Discharging LiPos to Storage Charge Level

[Frank Skilbeck]

5 hours ago, Ron Gray said:

Do you discharge multiple packs in one go? 

Only because I have a dual and single outlet chargers. But if the battery has been flown then I just leave and charge up before the next day.

 

Usually reasons for not using all lipos at the field would be strip grass is too draggy for my EDFs or I've had a very thermally day with my electric gliders.

[Tosh McCaber]

Wow- Didn't really think that my question would generate so much useful information!  Firstly, due to the problem push button, it's going back! 

However, there seems to be a chasm between those who discharge after every session, and those who don't.  But, from now, to be on the safe side, I'll leave my packs discharged after use in a flying session, and charge them the night before I go out again. 

I can give them an easy discharge, if prolonged, via my SkyRC D-100

To further the discussion, with regard to some of my older packs that have been sitting around for ages.  Apart from installing the battery in a model, and waiting for a crash because of a faulty pack, be it caused by constantly leaving the battery at full charge(!!) or other, is there an easy quick way of checking/analysing the battery life on the bench, in terms of inserting a load, and timing it, seeing how long it takes to discharge?

I suppose that I can install the battery in a model, and check it out on the bench?  Just a thought....

[PatMc]

15 minutes ago, Tosh McCaber said:

To further the discussion, with regard to some of my older packs that have been sitting around for ages.  Apart from installing the battery in a model, and waiting for a crash because of a faulty pack, be it caused by constantly leaving the battery at full charge(!!) or other, is there an easy quick way of checking/analysing the battery life on the bench, in terms of inserting a load, and timing it, seeing how long it takes to discharge?

 

I suppose that I can install the battery in a model, and check it out on the bench?  Just a thought....

 

Telemetry ?

Edited October 14, 2023 by PatMc

[leccyflyer]

Without a baseline to compare it with, there's not much useful, practical information to be gained in cycling a lipo in that sort of a manner. An easily measureable indication of battery health is to keep tabs on the IR (internal resistance) of the invidual cells in each pack, but again, it's a quantity that is best used in terms of keeping tabs of it over time.

 

For sports model use the best indication is how the pack performs in practice -if you find that your batteries are running out of grunt, giving less thruat on a know set-up or giving shorter flights before the power declines, then that's really the measurement that matters in practice and is fairly inexact and a bit subjective. If your model is equipped with telemetry and flight logging it's possible to be a bit more objective, but realistically for most of us it's how the pack performs in use, rather than any hard fast numerical limits which governs how happy we are with the pack and whether it needs to be retired. A periodic review of IR, individual cell voltage (NOT whole pacxk percentage!", puffiness, cell temperature at the end of a flight and how long it takes to come to a nicely balanced state is a good way of monitoring the health of our packs.

[GrumpyGnome]

Wow @leccyflyer - you are so much more organised than I am.  But I suspect you have more batteries and models than me.  I'm down to just 14 packs now (8 x 2200 3S, 6 x 1300/1500 3S) and just a couple of models (Riot and Viper/Hawk) so it's easier for me.

 

@Tosh McCaberflight performance tells me when I need to retire/repurpose a pack.  All my models fly to a timer and if performance drops off before that point, I know the pack is 'suspect'.  Incidentally, I've never had a crash caused by a faulty pack - in 4000+ electric powered flights (I keep a basic log of flights per plane) - maybe I've been lucky.  

[Dickw]

I just wondered how many people who discharge packs with their "charger" realise that it is often possible to increase the discharge power level by adding a resistor (e.g. a 12v bulb or two) between the pack and the charger?

I have attached extracts from my iCharger manual to show it is an approved method and not just my own fantasy 😀

I also do this with my 'Chargery' charger, so it is not just the iCharger that does this and maybe most chargers can do it. The principle involved is sound! The charger controls the current and monitors cell voltages while the resistor dissipates much of the energy.

 

Actual example of a 10s pack being discharged at 1.5 amps on my Chargery 50010 is shown - total discharge rate is 38.325v X 1.5A = 57.48 watts, but the charger is only showing a discharge rate of 26 watts.

 

It might be worth checking your own charger manual to see if it mentions this.

 

Dick

ps. I ended up making myself a switched bank of suitable resistors to speed up and optimise the the process for different size packs.

