A mod for the Intermatic SS8C digital timer that replaces the motor/gear/mechanical switching system.
Background:
I have found (as I am sure many of you have as well) that the small stock motor used for switching burns out rather quickly in the Intermatic SS8C timers, especially when used with fluorescent lighting. Inevitably these failures always occur for me when I am on vacation, and they always seem to fail in the “on†position. There is nothing like coming home to discover that your halides have been on 24 hours a day for the past week.
Rather than just replacing the motor with a new one and running the risk of future failures, I wanted something that would be more reliable, suitable with any device I wanted to operate with the timer, small and cheap. What I came up with is to replace the motor with a small relay with a 1.5 VDC coil. This relay is used to trip a small switching circuit based on a hex-invert, which in turn operates a relay used to switch your device on/off. There are several advantages to this design: 1) The type of device operated by the timer is solely limited by the choice of the second relay. 2) By using a DPDT throw relay for switching you can completely isolate the timing circuitry from that of the device operated by the timer. 3) Because of the shorter operating time for the first relay compared to the motor it replaces (fraction of a second vs. several seconds per switching event) battery life for the timer is extended (i.e. more events per battery). 4) Having two separate “on†positions opposite each other allows the timer to control two devices with exactly opposite schedules. The main disadvantage to the design is that it requires an external power source to operate the hex-invert circuitry and the second relay. However, this does allow you to connect the timer through a voltage divider to the source powering the hex-inverter circuitry and second relay, and replace the stock alkaline battery with one that is rechargeable. The advantage being that you would not have to replace the battery anymore.
About the mod:
The switching circuit used to operated the second relay can be found here (http://www.uoguelph.ca/~antoon/circ/alt1.htm) or through the Discover Circuits website. I did not design the circuit, I just simply adapted it for my application, so follow the original designer’s recommendations for component choices and construction (except for the micro-second switch, see below). If you are inclined to use their PCB layout, be aware that the timer won’t be able to fit into a single residential electrical box after its’ moded.
The micro-second switch in the hex inverter circuit is replaced by the contacts of the 1.5V relay, connected to Comm and NO. The relay coil is connected where the motor normally is on the timer, with a diode reversed and connected in parallel to the relay coil to protect the timer. Normally when the timer initiates a switching event the motor receives a 1.5V signal that lasts until the timer senses that the mechanical switch has tripped or if the timer doesn’t sense that the switch has tripped the signal is terminated after a few seconds. When the motor is replaced with a relay, the relay is tripped sending a signal to the hex-inverter, which then trips the second relay where the sensing mechanism for the timer is connected. This happens so quickly that the first relay acts like a micro-second switch.
After an initial signal (on or off) the hex-inverter circuit keeps the second relay energized or de-energized until a second signal is sent from the timer. So for example, with the first signal from the timer the second relay is energized switching your device on. The device will stay on until a second signal is sent from the timer telling the hex-inverter to cut power to the relay, in turn switching the device off. Whether or not the relay is energized or not in the “on†(as displayed on the timer LCD) position is solely determined by where the sensing lead from the timer is connected, and that depends on whether you want the default timer position to be “on†or “off†(i.e. whether your want the device on or off if power is interrupted to the second relay’s coil). The small diameter black lead from the timer (normally connected to Comm on the stock mechanical switch) is connected to Comm on the second relay. By connecting the small un-insulated lead from the timer (normally connected to NO on the stock mechanical switch) to NO on the second relay the default position is “on†or by connecting it to NC the default position is “offâ€Â.
Note that by using a DPDT relay for the second relay the device can be isolated from the timer by connecting the sensing leads to one set of contacts, while connecting the device to the other. Also, having two positions on the timer allows you to operate two separate systems on opposite schedules from a single timer: Like switching the refugium lights on when the display lights switch off, or switching moon lights on when the display lights switch off…
This mod requires that the timer be connected to a 12VDC supply to power the hex-inverter circuit and the second relay. For my purposes my tank already has a 12VDC supply that operates the moon lighting, cooling fans and the switching circuitry for the battery back up. But if you are installing the moded timers where a 12V supply is not already present you will need to supply one, the size of which will be determined by the type of relay chosen for the second relay.
Parts and Supplies:
What I list here are the parts I used, with where they were purchased from, part number and cost. Items with (*) will supply several builds.
