Advice on power switch amps

[Bach On]

I'm trying to build a project where I need a 4PDT toggle switch. This is a 12 volt (nominal) project. I'll use an inline meter that measures voltage, amps, watts, accumulated amps used, etc..

This sellers of this meter claim it can take 50 amps continuous without a shunt. The write-up even says it can take 100 amps for short-term use. Frankly, given that the wires look like no more than 14 or 16 gauge, I doubt the claim. There are two wires that go into the meter. And two wires that go out of the meter to your load. (I bought it from someone on Flea-Bay. Paid right at $30 for it about a month ago. Now there is some selling what appears to be the same units for $9.95 - out of Hong Kong.) I've looked, but I don't see a brand name on the meter.

I have been testing this meter with an emergency light project that uses a 12 volt deep cycle battery and some LEDs. I've tested the meter's measurements with a couple of volt/ohm meters. The meter's results seem to agree with my independent meters. The verbage even says this meter can be used with a charging circuit to measure how many amps/watts/etc. are going from a solar panel (or other chargers) to your battery. This sounds like an ideal idea. I've seen several discussions on this board where people wanted to measure this.

I want to use one of these meters in a 12 volt battery circuit for a portable water system. Knowing how much I've drained the battery would be helpful while I'm out working.

I want to use the 4PDT switch to configure the meter to work for measuring output to my water pump. Then I want to use the same switch at night to reverse the circuit so the same meter can measure the input from a battery charger.

Sorry for the long intro.

Question: I see toggle switches rated for 15 amps at 120 volts. My system will be running at 12 volts. How do I figure how many amps at 12 volts would be reasonable for these switches to be able to handle?

I don't expect to do 50 amps on this project. But situations might come up where I'd want to use a toggle switch in a larger solar panel project, for example. I want to know how to determine what is a safe limit for any switches I use. Too, being able to build an electronic circuit to turn such a project on or off might be useful too.

Any input and advice on how to calculate the reasonable expected capability of such switches would be appreciated.

Bach On

(And for those who might want to measure your solar panel output, you might want to check out fleaBay. Do a search for watt meter.) I promise - I'm not involved with anyone selling these meters. But having used one, I'm impressed. Who knows how long it will hold up? And I sure wouldn't use if for 50 amps.

 

[misterT]

Question: I see toggle switches rated for 15 amps at 120 volts. My system will be running at 12 volts. How do I figure how many amps at 12 volts would be reasonable for these switches to be able to handle?

It is rated for 15 amps so that is the limit.. no matter what the voltage is. (voltage limit is 120 volts, no matter what the current is.)

I'd want to use a toggle switch in a larger solar panel project, for example. I want to know how to determine what is a safe limit for any switches I use. Too, being able to build an electronic circuit to turn such a project on or off might be useful too.

That is one serious solar panel if you doubt 15 amps is not enough!!

 

[Bach On]

So you're saying the current capacity on that switch is 15 amps at 120 volts or 12 volts? That is surprising. I'd think that lower voltages would increase the amperage.

As for the 15 amps - I'm talking about the load FROM the battery - not the charging current from the panel. The switch would have to handle both. Yep, that would be a serious solar panel array.

Thanks for the input. This may not be the correct forum for such questions.

Bach On

 

[misterT]

If the spec says max 15 amps then the limit is 15 amps.

I'd think that lower voltages would increase the amperage.

No. Maybe in short pulses, but.. no. If there is a current limit then that is the limit.

 

[MikeMl]

So you're saying the current capacity on that switch is 15 amps at 120 volts or 12 volts? That is surprising. I'd think that lower voltages would increase the amperage.

As for the 15 amps - I'm talking about the load FROM the battery - not the charging current from the panel. The switch would have to handle both. Yep, that would be a serious solar panel array.

Thanks for the input. This may not be the correct forum for such questions.

Bach On

Switch/Relay current ratings for DC and AC are radically different. When opening an AC current-carrying circuit, the arc that forms as the contacts open is extinguished naturally at the next zero-crossing of the AC waveform. When opening a DC current-carrying circuit, the arc goes on until the contacts open wide enough to extinguish it. I have never seen a switch which has a higher rating when switching DC than when switching AC. Usually, the opposite is true.

Topic has come up before.

A good discussion of extrapolating switches rated for AC, but using them on DC is here

 

[Bach On]

Looks like it is going to be difficult to find a 4PDT switch for 12 volts with over 15 amps of capacity.

I've seen automobile switches for 25 or 30 amps DC. But they are mostly SPST or DPDT.

I may have to consider electronics to get up to 20-30 amps, or more DC.

Thanks,
Bach On

 

[alec_t]

I've seen automobile switches for 25 or 30 amps DC. But they are mostly SPST or DPDT.

Depending on any critical timing requirements for the switching operation you could perhaps use two DPDT relays (or four SPDT) energised in parallel?