Quote:
Originally Posted by dh1
That's the idea but just 1 switch. I don't know how to draw pic on the computer.
Batt+ 48volts to 1 coil A small terminal.
other small terminal coil A to 1 small terminal coil B
other small terminal coil B to Batt-
If both coils the same voltage drop across them should be the same, 24volts.
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It's much easier/straightforward to drop the voltage with a resistor rather than using a second contactor coil if you want to keep the load spread across all the batteries: Measure the current through the contactor coil at the rated voltage (i.e. 24V in this case), say it's 0.150A. Divide the voltage by the current to get the coil resistance (24V/.15A = 160 ohm). So add a 160 ohm resistor (anything between 140 and 180 ohm would be fine) in series with the coil (i.e. - bat to one side of coil, other side of coil to one end of the resistor, the other end of the resistor to your on/off toggle switch, the other side of your switch to 48V) and you have a balanced load across the whole string, but the coil running at half the string voltage. Note that the resistor needs the appropriate power rating: 0.15A*24V=3.6W, so use a 5 watt resistor, or three 50-ish ohm two watt resistors in series, or three 480-ish ohm two watt resistors in parallel.
If you already have the second contactor and don't want to make a trip to the resistor store, using the second coil to drop the voltage is also fine, but there is no need to run the power through it's contacts... just wire up the two coils in series and run the motor power through one contactor and you're done (assuming it's rated for the motor current).
Dang it... an electric mower wasn't even on my list of things to do until I read this thread!
-Pete