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-   -   New Lipo User with Questions about Storage (http://www.Wattflyer.com/forums/showthread.php?t=73568)

Angoid 04-16-2014 01:16 PM

New Lipo User with Questions about Storage
 
Hi all,

I'm a new LiPo user, with a project on the go (that has been shelved for far too long due to other commitments) and an EastStar that I've just upgraded from the stock set up to LiPo and Brushless (Inrunner).

The question I have is on how to charge the batteries up for storage. I'm aware that you don't store LiPos either fully charged or empty, but the question is how to use my existing equipment to get that 80% or so storage charge.

And as a side-issue, if you can merely charge a battery up from storage charge to full before you start using it again.

The charger I have is a Fusion Elysium LX60B Pro:
http://www.actionhobbies.co.uk/Logic...x#.U05g8_ldViY
http://www.logicrc.com/?ItemId=O-FS-LX60BP&s=c:0,c:40

So I'll always be balancing with the charging, but the charger does not appear to have a "storage" mode - just charge and discharge modes.

I saw a YouTube video where someone had connected a 12-volt light bulb to his 3S battery and a voltage sensor to the balance port to tell him when the voltages on each cell got to 3.7 volts, but there has to be a better way? Surely? Or is it a case of take off, do one circuit and then land again to get rid of the 'excess' charge before storing the batteries (disconnected, outside the plane and in a LiPo bag)?

I'm aware that you need to charge in a LiPo bag on concrete and well away from anything flammable such as buildings and vehicles etc.

Unfortunately, due to circumstances beyond my control (for example the Great British Weather has this wonderful 'weekend sensor' that causes all the rain and wind to come our way over the weekends with only the occasional day off here and there) I can only ever be an occasional flyer so my batteries can end up being stored for reasonable lengths of time between flying sessions.

Any ideas and suggestions will be gratefully received!
Thanks.

Turner 04-16-2014 02:06 PM

It's hard to imagine that that charger will not do storage. Equally hard to imagine that it will not display individual cell voltages.

I looked briefly at the manual but could not find anything useful. If the charger is still new I would return it and get something else. If that is not an option try and find someone or some discussion on that charger.

Failing all that it should be easy to monitor cell voltages during charge. When you reach 3.85-3.9 volts per cell stop the charge and you are at storage level.

Once ready to fly you simply begin the charge from storage level. Cycling is generally not useful or necessary with LiPo packs.

JetPlaneFlyer 04-16-2014 02:28 PM

Many older design chargers wont do automatic storage charging/discharging, and it looks like yours is one of those.

The precise storage voltage is not critical, as long as they are not fully charged or fully discharged. Chargers that do storage mode usually aim for 3.85v per cell, but really anything in the range 3.7-4.0v should be OK. Providing you don't over-discharge when flying then it's OK to just store them as they come off the plane.

If you need to discharge down to storage voltage then you could use the discharge feature but use one of those voltage alarms on the balance port to give and alarm when the voltage hit 3.8V on any cell.

You can also minimise degradation during storage by putting the batteries in a sealed container and putting in the fridge.

Be aware that the charger you have has a very low discharge power of only 5W so discharging anything other than very small bateries will take a long time.

fhhuber 04-16-2014 04:28 PM

Best storage is in the refrigerator at 3.7 to 3.8 v/cell. It turns out the best storage temperature for milk (35 to 40 F) is the best storage temperature for LiPos.
LET THE PACKS WARM BEFORE USE. They don't deliver current well when cold.

Anything else will give less shelf life.

Yo also improve overall pack life by never discharging below 3.5v/cell at rest. (you can store the pack there and its fine)

Storing at room temp (about 70 F) instead might reduce shelf life by a few percent. (you'd have to keep really good records to notice)

Storing above 100F (in a car in the summer) and full charged you can destroy a pack in under a month. You also risk the pack spontaneously burning when it puffs... if it vents (bursts the metalized plastic envelope) it will burn.

You don't have to be paranoid about LiPos but you need to give them reasonable care.
Store in a location where if they do burn they won't catch something else on fire.

