Hi,

If a relay is rated to have a Nominal switching capacity of 16A 277V AC, what will be the maximum current if 12VDC are switched instead?

 

The ratings for contacts, both AC and DC are usually stated in both Resistive and inductive, for DC the current would typically be more for the lower DC voltage range, but less at the equivalent rated AC voltage value.,
You really need to consult the manuf. spec if they are available.
Do you have a part number in mind?
Max.

 

Thanks for the reply.

I was considering this relay to switch a 12V 10-12A load:

http://www.rapidonline.com/pdf/60-5030.pdf

 

After seeing the datasheet the proper answer is.. Its not rated for DC at all and thus should not be used for switching DC..

 

Hi, What makes a relay good for switching AC but not DC?

 

DC, especially an inductive load requires rapid release action and adequate contact area.
The relay you show, is not only recommended for AC but a resistive load, which is not so demanding on the contact composition.
Max.

 

So is the relay below a better option:

http://www.bosmic.com/editor/UploadFile/2009818121512147.pdf

The load will be a DC brushed motor.

 

That would be a better choice, it is similar to automotive relays, which incidentally you can pick up fairly cheap, especially at a recycler.
If the motor has other control such as DC speed controller, it is best to make sure is low speed or stopped before operating the relay if possible.
Max.

 

Thanks for the info.