# Contactor Failure



## JRP3 (Mar 7, 2008)

Did you have a precharge resistor and a diode on the contactor?


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## Automcdonough (Sep 1, 2010)

yeah inrush could be well over the 400A but not for long enough to pop the fuse.. just long enough to arc weld the hell out of the contactor.


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## Tesseract (Sep 27, 2008)

dhrivnak said:


> ...I was VERY disappointed with the Tyco as it is rated at 500A and 360V and our system is 144V and with in-line 400 amp fuses that did not blow. _I fail to see why the contactor failed._


There are several things you probably missed, then...

First is that a typical 400A DC-rated fuse (e.g. - Class T) will carry 1000A for around 10 seconds before it blows. 

Second is that your contactor almost certainly _closed_ into a dead short. Few contactors will survive that even if grossly over-rated. The 360V rating you are quoting is the maximum system voltage the contactor can interrupt and is irrelevant here. The 500A rating is the maximum DC current the contact can pass - not necessarily switch - _with_ appropriate heatsinking of the contacts. 

Third is that it sounds like you either didn't have a precharge resistor/relay across the contactor, or did not allow enough time for precharge to take place. IIRC, the 1231C has 7200uF of capacitance and a 750 ohm resistor for precharge is recommended. You need to wait a time period of 5*R*C before closing the main contactor, which in this case would be 27 seconds. If you didn't wait 27 seconds or longer every time you started precharging before turning on the controller then you slammed the capacitors with a huge burst of current. 

For example, say you only waited 5.4 seconds (1RC in this case). The capacitors would have charged up to 63.2% of the battery pack voltage, or 91V. Close enough, right? Well, the surge current that would flow when the contactor is closed is the difference in voltage between pack and caps (144V - 91V = 53V) divided by the total system resistance, which should be a few milliohms to a few tens at the most (depends a lot on the ESR of those capacitors - the film capacitor inside the Soliton1 has an ESR of 0.5 milliohm).

So 53V divided by 10 milliohms results in a surge current of 5000A. If you check the notes on the EV200's datasheet it states that the maximum make current (what it sees upon contact closure) is 650A.

If you never used precharge and the contactor survived more than 1 cycle then you should be PRAISING it, as it certainly far exceeded all expectations and claims in its datasheet.


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## zwmaster (Nov 23, 2009)

I second that.

One other question to mr. Jeffrey.
Internal capacitor resistance of 0.5 milliohm, is this combined of all caps or single one?
I assume these are pretty big caps inside


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## dhrivnak (Sep 25, 2008)

Actually I do have a 750 ohm precharge resistor and a coil supression diode. I have stout 2/0 wires going to and from the contactor and the battery wire was going to the A1 terminal with A2 going to the controller. I have attached a picture.

What would you recommend as a contactor?

The fuses I have are the faster blowing CNN 400 amp. I have a split battery pack so one fuse is in the front pack and one in the rear. Neither fuse blew.

www.hrivnak.com/electric_jeep.htm


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## Tesseract (Sep 27, 2008)

dhrivnak said:


> Actually I do have a 750 ohm precharge resistor ...


And did you precharge the controller for 27 seconds or longer every time you started it up? I personally think this would try the patience of even the most die-hard EV enthusiast. If so, then maybe check to make sure that the resistor hasn't gone open circuit on you. 

BTW - you could use a 25W/220 ohm resistor to cut the precharging time down to ~8 seconds.



dhrivnak said:


> What would you recommend as a contactor?


The EV200... it's hard to beat, actually. The only thing the Albright SW200 has going for it is the contacts are replaceable. Like I said above, closing a contactor into a dead short is the worst possible thing you can do to it, and an insufficiently precharged controller is pretty much the same thing as a dead short. Additionally, this huge pulse of current will induce a huge spike of voltage across any stray inductance in the wiring which then zaps the semiconductors inside the controller. In fact, it is very likely that the controller failed right when you turned the main contactor on.



dhrivnak said:


> The fuses I have are the faster blowing CNN 400 amp. I have a split battery pack so one fuse is in the front pack and one in the rear. Neither fuse blew.


Not sure what to tell you here except that fuses don't blow if neither their i²t or peak let-through current ratings aren't exceeded. An 400A A3T series fuse from Ferraz-Shawmut has a peak let-through current of 10kA, btw.


zwmaster.... it's a single special-purpose film capacitor and it takes up over 50% of the internal volume of the Soliton1.


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## zwmaster (Nov 23, 2009)

Tesseract said:


> zwmaster.... it's a single special-purpose film capacitor and it takes up over 50% of the internal volume of the Soliton1.


It must be UFO kind of thing then


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## EV-propulsion.com (Jun 1, 2009)

So Jeff, the following is false info I received (direct from curtis) a long time ago about precharge time for the 1231C using their recommended resistor.
"Yes, about a second, the resistor actually becomes part of the time constant as the R in the RC circuit across the contactor terminals as the capacitors charge up."

I guess their concerns were for protecting the controller, not any contactors! I guess that's to be expected from a controller manufacturer with a 30 year old design 

In our builds we always checked precharge time with a voltmeter, and adjusted resistor ratings and our time delay for contactor closing accordingly. 
Mike
www.EV-propulsion.com


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## etischer (Jun 16, 2008)

I have another possible reason the contactor could have welded it's contacts. 

