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BrianG · 02.09.2006, 07:12 PM

Go to http://www.bk-electronics.com/

- Enter the flag for language of choice.
- Click on the left motor at the bottom center
- Select Series 20
- Select Dimension

All it says there is the voltage, max rpm, and current range for each size can. It's not really useful as wattage is V x A and at 40v and 120A (for the XL), that's 4,800 watts - substantially higher than I would think that small can could dissipate. Also, it would depend on the number of turns.

So, in an attempt to extrapolate the wattage, I would take that 120A as the worst case amperage at the lowest turn count (6). Then, assuming that is when turning at the max rpm of 80,000. At a Kv of 2501 (which is the rated kv for the 6XL), that's about 32v. 32v x 120A is 3840W, but most people won't run these that high. Anyway, 32v/120A = .2667 ohms average. Divide that resistance by the number of turns (6) to get the "ohms per turn" (I'll call "ohms per turn" "R/T" for short), which is .0444 R/T.

Now, taking the 8XL as an example, the total resistance would calculate to .0444 R/T * 8 turns = .355555 ohms total. Take whatever voltage you are running, say 18 cells (21.6v) and divide them to get current: 21.6v / .3555ohms = 60.76A. Then multiply the current and voltage to get wattage: 60.76A x 21.6v = 1312W. The total rpm would be kv x 21.5V = 40,313 rpm.

60.7A for an 8XL sounds a bit low to me, but the whole calculation is built on a lot of assumption anyway. I didn't even take the fact that these motors run 3-phase A/C voltage into consideration - that would've given me a headache. :)

Yeah, I know; that was useless - but I was bored!

	(#3)
BrianG RC-Monster Admin Offline Posts: 14,609 Join Date: Nov 2005 Location: Des Moines, IA	02.09.2006, 07:12 PM Go to http://www.bk-electronics.com/ - Enter the flag for language of choice. - Click on the left motor at the bottom center - Select Series 20 - Select Dimension All it says there is the voltage, max rpm, and current range for each size can. It's not really useful as wattage is V x A and at 40v and 120A (for the XL), that's 4,800 watts - substantially higher than I would think that small can could dissipate. Also, it would depend on the number of turns. So, in an attempt to extrapolate the wattage, I would take that 120A as the worst case amperage at the lowest turn count (6). Then, assuming that is when turning at the max rpm of 80,000. At a Kv of 2501 (which is the rated kv for the 6XL), that's about 32v. 32v x 120A is 3840W, but most people won't run these that high. Anyway, 32v/120A = .2667 ohms average. Divide that resistance by the number of turns (6) to get the "ohms per turn" (I'll call "ohms per turn" "R/T" for short), which is .0444 R/T. Now, taking the 8XL as an example, the total resistance would calculate to .0444 R/T * 8 turns = .355555 ohms total. Take whatever voltage you are running, say 18 cells (21.6v) and divide them to get current: 21.6v / .3555ohms = 60.76A. Then multiply the current and voltage to get wattage: 60.76A x 21.6v = 1312W. The total rpm would be kv x 21.5V = 40,313 rpm. 60.7A for an 8XL sounds a bit low to me, but the whole calculation is built on a lot of assumption anyway. I didn't even take the fact that these motors run 3-phase A/C voltage into consideration - that would've given me a headache. :) Yeah, I know; that was useless - but I was bored!