Anyone using hexTronik 3S Cell Saver & Balancer???

[pcar993]

I cant tell if its working or not but i did notice it takes alot longer time to charge my lipo using the balancer in between the charger and battery compared to just plugin the battery directly to the charger without balancer. Does anyone else notice the same?

[Jermo]

I use the Cellpro 4S which actively balances during charge and it's faster than using a seperate passive balancer/charger.

[kgfly]

Balance charging is always slower than simple charging since the balancer dumps some of the current to hold the high cells while the low ones catch up.

[Jermo]

Ken in passive balancing true..... active balancing not so true ;)

[Probedude]

Ken in passive balancing true..... active balancing not so true ;)

Not so true, but still true in the sense that it's slower than no balance charging. You can see it in the owners manual of the new 4A Cellpro charger. page3. 2C charging isn't 30 mins total charge time, 3C charging isn't 20 minutes total charge time.

From the manual under 2.0C mode "Packs smaller than 4AH will charge completely in about 40 mins" and under 3.0C mode " Typical charge time for packs under 1.5AH is 30 mins"

That said though, one shouldn't be charging higher than 1C unless you're balance charging anyways - which we're all in agreement on. Also 'smart' balancing ('active') is faster than 'afterthought' ('passive') balancing, and any balancing is safer than no balancing.

Dave

[Jermo]

Dave,
When I was charging with a blinky balancer (passive) my packs were well over an hour for 1600mAh. With my Cellpro set to 1C it's done under an hour (approximately 50 minutes), at the 1.4C fast rate it's 40 something minutes.

I think it really depends on the setup. I believe active balancing is faster than passive especially if the charger can ramp up the charge rate after the packs are balanced. Having the ability to adjust the main charge current in response to single cell status is key IMHO.

[Probedude]

I believe active balancing is faster than passive especially if the charger can ramp up the charge rate after the packs are balanced. Having the ability to adjust the main charge current in response to single cell status is key IMHO.

No argument there, we're both in agreement (active vs passive vs no balancing).

My only question, which is more curiousity than anything and is not directed at you at all is the different kinds of active balancing and the advantages of one over the other.

The 2 methods I see are:
A - The charger can balance during charging, bringing up the lowest cell to match the others then charge all together at a higher rate but still 1C
B - The charger can balance at the end, start off at 1C from the beginning and let the cells charge up at any speed they want until the first cell hits 4.2V at which point it is clamped at 4.2V. The rest of the cells charge at 1C until another hits 4.2V and the cycle repeats for all the cells. Finally when all cells are at 4.2V, the voltage is held constant until the current drops.

From what I've seen on packs I've overdischarged, there are some imbalances in the cells (say ~ 0.2V) but the imbalance pretty much goes away on its own as the cells come up to full charge (~ 0.02V imbalance).

The area under the curve of Amps/Time if plotted is the amount of charge put back into the packs. In my mind (since I don't have real data) I don't see that either A or B would have an advantage over the other. In either case the cell with the lowest capacity left would still dominate the charge time whether you throttle back the charging at the beginning for it to come up to the same level as the other cells, or throttle back the full cells while the still depleted one comes up.

Again, just curiousity and out loud thinking.

Regarding the Cellpro taking less than an hour, I think this is due more to the algorithm used to determine the charge rate. My Cellpro seems to settle at about 1.2 - 1.4C even though I have it set to 1.0C. Just an observance, not saying this to contradict you.

Dave

[pcar993]

Is my setup passive balancing? I have the balancer between the charger and battery while charging.

[Jermo]

Pcar without knowing your setup it's hard to say.

Dave,
No worries. I could be barking at the moon. To me the difference is the ability of the charger to adjust the charge rate during balancing and kick it up when it has balance or back off when it's out. At the same time the balancer is doing it's thing (as you described). I use the term active balancing to indicate the charger is aware of what the balancer is doing (monitoring the cells/affecting charge rates) in contrast with a passive balancer where the charger and balancer work independantly to what we hope is a successful charge/balance.
I don't think the Cellpro algorithm is exactly what I'm describing but it's doing something during charge because I've watched the cells come into balance before the charger officially goes into balancing mode.
From what I've seen at the field the TP1010 with it's balancer does the same thing (from my observations).

You've got more testing on the cellpro what have you seen?

[Probedude]

I don't think the Cellpro algorithm is exactly what I'm describing but it's doing something during charge because I've watched the cells come into balance before the charger officially goes into balancing mode. You've got more testing on the cellpro what have you seen?

I need to build the PC interface and see what the PC is telling me the Cellpro is doing. Just looking at the LCD and also measuring the tap connectors, I don't see that it is doing any balancing until the end, but then again my packs for the most part seem to balance themselves pretty well. Using the PC interface maybe there is more information and some quick pulses now and again on the balancing transistors to do some balancing during the fast charging.

As I mentioned before but didn't explicity describe, I have charged packs that have appeared to be out of balance at the beginning of charge (especially when I've over discharged them) on a non-balancing charger (Triton) but the amount of imbalance towards the end of charge wasn't as great. One of the battery gurus (guru as in "lots of experience", not a battery engineer) on RCG mentioned the same thing - packs look worse for imbalance when depleted than say 1/4 - 1/2 way charged. Good packs anyways.

The Triton I used is a co-worker's. Because of what I saw with my packs pretty much staying in balance by themselves I went ahead and added a Polycharge 4 to my arsenal. Makes getting ready for a weekend of flying much easier since I can charge 5 packs at a time (6 if I decide to enlist my Duratrax ICE also). Figure I'll rotate them through the Cellpro to 'freshen' their balance up regularly.

Dave

[kgfly]

The risk of non-balance charging is that the highest cell in the pack can be pushed past 4.2V while the rest catch up. Since without a balancer 100% of the charge current is passing through all cells, it is a high probability that at least one cell will be over-charged, at least biefly, before the overall pack voltage reaches the CC-to-CV transition threshold (usually 4.2V/cell). When you add in the tolerances for the charger's voltage measuring circuitry and the possibly uncompensated wiring losses this can lead to a reduction in pack lifetime. If you have high quality packs that remain closely in balance then balance charging adds little to the overall charge time anyway.

Hence IMO balance charging should be the norm for maximum safety and pack longevity.

[Jermo]

Ken,
The question is balance time with regard to active balancing and passive balancing. Is there an optimal way to decrease the time while maintaining high charge rates? The implication is such that a pack already balanced would yield the fastest possible charge time as a baseline. The method/algoritm would be optimized to approach this baseline.

I think we agree that active balancing is faster/safer because the main charge process is monitoring the balance and can adjust.

hehe..we're more in a discussion of what could be done or what might be used ;) .