Lipo charging

[Dave Potter]

Hi Guys. When charging my 2.2 lipo Batteries on my charger they charge to 0.0A on my charger but the charger never reaches full. when I checked them on my tester it gives me a reading of 12.56V and 98.56 % is this ok to fly?

Regards Dave........

[Keith Sharples]

Hi Dave. That sounds perfect to me. All my 3s lipos charge to approx 98-99% every time which is the norm. The accepted max charge level is listed as 12.65V which is 100% so your 12.56v is correct. The lecy techies on here will no doubt have more info for you.

Keith

[Alan H]

I agree with Keith, a fully charged cell is around 4.2V so a three cell pack will be around 12,6V immediately after charging but this will quickly drop back to the sort of level you are seeing. I would check what the individual cells read on your tester to make sure they are reasonably well balanced.

[Nigel R]

Sounds like the charger had reached full, as far as it is concerned.

As said cell voltage drops a bit once removed from the charger.

You're within a percent or two. Plenty close enough.

4.2v per cell is completely full. It's s bit of a grey scale though. More volts equals faster rate of cell damage.

For what it's worth one if my chargers goes to 4.16v per cell which is plenty full.

[Dave Hess]

The problem is the accuracy of whichever measurement device yo use. If you use three different ones, you'll most likely get three different voltages. Anything up to say 0.03v difference per cell is pretty normal.

We generally take 4.2v per cell as the charge cut-off point, but that's just a compromise between capacity, life and safety. If you charge to a lower voltage (say 4.1V) and don't discharge below 3.5v, your lipos will last a lot longer. At those voltages, you're not giving away much capacity because the voltage vs charge graph steepens above 4.1v and below 3.5v.

[Former Member]

[This posting has been removed]

[Biggles' Elder Brother - Moderator]

No the problem is your charger is trying to balance the battery and failing to achieve what it considers a satisfactory balance - as it nearly always will. Which is why I say (to great dismay in some quarters) that in practical terms balance chargers don't work!

The scenario goes something like this:

1. you put the battery on charge at say 1C. Initailly - and for about 40-50 mins it charges at 2.2A, gradually decreasing the current towards the end as the battery nears full.

2. One cell hits 4.2v - everything stops - can't just keep on charging because that cell will end up over charged and potentially damaged.

3. Enters "balancing mode", loads the high cell to pull it down. The 0.0A bit - its actually pulling small amounts of negative amps!

4. Having reduced the high cell, returns to charging - usually at a cautious 0.1A in the hope that the low cells will close the gap - which they do but very, very, very slowly!

5. Before it can get to a balanced state - the charger's timer calls "end" and it all stops, the battery is still unbalanced because the charger's threashold of what "balanced" means is still less than the diffeence between the higest and lowest cells.

This state of affairs is why your battery is never 100% charged, always 98% or so. Some of the cells are slightly lower the 4.2v, in fact there is most probably just 1 high cell and 2 lower ones. By the way, don't bother to extend the timer if you can, in the hope that the charger will reach balance - you won't live that long!

I believe I have a solution to this and I explain it in the next issue of the mag in my "Current Affairs" column - that will sort it for you! Hopefully!

BEB

Edited By Biggles' Elder Brother - Moderator on 01/09/2018 20:40:25

[Biggles' Elder Brother - Moderator]

Posted by Ikura on 01/09/2018 20:35:17:

Having charged to 4.15v per cell (95%) my LiPo's and discharging after every flying day to 3.8v my LiPo's are in really good condition with no signs of puffing of performance loss.

Prior to that I just left them until I next charged them to 4.2v and within a year most of them had started to get puffy and my flight times were slightly reduced.

I'm sure there will be a lot of people who will say they fully charge theirs and never get problems but this routine works for me and I like it that my LiPo's stay flat.

Edited By Ikura on 01/09/2018 20:36:10

I agree Ikura - one of the main causes of puffing in my opinion is keeping batts fully charged on the shelf too long.

BEB

[John Tee]

Most chargers I use only show two digits so can't display 100%.

John

[Biggles' Elder Brother - Moderator]

Perhaps because they know you're never going to get there!

BEB

[Nigel R]

A single 2.2ah lipo can be balanced by a B6 clone given enough time.

Didn't we do this on another thread?

With a brief analysis of the circuits in use deriving the balance rate to show this?

[Dave Hess]

Posted by Biggles' Elder Brother - Moderator on 01/09/2018 20:40:04:

No the problem is your charger is trying to balance the battery and failing to achieve what it considers a satisfactory balance - as it nearly always will. Which is why I say (to great dismay in some quarters) that in practical terms balance chargers don't work!

The scenario goes something like this:

1. you put the battery on charge at say 1C. Initailly - and for about 40-50 mins it charges at 2.2A, gradually decreasing the current towards the end as the battery nears full.

