Wattflyer RC Network: RC Universe :: RCU Magazine :: RCU Forums :: RCU Classifieds :: RCU User Reviews :: RCU YouTube
Home Who's Online Calendar Today's Posts RealTime Post Spy Mark Forums Read
Go Back   WattFlyer RC Electric Flight Forums - Discuss radio control eflight > R/C Electric Power - Batteries, Chargers, ESCs and More > Batteries & Chargers
Register Members List Wattflyer Extras Articles Search Today's Posts Mark Forums Read Social Groups

Batteries & Chargers Discuss Li-P, Li-Ion, NiMh, Nicad battery technology and the chargers that juice 'em up!

Thank you for your support (hide ads)
Reply
 
Thread Tools Display Modes
Old 10-10-2005, 02:29 PM   #1
Warden
Member
 
Warden's Avatar
 
Join Date: Aug 2005
Location: Central Pennsylvania
Posts: 283
Thanked 2 Times in 2 Posts
iTrader: (1)
Friends: (0)
Default Lipo Dilemma

I recently repowered my RCM Funster (low wing version of the Telemaster 40) with an AXI 4120/14. The 1900 mah nicad pack I'm using with this motor doesn't seem to be cutting it. Duration is not good and the pack just doesn't seem to have the discharge capacity I need. I've been using the pack for awhile and I'm thinking it's on its way out. I know lipo's are the way to go in this plane but I see Lipo's as a large mine field of problems.

The motor with a 12X8 prop draws 49 amps on the bench so I need a pack that can provide at least 50 amps, and to get the proper voltage I'd need a 5 cell pack. Knowing what I need is the easy part; choosing, charging and maintaining the pack is where my problem comes in.

I've got an Astro 110Deluxe with the chip that converts it to a 109 so the charger is covered. My concerns fall into three areas: First is flight duration and time between flights, second is balancing and maintaing the pack, and third is the cost of the pack.

I'm looking for a ten or twelve minute flight using half to three quarter throttle with some bursts of full. And I'm looking for several flights during one trip to the field. Some of the charging routines I've seen call for charging each cell indiviually. That would effectively mean one flight and done! Unless I chose a very large capacity pack where I could get several flights out of one charge.

Balancing and maintaining the pack is another issue. It seems to me that every manufacturer is coming out with their own proprietary balancing system which means I'd have to use one brand of pack exclusively or I'd have to buy a balancer from each different company. I don't like either one of those options.

Then there's the cost factor. I just don't see myself laying out $450-$500 for a battery pack. One way to get the capacity I need is to parallel packs but that ups the cost considerably and keeping the pack balanced becomes even more of an issue (read that problem) with multiple packs in parallel.

What I need is a large capacity (4000mah +/-) 5S pack with a balancer I can use on other brands of packs that I don't have to sell my first born son to afford.

Battery technology is changing so rapidly; I was hoping to wait until spring to begin the search for "my" lipo pack because I figured things may be very different by then but with the apparent "failing health" of the nicad I'm using now I'm starting my quest a little early.

Any help or suggestions would be apprecaited.

Warden

Always strive to be the person your dog thinks you are!
Warden is offline  
  Reply With Quote
Old 10-10-2005, 03:59 PM   #2
Matt Kirsch
Super Contributor
 
Matt Kirsch's Avatar
 
Join Date: Jul 2005
Posts: 2,086
Thanked 70 Times in 68 Posts
iTrader: (0)
Friends: (1)
Default

Right now, you're asking for Mercedes features for Hyundai money... With time and competition in the marketplace, the prices will start to come down, but that's probably at least a year down the road.

The two integrated balancing systems I'm aware of are both charger-based. That is, the circuitry that monitors the cell voltage and balances the individual cells is external to the pack. The packs themselves are simple packs with taps to each cell; there is no special protection circuitry within the pack. Truth be told, one pack could be adapted to the competition's system with a simple connector swap. Third-party packs can also be adapted to either system through the addition of cell taps and the appropriate connector.

Both integrated balancing systems are signifigantly more expensive than "raw" LiPoly packs, though... You could simply buy raw packs now and adapt them later, or you can manually balance the packs.

Balancing doesn't have to happen EVERY time you charge. It's nice to have, but not absolutely required. There are literally tens of thousands of packs in use that don't get balanced every time they're charged, and I would dare say most of them aren't being balanced at all. That's not to say that it isn't necessary, or a bad thing to do. What I am trying to get across here is that cells getting out of balance enough to cause trouble is an extremely rare occurrence.
Matt Kirsch is offline  
  Reply With Quote
Old 10-10-2005, 04:01 PM   #3
Matt Kirsch
Super Contributor
 
Matt Kirsch's Avatar
 
Join Date: Jul 2005
Posts: 2,086
Thanked 70 Times in 68 Posts
iTrader: (0)
Friends: (1)
Default

Continued:

What I've been doing right along is building my larger LiPoly packs from smaller 2- and 3-cell packs, using series and parallel connectors. This way, I can easily break my packs apart and charge each pack individually once in a while, and assess its health.
Matt Kirsch is offline  
  Reply With Quote
Old 10-10-2005, 04:48 PM   #4
Fred Marks
Member
 
Join Date: Sep 2005
Posts: 187
Thanked 0 Times in 0 Posts
iTrader: (0)
Friends: (0)
Default

Originally Posted by Warden
Battery technology is changing so rapidly; I was hoping to wait until spring to begin the search for "my" lipo pack because I figured things may be very different by then but with the apparent "failing health" of the nicad I'm using now I'm starting my quest a little early.

