250V DC CONTACTOR

hurk27

Senior Member
Thanks for your help.

The DC supply is from a rectifier. Two 2-pole contactors are needed to directly change the polarity for reversing.

For the main poles of NEMA or IEC contactor, switching 250VDC is not a big deal, we can connect 3 or 4 poles in series to improve the ability. But it is really hard to find a coil rated 250VDC. Maybe nowadays it is not common in use, but only for some special applications like mining or railway.
You might be supprised to find that there are allot of industrys that still use 250 volt DC, many cranes are DC while most newer ones are run with drives, many older plants still rely on contactor control, the link I posted in my earlier post EC&M has the double interlocked two pole DC relays, but you order 4 singles with two pole kits (in your case NEMA size 2), the coils for a two pole configuration is 120 volts and are wired in series so if one fails both drop out, but they are quite pricy.
Click on this link: EC&M DC controls click on the 7004 PDF catalog to get the prices
 
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petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Thanks for your help.

The DC supply is from a rectifier. Two 2-pole contactors are needed to directly change the polarity for reversing.

For the main poles of NEMA or IEC contactor, switching 250VDC is not a big deal, we can connect 3 or 4 poles in series to improve the ability. But it is really hard to find a coil rated 250VDC. Maybe nowadays it is not common in use, but only for some special applications like mining or railway.
they are still listed in the siemens catalog as being a standard option for their IEC contactors.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Yes. ABB has DC contactors listed as well. I think in both cases they are very long delivery items.
I think they also list an electronic coil that has a wide range of voltage options DC/AC that covers 250VDC. The only way to find out is to call the local Siemens distributor and ask.
 

zxfabb

Member
Location
LS
If it is a DC series motor, reversing the supply polarity won't reverse the rotation.


If the supply is from a rectifier, can't you operate the control circuit and contactor coils from the AC that feeds the rectifier?
Just reverse the polarity to armature, not the series wound.

There is a battery connected to the busbar as a backup power source. The valve is a critical load thus both mains and control supply must be taken from DC side.
 
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zxfabb

Member
Location
LS
I think they also list an electronic coil that has a wide range of voltage options DC/AC that covers 250VDC. The only way to find out is to call the local Siemens distributor and ask.
Yep, I've asked Siemens yesterday about 3TC series. Unfortunately only 24VDC and 110VDC coils are available.
 

zxfabb

Member
Location
LS
Check out Eaton Electrical, aka Cutler Hammer who still manufactures the old Westinghouse DC contactor's. Thee are two, the ME that goes from 5-150a and one that goes from 5-1800a. The design as to have been around since before electricity was even discovered.
http://www.eaton.com/Eaton/Products...ol/MillControlProducts/DCContactors/index.htm
180VDC-280VDC is the lower and upper limits during battery discharging and charging.

The Eaton ME looks good, but the coil operating range 80%-110% doesn't meet the requirement. Maybe I have to ask for a customized one.

Does Westinghouse still produce electrical components like contactor and industrial control relay?
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Yep, I've asked Siemens yesterday about 3TC series. Unfortunately only 24VDC and 110VDC coils are available.
As I warned you, finding a Siemens distributor who knows what he is doing is going to be a challenge...

Siemens 3TC48 w/ 230VDC coil data sheet

It's a 230VDC coil, but you can just drop your 250V with a resistor, but watch the watt rating of your resistor, it has to match the coil current.
 
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templdl

Senior Member
Location
Wisconsin
180VDC-280VDC is the lower and upper limits during battery discharging and charging.

The Eaton ME looks good, but the coil operating range 80%-110% doesn't meet the requirement. Maybe I have to ask for a customized one.

Does Westinghouse still produce electrical components like contactor and industrial control relay?
Remember that Westionhouse itself no longer exists as the Electrical Distribution Protection and Control Business Unit was purchased by Eaton back in 1995 and combined with their Cutler Hammer Division basically just short of tripling Cutler Hammers size. I believe that Eaton is in the process of transitioning the name of Cutler Hammer to be Eaton Eaton Electrical.
Have you contacted them yet? They may have custom coil voltages avaikabe on the master drawings but someone would have to pull it first to varify.
I may have so old instructions for the ME with renewal paets but I have to look as I have been in the process of cleaning my old files out.
 

templdl

Senior Member
Location
Wisconsin
Hi, guys

I'm looking for a contactor to control a 250V DC motor-operated-valve.

