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Old May 20, 2002, 07:54 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,432 Posts
Dan,

Thanks for jumping in. Your charger sounds like the answer for these cells.

Dave, your plane sounds great. Start building. I've gone the Pixel balsa sheet route. I have to see if it all works.
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Old May 20, 2002, 09:23 PM
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Fly_joy's Avatar
Rochester, NY
Joined Mar 2001
226 Posts
Dan's charger looks like a good solution for 2 cells.

If you want the flexibility of being able to charge up to 3 cells consider the one Dave Lewis sells at Homefly.com. I costs $40, handles up to 3 cells and has 5 charge rates. I have one and am very happy with it.

Larry
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Old May 21, 2002, 07:54 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,432 Posts
Graham has given me an idea. Obviously we are not going to see $4 135mAh LiPolys to us. But, after a vendor pays shipping, insurance, customs fees, and possibly taxes, we could see these cells in the $8 to $10 range. How about contacting your favorite vendor(s) and letting them know you would buy some or a bunch of these cells. I'm up to 10, and now have quite an investment in them. I would have preferred to have this investment cost half, but I wanted them. Let them know there is demand out here. We now know there are at least two reasonably priced chargers available from Dave Lewis and Dan Krieg. Now we need the cells available so we can afford to go flying with a bunch of them in our field boxes.

Dan, I realized my mistake. Your site says to only use 2-cell Lithium-Ion charger for your LiPoly pack. On the page with details for the charger it is labeled a 2-Cell Lithium-Ion charger. Further down, it says it can charge 1 or 2 Li Ion cells. I missed that. Given the interest, you might consider putting the information about the different charge rates on your site and emphasize the number of cells it will support and sell even more of these chargers. BTW, I've noticed you are an early adopter of new technologies and making them available for sale to us. Thanks.

So, start emailing vendors.
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Last edited by Gordon Johnson; May 21, 2002 at 08:05 AM.
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Old May 21, 2002, 08:43 AM
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Dave Wulff's Avatar
USA, FL, Fort Lauderdale
Joined Feb 2002
1,902 Posts
Gordon,

Nice DR1...I think the next step to seeing better availability/pricing of the Li-Polys will come with some solid info on life expectancy at these current draws. Unlike the 70 nimh, these cells seem willing to give up the current we need, but until there is some hard data on how long they will last it will be tough to get someone to stock them in the quantity needed to get the price down. That is a simple enough task on the bench, and I will get to it as soon as my cells show up.....but you will probably beat me to it, as usual.

Dave W.
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Old May 21, 2002, 09:10 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,432 Posts
Dave,
I was planning to find out what the life is by flying. I'll let you do the expected life tests, as right now I'm back in building mode. But, I really don't think it will be a problem. I think these are similar/same technology to what Dan Krieg is selling in his larger cells. If there is anyone who has put LiPoly cells through a lot it is probably Dan. I'm confident that if he is selling them, he put them through the ringer first. I think they will last. Let us know what you find.

I wish some testing of the 70's had been done before vendors stocked them to sell and then we would have known they were not simply smaller versions of the 120's we had such good success with.
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Old May 21, 2002, 10:18 PM
high-speed freak
opualuan's Avatar
San Jose, CA
Joined Sep 2001
3,863 Posts
I will be selling lithium-polymer cells starting in 2 weeks through my company, the buckshop. rated at 2C continuous, 5C pulsed. protection circuits are on each cell. from 100ma (4.5gram) all the way up to 3800ma! prices will be as low as I can make them while still making it worth my while. full weight/volumetric&weight charge density, discharge graphs, and torture tests will be done on these cells and published on the site.

for closet zagi freaks (I know, wrong forum) (3) 3000ma cells weigh 40 grams less than an 8-cell 1700au zagi-x pack, yet should provide similar power and almost TWICE the duration...

the 100ma cells are really cool, only 1mm thick! lots of cells, big to small. I'll keep you posted, I'll announce in the for sale forum when I'm ready to sell.

I'm also planning to sell a 1-4 cell variable rate li-ion/polymer charger as well, again, priced reasonably.
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Old May 22, 2002, 07:17 AM
Sticky Shepherd
Graham Stabler's Avatar
Oxford/England
Joined May 2001
4,017 Posts
That sounds good, are these the Kokam cells or some others? Nice if the 5C pulses are long ones

Please post a small announcement in the micro forum as well, I (and others?) never get over to the for sale forum.

