Battery switching without tears

Switches are generally rated according to interrupt capacity, and that's why the AC and DC ratings are different. In the immortal words of a friend of mine in the business, "DC just doesn't switch worth a ****". As the contacts open, an arc is struck. With AC current, the arc self extinguishes (for small switches) when the current goes to zero. The arc persists longer with DC, causes more contact wear, hence a reduced rating.

A "1A DC" switch is not going to fail or in any way be stressed by keying the mic and momentarily running 2, or even three or four amps. Try not to turn off the master while you are talking on the radio :-).

My panel has a CN2, CNv, radio, flarm. I have the standard issue Schleicher rotary switch, no modifications. Switching between batteries is simple: turn the knob. No drama, no instrument problems.

Evan Ludeman

On Monday, April 6, 2020 at 8:33:37 AM UTC-7, Tango Eight wrote:
Switches are generally rated according to interrupt capacity, and that's why the AC and DC ratings are different. In the immortal words of a friend of mine in the business, "DC just doesn't switch worth a ****". As the contacts open, an arc is struck. With AC current, the arc self extinguishes (for small switches) when the current goes to zero. The arc persists longer with DC, causes more contact wear, hence a reduced rating.

A "1A DC" switch is not going to fail or in any way be stressed by keying the mic and momentarily running 2, or even three or four amps. Try not to turn off the master while you are talking on the radio :-).

My panel has a CN2, CNv, radio, flarm. I have the standard issue Schleicher rotary switch, no modifications. Switching between batteries is simple: turn the knob. No drama, no instrument problems.

Evan Ludeman

No, a 1A DC switch will probably not instantly fail at 2A. An engine redlined at 7000 will probably not instantly fail at 8000. A glider rated at 5.5G will probably not instantly fail at 7G. Still, designing something to routinely operate out of spec isn't considered good practice in my shop. And the switch might fail with an inrush current of 20A, while switching, after awhile.

CN, like most other manufacturers designed to the reality of switching power sources in operation. LX, apparently, did not. I have no problem with switching my break-before-make rotary switches on a full panel of (non LX) electronics - nothing resets.

The continuation of this thread is proof that we are quarantined.

On Monday, April 6, 2020 at 11:33:37 AM UTC-4, Tango Eight wrote:
Switches are generally rated according to interrupt capacity, and that's why the AC and DC ratings are different. In the immortal words of a friend of mine in the business, "DC just doesn't switch worth a ****". As the contacts open, an arc is struck. With AC current, the arc self extinguishes (for small switches) when the current goes to zero. The arc persists longer with DC, causes more contact wear, hence a reduced rating.

A "1A DC" switch is not going to fail or in any way be stressed by keying the mic and momentarily running 2, or even three or four amps. Try not to turn off the master while you are talking on the radio :-).

My panel has a CN2, CNv, radio, flarm. I have the standard issue Schleicher rotary switch, no modifications. Switching between batteries is simple: turn the knob. No drama, no instrument problems.

Evan Ludeman

Case in point to illustrate Evan's statement: I've tried to use a small water heating tank to use excess solar power to heat some water. Its heating element is rated 120VAC 15A. It has a thermostat with an internal switch to match. I fed it about 50VDC 6A from solar panels. That switch died in short order. Also note that we're warned not to disconnect solar panel connectors while the sun is shining and the power is being used, because the arc will damage the contacts in those connectors.