[Lee Hart]

Originally Posted by waveformblue

- wire a 2 to 5 Watt Zener in series with a 12-Volt ice-cube relay coil, and place it on the cap bank side of the line contactor, like this...

+ -----|<-------CCCC-------- -
[ zener coil ]

The ice-cube relay will not close until there is about 9 Volts across it - assuming it's a 12-Volt one. With a Zener in series, it will not close if the voltage is higher than 9 Volts for the coil plus the Zener Voltage. This can be used as a precharge timeout.

For an 80-Volt system...

68-Volt Zener + 12-Volt (closes at 9 Volts) ice cube = ~77 Volts. The contacts of the ice cube will not close until the cap bank reaches about 77 Volts. You can use this as a time delay. In this example, a 5-Watt zener will be needed if the 12-Volt relay draws 50mA.

This is good in theory. In practice, an 80 volt nominal pack actually varies from something like 70v (dead) to 100v (fully charged). With a 77v zener, the relay coil voltage would vary from 0v with a dead pack (won't pull in, so you can't even creep the car to a charger), to 23v with a fully charged pack (which would burn out a 12v relay coil).

Here's a practical circuit for doing what you describe. I have it in my LeCar EV.

ControllerB+------R1------K1------R2------ControllerB-

R1 and R2 are 1.5k 5w resistors. K1 is the coil of a relay with a 120vac 1.66kohm coil. On DC, it pulls in at 35vdc at 21ma. With the two 1.5k series resistors, it thus pulls in when the controller voltage reaches 98vdc.
This works fine with my 120v nominal pack (which ranges from 105-150vdc). Even at 150vdc, the current is low enough so the coil and resistors don't overheat.

The contacts of K1 are in series with the main contactor. To precharge:

• The keyswitch pulls in K2, a small relay that connects a 75w light bulb across the main contactor's contacts. This precharges the controller.

• When the controller input voltage reaches 98v, K1 pulls in. This in turn lets the main contactor pull in.

And away we go! :-)

[Lee Hart]

Originally Posted by Conelrad

in my years of high-power electrical work, relays/contactors get burns when de-energizing under load.DG

Exactly right!

Originally Posted by Conelrad

It doesn't seem there would be much going on when time to open the circuit in an EV. No demand, eh, since the controller would've already ramped the current down?DG

When everything is working correctly, the main contactor only opens and closes at zero (or nearly zero) current. Its contacts therefore last a long time. The mechanical life of these contactors is on the order of one million cycles.

But, the contactor is there in case something goes wrong. If the controller fails "fully on", then the contactor will open to stop the current. In this case, it may be asked to interrupt some hellish current -- the worst case current that the batteries can deliver!

That's why you need a big contactor, rated to safely interrupt the worst-case pack voltage and current in an emergency. It only has to do it once. Most big contactors like this have replaceable contacts.

Originally Posted by Conelrad

The other item I have not seen mentioned is most professional DC contactors have permanent magnets adjacent to each contact set to blow out the opening arc.DG

Yes, that is the case here as well. Blowout magnets significantly increase the DC voltage rating of contacts. Without them, you're forced to use the contact at about 1/4th of its AC ratings. A 120vac contact is only good for 30vdc, etc.

[mizlplix]

This a very interesting thread, but I am somewhat at a loss.

1. My old Jet Electra was 30 years old. It had the original Albright, open air, contactor. It did NOT have a pre-charge resistor. Never did. Still does not. Still works fine. Maybe all 5000 of them were just "lucky"?

2. My present AC50 set-up states "No precharge resistor necessary". I guess the controller magically takes care of it?

Not to be sarcastic, but there are certain circumstances where none of this is necessary, or even desirable.

Miz

[major]

Originally Posted by mizlplix

This a very interesting thread, but I am somewhat at a loss.

1. My old Jet Electra was 30 years old. It had the original Albright, open air, contactor. It did NOT have a pre-charge resistor. Never did. Still does not. Still works fine. Maybe all 5000 of them were just "lucky"?

2. My present AC50 set-up states "No precharge resistor necessary". I guess the controller magically takes care of it?

Not to be sarcastic, but there are certain circumstances where none of this is necessary, or even desirable.

Miz

Hi Miz,

Newer controllers, like the 1238, handle the turning on of the main contactor and do the precharge using a circuit inside the controller rather than an external resistor.

The case with the Jet Electra is weird. I don't know if it was originally made without a precharge circuit or if it was modified at some point. The fact that it functioned without a precharge could be due to a combination of rather low voltage, high battery and circuit resistance, low controller capacitor size and robust contactor. And I doubt that Jet Industries made 5000 of anything.

I have had smaller non-road EVs which have gone without precharge resistors for long periods for various reasons. Sometimes they seem to work just fine. One eventually welded the contactor and the usual wrap with the wrench wouldn't unstick it. So I left it on, for like a year until I fixed it right. In another case, the guy I worked with decided not to use the manual precharge switch. He didn't see why. So after a year or two, the little Curtis blew up. Cause and effect?

You have your right way of doing things and then ways that appear to work. Wire your controller the right way per the instruction manual.

major

[Lee Hart]

Originally Posted by mizlplix

1. My old Jet Electra was 30 years old. It had the original Albright, open air, contactor. It did NOT have a pre-charge resistor.

2. My present AC50 set-up states "No precharge resistor necessary". I guess the controller magically takes care of it?
Miz

Hi Mizlplix,

The Jet EVs used GE EV-1 controllers. These controllers did not have input filter capacitors, so they did not need a precharge resistor to charge them.

However, no capacitors also meant that battery ripple current was high. This shortened the range you could get from your batteries.

The Solectria/Azure controller have input capacitors, as well as built-in precharge circuits. An external precharge resistor is thus not necessary.

[lazzer408]

I sent a PM to OP today about this thread but he hasn't been on in a couple months so I'll ask the viewers.

Do you guys need a starting/latching/precharge circuit that actually monitors the controller's cap voltage and activated the main contactor after they are charged? One that works with any setup? Doesn't matter what the pack voltage is or which controller your using. It's all automatic. No programing or adjustment required. It can also signal it's precharging with a red LED and beep until it's charged and the beep stops and the light goes green. It can also have a brake interlock that would open the main cont. if your foot is on the brake. Good for panic stops? Probably get anoying with the MC clunking in and out all the time plus the wear on it.

[crashedup]

What about the soliton 1 does it need a precharge circuit?

[Yabert]

Originally Posted by crashedup

What about the soliton 1 does it need a precharge circuit?

No!
Watch the second point http://www.evnetics.com/soliton_specs.php

[crashedup]

Ah ok thanks for the link. Thats good to know. Yabert you have a soliton 1 right?
How do you turn off the car? Do you cutt all power from pack? If so how?

[Ziggythewiz]

It's okay to read Yabert's link, really.

"Main contactor and precharge/discharge control built-in!"

When the controller turns off, the car turns off.