[ThomasJ]

I have been in the RC model boats and planes hobby for a number of years but decided to branch out into the world of EVs.
In RC pretty much everyone uses brushless motors, and the majority of those use outrunners for their good efficiency and thermals. I have recently come across some enormous brushless outrunners here for example. I have used lots of these motors in the past through the hobby and would be confident in using a large one like this with the appropriate ESC's and batteries however, nobody seems to use these in EVs (that I have seen). Is there any reason for this?
I am fairly interested in doing an electric boat conversion using said 40kw brushless motor, but don't want to blindly throw money at a lot of new electronics for them to fall flat when I try and use them in the boat.

Thomas

 

[brian_]

"Brushless motor" effectively means a synchronous AC permanent magnet motor driven with square-wave or trapezoidal power. In old-style conversions of cars people use brushed DC series-wound motors, and many conversions have used induction motors (HPEVS is the usual DIY supplier), but the best available technology (commonly salvaged from production EVs) is synchronous AC permanent magnet motors driven with 3-phase sinusoidal AC. So it's not so different. Sinusoidal drive is typically used (rather than trapezoidal drive) in vehicles larger than an e-bike because it is smoother.

Of course an ESC is an electronic speed controller, which is called a controller or inverter (because it's really an inverter with a controller) in EVs. I see that Freerchobby lists "kelly" in the controller spec (with MGM as an alternative) for a couple of their larger motors - other Kelly controllers have been used in DIY car conversions.

Outrunner motors are popular for model aircraft propeller drives because they have high rotor inertia and are suited to high-torque/low-speed applications, but high inertia not a desirable characteristic for cars and cars use a gearbox to operate the motor at whatever speed is required, so outer-rotor motors are rarely used.

I don't know of any technical reason why the proposed motor and controller wouldn't work well in a boat, and with the right prop perhaps a gearbox could be avoided. I suppose a couple of basic observations would be that continuous power rating is more important than peak power, and that motor cooling needs to be considered.

 

[ThomasJ]

That's very interesting, thank you. I have just learned a lot about these things I have been bolting to the front of my model planes for years.

I believe I was talking about induction motors when I was referring to the not brushless type motors I see in a lot of EV conversions, but your explanation has just cleared that up for me. I have just had a quick look at Sinusoidal drive, and I will continue to research it further later however from my brief looking it seems to be a method ESC's use to smooth out motor rotation? Sorry if that is a horrible simplification or completely wrong, it just seemed to be logical from what I was reading.

In reference to the ESC's, I am quite familiar with MGM through performance RC boats however from memory their controllers only go up to 15S Lipo batteries or 55.5 volts which is about half of what I want for the large motors I have been looking at.

This has brought up another question I had. For example, could I choose a much higher KV (of course being rpm/volt) motor and run it at a lower voltage to achieve the same result? In the past, I have always stuck to what they suggest for fear of breaking something. This would be ideal because my rough plan involved using LIPO batteries (potentially a poor idea in EVs though I don't know) and I didn't like the idea of creating a 24s pack by sticking 4*6s packs together in series. It would be good if I could use an MGM 15s controller, and then just opt for 121KV or 80KV options and have to worry a lot less about the batteries. Obviously to achieve the same power on a lower voltage the current would be higher but MGM have some very large ESCs.

I was also hoping to avoid a gearbox, but potentially that is just me being naive. Also yes that is a good point and I agree, the continuous power rating is around 25KW so a little under half and the motors I was looking at all have options for water cooling so I was planning on putting a pickup on the hull somewhere and just feeding it fresh water.

Thank you for your explanations, they have been very helpful.

Thomas

 

[floydr]

How long would the motors last being as light as they are?
later floyd

 

[ThomasJ]

Sorry if I am misunderstanding, but do you mean the weight is important as they have a low no-load current? Because I would imagine the weight of the motor, being 6kg or so, is inconsequential in comparison to the boat's hull being around 300kg?
But the point on duration is very good, as I realise using traditional hobby LIPOs will not work. For example, buying a few turnigy 20,000mah 6s lipos, would leave me with 20 amp hours of battery for something that draws between 100-200 amps or more. If ill be cruising at 100 amps, that'll leave me with 12 minutes of runtime.

