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Topic: N moffet clarification (Read 2139 times) previous topic - next topic

Skooks

Hi everyone, I'm a mechanic just starting out in electronics and done a fair bit of reading so far on n misfit transistors but just after clarification on something. My first decent project is to intergrate Arduino into a 48 v golf buggy. The buggy gets up to 60 v when charging (dc) so by using a logic mosfet rated at 60 v and 30 amp is maximum values and will happily work anywhere between those values ? Ie: 48 vdc and 10 amp
It's basically in a Crude sense same result as car relays ? Small voltage in to switch larger voltage supply out, is that correct ?

CrossRoads

What are you trying to do?
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Skooks

At this stage I was thinking about some sort of rfid ignition key bypass. I work on a tropical island that has multiple golf carts each have a unique key and no master key for the ignition so each time one breaks down as the only mechanic on island  I have to travel back to my workshop and get the spare key if they haven't left the key in it. So I'm thinking just cause I can.... For something to learn ill make a rfid or similar circuit to bypass the ignition which without testing yet is likely to only be 48 v and maybe 5 amp or less, but still learning how to incorporate Arduino into higher voltage applications

CrossRoads

So you need to connect the ignition to Gnd to get it started? That's pretty straightforward.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.

Skooks

Theres actually a 48vdc supply from  the onboard motor controller then through the ignition switch and back into the controller so yes its a simple task and a overkill to make a RFID circuit for a task that a simple switch can do but its a learning arduino thing for me that may benefit my daily work load. :)
From what I understand using a N-mosfet logic transistor rated at 60v 30amp will switch on at 5v and happily handle 48v and 10 amps and that the 60v 30amp rating is a maximum reading ? such as the RFP30N06LE.
I just wasn't %100 sure on that cause most pages I read start getting too technical on explaining it  and my brain is still in the mechanical engineering mode rather than the electrical circuitry mode hehe, so just thought id ask for clarification :)

thanks

MarkT


Hi everyone, I'm a mechanic just starting out in electronics and done a fair bit of reading so far on n misfit transistors but just after clarification on something. My first decent project is to intergrate Arduino into a 48 v golf buggy. The buggy gets up to 60 v when charging (dc) so by using a logic mosfet rated at 60 v and 30 amp is maximum values and will happily work anywhere between those values ? Ie: 48 vdc and 10 amp
It's basically in a Crude sense same result as car relays ? Small voltage in to switch larger voltage supply out, is that correct ?


If the supply gets to 60V you cannot use a 60V MOSFET, it'll breakdown (that's the absolute
maximum or avalanche breakdown voltage).  Use 100V one.

Never select a MOSFET by current rating - this is not how it works - put 30A through
a 30A MOSFET and it won't survive (unless water-cooled and you don't mind a very
inefficient switch).

You calculate what _on resistance_ you want (power dissipated = I-squared-R).  Check the
on-voltage will be low enough for your requirements (and a lot less than the gate-source
voltage), then find MOSFET with that low an on-resistance (or parallel some up if needed).

You situation probably requires high-side switching with a p-channel MOSFET, which will
need a 48V level shifting circuit to control it.  A relay would probably be easier to drive if so.


[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

Chagrin

The ignition is just a switch that needs a key to turn it, isn't it? All you need to do is hide a second switch or use a group of rotary or toggle switches with an obfuscated pattern to use as a backup.

Using RFID or such is a little over the top when all it takes to "hotwire" it is to pull out the ignition switch.

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