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Ratings Switches

Old 08-21-2016, 09:10 PM
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Default Ratings Switches

I am moderately experienced with making R/C combat robots, and I am preparing some documentation for the new machine shop director at my school regarding which parts to buy for the combat bots class.

I've written up an explanation regarding how to select the on/off switches we need, but I'd appreciate it if someone to would check my reasoning. The text of the explanation follows:
These switches are rated for 250 Volts and 6 A or 125 Volts and 10 A. Our batteries will typically be about 7.4 V with 1000 mAh (1 A) and up to 30C. When undergoing strenuous use, a battery with 30 C can discharge up to 30 times the Amps it's rated for, so just to be safe we need our switches to be able to survive (1 A x 30 C = ) 30 Amps at 7.4 V. Given that these can survive 10 A at 125 V, we should be fine.

Part of my hesitation is that the way I'm calculating it, I'd predict that these switches would be able to handle upwards of 150 Amps when at 7.4 V. (Reasoning: 125 V / 7.4 V = 16.9; 10 A * 16.9 = 169 A; As voltage is reduced, amps can be increased, following a linear relationship.) However, 150 Amps in anything as small as this seems unrealistic.

Any feedback is appreciated. Thanks in advance.
Old 08-22-2016, 05:38 AM
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I don't think so. You are considering total wattage, not current. Furthermore you are looking at an AC rating versus a DC rating. The issue in switches is how much internal resistance there is and higher current means higher voltage drop across the contacts. Also there is the issue of sparking caused by the higher current. I would look for a 28VDC switch with a 50 Amp rating.
Old 08-23-2016, 07:32 PM
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Thanks rgburrill, that helps me look in the right direction.

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