Can 110-VAC Contactor Coils Operate from a 110-VDC Supply?

In a word, No.

AC coils and DC coils are wound in completely different manners.

No.

Is it 110 V DC coil dc contactors.or 110v DC coil ac contactors.

Generally these contactor coils are slow moving items ,will not be readily available in the open market.May be you can contact the manufacturer of the contactor and they can supply ,but they may require lead time.

If you are desperate you could use a variable voltage DC supply and monitor current & voltage. Run it up until the contactor just pulls in reliably and go about 20% higher with the voltage. Then use your voltage and current readings to calculate the value needed for a dropping resistor to drop the 110VDC to this voltage--110V-(pull-in voltage + 20%)divided by current reading=resistance in ohms. Then multiply this voltage by the current to get the power that will be dissipated by the resistor and at least double it to get the necessary power rating of the resistor for reliability. Check the wattage rating of the coil to be certain you are not exceeding it by multiplying the new DC coil voltage by the new DC current.

If you do not have a variable DC supply you could use a variac feeding an unregulated fixed supply as long as it is not a switching type or you could feed a bridge rectifier with the variac and filter it with a large value electrolytic capacitor of an appropriate voltage rating. It would also be possible to use a rheostat to drop the 110VDC for this calculation if you have one.

This is probably not a good idea. It is likely that the amount of current you would need with the fewer number of turns likely to be on an AC coil would create excessive power dissipation in the coil.

I would say if you are desperate try rewinding the coil with more turns of smaller wire, assuming you can disassemble the device.

Hello Asitha,

AC Contactors/Relays and DC Contactors/Relays have different magnetic circuits too.

AC Contactors do not require any extra small airgap, because being AC supply,the magnetic circuit is switched through zero, each time the polarity of the applied AC reverses - The return springs then quickly pulling the poles apart on power-off to the operating coil.

DC Contactors normally require a small air gap, sometimes retained by a small non-magnetic "button or rivet", between the opposing pole faces.

This airgap prevents the two pole faces from making full contact, with the attendant risk of the poles sticking together, upon power removal to the operating coil.

Yes, I do know that springs are there to ensure pole separation on power removal to the operating coil.

If you look at the Contactor/Relay construction, you should normally see the small article, which maintains a tiny airgap, on DC Contactors.

AC Contactors/Relays must therefore be used on AC sinewave supply (What they are designed for)

DC Contactors/Relays must therefore be used on DC supply (What they are designed for)

Kind Regards....

Dear All,

Thank you very much for all your valuable supports.

Well put! As usual!!!

http://cr4.globalspec.com/comment/124127

if you are still desperate and can calculate the resistor value (don't forget the power rating of the resistor) using a KTBG DC contactor as a reference, this is another option.

No , if you use 110v Ac contactor coil , it shall chatter and shall make & breakas the contact per the supply frequency.

Hi Asitha,

DC: Direct Current; AC: Alternative Current.

So they are different and you have to use DC equipment for DC power supply and AC for AC.

If you want to use 110 VDC power supply for Contactor with DC coil you can build a circuit that transform 110 VDC to 48 VDC or 24 VDC e.g. adding a resistance in serie to coil; or serial connecting 2 coil of 2 contactors with 48 VDC,.....

good luck

AC coils will not cause a DC contactor to chatter.

You will probably find that a 220 Volt AC coil fitted in your DC contactor will operate ok at 110 volt DC give it a try out of circuit to prove it.

Or if you cant find an AC coil for your contactor a 220 volt AC contactor will probably be ok but be careful with the current rating you will probably have to up size for DC power.

Dear Friend

We manufacture battery chargers for power plants and substations and regularly use 110 V DC rated contactor with 110 V DC coil in same. We have supplied these equipment in India & abroad. In our design we have found that these coils very very rarely fail and therefore cannot comment on why the coil has failed, in the first place, in your equipment. Failure of DC coil is a serious failure. Please send me contactor part no. or the make and current rating so that the right solution can be suggested.

Thanks and regards

Ashok Toshniwal, Bangalore, India

The Coil will fail. AC coils have impedance which is due to the inductance and resistance of the coil.In Dc current is limited by Resistance only.So u can understand now.

We use AC solenoids on DC supplies for many projects with one important caveat. The coil dissipates more power and will burn out in short order. Therefore, we only use this arrangement in applications where the solenoid is activated for short time intervals at low duty cycle. Do NOT consider leaving the coil activated for any length of time.

What computer program do you recommend to control the relays for a bio-diesel plant? The type of computer program will also set the control voltage for the relays that are used for control motors, valves, heaters, etc. What control voltage should these relays be?

Thanks for the info. D Fuller

Probably Programmable Logic Controllers (PLC) could do the job.

To arrange their programs you need:

• to have the lists of relays / contactors / heaters i.e. outputs in entire system
• to have the list of inputs as push buttons, sdensor, meters etc
• selected type of PLC (e.g. Rockwell, Siemens)
• software for these PLCs
• have a knowledge to enter the program (Logic Ladder, Block or other) from the computer (download) to PLC memory.

Some of gen-sets have their own controllers.

Again your question is not clear enough to give more specific suggestion.

