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Post up a thread for your EV. Progress pics, description and assorted alliteration
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Post by coulomb » Tue, 30 Mar 2010, 05:41

Johny wrote: Note lots of extra holes for extra devices.

I wonder if they re-used the same PCB as the one for MOSFETs? In other words, they may need fewer IGBTs than MOSFETs and even get higher power with them.

I assume that since they both have gates, if you choose the right part, the same MOSFET gate driver might drive IGBTs... anyone know?

Maybe there is a voltage drop monitoring circuit that needs a bit of tweaking to accommodate IGBTs instead of MOSFETs though.
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Post by Squiggles » Tue, 30 Mar 2010, 12:45

Some gate driver device data sheets refer to both MOSFETs and IGBT so it is likely they can be exchanged.


Edit: For example IXDD414 from IXYS for "Driving MOSFETs and IGBTs"
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Post by Tritium_James » Tue, 30 Mar 2010, 13:29

coulomb wrote:I assume that since they both have gates, if you choose the right part, the same MOSFET gate driver might drive IGBTs... anyone know?
Yes and No. For low power, you can use the same part. For higher power, IGBTs should really be driven to a negative voltage to keep them held off. Though you can argue the same for really high power MOSFET drives too.

You need to drive the gate negative (esp with the low-side device) so that the capacitive coupling between the gate and drain (ie, phase) doesn't turn the gate on when the phase voltage slews upwards rapidly when the high-side device is turned on.

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Post by Nevilleh » Wed, 31 Mar 2010, 12:52

evric wrote:
Curtis controllers whine at low speed... do LogiSystems controllers whine?


No, only their owners!

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Post by Nevilleh » Wed, 31 Mar 2010, 13:00

a4x4kiwi wrote: Can you post a pic of the logic board? I will compare it to the one I am working on. I might be able to make some suggestions if the layout is at all similar. From memory they are ALL LM339 quad op amps in the Curtis.


Yes, I'll get a picture, but I have now managed to read enough numbers off the charcoal to figure out what they are. Amazing what can be done with double magnifiers, a jeweller's loupe and a bit of UV!
It has 3 X LM239, 2 X LM293, 2 x LM258 and 1 x LM224 and a TC4420 mosfet driver. I haven't looked all those up yet.
Sort of good that they didn't use a micro as I would definitely have had to go grovelling to them if they had.
There's still a lot of work in fixing this thing, so I'm going to build a ReVolt Cougar controller. I've read good things about it and then I'll at least have a spare for the next time I do something really stupid.

Here's a picture with a diagram showing the ic locations:

Image
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Post by Electrocycle » Wed, 31 Mar 2010, 22:59

aha, looks exactly like an old curtis board :)
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Post by avolt » Wed, 31 Mar 2010, 23:39

Hi Nevilleh
i know how you feel about the Logisystem controller the first time yours blew,as just after your went mine went as well on its first time around the block,i only got 800m,it did not blow like yours but just stopped,then came the drama getting it home and up the hill back into my shed.
i have started building the ReVolt Cougar controller and here is what the board looks like so far.

Image


you can get all the parts from Ian at http://www.hometheatre.net.au/index.php ... c23995ed4f

you probably know that already but just in case
i have not got my Logisystems controller back yet,i sent it back for repair 2 weeks ago.
you have lots of motivation like myself to build the Revolt controller now,it's fun anyway and you get to learn heaps too!
also the people building them seem to be great blokes and helpful too.
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Post by a4x4kiwi » Thu, 01 Apr 2010, 00:13

Its very similar but not the same as the Curtis.
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Post by Electrocycle » Thu, 01 Apr 2010, 03:35

maybe a different version of curtis?
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Post by Nevilleh » Thu, 01 Apr 2010, 12:09

Nice looking pcb!
I have received a couple of boards already and am now waiting on the rest of the bits - for the Cougar as well as the LogiSystems.
I will repair the latter and I even wondered about chucking its control board and replacing it with the Cougar one. Maybe.
Keep us posted on your progress building the thing.

