# Building bulletproof.



## voltmatic automaton (Nov 2, 2008)

Okay so I have stopped crying into my beer for now, what with the failure of my controller. (feel free to read the thread about dropping my car off at the nearest recycler) 

Heres where I stand...the controller in question was salvaged by combining the Power stage of a Logisystems and the Control Board from the Open Revolt design.
Its actually surprising it lasted as long as it did considering the power stage and control board were not designed for each other....

Anyway.

I have a feeling the Control Board is still good and the Power stage is toast.

Heres my intention, to build a Power Stage as designed by the Open Revolt team to work with the Control Board they actually designed for it (duh)
My question is how to build the Power Stage to be a lot more resistant -bulletproof-.

Would heavier Capacitors and bigger spec MOSFETs simply be a plug in solution than the ones recommended or would I have to consider the Control Boards ability to work with the various changes in components.

I am thinking this way because in all the controllers thus far it was the Power Stage has been the one to fail -explode-

So if I'm going to build I want to build bulletproof.

I already have in mind large heatsink and water cooling layouts and I believe I will use a combination of both.

My setup is a 120V pack 20 x 6V 260ah. The vehicle is 3800 lbs and it has gone over 40 miles on a charge when the controller would work.


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## DawidvC (Feb 14, 2010)

If you really want bulletproof, go for an IGBT. The hard work is driving them, and some you can buy with the drivers built in. It sells as IPM modules. You would still need enough capacitors, and you need to keep inductance down. If you are concerned about the on state voltage of an IGBT, just add a battery.

Dawid


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## Duncan (Dec 8, 2008)

Hi Volt

Somewhere on the OpenRevolt thread is the details of the bits to upgrade to go from 
150v - 500amp to 200v - 800amps

I think you have to change all of the electronic bits, capacitors, FET's and diodes but the board hardware (busbars and the like) stays the same

The control board also stays the same

That would give you some more headroom


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## 9852 (Jan 17, 2010)

paul holmes is working on a 1000 amp mosfet based controller, and there are some IGBT driver boards out there but I think for more duribility I would use IGBTs semikron makes some with a freewheel diode built in. just my .02


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## PZigouras (Jun 5, 2010)

Don't feel bad. Designing a reliable controller that can take the massive surge of launching a 4000-pound car hard is no easy task. 

The company I work for has some extremely talented engineers and electronics people, and it took us hundreds of man hours to design a controller that was bulletproof. In theory, holding 80mph on the highway required 'x' amount of power handling capability. But in reality -- after all the testing was done -- it actually took almost 4 times 'x' to get the reliability we wanted. More often than not, the drawing board does not reflect "real-world" driving, and even good engineering companies have found that out the hard way.

The Power stage of a Logisystems controller is part of the problem. Twelve tiny Mosfets (all of which just slightly bigger than your thumbnail) is not enough to carry the start-up load of a 4000-pound car -- at least not for any length of time. A single 300-amp IGBT can carry that same load, which by itself is no where near large enough to move a heavy car in real-world driving. 

For example, the company I work for only builds a few different types of motor controllers -- two of which are DC. The SMALLEST of the two uses FOUR 400-amp IGBTs. The next one up uses double that. And we consider those controllers to be "medium-duty", not heavy duty. 

When you sit down and draw out a mental image of what you need to drive your car, make sure you multiply it by 4 before you build it. It may sound a little extreme, but in the real world, that's the type of power handling that will survive the tortures of driving.

- Paul


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## Qer (May 7, 2008)

PZigouras said:


> The company I work for has some extremely talented engineers and electronics people, and it took us hundreds of man hours to design a controller that was bulletproof.


And yet you haven't made something bullet proof. You've just added enough overkill so it won't be the weakest link, nothing else. The lack of self regulation and limitations will probably play out in either of two sceraios:



Since the controller doesn't have any built in limitation it will just continue to provide current until something else gives in. My guess; the battery pack. Sure, the controller will survive but the 5 digit dollar battery pack will be toast. Horray.
Batteries are continuously improved and especially racers continue to push the bar. Sooner or later someone's gonna add enough motors and use powerful enough cells for your overkill to be overkilled. BAM goes the controller.



PZigouras said:


> In theory, holding 80mph on the highway required 'x' amount of power handling capability. But in reality -- after all the testing was done -- it actually took almost 4 times 'x' to get the reliability we wanted.