[Tosh McCaber]

My Voltage meter, similar to this one and several others on the market, only shows Voltage readings.  And I find it invaluable during my flying sessions.

https://www.amazon.co.uk/RUNCCI-Digital-Battery-Capacity-Indicator/dp/B07KW2WJ67/ref=asc_df_B07KW2WJ67/?tag=googshopuk-21&linkCode=df0&hvadid=309785472429&hvpos=&hvnetw=g&hvrand=14468455774494062886&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9046836&hvtargid=pla-597079953270&psc=1

How important is it to have one that reads IR?  I haven't found the need so far, but this discussion seems to be persuading me to buy one like this:

https://www.amazon.co.uk/dp/B09Q2CF2GM/ref=sspa_dk_detail_2?psc=1&pf_rd_p=84ea1bf1-65a8-4363-b8f5-f0df58cbb686&pf_rd_r=WZJPTYCZ031N7AKJ7Z91&pd_rd_wg=09bIC&pd_rd_w=sV17V&content-id=amzn1.sym.84ea1bf1-65a8-4363-b8f5-f0df58cbb686&pd_rd_r=52904cd9-944d-4b42-a331-8299f545be10&s=industrial&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw  which does have IR

Worth the extra investment??

 

PS After all our discussion, I must say that I haven't actually had any problems with batteries since getting back into the game 4 years ago!!

But- Oh for the smell of castor oil!!!

 

 

Edited October 14, 2023 by Tosh McCaber

[leccyflyer]

Tosh - doesn't your charger  display IR?

 

 

You shouldn't need to buy a separate meter.

[Andy Gates]

I am with Ron, Leccy & GG.

 

My packs only get discharged in the models flown.

 

I generally fly at the weekend so charging my packs takes place on Thursday / Friday / Saturday. If I don't fly then the packs stay as is until the next time.

 

My only changes to this pattern are if I am not going to fly for 6 -8 weeks or more, then I may consider taking the packs down to storage.

[Tosh McCaber]

Leccy- my ignorance- your right- my Sky charger does!!

Thank you!  Again!

[Phil Green]

The one thing you definitely mustnt do is to fully charge them outside in the cold, then bring them fully charged into a warm environment.

 

[leccyflyer]

Phil - that's what is keeping me from fully utilising my outdoor Lipo bunker. My 6s1p and 5s1p packs are all at storage voltage, so safely stored outdoors - min temperature to date has been 4 degrees C. Hovever my 4s1p, 3s1p and 2s1p packs have all got a few which are at close to full charge - I routinely charge to 4.19v/cell. I think I'm probably okay to put those out, since they are never charged at low temperature, but would be happier if they were all at storage voltage before putting them outside. It'll need a step change in organisation to achieve that in practice, as the packs will need to be brought indoors at least a few hours before charging to let them come up to ambient temperature, which is 16 degrees C for the workshop.

[Phil Green]

Its ok for them to drop in temperature Brian, its heating that causes the voltage rise.  A very cold cell charged to 4.2v and subsequently raised to room temperature can easily go well over the cells absolute max v 

In the opposite direction warm->cold it isnt a problem, if anything the voltage will drop as the cells cool 😉

[Cuban8]

18 hours ago, leccyflyer said:

Having been a charge at the field and leave the batteries as they are from one session to the next practitioner for many years, I've had to modify my charging regime as the time to charge at the field is now much more limited - with a 90 minute+ drive to my old club field, waiting half an hour with two chargers working to start off the first few packs eats into the time too much. I still don't like to have all my batteries at storage voltage and for my smaller packs I don;t bother discharging them - they get cycled much more frequently in use than the larger packs.

 

I'd intended going flying this afternoon, but the wind got up this morning and it's now blowing a hooley. Then still having two sore arms from my jags yesterday, I've just been stung on the ankle by a massive wasp -in October! Very painful. So I'm feeling a bit sorry for myself and am down to a single unpunctured limb 😞. Forecast is a little bit better for tomorrow, so some of the charged packs will get used, hopefully.

 

Here's the current Lipo Charge State board, showing how many packs are charged, since my last flying session on Monday last. It's a whiteboard, so is updated daily - the tally marks keep tags on how many packs are charged. The printed sheets list some of the models that are in service, colour coded by their preferred pack and which transmitter that they are assigned to. Bottom right of the whiteboard has the  selection of aeroplanes for the day listed, to help make sure that I don't leave any at home - that's also weather and field dependent. It'll do for tomorrow morning instead.

Puts me in mind of 'The Good Life's' Tom Good and his activities board....................

[Phil Green]

1 hour ago, Cuban8 said:

Puts me in mind of 'The Good Life's' Tom Good and his activities board....................

