switch rating

Toby · 2009-05-13T09:28:00+00:00

Hi allI'm constructing a petrol-electric loco for 5" gauge. B&S engineturning a car alternator and also a 12V DC motor (ex power shower) asa generator to supply the alternator field current through a highpower rated rheostat. The alternator output runs a pair of 24V, 12ADC motors to drive the wheels.Reversing the connection between the motors and alternator willobviously reverse the loco. I have quite a number of double pole,double throw switches rated at 10A 250V AC which can perform thisconnection reversing. Its pretty essential that the current is atzero before this reversing occurs and this is easy enough - just turnthe speed control down to zero.The question is - how many of the AC rated switches should I be usingin parallel to safely carry the DC load assuming the load is zero whenswitching occurs? How are switch ratings assigned? Is it based onswitching full load current and issues of arcing or on currentcapacity to avoid overheating?cheers for your thoughts,Toby,Fareham

May 13, 2009 21 Replies

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Harry Bloomfield 17 years ago

Peter Fairbrother submitted this idea :

You can actually get over 100v if the voltage control system is removed.

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Alun 17 years ago

Dangerous advice.

Both ends could weld to the battery, and if wire is of sufficient gauge (eg a spanner) then explosion + fountain of hot acid results

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