Graham
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Old May 22, 2002, 02:40 PM
Registered User
Thousand Oaks, Ca
Joined Jan 2002
127 Posts
Lipoly powered pennyplane

Fill
It flew at a slow to medium walking speed. No pictures to date. Have not tried to post picture yet but will try in next 2 to 4 weeks.
To fly in a 20 by 20 room should be possible but turning radius needs more work as turns with prop torque are much tighter than turns to the right.Still more work to be done for better turn control.Moving the vert stab and rudder below the horz stab was a good step in the right direction to even the turns.Turn radius seems to be a tight as 10 to 15 feet dia but need more fight time to perfect the turn capability.
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Old May 22, 2002, 03:44 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,432 Posts
I was talking to Clarence Hurd last night and there are issues with these cells that I have a small amount of information on. I still haven't got the data behind these graphs on my site, hopefully tonight. But, the M20-HV Toytronics motor with this setup pulls between about 0.38 and 0.34 amps for the first 10 minutes or so of motor run, at full throttle. The M20-LV pulls between 0.70 and 0.50 for the first seven minutes of motor run from a NiMH. From the 135 LiPoly cell the LV pulls between 0.75 and 0.63 amps. BUT, the manufactures site lists this cell at 260ma. The question is whether we fly at full throttle flight after flight, or do we fly with short bursts of full throttle. I don't know what effect either of these will have on battery life. Maybe Dave will sacrifice one of his two cells for the common good. I suspect that Dan Krieg may know the answer. He flys a lot, does a lot of hovering and other manuvers that abuse the battery. So, if the larger cells he is selling are similar to these cells, we can probably get some kind of idea from his experiences.

{corrrected}
Here's what I can say. At the end of a sustained 21-minute full throttle run with the M20-HV, the cell was the same temperature it started. At the end of a ten minute full throttle run with the M20-LV pulling considerably more amps, the cell was slightly warm. By slightly I mean not hot, and I could just detect that it was warm. Other than this, I have no idea how long they will last except it's doubtful I'll put this much stress on them when flying.

Dan???
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Old May 22, 2002, 03:57 PM
Sticky Shepherd
Graham Stabler's Avatar
Oxford/England
Joined May 2001
4,017 Posts
My Se5a flys around with two 50mAh cells and a low voltage m20 (kpoo orange gear). With a carbon prop it climbs like theres no tomorow and flys for about 4min. With one of these cells I loose a few grams and gain a few volts. The load on the motor will be less so I assume the current will be. I could even reduce the wingspan to take advantage of the reduced weight.

The lack of heat is promising and I suspect they under rate them as they are designed for mobile devices etc i.e. 100's of charges.

I'm hopefull, but we shall see.

Graham
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Old May 22, 2002, 04:12 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,432 Posts
Sorry, I reversed LV & HV above when typing. The HV pulls less current and did not get warm at all. The LV pulled more current and got a slight bit warm.
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Old May 22, 2002, 07:45 PM
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Dave Wulff's Avatar
USA, FL, Fort Lauderdale
Joined Feb 2002
1,902 Posts
Gordon,

My Li-Poly charger is on the way from Dan, hopefully it will be here by the weekend so I can start some bench tests. The closest gear set I have is 5.8:1 so that will have to do for now. I figure I will aim for 600 - 700 mah and see what happens. At that voltage I may have to trim the Gunther a bit to keep the current down. I envy Graham's numbers, but I fly only outdoors so I am looking for something a bit bigger.

Dave W.
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Old May 22, 2002, 10:49 PM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,432 Posts
I've got the LiPoly static tests on my site now. These have the numbers behind the graphs, and the other measures like RPM and Amps.
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Old May 23, 2002, 02:08 AM
Dangerous
Spaulding's Avatar
LA
Joined Nov 2001
871 Posts
Great news Omar! I hope I can wait. Keep us posted as you find more info on the cells you will carry.
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Old May 23, 2002, 08:11 AM
in persuit of low wing loading
Gordon Johnson's Avatar
Boston, Mass
Joined May 2001
6,432 Posts
Dave,
I forgot to mention, for my digital tach, I rigged up a 12-volt halogen car headlight bulb which I position in front of the prop so it can shine through to the tach. I power this from either my 12v power supply, or my 12v field battery. You are right, even regular incandescent bulbs cause the tach to read incorrectly. With the 12v car bulb, you can turn off your room light if it is nearly overhead and interfering with your tach and you will still be able to see. In fact, I often plug in the car bulb when I'm working on tiny stuff because it throws off such good light.
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