# DC Brushless EV project progress



## rwt33 (Dec 4, 2008)

Hi all, great to join at last.
I'm a few months into an EV project with the motor + controller mostly done.
Being an electrical engineer I managed to source an awesome high power DC brushless (AC but not induction) motor with following specs:
10kW rated continuous, 750% short term over rating (75kW)
250Nm torque
~25Kg mass

I've built up a 100kVA inverter/controller and have spent last few weeks getting motor turning and working. I now have selectable torque/speed control with full regen.

The next stage is the donor vehicle and batteries.
For batteries I have a contact in Hong Kong who is sourcing me 108 40AH ThunderSky batteries (plus few spare) providing ~14kWh. I've got a prototype modular BMS which can monitor/shunt 12 series connected batteries. As many as required can be connected onto common data bus to read each cell voltage and shunt each cell. Got 9 350 Watt power supplies on the way for charging which gives total of 3150 charge power charging at 0.17C (~6 hour full charge).

I'm finding it a slow game trying to find a suitable donor vehicle. I want a nice light weight one (doesn't need to be large as I'm using light weight LFP batteries), something like an old Starlet (RWD) or Charade (although not sure if there's enough room in engine bay as the motor's quite long). Keeping my eyes open for options. Any suggestions would be greatly appreciated! I'm planning on purchasing eaither blown engine or still running in the next few months

Any comments and or suggestions appreciated. Also, I'm keen to get involved with any EV events


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## frodus (Apr 12, 2008)

how's the cost on the motor"

what kind of size? weight?

are there smaller ones in the 6.7" category?


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## rwt33 (Dec 4, 2008)

Hi frodus,
thankfully the motor was a freeby. Was going to be chucked out here at work and was too good to let go.
The motor casing is about 460mm long, although about 150mm of it is for encoders etc. Diameter of 200mm. Weighs in at about 25 kilos.
That length means that it won't fit in most fwds sadly. 
I'm looking for something small and light weight. It's a shame there's no Meyers NnGs around as I'd love to be able to put it in a light weight, single seater vehicle!
http://evfr.net/coppermine/displayimage.php?pid=211&fullsize=1 looks good too!

A pic of the motor is attached. Note the low current RGB cables to the left and the black encoder cable. The stainless motor-looking thing is an old resolver that was replaced with an optical encoder


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## rwt33 (Dec 4, 2008)

*battery update*

Have just ordered 120 ThunderSky 40Ah LFP batteries (through a contact in Hong Kong). Have decided on battery management system and charging.
Time to buy a car!


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## samborambo (Aug 27, 2008)

Hi Robert,

Pretty exciting seeing kiwis building their own 100kW BLDC drives. Can you share the schematics and build log? I'm really keen on doing something similar.

I'm an electrical engineer too but I haven't seen any great deals on BLDC motors. I assume you sourced them through work. Are there any more available? 

Cheers,

Sam.


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## linz (May 18, 2008)

fantastic work, if your not planning to commercialise your designs would you consider posting them in a similar way as open source are posted?(perhaps under GPL if it needs get that formal).


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## rwt33 (Dec 4, 2008)

Hi,
In regards to commercialising, I have no intention to commercialise. I'll leave that to the big guys. I've come to acknowledge that this project just won't have what it takes to become commercial. Not to mention I don't have half a billion $ to have a stab at becomming commercial.

In regards to block diagrams, schematics etc I'm very keen to offer insight in to the project details but with one tiny exception: Some of the hardware ie the board that has the DSP, FPGA, level shifting etc (only the ones that directly control the motor) I've grabbed from work and are confidential. BUT, that said, there's absolutely nothing overly tricky about them and all the circuit blocks are standard types of circuits. A solution that won't violate work's IP and that will also assist in understanding will be if I provide block diagrams and schematic snippets where necessary. The snippets themselves will explain how each block works but won't be direct copies from our documents.

I'll keep you all posted

Rob

PS the ship with my 120 40Ah ThunderSky LFP batteries was due to set sail on the 9th of Jan 09 so hopefully they should be on route already


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## samborambo (Aug 27, 2008)

Robert, I've done some switchmode design in the past and embedded programming. I'd be keen to help fill in the blanks.

