# Big Sol or not to be Big Sol?



## LithiumaniacsEVRacing (Oct 9, 2010)

That is the question! 

Will the Big Sol ever get life?

Racers need MORE AMPS BABY!
I could use a dose of 2500.


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## steven4601 (Nov 11, 2010)

You could bypass the controller with a relay as pedal to the metal?
( Not saying you should.)


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## Tesseract (Sep 27, 2008)

LithiumaniacsEVRacing said:


> Will the Big Sol ever get life?
> ...


That depends on how many we could reasonably expect to sell per year. Five sounds like a realistic number to me, but that's not really enough to justify the development cost...




steven4601 said:


> You could bypass the controller with a relay as pedal to the metal?
> ( Not saying you should.)


Hmmm... and what do you suppose will happen when you turn the bypass relay off? All that energy stored in the motor's inductance has to go somewhere, you know...


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## valerun (Nov 12, 2010)

Tesseract said:


> Hmmm... and what do you suppose will happen when you turn the bypass relay off? All that energy stored in the motor's inductance has to go somewhere, you know...


Add a MEGA-frewheeling diode! ;-) Like 3 600A IGBTs with shorted G&E?


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## Tesseract (Sep 27, 2008)

valerun said:


> Add a MEGA-frewheeling diode! ;-) Like 3 600A IGBTs with shorted G&E?


Yep... but then you don't need the bypass relay any more...


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## valerun (Nov 12, 2010)

Tesseract said:


> Yep... but then you don't need the bypass relay any more...


buit wait, you don't even need those freewheeling diodes if you already have a Soliton1 installed and connected - it already has the freewheeling diodes rated for at least 1000A continuous so got to be ok for 2000A for a few ms, no?

not that I'd ever do that... ;-) My current biggest issue is coercing 1000A out of my pack at 5000RPM on a HV motor without breaking Soliton1 HV limit of 340V pack voltage...


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## rochesterricer (Jan 5, 2011)

You could always throw a bunch of money their way to speed up development. How much would it take to get your attention Tesseract?


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## Tesseract (Sep 27, 2008)

valerun said:


> buit wait, you don't even need those freewheeling diodes if you already have a Soliton1 installed and connected - it already has the freewheeling diodes rated for at least 1000A continuous so got to be ok for 2000A for a few ms, no?


If you bypass the controller then you have, by definition, lost control of the motor current, so who knows where it will top out at? 2kA? 3kA? 10kA?! It will depend on voltage and impedance of the battery pack and the RPM of the motor (higher RPM = higher BEMF opposing the battery pack voltage). 

Also, it typically takes anywhere from 50ms to 300ms for the motor current to decay through the freewheeling diodes and that is a long enough time period that you practically have to treat it as DC.



valerun said:


> ...My current biggest issue is coercing 1000A out of my pack at 5000RPM on a HV motor without breaking Soliton1 HV limit of 340V pack voltage...


Don't forget that max motor current is limited to 900A whenever pack voltage is 310V or higher. It's our unsubtle way of ensuring the 300kW limit is respected. Switching losses go up with voltage and current, and there's only so much heat that can be removed through the baseplates of the IGBT modules even with liquid cooling...


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## rwaudio (May 22, 2008)

Tesseract said:


> If you bypass the controller then you have, by definition, lost control of the motor current, so who knows where it will top out at? 2kA? 3kA? 10kA?! It will depend on voltage and impedance of the battery pack and the RPM of the motor (higher RPM = higher BEMF opposing the battery pack voltage).
> 
> Also, it typically takes anywhere from 50ms to 300ms for the motor current to decay through the freewheeling diodes and that is a long enough time period that you practically have to treat it as DC.
> 
> ...


Tesseract,

So at low RPM with a stiff pack of say nominal 310v before sag brings it below 310v there would only be 900 motor amps? (IE when duty cycle is below 100%)?!?!

Just wondering..


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## Tesseract (Sep 27, 2008)

rwaudio said:


> Tesseract,
> 
> So at low RPM with a stiff pack of say nominal 310v before sag brings it below 310v there would only be 900 motor amps? (IE when duty cycle is below 100%)?!?!
> 
> Just wondering..


Correct. The Soliton1 is a 300kW max controller, not a 310kW or 340kW, etc.


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## Yabert (Feb 7, 2010)

????????????
At 310v the soliton 1 is a 279Kw (900x310) controller and at 309v it is an 300Kw (309x????) controller??!? 1000A at low RPM (low V) is far away from 300Kw

How it work. How push 1000A thru the motor with a 320v nominal pack sagging at 270v?