Any help or suggestions would be apprecaited.

Warden
Open www.fmadirect.com or

(https://www.fmadirect.com/site/fma.htm?body=rc_appNotes)

and read the Li Po Handbook. Then click on What's new in Li Po Technology on the home page. It will also be helpful if you read the excellent article Tom Hunt wrote in the Nov issue of Fly R/C. Tom did one of the most thorough jobs we have seen in measuring the flight profile of a typical electric airplane in the range of your airplane. With regard to cost: With the proper FMA Direct charge and discharge control devices and heavy dduty packs, your system should last a lifetime, even longer than a decent glow motor. Cost to operate a good brushless motor and Li Pos over a 1,000 flight life (arbitrary) including initial cost, is about 1/10 what the cost is for glow with fuel at $15/gallon.
Fred Marks is offline  
  Reply With Quote
Old 10-10-2005, 06:10 PM   #5
hoppy
Watts up Doc?
 
Join Date: Oct 2005
Location: Florida
Posts: 491
Thanked 2 Times in 2 Posts
iTrader: (0)
Friends: (0)
Default

Warren,
Another avenue? Take a look at the battery performance graphs on this site. Many of the new NiMH packs will supply 60A.
http://flydma.com/batteries/performa...1=batterychart

For more lipo lifetime info, read your PM.
hoppy is offline  
  Reply With Quote
Old 10-10-2005, 08:08 PM   #6
Matt Kirsch
Super Contributor
 
Matt Kirsch's Avatar
 
Join Date: Jul 2005
Posts: 2,086
Thanked 70 Times in 68 Posts
iTrader: (0)
Friends: (1)
Default

Yes, there is that route as well. 1900mAh NiCds are pretty old tech. For the same size and weight, you can now get 3700mAh NiMH cells that are easily capable of the same discharge levels (50A bursts).

I've been pretty brand-neutral up to this point, but this is what I'd do: For about $200 at Tower Hobbies, you can get a 2S and a 3S pack of Kokam 3200 cells that are capable of 20C (60 Amp) bursts and weigh less than half as much as a NiMH pack of comparable capacity and voltage. It's the perfect solution:

The separate 2S and 3S packs are easy to check for balance, and a simple series connector is all you need to turn them into a 5S pack.

The cost really isn't all that much. You were figuring on $400, and this is about half that.

Weight reduction... 'nuff said.

60% more capacity... 'nuff said.
Matt Kirsch is offline  
  Reply With Quote
Old 10-11-2005, 12:25 PM   #7
Warden
Member
 
Warden's Avatar
 
Join Date: Aug 2005
Location: Central Pennsylvania
Posts: 283
Thanked 2 Times in 2 Posts
iTrader: (1)
Friends: (0)
Default

Thanks for the info, guys. I've been flying electric for close to 15 years so I'm not new to this aspect of the RC hobby. Lipo's, however, are another story. Obvioulsy I don't know a lot about this new technology. Your help is appreciated.

Always strive to be the person your dog thinks you are!
Warden is offline  
  Reply With Quote
Old 10-11-2005, 01:32 PM   #8
jonnyjetprop
Member
 
Join Date: Aug 2005
Location: Orlando, FL
Posts: 708
Thanked 14 Times in 13 Posts
iTrader: (0)
Friends: (0)
Default

Another way to go is with a 5s2p 4200 Thunder Power Pro lite pack. Runs $280 and weighs 17 ozs. Add a balancer unit for $60 and you're all set.

John
jonnyjetprop is offline  
  Reply With Quote
Reply

  WattFlyer RC Electric Flight Forums - Discuss radio control eflight > R/C Electric Power - Batteries, Chargers, ESCs and More > Batteries & Chargers


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Medical Dilemma Eric_N57105 Humor 1 05-29-2008 02:35 PM
Is It Possible to make two 1S Lipo Packs from a 2S Lipo Pack? Sam_K Batteries & Chargers 7 05-02-2008 11:34 PM
King Arthur's dilemma.... yank51 Humor 4 12-07-2007 10:49 PM
Blade CP PRO dilemma petkoo Micro Sized Electric Helicopters 10 10-21-2007 11:52 PM
FMA Direct LiPo Handbook PDF resource. Comprehensive lipo info! admin Batteries & Chargers 8 01-18-2006 03:00 PM


All times are GMT +1. The time now is 09:17 AM.


Powered by: vBulletin
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright 2005 WattfFlyer.com
RCU Eflight HQ

Charities we support Select: Yorkie Rescue  ::  Crohn's & Colitis Foundation



Page generated in 0.10817 seconds with 33 queries