ORIGINAL: chewytm But nothing for 2S A123 batts at 6.6V? I think A123 batts are quite common nowadays as they don't require regulators with most 6V capable servos. Will anything be done about that? chewy
28Dec09
Unfortunately there are too many different types of cells referred to as A123 with different voltages and cut offs which is why it is hard to find good chargers and few if any on board voltage displays.
I believe the engineers are trying to work on an answer but it could be a while.
Just two examples of cut off / loaded voltage measurement problems,regarding A123,availableon the net:
A123 Battery FAQ for Giant Scale and IMAC
"Here’s the biggest issue.. load testing. The beasties just don’t react like we expect.. a 1 amp load for 10 seconds will convince somebody not familiar with them that there’s something wrong with the load tester.. the needle won’t sag! I’ve even had guys start melting switch ports and connector housings trying to get enough load on the pack to use an ESV in the tried and true sense. Just doesn’t work. Because of the incredibly flat discharge curve and the ability of the cell to hold voltage while doing 'heavy lifting', using a standing voltage level under load to decide when to recharge can lead to a disaster
because when the cells go flat they do so remarkably fast. So, we go to the next question.."
A123 battery Information - SinCity Jets.
"The
battery's only downside is that you can not tell how much energy is left in the pack by reading the voltage. Because the discharge curve of the pack is so flat, the voltage will be almost the same throught its cycle, and then "cliff dive" at the end of its cycle. Because of this, it is important to become familiar with how much energy your vehicle uses during each use. For planes, I advise people to fully charge their batteries and then fly 2-3 flights. Then, fully charge the packs again and see how much energy (Mah) you put back in to the packs. Then simply divide the amount of energy by the number of flights and come up with your average Mah per flight. This will allow you to set your safe cut-off. It is advisable to only use 1800-2000 of the pack's 2300 Mah's. "
Update 18 Aug 2010:
Following recent upgrade ofAurorato V1.07 and Spectra pro Module to V2.0, user is now able to set voltage alert levels.
(View Version 1.07 Manual Addendum) - page 5 refers
Current related discussion elsewhere
regarding Eneloop cells.and benefit of battery voltage telemetry.
"Quote: Originally Posted by MikeMayberry - but take this situation for example: a guy was flying with a 5 cell 2000mah Eneloop RX pack that cycled easily to 2000 mah with a 1A load and worked fine in a sport application for over a year, but when that same pack was used in a larger application with multiple digital servos it fell flat on it's face and the low voltage warning would kick it under normal maneuvers.Of course if he had made a proper battery selection in the first place then everything else is moot.
The Eneloop cells are fine in transmitters and low load airborne use. But their high internal impedance makes them unsuitable for any kind of potentially high load use. Under load these cells have a large voltage depression due to the high internal impedance.
You do not need telemetry to tell you that - Silent-AV8R -unquote"
Response - Mike Mayberry
" Agreed that these batteries were the wrong tool for the job, but in this case the user was unaware that they were not suitable and luckily landed when the low battery warning went off, most likely saving the airplane. A loaded volt meter even at 2A (equivalent of one digital servo) would not have made a difference here as the load would not have been high enough to sag the voltage. Flight loads vary with the servos in use, but if you consider that a high power digital servo working hard can easily pull 2A each (or more) then the only accurate way to see how the battery handle the actual flight conditions is with telemetry.
Yes, most of you know what you're doing but so many R/Cers out there have no idea about how the flight loads can affect the battery voltage; this goes for BEC's used in Electronic Speed Controls which which with the higher voltage threshold of 2.4 is the culprit for so many brownout crashes. What percentage of pilots use a loaded volt meter every time they fly? Not many. How many with telemetry check their battery every time they fly? 100%
Sorry, I know this thread, as many others do, has morphed into a battery discussion but to say that telemetry is no replacement for a good voltmeter which most don't use, or that you don't need it to tell you that your batteries can't handle the loads because you should have already know this is not realistic. It may be easy for some of you to justify that you don't need it, but it opened up a whole new understanding for me as to actually what's going on with batteries and BEC's in flight that I never really knew, and I consider myself and expert too! It's not a novilty... it's a tool, and I would think that all radio manufacturers will have to encorporate it into their systems sooner or later just like 2.4ghz. . Mike. "
Aurora A9, Spectra Pro & Optima - FAQ & Undocumented Features
Update 30Dec10:
| Originally Posted by martyfly147 hi guys ,i want to use 2x Life/a123 batteries in parallel with no regulators plugged straight into optma rx's via the servo bus not spc ,will this be ok and what voltage would you set the alarm to considering the flat discharge curve of these batteries |
Usual specs of genuine 2S RX packs show
" Nominal pack voltage: 6.6V (3.3V per cell)
Fully-charged pack voltage: 7.2V (3.6V per cell)
Recommended cut-off voltage: 5V (2.5V per cell)
Minimum voltage: 4.0V (2.0V per cell)
Do not charge above 7.2V."
