WeMoTec Midi-what battery?  
View related threads: (in this forum | in all forums)

Tower Hobbies
Enter up to 4 keywords or Tower stock numbers
Logged in as Guest



Users viewing this topic: none
  Printable Version
       

All Forums >> Electric Aircraft Universe >> Electric RC Jets >> WeMoTec Midi-what battery?
Page: [1]

Login
Message << Older Topic   Newer Topic >>
WeMoTec Midi-what battery? - 2/24/2007 3:49:37 AM   
wsmalley



Posts: 1034
Joined: 2/16/2002
From: Monterey, TN, USA
Status: offline 		I have recently bought a Midi which I've hooked up to an Aveox 36/24/2 with a Phoenix 60(yea, I would liked to have bought an 80+). I'm at a loss as to what kind of battery I need to max what I have. I read of motors run on 3500, or more watts, and 'C' ratings, and burst rates, which mean zip to me! As I understand it, the midi should turn a max of 35K and 1000-1100 watts. I can't relate that to battery specs such as 3000, 5000 mAh's, 6S and a 20C bust rate. Can someone give me a clue-or direct me to a thread, or something to explain the relationship between this stuff. At probably $150+ a pop, I don't want to buy too little, or too much.

_____________________________

If I die, and I have the most toys, what do I win?
       Post #: 1

RE: WeMoTec Midi-what battery? - 2/24/2007 5:40:29 PM   
Larry Dudeck



Posts: 281
Joined: 11/20/2002
From: Williamsville, NY, USA
Status: offline 		try http://www.aveox.com/rc/virtual-test.html This is a virtual test stand for the Aveox motors.

At a Kv of 1820, you will need a lot of voltage to reach 35000 rpm, somewhere around 20 volts at the motor. That's probably a 6S LiPo pack (nominal V = 27.7). Limiting the current to 60 amps, the gross power is ~ 1700 W, at the motor, the power is 1200 W.

The "C" rating is an indication of how much current a LiPo pack can deliver. At pack with a 20C rating will deliver 20 times the battery capacity. For example, a 3000 mahr LiPo with a 20C rating will safely deliver 20 x 3.000 amp Hr or 60 amps. Usually the "C" rating is the nominal, the burst rating is usually about 33% higher. So a battery with a 15C rating (at continuous operation) will deliver a burst of power equal to 20 times the capacity, usually for very short (~15 seconds) periods of time

With a 20C rating, I'd guess a 6S2Px3000 mahr pack. The max current draw would be 20 (as in 20C) x 3amp Hrs (3000 mahr) = 60. This will supply 180 amp minutes (3 amp x 60 min) for a full throttle duration of 180 amp-min/60 amp = 3.0 minutes.

With a 15 C rating, I'd guess a 6S2Px 4000 mahr pack. Here the max current draw would be 14 x 4 = 56. This pack isn't enough to handle the full current draw of 60 amps.

With a 15C rating, you could try a 6S2Px5000 lipo. Here the max current draw is 15 x 5 or 75 amps, more than enough for the motor in question. This pack will supply 5.0 x 60 = 300 amp-min. At full throttle, the duration will be 300 amp=min/60 amps = 5.0 mins. This is the pack I would consider. But it will not be inexpensive.

You could build this pack from four(4) 3Sx2500 LiPo's plus the needed connectors. Two of these would be connected in series. These series connected packs would be wired in parallel with eachother. I'd be very surprised if you could do this for less than ~$250. If you find LiPo's that are significantly less expensive than the major brands (Thunder Power, Apogee just to name two), be very leery about them. Inexpensive LiPo's usually don't meet their advertised "C" rate.

Look at the web sites for the bigger battery suppliers. They will have a primer on the care and use of LiPos.

Also, you will require a high voltage ESC plus a good quality, LiPo specific battery charger and balancer.

Last but not least, improper handling of LiPo's can and will result in destroyed packs at the best, major fires at the worst

< Message edited by Larry Dudeck -- 2/24/2007 5:45:56 PM >

(in reply to wsmalley)
       Post #: 2

RE: WeMoTec Midi-what battery? - 2/24/2007 7:26:25 PM   
wsmalley



Posts: 1034
Joined: 2/16/2002
From: Monterey, TN, USA
Status: offline 		Thanks for the info! I appreciate the explanations, this is a new world to me. I've read enough at this point to have a healthy respect for the proper care and feeding of the lipo's! I like the idea of using the multiple battery solution. I think it would make weight distribution easier, and I think, one could get by with a smaller charger, and perhaps lower cost over the long haul. I like what I've read about the FMA charger.

_____________________________

If I die, and I have the most toys, what do I win?

(in reply to Larry Dudeck)
       Post #: 3

RE: WeMoTec Midi-what battery? - 2/25/2007 2:43:39 PM   
Larry Dudeck



Posts: 281
Joined: 11/20/2002
From: Williamsville, NY, USA
Status: offline 		..."and perhaps lower cost over the long haul..."


Low cost and high power EDF's are mutually exclusive. There aint no cheap way to do 'em.

(in reply to wsmalley)
       Post #: 4

RE: WeMoTec Midi-what battery? - 2/25/2007 3:30:30 PM   
wsmalley



Posts: 1034
Joined: 2/16/2002
From: Monterey, TN, USA
Status: offline 		Point made! My thinking, it's like putting all your eggs in one basket. If one cell dies in a 6S, buy new one, if one goes in a 3S........ I remember once before, my reasoning was erroneous...............

_____________________________

If I die, and I have the most toys, what do I win?

(in reply to Larry Dudeck)
       Post #: 5

RE: WeMoTec Midi-what battery? - 2/25/2007 4:27:04 PM   
Larry Dudeck



Posts: 281
Joined: 11/20/2002
From: Williamsville, NY, USA
Status: offline 		My preference is to build a large pack from a number of smaller units, exactly for the reasons you state. They can be located on either side of the air frame, in the wing roots, etc. And if one of the smaller packs does fail, you can replace just it. The main disadvantage of this approach is you don't have a single balance tap. So the individual 3S batteries would have to be balanced by themselves.

In my situation, after I balance the batteries individually, I connect the individual packs in series using a custom made harness. I then charge them together

Regarding the charger. I would buy a charger that is capable of charging at least a 6S pack. I don't know if a 12S charger exits (6S2P has a total of 12 cells). Either that or buy two chargers to minimize the time it takes to recharge the packs.

After thinking a bit more about it, I would revise my cost estimate to about $350~$400 for a 15C 6S2P battery.

Resign your self to a high cost power supply. Save money in other areas, such as food


(in reply to wsmalley)
       Post #: 6

Page:   [1]
All Forums >> Electric Aircraft Universe >> Electric RC Jets >> WeMoTec Midi-what battery?
Page: [1]





Jump to:


Google 



Search | Marketplace | Event Calendar | Local Clubs | Magazine | Product Ratings | New Products | Discussion Forums

Photo Gallery | Member Video Posts | RCU Video Gallery | Instructor Search | Field|Track|Marina Search

Advertisers | Hobby Vendor Resources | Rate Manufacturers | Sign In/Sign Up

SITE MAP!   : :   FORUM RULES

© 2001 - 2007 24-7 RC, LLC, all rights reserved.

Charities we support that also need your help
Yorkie Rescue | Humane Society | ASPCA | Crohn's-Colitis America

Kaango.com Classifieds

0.486RCU1