Hello guys.
Following a very interesting discussion on this thread, I am opening a discussion on that matter.
http://www.rcuniverse.com/forum/m_10..._2/key_/tm.htm

Jack Diaz has come with a very interesting point about possible causes for a lockout condition:

Thank you for sharing this very pertinent analysis Jack.

I am personally a big fan of parallel A123 2S1p batteries setup. I have used 2 Black and Decker Vx pack ( 1100 mAh ) directly plugged into a micro12 Weatronic receiver for now 5 years ( was a JR receiver before the Weatronic came out ) and have accumulated 600 flights on 3 airframes with this setup with 100 % success.

I am a big fan of redundant A123 Rx packs also, and on the bigger jets i even add a Froemco D-CUP capacitor as added safety.

Oli, are you using twin 1100mAh A123's in big models ? whats a BnD VX pack ?

Hi , Thanks for sharing that info, I am just in the process of finishing another turbine jet. I always use A123 Batteries with Jr receivers and so far no problem I do not use switches in between so no need to accidentelly have one battery not on. Once it is on all systems are go, and one battery is capable of running the system.

Please tell me what you are doing differenty now.

Thanks
Paul
Montreal Canada

One of the most important point about battery source and that is completely overlooked by most of us is the internal resistance of the pack.

This parameter is what characterize the health of the battery and its current capacity. To make an analogy with cars, the capacity of the battery would by the tank capacity of the car, the internal resistance of the battery would be the power of the car's engine.

So sizing your electrical system only by choosing the battery capacity can be very dangerous.
You can find on the market 5000 mAh batteries that will completely collapse ( 5V drop under a constant load of 40A) under load, and at the same time 1100 mah batteries ( like the A123 ) that will keep a fairly constant voltage under a constant 40 A load ( 1 V drop max ).
On that matter, there is a huge spread of quality among Chinese products, even among the same line of batteries.

It is a very good practice to do an internal battery check on a regular basis while doing through a cycle charge. Checking the charge capacity is absolutely not a guaranty that your battery will be able to deliver the required current load without voltage drop. The only parameter that will help you here is the internal resistance of the pack.

On that matter I recommend the Graupner ultra Duo 50 + charger. It is able to display the charge and discharge internal resistance for each element of the pack and log it into its internal memory. So you can track the evolution of your battery health with the time.

As a good practice, I discard my packs from flight use when the internal resistance has doubled from the original value.

Hi Lior.
Here is the pack: B&D VPX A123 1100 mAh
http://www.amazon.com/Black-Decker-V...6136352&sr=8-2

I use this setup on the medium size Supephoenix that is equipped with 8 JR 3421 mini digital servos.

Here is the official A123 documentation:

Nominal capacity and voltage 1.1 Ah, 3.3 V
Recommended standard charge method 1.5A to 3.6V CCCV, 45 min
Recommended fast charge current 5A to 3.6V CCCV, 15 min
Maximum continuous discharge 30A
Cycle life at 5C discharge, 100% DOD Over 1,000 cycles
Recommended charge and cut-off V at 25°C 3.6V to 2V
Recommended charge and cut-off V below
0°C
4.2V to 0.5V
Operating temperature range -30°C to +60°C
Storage temperature range -50°C to +60°C
Core cell weight ~40 grams




As you can see, the discharge curve is fairly flat, like all A123 cells. The voltage drop per element at 20 A is maximum 0,2 V at 20 A and stays linear up to 40A: 0,4 V per element at 40A or less than 1V for a pack.

Here are some discharge internal resistance values that I logged for the different packs I've been using over the time:

Sanyo CP3600HR Nicad 3600 mAh cell: 5 to 7 mOhm/cell
A123 2200 mAh cell: 11 to 13 mOhm/cell
A123 1100 mAh cell: 15 to 17 mOhm/cell
Eneloop 2000 mAh AA cell: 50 to 60 mOhm/cell
Thunder Power 3200 mAh Lipo cell: 10 mOhm/cell

Here is a good link about internal resistance or impedance consideration for our hobby:

http://www.hangtimes.com/rcbattery_faq.html

Here is a link on how to evaluate the electrical loads expected in flight:

http://www.rcuniverse.com/forum/m_92...tm.htm#9272010

I just use the same setup and have been very happy with this for many years.

