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Li-ion Rx packs? - 1/6/2013 8:48 PM   
Bill Clark


 

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Status: offline 		I rarely get to go out and spend the whole day  flying. Its usually a quick flight here and there, after work, etc. sometimes it can be a week or more before I get the pattern plane out. problem is having to discharge my rx and backup packs (lipo) to storage then recharging when I decide to fly. was thinking it would be nice to have packs I could leave charged for long periods of time without concern. my rx is a 730ma and my backup (tech aero) is a 250, both 2cell. anyone know whats available/reliable in the size ranges I mentioned in Li-ion ? I could tolerate more weight and/or capacity.I guess my other option is to just get bigger lipos and run them at storage charge but would like to explore my options not to mention I would feel a tad better about leaving Li-ions in the plane as opposed to the lipos

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RE: Li-ion Rx packs? - 1/6/2013 11:30 PM   
bjr_93tz


 

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Status: offline 		What scares me about lithium ion in airplanes is my experience with camcorders and my 14MZ.

When the packs have aged a bit, you can pull them off the charger and pop them in the device and depending on the temperature have very little useable power. I've pulled a 14mz battery from the charger and popped it into the radio and had less than 30% showing and dropping fast. Put the battery in the sun for a while and it's back up to showing 70-80%.

Personally I won't use lithium ion in an airframe until I have pack voltage telemetry with a warning, they just seem too iffy with temperature. YMMV

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RE: Li-ion Rx packs? - 1/7/2013 12:05 AM   
Bill Clark


 

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Status: offline 		valid point of concern based on the 14mz packs. I have experieced this too. Since I do load check and check voltage before every flight that should show a problem with a li-ion?

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RE: Li-ion Rx packs? - 1/7/2013 2:28 AM   
cmoulder


 

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quote:

ORIGINAL: Bill Clark

valid point of concern based on the 14mz packs. I have experieced this too. Since I do load check and check voltage before every flight that should show a problem with a li-ion?


Yes, I've had this happen a couple of times. Voltage looks fine until it gets a .5 amp or 1 amp load, then drops 3 or 4 volts. Saved a couple of models using redundant Rx power and testing voltage under load. In fact, it is probably a good idea to load test ANY Rx battery no matter the chemistry. I've had the exact same thing happen with NiCd, NiMH and LiPo. However, I don't check it before every flight, but before the first flight and then after perhaps 4 flights if I am putting up 5 or 6 or more flights during the day.

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RE: Li-ion Rx packs? - 1/7/2013 2:44 AM   
bjr_93tz


 

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Status: offline 		Yeah, load check is probably a good habit to get into, I'll be the first to admit I'm a bit too lazy that way.

With the RX Li-po's I just run the last two flights and put the plane away which leaves the pack about 50%, There's plenty left for another flight a week later but a quick 20min on the charger and I know it's good for at least one flight as long as it's showing over 8V (2s lipo) on the charger. Very rarely do I let it fully charge as I'm happy to pull the pin anywhere over 8v if a bit of free airspace comes up..

With the li-po I do a quick double check on the voltage the pack is at when it's plugged into the charger and how high it's at when it reaches full charge current (ramps up over about 20sec). If the voltage seems to climb too high too quickly then the IR of the pack is going down hill.

There's probbaly a lot of better practices than what I employ, but with a 1300mAh RX pack I've got plenty of overhead. I was a lot more fussy when I ran the 450mAh pack for a while

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RE: Li-ion Rx packs? - 1/7/2013 5:27 AM   
gaRCfield



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Status: online 		Why Li-ion and not lipo? Are Li-ion still safer? There are also the LiFe packs - people were using them at Nats and I bought one to try. Supposedly they are 'safer'. I don't use it mostly because I'm too lazy to keep track of charging another battery type.

I used a 2500mah li-ion from Central Hobbies when I ran glow. That pack worked well, but as others have mentioned it seemed fine when in fact it was dropping voltage significantly under load. I'm glad I found it when I did.

I have lots and lots of flights on my (2) 450mah Rhino Lipo packs.

