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        popcorn anyone?

#1 Rob Honeycutt Oct 06, 2003 11:01 AM

popcorn anyone?
 
Well, these lipos are like making a deal w/ the devil..

First is the inital expense.. sure it can be justified if you try hard enough.. milliamp vs milliamp.. weight, etc.. Once you get past the thousands you can spend outfitting your fleet,

there is the charging.... 2-300$ charger, (pre-astro days)... after you invest in the charger, you have to watch the batteries charge? Who honestly does this? this rates as high as paint drying, right? I try to watch them close, especially after Gary Wright's funtana burned up last week.. but charging 5 packs in the shop all day? almost 10 hours of charging....

If you don't monitor the packs while they charge, you could burn your house down, etc.. The technology surely has not reached main stream consumer level.

Then there is the durability. Two packs popcorn puffed so far here.. into a chemical mess.. Who knows exactly how it happened.. but they sure have a unique smell. Luckily I read a thread not to pop them...


and then there is the perfomance..
Man is it awesome. lightweight, long flight times.lots and lots of power.. open mouth glow guys staring in amazement...... but at what cost?

#2 Jerry Brown Oct 06, 2003 12:52 PM

How did you puff your batteries? Charger setting wrong or they just puffed? i have several pacls with no problems yet but I'm curious and trying to be safe.

#3 LuckyArmpit Oct 06, 2003 12:56 PM

I haven't gone to lipos yet. I do use some qualcomm 830's but thats the extent of lithium for me. Its the cost. I can't justify blowing big cash for 3 and 4 cell lipo packs. When for the same amount, I can build 2 or 3 KAN packs and charge them on my current chargers.

Dave...

#4 kelvin Oct 06, 2003 01:15 PM

Rob, do you ever split your large packs up and use the individual packs in smaller planes? It sounds like you may have charged a couple of packs together that were unequally discharged.

I'm not sure I would feel safe charging an 8s or 9s pack in series in my house after reading Gary's unfortunate experience with his Funtana. I would be OK with it if I charged the packs individually on separate chargers but then the expense of having multiple chargers is overwhelming. I charge my 3s4p 7.8 but I only charge at 5amps, under the 1C max of 7.8amps. Packs are always cool.

These lipos are like drugs. You take your first drink of them and you want all your planes to have them. Then you end up spending more money on batteries than planes, motors, radio etc.

I've come to some peronnal conclusions about all this

1. I'd rather have fewer planes that use lipos then a whole bunch that run on older cells

2. I'm finding the 4 planes is all I can support; building, maintenance, flying, charging, repairing, storing, transporting.

3. 16 cell models are about the limit to my financial resources.

4. The only way you are getting my Lipos is prying them out of my cold dead fingers:)

There is obviously going to have to be safer cells/chargers developed if the lipo technology is to become mainstream in the RC industry.

Kelvin

#5 Rob Honeycutt Oct 06, 2003 01:40 PM

Kelvin,

your personal conclusions are close to mine as well.. I guess I just feel like there are lots of sacrifices that go along with this technology..... more than say.. having the newest cell phone out, for example... or latest computer...

I am only charging 3 in series max.. which is what my example of 10 hours of charge time means.. Unless I buy more power supplies and chargers...

Jerry,

I 'puffed' the packs in flight. Two times now.. Yesterday as I walked up to the plane, I heard them 'puff' inside the battery compartment... I opened it up to see them pressed all up against the fuselage.. I quickly pulled them out of the plane and tossed them on the ground to avoid the plane catching on fire.. Probably too many amps.... It's funny.. Thunder Power batteries website recommends only a 5C discharge rate... yet some folks even drop down to 3P in lieu of 4P... Probably discharging close to 10C!

#6 Haldor Oct 06, 2003 04:23 PM

I for one is leaving LiPo's. I have $400 invested.

One selfmade 2s3p etec1200 pack, still working - never crashed
Two 2s4p TP1950's used as one - crashed. Some cells are dead/swollen.

Now, the risk of crash damage is obvious - even conventional cells can take damage during a crash. But the swelling of this pack did not occur untill 6+weeks after impact. Hadnt been in use since the crash except some cycling on the charger to check them out after they impacted.

Up untill then I wasnt put off on LiPo.

Then Gary's Funtana goes up in flames for whatever reason while he was charging the pack inside the model. Model/pack and charger is toast. If it could happen to Gary, it can happen to anyone for no apparent reason. Now I'm put off :(

We as efliers have abused our cells from the beginning of eflight and the NiCd/NiHM's are fairly tolerant to this abuse and in a case of failure they usually just vent. Not so with LiPo's - they are very voltage sensitive. Overcharge these babies and fire is the most likely outcome. I will not risk my house/family in order to get 15min airtime instead of 5. To me the risk is not worth it.

Bottom line - I just dont trust LiPo's anymore. Maybe I'm just a sceptic ;)

#7 garymac Oct 07, 2003 11:52 AM

Rob,
Recently I had a similiar problem with one of the TP 3S4P 8200 packs. After the 3rd 5 min. flying session on the Lazy Tiger P51, I saw that the pack had a "sausaged" cell after I removed it from the plane. The motor is propped for 40 amps max. with a cruise of about 30 amps or less. Previously I had been conservative and flown two 5 min. flights with 30 min. cooling between flights and after charging it appeared I had only used about 4000 mah. Voltage was still way over 10 v after that 3rd flight. I measured all component temperatures after each flight and the battery pack was only 115 deg F (with a 92 deg F ambient). I sent the pack back to TP but have not heard anything in weeks.

