240 VAC 10 amp / 120 VAC 15 amp switch used for 12 volts, up to 40 amps?

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,555
Been sorting out my project. Am adding a switch to it. The switch I have at hand is rated 10A @ 240 VAC, 15A @ 120 VAC. I need a switch that can handle 40A @ 12VDC. Will this switch work? Or should I make a run to my automotive parts store and just buy such a switch?
 

ebeowulf17

Joined Aug 12, 2014
2,938
I'll be interested to hear what others with more experience than me have to say.

Personally, I wouldn't use a switch for nearly 3x its rated amperage, no matter what the difference in voltage ratings was. But I've always been a play-it-safe type when it comes to the confluence of fire and electricity.

But like I said, this not my area of expertise, so I'll be interested in hearing other opinions.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,555
It's most likely I'll be switching the unit on with the blower speed set to its lowest speed to start off. However, you KNOW there's the chance I'll have it running at full speed, shut it off, and forget to turn the speed back down to near zero. Next time I turn it on - I can weld the contacts. So always plan for the worst case scenario and you'll be fine. Since I have to go out and pick up some stuff I'm thinking I'll just swing by the auto parts store and see what they have.

Also need a projects box. Will cross that bridge later.
 

MaxHeadRoom

Joined Jul 18, 2013
18,995
Apart from the low rating of the switch you want to use, what is the nature of the load?, A highly inductive load can cause contact welding and/or a plasma arc across the contacts on opening.
Do you have any auto wreckers close by?
If so, Pick up a handful of 60amp relays and use a simple switch.
Is it possible to use solid state?
Max.
 

OBW0549

Joined Mar 2, 2015
2,977
Been sorting out my project. Am adding a switch to it. The switch I have at hand is rated 10A @ 240 VAC, 15A @ 120 VAC. I need a switch that can handle 40A @ 12VDC. Will this switch work?
It might "work," but it's unlikely to last very long before it dies (and possibly catches fire) from overheating.

Or should I make a run to my automotive parts store and just buy such a switch?
Yes.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,555
This is what I've been constructing. The blower motor draws a good 36 amps at startup and runs continuously at about 19 amps. My plan is to repurpose this blower to stoke a fire pit. Hence, I don't want it running at full power. I have a dash lights dimmer control module from an old Toyota. It functions as PWM, so I'm using that to moderate the speed. However, knowing the possibility of forgetting to turn the speed down (or it being accidentally bumped to full speed) I want a switch capable of handling the potential current. The motor is DC and I don't think it is permanent magnet type. I've dead shorted the leads and I can still spin it quite easily.

Yes, I can use another IGBT as a switch, but I'm limited on how many I have.

Variable Blower.png
 

MaxHeadRoom

Joined Jul 18, 2013
18,995
The motor is DC and I don't think it is permanent magnet type. I've dead shorted the leads and I can still spin it quite easily.
Then it points to some kind of BLDC maybe, if you spin it, does it generate, (read on a meter)?
Max.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,555
I believe I need to amend my statement about the motor: I just ran it at full power (direct connect to the battery). Then I dead shorted the motor leads to themselves and the motor pulled to a very quick stop. So it may be a permanent magnet type motor.

Relays are too big for the box I want to put the project into.

[edit] Just got back from the auto parts store. Spent $5.00 on a 35 amp switch. Should be good enough. Only slightly over the rating, and I'm sure the manufacture of the switch under-rates their switch to avoid situations where they might be held liable should some critical device fail because of an under-rated switch.

I've seen engineering go as low as 102% of anticipated usage. I personally like 133% for non life critical things and 150% for life critical things. That's my personal opinion.

Yours may vary.
 
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Thread Starter

Tonyr1084

Joined Sep 24, 2015
3,555
You could switch the B+ terminal connection to the battery + instead?
Not sure if that would work. The 1KΩ is to pull the IGBT up (turn on). If there's a loss at B+ then SINK might not go low, leaving the IGBT floating. At first it sounded like a pretty good idea; but I'm not sure it would work that way. I COULD just unplug the battery. It's going to be a car battery, so it's not like some pocket sized battery that can stay in a projects box for the duration.
 
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