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Unread 11-04-2016, 14:34
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juchong juchong is offline
Electrical Engineer
AKA: Juan Chong
FRC #2655 (Flying Platypi)
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Join Date: Aug 2008
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Location: Greensboro, NC
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Re: Battery connected backwards to robot

While reverse polarity protection is usually overlooked since it's assumed that the user should never reverse the input polarity, it's good design practice to put some safeguards in place given that the components teams are required to use are expensive. Many teams are working with the single module given to them at kickoff and would rather spend their budget on travel costs rather than blowing up electronics.

A cost effective, very easy to implement solution would be to use a reversed P-Channel MOSFET in series between the battery input terminal and the PDP distribution node. Afrotechmods has a great video on the subject here. A transistor such as the SUM110P06-07L-E3 would work for the FRC PDP.

If you needed more current capacity (240A pulsed for the P-Type vs 440A pulsed for the N-Type) you could apply the same circuit, substituting a P-Type for an N-Type such as the STB120NF10T4, on the negative (ground) side of the circuit and achieve the same result. Both of these transistors have an RdsON = ~10mOhm meaning that the maximum power dissipated in the transistor under full load will be 4W @ 20A continuous.

Either one of these configurations would adequately protect not only the PDP, but everything else connected to it.
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Last edited by juchong : 11-04-2016 at 15:11.
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