MOSFET's, PWM and Large Motors. - Page 1
Forum section: electronics / beginners

author: cowboy303
author_rank: Regular Contributor
timestamp: March 06, 2016, 04:53:32 am
content: Howdy Guys,I'm working on a radiator fan controller for a vehicle, it currently uses relays and a temperature switch in the coolant. However they kick in needlessly and produce quite the jolt to the electrical system.So, I'm working on an arduino based fan controller and was going to use relays, but am now thinking about the possibility of PWM... Both MOSFETS and PWM'ing high current motors are outside of my knowledge zone. There are two fans each pulling about 40 amps on high @ 12 volts. I'm not sure on stall current.I would like to switch the high side of the fans, but can swap to the low side if that makes it easier (from some research this looks to be the case).If I were to switch the low side, I was thinking about something like an IRF3205http://www.irf.com/product-info/datasheets/data/irf3205.pdf] http://www.irf.com/product-info/datasheets/data/irf3205.pdf. Everything looks way to simple. 10v VGS *should* be very possible with the 12 volt battery system, and 8m ohms *shouldn't* make much heat, but if I have to run a couple in parallel I can. Then there's the protection, I really have no idea what's needed there, would a simple choke diode work, or is it a bit much for that?I really appreciate the help, if there's a detail I've left out please ask away.

author: max_torque
author_rank: Super Contributor
timestamp: March 06, 2016, 07:33:50 pm
content: Save yourself a LOT of trouble and just use a driver IC designed to do the job, in an automotive environment:http://www.infineon.com/cms/en/product/power/smart-low-side-and-high-side-switches/high-side-switch/channel.html?channel=5546d4624d6fc3d5014d9f398efd562fYes, they can be expensive in low volumes, but by the time you've designed, developed and tested things like gate drive, reverse battery protection, load dump protection, short circuit protection and over temp protection, you'll wish you just brought the IC designed to do all that for you!!

author: Simon
author_rank: Unknown
timestamp: March 06, 2016, 07:42:10 pm
content: ooh I might go for some of those as well. Seems there are lots of suckers born every minute that think getting a cheap brushed fan and trying to speed control it is cheaper/better than just using a brushless fan with signal control.

author: tautech
author_rank: Super Contributor
timestamp: March 06, 2016, 07:46:53 pm
content: Quote from: max_torque on March 06, 2016, 07:33:50 pm+1Upon sighting the thread title the first things that came to mind was snubbers and controlling back EMF's and to not have to worry about designing and incorporating all that into a circuit gets my vote.

author: Simon
author_rank: Unknown
timestamp: March 06, 2016, 07:49:08 pm
content: The only thing to be careful of is PCB capability. While i am in the middle of a design using "105A" mosfet's I am only wanting to put 10A through each simply to spread the thermal load and make the PCB easier as the cost of adding another mosfet versus hitting silly coper weights is probably lower.

author: Simon
author_rank: Unknown
timestamp: March 06, 2016, 09:57:03 pm
content: I wonder at what frequency you can use those intelligent switches. The slew rate is in the order of tens of microseconds when run at 12 or 24 V whereas your average MOSFET has a turn on and turn off time in the region of ns. If I have read one of the datasheet correctly a freewheeling diode is not necessary but perhaps under PWM there would be too much energy for it to dissipate.

author: Porch
author_rank: Contributor
timestamp: March 07, 2016, 04:41:57 am
content: I did the same thing with a golf cart motor.I copied the load side of a DYI DC electric vehicle controller.It used to be listed here, but the link is broken. So the schematic is attached to this post.ecomodder.com/wiki/index.php/Open_ReVolt/PCB_SchematicsThe trick to driving MOSFETs with rapid off and on times, is using a driver chip.Look at the schematic. I copied the MOSFET, diode, and cap layout, aka, everything on the second page, but went with less of them as I don't need to handle 500 amps.I used the MIC4451 MOSFET driver, but I used the TO-220 package, and wired it like it shows on the first page. The Arduino drives the IN pin of the MIC4451.Note that you will have to play with the Arduino timers to get the frequency high enough, as the normal PWM from the Arduino too slow.The hardest part I had to figure out was figure out was a heatsink. Even driving a golf cart motor very slowly, the inductive kick is massive and got the diodes quite warm.