More volts less amps ? Im slightly confused.

[liveforphysics]

36v 5kw controller , that's a lot of Amps and parallel packs. The top speed is sure to knock my socks off! For a daily commuter this would be fine at lower amps.

But I hear u on the safer lower voltages and simplicity of a low volt systems.


Thanks guys this has all made me slightly less confused 8)

30v on a 1-turn motor is identical speed/rpm range, identical efficiency, identical power output, identical torque etc as 300v into a 10-turn.

Assuming the same amp rated controller;
More volts will give you better acceleration and a faster top speed.
More amps will give you better acceleration but the same top speed. Although a faster speed uphill.
You can also push more watts through the same wiring at higher voltages without overheating the wiring.

Sounds like its time to re-read the thread and think of electro-mechanical devices in terms of power input.

Yes, for the same sized wire more current makes it hotter, but this is unrelated to what happens inside the motor where only copper fill% matters as everything else balances perfectly.

 

[StudEbiker]

Sorry to poach your thread, but for you guys with more experience, what is a reasonable length of time a MAC can sustain 2k watts?

It is hard to say without more detail. I assume you mean the 6T (or is it 8T?) in 20" wheel on your BikeE, maybe going up a steep grade so as to maintain 2kW. Those are rated for 500W, eh? Ambient temps?

Anyone know a comparable motor to try in the sim?

8T in 20" wheel. I guess for a baseline assume a 75f deg. ambient temp. I have two grades that I regularly climb that are steep, but neither are particularly long. I have just moved into the 2kw power range and want to stay as safe as I can.

 

[Jestronix]

Now I just got to work out where to get a 1 turn mxus, anyone wound one themselves ?

 

[John in CR]

Now I just got to work out where to get a 1 turn mxus, anyone wound one themselves ?

I have 2 turn cromotors available. 17 KV

A 1 turn MXUS wouldn't be a good idea unless you ran it as a mid-drive, or really wanted to run low voltage in small tire. You need plenty of current and still have to stay super conservative with the controller due to quite low inductance. I'd say 1.5turns at a minimum, but 2 would be better.

Zombiess 2 turn would be a fine motor with a. I've run 2 turn hubbies in that diameter. Put it in a 20" wheel and you'll get somewhere close to 60mph depending on your aero with 74V nominal battery.

Hey Zombiess, what's the phase-to-phase resistance on those motors compared to the usual 4 turn and what gauge wire are the phases? The fact that you still have them shows what little people really understand motors and the effect of windings. Shoot me a PM with a special Christmas price for the pair, and maybe I may not be able to resist and build them a sub 200lb long range 2wd road rocket to demonstrate their potential. I've got 24fet controllers on the way with irfp4468 and 4568 mosfets, so I can drive them properly.

John

 

[zombiess]

A 1 turn MXUS wouldn't be a good idea unless you ran it as a mid-drive, or really wanted to run low voltage in small tire. You need plenty of current and still have to stay super conservative with the controller due to quite low inductance. I'd say 1.5turns at a minimum, but 2 would be better.

Zombiess 2 turn would be a fine motor with a. I've run 2 turn hubbies in that diameter. Put it in a 20" wheel and you'll get somewhere close to 60mph depending on your aero with 74V nominal battery.

Hey Zombiess, what's the phase-to-phase resistance on those motors compared to the usual 4 turn and what gauge wire are the phases? The fact that you still have them shows what little people really understand motors and the effect of windings. Shoot me a PM with a special Christmas price for the pair, and maybe I may not be able to resist and build them a sub 200lb long range 2wd road rocket to demonstrate their potential. I've got 24fet controllers on the way with irfp4468 and 4568 mosfets, so I can drive them properly.

John

John, why do you say that about a 1 turn MXUS motor? The wheel diameter makes no difference as long as you can feed it the amps. A Watt is a Watt as far as the motor is concerned. The inductance issue is not as large of a deal as it's made out to be. I have tested numerous 18 MOSFET IRF4115 controllers on these 2 turn motors at 100V fully charged and made pulls until I got the MOSFETs to 100C, which only takes about 2 back to back 0-50mph-0 pulls.

If the controller is kept in PWM I've never had an issue. Just program the China controllers to never exceed 99% PWM and they work fine (at least all the ones I built worked great) with no noticeable loss in performance.

