Alan B wrote:I haven't taken any PC power supplies apart yet. So they have voltage doublers? Interesting. Do PC power supplies use IGBTs? I would think whatever they used is probably what we need to use. Perhaps even re-use what's there? Heatsink, check.
500 khz is not hard for an FET. Requires a good driver though, and good diodes. Might not want to go that high.
Since we want to have a programmable user interface with cell type, voltage per cell, number of cells, max current, shutoff percentage, time limit we need a micro. If we have a micro what's the SMPS chip needed for? Seems like extra parts.
For equipment protection I'm thinking an SCR crowbar across the input fuse. Output voltage ever spikes up too far, blow that fuse. Set the watchdog timer on the micro to shut everything down if it gets stuck, and use a real PWM output so it can't get 'stuck' on. I suspect the RC chargers work this way and they manage it up to a kilowatt.
Winding the inductor is not a big deal.
Yep, PC power supplies (the ones that have the voltage switch on them) use a voltage doubler topology - have a look at this project http://sound.westhost.com/project65.htm
to see how it works in practice.
They don't use FET's, they use transistors.
Higher the frequency, smaller the magnetics BUT the more critical the components. Making a big slow ugly SMPS is several magnitudes easier than a multi-Mhz, 100W/cm2 unit
No furthur comment on the Micro - good if you are using something like lead acid,with multi-stage equalization etc. but for a CC/CV unit, it only really needs to be a power supply with current limiting.
Winding an inductor that won't saturate at high currents, and change its inductance greatly over its operating current range is more complex.
Pre-done versions are cheap - http://www.coilws.com/index.php?main_pa ... 12_229_113
The IGBT's the DIY guys use are not suitable for the application - square peg - round hole. There are IGBT's approaching and exceeding mosfet switching times - problem is, you have the VF losses. So you balance VF losses vs. crappy SOAR curves of mosfets.
80-125Khz is a good compromise between size, layout complexities (there is a reason why PC power supples are 44Khz) component losses etc.
At 500Khz you approach AM RF frequencies, and designing for RF starts to get interesting. Its a black art, I used to fix FM transmitters and they never behave as you would expect (or model them) to do so. You also start to find that you are building an RF transmitter rather than a power supply and this is NOT a place for sensitive microcontrollers - diode junctions become radio recievers.
I've (accidentally) made power supplies that would wipe out radio reception in a 1Klm radius. Not desirable.
New evil decided - GNG offroad build on Craftworks DHR with 12S4P lipo. Aim - Light, balanced, powerful, able to climb a tree.
Project Vectrix restarted. Status - BMS + Charge control redesign (read faffing with batteries again)