On 01/08/2017 01:37 PM, Lee Hart wrote:
Sounds like what you need is a bypass contactor. This is an extra contactor that simply switches *full pack voltage* to the motor. Engage the bypass contactor with a switch that closes when you floor the accelerator.
But there's one caveat. You must not open the bypass contactor while the current is above the controller's current limit.
- Add a second larger freewheel diode that can take the higher peak current. (Its forward voltage drop needs to be chosen to be higher than the controller's diodes at low currents, but lower at high currents. This big new diode is not likely to be fast enough to efficiently switch at 15 KHz.
I was actually thinking about moving the diodes "outside the box" when repairing/upgrading my curtis controller. Because the diodes are the hardest part to source in the right package, I was thinking about using the best diodes I could find in any package, and mounting them outside of the controller between M- and B+.
I note that inside the controller each MOSFET is paired with a nearby diode, so I don't know how well separating the diodes from the MOSFET's would work (the diodes would be moved closer to the motor than the MOSFETS) but if that could be done, it would allow me to have a monster freewheeling diode pack that wouldn't need to be sized exactly to not interact badly with the ones inside the controller. [Not being an EE, this could be a hopelessly bad idea...]
- Use something like a big old slow "hockey puck" IGBT as your bypass "contactor". Turn it on hard, but let it turn off slowly (with a resistor-capacitor-diode network in its gate). That forces the motor current down so the controller can handle it.
If I were to do this, I like the "Hockey puck" IGBT with delayed shutdown idea the most, as it seems the easiest to implement.
Jay _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