I have seen people using old EV batteries like Nissan leaf batteries which have enormous capacities. Maybe it's an idea to try using these. It appears they come in cells, so I assume you simply stack these cells in series to get the desired output voltage.

Thomas

 

[floydr]

In comparing The motor weight to other brushless motors weight They Are seem very light. What is there mean time between failure rate MTBF? I didn't see it listed. There are several models that might work for my mower deck.
Later floyd

 

[brian_]

Sorry if I am misunderstanding, but do you mean the weight is important as they have a low no-load current?

The weight of the motor is just being used as a rough indication of how ruggedly the motor is built, and how much material it contains to absorb heat from occasional high-current operation.

 

[brian_]

I have just had a quick look at Sinusoidal drive, and I will continue to research it further later however from my brief looking it seems to be a method ESC's use to smooth out motor rotation? Sorry if that is a horrible simplification or completely wrong, it just seemed to be logical from what I was reading.

Roughly yes.

The three sets of windings in the stator each produce magnetic fields, which combine to form one resulting field through the stator and rotor (with pole positions). When the controller just turns each winding on or off, the position of the resulting field jumps from one position to the next around the motor. When the controller feeds each winding current which varies sinusoidally, and the three winding currents are evenly spaced around the 360 of a rotation, the resulting field is constant in strength and smoothly rotates in position.

 

[ThomasJ]

The weight of the motor is just being used as a rough indication of how ruggedly the motor is built, and how much material it contains to absorb heat from occasional high-current operation.

Oh I understand, thank you for clearing that up.

In comparing The motor weight to other brushless motors weight They Are seem very light. What is there mean time between failure rate MTBF? I didn't see it listed. There are several models that might work for my mower deck.
Later floyd

And I don't know of the MTBF however I'm sure you can email them to get a more specific datasheet. It is probably made so light as its main application is in enormous multirotors and paramotors, which both have to fly which obviously requires an insanely low mass:thrust.

I couldn't find a source for this but I had a feeling they made motors to order, so you could ask for an inrunner with slightly different specifications (e.g thicker shaft or lower kv).

Thomas

 

[brian_]

But the point on duration is very good, as I realise using traditional hobby LIPOs will not work. For example, buying a few turnigy 20,000mah 6s lipos, would leave me with 20 amp hours of battery for something that draws between 100-200 amps or more. If ill be cruising at 100 amps, that'll leave me with 12 minutes of runtime.

Not only is the runtime too short, the rate of discharge relative to the battery capacity (which is called the "C rate") is too high for the battery to be reliable.

I have seen people using old EV batteries like Nissan leaf batteries which have enormous capacities. Maybe it's an idea to try using these. It appears they come in cells, so I assume you simply stack these cells in series to get the desired output voltage.

Yes, salvaging EV batteries has become a common approach for DIY vehicle conversions, because it makes sense economically and because those EV batteries have the capacity required for an EV.

All production EV batteries are built up of modules, with each module being a combination of several (up to a few hundred) cells. The original-style Leaf modules each contain four cells, in a 2S2P configuration. In the Leaf battery, 48 of those modules are connected in series to form a 96S2P battery; 96S and resulting nominal 360 volts is typical for modern EVs. If you want lower voltage you can connect fewer modules in series, as long as that still gets you enough capacity. Most EVs use fewer modules, so each module contains more cells in series.

 

[brian_]

I couldn't find a source for this but I had a feeling they made motors to order, so you could ask for an inrunner with slightly different specifications (e.g thicker shaft or lower kv).

Some of that supplier's motors are described as having choices of Kv, so they do offer winding alternatives. They probably don't stock every combination, and can wind motors to order within the standard configurations offered.

