Step Down Transformer - Output Switch 110 & 240V - Page 1
Forum section: electronics / beginners

author: terryt
author_rank: Contributor
timestamp: April 08, 2016, 09:23:21 am
content: Please pardon the rookie question. My knowledge of things electrical is limited though fortunately I have managed to electrocute myself only once in 72 years.Some background info: I have recently purchased my first step down transformer, a "Czhengquan" 240V to 110V sinewave/voltage transformer bought off eBay. It came without a manual, the eBay seller hasn't answered my message and the Czhengquan web site is all in Chinese. The transformer is fitted with a 3-pin plug suitable for use with my local (Australian) power supply.My question concerns the 110/240V switch on the top of the unit. (Hopefully I have successfully managed to attach my photos).To set up the transformer for use with 110V devices (including a demagnetiser) I propose to turn the 110/240V Switch to "110V"; plug the power lead into my 240V wall socket; connect the 110V device to the transformer; turn the Red Button rocker switch to ON; and turn the 110V device ON. I presume this process would be one of several correct ways of using the transformer.But it is the "240V" option on the top 110/240 Switch that has me confused and prompted this post because I cannot see how it is useful enough to justify the expense of including it.I understand that with the Switch set to the 240V option the transformer can be used for USA 220V devices fitted with USA plugs but wouldn't it be much simpler and quicker to just use an International travel adaptor (pictured) for the same result? Or have I missed the point somewhere?Comments would be appreciated. Thanks.

author: tautech
author_rank: Super Contributor
timestamp: April 08, 2016, 09:36:27 am
content: Welcome to the forum.Quote from: terryt on April 08, 2016, 09:23:21 amYep, it is somewhat confusing and a quick check with a DMM might be needed to clear it up.

author: Kilrah
author_rank: Unknown
timestamp: April 08, 2016, 10:16:04 am
content: Yep measurement or even better opening to see how things are wired...2 possibilities:- The 240 position allows you to use it as an isolation transformer- The Chinese guy who decided to make that product thought it would be useful not to have to bother unplugging the transformer before you can plug a 240V device in the socket again... obviously overlooking how much more dangerous it is in the process, which wouldn't be any surprising and probably more likely than the first option.

author: SeanB
author_rank: Super Contributor
timestamp: April 08, 2016, 07:55:58 pm
content: Having done a similar reverse engineering with a similar voltage converter I will advise you to check the output first before use. The swich may do as the one i have does, and swap the transformer taps. In the 220VAC position it takes 220VAC as an input, and provides a 110VAC output, and same as yours 300VA rating. However, in the 110VAC position, it assumes the input voltage is 110VAC, and you want a 220VAC output, so switches the tap positions to do just that. Plugging in with the mains input being 220VAC and set to 110VAC will result in both the transformer burning out rather rapidly, and in the load being supplied with 400VAC or so, at least until the smoke billows out of the unit.Unfortunately the only way to see if this is wired the same is to open the case and trace out the wiring to the switch. If you do so a few pictures attached to your next post would help determine the connection method.

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 02:06:08 am
content: Quote from: tautech on April 08, 2016, 09:36:27 amThanks for the welcome, tautech. Going by your comment (and others) I'm just glad my question didn't have an obvious answer.It looks like I need to take some photos of the internals to help others help me. I just have to think about doing that. Undoing the four base screws shouldn't be a problem but breaking apart the plastic halves has my timid mind thinking of the risk of damaging something.

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 02:27:03 am
content: Quote from: Kilrah on April 08, 2016, 10:16:04 amThanks Kilrah. You posted: "[The designer]..thought it would be useful not to have to bother unplugging the transformer before you can plug a 240V device in the socket again... obviously overlooking how much more dangerous it is in the process...".My interpretation of your comment is: After using this transformer to power a 110V device it would be dangerous to NOT unplug the transformer from my 240V power source BEFORE I connected a USA 220V (or any 240V) device to the transformer and then switched on my 240V power source to the transformer?Have I got that right? If so, would you mind explaining why it is dangerous. I don't anticipate I would be swapping devices around like that but it's handy to know these things. Thanks.