Once more, that's because you went with overkill instead of style. It's "Get a bigger hammer"-approach. The problem with that approach is that sooner or later you'll find a nail that's too tough and that's when your hammer isn't good enough anymore.



PZigouras said:


> The Power stage of a Logisystems controller is part of the problem. Twelve tiny Mosfets (all of which just slightly bigger than your thumbnail) is not enough to carry the start-up load of a 4000-pound car -- at least not for any length of time.


No, the power stage isn't the problem (or at least not for the reason you claim). The problem is that Logisystems, like your controller, doesn't handle power limitation in any way. Oh, and their hammer were a lot smaller too...



PZigouras said:


> When you sit down and draw out a mental image of what you need to drive your car, make sure you multiply it by 4 before you build it. It may sound a little extreme,


That's because it's also totally absurd.

A controller for an electrical vehicle MUST have current limitation to protect itself, otherwise it will blow up. So you've thrown more transistors on the problem? Good, that means that it will survive longer by sheer brute force. You might even be able to handle that 4000 pound car thanks to overkill, but will the controller also survive it when the car's fully loaded with stuff in the trunk and is going uphill so the power consumption's multiplied a few times? How about hot days when the sun's shining and the temperature gets so high under the hood that your 400 Amps IGBTs should be derated to, say, 300-350 Amps instead?

Sooner or later you'll manage to stress the transistors more than they can handle and that's why a good controller must protect itself. If your controller is too weak for the task it should behave like this:






And not like this:










We've learned that (or rather, verified that) the hard way on the dyno. Seems you guys skipped that class, eh?


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## DawidvC (Feb 14, 2010)

Take a bit of time and read through Paul Holmes thread on th OpenRevolt controller in the forums of ecomodding-dot-com. Then find the thread which Qer and Tesseract used during the design of Sol 1. That should give you a good idea of what is required. The nice thing is, one controller uses mosfets (although jack bauer has a mod for igbt's ) and the other uses igbt's. Take a good note of the measures they take to ensure that these controllers can reliably handle the kind of current needed for normal ev driving. 

There are also a couple of other threads in various forums, but these two are the most succesful designs, and well worth studiyng.

Regards
Dawid


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## albano (Jan 12, 2009)

Qer said:


> If your controller is too weak for the task it should behave like this:
> 
> 
> 
> ...


Hey Qer,

I like that video clip


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## DawidvC (Feb 14, 2010)

Very nice video Qer. Very appropriate as well, as that is how most ordinary folk see current ev's.

Now add a couple of huge mastiffs in there 

Dawid


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## Qer (May 7, 2008)

DawidvC said:


> Very nice video Qer. Very appropriate as well, as that is how most ordinary folk see current ev's.


That's because they think this when they hear the term EV:










You don't need thousands of Amps to shatter that mental image, but you need a decent controller that doesn't go so hard into thermal cut back that the car moves like a glued snail.

The Z1K has a peak current of 1kA but a continuous current of approximately 300 Amps. Seems it's capable of really decent performance in ordinary cars "despite" that.


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## PZigouras (Jun 5, 2010)

Qer said:


> And yet you haven't made something bullet proof. You've just added enough overkill so it won't be the weakest link, nothing else. The lack of self regulation and limitations will probably play out in either of two sceraios:
> 
> 
> 
> ...


We may have skipped the dyno class, but there's one thing I can say for sure:

The EP-2000 has NEVER lost a race.... EVER. That's something that the Soliton and Warp controllers can never claim. So, if you think that our engineering is inferior, please, feel free to race. Just make sure you have the keys to your car ready to turn over... because winner keep BOTH cars


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## rwaudio (May 22, 2008)

PZigouras said:


> We may have skipped the dyno class, but there's one thing I can say for sure:
> 
> The EP-2000 has NEVER lost a race.... EVER. That's something that the Soliton and Warp controllers can never claim. So, if you think that our engineering is inferior, please, feel free to race. Just make sure you have the keys to your car ready to turn over... because winner keep BOTH cars


Should there be a definition of race? 1/4 mile? 100 mile? And perhaps you should take on the 1000A controllers with your 1000A controller, or do you need to use your 2000A controller to have a chance of beating them?