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RE: Li-ion Rx packs? - 1/7/2013 1:07 PM   
nonstoprc



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quote:

ORIGINAL: Bill Clark

I rarely get to go out and spend the whole day  flying. Its usually a quick flight here and there, after work, etc. sometimes it can be a week or more before I get the pattern plane out. problem is having to discharge my rx and backup packs (lipo) to storage then recharging when I decide to fly. was thinking it would be nice to have packs I could leave charged for long periods of time without concern. my rx is a 730ma and my backup (tech aero) is a 250, both 2cell. anyone know whats available/reliable in the size ranges I mentioned in Li-ion ? I could tolerate more weight and/or capacity.I guess my other option is to just get bigger lipos and run them at storage charge but would like to explore my options not to mention I would feel a tad better about leaving Li-ions in the plane as opposed to the lipos


Seems to me to use two small lipo packs such as 250mah would be the answer.

For me, I use several V2 super-light 250mah TP lipo packs as RX power source, and fully change them before the field trip. I replace the RX lipo with a fully charged one every 3 flights. The swapped out lipo will have about 50% charge left (40mah per flight, 40x3 = 120mah).

If I ran the tech aero hot standby setup, I could swap the two 250mah after the 3rd flight and swap them out after 6 flights. Each would be at 50% capacity. For next 6 flights, either charge them or use another fresh changed pair.









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RE: Li-ion Rx packs? - 1/7/2013 2:25 PM   
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Status: offline 		Well I wouldn't use Li-Ions since the discharge capability as well as the charge rate are quite restricted compared to other chemistries.

Most of the serious pattern guys around here use the small LiPo's which charge reasonably quick and don't weigh a whole lot even with their regulators.

I don't like Li-Po's so the only place I use them is for electric powered models where there really isn't a suitable replacement. All my other models use A123/LiFe batteries for the rx's and the electric powered stuff which needs a separate rx battery get an 1100 mah A123. It weighs three ounces but there's no need to worry about storing it charged, will charge in ten minutes or so, won't start fires and doesn't need a regulator.

If you go for an LiFe, make sure it's from a reputable vendor and has good discharge capabilities. Lots of issues with QA on these batteries and generally speaking the higher "C" rated batteries are better quality cells. Genuine A123's can put out 30C continous and burst to 60C, the LiFe's can be anywhere from 3C up to about 10C rated.

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RE: Li-ion Rx packs? - 1/7/2013 7:28 PM   
cmoulder


 

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Status: online 		Alternatively, you can run a VHV BEC from Dimension Engineering as your primary and have a small LiPo on a Tech-Aero reg as back-up, with the voltage set about .25 or .5 lower than the primary. I have more than 200 flights on just such a set-up with no issues at all. Theoretically the LiPo should never need recharging, but I find I need to "top it off" after about 10-12 flights just to be sure, and to check voltage under load, per above. After all, the back-up needs to be just as reliable as the primary. In fact, on one of the first few flights with my new Caelestia last year, it was discovered shortly after a deadstick landing mid-way through a contest flight that the APP arming plug was defective and the back-up did indeed save the day.

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RE: Li-ion Rx packs? - 1/7/2013 11:08 PM   
Bill Clark


 

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Status: offline 		thanks for the feedback guys
Bob, I think you came up with the solution. I have a proven reliable castle BEC pro not in use. I think I will use that for my main power then move the 730ma over to the hot standby side and leave it 50% charged. problem solved. thanks

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RE: Li-ion Rx packs? - 1/8/2013 10:42 AM   
Magne


 

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Status: offline 		I think that although storing Li-pos at 3.8V MAY increase their life, they are not going to die in a hurry even if they are stored fully charged.
I just charge them up fully after each flying session, and they are ready for next time, whether this is tomorrow, next week or whenever.
This method has worked fine for me for 8 years now.
But I replace the Rx-batteries after two years just to be sure. Measurements after two years use/storage has shown insignificant degradation of Rx-batteries.
(Main flight batteries is a different matter, these normally show degradation after one season use.)
Replacing your Rx-batteries every two or three years may be a good thing to do anyway, no matter how they have been stored.

