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Old Mar 20, 2015, 01:45 PM
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United States, TX, Midland
Joined Apr 2001
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High Power Electronic Switch?

Anyone know how to build an electronic switch rated for high voltage/amps (15S/200A)?
Something like this commercial product found here:

http://fliermodel.en.alibaba.com/pro...or_RC_ESC.html
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Old Mar 20, 2015, 02:36 PM
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ttabbal's Avatar
United States, UT, Herriman
Joined Jan 2012
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Using a bigger FET, you could get 120A...

http://www.rcgroups.com/forums/showthread.php?t=2367201
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Old Mar 20, 2015, 08:41 PM
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I'm the OP!

Quote:
Originally Posted by ttabbal View Post
Using a bigger FET, you could get 120A...

http://www.rcgroups.com/forums/showthread.php?t=2367201
I'm the guy who created this thread.

Next week, I've got some circuit boards and some MosFets coming in next week, and will post the final fail safe switch unit on this failsafe switch assembly for my giant scale models. The cost for the fail safe unit is around $5 each including circuit boards and MosFets. I've selected a "P-Channel" 20 Amp MosFet, to be compatible with the common receiver switches that switch the red positive leadwire.

These MosFets are available in pretty high powered versions now days. For the price of two lunches at McDonalds, you can buy a 400 Amp MosFet rated at 100 Volts DC.

http://www.digikey.com/product-detai...5T2-ND/2354430

As for turning them on and off, all they require is a simple voltage supply on their gate that supplies either zero Volts DC for "Off", or around 10 VDC for "On". That switch circuit shows how its done. In fact, you can just hook up your ohm meter to one of these things, check that it's open circuited. Then, place a 9 volt battery with a 10K limiting resistor from negative to the gate to turn it on. And your ohmmeter will show a dead short. The gate is holding a "Floating Charge" to keep the thing turned on. Remove that 9 VDC battery and it will stay a short. Until you ground out the gate to battery negative with a jumper wire.

Also note that when pulling these types of currents continuously, those MosFets depend on a good sized aluminum heat sink to carry away what ever heat is generated.

(Now days you can also buy pretty hefty diodes, capable of 10,000 Amps. They are six inches in diameter )
http://www.pwrx.com/pwrx/docs/rds8_10.pdf
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Last edited by vollrathd; Mar 20, 2015 at 08:52 PM.
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Old Mar 21, 2015, 03:01 AM
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United States, TX, Midland
Joined Apr 2001
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Very cool

Thanks Vollrathd.

I'm good at building electronics stuff but not designing. I'm looking for something to eliminate the need for a manual arming/anti-spark jumper. Will this circuit with the appropriate MosFet handle the in-rush current to the ESC caps? I will be using a locking toggle to activate the circuit. Anything else I need to keep in mind?

Thanks again,

John
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Old Mar 21, 2015, 05:08 AM
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I was going to suggest something like this, but couldn't find anything that could handle more than 45 ADC.
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Old Mar 21, 2015, 10:21 AM
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400 Amp MosFet Switch

Quote:
Originally Posted by nadt770 View Post
Thanks Vollrathd.

I'm good at building electronics stuff but not designing. I'm looking for something to eliminate the need for a manual arming/anti-spark jumper. Will this circuit with the appropriate MosFet handle the in-rush current to the ESC caps? I will be using a locking toggle to activate the circuit. Anything else I need to keep in mind?

Thanks again,

John
Hi John

The part specified has a 1000 Amp repetitive peak current rating with a maximum of 75 Volts DC voltage rating. You should be OK. As for driving that MosFet, its maximum gate voltage is 20 Volts DC. If your supply voltage is over around 12 VDC, just hang a 12 VDC zener diode across the gate of the Fet, and limit current from your power source with a resistor around 5K or 10K or so. Value is not critical. (That zener diode will also protect the MosFet gate against accidental static discharges.)

Also buy the larger version of this MosFet per this part number. The smaller version can handle far less current. And be sure to bolt the MosFet to a heatsink. With no heat sink, your max continuous current will be limited to perhaps 40 Amps or so. As for fail safe, be sure to be able to shut down the battery in case something fails.
http://www.digikey.com/product-detai...5T2-ND/2354430

I did this a long time ago. Had to parallel connect six smaller MosFets. Still have that thing somewhere.

For those not familiar on how to hook up a MosFet, this JPG shows how. Not to hard to do!

Important Note!
If your model uses an external uBEC, that external Battery Elimination Circuit must have its DC input connected directly across the DC input to the ESC. That way, when the ESC is powered up, the uBEC is also powered up. Do not connect that external uBEC directly to the battery plus and minus wires.
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Last edited by vollrathd; Mar 21, 2015 at 03:23 PM.
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