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Old May 05, 2013, 04:23 PM
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Popped a fuse again (P6 and MPA)

Preparing to head to field late this afternoon (will be leaving presently).

Grabbed 4 Turnigy 2200 3s packs that are all roughly the same number of cycles (maybe 20 tops) and all were at storage. Fired up the PL6 Faster charge setting, listed 4 parallel, chose 2.0C charge rate and off they went. I was in and out of the room loading the car, but they were done in about 40 minutes, though they listed 98% and my little 3 in 1 voltage checker was showing 4.15 volts per cell.

Hmm.

Threw on 3 3s 1300 mah eflite packs with 2 1600 mah 3s turnigy nanotechs from my stack of storage charged packs. Moved to high power preset but said no to the parallel, added up capacity (7100) and ran ~2.5C when I set 17A. Back to loading and in and out of the room.

Says done a pretty short time later. Checking cells I'm getting several packs with voltages similar to 4.18, 4.18, 4.23. I don't trust my little 3in1 so I start putting them back on the charger solo, wanting to start them discharging to storage so I can get them in balance. Errors out on bad cell count. I change connectors, then change channels, then realize the 40A fuse is blown on one channel. Great, changing those fuses is a pain in the tail. So my MPA is a 5 channel for now, and I need to figure out what triggered that so I can not do it again.

Now I see one of the original turnigy 2200s is now showing 4.15, 4.15, 4.08.

Don't know what the hell to think, don't want to call off a rare chance to get to the field.

What did I do?
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Old May 05, 2013, 11:30 PM
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Fuses blow when there is excess current. Unless the fuse was faulty it did its job. As to what causes this and what happened, there isn't enough data to go on.

As for what to do next, first fix the fuse. The use an ohm meter to make sure there are any shorts on the board. Especially on the connector or adapter associated with that fuse.

Going forward, check your packs before they go on the charger. If they are imbalanced or significantly different than the other packs to be charged in parallel, charge them separately.

Once the charge cycle is complete check the packs again. If they started in good shape and ended in bad shape, that group of packs cannot be charged in parallel. Issues may arise from mixing pack sizes, or packs with very different IRs. Break them into smaller groups of "like" packs. See if the results are better. Then add a dissimilar pack and see if the balance issues worsen.

Not every combination of packs parallel charge well together. Often times mixing mah doesn't cause an issue. But it can happen. Also one weak cell in one pack can cause balance issues for all packs in parallel. Parallel charging masks an issue in a single cell making it harder to track down.
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Old May 06, 2013, 08:25 AM
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Quote:
Threw on 3 3s 1300 mah eflite packs with 2 1600 mah 3s turnigy nanotechs from my stack of storage charged packs. Moved to high power preset but said no to the parallel, added up capacity (7100) and ran ~2.5C when I set 17A. Back to loading and in and out of the room.
When parallel charging IMO with mixed capacity,C ratings and past useage history LiPolys it is best to start with a low rate charger (1/2 C or less) and wait until all cells are very close to same voltage then increase the charge rate.


Quote:
Says done a pretty short time later. Checking cells I'm getting several packs with voltages similar to 4.18, 4.18, 4.23. I don't trust my little 3in1 so I start putting them back on the charger solo, wanting to start them discharging to storage so I can get them in balance. Errors out on bad cell count.
That degree of inbalance would have been fine and the Bad cell count was caused by the 4.23 volt slightly overcharged cell(s) most likely,based on my past experience.


Parallel charging is a fast ,easy way to get a bunch of Lipolys charged as well as taking advantage of high power chargers but there are issues. It works best with matched LiPolys is one is using high charge rates and works best at slow charge rates with mixed LiPolys.

Way back seven or eight years ago when I first started parallel charging there were no balancing chargers,off the shelf balancers and only a couple of LiPo9ly brands with balancing leads. I parallel charged with good sucess by checking each LiPolys voltage started a 1C charge on the lowest voltage one and when it reached the voltage of the next closest one at that one and continued until they all were added then increased charge to 1C total. With today's equipment such extreme care is not required but a little planing never hurts either.

It is a personal choice but I prefer not to do parallel charging as I like to see exactly what each cell is doing. I do routinely parallel small 1 and 2S LiPolys such as used in the micro class aircraft but I look at those as being extremly expendable and in addation the lower the cell count the lower the odds of inbalance being an issue.

Charles
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Old May 06, 2013, 10:44 AM
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Thanks Gregor, and good to hear from you Charles, I had read that you may have lost your patience with the endless newbie questions a while back, good to see you're still putting up with silly questions like mine.

After all that rush the field was very windy, directly in my face so it was a crosswind, I ended up just flying an EPP foamie almost like slope soaring.

I used the MPA to discharge all 9 packs back to storage last night after I got home. I obviously used a different channel on the MPA, I did one battery at a time, running a discharge rate of 10A, I didn't think that would be too high a rate, these are all 20C or better cells and the smallest is 1300mah.

Most of the packs came out at 3.83-3.90V after discharge, most had slight variation in voltage, such as 3.85, 3.86, 3.87. A few had higher spreads across the cells, up to 0.06 volts. I'm just guessing but is the PL6 more effective in balancing packs during a charge cycle than a discharge cycle?

I was getting errors when I was trying to use the channel that the fuse was blown on before I realized it was blown.

I'm wondering if one of the 1600mah packs may have been nearly fully charged connected to the other 4 packs at storage, could that pose a possible higher amp surge that would pop the fuse? This was one of the original fuses, not the one I replaced last year when I crosswired an adapter.

