[akorna]

I got one of these contactors with my 72v kit from e-volks.com. http://www.gigavac.com/pdf/gx12.pdf

After finishing all the electrical connections in my conversion, It worked twice and then stuck in the closed position (current flow). I disconnected the 12v power leads and the contacts still remained closed. After tapping the case a few times the switch opened. I applied 12v and the circuit closed, but still would not open when I de-energized the circuit.

Is there anything I'm missing here (residual voltage) or is it just faulty - I plan on returning under warranty - which of course will slow down my progress.

Anyone have one of these in service on their EV?

[piotrsko]

based on my experiences you have a bad contactor.

there were a bunch around for a while perhaps 10 years ago in the aircraft field whereby the contactor for the motor starter wouldn't disengage. really annoying but not uncommon.

[akorna]

Actually,
I spoke with Rodney Nash - Application Engineering at Gigavac. He told me that the contactor was fine, but the problem was the in-rush of current as the voltage is applied to the motor and the amps spike. The field created keeps the switch closed. He said that the system should have a "soft start" circuit installed to prevent the spike.

In looking at the tech/installation info for the Alltrax controller (re-labled by D&D Motor Systems and provided w/the motor in the kit) it identifies the need to add a pre-charge resistor across the primary terminals on the contactor, as well as a diode across the control wiring. Anybody know if this resistor/diode is a common requirement or have installed in their application?

[elevatorguy]

You should have a precharge resistor across the main contactor to prevent damage to your controller and main contactor contacts. There was a good explaination on this in the controller section. A diode should be across the coil to prevent back emf spikes on the 12 volt side. I have noticed the contactors drop out quicker with the diode in place.
I still suspect your contactor is bad or holding residual magnatism this is keeping it in too long.

[akorna]

Jerry,
Thanks - I ordered a pre-charge resistor (1000 OHM 10W) and a diode (1N5408 3A) as specified by the controller manufacturer and will install next week. If that doesn't work then I think you're right about the contactor being bad.

[dimitri]

A good option for precharge resistor is an incandecent lamp. I was researching info on precharge yesterday and found a very informative post on EVDL, copy of it is here .

I will be adding it to my EV today after I go to Lowes and pick most vibration and shock resistant lamp I can find.

If you have a single contactor design, precharging has a downside of leaking current from the pack, unless you use relay on precharging circuit. In my EV I used 2 contactor setup from EV America, in which case you just hardwire precharge across the positive side contactor, the one controlled by throttle cutoff switch.

After 3 months of use I notice arcing marks on this contactor, plus it stresses the hell out of controller caps, so it seems pretty obvious to add this cheap protection to prolong component's life.

Even though Curtis has good reputation and low failure rate, why add risk if the fix is so simple? I don't get why they don't have it on all EV schematics.

[akorna]

Interesting thread - The recommended 1K OHM 10W resistor costs like $0.39 - so I'm going to just do that along with the diode. I'm hoping this will fix the contactor sticking problem. Haven't had a chance to experience wear - only drove the car a few feet forward and back.

[piotrsko]

Ok if it is a "precharge current, it ought to stop when you remove excitation and have the relay open by itself. therefore to test: disconnect the bugger and see if it opens

My fault, I thought you had disconnected it and still had a problem.

[akorna]

You were right - the contactor remained closed even after I disconnected everything and removed from the vehicle. Needed 5-10 raps of a screwdriver head to open after that.

UPDATE: I installed the resistor and diode in the circuit. The contactor still stayed closed after the second power application cycle. The component kit supplier - e-volks - agreed to exchange it for a Kilovac EV200. They said that they had problems with the Gigavac and was no longer providing them in their kits.

Interesting note - with the precharge resistor in place (1000 OHM, 10W) the controller light was ON and was receiving 14 + volts, and would be at all times unless another switch was placed in the circuit. I now understand why people place two contactors in the circuit (safety and voltage drain).

[EVpat]

Dear EV folks.

