Charge rates

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Charge rates

Postby jpreou » Fri Aug 19, 2011 6:34 am

For months I have been using a Hyperion charger running off mains. Even when I select a 6A charge rate for my 5000mah 6S DN Power batteries it only ever charges at 2A and decreases as it gets closer to the end. I suspect if I powered it from a power supply rather than mains it would do better; maybe I'll tets that now I have a PSU. Anyway, the battery takes over an hour to charge. I currently have two of them but have another two coming. I also have five 2200mah 3S, two 1050mah 3S and one 2500mah 3S. Needless to say, I spend all Friday night charging batteries even when I start early afternoon!

I just got a power supply that can do 13.8V 40A output to feed a new Hyperion charger capable of 20A. When I charge at the same rate it actually puts out the full 6A I asked for and the same battery charges in approx 26 minutes (again, charge rate tails off at the end).

Here's the question; the DN Power batteries are capable of a 5C charge apparantly. I'd like to charge the 5000mah 6S at 10A, which I understand is "2C" (yes?). Can anyone foresee any issues?

Cheers
JEFF
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Re: Charge rates

Postby kaptain_zero » Fri Aug 19, 2011 9:34 pm

While those batteries you mention are listed by the manufacturer as being capable of being charged at 5C, there is no free lunch. You will be charging quicker, but you will be giving up some of your total number of usable cycles. Conventional wisdom dictates a max 1C charge rate to maximize the number of cycles you can get from your packs. You would also be wise to stop some 20% short of running the packs down before recharging (as in land before your ESC cuts out) This will also add life to your packs. Lithium Ion cells do not like deep cycling, but prefer shallow discharge and gentle charging.

You have done the correct thing by going with more chargers.... It will be kinder to your cells. If you have many packs of the same capacity/cell count and preferably the same brand/age, you can consider parallel charging them with the same charger by using a parallel adapter, either home made or purchased. It's best to have well behaved packs as you won't be able to balance charge during a parallel charge, so use parallel charging with some caution, checking the cell balance of the packs with one of those hand held meters that can check the balance for you, just to keep an eye on things.

About charging speeds... The correct charging cycle for Lipo cells is CC/CV where on a typical cell that is fully exhausted will be charged at a 1C Constant Current for about 1hr and then finishes charging with Constant Voltage where the current gradually drops to 1/10th of the initial charge setting which would take around 1 hr as well, so figure 2 hrs to charge a lipo cell that is drained to minimum permissible voltage. Note that I speak of cells, not batteries which are several cells in series. If the cells are balanced, the same 2 hr charge time will be roughly the same, but if the cells are out of balance, and you are doing a balance charge cycle.... it can take significantly longer as the balancing takes a significant amount of time in most chargers.

Regards

Christian
Last edited by kaptain_zero on Sat Aug 20, 2011 2:40 am, edited 1 time in total.
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Re: Charge rates

Postby jpreou » Sat Aug 20, 2011 2:05 am

Thanks for that. The Hyperion chargers balance as well. I don't mess with any of the advanced functions. I only ever run the packs down to around 30% or so. I carefully time all flights and check the battery afterwards on a battery checker that read out the voltage (including per cell) and the % charge. The new Hyperion charger has capacity for two outputs and 20A charge rate out of each channel. I think I shall charge the 5000mah at 5A, one per channel, so I can do two at a time and the smaller batteries on the 'old' Hyperion charger. I did the 2200s on both chargers last night at 2C and the difference between either one was just a few minutes, so no gain there. Looks like to maximise battery life and get sensible, if not blistering, charge times I'll use the new charger for larger batteries as it can push the current, and the old one for smaller batteries as it can push the smaller current with no problem. When I don't use the batteries I always put them in 'store' mode, which the Hyperion charger has a setting for (its about 59% charged, I think). Cheers.
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Re: Charge rates

Postby kaptain_zero » Sat Aug 20, 2011 2:56 am

I had to make a correction to my previous answer. I initially wrote that the CV portion goes until charge current hits 1/10c which was incorrect, it goes until it hits 1/10th of the initial charge rate that you set.

