[MalcolmB]

I just came across this German start-up today while searching for lower voltage alternatives. I'm curious to hear the opinions of those with more electrical engineering insight than me.

https://molabo.eu/technology/

Extract:
ISCAD describes a paradigm shift: 48 V instead of 800 V and aluminum bars instead of copper coils. Every single bar of the stator cage is supplied by a dedicated power electronics unit. The number of pole pairs can be varied. The result is a virtual gearbox.
Another special feature of the construction is the integration of the power electronics in the motor through which an optimal utilization of the machine volume is achieved.

The company looks to have good credentials and has just started production of its first motors.

I can see some significant benefits in a low-voltage alternative (safety, simpler BMS) especially for DIY builders, but understand the arguments for high voltage (efficiency, weight saving). I'd just like to understand how this approach gets round the problem of I2R losses. I see the motor has an integrated controller, presumably to keep conductor lengths as short as possible. I guess it would also require the battery to be as close as possible to the controller. Comments?

 

[brian_]

It does make sense in some ways, and I had been thinking of a similar configuration, but I doubt that they have built even one fully functional prototype. It could be that the only part they have made is that branded end cover. They appear to have pasted the lettering on the side of that ski boat in a photo editor - the real boat could be running a gasoline inboard, although apparently they used an electric boat from my-Electroboat. Despite their insistence that they demonstrated a boat with their motor, they show a photo in a boat... without the motor visible! I call PR nonsense. And if they have really started production, why not show it? I believe that despite the news release title, they are only "going into production", which means "we really can build one if someone just gives us enough money".

I suppose that seem very sceptical about this, but the stupid and dangerous claims of superior safety really bother me. No, 48 volts is not "safe to touch": do you randomly grab your car's starter battery terminals and let metal objects touch them together? Higher voltage is not unsafe in boats any more than it is unsafe anywhere else, and ships routinely use several hundred to thousands of volts in their propulsion systems.

Back to the technology... The controller needs to be closely integrated with the stator because there are so many phases. It's presumably under that pretty purple end cover.

The low voltage doesn't seem like a good idea to me. Sure, a single bar is easier than a few turns of wire, but you end up with a huge current at a low voltage, which is much more expensive in electronics and much less practical in DC link wiring than the same power at high voltage with low current. A more sensible design would be to use bar winding like the BorgWarner HVH and GM EV motors such as those in the Spark, Volt, and Bolt, just with fewer turns connected to each of more inverter channels instead of just half a turn each at stupid current levels. Yes, DC link cables (battery to controller) would need to be massive (80 kW / 48 V = 1667 A), so keeping them short would be critical.

One way to picture how this could work is to look at a typical brushed DC motor, flip it inside out so that the many winding segments are in the stator instead of the rotor, and imagine each of them separately powered instead of connected in series with each other. The voltage across each winding segment (a single turn in their case) is obviously small. The field form could be non-sinusoidal if desired - a brushed DC motor essentially just switches each segment on in one polarity, then briefly off (during the brush overlap across commutator segments), the on in the other polarity, then off... in a rolling box wave. This would probably work with an induction rotor (rather than the more obvious permanent magnet rotor), so they can change the number of poles - as long as there are enough bars on it, I assume that an induction rotor will work regardless of the number of stator poles - but the datasheet describes a typical reluctance-assisted PM synchronous rotor... which makes little sense to me with a variable number of poles.

 

[MalcolmB]

Thanks for your detailed reply Brian. I agree that the company seems rather PR heavy and light on real-life examples, although they do have some YouTube videos showing the motors in a lab setting and in prototype car conversions. They seem to be focusing on boat conversions now, not sure why.

I was a little dubious about their claim of improved efficiency for the controller, without any mention of whole system efficiency, but I'll keep an eye on this motor just out of curiosity. Personally I'd like to see more low-voltage motor/controller options available, even at the cost of some efficiency loss, as I believe it would make the conversion scene much more accessible. I agree that 48V is not completely safe, but it seems considerably safer to me than 400V when working on a car.

 

[brian_]

Thanks for your detailed reply Brian. I agree that the company seems rather PR heavy and light on real-life examples, although they do have some YouTube videos showing the motors in a lab setting and in prototype car conversions.

Ah, yes, YouTube: the home of serious corporations. It is good to know that they have actually built something.

They seem to be focusing on boat conversions now, not sure why.

I was a little dubious about their claim of improved efficiency for the controller, without any mention of whole system efficiency, but I'll keep an eye on this motor just out of curiosity. Personally I'd like to see more low-voltage motor/controller options available, even at the cost of some efficiency loss, as I believe it would make the conversion scene much more accessible. I agree that 48V is not completely safe, but it seems considerably safer to me than 400V when working on a car.

