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Topic: 5v relay w/ 12v ~500a load (Read 2016 times) previous topic - next topic

toonamo

I have a project where i need to control the starter of a vehicle. I cannot tap the solenoid wire but the actual starter itself. I know some vehicles can even get up to 1000 amps or more to start a vehicle. Does anyone know of a relay that can handle that kind of load and also heat being in the engine compartment?

cjdelphi

A 5v relay switches on a larger 12v relay....?


toonamo

i meant that a relay that can by trigger with 5v across the trigger but will allow 12 volts with high current to pass through the relay. Basically a starter relay with a 5 volt trigger.

cjdelphi

I don't understand. 

You want a relay you feed 5v which cranks over the engine?

Good luck finding one with those specs, i'd switch a 5v relay which in turns switches a 12v relay to the starter motor

toonamo

I would normally agree with you. The problem is size. I don't have room for two relays. I know it exists because a device was made that does what i am looking to do. Problem is that person is no longer around nor is his company.

zoomkat


I would normally agree with you. The problem is size. I don't have room for two relays. I know it exists because a device was made that does what i am looking to do. Problem is that person is no longer around nor is his company.


There are fairly small relays available. What is the measured current draw of your starter relay (the current used to close the starter relay)?
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toonamo

Also another issue is i can not put this relay pre-starter relay. Due to insurance laws this cuircuit needs to be mounted to the starter itself with a tamper resistant caseing so that a car thief can not simply bridge/ bypass the relay and start it. (These vehicles do not have a ecu.

zoomkat


Also another issue is i can not put this relay pre-starter relay. Due to insurance laws this cuircuit needs to be mounted to the starter itself with a tamper resistant caseing so that a car thief can not simply bridge/ bypass the relay and start it. (These vehicles do not have a ecu.


Encase both relays in a big blob of epoxy. Instead of a pilot relay, you might be able to use a power transistor to operate the starter relay.
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dc42

The only 500A relay you will get at reasonable prices will be a car starter solenoid. So why not use a starter solenoid, fed from the car 12V supply and controlled from the Arduino by a mosfet and opto isolator?
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jackrae

What insurance laws are you referring to and explain exactly what the project involves so's you can maybe get a decent answer.

I am of the opinion that you will not find a 5volt relay, driven directly from an arduino, with the mechanical power to force close a circuit designed to carry several hundreds of amperes DC.  Remember that once a relay has de-energised a great deal of mechanical force is necessary to rapidly pull open the contacts to prevent welding.  This de-energising force is always less than the force required to initially close the contact.  I think you would therefore be looking at a coil dissipation of several 10s of watts, which at 5 volts would require several amps.

As others have suggested you could use a FET to close a suitable solenoid and if there are "insurance" issues we'd like to hear about them.

toonamo

Makes sense i just have to find a affordable relay that can handle the power such as a solenoid mentioned above. The new insurance law states that a vehicle must have a electronically controlled starter (canbus or otherwise) that is triggered by a encrypted signal to function. It also can not be exposed (so that you can not bridge the pins). Any "newer" vehicle has this already as the starter has a canbus controlled micro controller. Even if the unit doesn't have canbus the starter usually has a integrated solenoid that uses 12v DC of up to ~30A. For the time being i will focus on a basic relay with maybe a mosfet N-Channel to save the pins. For cars in which the starter doesn't have a built in solenoid we will have to consider manufacturing a starter that does so that the starter can not be bridged or powered separately.

janost

What country has a stupid law like that?

Without ignition you can crank the engine as much as you like and it will never start.
An antitheft system doesnt disable the starter but the ignition.

I would say that you cant find a carstarter that doesnt have a solenoid.
So any normal carrelay can handle the starter.

TomGeorge

Hi, what starter motor, these days, doesn't already have a start solenoid mounted on it, thats how you start the car, turn the key/press button and 12V at about 1AMP supplies the motor mounted solenoid, and broooom.
The only starter motor that I know of that didn't have a solenoid was on my Leyland/Morris Mini, it had a separate solenoid mounted near the starter and was controlled by 12V from key.
If you can track down mini spare parts, they may help, the part was made by LUCAS, but it was for a small 1100CC motor, Great Car.
(If you want to know how it engaged without a solenoid to throw it into the crownwheel, google Bendix Drive.)
Tom.
Everything runs on smoke, let the smoke out, it stops running......VK3DMK

sbright33

How can you "hide" the motor terminals?  Seems silly.  Failing that, all the thief has to do is connect them to the battery with jumper cables.  Of course disabling the ignition is key.
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