For my 500V battery pack I need a charger that can supply provide 600VDC at 5A. (Although I'd be happy with 2A output for now)
Is there an easy way to adapt your circuit to provide that high a voltage?
A 500V Pack! Wow! What motor controller are you going to use? Even the zilla has a max of 400V!
Anyway, this part of the charger would be easy to adapt. It's essentially a buck mode charger and'll convert any voltage to a lower voltage. You'd need mosfets/diodes/caps that can handle the high voltage (and maybe check that the inductor laminations can handle it too?). As you stated though, your current requirement would be much lower, so it might be relatively easy to find something suitable.
I assume I'd have less cooling problems with lower current?
As far as heat generation, you're looking for something that'll handle 4 times less current, so that's 16 times less heat generation (assuming the same Rds_on). Rds_on will likely be higher for a high voltage device, but not 16x! Diode losses would be proportional to current as well, so 4x less heat with 4x less current.
I think you're issues will be finding a source with a high enough voltage. Besides your voltage doubler method, you could use a boost circuit before the buck circuit to get to a high enough voltage. A PFC controller would do this while timing the PWM to increase the power factor. Here's some light reading:
http://services.eng.uts.edu.au/~venk...3/ch07s3p1.htm
I just read the complete thread and was just wondering if you ever condsidered using IGBT's instead of MOSFETs?
From what I understand, IGBT's have a constant voltage drop like a diode does. I think they're good for high current high voltage applications (like the zilla), but mosfets might be better for this project.
Do you have a complete circuit diagram, incl. the PWM setup?
Currently, I'm just using a 555 timer as the PWM source. I'm reading through the Atmega stuff and trying some things out on the STK500. I'm learning slowly... Here's the 555 circuit:
DPRG: A Simple PWM Circuit Based on the 555 Timer
About adjusting the current in fine tuning: I recommend looking at PWM controllers that are meant for SMPS design,
I started out looking at actual Lead Acid charge controllers. Some draw backs, I think, are:
1. they all use a resistive device as a current sensor (which is why I initially had a shunt that was going to be amplified with an opamp)
2. they all have unfamiliar ways to tune the feedback loop so that it is stable... it's been a while since I had a control theory class.
3. in the end, we'd be adapting something to work in an application it wasn't designed for. This brings a lot of unknowns and challenges that we'd have to deal with. At this point, programing a micro seems like it'll provide the most flexibility to adjust the charge profile to whatever we want it to be and eliminates all the band-aids to get a different product to work.
As I always say though, these are the reasons I'm headed down this road and should only be a consideration for others. Another option might be better, but we won't really know until someone tries it out! (I thought those initial ST mosfets would be good due to their 60A rating... little did i know that the non-isolation would cause electrical problems and electrically isolating them would cause heat problems)
Feel free to try other things out and let us know how it works!
As for coils, would these be ok, do you think?
Here's a good resource for many buck-converter parameters:
http://www.google.com/url?sa=t&sourc...tq1ee3ryq5Qhpg
I actually sized my inductor from an equation in a TI application note. See equation 12 on page 11. I selected it to have constant current at 2A minimum at 100khz. Not that I'm at 20 khz (to reduce switching losses), I don't have constant current until about 5 amps...
http://focus.ti.com.cn/cn/lit/an/slua019/slua019.pdf
As for isolation, I've struggled with this one. It appears the high power chargers such as the PFC-20 and Russco's are not isolated. My design won't be isolated - the positive rail is connected to B+ while B- and the (-) rail are switched on and off with the mosfet. I think the only way to isolate them would be to use a very large isolation transformer which would be large and heavy and expensive. Consequently, it is greatly recommended to isolate your traction pack from the vehicle and clean the batteries frequently to reduce leakage paths.
No answer yet on a Sunday? Awe, c'mon, I wanna get started NOW :-D
ha! I love the enthusiasm! I was fishing this weekend which provided many hours to think about how to program this sucker. DIY stuff can get addicting! Do it up, and let us know how it works!