[ElectriCar]

Just curious with your electrical knowledge why you wouldn't just use like an Omron 12V on delay timer. A timer and mounting block would only be about $65 or so with shipping.

You turn on the ignition which starts the countdown and energizes the resistor relay. Once it times out, it energizes the contactor. I'm sure you have already thought of this I'm just wondering what your reasoning is to "reinvent the wheel" so to speak.

One relay I found.
http://www.newark.com/omron-industrial-automation/h3-4-12dc-30s/timer-on-delay-12vdc-30s/dp/07WX9125

[rfengineers]

Originally Posted by ElectriCar

Just curious with your electrical knowledge why you wouldn't just use like an Omron 12V on delay timer. A timer and mounting block would only be about $65 or so with shipping.

You turn on the ignition which starts the countdown and energizes the resistor relay. Once it times out, it energizes the contactor. I'm sure you have already thought of this I'm just wondering what your reasoning is to "reinvent the wheel" so to speak.

One relay I found.
http://www.newark.com/omron-industrial-automation/h3-4-12dc-30s/timer-on-delay-12vdc-30s/dp/07WX9125

I considered that, but I wanted the flexibility of a microcontroller.

[kittydog42]

Those relay contacts are rated for 30VDC max. You will have a very hard time finding an affordable relay with contacts rated over this. Since the current is so low, most people just use these relays anyway for KSI, with no problem, switching pack voltage. Another option that works with certain controllers (Curtis 1231, for example) is the tap 24V for use with the KSI signal, to stay within the relay ratings. This would not work with a Logisystems, though, so check the documentation for your controller.

[Gavin1977]

RFEngineer. Interesting article, and I think your device is a good solution to the problem of switching on the contactor without enough precharge for people who want the HV completely isolated when parked up.

My 2pence worth is that I think people are worrying far too much about leaving the precharge on all the time. The current drawn from the traction pack is negligible, the available power is tiny, therefore in a fault condition, the vehicle is not going to go anywhere. And even if you do disconnect the precharge, High voltage remains on the controller input terminals for many hours after disconnect, so extreme care needs to be taken to safely discharge the caps before maintenance even with the HV disconnected.

Dont get me wrong, I think a power switch / kill switch is an extremely good idea for maintenance / emergencies, I just dont think they need to be used every time you park up. Just my opinion as an EE who designs drive controllers (But not in the EV power requirements)

[ElectriCar]

Originally Posted by kittydog42

Those relay contacts are rated for 30VDC max. You will have a very hard time finding an affordable relay with contacts rated over this. Since the current is so low, most people just use these relays anyway for KSI, with no problem, switching pack voltage. Another option that works with certain controllers (Curtis 1231, for example) is the tap 24V for use with the KSI signal, to stay within the relay ratings. This would not work with a Logisystems, though, so check the documentation for your controller.

It would be switching the 12V for the relay coil, not HV so it's not a problem for that. It would operate off the 12V system when you turn on the ignition it would energize the relay. After the delay that connect the 12V to the KSI relay.

[rfengineers]

Originally Posted by Gavin1977

... And even if you do disconnect the precharge, High voltage remains on the controller input terminals for many hours after disconnect, so extreme care needs to be taken to safely discharge the caps before maintenance even with the HV disconnected.

When I shut off my contactor and precharge relay the Voltage on the controller side drops from ~120VDC to less than 50VDC in under 30 seconds. That is with nothing connected to the input of the controller (other than a 250mA DC-DC converter running the digital Voltmeter) and just the motor on the output.

[rfengineers]

Originally Posted by kittydog42

Those relay contacts are rated for 30VDC max. You will have a very hard time finding an affordable relay with contacts rated over this. Since the current is so low, most people just use these relays anyway for KSI, with no problem, switching pack voltage.

You are quite right about the relay, but it seems to be working reliably for me so far. The precharge relay is socketed. If the contacts fail it only costs $2.50 and takes a moment to change it.

[engineer_Bill]

Originally Posted by rfengineers

That is doable, but I would modify it to leave the precharge on after the contactor closes.

I prefer my step-start device since it allows me to turn on the ignition switch without applying precharge.

I setup my system to do this a contactor coil connected through a mushroom EMO button NC to the ON IGN wire, (main contacts to controller minus and battery minus). A second contactor has a precharge resistor permanently connected across it ,coil connected to a latching relay connected to IGN START, (main contacts are to battery plus and controller plus). This gives me two open contactors one on each leg in case of failure, and when off the pack is completely isolated except the resistor. If I should accidently touch across it, it will shock, but the current through the resistor shouldn't be enough to kill me. a 15count gives enough precharge that the inrush current is less than the rated current of the contactor. a perfect system would have a time delay on the start relay to prevent premature start with warning light like the glowplug light on the diesels. This system is simple and gives me enough redunancy to feel confident that even with a complete failure of one contactor, I will still be able to turn off the car. Since the minus contactor never opens or closes with current flow unless the emo button is pressed, it should last a long time. Both contactors are rated at 200VDC 1000AMPS, one has a 12vdc coil the other has a pack voltage coil the latching relay has a double pole; one is used for latching 12v from the start signal; the other pole switches the pack voltage to the coil of the second contactor, and the on signal for the controller. the keep voltage of the latching relay is the IGN ON signal, so it drops out when you turn off the key. We can debate this to death, (there is more than one way to skin a cat), this is a setup that works.

[rfengineers]

Originally Posted by engineer_Bill

I setup my system to do this a contactor coil connected through a mushroom EMO button NC to the ON IGN wire, (main contacts to controller minus and battery minus). A second contactor has a precharge resistor permanently connected across it ,coil connected to a latching relay connected to IGN START, (main contacts are to battery plus and controller plus). This gives me two open contactors one on each leg in case of failure, and when off the pack is completely isolated except the resistor. If I should accidently touch across it, it will shock, but the current through the resistor shouldn't be enough to kill me. a 15count gives enough precharge that the inrush current is less than the rated current of the contactor. a perfect system would have a time delay on the start relay to prevent premature start with warning light like the glowplug light on the diesels. This system is simple and gives me enough redunancy to feel confident that even with a complete failure of one contactor, I will still be able to turn off the car. Since the minus contactor never opens or closes with current flow unless the emo button is pressed, it should last a long time. Both contactors are rated at 200VDC 1000AMPS, one has a 12vdc coil the other has a pack voltage coil the latching relay has a double pole; one is used for latching 12v from the start signal; the other pole switches the pack voltage to the coil of the second contactor, and the on signal for the controller. the keep voltage of the latching relay is the IGN ON signal, so it drops out when you turn off the key. We can debate this to death, (there is more than one way to skin a cat), this is a setup that works.

You are quite right about skinning a cat, Bill. Your system sounds great.
I put mine together because I wanted the flexibility to alter the program in the microcontroller to meet different needs. I'm offering it to others since the cost of producing two dozen circuit boards was not much more than having just one made!

[micheljaw]

Thank! Very nice answer...thanks.
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