What batteries for 5" fan?
12-31-2011, 05:28 PM
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RE: What batteries for 5
Not knowing anything about the 5" fan you have, I'll take a stab at this.
Just guessing 25000 rpm with a kV=700 motor:
25000/700 = 35.7 v
@3.7 v/cell LiPo, 35.7/3.7 = 9.6 or 10S
Limiting current to 100 amps, power would be 10*3.7*100 = 3700 watts, bare minimum
If it were mine, I'd consider two 5S x 5000 mAhr packs wired in series. These would have to be good quality packs rated at 40C.
Not ever flown anything larger than 70mm, I might be way off in my guesstimate.
Just guessing 25000 rpm with a kV=700 motor:
25000/700 = 35.7 v
@3.7 v/cell LiPo, 35.7/3.7 = 9.6 or 10S
Limiting current to 100 amps, power would be 10*3.7*100 = 3700 watts, bare minimum
If it were mine, I'd consider two 5S x 5000 mAhr packs wired in series. These would have to be good quality packs rated at 40C.
Not ever flown anything larger than 70mm, I might be way off in my guesstimate.
01-01-2012, 08:24 AM
#3
RE: What batteries for 5
Thanks for the input! At least now I have some idea of a starting point. I have two of these to try and shoehorn into an SU27, space for the batteries being the problem. The second motor, as yet, is unmodified....that is ceramics. So, I may try your configuration on that one first. Your combo keeps the voltage below the 48v max of the motors. Thanks, Bill
01-01-2012, 01:51 PM
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RE: What batteries for 5
What fan is it? True 5" fans are dynamax and ramtec, and 700Kv is high for either of them so as Larry said 10s would be the max you would want to use with your ESC. If its a chinese fan then its 120mm not 127mm, and presents a lower load and less efficiency with the 7 blade? I am guessing rotor, and could need 12 cells.
01-03-2012, 08:15 AM
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RE: What batteries for 5
My guess is you have either the 7-blade Haoye or 4-blade ChangeSunfan from hobbyking, since I have the same 700Kv motor from them. My input will be for either of these two fans based on my experience. If you have a different fan then this may not apply...
Note: withANY 5"fan, a 12S pack and 700Kv motorshould push the fan to its critical speed (roughly 36000 rpm at sea level,lower rpm for higher altitude) so you definately don't want any more battery than that, period!!A safe max speedin orderprevent the the rotor tips from going supersonic on any fanat anyreasonable altitudewill be roughly 30,000 rpm, which with a 700Kv motor means 10S max.
However, I've taken both fans to 30k+ rpm and both fanshad cracks in the motor mounts after about 5 minutes of sustained 30k+ speed. There are some extraneous conditionssurrounding my tests, but for safety I wouldn't suggest maintaining an excess of about 25k rpm sustained speed on either fan.
With a 700Kv motor oneither fan, 25krpm means an8S batterymax. My opinion would be to get a 600Kv motor insteadon 10S or 480Kv on 12S to lower the amps andprotect the esc. My guess is you'll bereachingthe threshold forthe100AESC on 10S with a 700Kv motor if you have the 7-blade fan. The 4-blade fan will probably runaround 100A with the 700Kv, but you won't be getting much power out of the fan at that point.
That's my two-cents based on my experience. Take myadvice at your own discretion.
Note: withANY 5"fan, a 12S pack and 700Kv motorshould push the fan to its critical speed (roughly 36000 rpm at sea level,lower rpm for higher altitude) so you definately don't want any more battery than that, period!!A safe max speedin orderprevent the the rotor tips from going supersonic on any fanat anyreasonable altitudewill be roughly 30,000 rpm, which with a 700Kv motor means 10S max.
However, I've taken both fans to 30k+ rpm and both fanshad cracks in the motor mounts after about 5 minutes of sustained 30k+ speed. There are some extraneous conditionssurrounding my tests, but for safety I wouldn't suggest maintaining an excess of about 25k rpm sustained speed on either fan.
