Looking after your LiPo cells

[IanN]

No, haven't charged them - voltage on delivery (from giantcod) was 8.9v.

 

[IanN]

Could be that my dvm's iffy. I'm advised

 

 "A common problem with cheap DVMs is that the low battery limit warning is not set correctly. The instrument compares part of the voltage to be measured with a reference voltage. If the battery in the DVM is low, the reference voltage can fall and make any voltage you measure appear to be high."

I'll get a new pp3 for my dvm later, and see if that makes it read differently. All part of the electrickery learning process, I guess........

 

[Tim Mackey]

Most suppliers ( including Rob at giant cod ) check the voltage of any batteries sent out before dispatch, and they are normally only at around 3.7 - 3.8V per cell. Your 2 cell pack should be at 7.6V or so when delivered, and most certainly should not be as high as 8.9V

Lipo cells are very in-tolerant of overcharge even by a very small amount

[IanN]

I put a new pp3 in the budget dvm, the maplins item, and it then read lower .

 

The lipo is within limits - no problems there at all, giant cod.

 

I then tried the dvm on various other batteries (car, 12v gel starter cell, 4.8 r/x packs) using the old and the new dvm batteries, and when using the old battery the voltage reading was higher every single time, compared with the reading obtained using the new battery.

 

I guess the learning from this is that a budget dvm is useless for reading voltage unless you're gonna put a new battery in it every time you use it......??

 

Edited By IanN on 15/08/2009 10:15:57

[Romeo Whisky]

On several threads I have read that LiPos should be charged to 50% for storage, along with the mysterious assertion that "most modern chargers have a program for charging to this storage level".

 

Well I have four popular brands of modern chargers capable of of charging LiPos - all different makes - (Ripmax Pro-Peak Sigma, Graupner Ultramat 16, Multiplex EN3008EQ and RCM Pelikan Shark 10) - and NOT ONE of them makes any mention of such a storage program in their manuals, nor can I find such a program in the menus of any of these chargers.

 

So please can someone tell me how can I program these chargers to charge only to 50% using the  Constant Current-Constant Voltage process?

[Tim Mackey]

Well you cant "program" them to do it if its not available withinn the software of the device. However, you have two choices at least.... neither ideal, but workable.

1) Use the normal 1C Lipo charge algorithm ( CCCV ) and simply disconnect the battery manually when the required votage is shown on the display.This will likely occur after about 30 mins or so, depending of course on how "empty" they were to start with.

Depending on how long the storage time is going to be, anywhere between 40 - 60% full is fine. This equates to 3.75V - 3.85V per cell.

2) Use the LiFEPO4 settings ( if available on your charger ) which will generally terminate the charge at around 3.6V per cell, which is pretty much empty TBH, but still better than storing at full.

[Romeo Whisky]

Thanks Timbo - a third solution occurs to me which might be preferable in some ways - ie. charge to full capacity as normal, and then use a bench-run with a Watt-Meter to take out about 50% of the capacity. 

 

As you say, any charging method must take account of the residual capacity at the start of the charge, which is problematical if the charger doesn't do it, whereas this way you start from a known (100% charge) and then work backwards. 

 

Is this as reasonable as it seems, or am I missing something?

 

I think the assertion about "most modern chargers" is something of an inappropriate generalisation though, since all mine are current models of respected and popular chargers which many others will also own.

[Tim Mackey]

Yes indeed that is feasible - yet a little time consuming.

I accept your point abou the term "most" - and thanks to the joy of moderator priveledges, I have amended this to "several".

[Tom Foreman]

Storage Charge & C-rating

When I first got into elec-trickery models two years ago I always kept my LiPos fully charged and used the size recommended by the kit manufacturers. I quickly found out that a combination of using a battery at near is maximum continuous C-rating and keeping them fully charged resulted in lower performance as soon as 3-months later or about 50 cycles.

 

I have now learnt the hard way to spec my batteries so they never work harder than 70% of max C, or if possible 50% of max C. When I charge the batteries, I always storage charge, and only charge them up fully the day I'm going to the field. This seems to be working well as the batteries are lasting a lot longer.

 

Tom

[Geoff Daunt]

Timbo, can you advise please.

I have a 2100 mA lipo 3s which l use in my electric Multiplex 27 Alpha glider.

The lipo is about 6 months old and l have charged perhaps 20 times.

I usually charge at 1/10, so on a slow charge.

On this occassion, charging at 200mA ,it was cutting out after an input of only 220mA.

I reset at the same rate and again it put in exactly another 220 mA before beeping.

I decided to go back to basics and discharged at 0.5. It took out 1176 mA.

So l started again with the following results.

Charge at 200 mA .......cut out at 220

Charge at 500mA.........cut out at 550

Charge again at 500.....cut out at 550

Again at 500.........cut out at 550

Again at 500.........cut at  84mA.

So in total it took just under 2000....ie about full  but WHY is it cutting out with such a regular input.

I am using a Multiplex LN 5014 digital charger and l always charge/discharge with a balencer.

I have not had this problem before.

I have heard of DELTA peak cut out but do not understand it's meaning.Is this the problem? or something else?

If you or anyone else can assist l would be very gratefull

Geoff.