Here's an idea; if you're happy for your work (not your company's) to be in the public domain, how about we 'sourceforge' the design? Keep it under the GPL open source license, etc.

Sam.


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## rwt33 (Dec 4, 2008)

*Finally got a donor vehicle*

I've finally bought my donor vehicle: A 1990 Toyota MR2 auto in mint condition. Just got it on Saturday and drove it back home. Goes like a dream, they really are a drivers car (though I may be biased...)
Found the full manual (mech + elec) online and also a heavily documented set of pages on how to remove the engine (dropping it out the bottom). Am planning on removing petrol engine in a month or so.
Batteries are well on their way and are due in to port on the 29th of Jan.
Have been busy developing software for the center console PC which will display motor parameters such as current, power, mode (torque, speed, position control), battery conditions etc. which required developing a high speed (1M baud) comms link between the motor controller and PC. Only a few thousand lines of code to go!
Investigations into the onboard supplies (12v for accessories), 3kW charger, and battery management is well on the way too.


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## Jens Rekker (Oct 26, 2007)

The MR2 is a good conversion glider. What makes it special is the engine / transmission bay between the passanger compartment and rear boot. There is a really useful amount of space and it's shaped just right. Dave Faigan managed to get 10 12V deep cycle batteries into his conversion of an older shape MR2 recently. It seemed to balance well for weight.

The power steering pump is available as an electrical unit apparently, I remember dimly from some other discussion. Dave didn't get that far as polishing up the road legal side of things, he stripped the electrical gear out of the MR2 in favour of his MGF project.

Good luck with the conversion. Dave and I would be curious to see some vids eventually.


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## rwt33 (Dec 4, 2008)

Yeah the MR2 is ideal for many reasons. The space for batteries is definately one biggie. I'm hoping to mount my 120 40Ah Lithium iron phosphate cells in the engine bay and also under the bonnet (put the space saver tire behind the passenger seat).
The eletro-hydraulic power steering was also a great help not having to worry about making some custom power steering pump solution.
To top it off, as all the compartments for mounting batteries are isolated from the passengers, I don't need to go to the extent of having to make explosive-proof containers with ventaltion for the batteries.
With any bit of luck I'll still have the boot space empty.
Will keep you all posted


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## Jens Rekker (Oct 26, 2007)

Hi Robert
Agree with the MR2 advantages that you mention. Just bear in mind that I had a slightly different interpretation on the requirement for explosion-proof vented battery box in my own EV's certification. I have 18 lead acid batteries in their own "box" behind the ute's cab and another six under the bonnet sitting in battery racks.

As the current draft guideline for EV conversion in NZ is written, any battery needs to sit in a vented box. Not ifs not buts. At one stage in my certification process, they where talking about me needing to place all six engine bay batteries in special vented boxes or alternatively I could make all gear in my engine bay intrinsically safe (i.e. spark-proof). In the end some robust discussion and some calculations of the air volumes and Lower Explosion Limit hydrogen concentrations turned around the need for special venting in the engine bay. I still had to install plastic boxes around each battery rack to contain acid spillage.

The draft guideline makes no distinction between flooded lead acid, sealed, gel, AGM or LiFePO4 batteries. That's despite the fact that only the flooded lead acid batteries present any real spillage or explosive gas generation risk. It might pay to select you certifier early and start talking over these matters. The certifiers have a lot of room for using their discretion. However, where they decide against following the guideline they need to be convinced of the wisdom of doing it differently, because thay carry personal liability on each and every conversion.


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## rwt33 (Dec 4, 2008)

Today I am one very happy boy. My 120 40Ah Thundersky LiFePoO4 batteries have just arrived. And boy are they tiny! You can study dimension documents for hours but you never get a real sense of their size until you really see them. I'm feeling pretty confident now that I should be able to fit all 120 of them in the engine bay and under the bonnet, leaving the boot free


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## samborambo (Aug 27, 2008)

Robert, what decision did you come to for the 12V converter? I've been thinking that an ATX computer power supply could be a good option if you remove the front end rectifier and filter. Use one that doesn't have PFC built in.