This failure method only applies If your EV200 contactor has Aux contacts, and you are using them to maintain latching of the coil. My EV200 Aux contacts got welded, and caused the Main contacts to come on instantly with the key (no preharge) 

http://www.diyelectriccar.com/forums/showthread.php?t=42667


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## EVfun (Mar 14, 2010)

Look at the picture of the precharge circuit. There is no precharge time to worry about because the controller is always precharged. This is the way the Curtis schematic shows precharge being handled and is very common with older Curtis powered conversions.


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## etischer (Jun 16, 2008)

EVfun said:


> Look at the picture of the precharge circuit. There is no precharge time to worry about because the controller is always precharged. This is the way the Curtis schematic shows precharge being handled and is very common with older Curtis powered conversions.


 
What if the driver tries to drive off with out first closing the main contactor? Then the controller will need to be re-precharged. This is about the time the driver might prematurely turn the key and fry the contacts in the EV200.


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## EVfun (Mar 14, 2010)

I'm thinking that the owner would tell us the failure happened after trying to drive away without turning the car on. Actually, that little problem is easy to fix and should be fixed.

It is common to wire ksi directly to pack positive with Curtis 1221 and 1231 controllers. When you do this the controller is ON all the time the it's precharged. If you hold the clutch in (or put the vehicle in neutral if it is clutchless) and press the throttle you can usually hear the motor spin a turn or two when you push the throttle if this is how the controller is wired. While common, this is a bad idea. ksi takes enough power that the controller will never properly precharge with a 750 ohm resistor. Every time you turn on the vehicle there is a 10 to 30 volt jump when the main contactor engages. I used light bulbs as prechage resistors so I don't know just how much, but it will be too much. This is hard on the main contactor.

The solution is to add a relay, in parallel with the contactor, to switch pack positive to ksi only when the main contactor is ON. You could use the auxiliary contacts of the contactor, but I doubt they are rated for high DC voltage. 

I also don't really recommend using a diode across the main contactor coil. The main contactor will have a pretty powerful coil so you should use something, but a regular diode slows the contactor's dropout speed. That is never good when trying to interrupt high voltage. You should use something like the coil suppressors supplied with the Zilla controller (I'm not at home so I cannot look at the part number.) You can also use a pair of 20 volt zener diodes connected band to band with the ends connected in parallel with the coil. This will cause the contactor to open more quickly than adding a freewheel diode.

_The Zilla controller ships with one or more (depending on options) 1.5KE24CA-T Transient Voltage Suppressor, also known as a TVS diode. I found the info in a previous post of mine._


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## Tesseract (Sep 27, 2008)

EV-propulsion.com said:


> In our builds we always checked precharge time with a voltmeter, and adjusted resistor ratings and our time delay for contactor closing accordingly.


And how long did it take for the voltage across the resistor to drop below, say, 10V? I'm guessing it was a lot more than just a second or two!


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## EV-propulsion.com (Jun 1, 2009)

We try to get it to be @ 10 seconds, about the time it takes to put a seatbelt on, that's about all the patience we have for it to charge!
Mike
www.EV-propulsion.com


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## dimitri (May 16, 2008)

EVfun said:


> Look at the picture of the precharge circuit. There is no precharge time to worry about because the controller is always precharged. This is the way the Curtis schematic shows precharge being handled and is very common with older Curtis powered conversions.


Having precharge resistor always on causes it to bleed current into other devices, like DC-DC for example, causing resistor to get hot if its value is low enough. This could be a fire hazard and it could eventually bleed the battery.

IMHO, precharge relay is a must have feature.


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## JRP3 (Mar 7, 2008)

EVfun said:


> I also don't really recommend using a diode across the main contactor coil. The main contactor will have a pretty powerful coil so you should use something, but a regular diode slows the contactor's dropout speed. That is never good when trying to interrupt high voltage. You should use something like the coil suppressors supplied with the Zilla controller (I'm not at home so I cannot look at the part number.) You can also use a pair of 20 volt zener diodes connected band to band with the ends connected in parallel with the coil. This will cause the contactor to open more quickly than adding a freewheel diode.


Yes we had a discussion about this somewhere, and I think Tyco/Kilovac has a bulletin on it.


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## EVfun (Mar 14, 2010)

dimitri said:


> Having precharge resistor always on causes it to bleed current into other devices, like DC-DC for example, causing resistor to get hot if its value is low enough. This could be a fire hazard and it could eventually bleed the battery.
> 
> IMHO, precharge relay is a must have feature.


And that is why I like the light bulb so much  With a ksi relay a Curtis 1221B controller only needs a little 7.5 watt light bulb for the precharge resistor. That is about a 2000 ohm resistor when hot (brightly lit) but only about 200 ohms when making barely any visible light. 

If you don't have a ksi relay (bad idea, controller is always on inside) then you need about a 40 watt light bulb. The "brains" of the Curtis controller uses a lot more power than the resistor that bleeds the ripple capacitors. 

You should never put your DC to DC on the controller side of the contactor unless you can verify that the DC to DC will not have any 12 volt load on it when the controller is precharging. If the DC to DC is loaded it can prevent, or significantly delay, the controller precharge. This is also true of the cabin heaters. If you really want to have either of these behind a main contactor you should be using a duel main contactor system.


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