If you set your initial charge rate to 5A, the charger will stop charging when it reaches .5A during the CV portion. If it is set to 1A, it stops at 0.1A... just something to remember. High rate charges are faster, but the charger also cheats by shutting down the CV portion sooner. You decision to stick to 1C will be beneficial to your batteries and will not increase your charge times all that much.

One thing that bears mentioning about these newer high charge rate packs is that they apparently, and I am going by articles I've read in various hobby magazines, is that they do not like to sit fully charged for very long. One article suggested that you should charge them up the day you are going to use them so they only sit fully charged for a matter of hours, not days.

And one last thing... a cycle is a cycle with Lithium batteries. Every cycle adds wear to the pack and it will never improve it like it does with Nicads and NiMH cells that have sat for a while. Charging Lipo's up and then putting them back into storage charge without actually using them, just adds a cycle of wear and tear for no reason. So the moral is, charge the packs you KNOW you'll use and if you think it might be a great day... bring some extra packs, but only toss them on the charger at the field if you know they'll get used. I know..... I'm a bit anal about these sorts of things! :mrgreen:

Regards

Christian
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Re: Charge rates

Postby jpreou » Sat Aug 20, 2011 5:12 am

Yeah, I get real frustrated when I charge Friday night and then can't fly for weather or some other reason. I also just noticed my new charger has ONE output lead and two balance plugs so it can do higher than 7S. Not sure now if I can charge more than one 5000mah 6S. The charger is capable of handling the current (in theory) but I don't know how to organise the wiring. Man, at this rate I'll need to dig out the destructions! :-)
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Re: Charge rates

Postby kaptain_zero » Sat Aug 20, 2011 4:50 pm

The book of words, is your friend..... until you read it the wrong way and screw something up....... and don't ask me how I know that! <groan>
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Re: Charge rates

Postby ergocentric » Sat Aug 20, 2011 9:16 pm

if you bought this one: Hyperion EOS 0606i DC input - 6S, 6A max, 50W
it is clearly limited to 50W

6s times 4.2 Volts per cell times 2 Amperes is 50 Watts

so you may need a more expensive charger
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Re: Charge rates

Postby jpreou » Sun Aug 21, 2011 5:29 am

My first charger was the 0606i AC/DC and, yes, it has been the limiting factor. I just bought a new charger with a power supply so I now have two chargers. The new one is good for the big batteries and the old one for the smaller batteries. I think I have it covered now. Will still take several hours to charge *all* batteries though as I don't want to push charge rates too high, especially for the bigger more expensive batteries.
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Re: Charge rates

Postby RCModelReviews » Mon Aug 22, 2011 1:10 am

Ergocentric has nailed it -- the limiting factor is the total wattage you're putting into the battery.

Although a charger may claim to be able to deliver 5A, that's only if you haven't reached the wattage capacity of that charger.

the Wattage is the voltage times the current so, if you're charging a 2S lipo (to 8.4V) then a 50W charger can deliver the full 5A (because that's only 42W (8.4V x 5A)

However, when you try to charge a 6-cell battery, you're putting out 25.2V which means that if your charger can only manage 50W, the current will probably be around 2A (50W/25.2V)

Even if you set your charger to a 5A charge-rate, it will never achieve that once the voltage of your battery exceeds 10V.
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Re: Charge rates

Postby jpreou » Mon Aug 22, 2011 7:58 am

Yup, that's *exactly* what I am seeing!
Luckily, the new one can, and does, push out 5A all the way through the charge cycle, except at the end when it slows right down. Essentially, I now have two chargers; one for small batteries and one for large ones.

Another question then; if I field charge using my car battery as the input, what should I expect in the way of amps; could a normal car battery give enough to charge the bigger batteries at 5A (1C), or should I accept I'll only be charging the smaller batteries that way?

Ok, two questions! I know from previous that I *can* charge the bigger batteries at the field from my car battery, but again the old charger (now I know is W limited) only did 2A which is less than half a 'C'. Are lipos ok charging at that lower rate (since most folk recommend 1C)?

Cheers
JEFF
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