Standard light switches can burn out

I have been using standard light switches to turn my fuel pump on and off … It was 10 below F this morning …My red truck would not start. It had plenty of crank and ran for 3 seconds and quit. … The switch sits on my dashboard in sunlight. Best I can figure is the sunlight got to it … I didn’t make it to my meeting … I’d suggest putting in a metal box or the such. I had mine external as I have nickle chromium wire attached to it so it has to be in the open … Stay warm, Mike LaRosa

4 Likes

Could heat from the nickel crome helped the switch to die?

1 Like

Mike when you say" light switch" you are talking an automotive dc one right?

1 Like

I think I’ve seen pictures of Mike’s set-up using a household light switch. Maybe they can’t handle the increased amperage?

[email protected] 120VAC is 0.83 amps, but at 12VDC, that’d be 8.3 amps. I’m not sure what a fuel pump draws, but it’s probably higher amperage in 12VDC vs some lighting at 120VAC.

:EDIT: it looks like most household light switches are rated at 8-15 amps.

Thanks Brian,
Household light switches are usually 49 cents … They work fine. It was around 10 below zero that morning and I didn’t think to switch the switch to get ice out of it … I have it in the truck to re-install it when things warm up … I don’t plan to replace it. I can’t even unlock my black truck right now …
brrrrrrrrrrr I’s around 10 below right now and going down …
regards, Mike
PS, big difference between DC and AC but a fuel pump only draws around 4 amps or so …

2 Likes

Hello I found this site the other day and have enjoyed reading some of the posts. Anyway when I saw this one I figured I would reply . I was a controls engineer for over 17 years in industry and the contacts on ac and dc switches are different . AC switches depend on the wave form passing through zero volts to break the Ark in the switch if they are used with dc the contacts will pit faster and fail because the dc ark on the switch won’t brake till the contact gap gets too big for the voltage to jump the gap. That is off the top of my head but I learned a long time ago buy dc contacts for dc current they usually cost more but will last longer. you can find industry dc switches at allied electronic for a decent price. Hope that helps a little.

5 Likes

So Mike the rule of thumb I was taught was to derate ac switches by a factor of 10 when using them in dc. That ac wall switch would be limited to 1.5 amps by that rule. The contacts get all carbonized to the point where they fail. As mentioned above they rely on the switching voltage to break the contact dc arc a lot more.
Best regards, David Baillie

2 Likes

I think another reason to be carful when using ac switches on dc is that they will arc and they do sometimes weld the contacts together and you wont be able to cut the power to whatever your feeding
Dave

1 Like

Hi, Mike!
19. of December 2016

Additionally, on DC you may have a motor- or a solenoidpump!
Both act like an electric inductance with an iron core.
That makes “prolonging” of the brake function, resulting in a
substantial arc = welding heat on the contact surfaces.
A suitable (chosen) capacitor parallel with the switch may help,
as with ignition brakers + condensator. Quelling coil inductance.

A radio on MW off stations is the best detector how well the condensator
dampens the sparking.

2 Likes

I had the same experiance with useing the 240v swich for a 12v fuel pump. It burnt out within a couple of weeks time. It was rated for more amps thain the fuelpump draw but it just didnt hold.
Interasting, the 25% petrol hybrid swich with the fuel pump an a solenoid resistor was the first to go. If operated for a bit longer times, it got quite hot.
I now use 12v dc swich now, works like a charm for about 3 months of everyday use.

1 Like

Maybe I am getting a little nit-picky here, but recently I bought something at allied electronics and their shipping cost was higher than anything I ever bought anywhere on line.
I just located a 28VDC 20 amp toggle switch there for $2.77 and cheapest shipping was $6.98
So, I suggest that, if you need a 12 volt DC switch for something, just go to your closest auto parts store. You probably need something else there anyway.

Pete Stanaitis

3 Likes

Thanks guys … If I had flicked the switch even one time the car would have started. My brain is a little off after being in a coma for a day in May and then getting hit by lightning and then the following stroke. I am familiar with DC vs AC … I have a 6 gallon water heater that runs off 160V DC from 4 160 watt panels … I had to add an SPDT (typical) thermostat to it and a capacitor resistor network discharge to it to prevent sparking and welding the contacts. Live and learn. It’s worked great for around 10 years now. I got one truck running today … I can’t even work the locks on the others yet. They are too frozen … Stay warm and well … It’s up to zero here now F … regards, Mike

1 Like

Did l read right? You got struck with lightning??

1 Like

Kristijan,
Yes you read right … The bolt came down about 10 feet ahead of me and wiped out my buried phone line under my feet … I can’t describe the feelings in my hands … 5 seconds later a second strike hit my phone line about 50 feet ahead of me but I didn’t feel that one.
I’m typing on 800 feet of 17 gauge electric fence wire nailed to trees now … I will never bury another line here again … I have 8 dead cables now … This line has been hit twice since but a pair of pliers is all it takes to fix it … I saw those strikes too …
Mike

3 Likes