I've not given my packs the best care and never had one burn without my purposefully puncturing the pack.

(I burn bad packs before putting in the trash... so the garbage truck won't light up when they compact the garbage)

****************

I NEVER use the charger to discharge down to storage voltage... it would take a VERY long time. (200 ma discharge rate for a 5000 mah pack = 12 to 24 hours per pack)
I just run the packs down with the model to LVC (set at high option) then charge back to storage voltage. I can do this in about 15 to 20 min from full, since my LVC is very close to storage voltage.

Angoid 04-16-2014 05:18 PM

Many thanks all .... very well thought-out replies, all giving a slightly different take on this, much appreciated.

To pick up on one or two points though as a matter of observation:

The charger is new in that I'm only just beginning to bring it into use but I have had it lying around for a year or so in anticipation of the switch to LiPos so I don't think taking it back is an option. It will also charge other battery types including NiMH and Pb.

It is simple enough to operate - I was just hoping that someone might have been familiar with a "storage charge" mode which I couldn't find! But you're right - the manual is accurate in what it describes but doesn't seem thorough enough somehow. You're left to figure a few things out for yourself.

The guy who made that YouTube video I referred to in my opening post did try to use his charger's discharge function, but said it got very hot in the process. It seems as though 5W for an 11.1V LiPo would result in a current draw of around 450mW - barely enough to get warm but will take a long time as pointed out.

Although it's not an exact science, would it be possible to take a purely mathematical approach, for example:

Assuming a fully charged 2200mAh 3S LiPo, so 11.1V.
Not an exact science so let's call that 11V.
Discharge current = 450mA (from P=IV, I=0.45 * V=11 => 4.95W, close enough to 5W for this purpose)
So to discharge the pack at that rate would take 2200/450 = 4.89 hours.
To lose (say) 20% of the charge, set it discharging for about an hour.

Assuming an even discharge and not forgetting about it(!), would that be a feasible approach? Certainly far less fun though than taking off and landing after 1 circuit! But sometimes needs must.....

Thanks!

Flubber 04-16-2014 05:51 PM

If you can discharge packs with your charger, you should be able to discharge to the desired storage voltage. Can you set the low voltage for discharge?

With a similar charger I placed it on a floor tile and discharged the batteries to 3.8 volts per cell. It took awhile with 4000 mah packs and it would get warm, but not as warm as a light bulb.

My newest charger has a fan to keep it cooler during discharge.

solentlife 04-16-2014 06:39 PM

Don't forget also that a Storage function on a charger not only charges / discharges to get to the set voltage point ... but it also balances the cells to the storage level.

Saying that a pack will reach x.xx volts at xx time is in ideal world. If one cell is hard to balance - then that function may persist for considerable time - till maybe charger times out.

I've given up waiting for low rate dischargers to work - they work on principle of dissipating energy in heat .... that I built a Light Bulb discharger and it's a present from Heaven ! I can discharge a 3S 2200 pack to storage in under 15 mins.

Nigel

Turner 04-17-2014 01:39 AM

Quote:

Originally Posted by Angoid (Post 945602)
...Assuming a fully charged 2200mAh 3S LiPo, so 11.1V.
Not an exact science so let's call that 11V.

A fully charged LiPo is 4.2 x 3 cells = 12.6 volts.

Your calculations for discharging may or may not be correct but you really want to monitor this and any charging or discharging of LiPo's. Bad things can happen when you are not paying attention.

Quote:

Originally Posted by solentlife (Post 945606)
….but it also balances the cells to the storage level..

The common four button chargers and the many clones do not balance when discharging to storage levels. Not sure they balance when charging to storage either.

kyleservicetech 04-17-2014 01:47 AM

Quote:

Originally Posted by Turner (Post 945626)
A fully charged LiPo is 4.2 x 3 cells = 12.6 volts.

Your calculations for discharging may or may not be correct but you really want to monitor this and any charging or discharging of LiPo's. Bad things can happen when you are not paying attention.



The common four button chargers and the many clones do not balance when discharging to storage levels. Not sure they balance when charging to storage either.

