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View Full Version : glow to electric and NiCd to Lithum conversion


William L Baker
08-17-2006, 07:52 PM
I have sucessfuly converted my glow Old Timer fleet to electric using brushless motors and lithium batterys. Also I have recently converted some other planes that were electric from the start, over to lithium from NiCds.The major problem for all has been maintaining proper center of gravity.From years of glow practice we put our servos at the aft end of the cabin space. When you can ,move these forward, and /or use smaller servos. The HS -81 and 85 servos have enough torque to replace the old "standard size "servos and weigh less. Glo to gas the fuel tank space is a good place to put batterys, and in some designs the battery can even occupy space under the motor, this might make necessary a hole in the firewall.My philosop[hy was to add as much capacity as possible instead of ballast weight .So my larger models have 3200 to 4000 mah lipos: smaller batterys would have meant adding lead. On the other hand I had a fine flying electric with a brushed motor and NiCds. Converting it to brushless and lithium required adding lead ! Here is why:The 12 niCd cells were so heavy , that to retain the CG meant adding lead even though I used a 4000 mah lipo in place of the 1700 mah NiCds ! So on this conversion I did not save weight, but I gained some power and a heck of a lot of capacity ! The model flew fine with the NiCds, was not overweight, but the gain in capacity was dramatic.When you remove the engine in a glow to electric conversion you immediately have a tailheavy problem : most engines are heavier than the motors that replace them, so the work of conversion is a battle to maintain the CG. It is, in my opinion, worth it .:)

Dereck
08-20-2006, 11:58 PM
Not so sure that I'd give up on NiMh cells just yet, especially in the likes of an OT or 'Just Cruisin' Around' model.

Especially with conversions, there's that CG thing to be taken care of - and it must be addressed correctly, as there's no court of appeal for the breaking the laws of aerodynamics.

Okay, there's weight, but big deal - I think the heaviest Kadet Senior I ever got involved in was estimated at 10lbs, but the owner refused to weigh it in case he got scared to pick it up. Flew like a dream on 24 big old round jugs - back when 2000Ma was a good trick. Now, replace its Astro 40G with a BL and fit 16 - 20 3800 NiMh, you got yourself a good big loafing around machine.

I just caught up with the 21 st century and got some LiPos. Fortunately, my two regular sports aerobatics were designed and built with the middle of the battery pack atop the CG, so it doesn't matter what the pack smells like when it catches fire ;)

Of course, you need access to a really good design/build service to get models set up like that ;) I'm electrocuting a 'seasoned' Sig kit for a mag review right now, and the snag is, the pack's going to have to go right up the sharp-ish end. Not so bad, but I'm also reviewing it with 3S and 4S and even this old geezer knows that 4 lipos gotta weigh more than 3, no matter how good they are...

Intend to make it my last kit, am reverting to my previous custom design/build/finish/test fly service for future models

Regards

Dereck

William L Baker
08-21-2006, 02:42 PM
Dereck is right, that NiMh cells now available will give long runs. I had a model that required a pound of ballast to get the CG right. I looked through battery lists and found that 8 NiMh cells of about 3200 mah capacity weighted that much so that is what I used . The results were great. HOWEVER what I failed to say in my initial discussion is that I want my models to be capable of thermal soaring , which is why I build mostly Old Timers, and so weight does matter to me.After many happy flights with that model I did convert it to Lithium too, moved the battery forward of the firewall below the motor (it had been behind leading edge bulkhead) and used a battery of a little less capacity as that was all the room there was, and I had to add some lead to regain the CG. So I lost capacity in that deal and but still lost some weight which should improve thermaling .

phil007
08-23-2006, 04:32 AM
Don't forget to look at the Milwaukee V28 Emoli Cells for the larger planes listed in the Sept 2006 issue of Quiet Flyer. Lighter than NiMH but a little heavier than Lipos. They're also safer than lipos and can be charged in about 30 minutes at 3C. I have a Hanger 9 P-51 Mustang that I'll be building soon and it will be powered using these cells. Oh...and they are about half the cost of Lipos.

