We have a DPDT ON-OFF-ON (1-0-2) Cam switch that manually transfers power from a solar/battery system or from a AC power supply. The switching is DC, set at 14.4V, around 35A max. Typical current loads are around 15A, but the system idle current seldom exceeds 5A. This is tested daily and I have noticed some contact wear as evidenced by having to slightly rock the switch sometimes to get full contact. These are older legacy systems but part of a system that works well and has been reliable.

The power is for UHF and VHF radios, low power task lighting (incandescent and LED) and satellite phones. I would guess radios are mostly inductive loads but I’m not sure.

The cam switch itself has only an AC rating (600V at 40A ) and no DC rating, which I figure might be part of the problem. The switch breaks both the positive and negative DC leads, I’m assuming to be able to isolate the equipment from any power source at all.

It’s been suggested that we install premade snubber circuits to help reduce any arcing since the system is always on. My question is:

Where would I install the snubbers? Would it be acceptable to install them just on the POS and NEG DC buss inside the same enclosure since all loads are DC? or install them on every active contact?

Thanks in advance!

Ken

 

Possible bad news here! Radios usually use a few bypass capacitors, and also filter capacitors, to avoid coupling signals between stages. So most radios are mostly capacitive loads, in addition to the effective resistance of the active circuits.

A "cam switch" may slowly make and break the contacts, or it may have a cam driving a snap-action motion. The reality is that all switches wear from operation, a bit more when switching under load, even within the specifications. Many switches have a claimed lifetime of some number of operations , often at the rated load current.
So switches do not last "forever", although it may seem that way.

 

Thanks for your comments. The cam switch is snap action, not sure if that's good or bad since there is likely no wiping action. The next failure I decided I'd disassemble the switch and see if I can detect any contact damage or wear just to make sure I'm heading in the right direction.

Thanks again for your response.

 

As MB2 noted, the load is probably highly capacitive, so high surge current rather than inductive arcing is the more likely cause of any contact erosion.
One way to minimize that is to place a NTC thermistor inrush current limiter in series with each source of power (not in the load circuit).

 

Mostly, snap-action is the better choice for switch operation, the only pace where it might not be the best choice would be low-level signal circuits.

 

As MB2 noted, the load is probably highly capacitive, so high surge current rather than inductive arcing is the more likely cause of any contact erosion.
One way to minimize that is to place a NTC thermistor inrush current limiter in series with each source of power (not in the load circuit).

Thank you for the reply. It seems to me that the a thermistor could generate some heat, although I must admit I'm a bit shakey on the theory.

 

It seems to me that the a thermistor could generate some heat

Yes, it needs to dissipate some power to stay in its low-resistance mode.
The power dissipated equals the load current times it resistance at that current (from its data sheet).