Just my opinion, of course.

Magne

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RE: Li-ion Rx packs? - 1/8/2013 1:37 PM   
cmoulder


 

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Status: online 		Bill, that is a bit heavier set-up but will work fine. If you take it to the Nats and find the need to shave a few grams, it is easy enough (if not exactly cheap!) to change to lighter components.

The CC BEC amperage rating of 20 amps is waaaaay more than needed, but it should last for all eternity with no issues.


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RE: Li-ion Rx packs? - 1/8/2013 2:50 PM   
nonstoprc



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Status: offline 		I find Thunder Power G6 Pro Lite 25C Series lipos are very reliable and light. I exclusively use them for RXs.

For backup ones, you could put two 125mah cells (TP125-1SPL25UM) into a 7.4v pack for a total weight of mere 10grams.

I like the idea of replacing RX packs every 2-3 years, depending on the # of cycles. It may also be a good idea to replace the switch.

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RE: Li-ion Rx packs? - 1/8/2013 3:45 PM   
MTK



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Status: online 		Interstingly enough I will be starting my 4th season this Spring on both a 2 cell LiPo (1780 ma, Radical RC) and a 2 cell Liion (2200 ma, Troy Bilt) on the same plane. I power both the radio and CDI with these sources (I alternate between them). Each gives me 75 minutes of flying per session discharging to very nearly identical voltages and each has seen about 75 cycles in the past 3 years. Neither is showing much in terms of power loss. As Magne stated, I too have not been particularly careful with their care and feeding; except I am fairly religious about voltage checks between flights, and things continue to track very similarly and reliably....Until I see a difference in discharge curves, why change?

That's the practice that works well for me....As always, YMMV.


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RE: Li-ion Rx packs? - 1/8/2013 9:38 PM   
arnstein


 

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Status: offline 		I built my own Li-Ion packs using 18650 type cells (laptop). Use a single battery pack to power both radio and CDI unit, the 2600 mah gives me 80 minutes of flying (5 x 16 min) with a good margin. And the battery pack is only 100 grams. However, I have no experience with lower capacity Li-Ion cells. But as long as the discharge rate is within spec. you are probably fine. The reason for not using Li-Po’s is vibration.Arnstein

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RE: Li-ion Rx packs? - 1/9/2013 1:59 AM   
Rendegade



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Status: offline 		I prefer the A123 or Li-P04 for rx batteries in general flight.

The voltage is different, and the construction is also different. They're great.

I love them, and have all but given up on NI-XX chemistry for rx packs. A123 all the way!

For F3A however, I haven't found a lighter redundant setup than a 2 port powerbox regulated switch, and a small lipo, and tap from the main battery pack.

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RE: Li-ion Rx packs? - 1/9/2013 4:01 AM   
Bill Clark


 

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quote:

ORIGINAL: cmoulder

Bill, that is a bit heavier set-up but will work fine. If you take it to the Nats and find the need to shave a few grams, it is easy enough (if not exactly cheap!) to change to lighter components.

The CC BEC amperage rating of 20 amps is waaaaay more than needed, but it should last for all eternity with no issues.



I'm not at the level you guys are at so i probably wont have to worry about the Nats. besides this particular plane is a 110 size electric that is already on the light side so no weight issue. I am installing a momentary micro switch one the backup in addition to the BEC so I can do a control check on the lipo/hot standby then power up the the motor battery/bec then push the switch to check the bec. in addition to the voltage check on both sides this lets me check the techaero system quickly which all helps achieve the main goal......getting the plane unloaded and in the air asap with with minimal foreplay

Ren,I like the a123's too. use them in my 35%'er unregulated.

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RE: Li-ion Rx packs? - 1/9/2013 11:55 AM   
cmoulder


 

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Status: online 		Sounds good. Just make sure to have a helper with a firm grip on the model the first time you power up and go through your checks to make sure Tx and ESC failsafes are set properly!

With mine, I simply alternate the sequence of connecting the arming plug or turning on the reg switch.

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RE: Li-ion Rx packs? - 1/10/2013 12:46 PM   
Bill Clark


 

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