My Maxi-Joker Helicopter is flying on 32 NiMH packs and in a few weeks I'll get a 10s2p Emoli pack for $300, a Lipo pack for this big bird would be $600-$800.

Phil

Battery Sources:
Custom made packs www.bigerc.com (http://www.bigerc.com)
Cells for $14 each www.m2energysolutions.com (http://www.m2energysolutions.com)

William L Baker
08-23-2006, 11:01 AM
I have no knowledge of these cells. Are they NiMh or something new ? Where are they available ?. I have flown with NiMH cells 3200 and 3800 mah and they worked fine , especially in aircraft where weight was needed to get the CG in place.If the V28 cells are lighter than the NiMh cells I know about, they certainly are of great interest:) . Thank you.

phil007
08-23-2006, 04:37 PM
Battery information from http://www.bigerc.com/

Emoli Cell Information

Cell Type IMR26700 Manganese
Size 26mm diameter; 70mm length
Weight 100g
Capacity 3000 mAh
Voltage 3.7V nominal, 4.2V fully charged.

Benefits

Emoli packs are best suited to larger planes that dont mind the weight increase. They are about 30 percent heavier than lipos but are MUCH lighter than NiMHs and are VERY damage resistant. You do not have to worry about combustion or thermal runaway. When the cell reaches the point of combustion a fuse-like system pops, breaking the electrical connection and rendering the cell useless. Voltage will read zero and you can safely dispose of the cell. You can charge them up to 3C without having to worry about cell damage.

Dereck
08-23-2006, 07:11 PM
http://www.power-motion.com/

Idle thought here - "Saphion" have been selling these cells for a year or so now! THe URL above is their hobby online store,

http://www.valence.com/saphion.asp

Is the head office or whatever it's called.

Unfortunately, due to circumstances beyond the control of my model flying workshop (earning a living, etc, etc :( ) I never got to fly the 3S Saphion pack I assembled overly long back, and shortly before I realised I should have gone 4S, as that closely replicates my old faithful 10 BRJ packs, and isn't too far from 3S LiPos.

With the way things vanish into downtown Peking and come out copied, badly labled and cheaper, there could be a connection between Saphion, A123, EMoli and the powertool packs ....

Have never learned why they come in long skinny metal cases, when the vast majority of larger canned cells come in what we loosely call 'Sub C', so there can be fitting issues for existing models, plus dedicated chargers seem scarce. Most of the users employ some kind of workaround - LiPodaptor, knowing what to do with their electronics workshop, etc.

Even though I have some LiPos right now, I'll be on this new bandwagon pretty quick when it gets its serious wheels on. A little heavier, I can live with - my building service has a lot of time on airframe weight reduction issues. Safer to charge? - okay, own up - who likes watching a lipo charge? Though it's no less boring that watching TV or moneyball sports ;).

Chargers are a Saphion etc issue too - I just got a FMA DIrect Cellpro 4S and it reduces charging LiPos to how I like chargers to work - plug it in, turn it on, let it get on with it.

I never bothered much about how glow fuel was made either, way back when. :D

Am bloody awful for being marketted to - have never shown any interest in buying something first day in the store, just because someone tells me that it's "NEW! EXCITING!"

This makes me a real bad "new technology adopter", but means I seldom spend money on dead end trails ;)

Regards

Dereck

dimadee
08-24-2006, 04:10 AM
I don't seem to be able to find any information regarding the maximum and burst discharge rates for the V28 Emoli cells.

Is anyone able to fill me in? :confused:

phil007
08-24-2006, 05:02 AM
The Newest Gen Li Io round cells in our helis? post on RCGroups will give you a lot of information.
Link: http://www.rcgroups.com/forums/showthread.php?t=456011 (http://%5BURL)

Found this info on the maximum and burst discharge rate.

"I would rate these at 12-15C, with a 20-25C burst capability..."

Phil