Quantity, Part, Supplier, Part number,Cost each
2, 100K ohm resistors, Mouser Electronics, 271-100K-RC, $0.09
1, 10K ohm resistor, Mouser Electronics, 660-MF1/4DC1002F, $0.03
1, 0.01 uf capacitor, Mouser Electronics, 140-50Q5-103Z-RC, $0.08
1, 0.1 uf capacitor, Mouser Electronics, 140-L50V.1, $0.18
1, 4069 hex-inverter, Mouser Electronics, 511-4069U, $0.19
1, 14-pin IC socket, Mouser Electronics, 575-199314, $0.55
2, 1N4001 diode, Mouser Electronics, 512-1N4001, $0.06
1, PN100 transistor, Mouser Electronics, 512-PN100, $0.09
1, SPDT relay 1.5 VDC coil, Ebay: seller dmmwem, $0.50
1, DPDT relay 12 VDC coil, Mouser Electronics, 653-LY2-0-DC12, $6.38
1, Perforated circuit board*,Radio Shack, 276-1394, $3.29
1, Epoxy*, Lowes, 152007, $2.97
1, 1/8 to 1/16 heat shrink tubing (pack)*, Lowes
Assorted wire
The step by step build:
1. Pop out and save the battery holder.
2. The back of the timer, gears, motor, mechanical switch and remote switching lead (red lead) need to be removed. If you will be using a remote switch leave the red lead intact and connect it as directed by the manufacture after the mod is complete. Be sure to note which lead is black and which is white before you remove the motor. There are ten tabs around the middle of the timer that hold the case together, four pointing to the front and six pointing to the back. Only the six tabs pointing to the back of the case should be pried open.
3. Once the case is open and parts removed, place the timer on its side and cut the back flat with a hacksaw blade. It doesn’t need to be perfect, just flat enough to epoxy the new workings to. Be careful not to beat the timer around to much when you do this and be sure to shake out all the filings before turning the timer LCD side down, otherwise you will wind up with plastic shavings trapped between the LCD and its diffuser.
4. Build the hex-inverter circuit outlined at http://www.uoguelph.ca/~antoon/circ/alt1.htm. Use a pair of wire leads for connecting to Comm and NO on the 1.5V relay (green/white-green in figure) and a pair of leads for connecting to the coil of the second relay (blue/whit-blue in figure), rather than trying to include the relays on the board. Also connect a long pair of leads for connecting to a 12VDC supply (orange/white-orange in figure). Be sure to construct the board as small as possible. If you are using perforated circuit board like I did the circuit can be constructed on a piece as small as 9 x 7 holes.
5. Connect the black and white leads from the timer (motor leads) to the coil of the 1.5V relay and connect one of the two diodes in parallel to the coil in reverse (band on the diode should be connected on the same side as the white lead). Use short pieces of wire to extend the lead length and use heat shrink to insulate the leads from each other. If you are using the same 1.5V relay that I did connect a short piece of wire between the NO pin and the unused pin on the left hand side of the relay bottom. This will make it possible to connect the leads from the hex-inverter once the relay is glued in place.
6. Glue the 1.5V relay, hex-inverter circuit and second relay to the back of the timer using epoxy, making an effort to position these parts so that the timer is no bigger than before the mod. Make sure not to cover the opening for the battery holder.
7. Once the epoxy is set, connect the leads from the hex-inverter circuit to the 1.5V relay and the second relay coil. If you are using the same 1.5V relay that I did, you will connect one lead to the top of the relay and the other to the unused pin that you connected to NO in step 6.
8. Attach the black sensing lead from timer to Comm on the second relay and attach the un-insulated sensing lead from timer to NC or NO on the second relay, depending on what you want as the default position. I found it necessary to extend the lead length to be able to connect them to the relay.
9. Connect leads to the second relay so that it can be wired to control some device. I used the factory leads from stock mechanical switch, with the black lead connected to Comm and the blue lead connected to NO (note that this configuration is for a default position of “offâ€Â, for a default position of “on†the blue lead would connect to NC). Attach a third lead to the open pin if you plan on using the timer to control two devices on opposite schedules.
10. The mod is now complete. To install the timer connect the supply leads from the hex-inverter circuit to a 12 VDC supply and connect the leads from the second relay in line with your device. Once the timer is connected re-install the battery and holder.
Comments:
I have been using two of these modded timers on my reef for about a month now. Switching is quieter, quicker and much more reliable (hasn’t failed yet) than with the stock configuration. I am quite pleased with the out come.
