Does cycling an SMPS cause excessive wear/damage/danger? - Page 1
Forum section: electronics / beginners

author: mortrek
author_rank: Contributor
timestamp: October 07, 2020, 03:45:47 pm
content: I have a mid-range Chinese-made 200W SMPS for an LED array/fixture that I need to switch on for a short amount of time every ~10 minutes. Right now, it's set to be on 10 seconds, off for 10 minutes, on loop, for 10 hours a day. Its on constantly for the other 14 hours of the day.Is there any problem with doing this? Does this sort of usage profile cause any kind of excessive wear to a typical SMPS? Or the LEDs themselves? Any fire hazard or anything else that I should know? Power is controlled through a UL-certified relay system, so that part seems pretty safe.I'd like to reduce the on-time to be less than 10s, but I figured that 10s would hopefully be enough time for everything to warm up and reach peak output. If it needs to be longer, I'm willing to change that as well.Thank you.

author: Gyro
author_rank: Super Contributor
timestamp: October 07, 2020, 03:53:09 pm
content: The main thing that can cause problems with an SMPS is the input surge current (through the rectifiers etc). This is normally limited by a series connected NTC thermistor, cycling quickly doesn't give this time to cool down and increases the surge current.Luckily, in your case, 10 seconds on and 10 minutes off will give the thermistor ample time to cool down (and the SMPS very little time to heat up), so I wouldn't expect it to shorten its life significantly.P.S. Cooler operation of the LEDs ought to increase their lifetime too.

author: magic
author_rank: Super Contributor
timestamp: October 07, 2020, 05:08:33 pm
content: Turn-on behavior may be different (perhaps more gentle, or am I asking for too much?) if there is an active PFC rather than just a rectifier + big-ass capacitor. 200W is around the region where there might be one.

author: mortrek
author_rank: Contributor
timestamp: October 18, 2020, 01:22:31 am
content: So.. after about a week and a half of running the SMPS this way, it has failed. I'm not sure why it failed from my use case. 10 min off, 10 sec on, for half the day. The rest of the day it's constant-on.It's very frustrating. They even included a power timer with the LED setup, so it's clearly meant to have the line voltage cycled. Maybe the PSU was crappier than I had thought.Their higher-end lights use Meanwell supplies, but I thought that their mid-range PSUs, while not Meanwell-brand, would still be reasonable. If anyone is curious, I'm dealing with Mars Hydro. I don't know what they are planning on doing with the warranty... I'm worried that if they just replace the PSUs with identical ones, they will fail if I use them this way again...

author: TimNJ
author_rank: Super Contributor
timestamp: October 18, 2020, 01:36:47 am
content: Depending on what you mean by "half a day", that means it was powered up about...500 times? Surprising. I feel that most (decent) power supplies should at least be able to turned on a few thousand times, maybe 10,000-ish.Does it have any inrush limiting at all? The inrush limiter is usually a green or black disc, 8-15mm diameter on average. Could be improperly rated fuses. I2T rating too low. Or PFC diode couldn't handle the surge current.

author: BrianHG
author_rank: Super Contributor
timestamp: October 18, 2020, 02:15:31 am
content: Your better off getting a power supply which has an enable/disable input pin designed to be switched on & off many times a day. Or, an LED power supply designed without an input capacitor stage on the mains. However, those types of supplies tend to flicker the LEDs at 120Hz / 100 Hz, though their power-factor is usually very high.

author: BlackICE
author_rank: Regular Contributor
timestamp: October 18, 2020, 03:12:04 am
content: If you're not too concerned about power consumption how about turning the power off and on after the power supply and leaving the power supply turned on.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: October 18, 2020, 03:34:18 am
content: In SMPS I have designed myself at power up I let the caps charge up then apply low power for a little while to stop surges.

author: mortrek
author_rank: Contributor
timestamp: October 18, 2020, 04:21:07 pm
content: This is why I asked the question initially. I was worried that the PSU wouldn't be able to handle power cycling.I guess that, if I get replacement PSUs or fix the ones that I have, I could try using a relay to switch the output power on and off (likely something like 50V at 5A, very roughly, but I haven't measured it), but I'm worried that there would be an issue there as well.I wouldn't mind a PSU with an output enable/disable pin but I don't know if there is a drop-in replacement for my lights.Total power cycles were probably approaching 1000 or so. I wasn't aware that SMPSs were so fragile. Even one that could handle 10000+ would not work for me. I need it to work for months or years if necessary.

author: mortrek
author_rank: Contributor
timestamp: October 18, 2020, 04:52:50 pm
content: Alright, so I have a question. Would switching the output load on and off with a relay cause some kind of excessive wear to an SMPS?

author: BlackICE
author_rank: Regular Contributor
timestamp: October 18, 2020, 10:31:21 pm
content: I doubt if switching the output load would hurt the power supply it was properly designed. Also you can use a power mosfet instead of a relay if your loads are purely resistive and non- inductive. The power loss with just a 5 amp load will be minimal. If you're concerned about damaging the power supply you can ramp the voltage from 0 to full 50 volts over a short. Of time to ease the strain.

author: amyk
author_rank: Super Contributor
timestamp: October 19, 2020, 12:37:23 am
content: Quote from: mortrek on October 18, 2020, 01:22:31 amWithout knowing why it failed, it is hard to make any recommendations.On the topic of power-cycling SMPS, I have AT PSUs from PCs that were turned on and off at least once a day for a decade, and they still work perfectly fine, so I don't think there should be any problems with doing that. (These are AT ones, the type with a Big Red Switch that controls the mains input directly, not the newer soft-off ATX type.)

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: October 20, 2020, 04:04:02 am
content: If you dont use low power mode to start with in the SMPS the surge is much more because it is the surge into capacitors plus output load current too plus output capacitors load.My method of having a power up delay reduces the power on current.There are millions of TV sets in the world with SMPS so it must be possible to work reliably.Some use PFC which in itself is a resistance between mains input and smoothing caps.

author: m k
author_rank: Super Contributor
timestamp: October 22, 2020, 09:00:05 am
content: Quote from: BlackICE on October 18, 2020, 03:12:04 amI'd probably do that.With dummy parallel load and oversized supply.

author: Alti
author_rank: Frequent Contributor
timestamp: October 22, 2020, 10:27:11 am
content: Quote from: mortrek on October 18, 2020, 04:52:50 pmThis depends on the mode of SPMS. If this is a SMPS for led lighting then this is a current source. So by opeing the circuit you decrease the load but the output caps are going to stop on the voltage limit. On closing a relay whole charge from output caps is dumped to LEDs in useconds.