is it possible / safe to use 10A switch with some resistors in a 30A circuit? i am trying to use 10A DPDT switch for a circuit with 3 units of 12V/10A batteries to select between paralel (12V/30A), series (36V10A) and off. can someone please confirm that i can just use the extra DPDT rated 10A switch that i have or do i need to order (and wait a few weeks) for the one with 30A ratings?


closed as unclear what you're asking by Turbo J, Andy aka, PeterJ, Dave Tweed Dec 5 '15 at 14:34

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    \$\begingroup\$ My crystal ball says: Switches rated for 10A AC will not tolerate switching 10A DC current (for long). \$\endgroup\$ – Turbo J Dec 5 '15 at 14:16
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    \$\begingroup\$ If you went to buy a hat or a shirt would you buy stuff that is three times smaller than you are? \$\endgroup\$ – Andy aka Dec 5 '15 at 14:23
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    \$\begingroup\$ Don't switch with current flowing. Zero current flow should eliminate arching. \$\endgroup\$ – Optionparty Dec 5 '15 at 14:39
  • \$\begingroup\$ Zero current flow should eliminate arcing, but 30A flowing through a 10A rated contact could also weld the contacts shut. \$\endgroup\$ – R Drast Dec 7 '15 at 15:42

Can I put 6 liters of juice in this 2 liter bottle? It's not a perfect analogy, but I'd say it's close.

First of all, you need to take time to analyze your system and see what's going to happen in it if your switch fails closed, melts, catches on fire and so on. If you have reasons to believe that nothing bad will happen, then go ahead.

Usually, it's the opposite. If you have a reason to ask will it work, it probably won't work too well. For example, if you have 30 A current running through the switch, and you use the switch to break the circuit, this will generate a spark inside of the switch. The "size" of the spark will be proportional to the current going through the switch. In general, a 10 A switch will not be designed to survive breaking 30 A current for long (or maybe even for one time!). As I previously mentioned, the switch could weld itself in a certain position, the contacts will deteriorate and that could negatively affect the rest of your system, the switch could overheat due to contacts having deteriorated, the heat from overheating could affect the rest of the circuit and so on.

Another thing that was mentioned in the comments, and was not mentioned in your question, but needs to be addressed is the rating of the switch.

Usually, switched will have AC and DC rating and AC rating will be considerably higher than DC rating. The reason is the fact that in AC current, voltage will go down to zero at one point. If you have a large spark in the switch, it will die out at that moment. If you have DC current, you will have to wait for it to die out on its own. The damage the spark makes to the switch is proportional to its duration, so in DC case,with each operation of the switch, you'll do more damage to contacts than in AC case.

So in the end, if your device needs to be switched more than a couple of times, get switches that are at least rated for 30 A DC current, since you're using batteries. In general, it's a good idea to get switches that have even higher rating than 30 A, just to be sure that it doesn't break down when you expect it the least.

  • \$\begingroup\$ thank you for helping me build my own crystal ball and help me see it clearer but what if i found an unused optocoupler relay randomly in my magic bin? will that give my 2 liter bottle a spillover pipe to a backup container ie: will the use of a relay be a safe alternative? \$\endgroup\$ – harayz Dec 5 '15 at 14:52
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    \$\begingroup\$ @harayz Well a relay is still a switch. It's just an electrically operated switch. So you must follow all specifications for switches for relays as well. \$\endgroup\$ – AndrejaKo Dec 5 '15 at 14:54

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