Charge rate
 

Hi from the UK,not posted here before,but heard good things.I am waiting for my Hyperion g3 vx6500-5s lipo to arrive,and can't seem to get my head around this 5c charge rate,if i am right thats 5 x 6.5a=32.5a charge rate,is that right?,if so can anyone recommened a suitable charger:smile:

Yes, that would be the max charge rate. Save for a dedicated lab supply, I cannot think of a charger that can push 32 amps at 20+ volts. The hyperion 720I can do 250 watts, but that is 12amps at 5s, or so. You will need a big power supply to do that.

Yes thought so,thanks for the reply confirming it,can't wait for the battery to turn up,getting impatient to get the Truggy on the track.

Post up some info & pics in the Truggy sub forum, always nice to see another Brit on the forum. :yes:

this charger is dirt cheap for what it can do. you can charge your lipo at ~18a with it.

http://hobbycity.com/hobbycity/store...alance/Charger

There isn't really a charger out yet that can do 5c charge on a 6500mah pack. I did 5c charge on my 2x 3s G3 packs and they sure can handle the charge, really quick! But now I just charge the two packs wired in series (wish i had got a 6s pack in first place), in un-balanced mode at 10 amps, quicker and more convenient than charging two separate packs. I check balance between cells every few runs, but they always are in perfect balance (around 0.002v).

You don't actually get a linear decrease in charging time per charge rate, it is merely the MAX charge rate during charge, the higher the C rate you set the charger at, you will hit CV phase after CC phase exponentially sooner, thus making the very top end of the C rate spectrum, the benefit seems to drop off a bit. I have found 4C is only a few minutes longer than 5C, and definitely not 25% longer, which it would be in theory.

That charger would also require a 350-400watt powersupply.

Just go buy a 12 lead acid batt, all the power you will ever need, that's what I did, and actively charge it with my programmable power supply. The Pd should preferably be a deep cycle, or a large gel cell.

That makes sense. Cell resistance plays a definite role in this. The higher current you charge, the higher voltage it will take to generate that current, and so hits the 4.2v/cell threshold faster.

Yah, precisely. Ideally, if you could increase the max charge voltage as you increase C rate. You can do this with A123's however, I usually use 3.7v/cell for charging 5 amps/cell for a 2p pack, and then 3.8v/cell, sometimes even 3.9v/cell at 10 amps for a 1p pack.

I would be interested in finding out how a G3 cell would handle a 4.3v/cell charge threshold at 5C rate. I could only do this using my programmable power supply however.

As resistance decreases in lipo cells even further, 4.2v/cell should be sufficient for 5C or more charging to get the benefit. Like you said, it is mostly limited by the cells Ri.

You may all like the i-chargers from junsi and can be found here to purchase in the usa. Progressive is a great guy to deal with. The 208B is probably the best deal going right now for 20 amps and 350 watts up to 8S.
http://www.progressiverc.com/index.p...id=1&Itemid=18

I have a tiny bit of experience with increasing the voltage on lipo during the charge , since all my old packs are so worn out that I can set the rate at nearly anythig I want and they will hit the cv stage very early (sooner) in fact most times I leave all chargers set to max current and even on a tiny battery if the rate goes over the max at the beginning it's no big deal.

Here's what I did after most said I was crazy: My theory was that it wasn't the high voltage that ruined a lipo while charging, but rather the voltage at rest above 4.25 (or whatever you like for a max) I like saying "4 and a quarter" it sounds nice. Anyways I figured that whatever the voltage was up to the full mark was going to be ok and it only climbed to 4.5 on a cheap cell. I still maintained the max current spec of the cell and charged it with CC , and eliminated the CV stage alltogether.

This allowed the cell to charge as fast as a NI cell (at a constant rate) There's no apparent cell damage or heat increase , but the trouble is predicting the "full mark" which I am working on. I'll post a graph as soon as the garage pc is up and ruinning again.

ps , std warning "don't try this at home" or the world may end. That's what most told me. :na:

Well, you can't really predict the 'full' mark' on a lipo pack if you were to increase the charge voltage, as it would just keep going until it permanently damaged itself.

A123's are different, the chemistry only has a limited amount of lithium ions in the cell, so once it nears the end of charge, the voltage rises quite rapidly... so you would be able to see a 'sign' of being full when using strictly CC phase. Life chemistry is better in this way, as it is safer for charging. This, I suppose you could call the traditional 'peaking' method as used with batteries like NiMH, but not quite the same outcome, or repercussions if things go wrong.

Lipo cells have, IIRC, over twice as the amount of lithium ions that are necessary, so you cannot see a voltage 'spike' at end of charge, which makes things dangerous.

I have found, when charging an A123 cell, you can use 3.9v/cell @ 10 amps using only CC phase and get, I would say, at least 95% capacity into the cell.

I predicted the full mark based on total capacity and am working on perfecting it. It sure isn't very complex, but so far haven't found a fool-proof method. I can charge a familair cell at the max rate right up to the full mark without the cv routine. If I can duplicate the methond I use manually then an automatic proccess can be used and save a bunch of time. The voltage can climb to whateverr it wants to 5 volts perhaps, my theory is that the voltag attained during the charge proccess is irrelevent. Only the ending voltage AFTER the current is stopped.

5volts = fire

That's what everyone else said too. Here is one such graph that go to 4.5 volts. I will do one to 5 volts and see temp and pressure.