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## rwaudio (May 22, 2008)

Yabert said:


> ????????????
> At 310v the soliton 1 is a 279Kw (900x310) controller and at 309v it is an 300Kw (309x????) controller??!? 1000A at low RPM (low V) is far away from 300Kw
> 
> How it work. How push 1000A thru the motor with a 320v nominal pack sagging at 270v?


That's exactly what I'm getting at. At low duty cycle when the output power is FAR from 300kw, will the controller put out 1000A to the motor?

It is what it is, but I'd like to understand it so that I know what to expect. It might actually be enjoyable to drive that way though, as you are accelerating and the voltage sags there is a bit of a boost from 900-1000A when the voltage sags below 310v.

I blame Qer for being so thorough at protecting the Soliton from itself and it's users


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## alexcrouse (Mar 16, 2009)

I am considering building a dumb, high power controller. Something like 4000amps of IGBT with nothing but current control. 0-100% throttle = 0 - 3000amps. No thermal cut back, no battery monitors. Just Power. I think theres a market for that. Especially if you can swap out their own IGBT's, and they are isolated in a metal box to protect the rest of the system during a catastrophic failure. The voltage rating would only be limited on the capacitors.


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## Qer (May 7, 2008)

Yabert said:


> At 310v the soliton 1 is a 279Kw (900x310) controller and at 309v it is an 300Kw (309x????) controller??!? 1000A at low RPM (low V) is far away from 300Kw


Well, yes. That's always the case. When a series wound motor is still (0 RPM) the Soliton will "only" generate about 20 kW power to the motor. And you know the worst part? As long as the motor hasn't started to spin, all those 20 kW only generates excess heat, not one ounce of mechanical power. Power is, after all, torque times RPM so if RPM is zero you get no power.

Now, since RPM is proportional to back-EMF it means that as long as the RPM is low it won't matter how many thousands of Amps you push into the motor, you won't get hundreds of kW no matter what (but you might melt the motor). It doesn't matter what controller you have, before the motor speeds up you won't get much power at the shaft. Basic physics.

And about those 900 Amps at 310 Volt, we've never kept that a secret. Really. And if we're gonna theorize about it, the controller is a 309 kW controller at 309 Volt and we give those extra 9 kW away for free! 



alexcrouse said:


> I am considering building a dumb, high power controller. Something like 4000amps of IGBT with nothing but current control. 0-100% throttle = 0 - 3000amps. No thermal cut back, no battery monitors. Just Power.


Good luck. You'll need it.


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## Yabert (Feb 7, 2010)

Well, I perfectly understand your explanation and the physics laws (rpm x torque /5252)... but what I need to understand is the torque capability of the motor with a pack voltage over 310v!
Exemple, some motor generate roughly 100 lbs-ft with the soliton connect at a 300v battery pack but this same motor will generate only 90 lbs-ft with the soliton connect at a 312v battery pack?? But what about the voltage sag (312v to under 310v)?

My question it is more clear? I think the Rwaudio question is also clear!
It's just that this sentence is not clear to me.



> Don't forget that max motor current is limited to 900A whenever pack voltage is 310V or higher


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## Tesseract (Sep 27, 2008)

Yabert said:


> but what I need to understand is the torque capability of the motor with a pack voltage over 310v!


The torque capability will be reduced by approximately 10%.

This seemingly peculiar derating is to protect the *freewheeling diodes*, not the IGBTs. If there is 1000A of motor current and the IGBT duty cycle is 5% then the average current through the IGBTs is approximately 50A while the average current through the FWDs is 950A. So you see, there are components in the controller that are severely stressed even at very low output powers.

This is just how a buck converter works. Average current through the IGBT is Imotor * Duty while average current through the FWD is Imotor * (1 - Duty). This means that the FWD is at maximum stress when the buck converter is operating with a very high input voltage while delivering a very low, but non-zero output voltage at high current.

I admit I am being somewhat paranoid here but the cost to performance is, I feel, worth the enhanced reliability.


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## valerun (Nov 12, 2010)

I, as others, haven't realized that limitation at low duty cycles. This means that there is no point for me to go beyond 90 cells in my car, right?

Just to make it super-clear: If I have a 100-cell pack with 335V at rest and floor the pedal, the *motor* current will behave in the following way (assuming batteries can deliver):
1. maxed out at 900A initially
2. as RPMs build and battery sags below 310V, current ramps to 1000A. With 100 100AH CALB cells with combined IR of 0.05 Ohm, this will probably mean that 900A->1000A ramp happens at ~1000 motor RPM or so.

is this correct?

Thx!


