Ion Lipo's

[andys]

should the 2 sets of cells for my ion be the same voltage before they are connected? one pack is 20.85 the other 20.80, if so how do you discharge one to match the other?

Ive been told that if they are differnet as above, you stand a chance of puffing the cells, mine are TP8000 5s4p G2

thanks

[MinAirChris]

You can either use your charger to bring up the lower one or some load to bring down the higher one. Ideally, a blancer, but since yours are Gen 2's, try the charger method.

Stay off the limits of the batteries and you won't puff them. Take all the numbers on the labels and multiply by 0.75...discharge an 8 amp*hour battery only 6 amp*hours, charge at 0.75 C. You should do fine.

Pushing the limits is usually what does these things in. Trying to get the last mA of charge out of them or charging them at 1C or greater all day long or over-exerting them with long, drawn out, head speed robbing maneuvers will all reduce the lifespan of a battery.

Chris

[andys]

Hi Chris
stupid question, what do you remommed I use to load the cell pack to bring it in line with each other? do you recommend they are used at the same voltage, or does it not matter?

Ive fitted taps to the packs and charge with the tp205 connected

Andy

[MinAirChris]

If you have added taps, you can use the TP balancer, right?

Otherwise you could just use a 210 ohm power resistor (maybe 10 watt) across the higher voltage pack a little at a time until the voltages match. Be careful here, DO NOT walk away from a battery with a load plugged in. Also, watch that resistor as it will get hot.

I would under no circumstances recommend that you try to bleed down each block in the pack through the taps...this is a sure recipe for disaster.

You could use the taps to CHARGE each of the parallel blocks to balance up the pack, much safer than trying to discharge each block to the same level. Be sure to allow similar rest times after the charge before you measure the cells, endeavor to keep everything the same with regards to charge rates and times.

Chris

[andys]

Hi Chris
yes im using the tp205's to balance when charging, and ive now got the pack spot on

thanks for the advise on the resistor, i will get one and mount it on a heat sink, just wasnt sure what to use to load it up

thanks

Andy

[Russ McC]

Hi Andy,

Just to help clear this up for you, the only reason to have your tow packs at the same voltage before discharging is because you could damage the lower pack if you discharged them to there limit, or beond there limit wich is what will puff your pack. Your packs are so close that if you did that you would ruin both your packs. No, your packs do not have to be at the same voltage before discharge, there is not some invisible cause that would just puff your pack by having them unmatched, you are only discharging them at the same time but they are living there own separate lives, one battery does not affect the other when in series.

The trick is as Chris said do not discharge them to there limit, leave 20 to 25% in reserve and you wont have any problems even if your packs where off more then yours are. I even run my UBEC off only one pack and sense I never discharge to the limit there is no problem. My chargers are also unmatched so I always charge the pack that powers my UBEC with the charger that charges to a higher voltage.

Now as you probably know Charging is a different game. If you’re charging packs together in series and plan to charge to the limit then they better be at the same voltage or you will over charge the higher pack. This is the same with the parallel sets that are wired in series in each pack, if they become un balanced you will over charge the higher cells and could in theory over discharge the lower cells if you discharged them to the limit, that is why you are using your cell balancer.

So to close, your batteries are plenty close, just go fly and don’t discharge them to there limit and you will be fine, even if they where perfectly matched you would still not discharge to the limit because that is hard on the batteries and could still damage them and or shorten there useful life. Have fun & be careful :glasses2:

[andys]

Hi Russ/Chris
thanks for the coments, ive flown today for about 7mins, just checking the ion out, not been flown for at least 7 months, and as you would expect it was smoooooth.

The cells are recharged and took back in only 3.4mAh, what is the best normal charge current for the cells, ive used in the past 1c which with these cells is 8A, but it turns out the TP G2 cells were 7600mAh, ive chaged them today at 3A, took about 95mins

what do you recomend?
Andy

[Russ McC]

7 amps is good.

[andys]

Thanks
7 amps it is

Andy

[3DWannaBe]

I have been taught to charge at the .75C rate at the field when needing the packs only and charge at about .5C or less once you are at home and have some time.

What Russ is saying about only taking them down to .75 or less and not having to be matched when run is correct.

Good info in this thread.