 

[Tim Mackey]

Hi Geoff - my best guess is that the very low charge current you are using is perhaps notallowing the charger to correctly identify the cell count, and its terminating. Try discharging to 3V per cell, and then charging at the recommended ( and normal ) 1C charge rate - in this case 2.1A. There has, to my knowledge, been no real evidence to prove that charging Lipo at less than 1C is beneficial, so I never do, after all, why waste more time than necessary

Delta peak detect is only used on the chargers nickel charge settings and does not apply to Lithium. It works by detecting the ery small drop off in voltage from peak which nickel cells exhibit. this signals the charger to stop. With Lipo programmimg, the charger uses CC/CV ( constant current then constant voltage ) algorithms.

[Frank Skilbeck]

I have a Sigma charger and it asks you to put the battery capacity in and it will then cut off if the battery voltage is reached or at 110% of the entered mah, so if you entered 1000 mah it will cut off at 1100 mah.

 

I suspect your charger has the same safeguard so if you enter 200 ma it thinkis you are trying to charge a 200 mah battery and as a dafeguard cuts out at 220 mah even if the pack is not upto voltage.

 

 

[Geoff Daunt]

Thanks Timbo and Frank,

I have one of Andrew Gibbs Guides on Lipo's,

He suggests;

"generally best charged between C/5 and 1/C. In general the higher the charge rate the lower the lifespan of the cell will be....if time not critical, a lower charge rate of C/2 will probably help to extend the cell life"

I also remember reading in one of the Mags. that following testing of lipo,s at 1C and at lower rates the lower the charge the life of the battery was extended by some 30% or so.

That was my reason for the low charge rate.

However will have a go at your suggestion Timbo.

Geoff.

 

[CARPERFECT]

Hi. I am new to electric rc done ic for 20 years. In December i bought 2 lipos  and a charger from giant cod. Must have read those instructions 10 times before charging them for the first time. Well charged them both up at correct rate  and they both worked ok, as i connected them to the motor via the esc. Only run each batery for about 20/30 seconds. All were packed away a stored in loft with oter RC gear, yesterday got them out to find one has swollen up and lost all change and will not recharge.Sent email off to  Giant Cod but not willing to replace at this moment,Their answer was that lipo batteries are tempremental,should be stored in cool place and at 3.7v which they were.

Edited By CARPERFECT on 26/03/2010 07:55:39

[Former Member]

[This posting has been removed]

[CARPERFECT]

they were not put in the loft for about a week they were kept in the bedroom where i charged them. they were only put in the loft  along with the glider to hide them from the son.

[Marc Humphries]

Hi folks,

 

What are the accepted tolerences for a pack to be considered balanced?  I have a pack that has one cell about 0.1 (a tenth of a volt) lower than the other cells when fully charged. 

 

Is this within an acceptable range?

 

Regards,

 

Marc

[Jonathan Kimber]

Having read the entire thread i assume my LiPos will be safe if...

 

I charged them to full in my cold (approx 10 degrees c) shed, and have decided to store them in the house over the winter, whilst continuing to fly every couple of days.

 

I make this assumption because the capacity of a cell is less when cold so by bringing them indoors and warming them up, slightly, they will be slightly under capacity.

 

Is this right?

 

Jono

[stuart tickner]

i have mini titan e325 how long should i fly with stock battery learning to fly so only hovering and a bit of forward flight i am getting 3 2600mah 3s 30c batterys could you give rough flight times for these

[Pete B]

No experience on this model but it seems that most 450 helos last about 5-6 mins on a typical 2200--2500 pack, so about 6 mins will be your lot, IMHO.

 

As you're learning to fly, most of your early flights are going to be skidding around the floor and you'll soon realise when the battery is starting to sag - there is a noticeable slowing down and it doesn't want to lift any more!

 

The good thing is, you won't lose the model if you're not at height!

Using a battery checker, if you don't run the pack much lower than 3.7v/cell each time, they'll be fine.

 

You'll be able to adjust your times with experience.

Pete

 

[Kntt]

Hi Stuart

I have been flying electric helis for about 4 years now and i have a 450SE running on TP2200.

I would recomend that you time your first flight at about 4 minutes then recharge your lipo making a note of how much you put back in.

I don't drop my packs below a fifth of the pack capacity so to be on the safe side i would stop flying at about 2000ma.

You will need to do a few flights until you reach the max discharge, also your flying style will have an effect on the discharge rate.

I can do 5 minutes hard 3D before i am time up so you should be ok upto 7 min maybe more

Cheers

Kent

 

Edited By M0KWR on 26/01/2012 21:06:58

[John Cole]

If LiPos are stored well-charged they lose capacity. The higher the storage temperature, the greater the loss. The higher the charge-state, the higher the loss. This applies to all conventional (i.e. Cobaltate-based) Lithium Ion cells, not just LiPos.

 

Most references say store them charged / discharged to 3.7 volts (which is perhaps a bit lower than the voltage at which they are normally supplied), but Sony (who make them) advise storing at a MUCH lower voltage (and charge-state): 3.0 volts.

 

The lower the temperature, the less the loss. You will see people say "don't let them freeze". Nonsense, they don't "freeze". They don't have water in them

 

Sony give performance data down to minus 20 Celsius, which is below the temperature of a domestic freezer.

[DH Flyer]

Thank you Tim Mackey.

There is so much that the manuals don't say. The last Lipo I bought didn't even have a manual!

[nasher 546]

Brilliant!!!!!!!!

LiPos management made easy.

[Nick Burroughs]

Yesterday I was flying with a Maxpower 2500Mah 3S battery and after each charge I checked the cell voltages on my charger. All checks showed around 4.17V per cell. Except for the last charge which stopped with a message saying high voltage on one cell. A check showed 2 cells at 3.9 Volts and the third one at 4.67 Volts. Is this battery dead?