Relay ratings, DC inductive loads, surge absorbers

[d x l]

Thanks Lfe, that helps.

 

[GaryS]

I have seen this many times and had to fix it many times.
The problem is with the relay or contactor ratings
The modern rating for DC are for SCR power supply, when supplying power the current naturally passed through 0 120 times a second where the generator supplied DC or CAP filtered supplied the current doesn’t go to 0 at all
The problem with modern contactor’s with DC is not when they close and allow current to pass but it when they open with SCR power supplies they naturally go 0 so the current supply voltage and current naturally got to 0 breaking this only requires a small arc gap. But with full DC of Cap Filtered supplies that doesn’t happen. So when the contactor open it must open with a very large gap, with a 500 VDC system that gap must be well over an inch to brake the arch. But the modern contactors don’t do that their gap is way to small to brake the arch they rely on the natural power cycling through 0 to do that. The wave form on the
power supplies are different and must be considered when selecting the hardware.
I have had to replace many contactors that were sized wrong usually after 3 or more failures and many hours of down time it is important to understand how current flows in any system to select the correct hardware.