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## valerun (Nov 12, 2010)

alexcrouse said:


> I am considering building a dumb, high power controller. Something like 4000amps of IGBT with nothing but current control. 0-100% throttle = 0 - 3000amps. No thermal cut back, no battery monitors. Just Power. I think theres a market for that. Especially if you can swap out their own IGBT's, and they are isolated in a metal box to protect the rest of the system during a catastrophic failure. The voltage rating would only be limited on the capacitors.


probably possible but:
1. 4000 amps of IGBTs (assuming 4000 amps is a combined continuous rating) will give you maybe 2000A peak. You will need to derate ~30-50% to allow for heating and then you need to derate for uneven current sharing (a LOT of derating if you use, say, 7 600A IGBTs). So in the end, you will probably have to use 10 600A IGBT modules to get reliable 2000A. Plus 10 similarly sized modules for freewheel diodes (unless, of course, you find dual IGBT modules - which are hard to come by used at that power rating).
2. Of course, at that point, you have several feet of busbars connecting things together (even more if you are using separate freewheel and switch modules). Every inch of a standalone conductor is ~20nH. at 2000A turned off in 1us, this will kick back with 40V inductive spike (assuming linear ramp-down which it ain't so likely 2x higher or so). 12 inches - with 480V, 2 feet - with 960V and so on. So proper bus designs etc are critical and even then you would probably be looking at 500V+ spikes at your desired current levels.
3. This means you *will* have a voltage limitation on your design. It will be tough to find modules with voltage ratings beyond 1200V. Also, other isolating components (Dc-DC for gate driver, isolator for drive signal, etc) can likely be taken to 1kV tops. Which gives you 500V max battery voltage input. But that's with zero margin so derate some more. Pretty soon you're at 300V pack voltage rating. 
4. You can reduce the voltage stresses by slowing down your switching. Then you will need to reduce switching frequency to keep the switching losses under control. But then you will have another problem of input caps becoming too large (as they need to support the switching current). At 2000A output, 50% duty (when they work the hardest), you are looking at 2000A draw for, say, 50us (10kHz switching) and then 2000A fill for same time from battery. If you want to limit your battery current ripple to, say, 10% (or 100A in this case), you are looking at 5V max voltage ripple on caps (assuming 100 100AH CALB cells with 0.5 mOhm per cell). 5V at 2000A for 50us is 20,000uF input caps. Chances are, with components you can easily find, switching frequency has to be reduced further. At 5kHz, you will need 40,000uF, and so on. All that is in addition to your caps needing to support 2000A ripple current which is not trivial and sounds like 20-40 high-ripple smaller caps in parallel on a laminated bus to me...

Overall, according to my analysis (not really expert but after having read a LOT of stuff and taking my pseudo-controller to ~500A), it will be 'really' hard to get more than 500kW out of the controller build with reasonably accessible parts. And I might be optimistic here, too... Then again, you have a 300kW Soliton1 and 500kW WarpDrive already built for you...

If you want to go higher than that, it's into the exotic land of 1600A 1700V $1000 IGBT modules, custom film capacitors, active shaping of the switching curves, exotic snubbers, etc.

Not impossible but far from just mounting a few IGBT modules on a heatsink.

PS. Don't have any vested interest in Soliton1 (yet, anyway ;-) - just appreciating what these guys did after having tried a few of those things on my own..

V


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## Qer (May 7, 2008)

valerun said:


> I, as others, haven't realized that limitation at low duty cycles. This means that there is no point for me to go beyond 90 cells in my car, right?


The Soliton is pretty much tailored at max 90 cells. If you charge all your 90 cells in the pack to 3.8 Volt that means you will end up with a pack voltage of 342 which, coincidentally, is the max voltage of the Soliton! When those cells drop down to less than 3.45 Volt (ie still above nominal voltage) the pack voltage drops below 310 Volt and you get your 1000 Amps motor current. So typically you might "suffer" from "only" 900 Amps until you do a quick acceleration or two, after that odds are that your pack has dropped in voltage enough for this to not be a problem anymore.

If you get more than 90 cells, let's say an even 100, this would of course be more of a problem since the cells need to drop to 3.1 Volt for the 900 Amp deration to go away, but on the other hand you can't even start the controller if the average cell voltage goes above 3.42 Volt. So kindly, please refrain from panicking over a problem that is more in the theoretical rather than the practical realm.

Comfort yourself instead with the fact that this solution actually made it possible to have 90 cells in series at all! Originally we talked about setting the limit to about 300 Volts, or 75 cells, but decided it would be nice to be able to have a higher pack voltage even though it would mean some derating of current while the top charge wears off.



valerun said:


> Just to make it super-clear: If I have a 100-cell pack with 335V at rest


Then you will end up sitting in the garage waiting for the pack voltage to drop enough so you can even start the car. You might want to buy some kind of serious dummy load so you can bleed off enough charge to get the pack voltage to drop down to close to nominal after the charger has topped off the pack.


