AC vs DC coil on large starters

[wolfie1a]

Looking for some feed back on why you would spec out a DC coil or AC coil on a large motor starter (size 5 or 6). I'm old school and back in my day we used DC to avoid vibrational issues associated with AC coil. Don't know if this is still a valid consideration or not. Your opinons will be greatly appreciated.

 

[dpc]

This is generally a design standard of the starter manufacturer. I would let them provide their standard design, whatever it happens to be. Starters with dc coils will come with their own rectifier, so it's completely transparent to the end user. DC coils will generally draw less current when pulled in, so are commonly used at Size 4 and above.

The vibration angle is a new one on me.

 

[jraef]

DC coils also generally hold in better under voltage drop conditions, something you are more likely to encounter the larger the motor gets. dpc is right, most larger starters have DC coils even if they are labeled as AC, they just have the rectifier built-in.


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[OperaHouse]

Be aware that some DC units are dual coil. That is there is a second coil for extra pull in power and this disconnects when pulled in. These extra contacts are potentially a source for failure.

 

[itsmoked]

I wondered, because DC coils normally draw far more power pulled-in than equivalent AC coils.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Skogsgurra]

There are also contactors with a little rectifier + switcher and a controller that makes the coil draw a heavy current for the pull-in and then reduces current considerably for holding the armature.

Those contactors do not chatter or drop out when the line is going low during a heavy start.

Gunnar Englund

http://www.gke.org

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[waross]

Normally it is not wise to spec a contactor coil as AC or DC. You will just eliminate a lot of good equipment from your list of choices.
The contactor manufacturer will choose the coil in the design process and will not change the design for one sale.
The exception would be where your favorite contactor had a DC coil where all others used AC in that size. Spec'ing a coil type that is only available from one maker will effectively steer the selection to your favorite. This is probably not ethical but it is done.

Bill
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"Why not the best?"
Jimmy Carter