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Power System Cooling - 7/10/2008 10:55:36 PM   
Michaelj2k



Posts: 307
Joined: 9/15/2006
From: Newark, DE, USA
Status: online 		OK guys, I've been around this RC patch for more years than I can remember. So......I've decided to take one of my IC birds and convert it to electric. The airplane is the Bill Northrop designed "Duster" (pic on right) from around 1964. Over the winter, I stripped the airplane down for recovering and refurb. I've decided to install an Axi 4120 motor and an associated speed control. I've not decided on batteries yet, but will probably go with NiMh for the first go around. The motor will be fully exposed on the firewall with a large ring cowl but my concern is cooling of the speed control and battery pack. I'll be opening up a hole in the firewall for the wires but will that be enough? What is the rule of thumb for cooling?

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< Message edited by Michaelj2k -- 7/11/2008 12:56:18 PM >

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RE: Power System Cooling - 7/11/2008 12:29:29 AM   
normgoyer


 

Posts: 723
Joined: 5/18/2006
From: Apple Valley, CA, USA
Status: online 		Hi, I have been running a 4120 in a large PT-19 for two years with great success. I have a 70 amp ESC and run 22.2 volts @ 3400 ma and the combo is bullet proof. Dump the idea of the niHi or nicads, go with A123 or Li-poly, Norm

(in reply to Michaelj2k)
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RE: Power System Cooling - 7/11/2008 12:55:33 PM   
Michaelj2k



Posts: 307
Joined: 9/15/2006
From: Newark, DE, USA
Status: online 		Thanks Norm,

I've also considered A123's as well. But I'd like to know something about cooling airflows around the battery pack and speed control. Or should I forgedaboudit.

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He's crazy Lew, he,...he builds toy airplanes!
Waco Brotherhood #6

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RE: Power System Cooling - 7/11/2008 3:30:48 PM   
normgoyer


 

Posts: 723
Joined: 5/18/2006
From: Apple Valley, CA, USA
Status: online 		Hi, I live in the High Desert where it runs 100 to 106 in the summer and cooling is a non issue. I put the ESC in the cowling and my 123 cells in the fuselage permanently and if I am using LiPooly I cut a hatch in the firewall slide them 1/2 into the fuselage and remove them for charging. I have had zero heat issues and I have 3 large electrics with 123a and 2 with Lipolys. Forget al the negative aspects and go fly, the word is fun not frustration. Norm

82 years old today and going strong.

(in reply to Michaelj2k)
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RE: Power System Cooling - 7/11/2008 4:45:37 PM   
Michaelj2k



Posts: 307
Joined: 9/15/2006
From: Newark, DE, USA
Status: online 		Thanks Norm, I just don't want to toast the stuff.

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He's crazy Lew, he,...he builds toy airplanes!
Waco Brotherhood #6

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RE: Power System Cooling - 7/11/2008 7:06:50 PM   
normgoyer


 

Posts: 723
Joined: 5/18/2006
From: Apple Valley, CA, USA
Status: online 		I love the A123 li-ion. I buy the 2300 ma ones from 22 bucks for 2 cells. I use an Astro Flight A123 specific charger. These cells don't burn, blow up or self destruct like LiPolys, and they can dump full power for short period making for shorter flights but much lighter packs. I fly a BH T-28 with a 1420 size off brand motor and power it with a 60 amp Esc and 5 2300 A123 cells and it flies just great and long enough to scare me several times, then I dump the flaps and land, to have fun simplify your hobby, worry less, fly more. Norm

(in reply to Michaelj2k)
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RE: Power System Cooling - 7/12/2008 9:38:11 AM   
tIANci



Posts: 8436
Joined: 1/15/2004
From: Kuala Lumpur, MALAYSIA
Status: offline 		Go with lipos as later you can use them on planes that might want a light power supply but for bipes that are floaty, NiMH are fine.

My own rule of thumb for cooling is to run an ESC that is a class bigger than what you will need, e.g. if your system pulls 40-45A then go with a nice 60A ESC, if it pulls about 60A and you are flying a Tiger Moth then 60A ESC is fine as you will not be on WOT all the time. For your plane you can leave the ESC outside the plane, below the cowl area if you feel the tank compartment is tight.

As for batteries I do my best to push my lipos to only 80% of the constant discharge capability, e.g. system pulls 60A, I use about 80A-100A batts. My Sebart Angel pulls about 60A but I am using batts that are able to handle a constant 125A. Only when I am stiffed on weight that I will use batts that will be pushed to its limits. My Fun Jet pulls about 45A and my batts are good for 60A.

Based on what I do I am not too concerned about airflow through the plane.


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