I am sorry you had a problem with our EPIC sealed contactor. Those of us that founded GIGAVAC came from Kilovac, and are the team that first developed and marketed most of Kilovac’s EV contactors, including their EV200. Our GX12 EPIC sealed contactor is the next generation of sealed contactors and should work well. We also have some new coil options that required only 1.1 watts of hold power, the lowest in the industry.

I believe our Rodney was right, the sticking of the contactor contacts was the result of no pre-charge of the capacitors in the motor controller. Don’t feel bad, GM had the same problem when they first developed the EV-1. Unless these capacitors are pre-charged, when the contacts close they see infinite current at full system voltage, limited only by the internal resistance of the system. The solution is to pre-charge the capacitors at least 90%. Depending on the size of the resistor use and your battery voltage, you likely could use an inexpensive auto relay for the pre-charge, and save all of the fooling around we a resistor or light bulbs, etc. Just calculate the voltage the pre-charge relay contacts will see and make sure the relay is rated for the DC voltage you plan to switch. Two contactors would also work as mentioned in this blog.

A common misapplication with many relays & contactors is the use of a single diode across the coil. This is not good. What happens is it slows down the contactor release time. With highly inductive or high voltage loads, this can extend the arcing time so the contacts vaporize very quickly, resulting in only a fraction of the manufacturers specified life cycles rating. We explain this on our application page at http://www.gigavac.com/apps/relays/index.htm (see “Coil Suppression”).

GIGAVAC GX contactors have been designed to withstand some tack welding. Some tack welding is good because the weld reduces the contact resistance. To break the tack weld, our GX contactors have a built in impact break mechanism that acts as a hammer that breaks the tack weld when power is removed from the coil. When a diode is put across the coil, the release time becomes slow & sluggish and the impact break does work property. It’s got to be a quick break. It’s like comparing a pro-baseball player hitting a ball to a kid hitting a ball at a pony league. We totally understand why you don’t want the coil back EMF traveling in your coil circuit, so we have made “built in” coil suppression in all of our GX contactors. We test the contactor with this suppression installed, so we know it will meet all of its published spec. There should be no need to add more suppression with GIGAVAC contactors.

Discussed above is what we would call “Normal” conditions. For EV contactors, it’s the “Abnormal” condition that can be a life or death matter. Should the controller become shorted (the common failure mode) the contactor could be the last resort to turn off the power to prevent a crash. Lead acid batteries can put out a lot of power, so it’s really important to select a contactor that is rated to interrupt the current and voltage of your system. I am not saying this because we sell contactors, but DON’T TAKE THIS LIGHTLY AND DON’T SKIMP in this area. One contactor should be fine, but two is even better because of redundancy. Imagine of something went wrong with the pre-charge circuit and the contactor welded as discussed here. You would never know it was welded until you turned off the power, and it that could be too late. Something I saw early on when we first started going to the EV races in Arizona was that open frame Albright or GE type contactors were commonly used. These were reliable low cost low voltage contactors, designed primarily for 48Vdc golf carts and batter back up systems. But when higher voltages were used in more modern EV’s, people kept using them and they were not rated, nor could they interrupt the fault current. Another mistake some people made with these open contactors is they would mount them close to a wall. Because the arc has to be extended to extinguish itself, the arc would go back into the contactor and there would be a meltdown and/or or fire. TIP – Make sure the contactor is rated to break your maximum load.

I hope you find this info of interest, and encourage you drop us a line if you should ever have any problems again. As our tag line says, Today’s expert in high voltage relays, and we are. We will contact the people at e-volks to see why they decided not to use our contactors. FYY, we soon will be coming out our GX200, that will be a drop-in alternative for the Kilovac EV200.

About the name Kilovac. Kilovac is a registered Trade Mark of Tyco International. GIGAVAC does not sell the Kilovac branded EV200 contactor, but offers the GIGAVAC alternatives that we feel are better because of the EPIC® seal and other design enhancements.

Regards,

Pat