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Post up a thread for your EV. Progress pics, description and assorted alliteration
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Post by Squiggles » Fri, 09 Apr 2010, 02:08

What are it's dimensions?

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Post by Speedily » Fri, 09 Apr 2010, 02:27

505/205 and 160 high

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Post by Squiggles » Fri, 09 Apr 2010, 02:29

Thanks, I figured it must be pretty big but you can't tell in the photos I have seen.

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Post by Nevilleh » Fri, 09 Apr 2010, 13:24

a4x4kiwi wrote: Have you pulled it apart already? Image


Yes, dismantled the entire thing now. Still to clean up the power board - remove silicone and de-solder the pads where the IGBTs were (I just cut their legs off).
I have repaired the controller board and it is operating again. It actually runs off 15V derived from a regulator on the power board, so I have just connected it to my bench power supply. Generates nice pulses which vary in width as I rotate the throttle pot.

I am concerned about the lack of current sensing though.

The evnetics thing does look nice, but what a price! I can't bring myself to pay that much for a motor controller.
Last edited by Nevilleh on Fri, 09 Apr 2010, 03:26, edited 1 time in total.

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Post by EV2Go » Fri, 09 Apr 2010, 16:20

You only get what you pay for... mind you I am investigating all options to buy the cheapest one I can.
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Post by Nevilleh » Fri, 09 Apr 2010, 16:32

I have a very nice LogiSystems controller, nearly rebuilt, that can be yours for a very competitive price!


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Post by EV2Go » Fri, 09 Apr 2010, 16:52

Nice try Image I meant the cheapest Soliton1 I can buy.

Unfortunately I don't have the electrical understanding that many of you guys on the forum have, I try to follow it and sometime partially understand it, but I am compelled to buy the best that I can to avoid doing things twice.

I am hoping to play catch up on the fabrication side of things which is where I am better suited.   

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Post by Nevilleh » Fri, 09 Apr 2010, 17:22

Well, I have put so much into this LS controller now taht it is almost a family member!
Image

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Post by EV2Go » Fri, 09 Apr 2010, 17:40

I really envy you guys, I would love to get my hands dirty building my own controller but you really have to know and except your own limitations. In nearly thirty years of driving I have only ever bought one reconditioned engine for a car I owned, and that was purely a time thing for a car I was selling.

Life experiences have taught me there is only one person in this world I can trust to do it right and that is me. While I don't foresee any issues with the 12v stuff (even I can manage that) I have to buy off the shelf parts for the EV side of things.

Since I have no control over the stuff I have to buy, experience has taught me that by the time you try to do it on the cheap, it will almost always work out dearer than buying the best to start with.

On the plus side at least I get to build the vehicle :)

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Post by antiscab » Fri, 09 Apr 2010, 17:41

next stop current limiting, etc ..... profit

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Post by Nevilleh » Fri, 09 Apr 2010, 17:54

I have ordered all the parts for the Cougar controller and it strikes me that the Hall effect current sensor used in that could easily be added to the LS thing and used to do proper current limiting. That would make the thing fairly bullet proof, especially if I reinstate the temperature sensor as well.

I do wonder about the expertise of the LS people.

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Post by EV2Go » Fri, 09 Apr 2010, 17:58

EV2Go wrote: Life experiences have taught me there is only one person in this world I can trust to do it right and that is me.


We learning yet Image the very same statement probably applies to you too Image

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Post by Nevilleh » Sat, 10 Apr 2010, 14:03

I am a bit puzzled by this motor controller. I can find nothing that senses current and yet the set up instructions refer to changing the current limit by adjusting one of the pots. I suppose they really just set limits to the duty cycle and the current flow will depend on the load.
Haven't played with the adjustments yet.

I have just built the world's most expensive light dimmer! I have the controller board driving a single IGBT from a 15V supply and a 12V 50W halogen lamp connected as a load. You can control the brightness very nicely!

Some people might be interested in the gate drive waveforms. Shown below. The first is with a 200 ohm gate drive resistor and the second with 50 ohms. The trace labeled "Drive" is the output of the controller board and the one labeled "Gate" is straight onto the gate pin. Interestingly enough, I connected a 350mm length of wire between the controller board and the gate resistor (ie extended the drive signal path by 350 mm) and didn't see more than about 5 nS difference in the delay. Makes me think the long traces on the board aren't as much of a problem as I thought they might be. But notice the relatively slow turn on and turn off with the 200 ohm gate resistor.

