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Old Jun 24, 2014, 08:24 PM
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Canada, AB, Calgary
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I find the same thing balance charging my LiPos at 1C or so rate: the bulk of the charge happens in the first 40 or so minutes and then it can take over 3hrs to "balance" the pack. I usually give up at 2hrs and figure "close enough". Initially this didn't happen. I assume it is something to do with the packs. I always store mine in "storage" mode.

Thanks Pete for the info on NiMh charging. Very useful and I will correct my ways on that.
C
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Old Jun 25, 2014, 09:19 AM
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Originally Posted by AlThuban View Post
I find the same thing balance charging my LiPos at 1C or so rate: the bulk of the charge happens in the first 40 or so minutes and then it can take over 3hrs to "balance" the pack. I usually give up at 2hrs and figure "close enough". Initially this didn't happen. I assume it is something to do with the packs. I always store mine in "storage" mode.
I have the same experience sometimes, although I've never cared enough to see if it's just certain packs. I've always assumed that what's happening is the charger is simultaneously discharging and charging at the same time to get the cells balanced, which may never happen on some batteries. I think what it really ought to do is stop charging when a 3S pack hits 12.6, and then only discharge until cells are balanced.

In practice, I'll set up 4 batteries to charge. When the charger beeps, usually one says "Full" and the others are at 12.6, and I just take them all off the charger.
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Old Jun 25, 2014, 10:27 AM
PGR
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I have an X2 and an X4, and I don't notice any significant time difference between charge and balance-charge modes, at least when I charge my own packs. But I have seen an increase in balance mode times when some other people use the same chargers

At the risk of starting another round of premium brand bashing, I think it has a lot to do with the fact that I fly Thunder Power packs, and they still do an excellent job of matching cells in a pack. Consequently, the cells discharge and charge at the same rate and the packs don't go out of balance during normal use.

That isn't the case with many (most?) of the budget brands, though. The manufacturers of those packs assume that they will be balanced each time they're charged so they don't make much effort to match the cells in a pack, so they discharge and charge at different rates and take a lot longer to balance. That's not to say that all budget packs are bad, but the ones that naturally stay in balance are usually the product of luck rather than good manufacturing practices.

FWIW, I used LiPo packs for about 2 years before I ever even saw one with a factory-installed balance plug, and it took another couple of years for that to become the rule rather than the exception. Pack manufacturers went to great lengths to test and use cells with identical characteristics in a pack and the good ones (Kokam, Tanic, Thunder Power) could be charged and discharged 100+ times without going out of balance enough to matter.

Try that with the current generation of budget packs.

Pete
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Old Jun 25, 2014, 01:38 PM
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Another thing to consider as it relates to balance charge times...

Different chargers (or different channels within a multi-channel charger) may have some variability in individual cell voltage calibration. Thus, changing chargers (or channels) can extend balance times as the two chargers are effectively fighting one another. The charge time can increase greatly with large capacity packs (parallel charging), large calibration differences, or with lower end chargers that have low balance current or poorly designed balance circuitry. It's for this reason that it can be very helpful to always balance charge packs on the same charger (or channel).

The above is also one of the reasons why I always recommend high quality charge gear (FMA and iCharger) that is accurately calibrated (or can be calibrated by the end-user) and that has balance circuitry that is carefully considered and can be adjusted to suit the user's needs. It's also why I always calibrate the individual cell voltage on all of my chargers.

Mark
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Old Jun 25, 2014, 01:51 PM
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The voltage peak (peakV) happens before the pack is fully-charged. How "before" depends on the charge rate, but for NiMH cells it typically happens at 90-95% saturation and with NiCd cells it's 80-85%. The cell chemistry continues to absorb energy after peakV, but the voltage actually drops a little during that final few percent and it's that voltage drop, known as the negative voltage delta (-deltaV), that the charger uses to determine when the cell chemistry reaches the energy saturation point.

For NiMH cells that voltage drop (-deltaV) from peakV to the energy saturation point is around 4mV at charge rates below 0.5C, but it's between 8-10mV for NiCd cells. Consequently, if you stop charging a NiCd cell at the best -deltaV for NiMh cells you're essentially ending the charge cycle prematurely.