Jay
Background:
I have found (as I am sure many of you have as well) that the small stock motor used for switching burns out rather quickly in the Intermatic SS8C timers, especially when used with fluorescent lighting. Inevitably these failures always occur for me when I am on vacation, and they always seem to fail in the “on†position. There is nothing like coming home to discover that your halides have been on 24 hours a day for the past week.
Rather than just replacing the motor with a new one and running the risk of future failures, I wanted something that would be more reliable, suitable with any device I wanted to operate with the timer, small and cheap. What I came up with is to replace the motor with a small relay with a 1.5 VDC coil. This relay is used to trip a small switching circuit based on a hex-invert, which in turn operates a relay used to switch your device on/off. There are several advantages to this design: 1) The type of device operated by the timer is solely limited by the choice of the second relay. 2) By using a DPDT throw relay for switching you can completely isolate the timing circuitry from that of the device operated by the timer. 3) Because of the shorter operating time for the first relay compared to the motor it replaces (fraction of a second vs. several seconds per switching event) battery life for the timer is extended (i.e. more events per battery). 4) Having two separate “on†positions opposite each other allows the timer to control two devices with exactly opposite schedules. The main disadvantage to the design is that it requires an external power source to operate the hex-invert circuitry and the second relay. However, this does allow you to connect the timer through a voltage divider to the source powering the hex-inverter circuitry and second relay, and replace the stock alkaline battery with one that is rechargeable. The advantage being that you would not have to replace the battery anymore.
About the mod:
The switching circuit used to operated the second relay can be found here (http://www.uoguelph.ca/~antoon/circ/alt1.htm) or through the Discover Circuits website. I did not design the circuit, I just simply adapted it for my application, so follow the original designer’s recommendations for component choices and construction (except for the micro-second switch, see below). If you are inclined to use their PCB layout, be aware that the timer won’t be able to fit into a single residential electrical box after its’ moded.
The micro-second switch in the hex inverter circuit is replaced by the contacts of the 1.5V relay, connected to Comm and NO. The relay coil is connected where the motor normally is on the timer, with a diode reversed and connected in parallel to the relay coil to protect the timer. Normally when the timer initiates a switching event the motor receives a 1.5V signal that lasts until the timer senses that the mechanical switch has tripped or if the timer doesn’t sense that the switch has tripped the signal is terminated after a few seconds. When the motor is replaced with a relay, the relay is tripped sending a signal to the hex-inverter, which then trips the second relay where the sensing mechanism for the timer is connected. This happens so quickly that the first relay acts like a micro-second switch.
After an initial signal (on or off) the hex-inverter circuit keeps the second relay energized or de-energized until a second signal is sent from the timer. So for example, with the first signal from the timer the second relay is energized switching your device on. The device will stay on until a second signal is sent from the timer telling the hex-inverter to cut power to the relay, in turn switching the device off. Whether or not the relay is energized or not in the “on†(as displayed on the timer LCD) position is solely determined by where the sensing lead from the timer is connected, and that depends on whether you want the default timer position to be “on†or “off†(i.e. whether your want the device on or off if power is interrupted to the second relay’s coil). The small diameter black lead from the timer (normally connected to Comm on the stock mechanical switch) is connected to Comm on the second relay. By connecting the small un-insulated lead from the timer (normally connected to NO on the stock mechanical switch) to NO on the second relay the default position is “on†or by connecting it to NC the default position is “offâ€Â.
Note that by using a DPDT relay for the second relay the device can be isolated from the timer by connecting the sensing leads to one set of contacts, while connecting the device to the other. Also, having two positions on the timer allows you to operate two separate systems on opposite schedules from a single timer: Like switching the refugium lights on when the display lights switch off, or switching moon lights on when the display lights switch off…
This mod requires that the timer be connected to a 12VDC supply to power the hex-inverter circuit and the second relay. For my purposes my tank already has a 12VDC supply that operates the moon lighting, cooling fans and the switching circuitry for the battery back up. But if you are installing the moded timers where a 12V supply is not already present you will need to supply one, the size of which will be determined by the type of relay chosen for the second relay.
Parts and Supplies:
What I list here are the parts I used, with where they were purchased from, part number and cost. Items with (*) will supply several builds.