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Post by Nevilleh » Thu, 01 Apr 2010, 12:20

a4x4kiwi wrote: Its very similar but not the same as the Curtis.


Hey Mal, have you traced out the circuitry at all? Be interested to see it if you have.

Looking at the power board, the IGBT drive signal is fed in near one end of the 235 x 115 board and then it runs right around the perimeter for a total length of over 500mm before getting to the last one. That strikes me as a recipe for disaster! The time difference in the gate turn-on signals must be appreciable. The thing could probably be made more reliable by using maybe 4 driver chips spread around that perimeter. Perhaps even running wires direct across the board from driver to gate would help matters.
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Post by Squiggles » Thu, 01 Apr 2010, 12:48

Good spotting Neville, the distance from driver to gate should be exactly the same for every device.

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Post by a4x4kiwi » Thu, 01 Apr 2010, 15:28

I don't have a schematic, but there is a close one http://www.evdl.org/lib/index.html

It is called Curtis 1221...
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Post by coulomb » Thu, 01 Apr 2010, 15:37

Mal, you ended up with a space in the URL, so it doesn't work without chopping the space off the end.

Direct link: http://www.evdl.org/docs/curtis_1221b_schematic.pdf.
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Post by Electrocycle » Fri, 02 Apr 2010, 01:02

yep, I was pretty amused at the super long loop of skinny track the Curtis uses for gate drive.

I've played with small controller designs for robotics, and massive effort is put into gate drive circuitry and layout - even for tiny controllers with only a few FETs!

It's very easy to see the "first" FETs in the string turning on earlier and taking more than their fair share of the load in the Curtis design.
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Post by Nevilleh » Fri, 02 Apr 2010, 12:13

Not only do the "near" ones turn on first, but the "far" ones would turn off last. Maybe they thought that would balance out. Image

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Post by Electrocycle » Sun, 04 Apr 2010, 03:11

hehehe true!
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Post by Nevilleh » Mon, 05 Apr 2010, 19:40

Learning lots about the insides of a LogiSystems controller. I wonder why they replaced the fets with IGBTs. They are 600V devices, seems overkill for a controller rated at 156V. But they are fairly cheap.
I am replacing the diodes with 10 x 200V 60A ones, rather than the 12 x 600V 50A devices used originally. The caps have a rating of 250V, so why are all the semis 600v things? Very strange.
The controller is a bit basic and seems to be very similar to the Curtis one that I downloaded the circuit of, thanks to a4x4kiwi. They have made a few changes, used a TC4420 gate driver rather than a discrete one and they don't seem to have the low frequency drive that the Curtis used to stop jerky starts. Apparently LS's answer to jerky starts is to use a log pot. Makes sense, I suppose.
The thing has a regulator driven from B+ to supply the logic circuits (via another regulator) which uses a MOSFET and a 27V zener. All blown up, of course, but it then feeds a 15V regulator on the control board. The KSI input is just a high value resistor feeding a 12v zener and the input to a comparator.
I do wonder about just using a bunch of op-amps and comparators to drive everything. In this day and age, a micro just has to be easier, simpler, cheaper and more versatile.
Dismantling the power board is a bit of a pain as they have covered everything in silicone and its not easy to remove. Seems like a sharp blade is best, anyone got any better ideas?

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Post by Tritium_James » Mon, 05 Apr 2010, 20:17

They'll have 600V silicon because the crappy layout means big inductance which means big voltage swings across the controller. I can easily believe you'd see at least 2x the battery voltage on the switching devices. I suspect your 200V rated parts will live a short and eventful life.

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Post by Squiggles » Mon, 05 Apr 2010, 20:52

From what I am seeing and hearing one would surmise that Curtis & LogiSystems are a bit like back shed amateur designers rather than trained experienced engineers. There seems to be a lot of basic errors in their designs!