Hi Olivier,

I have been using the Black&Decker VPX battery too (but only in a VPX tool).
Seems like BnD is taking them out of the market, they are more and more difficult to buy. Apparantly the VPX tools haven't been a real commercial success.
Why not buying an R/C worthy pack like from http://www.rclipos.com/A123.htm ?
They have all thinkable combinations with the 1100 and 2300 cells.
Their product, quality, service and price is top notch, and shipping worlwide is free.
(Also SinCity Jets have such packs, but I don't think in 1100 MAh packs)
I would be scared to convert a VPX pack for R/C use... (the A123 cells are in my experience quite sensitive for DIY soldering)

PS. I am using some 30 pcs A123 packs at the moment, and use them in all kinds of applications (even where people would use a lead acid car battery). I find the 1100 series a bit "weak" under high amps, especially for an RX in a jet. If one of the two (redundant) packs fails, I have my doubts if the second pack (of 2S 1100 MAh) would be a solid safety net... Just my personal feeling (and the graphs will be against me)... As long as the redundant packs support each other, it will be fine...
I am using a single 2S 1100 pack in a Savex L-39 but that's about the maximum jet size I would dare to go with these...

Nicolas.

I use a very simple system for a brand new jet. After fully charging my battery pack , leave the system on while playing around with the control ontil the battery its dead then log the discharge time. Again recharging the battery and connecting a voltmeter to the receiver and exercise all control to see how must voltage lost under load (Making sure my voltage lost is above the receiver operating limits). Then after every flight checking my battery ontil i am comfortable. And I always used two receiver and two battery.

P.s

A very important point found by Jack, which has been raised a few times before in other threads, is that the minimum operating voltage of the Rx is sometimes now lower than that of the servos. Due to the brown-out problem of early Spektrums, people have become fixated on the Rx minimum voltage and keeping above that, but just above the Rx minimum could be below the servo's minimum and would explain some unexplained crashes where the model seems to have locked out and not gone into failsafe as if the battery had failed, yet those items which would shut down on loss of rx signal such as an ESC or ECU continue working which means the rx is working. Data on servos is not so easy to get as it is for Rx, for example Multiplex only has the instructions for one of its rarely used servos on its website and it states the operating voltage is 4V to 7V. The Multiplex M-link Rx minimum voltage is 3.5V, (whereas the previous PCM rx minimum was 4V) so in that instance if the voltage drops progressively the servo would stop working well before the Rx stopped working and we could see a bizzare loss of control where the servos freeze in last position but the ECU or ESC is still going, the telemetry is still working and reporting 100% link quality, yet all control seems to have been lost. Perhaps servo brown-out will become the new popular cause for a crash!

Oli, do you know of any other much cheaper, simpler device that can do the internal resistance check? I have a workshop full of chargers and won't spend another huge amount for the Graupner Duo!
H.

Hi Oli,

Great information, so when the internal resistance of a A123 pack reaches around 30mOhm/cell it should be discarded. ( would this be correct).

Thanks
Chatty.

Hi Harry,

I have the Schulze(next generation) which will show you the internal resistance of each cell. Bought it a few years ago for around 200+ euros. Fantastic Quality.

Chatty.

Olnico, sorry to veer off subject slightly, but in one of your other posts you mentioned setting up a new model then leaving it outside for i think aeound 30 minutes running "servo test" mode on your radio, thus cycling the servos back and forth.
How do you prevent the servos from overtravelling while in servo test mode ? i reckon that mode moves them +-100% travel.

You can use the ESR meter from Bob Parker:
http://www.flippers.com/catalog/index.php?cPath=3

It is sold as a kit.

Hi Lior.
Your servos should always be used at 100% of their travel to get the best precision and torque available to the flight control.
Use the flight control calc sheet, to obtain this:

http://www.geohei.lu/olin/data/model...20imperial.xls

Here is the method of setting the flight control geometry correctly:
http://www.rcuniverse.com/forum/m_92...tm.htm#9266994

Sry

Yes: 22 to 26 mOhm for 2200 mAh A123 and 30 to 34 mOhm for 1100 mAh A123.

I don't think this is correct information, I will check on the A123 systems site.

Mike

Hmm Interesting, if your cells are 2200Mah thay are not genuine A123 system cells, they only make them in 2300Mah and 1100Mah so your analysis and results are not on genuine A123 cells, you need to check this.