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 02:36:28 am
content: Quote from: JakeHuston on April 08, 2016, 11:04:52 amThanks for your post. Unfortunately I don't have the technical knowledge to understand your comment to your forum colleagues but I was curious about your "...this product is rated for 300 watts".The plate on the transformer says "O/P: AC-120V 600W". I'm assume "O/P" is "Output" and had assumed the transformer is rated 600 watts. But not so? How did you get 300 watts?

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 02:51:12 am
content: Quote from: SeanB on April 08, 2016, 07:55:58 pmThanks for the reply, SeanB. Unfortunately my non-electrical playing/testing experience lets me down. I don't know how to check the "output" (presumably it's with a multimeter) and I wouldn't risk damaging my meter or the transformer by poking meter probes into holes, willy nilly, while learning on-the-job.Don't know what a "transformer tap" is either. Not sure where that "300VA rating" comes from. But your comment "...at least until the smoke billows out of the unit" sure got my attention.As per my reply to tautech, I will think about opening up the transformer to take photos of the wiring so you guys can better advise me.

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 05:29:55 am
content: Have split the transformer case, haven't broken anything (yet), will send photos of wiring at first opportunity.

author: Kilrah
author_rank: Unknown
timestamp: April 09, 2016, 05:43:06 am
content: Quote from: terryt on April 09, 2016, 02:27:03 amBecause as long as there is a switch there WILL be a day where you'll connect a 110V device when the switch is set to 220V and destroy it, regardless of whether the switch was set wrong because of using a 220V device on the transformer before or just knocking it without noticing.Unless I could find a reasonable use for it if it was me I'd remove it and hardwire to 110V output.

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 08:36:58 am
content: Quote from: Kilrah on April 09, 2016, 05:43:06 amThanks Kilrah, I can see the logic now. At present, removing "it" (the switch?) and hardwiring to 110V is outside my understanding but maybe when I post up the wiring photos you might suggest how it can be done.An alternative to hardwiring I thought of is to set the Switch to 120V and super-glue in a metal plug so the switch can't be moved back to 240V. Maybe not as elegant as hardwiring but at least it doesn't require any electrical knowledge.

author: Zero999
author_rank: Super Contributor
timestamp: April 09, 2016, 08:53:02 am
content: Quote from: terryt on April 09, 2016, 02:51:12 amWiring an old fashioned 60W incandescent lamp in series with the transformer and changing the switch positions may help you with that. As long as there is no load on the transformer, the lamp should be unlit. If the unit is wired, as Sean describes, the high current draw will cause the lamp to light up.If you don't want to remove the switch, you could cover it with black electrical tape, so it's not possible to change it.

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 02:17:10 pm
content: To SeanB and others who suggested I post photos before they could offer better comments about the 240V option on the 120V | 240V Voltage Switch (and now, whether the wiring setup is safe and/or correct on this Chinese budget transformer).Please see attached photos and diagram which, hopefully, should provide sufficient detail. (I'll state the obvious to experienced members...all photos have been taken with the transformer upside down, resting on its top cover).Any comments or suggestions welcome. Please bear in mind that if things get too technical then it just goes over my head. Thanks.

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 02:44:10 pm
content: Quote from: Hero999 on April 09, 2016, 08:53:02 amThanks, that's an even quicker solution than mine.

author: Towger
author_rank: Super Contributor
timestamp: April 09, 2016, 03:00:19 pm
content: Switches the output between 240 and 120 volts and reverses the polarity.