From the experiment: "DC voltage for AC relay coil"

For relay/contactor with 110Vac needs less DC Volts:

1. to close (energize) e.g. 30 Vdc

2. to hold (keep closed) e.g. 11 Vdc

so for continuous work (holding it closed long time) you need to have;

1. Dc Power supply about 35 Vdc or specially selected resistor to drop 110 Vdc- 35 Vdc = 75 Vdc for relay coil inrush current

2. Additional resistor to holding branch (to keep holding current) just above measured (in this example 11 Vdc) dropping value. This branch uses usually auxiliary contacts of the relay.

First response is NO.

But, some small AC coils the winding wire is so fine the dominant term is resistive and not inductive, and those will work OK on DC also. This can be checked by taking the DC resistance of the coil, then dividing VAC/R and noting if it is the same current that the coil draws when energized with AC. If the AC current is much less then you have a large inductive component to contend with.

If you use series resistors with the coil you can limit the current to the coil. If you need momentary high current to pull in the contactor, then use less dc resistance and a normally closed contact of the contactor that will open and add the remaining resistance for holding levels. If the contactor tends to stick closed due to the residual magnetism in the contactor increased spring pressure, or the introduction of aluminum or brass shim stock into the gap of the armature will reduce the residual forces.

It is a fun bench experiment and gives good understanding of what is involved.

As an aside, an AC electric door solendoid lock was bothering people in an office. A small rectifier was put in place to drive DC to the solenoid, so rather than a buzz it was a click. It worked great!

Dear Friend

Are you looking for contacts of the DC contactor or the coil of DC contactor. PLEASE NEVER EVER USE CONTACTOR WITH AC RATING POWER CONTACTS FOR DC APPLICATION. YOU STAND A VERY HIGH CHANCE OF CONTACTS GETTING BURNT DURING MAKING/BREAKING IF AC RATED CONTACTS ARE USED FOR DC APPLICATION. DC RATED CONTACTORS are COSTLIER compared to AC RATED CONTACTORS.

Your problem is not a serious issue, just a question of PROPER SOURCING. Please give the contactor make, part no. & rating and we can EASILY supply same or tell you where to get it from.

We manufacture battery chargers for power plants and substations and regularly use 110 V DC RATED CONTACTS with 110 V DC COIL in same. We are approved by ALMOST ALL LEADING ENGINEERING CONSULTANTS IN INDIA & have supplied these equipment in India & abroad. In our design we have found that coils & contacts very very rarely fail and therefore cannot comment on why the coil/contact has failed, in the first place, in your equipment. Failure of DC coil & contact is a serious failure.

For any further details please contact.

Thanks and regards

Ashok Toshniwal, Bangalore, India 9448491293

Which is why I mentioned to up size the contactor for DC power.

Once again,"If you are desperate" to use a contactor with an AC rated coil,I had a chance to experiment today with an old Arrow-Hart ACC430UM30 3-pole 50 amp contactor with a coil rated 208-240VAC with about 238 ohms DC resistance. It pulled in at 50 volts DC and dropped out at 5 volts DC. The power dissipation at 50 volts DC is about 10 watts and that seemed a little high for continuous use so I tried using a 2200 ohm resistor in series on 120VDC to give about 11 volts on the coil with about 1/2 watt dissipation and added a 330 microfarad capacitor across the resistor to give the coil a momentary jolt to pull the contactor in and the steady state 11 volts kept it in until power was removed. It dropped out reliably every time. Don't be afraid to experiment. I am assuming you are aware of the dangers involved in playing with these voltages but once again good luck and have fun. The resistor will dissipate around 5 watts so a 10 watt power resistor should be OK and the capacitor I used was rated for 200VDC. And watch polarity.

I am happy to see someone actually applies theory and tests with experimentation.

Too many people on this forum obviously have little knowledge of what they are talking about!

(The safest professional engineer is the one that knows what he does and does not know!)

I am happy to see someone actually applies theory and tests with experimentation.

Too many people on this forum obviously have little knowledge of what they are talking about!

In response to this, thanks-maybe it's because I'm not an engineer but a maintenance tech. who often has to make do with what is available or get a piece of equipment up & running until correct parts come in. I also began each comment with "If you are desperate" and of course normally the original part would be easier and usually better but often something that should not work can be substituted if some mods are made. I've done this often with good results.

This is IT!

I did similar experiments but used two resistors:

First to energize the coil /close contactor with NC (NORMALLY CLOSED) contact in series , and second as a second branch (parallel) just to hold.

Better is to draw a diagram with values than just write dozens of statements that many times may confuse. But person asking for advise must state exact requirements and, of course in this case all available data.

Hooray!

We now have at least 2 engineers with a practical bent!

Hi I did tried what has explained by you. In mine case, contactor is switching on at 80VDC. I want to utilize this application at BTS telecom sites where battery bank voltage is 48VDC (max 60VDC). Is there any way out to lower the pick up voltage of this contactor? I know there are DC contactors available in this voltage but still I want to use AC contactor coil with DC voltage due to some specific reason. I am not a registered member, could u pls mail me at shamy_one@yahoo.co.in.

Here's another vote for 'no'.

They are wound in different ways, and not intended to be used on other types of supply.

At best, control fuses will blow.

At worst, .