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PostPosted: May 7, 2018, 12:00 pm 
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My toggle switch failed again this weekend. It seems like they really don't stand up to the vibrations of the car very well. Anyone have a recomendation on either a better toggle switch or maybe a great rocker switch?

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PostPosted: May 7, 2018, 2:50 pm 
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Had same problem with big box store cheapies...better luck so far with NAPA stuff....probably should try Aircraft Spruce for better still.


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PostPosted: May 7, 2018, 2:51 pm 
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Are you using DC rated toggles? And are the loads resistive? It is not uncommon for DC current ratings to be 1/10th the AC current rating. reactive loads reduce that even more.

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PostPosted: May 7, 2018, 3:02 pm 
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Location: BC, Canada. eh?
I think it's also worth mentioning that, in any circuit carrying substantial current (eg. lights, wipers, fan, etc.), it's better to go through a relay for the component's power, rather than run all the power directly through a switch. Mechanical switch contacts have an arc passing between them each time they're turned off and on, which creates a non-conductive corrosion on the contacts, leading to failure.

The lower the current passing through the switch, the less powerful these arcs are. When a relay is used to carry the actual main component current, the switch itself only passes a tiny amount (usually milliamps, vs. amps), just enough to trigger the relay.

I had a Porsche 944 which suffered two headlight rocker switch failures due to this. I noted that the switch was carrying the current for both headlights, all the interior lights, the tail & running lights, and a very powerful headlight-raising motor. It was probably passing something on the order of 100 amps at initial activation. In desperation, I installed a relay, and the failures stopped for the rest of the time I had the car.

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PostPosted: May 7, 2018, 7:31 pm 
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zetec7 wrote:
I think it's also worth mentioning that, in any circuit carrying substantial current (eg. lights, wipers, fan, etc.), it's better to go through a relay for the component's power, rather than run all the power directly through a switch. Mechanical switch contacts have an arc passing between them each time they're turned off and on, which creates a non-conductive corrosion on the contacts, leading to failure.

The lower the current passing through the switch, the less powerful these arcs are. When a relay is used to carry the actual main component current, the switch itself only passes a tiny amount (usually milliamps, vs. amps), just enough to trigger the relay.

I had a Porsche 944 which suffered two headlight rocker switch failures due to this. I noted that the switch was carrying the current for both headlights, all the interior lights, the tail & running lights, and a very powerful headlight-raising motor. It was probably passing something on the order of 100 amps at initial activation. In desperation, I installed a relay, and the failures stopped for the rest of the time I had the car.

This X2, relays are worth the effort in extra wiring. I didn't run relays in my stock car days and would go through at least 1 switch a year. I run relays in my DD K1500 project and have yet to have a failure in the 3 years I've been running it that way.


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PostPosted: May 8, 2018, 1:29 am 
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Chuck is right, many switches are not rated for much DC current. I think a good switch will say what it's rated for right on it...

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PostPosted: May 8, 2018, 6:42 am 
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I have used Ford starter solenoids as a HD relay many times. Use one on my legends car since 2003 - run all power through it. Replaced it once. I got the idea from an ambulance i had that used them for the roof lights, etc.
~$10 on amazon

https://www.amazon.com/Standard-Motor-P ... r+solenoid


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PostPosted: May 8, 2018, 7:43 am 
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It seems like the switch physically breaks as it no longer goes into position correctly. However I think you are onto something with too much current. Both the fan (mine pulls a lot of amps) and the fuel pump run through the switch. I have some relays so I will add them to the circuit and see what happens.

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PostPosted: May 8, 2018, 8:54 am 
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Quote:
It seems like the switch physically breaks as it no longer goes into position correctly.
This is one symptom of DC current running in an switch designed for only AC. The materials used for the contacts are sometimes different in DC switches. DC current does not reverse and cross thru zero like AC does causing a very long arc when trying to open the circuit. The AC current naturally limits the arc duration to 1/120 seconds. This longer DC arc causes much, much, much more heat buildup inside the switch at the contacts. Think Stick, TIG or MIG welding arc, melting and heat stressing parts internally. This heat and time is additionally exasperated by the back EMF from the fan.

I'm not saying this IS your problem, just saying that it may be. Installing a good 30A/40A automotive relay should solve your problem. I ran a relay on my e-fan controlled by my MS without fault.

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PostPosted: May 17, 2018, 6:50 am 
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As for a good brand of switch (not as a replacement for relays), I prefer Carling 15 and 20 amp rated, even if I only need 5 amps.

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PostPosted: May 17, 2018, 9:31 am 
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Loads like lights are one thing, but inductive loads (radiator fan, etc) are a lot worse. When running, there's a magnetic field surrounding the device, and when the switch is opened, the magnetic field collapses. As it collapses through the coil, it briefly generates its own voltage, which can be 100s of volts on even 12V devices. That high voltage causes an arc across the switch contacts, wearing it out pretty fast. The solution is to add a diode across all inductive loads, though it still doesn't get around the switch needing to be able to deal with DC loads.

One day at work (aviation) I wondered what a mechanical relay would do at altitude. Cut the cover off an ordinary automotive relay, put it in the vacuum chamber, and ran 10 amps through it. We could switch it all day long without any drama - until it was taken to altitude. Sucked it down to the equivalent of 25,000 feet and opened the relay contacts exactly once, and an arc started that never extinguished! Within about 5 seconds the relay was completely destroyed. So, yeah, pick the right part for the conditions.

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PostPosted: May 17, 2018, 4:51 pm 
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KB58 wrote:
Loads like lights are one thing, but inductive loads (radiator fan, etc) are a lot worse. When running, there's a magnetic field surrounding the device, and when the switch is opened, the magnetic field collapses. As it collapses through the coil, it briefly generates its own voltage, which can be 100s of volts on even 12V devices. That high voltage causes an arc across the switch contacts, wearing it out pretty fast. The solution is to add a diode across all inductive loads, though it still doesn't get around the switch needing to be able to deal with DC loads.

One day at work (aviation) I wondered what a mechanical relay would do at altitude. Cut the cover off an ordinary automotive relay, put it in the vacuum chamber, and ran 10 amps through it. We could switch it all day long without any drama - until it was taken to altitude. Sucked it down to the equivalent of 25,000 feet and opened the relay contacts exactly once, and an arc started that never extinguished! Within about 5 seconds the relay was completely destroyed. So, yeah, pick the right part for the conditions.


Yup. The voltage handling capability is reduced virtually linearly with respect to air pressure. Current rating goes down too but not as much. It is both the voltage and current that initiate and sustain the arc. Pikes Peak, which is about 1/3 the pressure of sea level would reduce the voltage capability of the switch. Not by 1/3 because switches are normally rated somewhere around 1000 meters to start with. You would have to check the mfgr's data sheet to find where they rated their switches for altitude.

Temperature too has an effect on the switch capability. As it is in a warmer environment, the air molecules are moving around lot more. It is easier to initiate and maintain an arc with less voltage.

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