Contact deterioration, arc forming on high power DC switcher

Question

I have a problem on a switch contactor on high power load control. It is expected because the load is up to 200 amperes at 48V DC, resistive load.

How do I protect the contacts from a full load turn off and prevent the arcing on the contacts?

The resistive load is low ohmic resistors that draw 20 amperes each from a high capacitty battery. Yeah, they are big.

The contactor is rated 200 amperes continuous load, the coil is 24V. Kink.

It is a Brazilian part, used for motor start, but can be used continuously.

If it is not possible to upgrade the design what other components are ideal for DC high load switching?

There is "nothing" on the circuit except the resistor, the contactor switch and the battery, switch on low side.

Answer 1

Fala! You probably want an automotive grade solenoid type switch.

Something like the one shown here.

I've had arcing issues with contactors and DC in the past.

Answer 2

From the datasheet, it looks to be intended for a 24V system. There is a huge difference in switching 24VDC and 48VDC. You need a relay with either:

1. A much larger contact gap, so the arc self extinguishes.
2. An arc quench magnet, which pushes the arc off to the side.

You need a relay rated to switch 48VDC at 200A, which this one is not.

While there is considerable debate about the effectiveness, it is possible that using two relays with the contacts in series, might be effective in the short term, until you choose a relay properly specified for your application. The series connection lengthens the total arc length when opened, and may cause the arc to extinguish before contact damage occurs.