Image

Image

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Post by Johny » Sat, 10 Apr 2010, 14:14

Nevilleh wrote: I am a bit puzzled by this motor controller. I can find nothing that senses current and yet the set up instructions refer to changing the current limit by adjusting one of the pots.
Could they be using part of the copper on the PCB as a shunt?

As for gate drive. I agree 200 ohms is very high in fact I'm amazed it doesn't cook as the IGBTs spend so much time switching! But changing them is going to result in a massive decrease in turn on/off times and I worry that there is a reason behind their apparent "mistake". You will probably find that the gate driver can't handle smaller resistors as well (when you change them all).

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Post by Nevilleh » Sat, 10 Apr 2010, 14:47

Johny wrote:
Could they be using part of the copper on the PCB as a shunt?

As for gate drive. I agree 200 ohms is very high in fact I'm amazed it doesn't cook as the IGBTs spend so much time switching! But changing them is going to result in a massive decrease in turn on/off times and I worry that there is a reason behind their apparent "mistake". You will probably find that the gate driver can't handle smaller resistors as well (when you change them all).


A good thought, but there's nothing sensing such a thing. There is another thing that puzzles me, a diode connected cathode to the IGBT collectors/motor - terminal and anode off to an op-amp input. It seems that it would detect the collectors going negative and shut off the drive if so. But I can't see it measuring current!

As you can see from the 'scope traces above, the switching times are shortened quite dramatically with a 50 ohm gate drive.
I have 20 x IGBTs in parallel and the driver chip can source 6A, so that's 300 mA per gate. With a 15V drive signal, that's 50 ohms per, so it should do it OK.

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Post by weber » Sat, 10 Apr 2010, 15:48

Nevilleh,

One of the things that puzzles you is the answer to the other thing that puzzles you. The diode with its cathode to IGBT collectors is there to sense current using the turned-on IGBTs as a very nonlinear current shunt. I think you will find that the anode of this diode is pulled up to 15 V by a resistor, at least when the IGBTs are turned on, allowing the op-amp to detect the saturation voltage of the IGBTs and turn off the gates if it exceeds a set amount. This is called "desaturation protection" or "desat protection" for short. The best gate-drivers have it built in. You just provide the high-voltage high-speed diode.

I too am concerned that there is a very good reason why they use 200 ohm gate resistors. I suspect they have to turn the IGBTs on and off so slowly to compensate for the poor physical layout that Tritium_James mentioned. The more rapidly the current changes, the bigger the voltage spikes due to stray inductance. I suspect they are effectively making the IGBTs act as their own snubbers. Awful.
[Edit: spelling]
Last edited by weber on Sat, 10 Apr 2010, 05:50, edited 1 time in total.
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Post by Nevilleh » Sat, 10 Apr 2010, 16:16

Thanks weber, I intuitively felt that this diode must've had something to do with current sensing and you have prompted me to track a bit more of the circuitry. It is actually connected to an op-amp input which is connected to a comparator output - don't know what the pullup is, but it must behave as you described. Makes me feel a little more confident about the thing.

I nearly have enough stuff to rebuild the thing in its original form. Once I have done this, I'll fire it up with some sort of dummy load and have another look at the gate drive signals. That's another piece of the puzzle isn't it - why use such large value gate resistors? Nothing I have read anywhere suggests slowing down the switching times for any reason at all. The only constraint I have seen is that the IGBT turn on should not be any faster than the reverse recovery time of the diodes. These are the things most likely to suffer big spikes from what I can see, but they are mounted directly to the motor drive output Al plate/heatsink with a heavy wire of only 40 mm connecting the cathode to B+. About as good as it is possible to mount them, I think.
The only "bad" bit is the long trace feeding the gate drive resistors.

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Post by Nevilleh » Mon, 12 Apr 2010, 16:14

I now have the controller pretty much rebuilt, lots of nice new Silicon to melt! I don't know what the diode is that I referred to above as it was completely destroyed, but I will just fit a 400V fast recovery one and hope for the best.

Something I noted when putting it back together is that the B+ busbar is connected to the copper plane on the board just through six mounting screws. It is positioned on the same side of the board as the B- plane and insulated from it with some small plastic spacers and a sheet of stiff plastic, so the only current path to the B+ copper plane (on the other side of the board) is the six screws - they are zinc plated steel of 4 mm dia. I measured the resistance between the end of the busbar and the copper plane at 1.2 milliohms. If I put 1000A through those screws, the voltage drop is 1.2V (which isn't much compared with the 150 or so available) but the power dissipated is 1200 watts. The voltage across the IGBTs is about 2V, so there's another 2000 watts and who knows what power is dissipated in the slow switching times from the 200 ohm gate resistors.

