Question: latching switch as a kill switch

Build threads
1

Would it be possible to use a latching switch instead of a sliding switch as the kill switch as long as it is rated for 3A (same as the common kill switch)?

I have my eye on a latching illuminated switch–planning to wire the switch to the battery on the one pole and the other pole to the Batt + pin on the proffieboard. The latching function would mimic a sliding kill switch–while latched, power would go from the battery to the proffieboard–seems easy, as long as my understanding of wiring isn’t flawed on this point–but how would I wire the two poles to make it illuminated? Normally, those would go to Free2 and GND–with SimpleBladePtr in the blade definition to light the switch.

Am I close or have i got this all wrong?
thanks,
js

2

Yes, a latching pushbutton should work just fine. Like you said, make sure its of high enough amp rating. Also, I would not wire anything downstream of the switch except the proffie.

As for wiring, usually it has dedicated pins for the led. So power would go in and out on 2 pins, then there is another 2 pins for +pos and -neg.

Post a link to the switch you are leaning towards and we can see if we can get any data on it.

3

Thanks!

12/16/19/22mm Waterproof Metal Push Button Switch LED Light Momentary Latching Car Engine Power Switch 5/12/24/220V silver1NO1NC - AliExpress

3-6V
12mm(1NO)
Self-locking

Red with power logo–not that that should make a difference.

4

Yep, you can see 4 wires in the pics. So the pins will be in, out, +, -.

Should be clearly marked, but you never know with ali. They show a wire diagram that may or may not be correct. You would just need an appropriate resistor.

5

I look for labels, but always test with a multi-meter before using buttons. Found one yesterday that already had NEG and one of the button pins jumpered, which forces the wiring a certain way.

6

We use more than 3A, but explaining why that is probably fine takes a long time.
Just make sure the switch doesn’t get warm/hot. If it does, get a different switch…

7

Isn’t a kill switch supposed to be rated for 10 amps ?

8

Would be nice, but the ones most people use are not.

9

They’re generally rated for 3A at much higher voltage. Since our batteries are 3.7v, there’s a lot more wiggle room in that rating.

2 Likes
10

Oh, cr@p. I am going to use bigger switches then. :thinking:

11

I mean… the 3A ones work fine is what I’m saying.

2 Likes
12

My understanding is that the BOARD only needs 3A. Standard wiring for batt+ to KS to proffieboard is 24awg which is rated for 3.5A. As long as the switch is only connecting the battery + and the board, a 3A 240V switch should be fine… and that’s the rating for the TS switches we generally use (red and tan).

Sometimes people ask about wiring the KS on the neg side (not me, ever), which requires the full amps to go through the KS (which could be 10+ amps). When you have B+ to the blade, the high amps go through the LED pins and Batt - to the proffieboard. Thats why I run 2x20awg from Batt - to the proffieboard, on 2 pins.

1 Like
13

Ok, let me try to explain…

First of all; there are no exact limits on how much current a cable can handle. If you put too much current through a cable, what happens is that it acts like a resistor; it gets warm and you loose energy and voltage that you could be using to power your LEDs. If you really go overboard, the heat will become a problem, things will melt and/or catch fire.

However, the wire itself will be fine. A silicone-wrapped wire will happily keep conducting while the rest of the saber melts around it. Obviously that’s not what you want, but the point here is that the limits aren’t limits, they are guidelines that keeps your wires cool and efficient.

The same is basically true for switches. In addition to all of this, switches are rated for a specific number of cycles, at max current and max voltage. Switches rated for 3A@250 volts has to be prepared for the fact that while the switch is turning on, there is a short period of time where the switch is not fully engaged, and during that time, the full 3A will go through a much smaller contact area than when the switch is fully on. Also, 250 volts can cause small amounts of arcing (in the micrometer range) . Both of these things can pit and scar the contact surfaces of the switch. A switch that is rated for 10k cycles with 3A@250 volts promises that this pitting/scaring isn’t going to be a problem until at least 10k operations.

Sabers are much nicer on the switches though.
We very rarely operate the switch while the blade is on, which means that the current going through the switch is usually quite low when we turn it on/off. Also, we only use 3.7v, so arcing is basically not a problem. This means that our surfaces stay pristine much longer, which keeps the resistance of the switch low for a much longer time. So how much current can we put through the switch? Well, there is no great way to tell from the data sheet, but we can measure the resistance and estimate. I have not measured my switches, so I can’t say exactly what the limit is, but it is almost certainly much higher than 3A. Again, there isn’t a limit, we just don’t want the switch to become warm.

Generally, it needs much less than that.
The board peaks at around 4A, but the average usage is much lower, below 1A.

5 Likes
14

But it was a valuable time expenditure! I never thought to consider arcing damage, so thanks!

1 Like
15

There is also several types of scratching and friction damage to consider… I don’t know how that works, but I bet it’s complicated…