FYI, the various Cellpro chargers, such as my Cellpro Powerlab 8 units do balance charge, either up to exactly 3.8 Volts per cell on a discharged battery, or down to exactly 3.8 volts per cell on a fully charged battery. Doing so is simple. Just scroll the menu to the "Storage" preset program, and do the keystrokes and go. You can program in any value of charge or discharge value desired, up to the maximum ratings of the Cellpro unit.

Turner 04-17-2014 02:27 AM

Yeah, I know the Cellpro's work that way. Fine piece of equipment.

Chuck75 04-17-2014 04:46 AM

Quote:

Originally Posted by Angoid (Post 945602)
Many thanks all .... very well thought-out replies, all giving a slightly different take on this, much appreciated.

To pick up on one or two points though as a matter of observation:

The charger is new in that I'm only just beginning to bring it into use but I have had it lying around for a year or so in anticipation of the switch to LiPos so I don't think taking it back is an option. It will also charge other battery types including NiMH and Pb.

It is simple enough to operate - I was just hoping that someone might have been familiar with a "storage charge" mode which I couldn't find! But you're right - the manual is accurate in what it describes but doesn't seem thorough enough somehow. You're left to figure a few things out for yourself.

The guy who made that YouTube video I referred to in my opening post did try to use his charger's discharge function, but said it got very hot in the process. It seems as though 5W for an 11.1V LiPo would result in a current draw of around 450mW - barely enough to get warm but will take a long time as pointed out.

Although it's not an exact science, would it be possible to take a purely mathematical approach, for example:

Assuming a fully charged 2200mAh 3S LiPo, so 11.1V.
Not an exact science so let's call that 11V.
Discharge current = 450mA (from P=IV, I=0.45 * V=11 => 4.95W, close enough to 5W for this purpose)
So to discharge the pack at that rate would take 2200/450 = 4.89 hours.
To lose (say) 20% of the charge, set it discharging for about an hour.

Assuming an even discharge and not forgetting about it(!), would that be a feasible approach? Certainly far less fun though than taking off and landing after 1 circuit! But sometimes needs must.....

Thanks!

Supposedly, you can set the discharge voltage

From the charger manual - - -

Setting Battery Voltages For Li-Po Battery Pack

Select the correct total battery voltage to be charged or
discharged with the INC & DEC buttons 3.7V, 7.4V, 11.1V,
14.8V, 18.5V and 22.2V [Vpack]

kyleservicetech 04-17-2014 06:02 AM

Quote:

Originally Posted by Turner (Post 945629)
Yeah, I know the Cellpro's work that way. Fine piece of equipment.

FYI the $$$$ Cellpro Powerlab 8 charger has a discharge to storage voltage mode that can be adjusted from 10 milliamps to 10 Amps, with a 100 Watt limit. Or, 1344 Watt limit, if you use the '8 charger to discharge your LiPo, and have the '8 charger send the energy to charge your big lead acid battery.

http://www.revolectrix.com/pl8_specs_tab.htm

Out of curiosity, which other brands of chargers are capable of discharging at 10 Amps, or 100 watts maximum? Might be good information to know for anyone looking to buy a quality charger at lower cost than the Cellpros.

Chuck75 04-17-2014 07:29 AM

Quote:

Originally Posted by kyleservicetech (Post 945641)
FYI the $$$$ Cellpro Powerlab 8 charger has a discharge to storage voltage mode that can be adjusted from 10 milliamps to 10 Amps, with a 100 Watt limit. Or, 1344 Watt limit, if you use the '8 charger to discharge your LiPo, and have the '8 charger send the energy to charge your big lead acid battery.

http://www.revolectrix.com/pl8_specs_tab.htm

Out of curiosity, which other brands of chargers are capable of discharging at 10 Amps, or 100 watts maximum? Might be good information to know for anyone looking to buy a quality charger at lower cost than the Cellpros.

The 12v batteries I have will not accept enough current to really be useful.
Maximum continuous current is less than 6A, unless the battery is really discharged.
The limiting factor is the safe voltage applied to the 12v battery, which is around 14.5-14.8 VDC,
and the battery heating.

