Home › Forums › DROK Customization › timer relay 200350 how minimize power requirement for battery operated situation
Todd P Cromwell IIIFebruary 8, 2021 at 6:52 amPost count: 0
I love the DROK timer relay, model 200350. I wish to be able when appropriate to use the unit in a battery operated situation, and therefore I want to know how to minimize the power requirement. (Note that many usage scenarios would not require battery power and one wouldn’t care about power, within reason; I realize that).
I wrote my questions up here initially, and then after that I read the SRD relay datasheet and it seems the relay takes 0.36W when on, so at 5v that should be minimally 71mA. After writing my initial questions up, I now think that the relay power governs all of the power requirements. One could presumably run at a higher supply voltage (at the cost of a more massive battery pack), and maybe get longer run life that way, since the current draw to get the same power (0.36W) for the relay would be less. (I find that 4.2v for the overall supply works well, but at 3.5v or less, the unit won’t operate the relay.)
At 4.2v supply, my measurements (with Fluke 87V DMM, verified with another less expensive meter) indicate the unit requires 18mA and 73-75mA with relay off and relay on, respectively, with backlight on too. When the unit enters sleep mode, I measure 13mA and 71-73mA, so that is evidence that the sleep mode does not save much power, a little surprisingly. That suggests that sleep mode saves only 2- 5mA at 4.2v supply; is that expected? Does sleep mode turn off the display and backlight entirely, or is some power still required for the display and backlight, even in sleep? Which pin on the display may I cut with a wire snip, and install a jumper on my board so the display takes no power, ever, with jumper not present? (this question is in Amazon product questions with no answer, and is relevant also because I would rather the unit not take power for the display and backlight for 10m when power is cycled (before entering sleep)). By the way, my unit takes 10m to enter sleep, not 5m like the manual says, is that expected? This number of 71mA for relay engaged in sleep mode is almost 50 percent higher than the manual says (50mA), is that expected (esp. in view of the the relay data sheet power numbers)? Finally, do you have any other ideas for optimizing the unit for use in a battery powered situation, especially with reducing the 71mA current when relay is on? (that should be only 33 hours of life on 3 AA batteries (at 4.5v) just to run the DROK timer, not counting other power requirements of whatever project the timer is enabling).
That all said, as I mentioned, I love the DROK timer relay. Thank you!Todd P Cromwell IIIFebruary 8, 2021 at 7:13 amPost count: 0
<span style=”font-family: Liberation Sans;”>Oh and, at 9-10v supply, I get 5.4mA/89mA (relay off, on), and I see the display is on enough to read but with no backlight, being in sleep mode. With backlight on, 22mA/104mA (relay off, on). Could be at the lower 4.2v supply voltage the display doesn’t take much current since perhaps the voltage is barely enough to run the display (hence appears entirely off at 4.2v supply when backlight off). But still, these numbers and the 4.2v numbers and SRD relay datasheet suggests one is not going to go below 72mA or so when relay on unless there are ideas I don’t know of.</span>Todd P Cromwell IIIFebruary 21, 2021 at 7:07 amPost count: 0
No posts from drok, but in case anyone else reads this, I finished a project using the drok timer relay, and have some numbers for you I measured off of that project. That project wasn’t a battery-powered project, and I was asking questions from a position of imagining its use in a battery operated setting. As before, my overall experiences with the unit are positive, and I recommend using it if the current requirements make sense for you. The unit is easy to use and retains settings after power-off.
The project I finished was making a timed-turnoff (auto standby) circuit for a subwoofer amplifier (Aoshike TPA3116). The circuit and bass amp are powered at 19.75vdc by a laptop power supply in the subwoofer cabinet. I used that high of a voltage because the tpa3116 wants to run at up to 25vdc in order to crank the bass amp and speaker with a sufficiently high wattage. The drok timer is set using mode 07 and for a 300 second timeout, and the drok timer relay trigger is off the left channel audio in, as low as desired using a voltage comparator against a threshold voltage obtained with resistor divider and the comparator realized with an LM393 chip (or LM339).
The current requirements for the drok timer relay and comparator circuit (but not the bass amp) at 19.75vdc are 18mA in standby mode, and 56mA when the drok timer relay is active (i.e., the relay in the relay device). At 19.75vdc, the display for the first 10m is easily readable, and the display appears to consume 7mA (so 18+7 = 25mA for the first 10m). If one ran the drok timer relay at the low voltages I discussed when thinking of battery operated projects, I think the display could be very dim and consume very little current even in the first 10m (or one could put an spst switch on whatever pin powers the display, say, for debugging). Comparing these numbers with my non-project-based measurements at the lower voltage of 4.2vdc (where one can’t as easily read the display), one gets 2-3 weeks of standby battery operation if one was planning a project with say, 3 2600mAH AA batteries, and less if the relay is on for much of that (since the relay datasheet shows it requires 0.36w by itself to remain on as I said before).
Naturally none of these are concerns when running in a non-battery situation, as half a watt of consumption is much less than even a conventional nightlight.