Quantity, Part, Supplier, Part number,Cost each
2, 100K ohm resistors, Mouser Electronics, 271-100K-RC, $0.09
1, 10K ohm resistor, Mouser Electronics, 660-MF1/4DC1002F, $0.03
1, 0.01 uf capacitor, Mouser Electronics, 140-50Q5-103Z-RC, $0.08
1, 0.1 uf capacitor, Mouser Electronics, 140-L50V.1, $0.18
1, 4069 hex-inverter, Mouser Electronics, 511-4069U, $0.19
1, 14-pin IC socket, Mouser Electronics, 575-199314, $0.55
2, 1N4001 diode, Mouser Electronics, 512-1N4001, $0.06
1, PN100 transistor, Mouser Electronics, 512-PN100, $0.09
1, SPDT relay 1.5 VDC coil, Ebay: seller dmmwem, $0.50
1, DPDT relay 12 VDC coil, Mouser Electronics, 653-LY2-0-DC12, $6.38
1, Perforated circuit board*,Radio Shack, 276-1394, $3.29
1, Epoxy*, Lowes, 152007, $2.97
1, 1/8 to 1/16 heat shrink tubing (pack)*, Lowes
Assorted wire
The step by step build:
1. Pop out and save the battery holder.
2. The back of the timer, gears, motor, mechanical switch and remote switching lead (red lead) need to be removed. If you will be using a remote switch leave the red lead intact and connect it as directed by the manufacture after the mod is complete. Be sure to note which lead is black and which is white before you remove the motor. There are ten tabs around the middle of the timer that hold the case together, four pointing to the front and six pointing to the back. Only the six tabs pointing to the back of the case should be pried open.
3. Once the case is open and parts removed, place the timer on its side and cut the back flat with a hacksaw blade. It doesn’t need to be perfect, just flat enough to epoxy the new workings to. Be careful not to beat the timer around to much when you do this and be sure to shake out all the filings before turning the timer LCD side down, otherwise you will wind up with plastic shavings trapped between the LCD and its diffuser.
4. Build the hex-inverter circuit outlined at http://www.uoguelph.ca/~antoon/circ/alt1.htm. Use a pair of wire leads for connecting to Comm and NO on the 1.5V relay (green/white-green in figure) and a pair of leads for connecting to the coil of the second relay (blue/whit-blue in figure), rather than trying to include the relays on the board. Also connect a long pair of leads for connecting to a 12VDC supply (orange/white-orange in figure). Be sure to construct the board as small as possible. If you are using perforated circuit board like I did the circuit can be constructed on a piece as small as 9 x 7 holes.
5. Connect the black and white leads from the timer (motor leads) to the coil of the 1.5V relay and connect one of the two diodes in parallel to the coil in reverse (band on the diode should be connected on the same side as the white lead). Use short pieces of wire to extend the lead length and use heat shrink to insulate the leads from each other. If you are using the same 1.5V relay that I did connect a short piece of wire between the NO pin and the unused pin on the left hand side of the relay bottom. This will make it possible to connect the leads from the hex-inverter once the relay is glued in place.
6. Glue the 1.5V relay, hex-inverter circuit and second relay to the back of the timer using epoxy, making an effort to position these parts so that the timer is no bigger than before the mod. Make sure not to cover the opening for the battery holder.
7. Once the epoxy is set, connect the leads from the hex-inverter circuit to the 1.5V relay and the second relay coil. If you are using the same 1.5V relay that I did, you will connect one lead to the top of the relay and the other to the unused pin that you connected to NO in step 6.
8. Attach the black sensing lead from timer to Comm on the second relay and attach the un-insulated sensing lead from timer to NC or NO on the second relay, depending on what you want as the default position. I found it necessary to extend the lead length to be able to connect them to the relay.
9. Connect leads to the second relay so that it can be wired to control some device. I used the factory leads from stock mechanical switch, with the black lead connected to Comm and the blue lead connected to NO (note that this configuration is for a default position of “offâ€Â, for a default position of “on†the blue lead would connect to NC). Attach a third lead to the open pin if you plan on using the timer to control two devices on opposite schedules.
10. The mod is now complete. To install the timer connect the supply leads from the hex-inverter circuit to a 12 VDC supply and connect the leads from the second relay in line with your device. Once the timer is connected re-install the battery and holder.
Comments:
I have been using two of these modded timers on my reef for about a month now. Switching is quieter, quicker and much more reliable (hasn’t failed yet) than with the stock configuration. I am quite pleased with the out come.
Jay
