100VAC SMPS on 120VAC  - Page 1
Forum section: electronics / beginners

author: Mikek400
author_rank: Regular Contributor
timestamp: December 17, 2015, 05:31:36 am
content: I have a SMPS that is rated for 100VAC 50/60HzI find it suspicious that it has such a narrow operating voltage considering they usually operate over a wide voltage range. I doesn't specifiy any kind of operating voltage window as a normal SMPS would such as 100-127VAC.I would like to operate it on 120VAC but want to know what you think about the impact of doing so. I relatively sure that plugging it into 120V wont release the magic smoke right away, but was wondering how sensitive SMPS are to voltage input. Are there any components I should be looking at to be sure its not overheating or check to be sure its not drawing too much current?The power supply is integrated and potted into the device I want to use, so the only other way to power the unit would be to build a buck transformer. It is low enough wattage to do so, but why bother if the SMPS can handle the voltage.Any thoughts?UPDATE========Since I didn't have any replies and was asking while I was work, now I am at home and tried out hooking it up to 120v via a step up transformer. It uses very slightly less current at 120v instead of 100v. drawing .021A at 120v .022A at 100v.I won't know exactly how much power it uses at operating current until I get it back to the US and try it out. But looking at the standby current it uses looks ok.Main filter cap rated for 180v so looks like it should be ok. Will see when I get it back to the us and can try it out on 60hz power but it is rated for 50/60Hz operation.If anyone knows anything I should look out for, please pass the info on.

author: Zero999
author_rank: Super Contributor
timestamp: December 17, 2015, 05:46:46 pm
content: It will work but a 180V filter capacitor means a maximum voltage rating of 128VAC so running it at or near that voltage will shorten its life.It sounds like it's a cheap, poorly designed PSU. Ideally the capacitor ideally should be rated to 200V or more, to give plenty of safety margin.

author: Ian.M
author_rank: Super Contributor
timestamp: December 17, 2015, 06:38:38 pm
content: How much is the device worth and how difficult will it be to replace once you are back stateside?From your measurements, you could buck the voltage with a 1VA transformer, with an 18 or 20V secondary which woud be approximatelt a 1 1/4" cube. Depending on clearances etc. that might even fit inside.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 17, 2015, 09:09:36 pm
content: Well, I've seen 160VDC caps in 120V equipment forever, so I doubt it's a big deal...It might not be rated for other voltages simply because it wasn't tested for sale in those markets. Dunno. There *might* be concerns like, not passing other FCC/CE regulations (EMC or safety) that are coincident with those regions, but those should be apparent from the lack of respective agency symbols on the equipment.Tim

author: Zero999
author_rank: Super Contributor
timestamp: December 18, 2015, 11:45:41 am
content: Quote from: T3sl4co1l on December 17, 2015, 09:09:36 pmWas it decent branded equipment?Running a 160V capacitor at nearly 170V (more if the mains is on the high side of its tolerance) is asking for trouble and certainly isn't going to do anything for reliability.

author: Mikek400
author_rank: Regular Contributor
timestamp: December 18, 2015, 03:35:43 pm
content: Actually its a tankless LP gas hot water heater.Came across it cheap and have space in my bag.It uses 150W max I think but really cant check much until its actually hooked up and working.Has Nichicon 105c caps inside it and looks to be built ok.Found a spec sheet for the unit.. Lists minimum voltage as 90V and max as 110.. Hmm.Voltage back home is usually from about 118 to 124v.Purely out of curiosity I would like to see the us version of this unit to compare the boards.For anyone who is curious about this board here are some pics.https://drive.google.com/open?id=0B7ll7KI4S3PNOUhqdDlfYUc4ZHpjSUhjUmpaUWNVMU9yeFBjhttps://drive.google.com/open?id=0B7ll7KI4S3PNRHNkNXNWemJDWFdiRkJadmhsWU1VSXZRNjZnhttps://drive.google.com/open?id=0B7ll7KI4S3PNRHNkNXNWemJDWFdiRkJadmhsWU1VSXZRNjZnhttps://drive.google.com/open?id=0B7ll7KI4S3PNenRNMTM5WHJxWndYeFZBT29wXzFtSjdiNVZzhttps://drive.google.com/open?id=0B7ll7KI4S3PNSzRac3luMU5hWDdyNGQwekstN2FEai1nSW5zAbout the EMF / Safety certifications, they make a very similar model which they sell in the US I believe, but this one doesn't have any markings for safety agencies in the US. Purely out of curiosity I would like to see the US model and compare the boards.

author: Mikek400
author_rank: Regular Contributor
timestamp: December 18, 2015, 04:43:09 pm
content: Seems that you guys think I should probably run it at its designed voltage.How is the best way of getting lets say 200W at 100V from 120V. I made a small 120v boost transformer here for testing things from a 100=>20V 2A wall wart. But I question the safety of leaving a transformer hooked up with its secondary powered at 120v. Are there any safety issues I should be worried about? Am I just paranoid? I would think that the enamel on the secondary is only insulated for low voltage.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 19, 2015, 01:09:07 am
content: Quote from: Hero999 on December 18, 2015, 11:45:41 amThink they were pulled from stuff like CRT TVs.Really, electrolytics don't mind a little overvoltage, as long as it's applied gradually. But long life, no, I wouldn't expect that from those things either.Tim

author: Ian.M
author_rank: Super Contributor
timestamp: December 19, 2015, 01:51:31 am
content: A high bus voltage will also overstress the magnetics, which will have been designed with minimum core area and turns count to save materials, and likely the switching semiconductor(s) as well.Quote from: Mikek400 on December 18, 2015, 04:43:09 pmI wouldn't care to run a cheap bare transformer with a metal bracket holding the core down as a buck or boost transformer, unless the secondary was on an insulating plastic bobbin, but a high quality split bobbin transformer, a fully potted PCB mount transformer or a fully insulated toroidal transformer will be fine.