High Voltage Hot Rodding (Full Version)

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rmh -> High Voltage Hot Rodding (12/5/2003 6:41 PM)

Someone who has actually tried this please:
we take a pair of 2C 1200 ma packs (LiPo) wire them in series Now we have 14 V?
The Ph 25 controller says ( modify the Rx connection to eliminate the power to it -and use seperate power to the bRx - (a tiny 4.8 setup I suppose)
Now -if we take a short can Hacker/ Himax etc., with lower KVA windings -
Can we get a "better " setup , than running the 3 Cell Lipos?
The current will now be at higher voltage and the amps will be lower.
From a practical standpoint - maybe this is simply je--ing off.
But has anyone actually tried it to see if the motor runs cooler/ better etc/
at same prop thrust ?
The larger motors all use higher voltages- up to 40 V
what is the real problem here ?
I am really serious here
My question is because I am doing a model which is a bit bigger / heavier --and I will use my 5400 KV Himax (3c) -or a 4100 at this higher voltage.
I also have Hackers -small cans -various winds .
I can buy a long can motor - but foist - will this really work?



rmh -> RE: High Voltage Hot Rodding (12/5/2003 10:03 PM)

No one knows?



mglavin -> RE: High Voltage Hot Rodding (12/6/2003 10:08 AM)

quote:

ORIGINAL: dick Hanson

No one knows?


Dick

I haven't gone here much, BUT I believe they guys that are pumping high voltage are doing so to deliver lots of power at minimal current draw. Verses high current draw and low voltage. seems that why your asking, I guess.[:D]

You've already eluded to in a previous thread the simple fact that it takes a given amount of power to spin a prop. Watts/power = voltage x amperage. So its pretty easy to extrapolate. In theory it should work. The numbers maybe to close to one another with your scenario at 11.1 to 14.8V to make a significant difference.



mglavin -> RE: High Voltage Hot Rodding (12/6/2003 10:33 AM)

OK, I was bored and intrigued. So ran some numbers through MotoCalc.[&:]

Anyway it looks like it would be worth a try.

Motor: Himaxx 2015-2800; 2800rpm/V; 0.4A no-load; 0.355 Ohms.
Battery: E-Tec ET-1200; 4 cells; 1200mAh @ 3.7V; 0.033 Ohms/cell.
Speed Control: Castle Creations Phoenix 25; 0.0065 Ohms; High rate.
Drive System: GWS GW/EPS-300C-DS; 11x4.7 to 12x8 (Pconst=1.18; Tconst=0.995) geared 6.6:1 (Eff=95%).

Best case I come up with is 22.6ozs @ 5.6A with a 12/4.7, eff% is reasonable so heat should be minimal with this setup. That 2-3amps less than a 4100Kv combo can muster on 3 cells with like thrust, well according to MotoCalc...

NC = 4
Gear Ratio = 6.60
Diam (in) = 12.0
Pitch (in) = 4.7
Batt Amps = 5.6
Motor Amps = 5.6
Motor Volts = 14.0
Input (W) = 78.5
Loss (W) = 18.9
MGbOut (W) = 59.6
MotGb Ef(%) = 76.0
Shaft Ef(%) = 72.0
Motor RPM = 33811
Prop RPM = 5123
Thrust (oz) = 22.6
PSpd (mph) = 22.8
Time (m:s) = 12:52

More thrust, a little more pitch and a little higher current draw;

NC = 4
Gear Ratio = 6.60
Diam (in) = 12.0
Pitch (in) = 6.9
Batt Amps = 7.1
Motor Amps = 7.1
Motor Volts = 13.8
Input (W) = 98.1
Loss (W) = 26.1
MGbOut (W) = 72.0
MotGb Ef(%) = 73.4
Shaft Ef(%) = 68.5
Motor RPM = 31676
Prop RPM = 4799
Thrust (oz) = 24.2
PSpd (mph) = 31.4
Time (m:s) = 10:09



Now for the realworld test Dick...



rmh -> RE: High Voltage Hot Rodding (12/6/2003 7:09 PM)

Well what the motor Calc says and what I see on my little homemade thing is "about" the same.
I also ran thru this with friend Rojecki - who has an arsenal of electric stuff he plays with .
The theory is good and saving amps , I already know, allows use of smaller conductor sizes ( less heat loss)
What I am looking to see---is if by doing this -- I can get good power runs from the cells I have --which are low output types - ( 4-1 6-1)
I know that there is no free lunch - but this one could be a bit tastier -.
I will have to cobble up a teensy batt pack for the radio --
actually - one , single cell Lipo should run it - but to be safe - a 4 cell Nimh - 100 ma pack. I will have to try a couple .



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