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Post by weber » Mon, 05 Apr 2010, 22:20

Nevilleh wrote: Learning lots about the insides of a LogiSystems controller. I wonder why they replaced the fets with IGBTs. They are 600V devices, seems overkill for a controller rated at 156V. But they are fairly cheap.
I am replacing the diodes with 10 x 200V 60A ones, rather than the 12 x 600V 50A devices used originally. The caps have a rating of 250V, so why are all the semis 600v things? Very strange.

I agree with TJ. Don't replace the semis with lower voltage devices. They will see huge spikes due to stray inductance. The capacitors won't see these spikes internally because, well, they are capacitors and that's their job. Its the stray inductance between the semis and the caps (and internal to the caps) that causes the spikes on the semis.

Knife is best solution I know to silicone coating. There are probably substances that dissolve silicone, but I imagine they are extremely nasty to work with and might dissolve a lot of other stuff too.

This is sometimes called a "conformal coating", but I think you will agree with my friend Warrick Beaty who also repairs such boards and calls it a "confounded coating". Image
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Post by Tritium_James » Mon, 05 Apr 2010, 22:55

Squiggles wrote: From what I am seeing and hearing one would surmise that Curtis & LogiSystems are a bit like back shed amateur designers rather than trained experienced engineers. There seems to be a lot of basic errors in their designs!
I wouldn't necessarily call them errors - yes, it means you need to use less efficient 600V parts instead of 200V parts. The long gate drive traces mean you need slow switching edges which increase your switching losses. But it means you can make it low cost and relatively easy to put together. It's "good enough" for most purposes, and they've sold thousands of them. I'd say that's quite a good design.

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Post by Squiggles » Tue, 06 Apr 2010, 00:00

Tritium_James wrote: It's "good enough" for most purposes, and they've sold thousands of them.


It's the "good enough" that bothers me. Image And the selling thousands does not make them a good design, it could mean there is good marketing and little competition.

Years ago I did some work in the clothing industry (when it existed) and there where some industrial machines that had some electronics in them that were sold by the thousand, the electronics was so bad it made me some good money fixing them Image . Quantity does not guarantee quality.

By the way I take your point that the EV application might be pushing them beyond their design spec. if they were originally designed for golf karts.

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Post by Tritium_James » Tue, 06 Apr 2010, 02:32

Squiggles wrote:By the way I take your point that the EV application might be pushing them beyond their design spec. if they were originally designed for golf karts.
Exactly.

For EVs it's possible to make something far better, with proper motor current control, battery voltage & current monitoring, controller & motor temp sensing, etc, etc. But any new product on the market unfortunately has to compete with the existing controllers that are already being mass manufactured (possibly for a different application) and are consequently cheap. The usual story for any new product, of course!

But it certainly bugs me that these controllers are the 'default'. Any time I see someone talking about rough starts, or cooking a motor or controller, or other weirdnesses, it really gets my goat, because it is quite simple to NOT have these problems exist at all, for hardly any additional expense in the controller. Any yet these things give such a bad first impression, and really make the whole EV area look amateur.

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Post by Nevilleh » Tue, 06 Apr 2010, 12:49

Thanks for the instructive comments guys.

Having had a look at the layout of the power board, I am inclined to hack it about a bit! Here's a sort of sketch:

Image

The black line around the outside is the existing gate drive track. The drive signal enters the board on the side about 3/4 way along. I propose to cut the track roughly where the crosses are shown and run wires from where the signal enters the board to the points I have shown ("WIRES"). The aim being to make all the wires the same length so the signal paths to all gates are as nearly equidistant as possible.There are 25 IGBTs and I will group them in fives as close together as possible and run a wire to the centre of each group of five. The wires will be as short as possible, but the min length will be constrained by the furthest group. This should ensure that the drive signal propagation times are as equal as possible.
The gate drive resistors are all 200 ohms which seems on the high side to me. I'll need to check the TC4420 specs and also the IGBT gate specs. It is possible that an improvement could be made by adding another TC4420.
Of course we don't want it to switch too fast as this will increase the spikes.
I bought a Unique UQ2062C digital storage 'scope (60 MHz, 500MS/s) last time I was in Sydney and this looks like being a good opportunity to try it out!

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