2. One cell hits 4.2v - everything stops - can't just keep on charging because that cell will end up over charged and potentially damaged.

3. Enters "balancing mode", loads the high cell to pull it down. The 0.0A bit - its actually pulling small amounts of negative amps!

4. Having reduced the high cell, returns to charging - usually at a cautious 0.1A in the hope that the low cells will close the gap - which they do but very, very, very slowly!

5. Before it can get to a balanced state - the charger's timer calls "end" and it all stops, the battery is still unbalanced because the charger's threashold of what "balanced" means is still less than the diffeence between the higest and lowest cells.

This state of affairs is why your battery is never 100% charged, always 98% or so. Some of the cells are slightly lower the 4.2v, in fact there is most probably just 1 high cell and 2 lower ones. By the way, don't bother to extend the timer if you can, in the hope that the charger will reach balance - you won't live that long!

I believe I have a solution to this and I explain it in the next issue of the mag in my "Current Affairs" column - that will sort it for you! Hopefully!

BEB

Edited By Biggles' Elder Brother - Moderator on 01/09/2018 20:40:25

That's true for iMax type balance chargers that charge through the power leads, but if you use something like a BC168 that charges each channel independently through the balance leads, you get perfect balance as far as the accuracy of the electronic components can measure it - none of that iterative process at the end of the charge cycle.

I got a cheapo charger with my RTF Carbon Cub +, which also charges 3S through the balance leads. It seems to be really good too, so you don't need to spend a lot.

I have a load of lipo alarns and various other cell-voltage measuring/indicating devices. It's surprising how much variation you get when you attach them to the same battery. I spent over 20 years as a quality manager in different industry sectors. One thing I learnt: You see a number on the measuring device readout/display, but it doesn't mean it's right.

[SONNY MONKS]

Which are the best brand of lipos,i have overlanders,but find them rather expensive,at 48 quid each,i only have three,having thoughts of getting another electric model!!

[john stones 1 - Moderator]

Posted by Ikura on 01/09/2018 20:35:17:

Having charged to 4.15v per cell (95%) my LiPo's and discharging after every flying day to 3.8v my LiPo's are in really good condition with no signs of puffing of performance loss.

Prior to that I just left them until I next charged them to 4.2v and within a year most of them had started to get puffy and my flight times were slightly reduced.

I'm sure there will be a lot of people who will say they fully charge theirs and never get problems but this routine works for me and I like it that my LiPo's stay flat.

Edited By Ikura on 01/09/2018 20:36:10

I suspect those that leave them fully charged, don't do it for long periods, I'm guilty of not storing mine properly and it has ruined them, ruined a few quids worth through my own laziness.

[Biggles' Elder Brother - Moderator]

Posted by Nigel R on 01/09/2018 23:40:53:
A single 2.2ah lipo can be balanced by a B6 clone given enough time.

Yes and I agree with the principal and always have - I do understand how a charger works believe it or not!, The theory is fine. Its the practice that is at fault here. You see the point is Nigel do you have any conception of how much time "enough time" is? Well I think, following some very extnsive (and extremely lengthy!) experiments, I do - I believe me you might not even live long enough!

BEB

[Geoff S]

Posted by SONNY MONKS on 02/09/2018 10:22:03:

Which are the best brand of lipos,i have overlanders,but find them rather expensive,at 48 quid each,i only have three,having thoughts of getting another electric model!!

I've had good service from Zippy Compacts from HK. I'm still testing Turnigy Graphene 3S 2200 but the 2 I have are performing well but if they live up to the longevity claims remains to be seen (up to 30 cycles so far) although I had one fail on one cell last year.

I've had several 4S 4AH Fluoron LiPos bought via eBay and they seem to be excellent with commendably low ESR (< 5mohms/cell). They're quite cheap too at around £25 posted IIRC.

However, I'm not convinced there's any one make that's 'the best'. I suspect the differences for the high C rating ones are mostly down to selection in the manufacturing process. I have a Wayne Giles ESR meter (as well as an iCharger which gives ESR readings) and few (if any) LiPos actually match the claimed C ratings. I more interested in longevity as none of my models push the C ratings.

Geoff

[Stephen Smith 14]

Cellpro 10S and 10X are capable of charging through the balance leads only (no need to plug the balance lead in) they see the cells as individuals not 1 battery and charge them at full power till they are fully charged giving perfectly balanced charges every time. So it's not strictly true that balance chargers don't work.

[Biggles' Elder Brother - Moderator]

You're quite right Stephen. But:

1. the CellPro (splendid bit of kit that it is) costs well over £200 and that doesn't include a power supply! For most modellers "balance charger" equals B6 type in various guises.

