Feeling a bit unbalanced.....

[TonyS]

Probably already covered but finding older stuff isn't always easy....

I have a Fusion Logic charger that also discharges when needed (although boringly slowly!)

I've been carrying out an inventory of my LiPo's and ensuring that they're in decent condition and at storage charge.

My question is this:

If I find a multi-cell battery has a single cell that is at a noticeably different level of charge to the other cells say for example a 4 cell with 3.97, 3.974, 3.969 and 3.7V will a balanced discharge followed by a balanced charge eradicate this discrepancy?

Thanks

Also, another quick question - how does everyone else ensure that their batteries are at storage charge all the time? I used to finish using mine then charge them fully ready for use but then find because of work, weather etc I didn't get to use them for a while. Discharging a 4000mAh battery from 98% to 50% takes a lifetime.

T

[Toni Reynaud]

If I find a multi-cell battery has a single cell that is at a noticeably different level of charge to the other cells say for example a 4 cell with 3.97, 3.974, 3.969 and 3.7V will a balanced discharge followed by a balanced charge eradicate this discrepancy?

Probably not in the long term. In fact there are those who will say that the battery is now no longer useable. Use for shorter flights only, checking at the end of the flight to see just how bad the imbalance is, or remove the low cell and make a 3s battery. Discharging using a car lightbulb (or two in series) while monitoring with a meter will take it to near storage (or below) fairly quickly, then use the charger to get to final balanced storage levels.

[Shaun Walsh]

You could try discharging to storage using something like this:

Discharger

I have used an HB3 50 watt quartz halogen car bulb to discharge a 3s battery that was beyond safe use, but it would need careful monitoring of the voltage to take each cell down to storage voltage.

If your charger has a "Balance" function you could use that to equalise the voltages but it may be to no avail if the internal resistance of each cell differs too much. It may only be good for low current/short flight use. If you have the necessary skill/tools you could strip out the duff cell and make it a 3s but it's not something I would attempt.

[Colin Carpenter]

Another one for bulb discharging whilst monitoring ✅

[MattyB]

Discharging with most chargers is pretty impractical since as you have observed they can’t dissipate enough heat to do it fast enough, especially if you have larger packs. If you are going to treat your batteries well it’s well worth investing in a decent discharge rig - I built one out of 3x cheap units bought online, it can discharge and balance really big packs in 15-30 mins, and fitted with a parallel charge board you can plug multiple packs of the same cell count too. Cost me about £40-50 all in, which means it would pay for itself if it extended the life of a few of my big packs...

Here’s some instructions on how to make your own... Setup like this the three units will create a safe 12A load and discharge and balance to any Cell voltage you choose (0.01V accuracy).

Edited By MattyB on 04/10/2020 18:09:29

[Jonathan M]

Interesting thread, especially re discharging fully-charged packs.

I also have the Fusion charger, but as it can only do one pack at a time and doesn't have a voltage cut-off when discharging (have to keep an eye on it which isn't practical!), last year I bought a G.T. Power Quad charger principally as it can charge and also discharge to a factory-set storage voltage a total of 4 packs at the same time.

This doesn't solve the problem of it taking hours and hours to slowly (cooly) discharge full packs, so if it looks like I'm going to run out of time to fly, I try to fly remaining packs on lots of throttle for a bit to bring them down to say 2/3 capacity, then finish them on the storage discharge setting at home.

[TonyS]

Thanks everyone for some really useful stuff.

I suspect the answer for me lies in some/all of this as I need a short term and a longer term solution.

Bit of a bummer re the imbalanced packs though..

T

[MattyB]

Another reason to get a high amp discharge rig in your toolkit... Your charger is probably the single most expensive piece of kit in your e-flight bag. Putting loads of hours on it dissipating heat is not a good idea (it’s significantly more stressful than charging, especially for the fans which are often not the most beautifully built devices!).

A lamp based discharger however has no moving parts and should never fail, other than maybe the odd cheap bulb. They do get hot though, so be careful putting it away after use and don’t leave the pack attached for very long periods after use as the discharger does draw a small current on its own.

Edited By MattyB on 04/10/2020 21:04:36

[Dale Bradly]

Don't be too hung up on "storage charge". It is simply a nominal part charge, somewhere between charged and discharged. The chemistry doesn't require an exact voltage.

The best way to partially discharge the batt is to fly the plane, and don't charge it if you aren't going to fly it.

I appreciate there is the odd time you might have to pack up unexpectedly, and therefore the odd slow discharge back at home shouldn't be an issue as this is the exception, not the norm.

[Allan Bennett]

Posted by TonyS on 04/10/2020 18:04:05:

Thanks everyone for some really useful stuff.

I suspect the answer for me lies in some/all of this as I need a short term and a longer term solution.

Bit of a bummer re the imbalanced packs though..

T

Another longer term solution is to buy a charger that can discharge quickly. I don't know about others in the Cellpro range, but my PowerLab 8 is able to discharge at at least 10A (that's the default setting, which I don't change) down to any pre-defined voltage for storage.

For complete discharge I use the light bulb method described by others. No need for any electronics or supervision, just leave it connected to the battery for 24 hours or so outdoors. A single bulb for up to 3S, and two bulbs in series for up to 6S.

[MattyB]

Posted by Dale Bradly on 05/10/2020 10:19:27:

Don't be too hung up on "storage charge". It is simply a nominal part charge, somewhere between charged and discharged. The chemistry doesn't require an exact voltage.

This is true - anywhere between 3.7 and 3.9V/cell will be ok. Don't go much lower though as there remains a small chance the pack could self discharge down to the level where permanent damage can occur (generally considered to be in the 3-3.1V/cell range).

Edited By MattyB on 05/10/2020 14:31:25