author: SeanB
author_rank: Super Contributor
timestamp: April 09, 2016, 03:02:48 pm
content: Nice clear pictures thank you.As to the "Steaming turd of the worst of Chinese Junk", well, that is not exactly good.On the plus side, it does switch both line and neutral wires, and the wiring is such that the switch marked 110/220 does indeed switch the output voltage between 120V and 230VAC. There is actually a functional eathing connection from input to output. Those are the only good things.Negative things are:Incoming live is connected to the output socket neutral, on the "Chinese Socket that fits all mostly poorly", and then the line connection is switched to either 110VAC from the transformer centre tap or the mains neutral. Thus either the wiring is swapped or your 110V device is floating on 230VAC at all times. Any power switch on the connected device only disconnects the neutral, leaving any fault that is a breakdown in insulation free to expose you to the full mains voltage.Distinct lack of any fuse, aside from that comprising the incoming wire and transformer windings. At least those look like they are going to handle 600VA and not burn out, and they might actually be copper wire, not CCA as used in most cheap appliances.Suggestions on fixing it to be a little more safe are:Remove the 120/230 switch, and replace it with a fuse holder with a 5A fuse instead. On the output socket remove the blue and yellow wires, and solder the blue wire to the N connection on the outlet socket. Connect the white wire direct to the socket L connection. Join the 3 blue wires, and insulate the join, or use a WAGO connector which does the same thing. Connect the yellow wire from the transformer to the fuse holder, and the other terminal of the fuse holder ( preferably the one most deeply recessed) to the yellow wire from the on off rocker switch.Close up, put in a 5A fuse to fit the holder and it will be a lot safer. Use some heatshrink sleeving on the soldered connections like originally used to protect them.At least this is not like the first voltage converters I used, which were symmetrical, having a US socket outlet on each side. One side marked 115VAC and the other marked 230VAC. power was supplied using a short power cord, one end having a EU spec 2 pin plug on it, to plug into the wall, and the other end having a 2 pin US plug on it, to plug into the appropriate side of the converter. Mains voltage on 2 fully exposed unsleeved metal contacts, and as a bonus they would either float at 115VAC above ground, or at 230VAC above ground, and you could plug them in backwards, giving you a 400VAC output for around a second till the smoke came out in copious quantities ( I did this), and as a bonus they came in a plain white box, absolutely no manufacturers name or markings on the box, and only 2 sticky labels on the steel sides ( did I mention steel exposed transformer with no ground either) that would fall off in short order. Only manual was a tiny strip written totally in Chinese, with a singlr line of characters on it, and no images at all.

author: Kilrah
author_rank: Unknown
timestamp: April 09, 2016, 04:20:15 pm
content: Quote from: SeanB on April 09, 2016, 03:02:48 pm

author: SeanB
author_rank: Super Contributor
timestamp: April 09, 2016, 06:11:27 pm
content: Why do you think I accidentally blew one up........ Luckily I had a few, so simply opened them up and made sure ( with epoxy) that they were wired correctly. Came with some Sony professional units, Mark ( Dexterslab2013) has a little of the one.

author: terryt
author_rank: Contributor
timestamp: April 09, 2016, 11:46:39 pm
content: SeanB:Thank you for taking the time to review and offer comments on my transformer, much appreciated. Nothing definite but I'm starting to get the feeling you're not a big fan of the Chinese budget transformer.I'll show your advice on improving transformer safety to someone more experienced in these things. In the meantime I will do a quick fix (tape; super-glue) to stop the 120V|240V Voltage switch from moving off "120V".If the answer is obvious to you, why would JakeHuston post a few days ago: "...this product is rated for 300 watts" when the plate on the transformer says "600W"? (He may not have read my post to him asking the same question).Again, thanks for your input.

author: SeanB
author_rank: Super Contributor
timestamp: April 10, 2016, 10:44:53 am
content: Opinion varies, I have a Chinese built inverter/charger, where the mains input is a 2 pin Euro connector. the case however is steel, and the output is a 3 pin socket, implying you can use a class 1 device with it, which requires a functional earth connection in case of faults, or to have mains filters work correctly. Other stuff is well built, and has proper attention to clearances and design.just that the cheap stuff is mostly good intention with poor implementation.

author: Gyro
author_rank: Super Contributor
timestamp: April 10, 2016, 11:27:03 am
content: Most of the problems (apart from the fusing and the switch) would be solved by swapping the incoming Live and Neutral connections. Then Output Neutral would be correct and Output Live would be 120V with respect to Neutral.This would best be done at the connections to the mains switch (but likely to be a bit of a pain to get to). It would be worth checking that the manufacturer hasn't already swapped the colours at the mains plug end too (ie. Blue Live).

author: terryt
author_rank: Contributor
timestamp: April 11, 2016, 02:33:28 am
content: Quote from: SeanB on April 10, 2016, 10:44:53 amOk. Shortly I intend to start looking for a larger transformer and shall spend more time researching before buying.

