Charging LiPo's for storage

[GodSpeed]

To start, my understanding is that it is not ideal to leave LiPo's when not in use (days or weeks between runs) at full charge.

I believe I have read that around 40% is most recommended.

Good so far?

So, how do I charge my batteries to 40%???

I have an Onyx 235 charger which I believe is similar to, if not the exact same as, a few other HobbyCo and DuraTrax chargers.

http://www.duratrax.com/chargers/onyx/dtxp4235.html

Can I set it to exactly 40% of full capacity somehow? Or any other tips/tricks for optimal battery performance and life?

Thanks guys.

[slapshot1979]

I always store at about 3.8V-4.0V per cell. If your charger doesn't have a storage mode you'll have to watch it.

[Charlie don't surf]

I've always stored mine a 7.60-7.75 for 2s. Been using that system for 5 years with no issues

[GodSpeed]

Awesome....I'm lost.

Isn't 7.4v full? ....wait, that must be per cell then. So 14.8 is full? Mine are 2S2P if that confuses things even more???

But once that's clarified, do you guys just unplug the battery at that point or do you set up a battery profile with those specs? (I think I can do that)

[Coelacanth]

Awesome....I'm lost.

Isn't 7.4v full? ....wait, that must be per cell then. So 14.8 is full? Mine are 2S2P if that confuses things even more???

Actually, no...a fully charged LiPo reaches 8.4V. So, charging them to 7.6V or so is considered a storage charge. I believe pretty much every modern charger will have a storage mode, and once you select the number of cells, it'll automatically charge to the correct storage volts capacity and beep when it's done. Recall that LiPo batteries are 3.7V per cell, which is their nominal voltage, or the midpoint of their operating range; the max voltage is 4.2V per cell.

I think the proper storage voltage for a 7.4V LiPo is about 60%. Somebody correct me if I'm wrong.

[GodSpeed]

These are the batteries I have -- http://www.hobbyking.com/hobbyking/store/__17265__Turnigy_nano_tech_6000mah_2S2P_65_130C_Hardcase_Lipo_Pack.html

I'd better take a closer look at my charger settings.

[Coelacanth]

The only specs that really matter as far as the charger goes are 2S and 7.4V. Discharge rate doesn't have any bearing on charging, only on how quickly a battery can "put out the juice" when discharging. "mAh" refers to the battery's capacity; in functional terms, how long it will last before being discharged. a 6000 mAh battery will last twice as long as a 3000 mAh battery, but everything else will be the same. It won't be any more powerful. It will take twice as long to charge, if charging up at the same rate as a 3000 mAh battery, but your charger should take care of that unless you play with your charge settings manually, and the charger would ideally use 1C as the charge rate, so any battery would charge up in approximately 1 hour--regardless of capacity. More on that next.

In theory, a charge rate of 1C will automatically charge the battery at 1 * battery capacity, in Ah (not mAh, so you divide by 1000). For example, it'll choose 4A to charge up a 4000 mAh battery in an hour; or 6A to charge up a 6000 mAh battery, in an hour. At a 1C charge setting, your battery should charge up in about an hour, regardless of the capacity. Charging at faster rates is certainly possible, but the cells won't balance as nicely.

Hope this helps.

[RC104ever]

What I do is run them until the lipo cutoff and then put them away. While that's not the 'recommended' way to do it (slightly lower voltage than storage amount), it will avoid the puffing and other issues with a fully charged lipo.

The key with lipos is this - unlike nicd and nimh, they do not lose much, if any, voltage while not in use. This means that they are very stable for a very long time. However, the chemistry inside means that if not used when they are full, they begin to puff. Not a good thing. So you store them below full charge. Depending on your ESC setttings, it will cutoff when it reaches a certain voltage. Mine is set so that it's pretty close to what a storage charge would be anyways I believe.

Also make sure you charge them in a lipo bag! Just in case...

[Coelacanth]

Good point, Chris, I should've mentioned that. I ruined an almost-new LiPo by fully balance-charging it, then forgetting it was charged up when storing it...and it puffed up.

Whether you choose to leave it almost-discharged or storage-charged is up to you, but you don't want to store it fully charged.

[GodSpeed]

Thanks for all of the replies guys. You're making sense (rather, I'm grasping it), but I have a further question....

My charger doesn't have a "storage" function but I can program 10 different presets and within each, certain parameters are adjustable (battery type, # of cells, mAh rating and charge rate in amps) so, for my 6000mAh batteries, to charge to 50% would I simply set it up to a 3000mAh battery?

The mAh rating is the capacity, like the fuel tank in your car, so to "fill" to half way, program it to half the capacity? Is it that simple?

When I set this, it automatically sets itself to charge at 3.0amps. It appears that at this setting, it's balancing the cells at about 3.9v each. Is that working correctly?

And how about when I want a full charge. Setting it to 6000mAh makes it charge at 6amps. Is that okay or too high? I could dial it back to 5amps (or lower), but it would take longer (I would also have to crank up the safety time limiter cutoff). I thought a slow charge was most ideal?

[bully]

Changing the charge amps only affects how long it takes to charge a battery,eg 6000ma battery charged at 6amp takes roughly an hour so 3amp with same battery takes 2hours roughly... Without a storage function you will want to charge them for around 40 minutes at 1c(6amp for a 6000mah battery) to get to the storage sweet spot...Hope this helps. If your a basher you can also take a fully charged pack and run it for a few minutes then put them away.. The storage thing is basically just knocking the top off the charge to bring the voltage down a little...

[GodSpeed]

My charger doesn't have a "storage" function but I can program 10 different presets and within each, certain parameters are adjustable (battery type, # of cells, mAh rating and charge rate in amps) so, for my 6000mAh batteries, to charge to 50% would I simply set it up to a 3000mAh battery?

The mAh rating is the capacity, like the fuel tank in your car, so to "fill" to half way, program it to half the capacity? Is it that simple?

I'm not sure this worked as planned.

I set up a battery profile as mentioned: LiPo, 2S, 3000mAh (of an actual 6000mAh battery), 3.00amps charge

Results for the first battery were --

55:37min, 2491mAh, 8.39vp, Cell 1: 4.198 Cell 2: 4.200....and other insignificant stuff.

Second battery (clearly not used as much) --

16:02min, 608mAh, 8.42vp, Cell 1: 4.197 Cell 2: 4.202....

So it looks like I did get half the spec'd mAh as planned, but did I get a full load of volts? Is it the volts I want to keep down for storage, or the mAh rating?

I kind of feel like full voltage is okay and getting "half a tank of gas" (mAh a.k.a. the capacity) is the right thing to do, but from what you're all telling me, it's the volts I want to keep down.

[Coelacanth]

I suppose the bottom line is not storing LiPo's fully charged, or fully discharged. How about charging up a battery, driving your car around for a while, then storing the battery in a partially-charged state? It doesn't really matter, I don't think...and your charger will always balance-charge them to capacity whenever you're ready for more driving.

[slotcarrod]

Your charger will always peak out at 8.4v for your 2s pack no matter the MAH you choose to charge at.

The best way to store a pack with out getting scientific, is charge fully, run for 1/3-1/2 normal run time and then store pack.

[GodSpeed]

So for sure it's the voltage you want to keep down, not the mAh?

To me the voltage seems like the zap. The punch. Whereas the mAh is the fuel in the tank.

Oh well. Easy enough to knock the top off with a bit of a run.