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  #101  
Old 08-14-2011, 09:33 PM
valerun valerun is offline
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Default Re: Another DIY DC controller mock

trying to size up the cap bank for this controller. Question: what is the appropriate amount of voltage sag to allow during the IGBT on-period? I know that high-frequency current pulsing is bad for the batteries so the caps have to provide most of the energy to the power stage. Do you know what it means in terms of allowable voltage sag during the on-time? Or the voltage sag does not matter and as long as I have much lower ESR on caps than on battery pack, I will be fine?

thx!
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  #102  
Old 08-15-2011, 05:12 AM
valerun valerun is offline
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Default Re: Another DIY DC controller mock

so on the long drive back from LA (with 150 more CALB cells, no less - woohoo!), did some calculations. In R(cap)<<R(battery) approximation, I got for the battery current during on-time of the IGBT (Ton):

I(battery) = Ioutput * (1 - exp(-Ton/(R(battery)*C)))

So if one wants battery current ripple to not exceed 100A at output current of 1000A, one would need exp(-Ton/(R(battery)*C))=0.9, which means

Ton/(R(battery)*C)=0.1, or C=Rb * 0.1 / Ton

Which, at R(battery)=50mOhm (100 CALB 100AH cells in series), switching frequency of 10kHz, and duty cycle of 50% (worst for the caps), would mean

C = 0.05 * 0.1 / 5*10e-5 = 10,000uF

Something like that. I might have missed a factor of 2 here to account for the fact that the battery continues to supply 500A current in this case so the caps need to supply only extra 500A during Ton (not full 1000A). In which case, 10,000uF would be sufficient for 2000A output.

Of course, to get R(b)>>R(c) you need film caps or a lot of elcaps. In the former case, you will need a lot of film cap to get the right capacitance. In the latter case, you need a lot of elcaps to get the ESR low enough and at that point your capacitance is overkill...

After looking at some elcap datasheets, seems to me 1000-2000uF caps are a sweet spot in terms of hitting both capacitance and ESR requirements roughly at the same time for 10kHz switching. And one would need 10 or so of those...

Am I on the right track here?
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  #103  
Old 08-23-2011, 05:00 PM
valerun valerun is offline
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Default Re: Another DIY DC controller mock

largely talking to myself on this thread it seems ;-)

Anyway, hooked up with the guys at SBE who make sweet power ring caps - film, 1000uF 600V in a 2" thick, 7.5" diameter with just TWO nanohenry inductance! Think of using 2-4 of those. If anyone is interested in a group buy, let me know.

Also, considering switching from a micro-based PWM driver to a dedicated chip-based driver. Something like LM2524D, datasheet at http://www.datasheetcatalog.org/data...r/DS008650.PDF. Page 9 has a reference circuit. Variable frequency, fully accessible error amp, cycle-by-cycle current control.

The arduino would run throttle readout loop and set the current reference for a PWM chip. Would also run less time-critical stuff like comms, temp control, etc.

What do you guys think?

V
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  #104  
Old 08-23-2011, 07:50 PM
JRoque JRoque is offline
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Default Re: Another DIY DC controller mock

Hello V, not much to add but since you ask for it...

Quote:
Originally Posted by valerun View Post
Anyway, hooked up with the guys at SBE who make sweet power ring caps - film, 1000uF 600V in a 2" thick, 7.5" diameter with just TWO nanohenry inductance! Think of using 2-4 of those. If anyone is interested in a group buy, let me know.
I think you mean these, shown here: http://www.engineeringtv.com/video/S...Film-Capacitor. Are those $1,200 a pop or so?

Quote:
Originally Posted by valerun View Post
Also, considering switching from a micro-based PWM driver to a dedicated chip-based driver. Something like LM2524D, datasheet at http://www.datasheetcatalog.org/data...r/DS008650.PDF. Page 9 has a reference circuit. Variable frequency, fully accessible error amp, cycle-by-cycle current control.
Dedicated PWM is the way to go unless you do FPGA or something similar. I like analog loops with digital references but that chip looks good.