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## Batterypoweredtoad (Feb 5, 2008)

So a controller that no one has ever heard of until about a month ago has never lost a race! Straight from the mouth of the guy who introduced them to us and is selling them? Sorry to say we will need more proof of the prowess of the "Big Dummy" line of controllers than the lonely word of the only person who seems to have ever seen one.


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## albano (Jan 12, 2009)

PZigouras said:


> there's one thing I can say for sure:
> 
> The EP-2000 has NEVER lost a race.... EVER.


Never last a race? I haven't heard of that controller, can you give me more info on that controller? 

Albano


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## cyclops2 (Feb 12, 2011)

A observation.

There is more to life than electronics.

Limiting maximum torque can be done VERY reliably with torque limiting couplings.

With voltage controlled magnetic couplings.

So there is a more reliable load limiter, than a BMS of unkown quality that can ruin a battery. The more mechanical types will not ruin a battery If they take a fit. Which IS VERY rare. You should see a warning on the instrument panel flashing....OVER CURRENT.
Or Just feel a reved up motor in neutral.


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## Qer (May 7, 2008)

PZigouras said:


> The EP-2000 has NEVER lost a race.... EVER. That's something that the Soliton and Warp controllers can never claim.


Let me tell you a bit about a friend I have. He used to be one of the mechanics in a racing team that usually raced with high performance SAABs. The engines were tuned to a level where something (usually the joints) broke sooner or later. About one race out of ten the car didn't even leave the starting line because the joints snapped when the driver slammed the throttle. It was still worth it, for those nine other races out of ten the car took off like a bullet and usually were the first into the first bend. I once asked why he didn't tune his own car, but he just replied that he preferred a higher success rate than 90% at the red lights.

Or other examples; Formula 1 engines are seldom used more than one race before being scrapped, an Indy Cars engine is often reused but it's more or less rebuilt from scratch after every single race. What makes sense in racing doesn't necessary make sense in a family car.

This thread is about a commuter, it's about reliability and uneventful every day usage. I wasn't gonna bring in the Soliton in this thread since I don't want to shamelessly promote my own stuff (guess that's why I'm just an engineer and not a hot shot salesman, huh?) but it wouldn't surprise me if a brute force controller without even basic built in safety will beat the Soliton at the tracks. Heck, a high power Bubba contactor will beat it provided you can guarantee the grip when the short circuit slams in like a sledgehammer. It doesn't even bother me, because the S1 (or Jr) were never built for the track, they were built for the streets.

The goal for the Soliton series is to be boring and uneventful, as all sane street car controllers should be. They protect themselves from blowing up and preferably should always protect the motor(s) and the pack. It's no coincidence for example both Zilla and Soliton (and I'd guess also WarpDrive and Synkromotive) can limit not only motor current and voltage but also battery current and minimum pack voltage, they share those features because they make sense. You don't want to spend thousands of bucks on motor(s) and batteries to just see them blow up because you felt like taking your beauty out for a spin on the high way.

You NEED to keep track of the current, one way or the other. If you don't something's gonna break, if the controller doesn't then something else will.

*Ye cannae change the laws of physics!*


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## PZigouras (Jun 5, 2010)

Batterypoweredtoad said:


> So a controller that no one has ever heard of until about a month ago has never lost a race! Straight from the mouth of the guy who introduced them to us and is selling them? Sorry to say we will need more proof of the prowess of the "Big Dummy" line of controllers than the lonely word of the only person who seems to have ever seen one.



The proof is all the cars that I now own, that once belonged to someone else who tried to beat me in a 1/4-mile run. And I would like to add your car to my collections as well.... so let's go! 

Off to the races!!!!! March will be national EV Racing month!


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## Batterypoweredtoad (Feb 5, 2008)

Are you trying to be a badass street racer or sell controllers? If you are trying to sell controllers YOU need to prove they are worth a damn, not me. So far I have a guy making big claims that he cannot validate. I dig the idea of a $2k controller that is tougher than the motor and the batteries with you right foot as your limit, I really do, but right now you are just a neat concept with no substance.


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## PZigouras (Jun 5, 2010)

rwaudio said:


> Should there be a definition of race? 1/4 mile? 100 mile? And perhaps you should take on the 1000A controllers with your 1000A controller, or do you need to use your 2000A controller to have a chance of beating them?