Mmmmmmm...... Felicity Kendal...  😀

[Cuban8]

1 hour ago, Phil Green said:

Mmmmmmm...... Felicity Kendal...  😀

Actually I think the activity board might have been in 'Ever Decreasing Circles' again with Richard Briars and............ Penny Wilton🥰

[Tosh McCaber]

Thanks for the advice so far!

I've just put some of my 3S batteries , which I've discharged to storage levels- 3.8v, on the SkyRC D-100, individual cells on all the packs being identical, or within 0.01v  of each other, to check the internal resistance of each.  The display on the meter shows two lines.  On the top line he readings were as follows,

in Milliohms:

a) 1300mah  45-90c          11  11  11      Total21, for the pack

b) 1800mah  20-30c         15  15  15     Total 45 

c) 1800mah  20-30c          14  13  13    Total 40

d) 2200mah  60-120c       7     7    7      Total 21

e) 2200mah    40-50c       7     7    7      Total 21

The bottom line was blank in each reading(?)

I'm not sure what are acceptable resistance readings.  I'd be obliged for any advice as to what readers think relating to these results?

[leccyflyer]

Those are perfectly acceptable for that size of battery.  Less than 10 mΩ is good, 10-15 mΩ is fine, 15-20mΩ is where you are maybe starting to see a bit of deterioration and some folks maintain that >20mΩ is time to retire the pack. I'm not as rigid as that, find it is highly dependent on the nominal capacity of the pack and happily use packs with higher IR than that, especially in the smaller sizes. It's probably more important that they are well matched - if you had one cell that was double the IR of the others in the pack that would give cause fpr concern, but your readings look fine to me. Now you can keep an eye on them over time and see if the IR makes any dramatic changes.

[Tosh McCaber]

Thanks Leccy, that clears up some more fog.  Interestingly, the two 1800 packs have been lying around in the bottom of my LiPo box for the past couple of years, fully charged. They read 99% before I discharged them yesterday.  Whilst very slightly puffed, they seem to be OK.

 

(Not sure how much puffiness can be tolerated!)

[MattyB]

Back to the original question re: dischargers, for those that do woant to do this there are much more economical solutions than the one purchased by the OP - I have three of these wired up to a parallel baord give me 450W of discharging power at very low cost:

 

 

https://www.aliexpress.com/item/1005002701340137.html

 

You can see more details and links on how to do this in these posts...

 

 

[MattyB]

PS - Here is the definitive RCGroups thread on how to make your own 450W discharger based on the AOkoda units above (they used to be available from a website called RCMart, but that now seems to be defunct)...

 

https://www.rcgroups.com/forums/showthread.php?2406395-An-effective-variable-load-automatic-LiPo-discharger

[Skippers Walker]

On 13/10/2023 at 16:41, Tosh McCaber said:

Don't know if anyone can help.

I've just bought an FD-200 discharger, on the advice of club-mates, who tell me that it is essential to store batteries at storage charge. 

https://www.amazon.co.uk/ISDT-Control-Battery-Balance-Discharger/dp/B07VW7HZLJ/ref=asc_df_B07VW7HZLJ/?tag=googshopuk-21&linkCode=df0&hvadid=501156581681&hvpos=&hvnetw=g&hvrand=5368442662330318663&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9046836&hvtargid=pla-823020257985&psc=1

I'm having problems (as several reviewers have pointed out) with the left hand button, which is somewhat non reactive and temperamental, not allowing various rates of discharge. However, I think that working it from the App for it will be OK.   I'll persevere a little before a decision to send it back to Amazon.

The instructions are not very clear.  To clarify a major confusion for a novice to batteries (me!), the discharger has, firstly, a selection of 2S up to 8S batteries (controlled by the temperamental button).  It also has various rates of discharge- ranging from 5 to 25 amps on the other button. (As well, there is obviously the C rating for the battery in the computation.) I don't want to discharge at a rate too high for the battery voltage and amp-hour rating 

To my question! 

Will I be safe to set a battery discharge rate to whatever the voltage (S Rating) the battery is, and then calculate the rate of discharge to make sure that it is below the Amp Hour rating x C rating for the pack?  For example, if I have a 2200mah 3S battery pack rated at 40-50C, I assume that, so long as the discharge rate is less than 2.2x40 = 80amps, I could select any of the discharge. But what safety margin should I use?

 

[Skippers Walker]

I tend to agree with most of the responses on this subject and discharge any used or fully charged battery to a 'storage level' (about 53% on my charger/discharger). I've never had any marked deterioration in the batteries during several years of use."If it ain't broke don't fix it" I guess?

Cheers

SW