Contactor Selection

KVS! I have a doubt on contactor Pick-up & Drop-off. IES 60947-4-1 Clause 7.2.1.2 mentions that 'contactors shall close satisfactorily at any value between 85% to 110% of their rated control supply voltage'.

Now, if I have a contactor with a 240V AC coil, the pick-up should be anywhere between 204 V to 264 V. If my contactor picks up at, say, 160V, does it pass the test or is it a violation of the above clause?

Similarly, I observed that the drop of is always within the band. For example, teh Standard says that for AC coils, the drop off is between 20% to 75% of Coil Voltage. (i.e.) for a 240V AC Coil, it is between 48V to 180V. But, I found that I always get somewhere around 80 V to 90V. Is it okay?

Thank you, KVS! That is precise!

Yes definetly KV sridhar, The Albright contactors do have blow outs to avoid arcing, but since it is not available, i have searched for Siemens and Schneider, but i hv not seen the similar contactors with DC contacts, i think they have only AC contacts. So i need to know if i can replace contactors of DC contact application with AC contacts.I need to have a definite approval before applying it..............

"So i need to know if i can replace contactors of DC contact application with AC contacts."

No, you can't. It may work for a while, but if the manufacturer has not explicitly rated it for DC use at your working voltage and current and with your load type, it will almost certainly fail - possibly catastrophically.

So i need to know if i can replace contactors of DC contact application with AC contacts.

In some situations yes, but you need to check the manufacturer provided documentation for DC operation de-rating and be aware that at currents as high as you are mentioning most contactors will not be suitable.

If it were me I would be looking at the supplier website and checking the contactors available, going up in contactor size until a suitable one could be found. Don't be surprised if you find that a suitable contactor has an AC current rating an order of magnitude or greater than its DC rating.

Additionally I would design and add snubber networks across the contacts to help with DC load arcing (but again only to increase the operational safety margin).

You sure of the name Albright International Manufactures DC contactors.

They still list a 350 Amp with coil voltages from 6 to 240v DC.

http://www.albrightinternational.com/lang/en/index.html

What I would suggest is going to a continuous duty rated industrial machinery engine starter type solenoid/contactor.

There are a lot of big machines that run 48 volt DC systems with starters that draw well into the 1000+ amp range while cranking and their starter solenoids have no trouble what soever with breaking of those levels of currents at 48 VDC.

For those that can help themselves.

Select your own contactor

I have seen in Siemens contractors of multiple poles that , if two or more poles are connected in series their voltage as well as current rating is increased. How come current rating increase?

For eg a 3rt1035 contactor has ratings

Coil : 48VDC

Contacts : AC-1/400V

• at 40 °C ambient temperature / rated value= 60 A

• at 60 °C ambient temperature / rated value= 55 A

AC-3 / at 400 V / rated value = 40A

at AC-4 / at 400 V / rated value = 35A

With 1 current path / at DC-1

• at 24 V / rated value 55A

• at 110 V / rated value 4.5A

With 2 current paths in series / at DC-1

• at 24 V / rated value 55 A

• at 110 V / rated value 25 A

With 3 current paths in series / at DC-1

• at 24 V / rated value A 55 A

• at 110 V / rated value A 55A

Here i m considering only DC section ie. DC-1 for 24V and 110Vdc at 1, 2 and 3 current path in series , as we can see for 110Vdc for 1 current path is 4.5A, for 2 current path in series is 25A and for 3 current path is 55A. Is this just their manufactured rating or is there any logic behind it?

s others have said, DC breaking is very sensitive to voltage. So, the more breaks there are in series, the better the breaking capacity. i give below an extract from a Siemens catalogue which hnestly depicts this. i hope it is readable. For example, a 3TB56 contactor can handle 400A @ 220V DC with three poles in series, but only 0.6A on a single pole !!! And practically nothing at all at 400V DC !!

Hello Everyone,

As mentioned in one of the post DC load are very difficult to break.

As you may be already know, the most important parameter in DC application is not current level, but DC voltage level on the load.

Bigger is the DC voltage on the load bigger will be the contactor.

As per Ayrton law each product get a specific arc voltage between his contact ( product design ).

This arc voltage is related to contact material use and distance between contact ( refer to Ayrton law for more details ).

To break safely DC load the arc voltage ( Technical data of product ) shall be bigger than load voltage.

Bigger is the difference ( 2 or 3 time ) faster we will break the voltage and in this matter you increase the electrical life time of your contactor.

Then in one post it is mentioned you do not find on big manufacturer ( Siemens and Schneider ) document on such product.

I will suggest in the Schneider product range ( if you DC load voltage is 48V it is not clear in your original question ) to use LC1F330ED ( This contactor is 48VDC coils and able to break 360A at 48VDC ).

You will find more details on Schneider web site http://www.schneider-electric.com/site/home/index.cfm/ww/ and in the MKTED210011EN catalogue in the DC table if you voltage load is different than 48VDc.

You may also use bar contactor which are quite efficient for DC application

You may also contact your Schneider country office and see with them what the best solution with your application is.

Actually i have already checked "LC1F330ED", but its contact ratings are for Utilization Categories AC-1 of 330A & AC-3 of 400A. But my load is an inverter driven Motor. Here connection is as follows:

Battery --> contactor --> Fuse -->Inverter--->Motor.

Here i do need a contactor of DC utilization category.

And please give a solution for my previous post ie. related to Siemens contactor also........

With batteries capable of delivering 350A+, if contactor or wiring to the contactor faults, you have a big problem. I would put the fuse in front of the contactor and as close to the battery as possible.

The Contactor as also DC rating you will find them in the MKTED210011EN catalogue in page 5/205.

Nevertheless I strongly recommend you to contact your Schneider Office in your country

So why not just use a large IGBT as a solid state contactor and be done with it?

Or for that matter why do you need a contactor anyway? does your inverter not shut down 100% when when the control circuits are turned off?

answer to the original problem mentioned by vipin:

use 2 nos of 24 V coil voltage auxiliary contactors. series their coil and supply 48 V to pickup. make suitable connections at their contact to supply 220 Ac for coil of a 350 A power contactor whose coil is 220 V ac. 220 V ac can be picked from plant lighting or as per ur wish. u can use 110 V ac also if it is readily available.

hope this may help to tackle the obsoletion.

Thank you