UK to US wall power supply converter question... - Page 1
Forum section: electronics / beginners

author: brokenbones
author_rank: Newbie
timestamp: December 21, 2019, 08:33:56 am
content: I'm new and still learning so please bare with me. I just ordered a piece of audio gear from the UK (i'm in the US) that requires:9–12 V (~), max 400 mA viasupplied (included) plug-in transformer connected to 230 V/50 HzNow the US/UK supply voltage shouldn't matter, correct? The internal PS in the device just wants to see 9-12V? Do I have that right or am I missing something? Could I just use a typical US wall wort PS? Or, will I run into polarity or cycle issues?I do own a US to UK power converter plug which I know would be the safest route but I have some other gear that occasionally requires that converter.TIA

author: johnkenyon
author_rank: Regular Contributor
timestamp: December 21, 2019, 09:21:16 am
content: The key things from your post are:a) "a piece of audio gear"andb) "9–12 V (~), max 400 mA"and probably because of (a)c) "plug-in transformer"The original design uses a transformer instead of switched mode PSU for a reason - they may be efficient, but they are electrically noisy.Your average wallwart these days will be transformerless/switched mode and will spit out DC.Use an US adaptor which matches the output of the UK one - namely 9-12V AC. The device is probably not going to be that sensitive to running off 60Hz rather than 50Hz.If you can't find a suitable wart, then find a 0-9 (4VA), 0-12 or 6-0-6 (5VA) transformer, and mount it in a box. Choose an encapsulated transformer, and throw in a 100mA* fuse on the primary and you should be able to get away with an ungrounded plug.*(Replace the 100mA fuse with a 250/500/630mA fuse if that's what you've got in your spares box)

author: Brumby
author_rank: Unknown
timestamp: December 21, 2019, 10:08:14 am
content: Quote from: brokenbones on December 21, 2019, 08:33:56 amCorrect.QuoteYou have that right - but there are 4 factors you need to get right.QuoteYou have that right - but there are 4 factors you need to get right.QuoteThe input frequency (50Hz/60Hz) will not matter at all, but youhaveidentified one of the 4 factors you need to get right.They are:1. Voltage.There is the obvious need to match a 9V requirement with a 9V supply - but you also need to be a little careful here. Some supplies are not as well regulated as others and these can have a higher (sometimes significantly higher) voltage when the load current is low. Such is the case with many (not all) transformer based supplies (these are almost always heavier and/or larger than switchmode supplies). The danger here is that the voltage presented to the device is too high for it to handle and damage could result. This problem is minimised when the voltage and current rating of the supply matches that of the device as the device will load down the supply. This is pretty common for transformer supplies.As a rule, switchmode supplies do not have this problem. You can identify them by being lighter and smaller than transformer types - but if you're not sure about this, then check the mains input voltage on the supply. If it says something like 90V-250V, then it will be a switchmode supply. As mentioned above, there is a caveat with switchmode supplies, especially used with audio devices, and the name gives you a big hint... Switchmode supplies work through switching a current on and off at a frequency much higher than the mains. Switching currents can cause EMI - both radiated and/or conducted - which can sometimes creep into the audio path. Much gnashing of teeth will ensue if this happens.2. Current.Obviously, if a device needs a particular amount of current, then the supplymustbe capable of supplyingat leastthis amount. Aside from the previously stated caveat regarding poorly regulated supplies, there is no problem with it beingcapableof providing more current than the device requires - the device will just take what it needs.3. Connector.This is a simple mechanical matching of the plug and socket between the supply and the device. Your typical barrel connector has 3 main dimensions - internal diameter, outside diameter and length. Get these right and you'll be fine.4. Polarity.Centre positive or centre negative? Getting that wrong could ruin your day.

author: johnkenyon
author_rank: Regular Contributor
timestamp: December 23, 2019, 06:05:12 pm
content: The OP stated that the power supply was "9–12 V (~)"That implies an AC output - no polarity issues, and the supply won't be regulated either.

author: Jwillis
author_rank: Super Contributor
timestamp: December 24, 2019, 08:49:55 am
content: Quote from: brokenbones on December 21, 2019, 08:33:56 amIt might matter. It depends on the architecture of the power supply. Most are Switch mode but some are not. Switch mode type will usually say on them Input 100V-240VAC or something similar. Those will work in both the UK and US.Linear type will not work correctly.And yes they do still exist and are still sold. If it says Just 240VAC then its probably a linear power supply and it will not work properly in the US .Instead of 9VDC It will only deliver around 4.5VDC.If it says 120VAC and used in the UK it will double the output if it doesn't burn out first.

author: brokenbones
author_rank: Newbie
timestamp: January 07, 2020, 12:25:20 am
content: So my unit arrived today and i'm having difficulty understanding the polarity requirement. Can anyone decipher from the plugs?**Edit. I'm posting as I test this out.I was able to remove the GB adapter to reveal a EU (adapter) power supply. I do have an EU to US adapter. When I plugged that in and took some measurements with a DMM I was able to get 6.3V. Switching the probes still read 6.3V so the plug is polarized.Now, if I want to use a non-polar US power supply, is this even possible? Does it matter if it's center neg or center pos?FTR, the unit does work fine with the EU/US adapter.

author: Jwillis
author_rank: Super Contributor
timestamp: January 07, 2020, 01:19:52 am
content: The first supply on the left is an AC/AC which means that the output will be 9VAC with 500mA . But its input is 230VAC .If its plugged into a US 120VAC the output voltage will be around half (6.3VAC) because it has a transformer inside not a SMPS.The second supply is the original? Its form is different so I can only assume it will do the same thing.SMPS supplies are used for a DC output.You need a 120VAC to 9VAC or 12VAC adapter .Edit: the second is the unit you want to supply with 9-12 VAC so that adapter is wrong . You can get AC/AC adapters in the US that will be correct.

author: tooki
author_rank: Super Contributor
timestamp: January 07, 2020, 01:31:10 am
content: Quote from: brokenbones on January 07, 2020, 12:25:20 amAs you’ve been told repeatedly, it’s AC, so there is no polarity. (The replies talking about getting polarity right clearly missed that detail.)Johnkenyon gave you a thorough and fully correct answer in the first reply to the thread. (So yes, someone was able to “decipher” the specs already.)Quote from: brokenbones on January 07, 2020, 12:25:20 amUmmmmm... just what exactly do you think “polarized” means? Because this statement leads me to question that you understand even the basics of polarity and DC vs AC current.Similarly, “non-polar US power supply” is... well, it’s words, but they don’t make sense. Again I think you think “polar” means something totally different from its actual meaning, and I can’t tell what it is that you think it means.

author: Jwillis
author_rank: Super Contributor
timestamp: January 07, 2020, 09:03:12 am
content: Understanding AC polarized plugs.The wider prong on a polarized plug will permit it to be plugged in only with the correct polarity. The large prong is common . The narrower prong is the "hot" or live lead and the switch to the appliance is placed in that lead, guaranteeing that NO voltage will reach the appliance when it is switched off. It's a safety feature for 2 prong AC plugs .Its NOT Positive and Negative as in DC.To reiterate you need a 120VAC 60Hz to 9VAC Wall supply. Those can be purchased in the US.

author: tooki
author_rank: Super Contributor
timestamp: January 07, 2020, 03:34:07 pm
content: I hope you’re addressing the OP, since I fully understand NEMA plugs, since I’m actually American. :p

author: Jwillis
author_rank: Super Contributor
timestamp: January 07, 2020, 03:54:38 pm
content: Yes tooki my apologies. Just wanted to clarify what AC polarization means to the OP.