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Automotive project...Transistors VS Relays

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thekyguy11

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Hi. I'm working on a project for my car. The point is to completely replace the ignition switch with a Start/Stop button. Some of you may have heard of a "Smart Key" or "Keyless Access"? If you would like to read more, here is the link...

http://www.electro-tech-online.com/threads/help-building-keyless-access-for-automobile.87738/

Anyway, I am trying to design the hardware, and I am down to the last few components. I don't know if I should use automotive relays, or if there are transistors I can use instead. There are 5 wires that need to be controlled, so it will call for 5 relays/transistors. I attached a schematic so you can see what I am trying to do. I thought it would be a good idea to assume that each wire could see as much current as what the fuse is rated for. Also, I would prefer transistors over relays, since they are smaller and have no moving parts. Any suggestions? Thanks.

Kyle
 
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Boncuk

New Member
The problem is that most of the car electric is wired the way that connection is done switching ground (chassis) to the consumer.

I would not recommend high side switching using transistors because of resistive losses. (P-channel MosFets generally have a higher RDS(ON) than N-channel types)

When switching low side you must remove all chassis connections and move them to the drain of an N-channel MosFet.

My suggestion: Stick to available good quality relays.

Boncuk
 
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