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Initial request for info on LiPo batteries in F!A was on SEN. I post my answer here. JIM
I have been transitioning from NiHi to LiPoly. Here’s some info.
Batteries all 7.4 volts nominal– note, at full charge they are typically near 8.4 volts. Range from $16 to $20 :
– home build pack from 4, E-Tec , 210mah resulting in 420 mah
– M&K use the ETec 7.4V300 HP, currently out of stock
http://www.allerc.com/product_info.php?cPath=3_4_69&products_id=1790
– PQ-300XP-2S close equivalent to the above:
http://www.robotcombat.com/marketplace_lipoly-pq.html
– Shorter thicker pack, fits when in the fuselage nose, True RC 350 mah.
http://home.comcast.net/~truerc/ready_pack/ready_packs.htm unfortunately on back order for several monthsI’ve used 2 regulators, these are from RC companies- goggle search will find them. I replace the wire with smaller wire- we don’t put near the amp draw as the RC guys do:
FMA Direct, VRLi1-LPO Sport– I replaced the 3 LEDs with smaller ones. Nice feature is the LEDs provide battery condition- Green- Yellow- Red. Out puts 5v
I’m currently using Novak #5460, has an “on” LED. bit smaller. I like it that it outs puts 6v. Servoes run better– Ken Bauer and Roger Morrel disagree with me on this, but I get little to no servo buzz when ussing 6v. The buzz happens when there is a load on the servo and the it can not get to the position the electrons is telling it to be at.
What I have not found yet is a regulator with a built in low voltage cut off. Very interested if one exsists!
I’ve ruined 2 packs by letting them run below 3 volts. One of these cell I thought I had saved by doing several short charges and letting it sit a day before doing the full charge. All seemed well. Two weeks later I went to the battery bag and noticed that one of the cells had “puff- fish”. Lucky it was not in a model and luckier it did not leak or even more flash burn. It seems it is difficult to get LiPo to torch off but when they do they are very dangerous. I saw a film of a guy who set up a test to torch one off, commands respect. I’m being even more careful. I’m dealing with relatively small stuff- can not imagine what happen if you make a mistake with a 2500 mah pack.
While on the subject of depleted batteries, I will mention everyone should check the current drain on older Black Magic timers. There are some very small resistors on this timer and if not properly soldered, the timer does not shut down after DT, in fact the current drain goes up, as much as 85 mah! So a 300 mah battery is good for only 3 1/2 hrs in the post DT condition. If you’ve been flying the model all day, the power drain is higher, Now combine this with running my transmitter and RDT off the same LiPo battery. The model lands in plowed field, I have a strong transmitter signal. I go back to the flight line. When I return, no signal, I’m sure the model was stolen by field workers. Fortunately, Peter Allnut insisted we take another try the next morning using his new Kenwood radio, Still no signal. More fortune– Dale Elders come out. We discuss the terrain and what he saw in the binoculars and says “is that red tip yours?”, 100 m away, there the model sat, with a dead 420 mah battery. Hence forth the discovery of the high current draw timer.
Thermals, JIM
So the moral of the story is stick to NiMH batteries until somebody has a good package that works without having to do this and that.
True, NiHi are a tried and true system but do note that NiHi also can be ruined by deep discharge. For us glider guys that use the batteries as nose weight, the trade is far less conviencing. For other weight concerned events, the LiPo are winning out.
For those going to 4 servos, RDT, the power density / weight ratio needed to fly all day are leading us to LiPo. The other advantage is LiPo store better– they do not lose charge. NiHi can lose up to 20% charge overnite– not a big deal but charging during the day is a good idea.
I’m hoping someone has already developed the regulator with low power cut off. If not, it won’t be long.
The main lesson is to check you Black Magic timer for current draw.
Lee Hines would say the lesson is I should use a separate battery for my transmitter!
JIM
Hi Jim,
I have worked around the timer current drain problem by having DT noise ‘on’. This gives a much lower current consumption than when my timer ‘goes to sleep’ – at least it does on the timer that gave me the problem. I use a 5 cell 160mAh NiMh on single servo models.
Hey Lee, I already use a separate battery for my transmitter! – a lithium thionyl chloride cell (sp?). From memory it’s about a half AA package – 1000mAH capacity 3.7V. Lasts several years and will run the beacon for months when new. (I turn it off between sessions!)
There’s a discussion about regulating LiPos on the UK FlyQuiet Forum at http://www.flyquiet.co.uk/smf/index.php?topic=824.0 The forum has a small FF section but is mainly an RC soaring site. F3K has the most traffic. I hang out there a lot since I got the discus launch RC bug.
There’s talk there of a device called LiPoPal that’s out of production now – original supplier at :- http://www.dlg-supplies.co.uk/ then go to – catalogue – LiPoPal. No longer produced but you can see what’s possible. It has an audio buzzer for a warning – an adaptation for your requirements must be possible……..
regards
Mike Fantham
F1A, F3KLooks like there is a lot of use for a regulator come warning system for 2-cell Li-Polys. Perhaps someone can spec something out and we can get a number made up ?
I think Jim Parker meant NiCad here:
“For those going to 4 servos, RDT, the power density / weight ratio needed to fly all day are leading us to LiPo. The other advantage is LiPo store better– they do not lose charge. NiHi can lose up to 20% charge overnite– not a big deal but charging during the day is a good idea. “
NiMH usually keep their charge up.
I have thrown several LiPo out of models now because they were a pain to charge, and not worth the worry. But I agree where you need the light weight, then you need to put some effort into making them work.
The models that I took them out of were supplied that way, and came with a cheap charger.
Dave,
No, Jim was right. Ni-MHs are renowned for loosing charge and their fragility. I have also had many Ni-MH cells quit over the years hence the thoughts on going to Li-Ploy. Li-Polys have many advantages but, as you say, you have to be careful with the charging. The technology is mature, other than the odd laptop, mobile phone et al doen’t tend to burst into flames.
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