By the way, essentially no one in the EV world uses the speed-voltage constant (Kv) to describe motors, although it is a standard term which is applicable to some motor types.

 

[ThomasJ]

Roughly yes.

The three sets of windings in the stator each produce magnetic fields, which combine to form one resulting field through the stator and rotor (with pole positions). When the controller just turns each winding on or off, the position of the resulting field jumps from one position to the next around the motor. When the controller feeds each winding current which varies sinusoidally, and the three winding currents are evenly spaced around the 360 of a rotation, the resulting field is constant in strength and smoothly rotates in position.

Oh that makes a lot of sense now, thank you.

All production EV batteries are built up of modules, with each module being a combination of several (up to a few hundred) cells. The original-style Leaf modules each contain four cells, in a 2S2P configuration. In the Leaf battery, 48 of those modules are connected in series to form a 96S2P battery; 96S and resulting nominal 360 volts is typical for modern EVs. If you want lower voltage you can connect fewer modules in series, as long as that still gets you enough capacity. Most EVs use fewer modules, so each module contains more cells in series.

Could I do something similar but halve the voltage and put the remaining half in parallel? I only need 100 volts but would like the extra capacity. I would assume yes but looking at some of the BMS's on the market - like this orion one - I wonder if they have options for configurations like the one I am suggesting. I could just put the modules in parallel and call them a higher capacity but then I worry about balancing trouble.
I was going to try and avoid the topic of batteries on this particular thread by opening up a second more specific question here, however, it has yet to be approved so I'm sure this is fine.

My main point of the other thread was to ask about packs like this on eBay, which seem quite expensive for 24khw. This is only about half of what I need, if the top end of continuous power is 22KW (100v * 220A) that would only last an hour on the water.
I have seen a lot of people making power walls by stacking 18650s themself. Is that a cheaper alternative, or even viable for EVs?

By the way, essentially no one in the EV world uses the speed-voltage constant (Kv) to describe motors, although it is a standard term which is applicable to some motor types.

Oops, something from the hobby that I assumed everybody would use. Is RPM more applicable?


Thanks,
Thomas

 

[brian_]

Oops, something from the hobby that I assumed everybody would use. Is RPM more applicable?

The speed/voltage constant (Kv) and speed are not the same thing. But yes, providing motor specs with speeds is more typical.

Yes, everybody from the R/C world assumes that everyone uses Kv to describe motor characteristics, but it doesn't apply to either the brushed DC series-wound motors which are traditionally used in car conversions, or to the induction motors which are commonly used. It's still valid for permanent magnet motors - just don't expect everyone to be familiar with it, and don't expect any supplier of motors for cars to provide it as a specification.

 

[brian_]

Could I do something similar but halve the voltage and put the remaining half in parallel? I only need 100 volts but would like the extra capacity. I would assume yes but looking at some of the BMS's on the market - like this orion one - I wonder if they have options for configurations like the one I am suggesting. I could just put the modules in parallel and call them a higher capacity but then I worry about balancing trouble.

Yes you can, and balancing is the issue. The usual approach is to assemble two (or more) parallel "strings", with modules connected only series within each string... and then to have separate BMS support for each string.

The early (all but the 63 kWh version) Leaf batteries are unusual because their modules provide large terminals to connect at every cell level, so they can be wired in parallel without needing to resort to multiple strings.

 

[ThomasJ]

The speed/voltage constant (Kv) and speed are not the same thing. But yes, providing motor specs with speeds is more typical.

I understand, I meant the resultant motor speed once given the voltage ill be using.

The early (all but the 63 kWh version) Leaf batteries are unusual because their modules provide large terminals to connect at every cell level, so they can be wired in parallel without needing to resort to multiple strings.

Is the average price for a 24kWh pack from a Nissan leaf around £2000 or have I just been looking in the wrong places? And if so, is there any cheaper alternative for example using individual 18650 cells or getting them from scrapped nissans more directly?