DC-5, series-motor:
Full load current at 250V DC: 41 A
Locked rotor current at 250V DC: 362 A

Contactor:
Main-pole: 250V DC nominal, ranging from 180V to 280V
Coil voltage: 250V DC nominal, ranging from 180V to 280V
Operating current of auxiliary contact at 250V DC: 1A

Much appreciated if you recommend a proper type and manufacturer.
OK! Are you ready?
By a stroke of luck I happen to have the engineering drawings for the ME DC contactor coils.
You asked for a 250VDC coil which has 15,000 turns of 0.0071 dia wire, 313 turns per layer. The avg. Cail resistance is 1270 ohms, 1302 max and 1178 min.
The coil assembly part number is 30B4376G10
 

templdl

Senior Member
Location
Wisconsin
Hi, guys

I'm looking for a contactor to control a 250V DC motor-operated-valve.

DC-5, series-motor:
Full load current at 250V DC: 41 A
Locked rotor current at 250V DC: 362 A

Contactor:
Main-pole: 250V DC nominal, ranging from 180V to 280V
Coil voltage: 250V DC nominal, ranging from 180V to 280V
Operating current of auxiliary contact at 250V DC: 1A

Much appreciated if you recommend a proper type and manufacturer.
OK! Are you ready?
By a stroke of luck I happen to have the engineering drawings for the ME DC contactor coils.
You asked for a 250VDC coil which has 15,000 turns of 0.0071 dia wire, 313 turns per layer. The avg. Cail resistance is 1270 ohms, 1302 max and 1178 min.
The coil assembly part number is 30B4376G10
The actual coil part number is 2A94113G05. The drawing notes state that there are (2) coils in series.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
3RT1054-6NP36

200-277VDC coil

out of stock - est 4-5 weeks.
To my earlier point on the difficulties of using AC contactors on DC power:

This specific contactor, DC-3 and DC-5 ratings:
1 pole is rated 160A at 24VDC, but at 220V DC, it drops down to 0.6A!
2 poles in series gets you to 2.5A
If you use all three poles in series, then it gets you back to 160A at 220VDC. That means for reversing, you would need 4 of these contactors.
 

templdl

Senior Member
Location
Wisconsin
To my earlier point on the difficulties of using AC contactors on DC power:

This specific contactor, DC-3 and DC-5 ratings:
1 pole is rated 160A at 24VDC, but at 220V DC, it drops down to 0.6A!
2 poles in series gets you to 2.5A
If you use all three poles in series, then it gets you back to 160A at 220VDC. That means for reversing, you would need 4 of these contactors.
If one looks at the distance an AC contactor's contacts open it should become very apparent why the don't do well with DC. The just don't have the capability to break a DC arc. Most breakers do a much better job at clearing a DC arc because they have the ability to disperse a DC arc with the help of the contacts opening at a greater distance and draw the arc up between the arc chutes.
And by placing 2 or 3 poles in series increases the DC voltage capability which essentially increases the distance the contacts open by adding the 2 or 3 poles together.
Incidently, with DC contactor's it is common for them to have what are called "blow out coils" which help to break the arc.
 

hurk27

Senior Member
If one looks at the distance an AC contactor's contacts open it should become very apparent why the don't do well with DC. The just don't have the capability to break a DC arc. Most breakers do a much better job at clearing a DC arc because they have the ability to disperse a DC arc with the help of the contacts opening at a greater distance and draw the arc up between the arc chutes.
And by placing 2 or 3 poles in series increases the DC voltage capability which essentially increases the distance the contacts open by adding the 2 or 3 poles together.
Incidently, with DC contactor's it is common for them to have what are called "blow out coils" which help to break the arc.
All the EC&M contactors we use on our 250 volt mill systems all have the blow out coil in the arc chute, we had a few maintenance people leave the chute open only to find that the tips don't last very long doing this, the other problem is the fact that the DC arc last a lot longer and will severely burn the tips of an AC contactor even if you series the contacts to get the DC rating, it may be fine for very low current control applications but I would not do it for any higher current as you will end up replacing tips very often which if this valve is mission critical as the OP stated, I would not want to design it to fail, sure it will be costly but so will it failing I would think by the sound of them putting a 250 volt back up battery system on it which makes me believe its an important system?