As a result, for high discharge rates, I use 100 and 200 watt "audio test" resistors (4 & 8 ohms) along with a cell checker. The DPL-8 will provide a discharge rate per side of ~10A (95W) internal, or 40A ~1300W regenerative (If you have a suitable LARGE 12v battery)

Without adequate heat sinks and fans, I'm limited to about 20A maximum using series parallel combinations of the load resistors.
So far, my search hasn't turned up (a) suitable aluminum heat sink(s)
at a reasonable price. (Even surplus!)

Most of the chargers on the market (all that I've found) have a discharge capability of about 10% (or less) of the charge rate, using internal loads.

There are "Dynamic Loads" on the market, but the cost is quite high for say a 500W load.

solentlife 04-17-2014 10:06 AM

I bought wound resistors of Ebay ... 100W 2.2Ohm jobs ...

They will replace the car headlight bulbs I use at present ... with LED's to indicate use.

Total cost of my apparatus incl. the bulbs in use now ... about $25.

It covers from single cell up to 6S .... will discharge my largest pack .. 5S 3300 to storage in just about 25mins. With the resistors - I have a bag full - will be quicker.

Nigel

Angoid 04-17-2014 11:55 AM

This has sparked quite a discussion! To pick up on a couple of things again though...

Quote:

Originally Posted by Turner (Post 945626)
A fully charged LiPo is 4.2 x 3 cells = 12.6 volts.

Your calculations for discharging may or may not be correct but you really want to monitor this and any charging or discharging of LiPo's. Bad things can happen when you are not paying attention. ...

Appreciate this and that the voltage of a fully charged 3S pack is 12.6 volts, but I'm using the nominal voltage of 3.7V per cell in the calculations (which are only rough at best because they don't cater for starting voltage and voltage drop). I'm presuming this comes from knowing that a fully charged cell is 4.2V, a fully discharged cell is 3.1V, so if you split the difference (4.2 + 3.1)V you get 3.65V, rounded up to 3.7V per cell.


Quote:

Originally Posted by Chuck75 (Post 945637)
Supposedly, you can set the discharge voltage

From the charger manual - - -

Setting Battery Voltages For Li-Po Battery Pack

Select the correct total battery voltage to be charged or
discharged with the INC & DEC buttons 3.7V, 7.4V, 11.1V,
14.8V, 18.5V and 22.2V [Vpack]

Thanks Chuck75 - those are the nominal 1S, 2S and 3S voltages, and the charger rotates through the valid values. I don't think, for example, you can set something that is not a multiple of 3.7V (for example, 5.0V is not a possible setting).

solentlife 04-17-2014 12:23 PM

Quote:

Originally Posted by Angoid (Post 945652)
This has sparked quite a discussion! To pick up on a couple of things again though...


Appreciate this and that the voltage of a fully charged 3S pack is 12.6 volts, but I'm using the nominal voltage of 3.7V per cell in the calculations (which are only rough at best because they don't cater for starting voltage and voltage drop). I'm presuming this comes from knowing that a fully charged cell is 4.2V, a fully discharged cell is 3.1V, so if you split the difference (4.2 + 3.1)V you get 3.65V, rounded up to 3.7V per cell.

In practical terms yes - but in fact a fuly discharged cell is zero. It just has very little in that last 3.1 to 0 ...


Quote:

Thanks Chuck75 - those are the nominal 1S, 2S and 3S voltages, and the charger rotates through the valid values. I don't think, for example, you can set something that is not a multiple of 3.7V (for example, 5.0V is not a possible setting).
I was wondering if he was inferring that using discharge function could stop at 3.7 (11.1v 3s) ??

Nigel

Turner 04-17-2014 02:24 PM

Quote:

Originally Posted by Angoid (Post 945652)
This has sparked quite a discussion! To pick up on a couple of things again though...


Appreciate this and that the voltage of a fully charged 3S pack is 12.6 volts, but I'm using the nominal voltage of 3.7V per cell in the calculations (which are only rough at best because they don't cater for starting voltage and voltage drop). I'm presuming this comes from knowing that a fully charged cell is 4.2V, a fully discharged cell is 3.1V, so if you split the difference (4.2 + 3.1)V you get 3.65V, rounded up to 3.7V per cell..

