# Brushed vs Brushless in EV use.



## somanywelps (Jan 25, 2012)

Efficiency: BLDC>AC>Brushed DC

Brushless:
Higher Efficiency
No Wear
Capable of Water cooling.
Significantly more expensive (is this due to the age of the tech or is there a parts reason?)

Brushed:
Lower efficiency
Brushes wear out (how long does this take anyway?)
Air Cooling only option
Less Expensive

Am I missing anything?


----------



## major (Apr 4, 2008)

somanywelps said:


> Brushes wear out (how long does this take anyway?)


It is very difficult, if not impossible, to put a guaranteed minimum number of miles on motor brush serviceability for an EV propulsion motor, especially ones installed by DIYers, and therefore no motor supplier gives this. And don't take my next statement "to the bank". Brushes will likely last 100,000 miles, maybe longer.


----------



## DJBecker (Nov 3, 2010)

somanywelps said:


> Efficiency: BLDC>AC>Brushed DC
> 
> Brushless:
> Higher Efficiency
> ...


Brushed motors aren't inherently more or less efficient. Efficiency is a curve, not a single number, making comparisons more challenging.

In a typical installation, a brushed motor controller requires only a single pass through a semiconductors, while an A/C controller requires two passes and 3x or 6x the number of active elements. An A/C controller also has much more opportunity to drive the motor motor inefficiently.

About the only general statement regarding efficiency is that brushed motors with advanced timing are much less likely to implement regeneration.

Brushes can last a very long time. Or, if the motor is undersized, they might wear out quickly. Replacement effort is largely an access issue, comparable to replacing spark plugs. Spark plug replacement varies from 30 seconds per plug to an all day job pulling the engine in order to access the rear plugs.

The "no wear, no maintenance" claims are bogus. There is always wear and aging, and always things that can wrong. We had our motor apart many times to track down a problem that turned out to be the armature spinning on the motor shaft. We've replaced the bearings, but not the brushes.

Motors of both types are typically air cooled, and most air cooled motors aren't easily changed to liquid cooled.


----------



## somanywelps (Jan 25, 2012)

Then what's the advantage of AC that makes it worth 3x the cost other than regen? Is it the high RPM limit for 1-speed transmissions?


----------



## bjfreeman (Dec 7, 2011)

somanywelps said:


> Then what's the advantage of AC that makes it worth 3x the cost other than regen? Is it the high RPM limit for 1-speed transmissions?


my #1 reason is that if the power stage of a DC fails the motor is connected to the full battery pack, having the vehicle take off like a bullet till the manual shut down is activated.
AC will possibly burn out the motor but the vehicle is stationary.
Next is the KW/kg difference.
in the range of AC Induction motors I use, they are $7K (150KW) to 20K(250KW)
there are some surplus 96KW AC that go for about $2K

Usually the Controller goes for $4K to $8K due to the Power stage. The IGBT goes for $150 to $800 each for 3 to 6 pieces per controller. Of course if Production gets up in the 10 of thousands then these prices will drop.


----------



## somanywelps (Jan 25, 2012)

bjfreeman said:


> in the range of AC Induction motors I use, they are $7K (150KW)


That's the Remy HVH250 or AFM140, isn't it?

What's the cheapest 150kw controller you've seen?

Also a $3000 DC controller and a $4000 DC motor will slap any comparable AC system silly in power.

Has anyone actually had a DC vehicle with a good controller go into runaway?



bjfreeman said:


> Next is the KW/kg difference.


I can't imagine it being more than 50kg difference.

Also are they quieter?


----------



## Qer (May 7, 2008)

somanywelps said:


> Then what's the advantage of AC that makes it worth 3x the cost other than regen?


Who told you that it was worth 3x the cost... 



bjfreeman said:


> my #1 reason is that if the power stage of a DC fails the motor is connected to the full battery pack, having the vehicle take off like a bullet till the manual shut down is activated.


You forgot putting a "may" in there somewhere. It was probably true for old golf cart controllers, but it seems that at the voltages that you usually use in a car the transistors can simply blow up instead because they don't survive the short circuit current. There's been several examples of cheap controllers in this forum that spilled it's intestines all over the engine bay and died an uneventful death.

I think there's been a few runaways too to be fair, but, typically, the best is that the controller doesn't blow up and a well designed controller shouldn't do that. Of course. The modern CPU based controllers where the CPU has a better chance of monitoring the circuit and thus avoid putting the transistors in danger or release the contactors if things go sour will probably also improve the statistics over time... 

Things can of course still go out of control, sure, but so can an AC-inverter. An AC-inverter has much more complex software (since it has to handle the role of the brushes as well) which of course increase the odds for bugs and a bug somewhere in that code could make the controller go wild and crazy.



bjfreeman said:


> Of course if Production gets up in the 10 of thousands then these prices will drop.


Which, I think, hasn't even happened in world history yet. I think the RAV4-EV holds the record of 1484 units produced, as far as I know no other type of electric car has surpassed that number.

I think you have to look at fork lifts or similar to find the 5 digit series productions...