The 2 turn Cromotors are 30uH phase to phase with a resistance 37mOhm. This is lower than the classic but famous X5 2 turn blows your controller in a few feet motor. There is some video of me riding this motor in my thread here. https://endless-sphere.com/forums/viewtopic.php?f=3&t=50763

I spent the last 2 months working in my lab figuring out why controllers blow and how to share current perfectly between parallel devices. I just simulated the board parasitic elements in SPICE earlier tonight with over 20 parallel IRFP4568's sharing current perfectly. I have a good feel for the board parasitics as I modeled an array of 11 parallel IRFP4568's that I built so I could learn more. I don't think I'll finish the 66 MOSFET controller I was going to build because I invented a better design. If I can sort out the gate drive for this I don't know where the physical limit will be. I'm pretty confident I can burst +2000A for > 10 seconds.

Those controllers would be pretty darn wild. With 100V and 2 of these motors in 16" setups you would be >80MPH and you would get there quick. In the video I posted I have one of these motors in a 14" MC rim and that setup rips. I never did feed it the amps it could take though. I originally got this motors to beat up on controllers.

 

[Jestronix]

Share feeding interests me your talking two controllers one motor ? Id love two smaller controllers working the one motor, redundancy would be nice when your 40ks from home. placement of the smaller controllers would be nice too. syncing phase must be the hard part ?

 

[John in CR]

John, why do you say that about a 1 turn MXUS motor?

You're right it's only a controller limitation A 1 turn will be more than twice as hard to drive than your 2 turn motors. I've got a 1.5 turn motor with more stator slots, and I'd never go beyond that, since I will never pay more for a controller than the motor it drives. The electric revolution needs cheaper better controllers, not more expensive controllers with marginal benefits. Controller improvements should advance far faster than battery advances, but both have been agonizingly slow from my perspective.

 

[liveforphysics]

John, why do you say that about a 1 turn MXUS motor?

You're right it's only a controller limitation A 1 turn will be more than twice as hard to drive than your 2 turn motors. I've got a 1.5 turn motor with more stator slots, and I'd never go beyond that, since I will never pay more for a controller than the motor it drives. The electric revolution needs cheaper better controllers, not more expensive controllers with marginal benefits. Controller improvements should advance far faster than battery advances, but both have been agonizingly slow from my perspective.

I completely agree. It's very strange, because the silicon has been improving at a decent rate (faster than batteries at least) and yet 99% of ebike controllers are still antiquated design junk in a box.

The moment someone (like Zombiess perhaps?) makes a compact controller with 1-turn friendly current rise rate capability and a more than a few hundred phase amps on tap for bursts, we can all enjoy much more simple batteries using around 24-36v and having kick-ass performance and efficiency with none of the hassles and corrosion potential of managing big series cell strings.

 

[cwah]

i found out the speedict is the best cheap way to replace a bms:
http://www.speedict.com/

 

[spdas]

Aloha, I am trying to understand this voltage/amp thing and here is where i am at....

OK Volts x Amps -Watts, regardless of whether you are using 24v or 72v into your motor, you will be using the same wattage.

------BUT

Is there not a big advantage to using more voltage and drawing less amperage?
ie smaller wiring to the motor, smaller controller, less heat generated in the motor (although the claim that the heat is the same). Able to use less battery discharge "1-2 C"? plus getting more rpm=speed?

Or am I more than "Slightly Confused"?

francis

 

[HamsterPower]

i found out the speedict is the best cheap way to replace a bms:
http://www.speedict.com/

Oh nice find! Pretty much everything I'd wish for in a BMS except that it's for Android only (no iPhone), and supports smallish series lengths.

 

[Lurkin]

Little confused as to the configuration pictures for that BMS. Is it saying it can take a max (@13S) of 13S15P?

 

[madin88]

It is worth noting that 50V 100A will produce a lot more heat on the rest of the system (wires, etc.) than 100V 50A. Perhaps this is part of the initial confusion.

Actually, it just needs 2x the copper cross section for the 1-2ft between the battery to controller. Then it's exactly identical heating.

The mass and cost of the wire is drastically reduced cost and hassle and engineering than having 2x the cell string to manage.

If we double the current, the cross section needs to be 4 times bigger for keeping losses equal, and not only two times. Its true that a conductor with two times the cross section can carry two times the current, but it still has twice the losses, since P loss = I² x R
Same goes for the controller resistance...

If we now bring up that efficiency of a given motor itself is always the same no matter what turn count, we should always keep in mind that:
it needs 4 TIMES larger wires and 1/4 of mosfet resistance for same produced heat or drive efficiency (referring to previous example with 100V 50A vs. 50V 100A).

I also share your point about simplicity of low voltage BMS and battery wiring and i also would like to see compact and realiable 5kw 30V controller for e-vehicles, but i believe we won't see such because of above reasons.