What bat. and speed controler for twin 300's?  
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 Training >> What bat. and speed controler for twin 300's?
Page: [1]

Login
Message << Older Topic   Newer Topic >>
What bat. and speed controler for twin 300's? - 5/4/2003 8:36:20 PM   
George C


 

Posts: 10
Joined: 10/22/2002
From: Corinth, GREECE
Status: offline 		I 've got a swift racer with a pair of Graupner speed 300's installed and I need some advice on what kind of batteries and speed controller I could use with this combo. I've got an 18 amp Kotronik speed controller and a 9.6v battery pack of sanyo nimh AA size at 1850 mAh. I've tried these but the speed controller cuts the power just above half throttle and the batteries get really hot. That happens when the motors are wired in parallel. When the motors are wired in series everything works fine but power seems marginal for the model. I have no idea what is going on. I'm really new to electrics and none of this makes sense to me. Any suggestions would be very much appreciated.

Thanks

George C
       Post #: 1

What bat. and speed controler for twin 300's? - 5/5/2003 10:00:25 PM   
Matt Kirsch



Posts: 7043
Joined: 7/5/2002
From: Rochester, NY, USA
Status: offline 		Here are a few basic concepts:

1. In series, current stays the same and voltage adds up.
2. In parallel, voltage stays the same and current adds up.
3. Rechargeable batteries have strict limits on how much current they can produce. If you draw too much, they get very hot and can become damaged.
4. The more current you draw from a battery, the lower its voltage goes.
5. Voltage and current are dependent on each other. Raise the voltage, and current must increase proportionally. Double the voltage, double the current.
6. Power is voltage times current. Double the voltage, and current must also double. This means that by doubling the voltage, you get four times as much power at the propeller.

Okay, here's what happened:

When you have the motors wired in parallel, the full voltage from the battery goes through both motors. Together, the two motors draw twice as much current as a single motor. The two motors running together are drawing more current than the batteries can produce, causing the low-voltage cutoff circuit in the ESC to shut off power to the motors.

When you had the motors in series, the voltage from the battery was split equally between the two motors. This means that the motors were only running at about 1/4 power, as compared to the parallel wiring.

All you should need is a different battery. AA cells are not very good for electric airplanes in general. You should get an 8-cell pack of 2/3A cells, like KAN950s or HECELLs.

(in reply to George C)
       Post #: 2

What bat. and speed controler for twin 300's? - 5/5/2003 11:12:42 PM   
George C


 

Posts: 10
Joined: 10/22/2002
From: Corinth, GREECE
Status: offline 		Thank you for your input, it was really helpful. I think I’ll keep the speed controller I’m using now and I’ll go for a HECELL pack. I did a quick search and found them in a site called edogfight.com They say they can give up to 16 amps. I hope that is sufficient. Further more it seems that the 8 cell pack is about 50 grams lighter that the one I’m using now.

Thanks for the help

George C

(in reply to George C)
       Post #: 3

What bat. and speed controler for twin 300's? - 5/6/2003 8:32:26 PM   
Matt Kirsch



Posts: 7043
Joined: 7/5/2002
From: Rochester, NY, USA
Status: offline 		HECELLs are good batteries, which is probably why I recommended them, eh?

If you're still running into that low-voltage cutoff problem, I would re-think the propellers and/or gearboxes on the motors. Speed 300 motors shouldn't be drawing more than 8 Amps each.

(in reply to George C)
       Post #: 4

Page:   [1]
All Forums >> Electric Aircraft Universe >> Electric Training >> What bat. and speed controler for twin 300's?
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

0.418RCU1