Three guesses:

• boats are less regulated than road vehicles
• 50 kW seems like a decent amount in a boat (at least one as large as most people are ever likely to own)
• the combination of electricity and water is scary to people, so the "safe" low-voltage approach is especially appealing there

I was a little dubious about their claim of improved efficiency for the controller, without any mention of whole system efficiency, but I'll keep an eye on this motor just out of curiosity.

I'm more than a little sceptical. High current at low voltage is inherently bad for efficiency.

Personally I'd like to see more low-voltage motor/controller options available, even at the cost of some efficiency loss, as I believe it would make the conversion scene much more accessible. I agree that 48V is not completely safe, but it seems considerably safer to me than 400V when working on a car.

That perception is important. In reality, has anyone heard of anyone having an injury incident working on an electric car, even though many people doing this have no idea what they're doing?

 

[olegil]

It does make sense in some ways, and I had been thinking of a similar configuration, but I doubt that they have built even one fully functional prototype. It could be that the only part they have made is that branded end cover. They appear to have pasted the lettering on the side of that ski boat in a photo editor - the real boat could be running a gasoline inboard, although apparently they used an electric boat from my-Electroboat. Despite their insistence that they demonstrated a boat with their motor, they show a photo in a boat... without the motor visible! I call PR nonsense. And if they have really started production, why not show it? I believe that despite the news release title, they are only "going into production", which means "we really can build one if someone just gives us enough money".

I suppose that seem very sceptical about this, but the stupid and dangerous claims of superior safety really bother me. No, 48 volts is not "safe to touch": do you randomly grab your car's starter battery terminals and let metal objects touch them together? Higher voltage is not unsafe in boats any more than it is unsafe anywhere else, and ships routinely use several hundred to thousands of volts in their propulsion systems.

Back to the technology... The controller needs to be closely integrated with the stator because there are so many phases. It's presumably under that pretty purple end cover.

The low voltage doesn't seem like a good idea to me. Sure, a single bar is easier than a few turns of wire, but you end up with a huge current at a low voltage, which is much more expensive in electronics and much less practical in DC link wiring than the same power at high voltage with low current. A more sensible design would be to use bar winding like the BorgWarner HVH and GM EV motors such as those in the Spark, Volt, and Bolt, just with fewer turns connected to each of more inverter channels instead of just half a turn each at stupid current levels. Yes, DC link cables (battery to controller) would need to be massive (80 kW / 48 V = 1667 A), so keeping them short would be critical.

One way to picture how this could work is to look at a typical brushed DC motor, flip it inside out so that the many winding segments are in the stator instead of the rotor, and imagine each of them separately powered instead of connected in series with each other. The voltage across each winding segment (a single turn in their case) is obviously small. The field form could be non-sinusoidal if desired - a brushed DC motor essentially just switches each segment on in one polarity, then briefly off (during the brush overlap across commutator segments), the on in the other polarity, then off... in a rolling box wave. This would probably work with an induction rotor (rather than the more obvious permanent magnet rotor), so they can change the number of poles - as long as there are enough bars on it, I assume that an induction rotor will work regardless of the number of stator poles - but the datasheet describes a typical reluctance-assisted PM synchronous rotor... which makes little sense to me with a variable number of poles.

48V is below 50V, and thus a part of the "extra low voltage" definition of IET and IEC. EU does not define it specifically, but has regulations for "low voltage" where anything between 50-1000V AC and 75-1500V DC is "low voltage" and below that, well you can do a lot more when you don't need to comply with EU regulations.

Extra-low voltage - Wikipedia

en.wikipedia.org

Low voltage - Wikipedia

en.wikipedia.org

Low Voltage Directive - Wikipedia

en.wikipedia.org

High voltage - Wikipedia

en.wikipedia.org

In short, there are some absurdly good reasons for staying below 48V AC, most of which are called regulations.

 

[brian_]

In short, there are some absurdly good reasons for staying below 48V AC, most of which are called regulations.

Right: regulations, not safety. If in your location there are regulations that are expensive and difficult to meet, then there is an advantage to staying just below the voltage which triggers them. In all of the builds in this forum, has anyone found a problem with that? Has anyone had to do anything to handle a 360 volt pack that they wouldn't have reasonably done with a 48 volt pack? Does anyone find the requirements of the 240 volt world of home wiring onerous?

 

[OR-Carl]

Has anyone had to do anything to handle a 360 volt pack that they wouldn't have reasonably done with a 48 volt pack?

I feel like you are saying that any voltage is safe, as long as you are being safe . The fact is, mistakes happen, and the consequences of those mistakes go up with the voltage. The consequences of touching a sweaty, bare hand to each pole of a 48v battery is not going to be the same as if it was 360v.

I do not have any actual training with high voltage, so I treat it with an abundance of caution. I cringed watching a battery tear-down where the guy is bare handed and using bare tools in the battery box. And what is the first thing he does in there? He pulls off all the insulators, and doesnt put anything down to prevent dropped tools from shorting out a module! It might not be a life threatening risk, but there would have been fireworks if he had shorted one of those modules.