# How do I properly calculate the requirements for an on/off switch?

I'm building an arc lighter to learn more about electronics and I'm not certain how to calculate what I need given the components I have. Do I go off the rating for the battery or the combination of battery and parts?

I want to buy the correct on/off switch. So far I have an 18650 battery 3.7v 3000mah, a charging board 5v 1A, a momentary push button switch 3A 120VAC, a high voltage transformer kit and a rubberized altoids case. I've put the links below if you're interested.

Any help with how I can calculate the requirements for an on/off switch would be great. If you see something I might be doing wrong off the bat I'd also appreciate the info.

https://www.ebay.com/itm/171933254204 5V 1A Micro USB 18650 Lithium Battery Charging Board Charger Module+ Protection

https://www.ebay.com/itm/222083901779 DIY kit DC High voltage Generator Inverter Electric Ignitor for 18650 Battery

• It comes down to what voltage and how much current you're switching (+ a safety margin). In your case anything rated at say 12VDC, 5A would more than adequately suit the bill. – JIm Dearden Mar 24 '17 at 14:35
• Also if a switch would be a problem for high current wouldnt a simple transistor + relay combination be able to do the job? – Zaid Al Shattle Mar 24 '17 at 14:56

Don't forget inrush current or other "rare" events. It practically means that sometimes it's not enough to look at continuous or peak rating, sometimes you have to actively limit them.

You need to figure out seven things:

1. What's the maximum total current (amps) I want to switch (including inrush if applicable)?

2. What is the maximum voltage I need to switch?

3. How many lines (poles) do I need to switch? 1, 2, 3...

4. Do I need more than just on/off (more than two "throws")?

5. How do I want to mount the switch? PCB Mount, Panel Mount, etc.

6. How do I want to connect the switch? PCB Mount, Solder Tabs, Crimps.

7. What "style" of switch do I need? Lever, button, weather-proof, etc.

Then find the switch that exceeds BOTH 1 and 2 and meets conditions 3–7.

• "Generally AC or DC doesn't matter" is not true when it comes to switching off and breaking the resulting arc. AC is much easier to disconnect, thanks to the zero crossings. – Brian Drummond Mar 24 '17 at 17:49
• @BrianDrummond ya I should qualify that. fixing – Trevor_G Mar 24 '17 at 17:51