miernik

I want to use the FMA Cellpro PowerLab 8 for cycling tests of 8S1P chain to test 8 cells at the same time.

It is important for me to have each individual cell charged fully to 3.6V and less then C/20 current acceptance so the SoC is 100% and then also each individual cell to be discharged to exactly 2.8V.

During charging: suppose one cell in the chain reaches full charge and doesn't accept any more charge, will the charger continue to feed current to the remaining cells in the chain through the balance leads?

And during discharge: suppose one cell in the chain reaches 2.8V and I don't want it to be discharged more? Will the charger stop sucking current out of the main leads, and discharge the remaining cells through the balance leads only (of course at max 3A) until every of them reaches 2.8V?

kyleservicetech

I've watched my Powerlab 8 charger charge up my 6S4P A123 packs. During the charge cycle, all cells have the same exact voltage while charging. (Also verified the same exact voltage with my 6 channel home made digital volt meter)

Have not tried the discharge test, I've got a West Mountain CBA charger for that purpose.

Howard Matos

how exactly does the balancing in the FMA Cellpro PowerLab 8 charger work?
I want to use the FMA Cellpro PowerLab 8 for cycling tests of 8S1P chain to test 8 cells at the same time.

It is important for me to have each individual cell charged fully to 3.6V and less then C/20 current acceptance so the SoC is 100% and then also each individual cell to be discharged to exactly 2.8V.

You will require the Charge Control Software to adjust the balanced A123 preset you require, make sure per cell voltage is 3.6V (Charge tab), termination is C/20 is default, found in (Termination tab). Start with an accurate preset for the most precise balancing. Discharge voltage can be found on the discharge tab.


During charging: suppose one cell in the chain reaches full charge and doesn't accept any more charge, will the charger continue to feed current to the remaining cells in the chain through the balance leads? Yes, that't the way balance charging works.

And during discharge: suppose one cell in the chain reaches 2.8V and I don't want it to be discharged more? Will the charger stop sucking current out of the main leads, and discharge the remaining cells through the balance leads only (of course at max 3A) until every of them reaches 2.8V? This is not the default method that PL8 discharges, nor is it recommended. PL8 does not do balanced discharge by default. First, it does not give you an indication of the actual capacity of the pack. Actual capacity is based on the weakest cell in the pack. When you balance discharge, you are allowing the strongest cell in the pack to give you the measure of capacity. If you discharged this way in the real world, you'd end up with damaged cells in the pack if you did not balance discharge during operation. Nobody manages a battery this way during application. The better way to discharge is to monitor all cells in the pack, and, when the first cell reaches termination voltage, stop the discharge. This provides you a real indication of capacity, based on weakest cell in the pack. The balanced discharge method actually un-balances the battery during discharge, and then the PL8 will have to re-double the efforts to re-balance it during the charge cycle. Nevertheless, a new version of the CCS/firmware will be available shortly that provides balanced discharge option because other customers have requested it.

miernik

I understand all this, however this is for testing individual cells (for better statistical value) and not the pack as a whole. I only want to use the balancing to avoid buying 8 chargers which would be too expensive.

I want to have 8 different readings of capacity at the end of each cycle, not just 1.

This is not about testing the pack, its about testing lots of individual cells, but cycling them 10000 times at 4C and measuring after how many cycles each cell died, and making statistical analysis on that.

So I need to have each cell discharged to exactly the same voltage to have useful data. I am looking forward for the new firmware, without it the charger is not capable of making the cycling test I need.

One more thing: does the charger log all the charging history internally (I want to have all possible information that the charger can displayed logged) or do I need to have a computer hooked-up all the time to log the data, otherwise it's gone?

kyleservicetech

I've been working with Howard to solve a problem I had trying to charge my A123 cells directly through the balance cables, not using the high power cables.

Howard pointed out to me that the balance connector should be wired with the negative battery balance wire connection should connect to the black wire of the Cellpro Balance cable. The next cells should connect in succession on the balance cable. BUT, the last cell in your balance cable should connect to the RED wire of the Cellpro Balance cable.

So, if you have a 3S A123 battery pack with 3.4 Volt DC cells, then is pin 1 common, pin 2 would have 3.4 volts, pin 3 would have 6.8 volts, pins 4, 5, 6, 7, 8 have no connection. And pin 9 would have 10.2 Volts.

So if you're wiring your own batteries, this is the connections you should be using with the Cellpro Chargers.

kyleservicetech

10,000 times?

Lets see, 4C indicates discharge in about 15 minutes, charging would be another 15 minutes. That's 1/2 hour per cycle. That makes a total time of 5000 hours, or 208 days! Guess that would be a long term test!

miernik

Yes, and I want the cells to cool down a bit in between, so about 1 hour per cycle. And maybe 10000 cycles is not enough to kill them, so I might run it even longer. A year or more.

Will the Cellpro PowerLab survive it?

kyleservicetech

I've been running my A123 cells at 30 Amp loads, discharging them to about 40% capacity in about 6 minutes. And after sitting in the hot sun, those cells actually cooled off after a flight. The cell temperature was measured with a Fluke 87V meter with its thermocouple temperature probe.

So, if you're discharging them in 15 minutes, not much concern about them running warm. Just aim a small fan at them to keep the air circulating.

LOL Good question, which will last longer, the Cellpro???

I've got three 6S2P A123 packs with some 200 flights and three years flying on each of them. And all three packs have the same exact performance as when brand new in 2007.

miernik

So let me understand this correctly - the cell temperature was lower after 6 minutes of 30Amp (how many C was that?) then before? Well, sitting in the sun, they might have had 40 degC or something. So in the plane there was share and they cooled down?

kyleservicetech

That is correct, after flights of my several models running A123 cells at an average of 25 or 30 Amps (about 15C) per cell or so in 70 degree weather, these cells actually cooled down by several degrees F after sitting in the hot sun.

Of course, keep in mind that the model had a 70 MPH blast of outside air blowing into the front of the model. But, one of the same models was previously equipped with twenty two 2400 Mah Nicad cells, with the same motor system.

Those Nicad cells got so hot that I had to use a blower to cool them down after a flight. Temperatures consistantly got over 140F during flight on those Nicads. (Sanyo SCR2400's) The current pulled out of those Nicads was on the order of 30 Amps, or about 12C.

Howard Matos

Hi,

The new firmware is currently in beta testing. The CCS version which supports it has already been released, but the PL8 won't support it until the new firmware is available. Fingers crossed, should be released next week.

The PL8 does not store data. Yes, it will need to remain connected to the computer to log the data.

Howard Matos

Hi,

On Monday, April 18, 2011, FMA will publish to the general public new firmware for the PL8 that enables the requested feature “balanced discharge”. When you update the firmware to v3.24, then the existing parameter “Bal. Discharge” (found on the Balance tab of the CCS) to “Yes”, the PL8 will balance the pack on discharge. Although we do not recommend this method for discharging, and therefore we will not establish it as the default setting, we are providing it in response to a few customer requests for the feature.

Howard Matos

Hi,

Although the newest firmware will support balanced discharge on this Monday, it will not be possible to measure individual cell capacities, as this would require 8 independent charge circuits with current measurement on each cell; effectively 8 independent cycling devices.