I think our 1000A can take on almost any 1000A out there.... but for me, I prefer the 2000A, which actually costs about $200 LESS than the Soliton or Warp controller. The EP-1000 is also about $1000 less than the least expensive "1000A" controller on the market today. 

It's nice to compare price, especially in an apples-to-apples comparison. If I say that my Lamborghini Murcialago has a much better breaking system than your Honda Accord, well then, it probably is. But I'm quite sure that the Accord also cost a lot less.... which is why the person probably purchased it in the first place (plus it's a lot more environmentally friendly). Otherwise, he would have gotten the Lamborghini. 

Not everyone that wants a highway-going EV can spend $3000+ on a controller. I know I couldn't.. which is why I went with a much less expensive unit. And it works great for what I need it for... daily driving. It may not be shiny, chrome-plated, and have lights all over it.... but it works. And it works good. And I saved $1600.00 (which for me, is a lot of money 


- Paul


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## Qer (May 7, 2008)

PZigouras said:


> It's nice to compare price, especially in an apples-to-apples comparison.


But you're not. You're comparing a brute force PWM control without any kind of safety control with sophisticated EV motor controllers. If it's just a money question, why not go with a huge piece of tube that you ram into a metal plate when you want to go forward? It's gotta be the cheapest solution, by your reasoning it must therefore be the best too. Right?



PZigouras said:


> Not everyone that wants a highway-going EV can spend $3000+ on a controller. I know I couldn't.. which is why I went with a much less expensive unit.


So safety isn't an issue in your world? You value money more than life?


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## PZigouras (Jun 5, 2010)

Honestly, I've never had a safety issue with any of the EP Series controllers. Although if anyone feels uncomfortable with using them the way they are, you can always add the limiter or thermal shut down... anything to make people sleep better at night.

But I don't really think there is a way to compare apples to apples here... might as well compare a F350 to a Mustang. I think preference has a lot to do with it too... people will always love the controllers that they love... and I don't think anything will change there minds.... it's like cigarettes. The Canadians seem to like our controller better than most, judging by the amount of controllers going up there.... I think about 40% of out orders are shipped up there. Who knew


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## Qer (May 7, 2008)

PZigouras said:


> Honestly, I've never had a safety issue with any of the EP Series controllers.


What batteries were you using that can handle a controller that doesn't have any built in limitations? How did you avoid damaging the pack? How did you make sure the motor never saw a higher voltage or got more current than it could handle?


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## PZigouras (Jun 5, 2010)

I'm using regular flooded 12v batteries... 120 volts total. I have 2 banks of 10 not-so-deep cycle (hybrid) batteries in parallel. I can't remember what the Ah is, but they are about 200 mins reserve capacity. 

One of the reasons I kept the flooded batteries instead of going to lithium (in addition to being a lot cheaper) was that the current draw doesn't seem to bother them very much. I've only had 1 go bad in two years.

My Kostov can handle 120V all day long, so I'm not worried about that. If anything is going to kill it, it's the amps (I don't have a current limiter installed), but I can only beat on the motor for so long before the batteries go under 50% charge.... and at the point, I back off the throttle because the non-deep cycle plates tend to flake off and fall to the bottom of the battery once you go below 50% charge. The whole pack was only about $2000, but still, I want to get as many years as I can out of them....


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## Duncan (Dec 8, 2008)

*My Kostov can handle 120V all day long*
Only at one specific rpm number surely?


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## Qer (May 7, 2008)

PZigouras said:


> I'm using regular flooded 12v batteries...


Which is your current limit. Floodies suffer from some serious voltage sag which will limit the current and thus hopefully protect the controller and motor.



PZigouras said:


> 120 volts total


Which is your voltage limit. Crude, but indisputable efficient.



PZigouras said:


> One of the reasons I kept the flooded batteries instead of going to lithium (in addition to being a lot cheaper) was that the current draw doesn't seem to bother them very much.


Considering your floodies ARE your current limit that's probably smart. If you change to Lithium your pack will indeed "be bothered" and you will probably kill it when the C-factor jumps through the roof. Unless the suddenly much lower internal resistance causes an instant current rush that blow something else up instead, of course.

So you pretty much just verified what I've been saying from the start, you need current limitation. Your way of limiting the current is using a battery chemistry with a high internal resistance might be successful, but as more and more people will go for Lithium instead that is not a long time solution. If you're happy with floodies and a mere 120 Volt in the pack I, however, guess you can keep cutting corners in the controller.