Pete
Do you have a link that backs up this assertion?
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Old Jun 26, 2014, 12:36 AM
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Originally Posted by PGR View Post
... I think it has a lot to do with the fact that I fly Thunder Power packs, and they still do an excellent job of matching cells in a pack. Consequently, the cells discharge and charge at the same rate and the packs don't go out of balance during normal use....
Pete
FWIW I'm seeing the same thing on I think all of my packs and they range from 8yr old EFlite 800mAh to 2yr old NanoTech A-Spec, Hyperion, 2200mAh, GensAce, etc.
When they are "waffling" on the balance I've often seen in cell voltage display mode: all cells 4.20V for a bit (as though it is applying 4.20V per cell) and then some kind of "rest" mode where they settle down to say 4.15V, 4.18V, 4.19V, then it repeats and applies 4.20V per cell, then rest, etc. That's why I figured it is the packs, and not the charger. It is as though the cells in the packs are not coming all the way up to 4.20V per cell.
Again, I haven't tanked any packs (below 3.3V per cell unloaded) and I store them in storage mode if leaving them for more than a couple of days.
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Old Jun 29, 2014, 01:25 PM
be all you can be
United States, CA, La Mesa
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I have had this charger for a few months now, I got it for my 6s lipos, my other charger lacked in that field of batteries.

I'm trying to come up with a portable field/home charging box, that I can plug in at home, and while I'm at the field, I can hook up to the old generator and proceed to charge packs and fly. With that being said, the recommended DC input for the unit states 11- 18 volts, with charging circuit power being at a 200W minimum (I think).

Have you guys ever built a charge box with the Hitec x4?
what power supply did you use for the setup?
12 or 24 volt?

I had read through and found that Chuck had bought one.

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Power Supplies - - -
Poking around on E-Bay (and exercising due care) can result in reasonable prices for decent power supplies. I recently bought two 24V (18-28V adjustable) 65A Lambdas at less than 1/10 new price. One was slightly used, and the other looks brand new.
Thanks in advance,
Joe
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Old Jun 29, 2014, 01:42 PM
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the recommended DC input for the unit states 11- 18 volts......Have you guys ever built a charge box with the Hitec x4? what power supply did you use for the setup? 12 or 24 volt?
24V exceeds the 18V maximum specified source voltage. You'll want to heed Hitec's specification to ensure that the 'magic smoke' stays in its proper place.
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Old Jun 29, 2014, 02:00 PM
be all you can be
United States, CA, La Mesa
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Originally Posted by mrforsyth View Post
24V exceeds the 18V maximum specified source voltage. You'll want to heed Hitec's specification to ensure that the 'magic smoke' stays in its proper place.
Yeah, because like what Chuck invested in was a 24v power supply, but was adjustable between 18 to 28 volts.

So I need to find something in the ballpark of 12v running at 350 watts? Being that the charger pulls 50W per port, should provide sufficient power to charge,

thanks,
Joe
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Old Jun 29, 2014, 02:05 PM
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Cell balance problems can be irritating, time wasters, and elusive to pin down to the cause.
Obviously, the charging and balance process is a factor. The balance leads and various connectors and connector pins are another. And, the charger itself.

Chargers usually have circuitry designed such that the cell voltage readings are taken from resistor networks that are replicated for each cell. The same voltage reading circuitry is switched electronically from one network to another. As the circuitry ages, there will be some additional tolerance added.

Since we are basically dealing in millivolt differences, stuff like connector pin mating and so forth has an impact. (Clean pins and contact surfaces can make a difference.) Crimp joints can also be involved.

It may be useful to gently "wiggle" the balance wiring between say a cell checker and a battery.
This can help show up shakey connections that can be part of the problem. Some female balance connector pins can be re-sprung to make the connections a bit more reliable.

Balance current can also be a factor.
First, the balance current can be some fixed current, or a percentage of the charge current
(C/10, C/20 are the usual percentages used.

As the balance current is increased, the the voltage drop across the balance leads will also increase. A difficult to balance Lipo may balance better if the set charge current is reduced, or the charger is told that the lipo has a smaller capacity. This can reduce the difference between cells at the end of charge.
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