Quote:
Originally Posted by MPaulHolmes
Your inductors are working nicely? I can't wait to see your parts list! I want to make one too!!!! Awesome job!
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Thanks for all the kind words! I'm pretty excited about getting to this stage. I thought the electrical stuff would really be tough, but it's been stuff like layout and heat dissipation that have caused problems (and I'm a mechanical engineer by day, sheesh!)
I will definitely play around with caps to try and reduce their temperature. Admittedly, I had a medium box fan blowing on the whole thing; they won't have such nice airflow in a real application!
The inductors are working well - this is the only issue (i think): You can tell when the current is high enough to keep the inductor charged during an entire pulse cycle. This occurs around half duty cycle and about 5 amps. At this point, there is always current flowing through the output loop and any slight change in duty cycle results in a very large change in amps. Like, I'll put my fingers on the knob and it'll jump up by an amp. I don't think the sensitivity will be a problem as long as there is enough resolution in the PWM duty cycle (might require adding a crystal like you did? I forget why you added it, but I think one of the results was higher PWM resolution).
Rather, I'm wondering about controlling the current when it is at lower power settings (like, a 2A gassing stage or something). The current will not be constant in the output loop and the sensor would require some sort of filtering in order to read an average current (i don't think we care about the peak current at this point). My current plan (no pun intended) for determining when charging was finished is with an algorithm that looked for a minimum current and stopped the charger.
One solution would be to go to a higher frequency and shorter pulse. There'd be higher switching losses in the mosfet, but it seems to be running pretty cool. It'd also have a side benefit of reducing ripple current which means cooler caps! Hmm... maybe something to look into. I'm at 20kHz now...
Another option would be to add inductance, but more components mean more money.
Anyway, here's a parts list with links for the electrical components as of now:
Inductor (150uH 50A)
E SERIES HELICAL WINDING OUTPUT INDUCTORS : CWS Coil Winding Specialist, manufacturer of transformers, inductors, coils and chokes
Mosfet
IXYS SEMICONDUCTOR|IXFN100N50P|MOSFET, N, SOT-227B | Newark.com
Output Cap
RUBYCON|450USC560M35X50|Aluminum Electrolytic Capacitor | Newark.com
input caps (2x)
CORNELL DUBILIER|380LQ821M400A052|Aluminum Electrolytic Capacitor | Newark.com
diode (2x)
IXYS SEMICONDUCTOR|DSEI30-06A| | Newark.com
Inrush current limiters
Inrush Current Limiters
Bridge Rectifier
40 AMP 600 VOLT BRIDGE RECTIFIER | AllElectronics.com