Also Square D also makes the same contactors that EC&M does, as they once owned EC&M for a while (1954 to 2003) when a couple of their executives purchased the line and brought back the EC&M name, so Square D could be another source as we also have a few of their systems with their contactors in them, and they are available, but again for reversing you have to purchase the double pole kits and the mechanical interlock kit then assemble them from 4 single pole contactors with 120 volt coils, each double pole will have two 120 volt coils in series, they do this so if one coil fails they both drop out.
 
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templdl

Senior Member
Location
Wisconsin
Wayne, thanks for sharing. There aren't all that many guys that have actual experience with DC contactor's, not just theory. My experience was limited to their sales, applications, and support. Because the were just a small portion of what my responsibilities were I still had to get up to speed on them in order to be a viable support resource as well as good support from my engineers.
 

hurk27

Senior Member
Wayne, thanks for sharing. There aren't all that many guys that have actual experience with DC contactor's, not just theory. My experience was limited to their sales, applications, and support. Because the were just a small portion of what my responsibilities were I still had to get up to speed on them in order to be a viable support resource as well as good support from my engineers.
I have worked on DC cranes before this job at the steel mill, but I'm a little rusty and get some things switched around in my mind as I did in post 16 which for some reason I was thinking a shunt motor:ashamed1:

But being at the mill for over a year now and getting back into the swing of trouble shooting the many DC motor applications we have out there has been a learning experience as some of the things I have seen are all new to me.

I do know that you can design the circuit to use the lower cost AC contactors to swap the polarity and use a single DC contactor to remove the motor load before each time the polarity is changed, the circuit drops out the motor then it is reversed then you can plug the DC contactor to start the motor in the reversed direction, this way the reversing set of contactors never break under a load and the arc problem is eliminated on the AC contactors, it could save a little cost on the price of 4 DC rated contactors but will add to the complexity of the control system and the trouble shooting, to maintain the battery back up but allow the control to use 120 volt AC coils or even 230 volt AC coils you can use a low cost DC to AC inverter that run on 250 volts DC and output 120 or 230 volts AC, this will allow you to design most of your control system around an AC circuit with only switching the DC contactor through a series set of tips from a control relay that only has to be sized for the coil load of the DC contactor, installing aux contacts on the AC reversing contactors will prevent the DC contactor from pulling in if the contacts on the AC reversing contactor have not yet made, this will prevent the AC reversing contactor from ever switching under a load, if a DPDT contactor rated for the motor load could be found the circuit could be made even simpler with only one coil to switch between forward and reverse, the common of each pole would be to the armature common 1 would go to A1, common 2 would go to A2, NC on pole 1 would connect to NO on pole 2 and connect to the DC contactor which the other side of the DC contactor would come from the positive feed, the NO of pole 1 would connect to the NC of pole 2 then feed S1 of the field winding, S2 from the field would go to the negative return of the circuit, with the reversing DPDT coil not energized the motor would run CW, energize the reversing contactor coil and the motor will run CCW.

Let me see if I can draw this up in paint to which I'm not very good at:happyno:

Ok heres a stab at it:

 
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templdl

Senior Member
Location
Wisconsin
Wayne, that makes so much sense. You're basically using the AC contactor's as a non load break switch to reverse poles. That's what you call thinking outside of the box.
You may be aware already that it is common for the coils of AC contactor's to actually be DC except they include a rectifier pack to change the AC to DC. As such the core of the coil doesn't have to be laminated like the common AC coils. They a quieter and pull in nicely.
Because the DC coil requires less current once its pulled in they also include an economizing contact that bypasses part of the bridge rectifier which reduces the current to the coil after it is pulled in. Without a rectifier I'm not sure how this would be accomplished with a basic DC coil.
Interesting stuff though.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
To my earlier point on the difficulties of using AC contactors on DC power:

This specific contactor, DC-3 and DC-5 ratings:
1 pole is rated 160A at 24VDC, but at 220V DC, it drops down to 0.6A!
2 poles in series gets you to 2.5A
If you use all three poles in series, then it gets you back to 160A at 220VDC. That means for reversing, you would need 4 of these contactors.
they are 3 pole contactors. why you you need four of them?
 
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