Drop off is extremely rapid,
ESC/BEC are now being supplied with min setting of 3.0v per cell for A123.
Users of A123 for RX packs suggest Low Battery Warning of at least 6.0v to allow time for landing.
Care with brand of LiFe pack, recommended reading:
Battery (Receiver packs) . LiFePO (aka A123 & LiFe) - Alert re False Labels & excess voltage
Battery (Receiver packs) . LiFePO (aka A123 & LiFe) - full thread
A123 Battery (aka LiFe PO4 cells) FAQ for Giant Scale and IMAC
A123 (LiFePO4) Cells for Receiver Packs - Very good graphs of the various battery chemistry type and relative discharge curves.
HYPERION G3 LiFePO4 Batteries for Radio Transmitters and Receivers - Warning
"SERVOS - Many servos on the market, and particularly many of the lower-cost analog types, cannot operate at the voltage supplied by these LiFe Receiver packs. Attempting to use a servo rated for maximum of 6V or less WILL RESULT in reduced servo life, and may lead to in-flight failure. Any such failure is the sole responsibility of the user."
"If you have any concerns about the voltage rating of your servos, you may choose to run a BEC unit, such as the 5V/6V selectable Hyperion SBEC (HP-TICOOL-BEC), in order to regulate voltage down to suit your servos. This offers greater safety compared to BEC units running off the main flight pack because even if your main flight pack is completely depleted in flight the radio and servos will maintain power via the Rx pack."
-
Aurora A9, Spectra Pro & Optima - FAQ & Undocumented Features -
extracts
.Loose Cell Battery Box & Switch harness - Included with Aurora & Optima set to aid Linking and Set Up only for those with EP Models in lieu of using ESC/BEC. Not intended for use in flight."
The battery holder is not mentioned in manual because it was a much later addition to aid EP flyers using unswitched BEC and others to simply link their Optima before installation.
. Aurora & Spectra 2.4Ghz module - Low Battery Warning
.Aurora A9 - Warning Alarms Battery types, voltage levels and consumption.
extract - "RX: Optima series receivers:
Operating Voltage: 4.8~7.4V From a receiver battery, or a speed controllers (ESC) power.
(7.4v is nominal = 8.4 max with fully charged 2S lipo battery)
4.8~35V Using SPC function (35V is the Maximum, do not exceed)
(Aurora A9 RX Voltage on Screen SPC voltage has preference over BEC voltage if using tap.)
Current Drain : 190mA (with sensors)
Optima RX - Installation RX, BODA Antenna, Volts & Range Test.. Quote:
"Notes 1. a. Reset voltage is 3.5v. The cause of many problems with 2.4 systems is when people use low power 4 cell packs with high torque servos and they brown out. Optima cut off voltage is 3.5v, so we suggest a 5 cell+ pack for the servos. Or... use the SPC to power the RX for additional safety. A small 2S lipo to SPC would guarantee the RX voltage would never sag. "
Hitec Transmitters:
Caution: Do Not Use A123 (LiFE) in Hitec Transmitters using a 6 cell NiCD/NiMH pack
.........e.g. Aurora 9 and Optic 6 Sport. Not only is the size to large for the pocket, the nominal voltage is already at the Low battery Warning level.
Hitec Transmitters using 8 cell NiCD/ 8 cell NiMH packs: e.g. Eclipse and Optic 6
A 3 cell A123 isreally to low and a 4 cell A123 (LiFe) is too high.
(A 3 Cell lipo is not ok without a regulator set aprox 10.5-11.0V)
Alan T.
Alan's Hobby, Model & RC FAQ Web Links
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