----------



## palmer_md (Jul 22, 2011)

Qer said:


> Which, I think, hasn't even happened in world history yet. I think the RAV4-EV holds the record of 1484 units produced, as far as I know no other type of electric car has surpassed that number.


I thought the 2500 Tesla Roadsters were AC Induction?


----------



## DJBecker (Nov 3, 2010)

Qer said:


> You forgot putting a "may" in there somewhere. It was probably true for old golf cart controllers, but it seems that at the voltages that you usually use in a car the transistors can simply blow up instead because they don't survive the short circuit current. There's been several examples of cheap controllers in this forum that spilled it's intestines all over the engine bay and died an uneventful death.


I'll second that.

We've only had one or two run-away events, all at 12V or 24V during bench testing. At full traction voltage the MOSFET source leads or bond wires fail before the contactor can open. Failure usually involves melted pieces and shattered cases, often with a conductive path from drain to gate.

We tried using a circuit breaker for protection, but it never opened in time. Eventually it weakened and wouldn't remained closed during normal uphill driving.


----------



## bjfreeman (Dec 7, 2011)

somanywelps said:


> That's the Remy HVH250 or AFM140, isn't it?


Not familar with those.


> What's the cheapest 150kw controller you've seen?


the one I designed and built is 250KW, but I think your referrring to commercial. The only two I have experience with is the Siemens and the Allison EP50, which is dual 150KW. The Siemens is $4,000 list.
.


> Also a $3000 DC controller and a $4000 DC motor will slap any comparable AC system silly in power.


Ah but can you Run a DC direct drive to the wheel.
also a DC willl not run an AC motor.
there are many things to compare beside the power a basic controller should do.


> I can't imagine it being more than 50kg difference.


what significance does 50kg have to dollar value.


> Also are they quieter?


Ever heard a 400HP Diesel.
that depends on how the motors were built.


----------



## bjfreeman (Dec 7, 2011)

Qer said:


> You forgot putting a "may" in there somewhere. It was probably true for old golf cart controllers, but it seems that at the voltages that you usually use in a car the transistors can simply blow up instead because they don't survive the short circuit current. There's been several examples of cheap controllers in this forum that spilled it's intestines all over the engine bay and died an uneventful death.
> 
> I think there's been a few runaways too to be fair, but, typically, the best is that the controller doesn't blow up and a well designed controller shouldn't do that. Of course. The modern CPU based controllers where the CPU has a better chance of monitoring the circuit and thus avoid putting the transistors in danger or release the contactors if things go sour will probably also improve the statistics over time...


it is the possibility, so I avoid it.



> Things can of course still go out of control, sure, but so can an AC-inverter. An AC-inverter has much more complex software (since it has to handle the role of the brushes as well) which of course increase the odds for bugs and a bug somewhere in that code could make the controller go wild and crazy.


I agree. the rule in software is if anything changes in code all other code that is dependent on the new code are considered beta.
Any software should be tested thoroughly before being released. That usually take 1-5 yrs.


> Which, I think, hasn't even happened in world history yet. I think the RAV4-EV holds the record of 1484 units produced, as far as I know no other type of electric car has surpassed that number.
> .


you forget production of EV commercial cars that use AC as well things like The EP50 that is in 1,000's of buses


----------



## bjfreeman (Dec 7, 2011)

somanywelps said:


> That's the Remy HVH250 or AFM140, isn't it?


I look these up. i use three-phase squirrel-cage (induction) AC traction motors. they are custom 250KW.


----------



## somanywelps (Jan 25, 2012)

bjfreeman said:


> I look these up. i use three-phase squirrel-cage (induction) AC traction motors. they are custom 250KW.


Custom? That can't be inexpensive...


----------



## bjfreeman (Dec 7, 2011)

somanywelps said:


> Custom? That can't be inexpensive...


it was way below the quote I got in 1999 for a custom one.
luckily this company is into building Traction motors and this is like the low end of the power range for them. They typically deal with 1000KW up.
the production price will be 20K I paid for the tooling and setup and own the rights to that configuration.


----------



## MN Driver (Sep 29, 2009)

somanywelps said:


> Has anyone actually had a DC vehicle with a good controller go into runaway?


Happened to a guy local to me with a Kelly controller a few months ago. Had it parked in the garage. The Warp 11 spun fast enough to dislodge the rotor windings which jammed the motor(good thing it didn't grenade!) and when he came out the Kelly controller was more or less a puddle of black goo. I saw it in person after the guy decided that he didn't want to spend the money to replace the bad controller and motor and gave the parts away and sold the batteries to different people. We couldn't figure out if his contactor was engaged or if it failed shut. It's not a bad idea to have an indicator inside the car to show that the HV is engaged so you know its on when you power the car off because that might have saved this guy grief, possibly at the expense of this happening on the road. Always use good fusing and a quality contactor.


----------



## Ziggythewiz (May 16, 2010)

MN Driver said:


> It's not a bad idea to have an indicator inside the car to show that the HV is engaged so you know its on when you power the car off because that might have saved this guy grief, possibly at the expense of this happening on the road.


Your voltmeter should be enough to let you know when HV is on. Also, a controller shouldn't be able to do any damage when starting full on if there's a precharge.