Quote:
Originally Posted by valerun View Post
The arduino would run throttle readout loop and set the current reference for a PWM chip. Would also run less time-critical stuff like comms, temp control, etc.

What do you guys think?

V
I've never done anything with Arduinos and it might be a good platform for what you need at the moment. But I'd start looking into breaking away from that and running your own micro with the things you need and none of what you don't. The Atmel micro on those is really great and can stand on it's own with little peripheral devices. I put them on everything I make, short of sprinkling them on my cereal. They come in dozens of packages and can run up to 20Mhz with external crystals or 8 Mhz with their internal resonator. They are so cheap and flexible I rarely use other logic, I/O expanders, etc and instead use a small micro instead.

Anyway, there's some babbling for ya...

JR
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  #105  
Old 08-23-2011, 11:35 PM
valerun valerun is offline
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Default Re: Another DIY DC controller mock

Quote:
Originally Posted by JRoque View Post
Hello V, not much to add but since you ask for it...



I think you mean these, shown here: http://www.engineeringtv.com/video/S...Film-Capacitor. Are those $1,200 a pop or so?



Dedicated PWM is the way to go unless you do FPGA or something similar. I like analog loops with digital references but that chip looks good.



I've never done anything with Arduinos and it might be a good platform for what you need at the moment. But I'd start looking into breaking away from that and running your own micro with the things you need and none of what you don't. The Atmel micro on those is really great and can stand on it's own with little peripheral devices. I put them on everything I make, short of sprinkling them on my cereal. They come in dozens of packages and can run up to 20Mhz with external crystals or 8 Mhz with their internal resonator. They are so cheap and flexible I rarely use other logic, I/O expanders, etc and instead use a small micro instead.

Anyway, there's some babbling for ya...

JR
Thanks JR.

I got a quote of $169 apiece at quantities of 10 for 1000uF 600V part. I think it's a super-deal. Digi-key has some 300-400uF film caps that are far inferior to these at that price... Want some? If I get a couple of people willing to buy 3-4 units total, I'll get a 10-pack from them.

Yeah, raw Atmel is the way to go I guess. I will get there slowly by first getting me a dedicated PWM chip ;-)
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  #106  
Old 08-24-2011, 01:40 AM
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jackbauer jackbauer is offline
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Default Re: Another DIY DC controller mock

Count me in
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  #107  
Old 08-24-2011, 07:37 AM
piotrsko piotrsko is offline
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Default Re: Another DIY DC controller mock

Quote:
Originally Posted by valerun View Post
largely talking to myself on this thread it seems ;-)

What do you guys think?

V
You are aware that there is a very limited amount of people that actually grok what you discuss?

OTOH, your comments and efforts are greatly appreciated by us.
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  #108  
Old 08-24-2011, 08:41 AM
Salty9 Salty9 is offline
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Default Re: Another DIY DC controller mock

I follow the thread but I am but an egg.
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  #109  
Old 08-25-2011, 05:41 PM
valerun valerun is offline
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Default Re: Another DIY DC controller mock

Quote:
Originally Posted by valerun View Post
Also, considering switching from a micro-based PWM driver to a dedicated chip-based driver. Something like LM2524D, datasheet at http://www.datasheetcatalog.org/data...r/DS008650.PDF. Page 9 has a reference circuit. Variable frequency, fully accessible error amp, cycle-by-cycle current control.
going with this schematic (attached). LMK what you think. Uses Hall sensor for current sensing hence avoids the problems related to using shunts. Can accept the Arduino output reference voltage that corresponds to throttle position.

Or you can connect the throttle pot directly (in which case there is not slew rate control, safety emergency disconnect, voltage limits, SOC measuring and other nice things that micro can provide).

PCBs on order. Will let you guys know what happens ;-)
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  #110  
Old 08-25-2011, 06:07 PM
aeroscott aeroscott is offline
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Default Re: Another DIY DC controller mock

Quote:
Originally Posted by Salty9 View Post
I follow the thread but I am but an egg.
me too , love your work . thanks !
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