Clock Powersupply. - Page 1
Forum section: electronics / beginners

author: John1988
author_rank: Newbie
timestamp: September 17, 2022, 12:09:23 pm
content: Hi, I am making a power supply to power all my clocks. So I don't have to keep buying C cells and also I wont have nasty stuff leaking on them out of dead cells. I was going to make a voltage regulator from LM317 but I found a cheap dc-dc converter to play with until the LM317 arrives.The electromechanical floating balance type clocks seem very happy with this and run fine. However some of the older quartz clocks don't seem to like it. they twitch but don't go round. Also one of my tuning fork clocks that works ok on battery power. hums but wont go round at all using my circuit. Although the other tuning fork clocks seem happy with the power supply as well. How can I improve it so all my clocks work please?IS there anything else I could add to make it safer and better?2 things I want to avoid are.1. My Flat catching fire. Think the fuse in the mains plug and after the transformer should stop this?2. Destroying my clocks. I was planning to add one of those resettable fuse things in series with the output and then a Zener diode across it to defend against short circuits and over voltage killing the clocks. Good idea?Thanks alot

author: ledtester
author_rank: Super Contributor
timestamp: September 17, 2022, 01:39:25 pm
content: What's the voltage of BATTERY_2 in your schematic?QuotePerhaps the electromechanical stepper is trying to draw too much current. I'd try increasing the capacitance on the output of the LM2596 module. You might be able to get by with less, but see if adding a 100uF cap helps.

author: John1988
author_rank: Newbie
timestamp: September 17, 2022, 02:01:29 pm
content: Hi, thanks for your reply.The battery is 9v. The dc before the converter is about 12v.Forgot to mention. I tried a capacitor and it didn't make any difference which surprised me. Ill try a different one.

author: SeanB
author_rank: Super Contributor
timestamp: September 17, 2022, 02:26:13 pm
content: The clock IC's work best with around 1.4VDC as input, with a 2200uF 16V capacitor, with short leads, close to the clock module itself, as they tend to draw a pretty big pulse of current. I have run them before using a simple red LED and a 10k series resistor, the red LED does not glow much, but the voltage is clamped to around 1V4, and the 2200uF capacitor provides the current pulse needed to drive the mechanism. Input was 12VDC off a SLA battery, charged up with a simple LM723 regulator out of an old burglar alarm panel. This actually powered a cordless phone base station so power cuts would not kill the phone, and it was the closest power supply, seeing as I also got tired of this clock eating a AA cell a month. Power needs to be switched to the clock after the module, as the clock oscillators tend to not come out of reset correctly if the power rises too slowly, and the DC DC converter definitely is too slow on rise time.

author: John1988
author_rank: Newbie
timestamp: September 17, 2022, 03:22:57 pm
content: Thanks alot.With a lower voltage the clock now works. I have given it a capacitor though it seems to work without it.Lead battery is what I am looking at now. I will try and grab one when the hospital throw a load out.

author: Terry Bites
author_rank: Super Contributor
timestamp: September 17, 2022, 06:18:25 pm
content: For the EM balance clocks, make sure to use a back emf diode across the windings. You need a separate diode to control back emf. If not you may well have a regulator and output cap malfunction. A second diode stops the output cap dumping it energy back into the regulator during a short circuit. See underYou could use a PTC/ polyfuse but frankly its overkill on the mains side. You don't need the first diode, the bridge rectifier will take care of that function.All batteries more than a few 100mAh could do with a fuse. Short circuit batteries are potentally explosive! Instead of using an SLA consider using a LiPo for the sake of the environment.LM317s are a lot less faff than DC-DC converters. If you go for DC-DC then the external leads feeding assorted clocks create an EMI problem with each lead acting as a broadcast antenna. Nah, If overall efficency is not an issue then I'd go for linear regulators. They're so cheap (eg CPC, 10x for £1.20 in the T0-39 package) you can go for one per clock supply. Run raw DC to the clocks, regulate locally. If one regulator fails the others keep going.Use a transformer that is properly rated for your worst case load. ie when all the clocks roll over at the same time.The best protection for your flat is to build your psu to a good physical and electical standard.Proper insulation, cable rating, connectors etc.Case it up it an fire resistant enclosure.If you go for a metal box, make sure you earth it.

author: John1988
author_rank: Newbie
timestamp: September 17, 2022, 08:34:48 pm
content: Ok thanks. lm317 in the post. Didn't consider the noise from the dc-dc converter. Really do not want more noise upsetting my radio! Efficiency doesn't really matter if I use a decent battery.I will try and design a nice pcb and have a separate regulator for all the clocks. Its a good idea.Can get free lead acid battery's from life support machine backup supplies. They change them often and they are very handy.What value resistor would you suggest in series with the clock?For the back emf diode can I use diode 1n4001?<3

author: BeBuLamar
author_rank: Super Contributor
timestamp: September 17, 2022, 10:15:38 pm
content: If the clocks run on 9V battery you can possibly run them all on 12V battery. I don't think they will be harmed.

author: james_s
author_rank: Super Contributor
timestamp: September 18, 2022, 01:22:39 am
content: While an external power supply is an option that should work provided the voltage is right, there is another option you might wish to consider, modern NiMH cells are quite good, the most common type are AA and you can get adapters to use them in applications needing C cells. A typical clock should run for around a year on one and you can just swap it out with a charged one on a set schedule. It's what I have in my clocks, never had a modern NiMH cell leak.

author: John1988
author_rank: Newbie
timestamp: September 18, 2022, 09:34:08 am
content: Its a good idea. I'm keen to make something useful though!

author: Terry Bites
author_rank: Super Contributor
timestamp: September 18, 2022, 10:06:08 am
content: Great news, keep those airwaves clean.