Relay necessary? 12VDC high current

[Mishael]

I want to be able to use a key switch in a circuit i have but the circuit runs >40 amps (yes i have all proper safety precautions) but the only key switches I have seen are rated at .5-2 amps which obviously is not enough. Would this be the time and place for a relay?
And if anyone has any informative sites on relays that are useful, those would be great to have too

 

[Dr_Doggy]

i would agree to use a relay, @40 amps you just need to watch your wire guages, maybe you could just use a industrial breaker switch>?

relays are simple, , one coil is a isloated electromagnet (2 pins vcc/gnd) the other 3 pins is like a 2pos switch that is toggled when first coil is powered

 

[ronv]

Share with us what you are switching. If it's in a nasty environment like a car the relay might be the easiest, but solid state might save a few $$.

 

[Mishael]

Its a car but an electric one I am building. I would post a link to the thread but I'm on my phone. Anyway yes it is a car but the car is electric and it would be rarely used out doors. I am designing it for use inside a large building. I think whatever is cheapest is best. As for wire gauge, yes I am making sure that my gauge is big enough but just to cover my bases, what is a good size? And if I don't have that size, will multiple wires of smaller ggauge accomplish the same task? Like if I need an 8 gauge but I have some 14 gauge, would doubling up on the 14 gauge be sufficient? Note: that's just an example, not the actual numbers I'm using.

 

[Dr_Doggy]

8 should be ok, i think i read 10guage @ 40amps(don't quote me) is good, depends how much you are goin over.

2 wires(same size, same length) in parallel will cut current in half.

You will need to refer to wire chart for current vs guages. If you start mixing guages you need to consider the resistance of each wire and parallel currents

also with motors you get a high current draw initially, which you may need to consider

 

[4pyros]

How are you controling your motors? You may already have a low current control. Andy

 

[Mishael]

The motors are positive, and negative wires. No speed control circuit. At this point at least

 

[ronv]

Sounds like you are turning the car on and off. If so the relay might be the best choice.

**broken link removed**

Doubling up is ok. Keep the length about the same.

 

[Mishael]

Whenever I turn the switch it breaks the connection between the battery and motor (the vehicle is electric)

 

[ronv]

OK. So now the key will turn on the relay which will turn on the motor. You might want to think ahead to what you will want in the long run. This set up will be bang bang. In the long run you will probably want some speed control (PWM?)
If you go this route add flyback diodes across both the motor and the relay.

 

[Mishael]

You lost me

 

[shortbus=]

Why did you start a new thread on the same subject?
https://www.electro-tech-online.com...ric-vehicle-motor-size-and-relay-help.113531/

 

[Mishael]

No one helped with the relay portion because i didnt really get specific enough on the requirements of the relay

 

[ben7]

No one helped with the relay portion because i didnt really get specific enough on the requirements of the relay

You can use a high current switching relay, they are very common in cars and trucks.

Did you find the proper relay for your needs?

 

[ronv]

You lost me

The diodes "clamp" the voltage you get from switching an inductor like a relay coil or motor. If you don't use them the contacts on your key switch and relay will arc making their life short.
Bang bang means all on or all off. Unlike gas engines DC motors have almost all their torque at zero rpm. So it will be like revving up the car and popping the clutch every time you start. This will be hard on your gears and may leave black marks on the gym floor.

 

[imix500]

Just a quick word on wire gauge. For a DC project running 40A continuous I would use stranded #6 and use the finest stranding you can afford. Generally #8 is good for 40-50 Amps, but to keep losses to a minimum I would go up a size.

 

[4pyros]

You will need some form of speed/direction control. Andy