author: terryt
author_rank: Contributor
timestamp: April 11, 2016, 02:37:30 am
content: Quote from: Gyro on April 10, 2016, 11:27:03 amGyro, thank you for your post. I've copied your comments (plus those of SeanB, and others) and will show them to someone who knows this stuff and who can help me "improve" my transformer.

author: terryt
author_rank: Contributor
timestamp: April 11, 2016, 03:11:05 am
content: Quote from: JakeHuston on April 08, 2016, 11:04:52 amThe sticker on my 240V:110V step down transformer says it is 600W but JakeHuston says it is rated for 300W? (I'd previously posted to JakeHuston asking the question, but no reply).600 or 300 is a rather big difference so I'd like to know the answer and not plug in a 110V device that is too big for this transformer.I have read somewhere you should add 50% to a device's rated capacity as a safety margin i.e. if the 110V device is 500W then best to use a transformer with >750W. (I know that's an oversimplification as there are other factors at play e.g. high energy start-up items like hair dryers etc but I'm just looking for a general rule-of-thumb).Any comments or enlightenment will be appreciated.

author: IanB
author_rank: Super Contributor
timestamp: April 11, 2016, 03:22:57 am
content: Quote from: terryt on April 11, 2016, 03:11:05 amNot that JakeHuston has only three posts. Note also that the post in question has no context and does not fit into the narrative of the thread.In short, the post has nothing to indicate you should pay any attention to it. Just ignore it.

author: Connoiseur
author_rank: Regular Contributor
timestamp: April 11, 2016, 04:32:04 am
content: Quote from: terryt on April 11, 2016, 03:11:05 amActually, the rating specified is misleading. Transformers are not rated in watts but in VOLT AMPERES (VA). Which is simply the product of voltage applied across the transformer and the current drawn by the transformer with the load connected.QuoteA transformer should never be loaded beyond its VA rating for anything more than a few seconds. Now Wattage is related to volt amperes asWatts = VA * Power factorNote: power factor value lies between 0 and 1.So assuming a typo, the transformer is rated 600VA which means you can draw 600/110 = 5.45A - losses in transformer; so you should be left with about 5A to use.Remember that not all loads have the same power factor, motors and cheap chinese SMPS/adaptors have substantially lower power factor than incandescent bulbs or high end IT equipments, which means you can extract far less "Watts" from your transformer. Higher the power factor higher is the wattage available (at PF of 1 wattage = 600).Excuse me if it made no sense; English is my third language.

author: terryt
author_rank: Contributor
timestamp: April 12, 2016, 04:27:19 am
content: Quote from: IanB on April 11, 2016, 03:22:57 amIanB: Thank you. I shall ignore JakeHuston's post.

author: terryt
author_rank: Contributor
timestamp: April 12, 2016, 04:41:35 am
content: Quote from: Connoiseur on April 11, 2016, 04:32:04 amConnoiseur, thank you for your comments.Anything I didn't understand in your post wasn't because of your English but more a case of my very limited understanding of things electrical in general, and transformers in particular.

author: Gyro
author_rank: Super Contributor
timestamp: April 12, 2016, 09:10:44 am
content: Quote from: Connoiseur on April 11, 2016, 04:32:04 amShow off!Your English is excellent. A lot of us around here struggle with our first language.

author: terryt
author_rank: Contributor
timestamp: April 13, 2016, 02:18:05 pm
content: Quote from: JakeHuston on April 13, 2016, 09:26:35 amThanks for getting back to me, no harm done.

author: radar_macgyver
author_rank: Frequent Contributor
timestamp: April 13, 2016, 10:24:53 pm
content: Quote from: SeanB on April 09, 2016, 03:02:48 pmOh cool, they sent you a fortune without the cookie!

author: Kilrah
author_rank: Unknown
timestamp: April 14, 2016, 07:55:41 am
content: Quote from: IanB on April 11, 2016, 03:22:57 amAnd given the commercial link in the signature the only purpose of this account is obviously spamming/advertisement. The game is to post things that while they make no real sense in the context they appear just enough on topic not to be removed.