Thye rate this thing as a 1000A controller but I can't see that being possible! I mean, more than 3.2 kW being dissipated in an Al box of about 270 x 150 x 80 with a couple of 12v computer fans bolted to it?
I think their 1 hour rating is 500A, but even that will produce 800 watts. Maybe that is the motor current rating and the input current will be quite a bit less. Even so, putting lots of amps through some screws has got to be a very bad way to do it. I wonder if brass ones would be better?

I have to say that I am not impressed with the design of this thing and it does not represent good value for money, being about the same price as a Zilla 1K - which I wish I had purchased instead.

The cost of all the replacement parts was just on $400, including rip-off freight charges. The Al housing, busbars and heatsinks would probably run out around the $300 mark. There's a lot of labour in putting it together, its all hand soldered and it took me about 8 hours to remove the black bits and put in nice, new shiny ones. I expect a production line would do it much quicker, maybe 4 hours. At a labour rate of $25/hr, that brings the raw cost of the thing up to about $800. That's NZ dollars, or about $US560. They are selling it at a retail of $US1895! Got to be good business even if a few blow up from time to time.
Last edited by Nevilleh on Mon, 12 Apr 2010, 06:25, edited 1 time in total.

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Post by Johny » Mon, 12 Apr 2010, 16:26

Can you add some solder lugs and wire around the screws? It sounds very suss regardless of the screw composition.

A rule of thumb in the electronics industry is that something must retail for around 5 times the bulk raw parts cost. Companies who try to cut these margins usually end up in financial difficulty. I guess I'm talking about products with plastic work as well but I am not surprised at the cost of the LS controller v/s parts. Just a shame that good engineering was left out of it.

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Post by HeadsUp » Mon, 12 Apr 2010, 16:38

do you have any new photos inside showing the components and heat path ?

maybe you can tweak things to improve heat transfer / dissipation and get a controller rather than an incendiary device

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Post by Nevilleh » Mon, 12 Apr 2010, 17:03

Thought I might add a few pictures:
You can see the insulating spacer on the bottom busbar here. The burn marks are from the caps going up in smoke - I cleaned them up as best I could.

Image


Image


The wire link replaces blown track.

Image

The mounting screws again carry the IGBT collector current - although the tabs are also in contact with the heat spreader bar (which is also M-)

Image

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Post by Johny » Mon, 12 Apr 2010, 17:08

Are the busbars tinned copper? Sorry if this was stated earlier.

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Post by HeadsUp » Mon, 12 Apr 2010, 17:24

where is the temp sensor mounted ?

can you have one mounted to the M- bus bar at the hottest point ( probably where 3 IGBTs are clustered ) using that one to limit current output above a threshold limit , and another to a dashboard temp gauge ?

what are the maximum rated temps for those ?

note also on the left of the second photo , the PCD board is only about 15 mm away from the IGBT's , so the PCB and components will also get radiant heat as there is no insulating barrier.

it really needs airflow blowing through the case doesnt it , but that could introduce moisture on wet days and dust particles which would cover all components in a layer of thermal " insulation "
unless you filtered the air coming in with a particulate (HEPA) filter

those bus bars really need to be extruded with a thick base and cooling fins on the other side with constant airflow through them.

be a pity to burn those nice new bits woodentit

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Post by weber » Mon, 12 Apr 2010, 17:31

Using screws to carry current is very poor design indeed. Surprisingly, brass screws would only be a little bit better than steel. Brass has only about 28% of the conductivity of copper. See
http://www.kp44.org/ftp/ElectricalCondu ... erials.php
And they may need some kind of conductive anti-corrosion paste (Inox?) to get enough reliable contact area. Johny's suggestion of lugs and cables is better.

You really shouldn't leave scorch marks (carbonised epoxy) bridging across high voltage areas. Do you have a small drill that can take a grinding type bit to grind it away, or you could maybe just drill a row of overlapping holes. It only needs a line a few mm wide cutting through the black. Maybe even sandpaper would get it off.
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Post by Johny » Mon, 12 Apr 2010, 17:41

So easy for us in the advice gallery to pour on the suggestions.
How about adding more screws?
Can you add more without drilling though any tracks? (Don't know how many layers the PCB has.)
BTW I'm impressed you got this thing going again in any case.

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