Wow,
Taking a quick look at Mouser,
IRFB4310, $3.83 ea, 100V, 127A
Another thought I had was that instead of just tying the transistors in parallel, using the microcontroller to switch two or more sets, so that the "on" time of each transistor is further reduced by at least half - which should help with the cooling issue.
If the trick Myles suggested of using a voltage pump to allow switching of all n-channel transistors instead of needing p-ch works, then the above transistors are certainly cheap enough to give it a try.
I'm sure I still have a LOT more to learn about the details - like layout of the circuit, figuring out how much cooling I need and/or can get out of the heat sinks, etc.
But at least these components are cheap enough that a hobbiest can play with it.
John
From: king_of_neworleans <no_reply@yahoogroups.com>
To: electricboats@yahoogroups.com
Sent: Monday, June 2, 2014 12:23 AM
Subject: [Electric Boats] Re: Motor Controller - transistors and questions....
To: electricboats@yahoogroups.com
Sent: Monday, June 2, 2014 12:23 AM
Subject: [Electric Boats] Re: Motor Controller - transistors and questions....
Yeh if not matched fairly closely, u got problems, but otherwise sure you can parallel them. Match all resistors, caps, etc in the circuit, too. One of the members here in fact has a design for a basic BLDC controller and a complete kit for 36v, too) using MOSFETs and he even suggests this, for higher currents. A more elegant approach of course is to just use a bigger transistor, but they get expensiver. I am actually Thinking about home brewing the controller for mkII re power using doubled or tripled pairs of IRFP4310's for 48v at 140a or 210a max, respectively, in his design. Craig's kit is for 36v using the IRFP3206. These little guys are pretty cheap. Blow a few, well, it's cheap entertainment. When the smoke leaks out, change a value here or there and try another pair. Don't forget you need a good heat sink. When and if I install the homebrew, I will still have the store bought Kelly KBL controller in reserve. Just sayin. Oh and Craig's design calls for optical encoding rather than hall effect sensing so if you want to use hall effect sensors you will probably have to do a bit of experimenting.
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Posted by: oak <oak_box@yahoo.com>
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