100% scale, Electric Lazair - Page 7 - RC Groups
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May 11, 2011, 04:03 AM
Registered User
The FMA PowerLab8 is an 8S charger rated up to 1344W/40A output.

When you connect packs in parallel the charger simply sees it as a single pack with larger capacity cells. Hence an 8S1P 2000mAh connected in parallel to another identical pack forms an 8S2P 4000mAh pack. The charger has no trouble charging and balancing that pack.

This is a good place to go to learn about parallel charging lithium packs: https://www.rcgroups.com/forums/showthread.php?t=932319

As I understand it, in this project the battery is formed from 4S 5000mAh packs. These are connected in series to form 8S 5Ah packs. Those are connected in parallel to form 8S4P 20Ah packs. Those are connected in series to form a 16S4P 20Ah pack for flight or in parallel to form an 8S8P 40Ah pack for charging.

The PL8 can charge an 8S pack at 40A, so yes, it can charge an 8S8P 40Ah pack at 1C and as a result, each of the individual 4S 5Ah packs will indeed be charged at 1C.
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May 11, 2011, 08:51 AM
Dale Kramer
KiloOne's Avatar
Thanks kgfly and well said.

Re: Balancing leads
All balance wire schemes have wires that connect to series connected cells (ie - +- +- +- + where - + is a cell) as follows: The lowest potential wire will connect to the - on the far left, the highest potential wire to to + on the far right and there will be wires of increasing potential connected to each of the +- cell nodes from the left to the right. The large power output leads will also be connected to the far left - and the far right +.

The difference between various brands and their balance schemes will be the physical type of balance connector used and in which pins these balance wires are connected to. However, no matter which brand and connector, all it takes to figure out the scheme is a simple probing with a DVM looking for the lowest potential wire and then the wires of increasing potential.

Re: Charger connection
Each charger is totally independent of the others. The final fully charged voltage of each 64 cell battery pack will be the same for each charger as long as the same charging parameters (presets) are used on each charger. For each motor, this allows me to combine each of the three 64 cell 16s4p battery packs in parallel (without much connection current cross feed) to end up with one large 16s12p 60ah pack that connects to the motors' speed controller. As the number of cycles on a pack goes up and the likelihood of a cell failure rises, I will be able to isolate the bad cell to a particular group of 8 cells that get parallel charged together based on the fact that I am controlling each charger from its USB cable and logging each charge that I do. Thus a I will be able to look at the graphs and see the voltage degradation of a group of 8 cells. Once a problem is seen I can quickly unplug those 8 cells from the PCB and quickly isolate and replace the weak cell/4s pack. I do not expect this to happen very often, if ever, in the 300 or so cycles I expect to get out of my packs before they are down to 75% or so of their original capacity.

Re: Capacitors
Yes I have 6 pcs of 75v 470uf low ESR caps on each PCB. These hopefully take care of the inductance of all the wire/traces in the battery pack and the length of wire I will have between the batteries and the controller. Have a look at this thread for some more info: https://www.rcgroups.com/forums/show...ending+battery . I have had to add some connectors and pushbuttons to each PCB to take care of spark suppression when connecting the final output connector, series jumper and charging harness due to these capacitors. These pushbuttons and resistor jumpers will force the voltage of the caps to either 0v, 30v or 60v just prior to the connection I am about to make, thereby reducing the connection spark to a minimum.

Good questions.
May 11, 2011, 01:26 PM
Registered User
Thanks guys, that's given me plenty more homework and research areas to get familiar with. I expect I'll be back later in my development and learning process with more questions if you don't mind. I'll be following your progress in the meantime. Is there a website?

May 11, 2011, 08:00 PM
Registered User
This website provides an excellent tool to visualise how cells and packs are connected in various series/parallel configurations: http://scriptasylum.com/rc_speed/lipo.html
May 25, 2011, 07:26 AM
Dale Kramer
KiloOne's Avatar

Quick Update

Been working hard on the project.

Expect to have first flight this weekend if all goes well.

Here are a few pics.

May 25, 2011, 08:35 AM
Registered User
Great project.
Just a note - the PL8 chargers can be "networked" as far as i know, so you can connect them together and charge directly as 16S.
It should be in the manual (i do not own PL8, but i know that).
May 25, 2011, 07:08 PM
Registered User
That looks great Dale. How much has this motor change affected the CG? the rotax 185 must weight alot more than this electric motor.
May 26, 2011, 12:01 AM
Dale Kramer
KiloOne's Avatar

If I charged at 16s with 2 PL8's I think I would have to buy 6 more chargers to charge the 6 packs I have, but then again they would charge twice as fast and I would need four 6800 watt generators to charge them instead of two.


The CG will change very little. Remember the 35 lbs of fuel and tank etc is no longer behind the pilot. This makes up for the reduction in motor weight and I have placed the batteries very close to the CG.

I just finished the first engine nacelle and the second is ready to assemble, here are some pics:
May 26, 2011, 03:28 AM
Registered User
I may be out of line here but the only inherent problem I have run across with charging with parallel balance connectors is that there is no way for the charger to recognize a broken or disconnected balance lead on any one or more of the packs.I puffed a cell on a pack that had a broken lead at the cell.
This happened to me with relatively small(3S 2200mah) packs while I was charging 4 of them in parallel.Seems to me that it could be a much larger potential liability if this happened using much larger collections of packs.
I considered it may be possible to build a parallel balance conector that could recognize one or more cells missed from the equation due to a broken lead or bad connection and terminate the charge process.All of the chargers I know of dont care if a cell is missing as long as the value for the specific cell set is within the correct value range.It has no way of knowing if all of the cells are actually connected in the set.
Just a thought.
May 26, 2011, 10:52 AM
Registered User
Since the packs are semi-permanently mounted and the balance leads are not being constantly handled and plugged in/out, I think the risk of a broken balance wire is vastly reduced compared to normal RC usage. If the connections all check out before and after assembly then they should be reliable IMO.
May 26, 2011, 12:58 PM
Registered User
Those motors look great. You should see if Hobbyking will sponsor you to cover some of the costs.
May 26, 2011, 09:13 PM
Dale Kramer
KiloOne's Avatar

Having 96 4s packs on board I can not think of a way to charge them economically without parallel charging. In addition to kgfly's comments, the individual 4s packs balance connector will never be touched during a normal charge cycle. I think I am doing pretty good using 6 PL8's to their maximum and have only 8 cells in parallel. I will be logging all my charge and discharges and should be able to isolate cell problems down to 8 cell resolution and when I suspect a problem I can simple unplug all those 8 cells to quickly identify the culprit.


Sponsors come with their own set of drawbacks and I just want to be free to do this without worrying about sponsor commitments. It would be nice though if HK would sell the motor with my winding configuration. I am not sure I want to rewind any more of these.

Today's pic:
Last edited by KiloOne; May 30, 2011 at 07:53 AM.
May 26, 2011, 09:31 PM
Nelapaty's Avatar

Just out of curiosity Have you given any thought about static electricity with everything being electric power?
How are you protecting the packs and electronics from static

Are you using static wicks on your aircraft..
May 31, 2011, 11:16 AM
Registered User
Awesome project Dale! Did you get a chance to Maiden?

Have you ever seen Staib's "Airy-Plane"? I could not find much info on it. I think it was circa 1967.

Humble admirer
May 31, 2011, 11:23 AM
Real Time Recon
realtimerecon's Avatar
WOW Dale, am I glad i found this thread.Best of luck to you.Will be keeping an eye on this

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