Wattage of Wanderer motors
 

Hey guys,

I couldn't locate the power rating of the various wanderer motors in the web store on this site. But ideally I'd like to be able to calculate the power levels of the various motors with varing cell counts. How would I do this? All I can find is the KV rating.

-Rob

well i've heard that the XL motors are capable of close to 1800 watts not sure about the others

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!

The watts are limited by the cells. A good gp cell supposed to produce a 100 watts.

A good equation for power output is Volt(amps) - resitance(amps)^2 - volts(noload current).

Thanks guys--this helps quite a bit. I'll have to create an excel spreadsheet with graphics to comprehend it all!

For my case I'm only considering XL cans. I'd just like to see the power cross over for higher turn motors (10xl - 11xl) with lower cell counts (12) and see where they start producing some serious power. I'm thinking of perhaps an 8xl - 10xl, but starting with 12 cells, and then switching to lipos to drop some weight and add some voltage later on :)

-Rob

Brian;

You can not determine the r/t value by dividing one motor and multiply it with the turns of another. the more turns a motor has, the thinner the wires will be. with this knowledge, you'll understand why a low turn motor is able to take more A's than a high turn motor.

I once saw a trustfull calculation of an 8XL, and according to that it takes 2200 watts, at a 92 percent efficiency so 176 watts is lost in the motor.

When you lose this many watts in a motor where does it go? Is that why the motor gets hot.

Exactly, Coolhand. The lost energy is heat.

Bingo Leroy!

Yeah, I know it's not right. It was based on a lot of assumption since the parameters aren't usually available. A big assumption was that all the XLs used the same guage wire, so the resistance per turn would be calculated. It was a "tongue-in-cheek" response, but I guess the intended humor was lost. :)

Lol, i hear you..

They don't run AC either.. It's a PWM DC...

Jokes too need some truth.. Right Daniel?? (who is dancing naked on the table when he gets a package filled with new toys from Mike)

From what I have seen. They accually do use the same guage wire. The just wrap more of them around in the case together. But it is like running a lower guage wire in a lower turn motor.

While PWM DC is not traditional sine-wave AC, the voltage does alternate from the motor's perspective, just with square-ish waves (there is some time needed for the low to high transition, albeit small). It was just easier to express it as AC.

Now, as to Daniel's (who is that btw?) dancing habits: that's wayyy too much information! :)

i agree :eek: :eek:

daniel is our very own danfi.

Daniel is aka dafni aka dafnerd.
There may be a video of that dance somewhere. ;)

i dont know if i want to see it

and for this very reason, the controller isn't 100 percent efficient.

At DC_on, the fetts are at their lowest R. But i guess you knew this. ;)

Yeah, I did. :)

Really though, I think the controller almost has to add a little time to go from on to off or vice versa, otherwise the back EMF spike from a perfect square wave would be very bad on the electronics! So, I guess that little bit on inefficiency is probably good in a way. I wonder if these ESCs use avalanche diodes to prevent such a thing? I don't even have my ESC yet (but was ordered today!) and already I'm planning to study the circuitry!

I don't know the name for it anymore, but there are diodes that create a near dead short if they are above their voltage (available in a large variaty) and ara capable of killing quite some power (peaks) and are really fast.

I talked about it with schulze, because of their 'loose contact' issue, but he put his head in the sand, eversince his controller is the most flawless controller available..

my idea was to use them on the motorside and on the battery side. A rather easy mod. but then his 'loose contact' story wouldn't be adequate anymore..

Yeah, there are several components that do this: MOVs, avalanche diodes, zener diodes, etc. Gotta be careful though, some components (avalanche diodes) actually generate RF noise. Since the motor wires pass AC (I know it's PWM, but it's still AC), maybe a $0.39 MOV would be the best bet. Something with a breakdown rating of about 1.5x the max battery voltage should work fine. And I would just put them across the motor leads since the motor is what creates that back EMF. There isn't anything in the battery side that would benefit so I don't think I'd put anything there.

It had another name, i will check my electronic guru friend..

schulze said that the loose connection from the batteries get the controller on a higher voltage, which causes the all familiar schulze meltdown thinking about it as logical as possible makes me wonder how a motor can produce a certain voltage, higher than the one that was needed to put it on that rpm.. a perpetuum mobilee generator perhaps...

Hey Serum. How can Schultze say they're controlers are flawless when they have a "loose connector" problem?

Doesnt every company think or atleast say they have flawless products?

Pity schulze is too stubern... I've got a rather large collection of smoked controllers that prove different though..

@brianG, they are called TRANCIL diodes..

I've never heard of such a thing.Are you sure it's a "Trancil" diode.

no, it's a transil, do a search for them on google.. they are the ones you want to use.