[OT-CNC]

I have 2 AEG LS 37 contactors that I'm using to power up 2 servo drives. The contactors I'm using are surplus, one of which cooked a coil on my 1st power up. Initial quick testing for latching worked fine.I'm not sure what went wrong.
These are 24v DC coil, the power supply I'm using is outputting 23.9V DC which I can adjust if need be.
These particular contactors use an external HS17 contact block that the coil pigtails tie into.Without this block, the coil does not energize. This contact is NC and opens when the contactor closes.
I think the plastic fingers on the external contact were not fully grabbing the body of the main contact mechanism, perhaps leaving the circuit closed too long when retracted causing the coil to cook? Is that a possibility?
I'm not fully understanding why these contactors came with this type of external contact. I believe this was called the late brake version?
Just to clarify, one of the contactors operates fine both were wired the same. I'm getting a replacement and want to make sure I wire this correctly in case I got this wrong.

Thanks
OT

[Al_The_Man]

It is very rare for DC coils to fail, especially burn out, it is however prevalent in AC versions due to the fact they have to pick up the coil armature otherwise the inductive reactance stays very low resulting in over current.
Are you sure they are not AC coils? If this is so it would explain the burn out by using on DC.
Al.

[OT-CNC]

Interesting. According to the part number I was told by the sales tech that the unit was DC.
Assuming it's DC, can you explain how this type of coil works with the external pigtails and NC external contact which opens when energized?

[Al_The_Man]

I am not familiar with that particular contactor but it looks like a typical DIN style version.
I could not see any pigtails you mention in the on line documentation.
Al.

[OT-CNC]

Al,

Have a look at the scan.
The pigtails are what the drawing shows as the "black leads built into coil" going into the late break aux contact.
Also, I assume polarity does not matter? There is a pos and neg shown for both terminals.

Attachment 260258

[Al_The_Man]

I don't think the polarity should matter? I have never implemented one with late break contacts.
Al.

[Al_The_Man]

I suspect the way the coil works is that the contacts are closed in order for higher current to pick the relay armature up, once a DC relay or solenoid armature has shifted it requires much less energy to keep it closed, if this is correct and the relay picks up but the contacts do not open for some reason, could cause burn out of the coil?
Al.

[OT-CNC]

I replaced the contactor with another one and all is good.
I'm still curious to the previous failure.
I'm certain that the iron laminations moved as the contactor closed so I'm not sure I understand the above explanation. Could it be that in a twin winding coil, 2 coils are used for the initial closing, then the aux switch opens to de-energize one coil resulting in less current draw. Let's say if that aux switch did not open (when not mounted properly) it could cause the second coil to stay energized and burn out?

[Al_The_Man]

Yes, as i mentioned in the previous post, the only reason I can think of is to simulate the advantage a AC coil has initially, which is a high current due to the low inductance and low coil resistance, which the DC coil does not posses, but once pulled in the DC has the advantage, and power can be reduced to retain it and save on energy required.
The dual coil appears to be a high current to initially pick the armature up and simulate the AC version, and once the late break contacts pick up it uses the lower current retaining coil.
If the contacts do not open, it probably would cause the burn out.
Al.

[OT-CNC]

Thanks Al for the explanation.