I'm keen on designing a 70kW inverter based around a dsPIC and a 1200V/100A IGBT six pack that I picked up off trademe a while back. The main thing I keep stalling on is what topology to use for the level shifting and gate drive. It seems to be the most complex part! I'd appreciate any advice you may have.

Also, snubber design for the IGBTs. I've never designed snubbers before. Do you have any good reference material on their design?

Cheers,

Sam.


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## rwt33 (Dec 4, 2008)

Hi Sam,
Re 12v supply: Depending on your bus voltage, ATX power supplies as you mentioned are great. I've used them before for running off DC for EVs without any problem. The guys at www.wellforces.co.nz sell a great range of power supplies at really low prices, and there's a huge range of powers and voltages. To top it off, they have a trimpot for adjusting the voltage (ie push a 12v up to 13.5v). Sadly I can't use any of these as my bus voltage ranges from 320v to 510v which is outside the range of supply's DC bus (~180 to 380v). Thankfully at work we're designing a 2*1.8kW isolated charger for charging super caps, and am hoping to get my hands on one of the prototypes and will rewind the transformer and change the rectifier to give me 13v (prob bout a kilowatt).

Re motor drive/inverter: I was lucky enough to be able to grab a semikron SkiM module which already had isolated gate drives. We also build isolated gate drives at our work. That said, Semikron and others build isolated gate drives if you don't feel like building one yourself. If you build one yourself it can be a bit tedious as you need 6 isolated supplies for each driver plus signal isolation

Re IGBT snubbers: you don't need them. The bipolar transistor characteristics of IGBTs mean that for most applications (ie inverters, motor drives etc) you don't need snubbers. As for any inverter though, you do need a healthy amount of decoupling caps (ie thin film) close to the module on the DC bus side, plus a fairly large bulk (electrolytic) cap to handle the ripple. I'm looking at probably at least 3000 uF at 600V!

Hope that helps,
Rob


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## rwt33 (Dec 4, 2008)

*Quick update*

It's been a wee while since I posted an update but I've been quietly moving along with progress.
In addition to the motor controller I have completed an isolated 1kW DC/DC converter, 8kW PFC charger and BMS.

The DC/DC is a 300 to 600V input, 15V (adjustable) output resonant converter. It's based on the UC3875 IC.

The charger is a relatively simple boost converter. The unity power factor controller and charge control are done in the same DSP as the motor controller using spare PWM and ADC channels. The code generation tools (from simulation) allowed for rapid development and implementation so that as soon as the hardware was built it was working in a couple of days. Was good fun testing with half a dozen large heating elements to get rid of the 8kW of juice!

The BMS has been the most time consuming and expensive part of the whole project to date. But it's incredibly rewarding now that I've finished the 20 balance boards (each one does 6 cells), the controller board with 10 LTC6802 devices and the aux micro for controlling the whole lot. The micro now periodically measures all the cell voltages and I've written a crude BMS module to perform balancing when charging. I've got a nice tech-app (c# on the PC) that can read all 120 of cell voltages from the aux controller and turn on/off the balance resistors. And just for fun I wrote a quick sequencer that flashes all the balance resistor LEDs. You can see them at http://www.youtube.com/watch?v=Yi118U_yXIc

Next step is to hook all the components together! It's going to be a mammoth amount of work as all the different controllers have to talk to each other but I've already gone a fair way to design and simulate (on pc) the basic comms methods. More to come soon!

Rob


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## the1cyrus (Aug 6, 2009)

Did you start another thread somewhere? I'd like to see what progress you've made. I would like to do an ev build sometime soon as well.


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## kiwifiat (Feb 3, 2009)

*Re: Quick update*

How about another update?



rwt33 said:


> It's been a wee while since I posted an update but I've been quietly moving along with progress.
> 
> Rob


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## cdichter (Dec 17, 2012)

I propose that rather than making huge brushless motor controllers, we use a low power controller to control solid-state-relays to handle the high-current switching?

That should make these more field repairable, and we can separate the high heat of the switching from the delicate controller electronics. Does that make sense?

--Carl Dichter


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