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| How Do I Convert DC Motor To Reverse With SPDT Switch? |
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| snub:
Here is my problem. I'm working on my '66 Corvette which uses two 12vdc electric motors to open and close the headlight buckets. These motors are 45 years old and parts are hard to come by. Someone has started reproducing these motors but they are $400.00 each. So I decided to reinvent the wheel, err, the system. My plan is to use a single motor mounted between the buckets with a driveshaft running to each one. I would like to keep the orignal 'up/down' switch as it is very classy looking. The only problem is that is a single pole double throw switch which won't work with any motors I have come across. On the original motor (which is much like any power window motor of past or present), the case is grounded and their are two 'positive' terminals. Power to one terminal is CW, power to the other is CCW. I have no idea how they wired these. I'm wondering if the wiring on a new motor can be changed to work like the old one. Or, if there is such a thing as a relay that would reverse the polarity of the wiring to the motor? Plan B is to simply hide a DPDT switch under the dash near the old one. Here is a diagram I made showing my current wiring. Please feel free to fill in the missing links on the bottom part. |
| russ57:
i reckon it would be fairly straightforward, you'll need to use 2 dpst relays. One is wired to switch positive and negative from the battery 'direct' to the motor, and the other to switch them 'reversed' . Use the SPDT switch to apply power to either relay as required. I assume the spdt switch is momentary? how do you know when to stop applying power? the original motor may have had some end of travel detection. you may need to consider some sort of limit switch, so that power to the relay is removed when it reaches the end of its travel. i could probably whip a simple diagram if you need. regards russell |
| andyf:
Snub, DPDT relays are common, and reading down this page may give you a start: http://www.distel.co.uk/DC_MOT_CON1.htm It shows a DPDT relay with its coil energised/de-energised by a simple SPST push button switch. Your existing SPDT switch could be converted by using its common terminal and just one of the other two terminals, unless it is a momentary switch. As Russell says, limit switches would need to be added, maybe operated by cams on your drivehaft. Andy |
| John Swift:
Hi Snub , you can use two single pole automotive relays connect the motor between the common relay contacts the negative supply to the normally closed contacts and the positive to the normally open contacts (on both relays ) until a relay switches, both motor terminals are connected to the negative supply when the existing switch operates one or other relay, the positive supply is connected to one of motor terminals if the motor torque is not too great you could just let the motor stall until you release the switch (assuming its normally off) other wise wire two limit switches , one in series with each relay coil John |
| 75Plus:
John, could you reduce the size of your schematic? As it is it is hard to see it all. Joe |
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