The 4 2200mah packs have been parallel charged together and discharged to storage together a number of times, they were bought as a group and tend to get used as a group. Should probably do some quality time with each pack individually, see if a weak cell on one is impacting the group in a parallel case.

Being able to charge a decent number of packs at once to get ready to leave for the field is very convenient but I'm seeing some drawbacks. Fortunately I'm also in early planning to add charge at field capability with a Honda, both for my use and as a minor backup for power outages from storms and to take camping. This reduces the need to charge 4 packs at 2C+ so I can get to the field.

I've accumulated a large batch of batteries of various ages and quality levels, at some point (probably end of season) I might do a mass discharge to zero and discard the majority, then purchase new packs on a targeted basis with better use practices. Currently only a handful have been marked ? (my indicator of questionable, so it doesn't go in certain planes and is a candidate to retire)
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Old May 06, 2013, 10:59 AM
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The default for storage is not to balance during discharge. This can be changed, but I would not recommend it.

Charging packs of mixed size and condition in parallel is likely the cause if your balance issues. Regarding the fuse, its possible that connecting a full pack to the MPA with a number of discharged packs is what blew the fuse. But it actual current rate depends on the state charge and IR of all packs connected. There will be a large current right after the packs are connected. Then it tapers off quickly. That may have been enough to pop the fuse.

Like my fruits and vegetables. I prefer to keep all my LiPos fresh and in good condition. I'm flying mostly helicopters. Because the performance of the model is so greatly impacted by the health of the pack, I prefer not to use under performing, older packs. Also as unhealthy LiPos can cause issues, I prefer just to discard and move on. I do keep a couple aged and unusual packs around for testing. But anything that can go, gets tossed.

I've switched over to field charging and much prefer it. No waiting around the night before, no need to stock up on tons of packs. I currently have only 2 flight packs for my larger models (600 and 700). With the high power of the Powerlab I am never waiting on the charger. Even if I could, I would be hogging the flight line.

I started with a single Pb battery. Which worked well for smaller models. I elected to move to a Honda EU 2000 vs adding a second Pb battery. For smaller stuff (mCPX and 130x) I just bring one of my larger LiPos and power the charger from that.
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Old May 06, 2013, 11:59 AM
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I always heed your and Charles' recommendations, I learn a lot that way.

I'll do some testing but I don't have a Fluke, best I have is cheap HF meters.

I'm getting over that initial rush of "I want one of every plane" and figuring out my lasting preferences. Tailoring my hangar and battery supply to that comes after that. I mostly fly scale and sport so I won't be flying the monster packs you need that demand a premium C rating for those hungry beast helis.

I prefer the generator because it has greater versatility aside from just my hobby use. Had too much downtime during Sandy, and an EU2000 can run electronics to keep my young children occupied in the event of an outage.

Grabbed a 100W Weller soldering gun to help get that popped fuse out, my Hakko I struggled with the last one.

In other questions, does the monitoring function put any sort of load or drain on a pack or just passively monitor?
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Old May 06, 2013, 12:30 PM
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Monitor mode does not put a load on the packs. Using a cell checker does put a small load on the packs. If you are seeing the voltage drop during monitor mode, that can be attributed to the normal voltage sag that occurs when a LiPo is done charging.
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Old May 06, 2013, 02:48 PM
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Makes sense, the small checker has to draw a small current to operate whereas the PL6 is externally powered. So aside from getting metaphysical with the observer effect the PL6 doesn't impact the pack.

What is the practical use of the monitor function? Just to get a more accurate voltage than a little 3 in 1 meter is likely to yield?

I had assumed that little bit of sag was based on the current and temperature dropping after the charge had completed, good to know.
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Old May 06, 2013, 03:08 PM
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Monitor mode allows you to use the charger's multi-channel volt meter to check a pack. More often than not, this is going to be far more accurate than a $5 cell checker. Go figure

But many tend to believe the cheap checkers over their high end chargers.
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Old May 06, 2013, 03:39 PM
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Monitor mode can also be used to graph indivual cells while the battery is being discharged using an external load such as aircraft's power system or often in my case a CBA II with addational CC electronic load devices,

The PowerLabs have better internal discharge capabilities than many chargers and using them in Regen.Dsc. mode are capable of up to 40A however the load is not instantaneous and even 40A is not that much of a load on many LiPolys.

Charles
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Old May 10, 2013, 01:23 PM
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I believe the high end charger much more easily than the cheap checker, though typically the difference between their displayed values is on the order of 0.02 volts. This little bugger isn't incredibly precise but it's fast and convenient and goes to the field with me a lot.

Replaced the fuse last night, having the larger Weller soldering gun was a big help in getting the old fuse and most of the old solder out. Had to scrape the last little bits out of the inside of the fuse blade slot with an exacto to make enough clearance for the new fuse.

Not really sure what to look for or test or check on the MPA, it's a fairly closed piece.

Will do a 1C solo charge on that channel this weekend, monitored on the laptop, see how it behaves.

I like the ability to do regenrative discharge at higher amperages but I don't have a battery that I would want to use as a mah dump to regenerate to. SLA batteries can provide field charging but the genset is much more convenient and utilitarian for me.

Charles unsurprisingly you have a far more advanced toolbox than I do though I am slowly getting better.
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Old May 10, 2013, 09:07 PM
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I'd start with an ohm meter across the connectors where the fuse was blown.
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