Lately I have been thinking about going back to glow for my couple of prop planes and reserving this LiPo stuff for my EDF jets. They are still a great advantage in those applications. I get 2 x 5 min flights with my F-18.

Gary

#8 ken_keeler Oct 07, 2003 01:40 PM

"We as efliers have abused our cells from the beginning of eflight and the NiCd/NiHM's are fairly tolerant to this abuse and in a case of failure they usually just vent. Not so with LiPo's - they are very voltage sensitive. Overcharge these babies and fire is the most likely outcome. I will not risk my house/family in order to get 15min airtime instead of 5. To me the risk is not worth it.

Bottom line - I just dont trust LiPo's anymore. Maybe I'm just a sceptic "

And therein lies the issue. Lots of fires, some with very experienced modelers. I think this is beyond "filling your lawn mower with gas while having a cigarette hanging out of your mouth" as stated in another thread.

I also don't trust them. I'll wait.

IMHO, YMMV

Ken

#9 Ed Lyerly Oct 17, 2003 08:19 AM

Rob,
Very sorry to hear about your damaged Lipo pack ! Also VERY GLAD to hear you had no additional damage. I will continue to watch my packs VERY carefully. I was considering switching to "3P" configuration on one or two applications that I'm now running "4P" configurations on (saving weight and cost by 25%) .....I think I'll wait to see how the "3P's" hold up for the "early adopters" before I change anything.
Ed

#10 Rob Honeycutt Oct 17, 2003 08:34 AM

Thanks Ed,

I did not intend for the thread to be a Lipo Bashing topic, because they certainly have advanced the capabilities of electric flight....and I like them.. I just ponder how they can be a safe and predictable, as well as an affordable technology..:)


Rob

#11 RD Blakeslee Oct 17, 2003 08:36 AM

Here comes the broken record again. Sorry.

I have overdischarged my Kokam 3270s two different ways: Voltage taken down too low and power drain too high.

I puffed one while series charging, nearly a year ago. Since then, I have charged them individually or in parallel only, flying them in series, and never had another failure.

- RD

#12 Dereck Oct 17, 2003 08:47 AM

FWIW - I reckon that about six months after lipos are adopted by the electric tool industry, I'll toss all my round cells, buy an Astro charger (push button, turn knob, charge battery - about my "interest in charging" level ;) ) and outfit the fleet with 'flat pack' batteries.

In the meantime, paying out lipo prices, buying chargers that might well turn out to be all wrong, watching packs charge in a fireproof safe and wondering if I can drive home from the patch without a battery setting light to my car are just all too exciting to this sports flier.

Heck, right now, I have an 8lb Cub that does over 15 mins - on nimh - and have twenty minutes of flying for my 4*40 - just have to land a couple of times and swap between her three nicad/nimh packs. Make that 25 mins if I fly her one more time on an aged pack of 2000mA nicads I have kicking about somewhere!

Anyone got a low mileage 24 jug pack of 2600 nimh or similar they want rid of? Be glad to (reasonably :) ) help you towards your next lipo pack if you have. Want to bury them deep in the nose of something big, bad, fast and very labour/cost intensive !

I really admire folk who rush out and 'early adopt' ;) but in the meantime, I've re-upholstered my fence - because fitting lipos to Sears electric tools will take a lot more effort than replacing nicads with nimh cells

Regards

Dereck

#13 Ed Lyerly Oct 17, 2003 11:41 AM

A smarter man would probably steer clear of Lipos until as Dereck says "they start using them in Sears power tools" ....but..... the advantage in capacity and weigh savings is just so incredibly large that I can't resist. I will continue to use them. I will, however, be VERY CAREFUL while doing so.
My rationale ....by the time Sears has them in power tools, I will be so old that my eyesight is failing and my reflexes are gone ....so Lipos won't do me any good then.

Ed

#14 Steve C Oct 17, 2003 01:13 PM

I have just recently got myself in to the Lipo game. I've been pretty careful, so no problems yet.

I do want to share one thing though. I needed a large pack and my lhs just got a bunch of the new 1500 Kokams in. They were in 2s packs, so I bought 14 of them for a 7s4p pack. Well, I was so excited that I didn't realize that they were wired with really tiny wire. I just got home and started cutting the shrink off of them. They are wired with large servo wire! All the tabs were bent over and hot glued for safety. Knowing how fragile these tabs are, that made it pretty much impossible for me to get the small wire out without breaking them.

This seems pretty irresponsible by the supplier of these packs doesn't it? They even say they're ok to 10 amps. So far I haven't had the wires melt down, but I wont be surprised when they do. I'll be sure to let the person at the hobby store in on this. If Fred Bronk is reading this...:)

Steve C

#15 Steve H. Oct 17, 2003 04:12 PM

I would guess they wont be in power tools for many many years, I dont think they even use NIMH yet and how long have they been around? By the time they are in power tools, if they ever are, They will still be able to get punctured and will still fail, just not as often, if they are in a heavy case then the weight advantage is gone.

The reason for using lipo is not flight time, to me anyway, it is the weight advantage. I have had some large planes that I was ready to get rid of cause they didnt fly well, but after flying them with the lighter lipos they were a whole different plane.

Anyone who uses lipos now is not an early adopter as they have been out a couple pf years already.


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