Electric Vehicle with No Starter Relay

2536 Views 7 Replies 4 Participants Last post by dtbaker, Feb 27, 2014

PSUstudent

Discussion Starter · Feb 25, 2014

The college I am at is currently revamping our electric vehicle. And while we do realize that in a normal vehicle (gas powered) there is normally a starter solenoid or relay. We were curious if the one in the vehicle was even needed. What would be the benefits/ downsides to having no starter relay in the vehicle. Instead, we were debating on going to a 2 switch system, where the initial switch is a single pull double throw, allowing us to turn on the peripherals (lights, music, etc.) and the second switch would turn on the controller, allowing for a double failsafe system. We are using a Curtis 1238r controller at the moment. Any advice would be greatly appreciated.

Save

1 - 8 of 8 Posts

dougingraham

· #2 · Feb 25, 2014

This is what I do in my conversion. First switch position closes the main contactor which powers up everything that was originally powered up in the accessory position and turns on the DC to DC converter. The second switch position applies power to the motor controller and once it goes through its precharge procedure the car can be driven. The start position is not connected to anything.

I think a lot of people set it up this way.

Save

PSUstudent

Discussion Starter · #3 · Feb 25, 2014

So is there any danger from a current spike when the power is first applied to the motor? A professor expressed his concern that this could be the case.

Save

Duncan

· #4 · Feb 26, 2014

PSUstudent said:
So is there any danger from a current spike when the power is first applied to the motor? A professor expressed his concern that this could be the case.

Yes - the motor controller has some large capacitors

Normal procedure is

Power the controller "brain" - normally 12v

power to one of the contactors
You will normally have a contactor (high power relay) in each leg of the battery

Pre-charge
If you close the second contactor you will get a damaging power surge
So you use a resister (I am using an old kettle element) to moderate that surge
When the voltage has climbed enough THEN you close the second contactor

Some controllers do this internally (Soliton)

See less See more

Save

PSUstudent

Discussion Starter · #5 · Feb 26, 2014

I really appreciate the advice! We are using the curtis 1238r controller, but we were hoping that instead of the suggested setup, which has a relay set up to turn on when on switch is flipped, we could replace it with a switch and resistor to limit current to prevent the spike.

Save

Duncan

· #6 · Feb 26, 2014

PSUstudent said:
I really appreciate the advice! We are using the curtis 1238r controller, but we were hoping that instead of the suggested setup, which has a relay set up to turn on when on switch is flipped, we could replace it with a switch and resistor to limit current to prevent the spike.

No you don't "replace it" with a switch and resistor to limit current
You use both

The switch and resistor are just for charging the capacitors - the main current is too much for a switch and is carried by the contactors

Save

dougingraham

· #7 · Feb 26, 2014

PSUstudent said:
So is there any danger from a current spike when the power is first applied to the motor? A professor expressed his concern that this could be the case.

Not when applied to the motor. Motors are inductors and current through inductors changes (relatively) slowly.

I think you meant the controller. That has a large bank of capacitors that must be precharged slowly or the relay/contactor/switch contacts will weld shut. This function is integral to the controller I used. The control logic to do it is part of most all of the controllers.

Save

dtbaker

· #8 · Feb 27, 2014

the Curtis controllers have relatively small capacitors compared to zilla or soliton. soliton handles pre-charge internally. even with zilla a pre-charge resistor is not always used.... the big main contactor pads slam shut pretty fast, and have a large area; unlikely to weld shut from the momentary arc.

look up threads regarding 'pre-charge resistor'

lots of people DO leave the DC-DC 'always on' to keep everything like interior lights, and clock running....

Save

1 - 8 of 8 Posts

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.

Top Contributors this Month