My instruments are affected by noise on the power line, solutions? - Page 1
Forum section: electronics / general

author: mcinque
author_rank: Unknown
timestamp: November 02, 2013, 03:40:36 pm
content: I have a very unstable power line that goes from 189V to 230V, so I installed a voltage regulator (APC Line-R 1200).The problem is that when the voltage regulator switches from one coil to another, that switch generates interference.With DSO connected to a not regulated electrical outlet (so that the instrument itself is not affected by the interferences introduced by the voltage regulator) I measured:- the ripple of a stabilized power supply (DP832)- the stability of 1MHz sine waveformBoth readings show interferences, expecially in the case of the power supply (800mV ripples!!!).What do you recommend?a. eliminate the voltage regulator and let your instruments go with a unstable power lineb. install an isolation transformer between the voltage regulator and the instrumentsc. eliminate the voltage regulator and install a double conversion UPSp.s. I know that the main problem is with the power company. But the voltage instability is not a problem that will be easily solved. The section of the cables that supplies us was ok many years ago; now the number of housing has increased and that small section is no longer enough to serve all us without problems. The power company will not replace the entire line just because I'm complaining, I need a lot more people to join me, but for them it is all ok, tvs turns on and all is fine.

author: SArepairman
author_rank: Frequent Contributor
timestamp: November 02, 2013, 10:09:35 pm
content: can you complain to a regulatory body ?

author: quarros
author_rank: Regular Contributor
timestamp: November 03, 2013, 03:52:11 am
content: Okay so the options:a, it is not really a good choice but depending on how well your DSO power supply is designed, it might work but it is definitely shortening the device lifespan.b, Using an isolation transformer won't do you any good, because the noise will still be there, (albeit it might be muffed a little bit) Your problem is that the power supply of the unit is susceptible to the noise that the regulator create. and that noise would creep trough a galvanic isolation anyways.c, That's the most sensible solution in my book.d, You can also try to use a simple mains filter between the regulator and the DSO and hope to get lucky.Additionally you can try something like a Power Conditioner but that's realy a whole another story (and most likely not help)https://www.eevblog.com/forum/reviews/power-conditioners/

author: Fsck
author_rank: Super Contributor
timestamp: November 03, 2013, 05:14:28 am
content: easy way: double converting UPS.grab an ancient one locally and add new batteries. you might be able to do it all under 200$, but it all depends on your luck

author: TMM
author_rank: Frequent Contributor
timestamp: November 03, 2013, 06:04:32 am
content: Yep, you want a double converting UPS. That way you are always powered by the inverter running off the batteries.An isolation transformer would probably kill that (?)200khz burst a fair bit, however is not nearly as good value as the UPS and you have the safety issue of floating instruments.

author: Alexandre Mello
author_rank: Newbie
timestamp: November 03, 2013, 11:33:20 am
content: I had a similar problem in the past, different equipment (pro audio), I bought an APC double converting UPS and the problem was gone.Definitely double converting UPS !!

author: quarros
author_rank: Regular Contributor
timestamp: November 03, 2013, 12:07:44 pm
content: One thing I forgot to mention.If you go by the UPS route than you really should buy one used, because you have to hack into it anyways. Why? Well your instruments do not need continuous power 24 hours a day, but because the way a UPS works it always eats up electricity. After all that is its main intended purpose not just power line isolation. So if you don't want to have a "light ball" that is always turned on, than you have to be able to turn the device off. But by design most of these UPS's don't have an off switch! You have to build one into it, that separates the battery, the charging/controlling electronics, and the mains. Otherwise it would pump out power from the battery continuously as long as any charge left in them, when you unplug the device. Therefore eating away its capacity in only a few month's (and also if you have one with sound alarm than.... Well you know).

author: DL8RI
author_rank: Regular Contributor
timestamp: November 03, 2013, 12:08:40 pm
content: If you have only Instruments with Switching-PSUs, look at their specs and remove the regulator. Most PSUs are controlled "wide range" and should not be affected by the Dips.

author: mcinque
author_rank: Unknown
timestamp: November 03, 2013, 01:34:55 pm
content: Thank you all for the replies, I'm grabbing an online UPS with double conversionThank you again!

author: SeanB
author_rank: Super Contributor
timestamp: November 03, 2013, 01:59:01 pm
content: I will also add that you look for a ferroresonant power conditioner or constant voltage transformer. They typically can both provide isolation and as well do a pretty good job of giving a constant voltage power output, you typically can have the output change by 1% for a 15% change in input voltage, and they will mostly ignore a 2-3 cycle dip in the input. If you do get one check the capacitors on the swing coil and the output, typically they are 50uF 440VAC motor run capacitors, and they do degrade with time. Do note that trying to measure the voltage across them during operation will prove to be hazardous to your meter, as they can have 400VAC across them even on a 110V line.