Maybe that's a benefit of being cheap on everything; I have a manual precharge and a curtis, so if it were to fail on, I would probably hear it whine when the precharge is flipped. It certainly would never complete the precharge, so I would know there's something wrong before engaging the contactor.


----------



## Qer (May 7, 2008)

bjfreeman said:


> it is the possibility, so I avoid it.


Which is fine and dandy and entirely your choise. Noone's gonna force you to choose a DC-system against your wishes, but it's still not good forum behaviour to spread FUD.

Personally I'm more afraid of all them other morons on the road... 



bjfreeman said:


> Any software should be tested thoroughly before being released. That usually take 1-5 yrs.


Um. That's not exactly my experience, not even in the industry these days. It used to be that the industry often used computer systems that were so ancient that they were more or less a living museum. Those days are gone.

Most modern industries today run PCs and Windows. The test cycle is, um, weeks or possibly months if you're lucky. Years doesn't exist on any scale, noone wants to pay for that. Heck, when I worked out in the industry I could even get 15 minute fixes sent to me through e-mail that I downloaded through my cell phone.

Wouldn't surprise me if some of the more capable inverters today run .NET somewhere in the core, them guys at Microsoft is really trying to branch out on every possible market these days. If you're LUCKY they don't have those PCs connected to the office network with Internet access...



bjfreeman said:


> you forget production of EV commercial cars that use AC as well things like The EP50 that is in 1,000's of buses


I didn't forget about them, I didn't know about them. 

That's a system for buses. Isn't that a bit on the overkill side?


----------



## bjfreeman (Dec 7, 2011)

Qer said:


> Which is fine and dandy and entirely your choise. Noone's gonna force you to choose a DC-system against your wishes, but it's still not good forum behaviour to spread FUD.
> 
> Personally I'm more afraid of all them other morons on the road...
> 
> ...


where are you getting the Idea I am using ancient technology?


> Most modern industries today run PCs and Windows.
> 
> The test cycle is, um, weeks or possibly months if you're lucky. Years doesn't exist on any scale, noone wants to pay for that. Heck, when I worked out in the industry I could even get 15 minute fixes sent to me through e-mail that I downloaded through my cell phone.


One of the big Corps I consult for, use Unix and linux.
They consider PC and windows a USer System, not a development system.
I have also consulted with Microsoft on it Campus for Software Application, They have a whole room of machines to run through their testing. Each day the bug list is generated for the software types to fix and restart the test.
and yes it does take a year or more.


> Wouldn't surprise me if some of the more capable inverters today run .NET somewhere in the core, them guys at Microsoft is really trying to branch out on every possible market these days. If you're LUCKY they don't have those PCs connected to the office network with Internet access...


the Reason RISK cpu were designed was to make them faster than a General CPU. They do many things in one clock cycle that even multicore CPU can not match.
to add a few megabytes of .NET would go against the whole principle.
if you take a hello world C compared to one of CPlus there is a 10,000 fold increase in code when compiled.



> I didn't forget about them, I didn't know about them.
> 
> That's a system for buses. Isn't that a bit on the overkill side?


 The Idea is there is more demand for AC motors, outside EV that will bring the price down.


----------



## Qer (May 7, 2008)

bjfreeman said:


> where are you getting the Idea I am using ancient technology?


You're quoting two different things out of context, then blaming me for opinions I don't have.

Eh?



bjfreeman said:


> One of the big Corps I consult for, use Unix and linux.


Still not years of testing behind them. Linux is notoriously suffering from quick pace development. I should know, I switched to Linux -96 and has been working professionally with Linux since then. 



bjfreeman said:


> the Reason RISK cpu were designed was to make them faster than a General CPU. They do many things in one clock cycle that even multicore CPU can not match.


Um. All ix86-CPU's since the Pentium Pro's are, actually, RISCs in the core that just execute CISC-instructions, sometimes several in parallel...

http://sunnyeves.blogspot.com/2009/07/intel-x86-processors-cisc-or-risc-or.html

So they're both CISC and RISC at the same time. On the other hand, RISCs today are so complex that they'd probably be called CISC back in the old days. Or not. Or perhaps they're a hybrid too. It's kinda messed up these days, this RISC-CISC-thingies.

Not that I see the relevance of that for this thread though.



bjfreeman said:


> The Idea is there is more demand for AC motors, outside EV that will bring the price down.


Myep. I think I've heard that argument since I became a member in this forum. Still not holding my breath.


----------



## bjfreeman (Dec 7, 2011)

Qer said:


> You're quoting two different things out of context, then blaming me for opinions I don't have.
> 
> Eh?
> 
> ...


OK you totally lost me.


----------



## Duncan (Dec 8, 2008)

Hi Qer

Don't bother about anything Bj is saying 
I think he makes it all up - 
He has certainly said a lot of dopy things

Don't know if he is still in primary school or in an institution


----------



## subcooledheatpump (Mar 5, 2012)

Try stalling a brushed motor with full current flowing watch what happens

I might have overlooked something but I haven't seen it posted yet. Another advantage of an AC motor, you can actually stall an AC motor and get full torque without destroying it. They do it all the time with elevators and cranes using AC motors.


----------

