Discharging batteries

[Craig Spence]

Hi all,

can anyone give me some advice as how to discharge battery packs because I have no idea.

Thanks all.

[Tim Mackey]

Well that depends on what exactly you mean by discharging Craig - in use, or for re-forming purposes etc?

Also, the methods and specs are very different for diffferent types of cells, so you need to be specific otherwise the answer could be long and complex

[Craig Spence]

Well I bought a multiplex permabatt 7 cell AA 1400 and it advises that you discharge and recharge to get full potenetial out of the battery. But I have also noticed alot of other talk on forums about dischrgeing battery packs and then chargeing them, is this balancing?, any info would be greatly appreciated as I would like to get the best from my materials.

 Thanks Timbo.

[Craig Spence]

Oh sorry its a Nimh battery as well.

[Tim Mackey]

Right. NiMh cells don't really suffer from memory problems quite as badly as older NiCDs used to. However if you feel you want to "cycle" them which will at least ensure they are properly discharged before being recharged, then they should be dropped to around 1.0V per cell so your 7cell pack needs to go to 7V, before being recharged.

Use a discharge current of around .25C or so, which is about 350m/a ( 1400 / 4 = 350 ) but its not too critical.

After discharging as above, monitor how much capacity goes back in to fill em up - should be close to the stated capacity of 1400. Significantly less indicates that the pack is deteriorating.

perhaps this thread here may help ?

[Craig Spence]

Sorry Timbo but how would I discharge a battery?, do you have to have dischargeing equipment, I have a pro-peak varipulse 2500vp charger will this help?.

Would dischargeing then charging the battery give more power to a brushed motor  as I was advised to do this by someone because I can not get my plane off the ground with the current set up. This reason has forced my hand to invest in a brushless set up from brc hobbies.

Will I have to balance/discharge li-po batteries or can I just charge them from the pack?.

Once again thanks.

[Piper Cub]

Your charger may have a discharger function. If so use that. Alternatively, you can use a 12v car bulb, soldered to some wire and the type of connector use for the Nimh battery. Connect the two then when the bulb goes out, your pack is discharged.

A discharging regime wont add any power to your battery pack but will ensure you get a full charge and longest motor run before having to re charge again.

[Jason Carr]

Hi fom "down under". I read somewhere that discharging was not neccesary as long they  were ballanced  before chargeing. You comments please.....cheers Jason.

[Craig Spence]

Piper Cub,

cheers for the info ill put that into practise, nice to know.

[Craig Spence]

Jason Carr,

I dont know about that myself but I think they probaly would be balanced when purchased.

[Tim Mackey]

They are highly likely to be UN-balanced when purchased, and should be given a "forming" charge to equalize them.

ALL nickel based batteries should be trickle charged at about 1/10C for the first few cycles to "form" them properly, equalizing cells and compensating for possible inbalance due to differing self discharge rates and possible gravitation during storage.

Did you read this as linked to earlier in the thread ?

[Craig Spence]

Hi Timbo,

thanks for the info, I will read the attached item you have provided but can you help me out again. I own a AC-DC Pro Peak varipulse and you charge in Amps going from 0.5 all the way to ten, so how could I incorporate this into charging, dischargeing, and forming of Li-Po batteries.

It doesent have a discharge facility but if you plug a battery in charge without the mains being plugged in the power light will illuminate, could you not discahrge like this untill the light goes off.

Your feedback would be greatly appreciated Timbo, im currently at work and will be for two weeks so I have little spare time, anything you tell me will be taken note of and taken home with me.

Cheers Timbo.

[Frank Skilbeck]

Craig, just had a look at your charger on the net, this is for Nicad and NiMh batteries only, it is not suitable for Lipo batteries and if you tried to charge a lipo, the lipo would be damaged and may even catch fire. Only charge a lipo with a lipo specific charger.

It doesn't look like it has an inbuilt discharge function as well.

Nicad's and Nimh packs don't need balancing, but do get better with a few discharge and charge cycles (cell forming). Probaly best to discharge at a low current and then charge at around 1/10c, say 140 to 200 ma on your charger. You could discharge it using your brushed motor (or any motor)  by just running it at say quarter throttle and then recharge, or fit a smaller prop, do this a couple of times and see if the pack gives any more power.

You might get a bit but it will probably not be significant, if you need more power then try a different prop.

Lipo's do not need forming, but do benefit from balancing, which is bringing each cell to the same voltage, this is mainly to stop and individual cell from being either overdischarged or charged, both of which will damage the cell.

Lipo's need a bit more care than Nimh cells, but carry over twice the power capacity per size and weight.

But a correctly sized brushless set up will be much better and a brushless set up with a lipo battery will be even better again.

I've just upgraded a friends electric glider which originally had a geared 380 brushed motor driving a 9 x 5 prop via gear box with a 8 cell 800 mah Nicad, it reved to just over 5,000 rpm and flight was very marginal with a shallow climb out. I put in a brushless outrunner (AXI 2217/16) with a 3s 2200 mah lipo and 10 x 5 prop and it balances the same. This combo turns the 10 x 5 at just under 8,800 rpm, haven't flown it yet, but it should go OK 

[Tim Mackey]

As Frank says.... NOT suitable for LiPo

After a few forming charges as Frank suggests, it would then be best to revert to approx .5C charging for NiMHs.