2. Th CellPro, as you correctly point out, does not use the same balancing method as a B6.

So perhaps it's fairer to say the balance charger used by the overwhelming majority of modellers doesn't work in practical terms on all but the most tiny of inbalances" - but that's a bit of a mouthful!

BEB

[PatMc]

How does the CellPro charge through balance leads that are not plugged in ?

[Stephen Smith 14]

Posted by PatMc on 09/09/2018 21:19:34:

How does the CellPro charge through balance leads that are not plugged in ?

Should have said no need to plug the main lead in

[Martin Harris - Moderator]

Posted by Biggles' Elder Brother - Moderator on 09/09/2018 21:07:38:

You're quite right Stephen. But:

1. the CellPro (splendid bit of kit that it is) costs well over £200 and that doesn't include a power supply! For most modellers "balance charger" equals B6 type in various guises.

2. Th CellPro, as you correctly point out, does not use the same balancing method as a B6.

So perhaps it's fairer to say the balance charger used by the overwhelming majority of modellers doesn't work in practical terms on all but the most tiny of inbalances" - but that's a bit of a mouthful!

BEB

I have to say that I'm struggling to follow the conclusions of your explanation BEB. While I understand the logic of your reasoning, I've used several different balance chargers on a regular basis, ranging from very cheap B6 clones to far better specified ones and all of them have achieved cell balance which satisfied their parameters.

Yes, packs which have become badly imbalanced do take a lot longer, but I don't think any of mine have taken more than a couple of hours before the charger has brought the cells to (sufficiently to satisfy their specified requirements) equal voltages.

How do you define "the most tiny of inbalances"?

[Frank Skilbeck]

I think that most balance chargers work by using the balance lead to bypass a small current around the highest voltage cells, if you charge at a high rate then even bypassing a small current will not allow the lowest voltage cells to catch up. I usually re-balance a pack by charging it, on the balance setting, at a low charge rate i.e. 0.3c this way the pack takes longer to charge up so the lowest voltage cells have more time to catch up. Works for me.

[Biggles' Elder Brother - Moderator]

Good question Martin! I suppose one man's balanced battery is another man's unbalanced battery - at least over a certain grey area anyway.

Fo myself, taking a 6s battery as a basis, I aim to have a voltage spread over all six cells of, at least, less than 20mV and preferably less than 10mV. My experience is that if the inbalance (by my definition) is say 25-30mV a B6 style charger might make an impact on that - given enough time. An inbalance of significantly more than that - well there may not be enough time left in the life of the universe!

But I have gone beyond just "my experience" - ie anecdoatal evidence - I have data logged the balance process for a number of batteries on different chargers and plotted out the esults. This is told me many things but one in particular is interesting - the convergence process seems to be assymtotic, therefore the rate of convergence decreases dramatically as balance approached. This is to be expected really and wasn't a big surprise, but the next bit was! The assymtotic nature itself might not be a problem - if the slowing in convergence happened very close to balance - but the evidence indicates it doesn't - it actually becomes significant with the curves flattening quite a long way back - when the voltage spread could be as big as 100mV.

This incidently would bear out Frank's statement above - I can see how slower charging might help. But for sizeable inbalances you would still be looking at very long times even under that system.

I report on some principle results from these experiments in my next article in the mag - so I can't say much more here just now.

To reiterate my basic view though:

1. Yes there are chargers that will perform much better - but they are very expensive. I have a solution that costs pennies - lierally!

2. Yes, theoretically, B6 style chargers balance - but the method they use is so slow that in all bar small decrepencies in my view it is impractical.

3. Yes, B6 balance chargers do a reasonably good job of charging a balanced battery and keeping it in balance. It's correction they have issues with I believe.

BEB

[Martin Harris - Moderator]

I can certainly agree that the degree of imbalance affects the time involved - perhaps I've just been lucky that my packs haven't got too far out of balance - I invariably balance charge them after each discharge, from new.

If others take the fast charge option available on some chargers, perhaps this explains larger imbalances which will develop quickly if only the pack voltage is detected as the termination parameter?

[Nigel R]

I realise I'm ping in the breeze here. But.

1) Frank - it makes no odds (practically) to the balance time to reduce the charge rate during the initial charge. The rate of balance improvement is fixed by the balance circuitry. You might as well charge as fast as you can during the initial period.

2) BEB, a B6 style charger can be made with a large balance charge current (and/or discharge). There is nothing inherent in the design per se that makes the cheap ones slow, simply that they have implemented the charger with a small current during balancing, to match the expected pack size. Sample size of one, but, I have a 20A B6 style charger which balances small packs far quicker than the two smaller 5A chargers I have.

I'm pretty sure the rate of balance improvement was calculated / discussed on the previous thread where a schematic of the small Turnigy B6 type charger was posted.

Either way, yes, we know cheap chargers are very slow to balance. They may only improve the pack by a few mV per hour. They simply need to be given an appropriate time.