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## Qer (May 7, 2008)

valerun said:


> probably possible but:


5. Not having any temperature deration means that you'll need liquid cooling to get rid of excess heat fast enough and if you don't get it perfectly right (might take a few test shots and evaluations to verify that the cooling's efficient enough) or if the pump stops working it means that at those power levels your transistors will go popcorn on you faster than you can say "Opsie daisy".

6. Handling high voltage is hard. Handling high current is nightmarish. Handling high voltage AND high current at the same time can be hell on earth and it gets exponentially worse as you crank it up. There are very good reasons the first Soliton 1's were 500 Amp controllers, going from 500 to 1000 Amp wasn't effortless and a few good transistors sacrificed themselves in the process.



valerun said:


> just appreciating what these guys did after having tried a few of those things on my own..


Thank you. And honestly, I never thought it would be this hard, really. I've learned a lot in the process, especially how little I actually still know about high power electronics. Before I teamed up with those guys in Florida I actually thought that building a controller on your own can't be that hard, now I'd never even attempt it.


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## valerun (Nov 12, 2010)

Qer said:


> Then you will end up sitting in the garage waiting for the pack voltage to drop enough so you can even start the car. You might want to buy some kind of serious dummy load so you can bleed off enough charge to get the pack voltage to drop down to close to nominal after the charger has topped off the pack.


LOL. Anyway, I have my chargers set at 3.5V CV which leaves a few % of capacity on the table but should get me quite a bit of pack life back (CALBs are rated for 3.6V CV). Within a few min of charge completion, cells drop below 3.4V. So I'm all good re 100 cells I think. 

BTW adding 10 more cells to my Fiat this weekend - for 90 total. Should finally get me to 1000A beyond 3000RPM (one can hope...).


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## piotrsko (Dec 9, 2007)

valerun said:


> Within a few min of charge completion, cells drop below 3.4V. So I'm all good re 100 cells I think.


It has been my experience in 40 some years of electronics test that "nominal" battery voltages are always "nominal" +/ 10%. we stopped using carbon zinc chemistry for calibration back in the '70's. take pictures of the sol smoke, please (I really don't think it will, I'll BET Tess and Qer have still more tricks up their sleeves)


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## valerun (Nov 12, 2010)

piotrsko said:


> It has been my experience in 40 some years of electronics test that "nominal" battery voltages are always "nominal" +/ 10%. we stopped using carbon zinc chemistry for calibration back in the '70's. take pictures of the sol smoke, please (I really don't think it will, I'll BET Tess and Qer have still more tricks up their sleeves)


won't smoke, I'm afraid - their components should be rated for way more than 342V limit to survive all the fun action inside ;-)) Caps are probably the closest but even then I'd expect 500V rating due to the need to absorb inductive spikes...


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## Qer (May 7, 2008)

Yep, there's some margins there + that the Soliton will abort the precharge the moment the cap voltage exceeds 342 Volts.


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## alexcrouse (Mar 16, 2009)

valerun said:


> probably possible but:
> 1. 4000 amps of IGBTs (assuming 4000 amps is a combined continuous rating) will give you maybe 2000A peak. You will need to derate ~30-50% to allow for heating and then you need to derate for uneven current sharing (a LOT of derating if you use, say, 7 600A IGBTs). So in the end, you will probably have to use 10 600A IGBT modules to get reliable 2000A. Plus 10 similarly sized modules for freewheel diodes (unless, of course, you find dual IGBT modules - which are hard to come by used at that power rating).
> 2. Of course, at that point, you have several feet of busbars connecting things together (even more if you are using separate freewheel and switch modules). Every inch of a standalone conductor is ~20nH. at 2000A turned off in 1us, this will kick back with 40V inductive spike (assuming linear ramp-down which it ain't so likely 2x higher or so). 12 inches - with 480V, 2 feet - with 960V and so on. So proper bus designs etc are critical and even then you would probably be looking at 500V+ spikes at your desired current levels.
> 3. This means you *will* have a voltage limitation on your design. It will be tough to find modules with voltage ratings beyond 1200V. Also, other isolating components (Dc-DC for gate driver, isolator for drive signal, etc) can likely be taken to 1kV tops. Which gives you 500V max battery voltage input. But that's with zero margin so derate some more. Pretty soon you're at 300V pack voltage rating.
> ...



I see a couple guys on here that only need it to last till the end of the strip.


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## Qer (May 7, 2008)

alexcrouse said:


> I see a couple guys on here that only need it to last till the end of the strip.


Yep. But they still have to stop the vehicle in an orderly manner. Continue to accelerate due to melted IGBTs until the strip ends and the car crashes into the terrain is not quite on the orderly scale...


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