For anyone else wanting more range than floodies can practically give you, I suggest looking at a somewhat smarter controller. After all, most controllers out there DOES have some basic limitations built in, even the old style all analogue Curtis 11221/231C has it...


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## PZigouras (Jun 5, 2010)

Funny thing is, if I had spent $2000 on Li-ion's (like I did with these flooded cells), I would have just enough power to make it down the street to the drug store and back. Instead, I can go about 10 times as far with the money I spent.

I addition to the price, the warranty also sucks on the lithiums. The flooded cells I bought from Wal-Mart (yes, WAL-MART!) have a 3-year free replacement, and 7-year pro rated replacement. So I'm 100% good for three years.... or longer. Plus I don't need a BMS.

If the lithiums where half price with a better warranty, I might have gone for them on this project.... but not at that price. I did my whole conversion for under $5000 -- including motor & controller. Not bad for a daily driver that can go on the highway for at least 6 exits.... unlike my other conversions, this one has actually paid for itself in fuel savings.... a first, for me.


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## DJBecker (Nov 3, 2010)

I can echo the statement that it takes quite a bit to make a reliable controller, both design and real-life experimentation.

You can take the approach of just overbuilding and using a small fraction of the capability, but you can still blow up the controller despite the extra expense and wasted performance.

The Open ReVolt ("Cougar") controller is the one used above. It has the minimum sensors required: it monitors the motor current using a hall effector sensor and temperature using a thermistor at a single point on the combined heat spreader.

The firmware monitors the current sensor at a 4KHz sample rate, but the actual current protection is done in hardware the old-fashioned way -- a variable resistor and analog comparator shuts off the gate drive within one 16KHz cycle of over-current. The firmware has to explicitly reset the trip to continue.

This hardware current limit must be set correctly (and conservatively) for the power stage used. The firmware does not explicitly limit current, it just runs a regular P-I feedback loop. This feedback will proportionally reduce the drive (pulse width) only after excess current is detected.

If you set the hardware current limit too high, the feedback loop will usually cap the current before things blow up. But not certainly. And hardware current limit doesn't adjust with controller temperature, so a setting that protects when cold may be too high when the MOSFETs are hot.

Our controller design is similar to Cougar, but with all of the limits implemented in the firmware. I very quickly learned that in direct PWM mode I can easily blow up a single-device-pair output stage even at 12V. I needed to check for over-current every sample and immediately set pulse width to 0. Even then I could see a 20% over-shoot at the next sample -- four pulses later.

It took me a little longer to figure out that I needed to do the same explicit check in P-I feedback mode. If I use the same P-I loop timing and parameters as Cougar, I can reliably blow up an output stage at only 24V. With the sample-by-sample limit in place I can repeat the same test without failure. I can tell that the limit is triggered without even looking at the log and counters because the motor squeals like a pig -- the sound of the overcurrent limit hitting a few hundred times a second, gradually reducing as the motor starts spinning and the current drops.

Why did we implement the checks entirely in software? Using the hardware approach of Paul's Cougar design would have definitely saved a bunch of MOSFETs, but we wanted the flexibility of software. Both because we can do a better job (decreasing the limit with increasing temperature) and because we have a slightly different cooling structure. We have separate heat sinks for the drive and freewheel devices, and want to independently limit current based on their temperature and device type. (MOSFETs work best cold, while silicon rectifiers have a lower voltage drop when hot). 

In retrospect we could have started with a Cougar-like hardware current check, and improved the software until it was never triggered. But it might have removed some of the motivation to fix problems. When you get the yellow flame and pieces of MOSFET scattering about, you can be pretty certain that it wasn't a false trigger.

Anyway, back to the point. This does remind me of something I should suggest to Paul: adding a tiny bit of code in the Cougar firmware to do better. He should implement a similar explicit over-current check in the P-I loop, and add a counter to both that and the hardware over-current clear. That way a user has a better chance of setting the limits correctly.

Unfortunately the AVR doesn't have enough memory to record the recent operating parameters. With a log of RPM, PWM width and current leading up to the event we could figure out the time constants of the specific motor-battery set and implement a softer current limit. (I expect an explicit limit would be better than an instability-prone P-I-D loop -- we want non-linear behavior when hitting a limit.)


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