With a 700Kv motor oneither fan, 25krpm means an8S batterymax. My opinion would be to get a 600Kv motor insteadon 10S or 480Kv on 12S to lower the amps andprotect the esc. My guess is you'll bereachingthe threshold forthe100AESC on 10S with a 700Kv motor if you have the 7-blade fan. The 4-blade fan will probably runaround 100A with the 700Kv, but you won't be getting much power out of the fan at that point.
That's my two-cents based on my experience. Take myadvice at your own discretion.
01-03-2012, 11:05 AM
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RE: What batteries for 5
You're dead on! These are the Haoye 7 blade and HobbyKing stuff I've had awhile. Some time back, the 'tech guy' suggested the mods to the motor( ceramic bearings) and, I think, the 700 motor as the best combo at that time. Right now, I have the fan/motor/ESC mounted in a test stand. The motor combo...shroud, etc. was test fitted into the plane's fuse for fit. The intended plane is much modified, from the original Bertelli plans, 108" OAL SU27. I still have an old Turbax fan coupled to an old Rossi .81, which I guess could be 'electrified'. Indeed, your experience is well noted! I won't exceed your recommendation, better to come up with an another fan/motor combo......given the amount of time I have already put into the plane! Battery prices have dropped enough to allow some experimentation. Thanks, Guys, for the input! Bill
01-05-2012, 06:42 AM
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RE: What batteries for 5
ORIGINAL: wsmalley
You're dead on! These are the Haoye 7 blade and HobbyKing stuff I've had awhile. Some time back, the 'tech guy' suggested the mods to the motor( ceramic bearings) and, I think, the 700 motor as the best combo at that time. Right now, I have the fan/motor/ESC mounted in a test stand. The motor combo...shroud, etc. was test fitted into the plane's fuse for fit. The intended plane is much modified, from the original Bertelli plans, 108'' OAL SU27. I still have an old Turbax fan coupled to an old Rossi .81, which I guess could be 'electrified'. Indeed, your experience is well noted! I won't exceed your recommendation, better to come up with an another fan/motor combo......given the amount of time I have already put into the plane! Battery prices have dropped enough to allow some experimentation. Thanks, Guys, for the input! Bill
You're dead on! These are the Haoye 7 blade and HobbyKing stuff I've had awhile. Some time back, the 'tech guy' suggested the mods to the motor( ceramic bearings) and, I think, the 700 motor as the best combo at that time. Right now, I have the fan/motor/ESC mounted in a test stand. The motor combo...shroud, etc. was test fitted into the plane's fuse for fit. The intended plane is much modified, from the original Bertelli plans, 108'' OAL SU27. I still have an old Turbax fan coupled to an old Rossi .81, which I guess could be 'electrified'. Indeed, your experience is well noted! I won't exceed your recommendation, better to come up with an another fan/motor combo......given the amount of time I have already put into the plane! Battery prices have dropped enough to allow some experimentation. Thanks, Guys, for the input! Bill
You have pictures?
Should be very nice!
01-05-2012, 02:33 PM
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RE: What batteries for 5
I'll see if I can get these pics to work, had to try to transfer them from another PC. The LG is all scratch built, I have put in leading edge flaps and maybe you can see the airbrake. Originally, I had 2 JPX (propane) turbines but found there was no way to get the fuel tanks in there. As mentioned, the plans are much modified Bertella plans.
01-06-2012, 09:42 PM
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RE: What batteries for 5
Wow Nice Project![:-]
Good ol balsa and ply
Space issue for the batteries?
I 'm sure you thought about it ,but some I saw someone putting batteries in a pod
Good ol balsa and ply
Space issue for the batteries?
I 'm sure you thought about it ,but some I saw someone putting batteries in a pod
01-07-2012, 06:54 AM
#11
RE: What batteries for 5
Yep, balsa and ply! I've done a little glassing at this point but kind of 'shelved' the project 'til working the power issue out. The batteries I think may be better camaflaged then the gigantic propane tanks. Somewhere I had pics of a flanker mounted with an underslung huge missle.......name starting with an 'M', I think? That would make the pod, I guess. Of course, if I had the 'Big Bucks', a couple of the newer smaller turbines would be perfect.