You really are over thinking this. My best advice is to get a decent charger that has storage mode capability and learn how to use it. There is no need to reinvent the wheel here.

hayofstacks 04-17-2014 06:37 PM

I sometimes use a tail light bulb, 1157, it has two lights and will discharge at 10-20 watts. i plan to daisy chain a few together eventually. even 200 watts on a 4000mah 3 cell takes a considerable amout of time.

fhhuber 04-17-2014 07:24 PM

Hard to get a faster discharge (with a safe LVC) than using an appropriate plane just tying the tail to a post....

Why buy or build something to do what your model will do just fine?

For FAST balancing... Turnigy 420 charger balances at up to 2 amps by charging. It charges each cell separately. The biggest issue is it does only up to 4 cells.
If the pack is way out of balance... this will fix it much faster than the common chargers' method of charging the whole pack and discharging the high cell(s) (usually at 200 ma discharge rate, though some do it faster now)
Another reason I tend to avoid buying packs larger than 4S, even though I almost never use the 420 chargers (I have 3) any more.
https://www.hobbyking.com/hobbyking/...ger_2S_4S.html

I've progressed through a lot of chargers and still have almost all of them. I could charge up to 20 packs at a time without parallel charging. And without overloading chargers I can blow the 100 amp fuse between source batteries (now 4 X 120 Ah 13.3 v nominal LiFeMg batteries) and the charging station on my trailer.

Turner 04-17-2014 08:00 PM

Quote:

Originally Posted by fhhuber (Post 945684)
Why buy or build something to do what your model will do just fine?.

Less wear and tear on the motor and systems. Less dangerous. More convenient.

solentlife 04-17-2014 08:01 PM

Quote:

Originally Posted by fhhuber (Post 945684)
Hard to get a faster discharge (with a safe LVC) than using an appropriate plane just tying the tail to a post....

Why buy or build something to do what your model will do just fine?.........................

WOW ! You sure haven't read RCG thread then :

http://www.rcgroups.com/forums/showt...2138690&page=3

I totally agree with you fhhuber .... and you'll see that my saying basically same got shot at seriously by one guy that I near questioned MY sanity !

;););)

Nigel

solentlife 04-17-2014 08:08 PM

Quote:

Originally Posted by Turner (Post 945687)
Less wear and tear on the motor and systems. Less dangerous. More convenient.

Average model flight ... 3 - 8mins .....

Time needed for that model to bring full pack to storage is only part of that ... lets say 40% of normal run time ?

If my motor and systems were that sensitive or delicate to a few extra minutes of run time - then I have the wrong gear.

Less dangerous ? How many times do you do a Wattmeter test ... ground run before take-off .... installation check of rotation of motor .... all static and either tied of as I do or simply you at opposite end of model holding it.

Oh ... nearly forgot - you say more convenient - what is ?

Put simply - there are millions of aeromodellers do ground runs of motors, not to mention boaters and other vehicles .......... the number of accidents resulting in 'recordable' injury must be a tiny %age compared to such activities as ... crossing the road ... driving a car .... riding the subway ....

C'mon ... bit of reality please ...

Nigel

Turner 04-17-2014 08:15 PM

I never said no one should do it with the model. We were asked for reasons. I gave three that are all valid. Do as you wish.

solentlife 04-17-2014 08:25 PM

Quote:

Originally Posted by Turner (Post 945690)
I never said no one should do it with the model. We were asked for reasons. I gave three that are all valid. Do as you wish.

No need to get upset ... I wasn't attacking you ...

Wattflyer is the nice forum - where we all respect each others views - unlike another I can think of.

I respect your view ... no problem. I was just putting forward an alternative opinion.

You could likely give me 10 reasons to buy BMW .. I can likewise give you 10 reasons why I would never buy a BMW ...

Nigel

Turner 04-17-2014 08:29 PM

I'm not upset, really.


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