left in it. Well, to be accurate, the only true way of knowing the ACTUAL capacity is to do a very low current full discharge. As a lipo ages, it's capacity drops, so you should adjust your flight time accordingly to extend its life.

In short, those checkers (I've got one myself) are a useful guide, but certainly not an accurate indication of capacity. Their best use is for checking cell balance, and as such can give an indication of a failing cell if it begins to go out of balance after a discharge cycle.

[Mark_T]

You are already using the best method, your friend is misguided.

[Mark_T]

Well, to be accurate, the only true way of knowing the ACTUAL capacity is to do a very low current full discharge.

I have seen it suggested elsewhere that you can get a good estimate of true capacity by doing the following :

¼ C discharge to 3.73V per cell
½ C charge to 4.18V per cell

The amount you put back in on the charge divided by 0.8 will roughly equal the real capacity of the pack.

I've not tested this enough myself to know for sure, but others with a lot more time invested in this sort of thing do seem to believe it is at least more reliably than just reading the label on the pack

[CW.]

Thanks guys, so I was on the mark in the first place..

I have a Powrelab 8 but haven't had it long and still haven't connected it to the PC. But ive read about a feature where it will work out accurate fuel tables for individual batteries. Has anyone tried this? would that do the job of working out the true capacity that you guys are talking about?

[PKNEC]

Hi Chris I thought your PL8 would have been the most accurate.
Have you done any comparison test with what the PL8 tells you at the start of charging and what it actually puts back in the pack.

[Mark_T]

Hi Chris I thought your PL8 would have been the most accurate.
Have you done any comparison test with what the PL8 tells you at the start of charging and what it actually puts back in the pack.

That will be no more accurate than the 'battery checker' unless you take the time to generate the fuel table for the pack.

[AcidDrink]

Thanks guys, so I was on the mark in the first place..

I have a Powrelab 8 but haven't had it long and still haven't connected it to the PC. But ive read about a feature where it will work out accurate fuel tables for individual batteries. Has anyone tried this? would that do the job of working out the true capacity that you guys are talking about?

I have done fuel tables for a couple of my packs, they give quite accurate results (as in percentage left etc.), but nothing better than looking at Ah in after the charge.
IMO, not really worth it, unless you are using these 1C/2C auto charge settings (I don't).

[scallybert]

Thanks guys, so I was on the mark in the first place..

I have a Powrelab 8 but haven't had it long and still haven't connected it to the PC. But ive read about a feature where it will work out accurate fuel tables for individual batteries. Has anyone tried this? would that do the job of working out the true capacity that you guys are talking about?

Calculating the fuel tables is quite time consuming, as it takes at least a 1C charge, 0.5C charge & 2 discharges (often limited to 100W)around 4-5 hours.

It's interesting to do, (and I guess it's a way of cycling new packs), but I've not really bothered too much. However, I guess it will give also you good capacity figures.

If you're into this sort of thing, you really want to use that PC interface. It unlocks loads of clever stuff.

[PKNEC]

CW have a look at this it sounds like the PL8 does it all for you providing you have a spare few hrs
http://www.rcheliaddict.co.uk/batter...el-tables.html

[Mark_T]

CW have a look at this it sounds like the PL8 does it all for you providing you have a spare few hrs
http://www.rcheliaddict.co.uk/batter...el-tables.html

Seems to be a slightly inaccurate statement of the benefits of using a custom fuel table on that link.

It really can't help you get more charge into a pack, what it will do is give you a more accurate fuel % and it will allow a 'C' based charge setting to be a bit more accurate, but it will never affect the actual charge put into a pack as that is managed on the voltage of the cells and the target you set for that voltage, it has nothing to do with fuel tables.

[cjcj1949]

I prefer to use the voltage on discharge as a guide. It corresponds to the 80% rule in many cases but gives a more useful result. The better a battery is the lower you can take it before it starts to get damaged. This drop in volts increases as temperature goes down and as the battery ages. By sticking to a known voltage 3.6 or 3.7 on load you can get safe discharges that automatically take account of how you fly and how much current you take out of your battery.80% doesn't quarantee that everything is ok. With an old battery or a high drain you may have to restrict yourself to 50%. Checking the volts stops the batteries getting more than warm which seems sensible if you want them to last.

[CW.]

Thanks guys,
The powerlab is closer than the battery checker with the % remaining but it still doesn't agree with the amount that goes back in.

I've got the usb adapter so will definitely get it plugged into the PC and start doing fuel tables for my batteries.

On that note, will I need to do a fuel table for every battery or just each type? for example one for all the Nano-tech 3S 2200mAh one for all the Turnigy 3S 2200mAh and one for all Turnigy 6S 5000mAh etc...

Chris.

[Mark_T]

This is going to take you a while so be real sure you want to do it as the benefit is close to zero ...

The only thing you are going to gain is a slightly more accurate fuel % and slightly more accurate charge if you use the 'C' rating approach rather than setting an amp based charge level.

You will not get any more charge into the cells, full is still going to be full.

If you really want to do this though I'd just do it once for each type. It won't be 100% accurate as the packs will be different, but 100% accurate doesn;t get you much anyway.