On 4/12/2013 11:48 AM, Michael A. Radtke wrote:
So, it's a good plan to block the reverse switching while the motor is
still spinning. Any suggestions for a simple way to detect that?
If the controller doesn't have this feature built-in, you can add a
relay to do it. The coil goes across the motor armature, so it pulls in
whenever there is voltage. To switch to reverse, this relay has to drop out.
Pick a relay whose DC coil voltage is about the same as your maximum
motor voltage. For example, a 110vdc coil for an EV with a 120v pack.
Put a resistor or light bulb in series to drop the voltage if you can't
find a relay with a high enough coil voltage.
Relays drop out with about 10% of their rated voltage across the coil. A
110vdc coil drops out at 11v, etc. So this relay turns off when the
motor is at less than 11v average (barely idling).
Wire this relay's contacts to control your forward/reverse contactor's
coils. If your forward/reverse contactors have auxiliary switches, it
would be wired something like this (view with a fixed width font like
Courier):
/ <------
___o o___ \
forward | S2 NO | \
| | _\_ _
o_________|___o--o___|___| | | |_____
/ K1a NC forward |
+12v____O o neutral contactor gnd
S1 / <------
o_____________o o___ \
reverse | S3 NO | \
| | _\_ _
|___o--o___|___| | | |_____
K1b NC reverse |
contactor gnd
K1 is the new forward/reverse motor speed detection relay. It has two
normally-closed contacts, K1a and K1b. When the motor is stopped, K1a
and K1b are closed. They open when the motor is running.
S1 is your forward/reverse switch on the dashboard or shift lever.
The forward contactor has an auxiliary switch S2, which is closed when
the contactor is on. The reverse contactor has an auxiliary switch S3,
which is closed when the contactor is on.
Set S1 for the desired direction; let's say forward. Then the reverse
contactor has no coil power and must be off. If the motor is stopped,
the forward coil gets power through S1 and K1a, and pulls in. Once it
has pulled in, S2 closes and holds the forward contactor on even when
the motor starts turning and K1a opens.
When you switch to reverse, the forward contactor drops out immediately.
But the reverse contactor won't turn on until the motor (almost) stops,
allowing K1b to close.
--
Ring the bells that still can ring
Forget your perfect offering
There is a crack in everything
That's how the light gets in.
-- Leonard Cohen, from "Anthem"
--
Lee A. Hart, http://www.sunrise-ev.com/LeesEVs.htm
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