Mike

Hi Oli, good idea to dedicate a thread to this issue.

I am reposting here my comments on the previous thread:



"One of the lessons learned after Gerardo's L-39 crash, was the dramatic difference between Li-Po and Li-Ion regarding battery voltage versus remaining capacity.

The easiest way to illustrate this point is with the attached chart.

Basically, at the voltage where a Li-Ion still has about 50% of its capacity remaining, a Li-Po is almost totally drained.
This is mandatory to understand, specially if you use both types of batteries.
Checking battery voltage will be useless unless this is fully understood."

Jack

Thanks Oli for the new thread.

In the other thread I've been recommending the JR/Spektrum powersafe RXs. They have dual battery inputs with large gauge wire and heavy duty connectors to bring the power to the RX. They also have circuitry that works to draw down the two batteries evenly built into the RX and offers some isolation.

I highly recommend the A123 batteries in a parallel setup as well, and agree with the great source of information you listed at Hangtimes hobby/No BS batteries. That whole site is recommended reading. One thing about internal resistance and voltage drop that is important to remember...when using a parallel setup, (two batteries with two separate paths to the RX) the internal resisitance is effectively halved giving you even less voltage drop for the entire system. Another plus to parallel setups.

With the performance of A123/LiFe batteries, the voltage drop under load is very low. There's been some concern in using two 1100mah packs in parallel to give a total capacity of 2200mah. The worry is that if one battery or connection fails, the single 1100mah pack will not be up to the task. By all accounts and data, it will be up to the task, but will not give you multiple flights...so you'd better be doing proper preflight checks to assure that both packs are supplying power to the RX and you haven't had a battery,switch, or connector failure.

With the JR/Spektrum powersafe RXs, you have an indicator light for each battery system that lets you know that both are supplying power to the RX.

The other thing that I try to do is avoid regulators and that's another reason why I dont use Lipos/Lions and have gone to A123/LiFe packs. Regulators are just one more component that can fail and cause trouble. For the same reason I also avoid D cups and other similar items. There's also some small variances in the outputs of regulators, even of the same make and model, that can cause some peculiarities in a parallel system (two batts thru two regs into a powersafe rx). One regulator putting out slightly more voltage than the other battery/regulator combo will supply most of the current to the RX and the batteries will drain unevenly when used with a powersafe RX or other device that tries to balance the two batteries in a parallel setup.

So a parallel system using A123/LiFe batts with no regulators is a great setup. Using a JR/Spektrum powersafe RX with the included softswitch is my choice because it also uses heavy duty wiring and connectors for better current carrying capacity, and removes switches from the power path that increase resistance and are another failure point. It also evens out the drain on the two battery packs and provides some isolation between the pack.

As for capacity, I try for five flights between charges and roughly 40-50% capacity left in the batteries after those five flights. Typically, we are going to use somewhere between 150-400mah per flight depending on the size of the model, number and type of servos, flying speed, and flying style. Using my rule of thumb for capacity, if you only use 200mah per flight that would be 1000mah used for 5 flights. With a 50% reserve capacity left in the batteries we'd therefore want to be carrying at least 2000mah onboard....So two 1100mah packs would be fine. If we were using 400mah per flight, then we'd use 2000mah in five flights and would want 4000mah onboard to have enough reserve. That would suggest that two 2300mah packs would be the ticket.


KMac

Oli, thanks a lot for pulling this out from the other thread. I truly believe there are a lot of crashes around that are power related and not really understood since the receiver was still working.
Great discussion!!

I've never considered the A123 route, but for no particular reason, just haven't too much thought behind it. However, not using regulators sounds like a big plus.
My big learning from all this is: Use whatever battery you want, but understand how it works. Learn what the discharge curve is, and how much power you have left.
And the other learning is: Redundancy means two independent systems where each of them is capable of flying your plane in the worst conditions. In my case, my system was redundant on flight 1, but by fight 6, it wasn't.

Exactly my point. Brownout is gone (assuming you have up to date equipment). The big problem is not enough power to the servos. At 4 volts or so, the receiver works, no failsafes, the turbine keeps running, but your servos are completely dead.
What do we see as a pilot?: my plane stopped responding and slowly turned right until it crashed, must have been a lockout...

Hope we can start having some light on some unexplained crashes

Jack