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PSU gone awry
Hi all,
Just before I connected up the PSU to this AOR comms rx I'd bought, I thought I'd best double check the polarity was right, because someone for some reason had spliced the cable at some time and put a new plug on it. ON checking, I noted that though the polarity was correct, this psu was putting out 19.33V - whereas it's rated output was stated as 12V! This is not some cheap Chinese psu; it's the original AOR Japanese psu made by them (or at least badged by them) for this receiver. What could cause it to go from 12 to more than 19V? Don't these wall-wart style supplies have over-voltage protection/crowbars, FFS?? Just curious... |
PSU gone awry
On Sat, 11 Jul 2015 12:14:27 +0000 (UTC), Cursitor Doom
wrote: Hi all, Just before I connected up the PSU to this AOR comms rx I'd bought, I thought I'd best double check the polarity was right, because someone for some reason had spliced the cable at some time and put a new plug on it. ON checking, I noted that though the polarity was correct, this psu was putting out 19.33V - whereas it's rated output was stated as 12V! This is not some cheap Chinese psu; it's the original AOR Japanese psu made by them (or at least badged by them) for this receiver. What could cause it to go from 12 to more than 19V? Don't these wall-wart style supplies have over-voltage protection/crowbars, FFS?? Just curious... Some supplies will not regulate voltage without a load. Try measuring it again with a small load (eg, a 1K resistor) across the supply. |
PSU gone awry
On Sat, 11 Jul 2015 10:10:40 -0400, Pat wrote:
Some supplies will not regulate voltage without a load. Try measuring it again with a small load (eg, a 1K resistor) across the supply. Good point! Still doesn't check-out, though. Rated current at 12V is 500mA, so a 50 Ohm resistor would be more appropriate. Managed to find a 47R power resistor and connected across supply. Now reading 14.45V, so deffo not right... |
PSU gone awry
On 11.07.2015 19:43, Cursitor Doom wrote:
On Sat, 11 Jul 2015 10:10:40 -0400, Pat wrote: Some supplies will not regulate voltage without a load. Try measuring it again with a small load (eg, a 1K resistor) across the supply. Good point! Still doesn't check-out, though. Rated current at 12V is 500mA, so a 50 Ohm resistor would be more appropriate. Managed to find a 47R power resistor and connected across supply. Now reading 14.45V, so deffo not right... AOR Japan - that supply is for a radio, right? That reminds me of the (maybe similar) power supply of another radio. Last year I bought a Yupiteru MVT-7500. It's a small handheld radio with a 100 kHz to 1.3 GHz continuous frequency range, operable from either 3 AA cells or an external power supply. It came with a linear PSU, rated for a 100 V AC mains input (Japanese) and a 12V DC output. At least, 12V DC is what's printed on it. Since I don't have a 100 V mains socket at home, I couldn't test it right away - had to get a 230 to 2x48 V transformer first, and use the secondaries in series (96 V nominal) as a practical approximation. Unloaded it happens to be slightly over 100 V, but should be within usual tolerances. When I plugged the Yupi's power supply into it and checked the output with a multimeter (unloaded), it went up over 17 V! At first I thought my improvised primary supply was iffy, but nope, the primary was OK. Then I tried loading it and it just barely got near its rated output under maximum rated load of 200 mA. But since the radio never really uses the full 200 mA anyway - either 80 or 150 mA depending on the state of the LCD backlight - the power supply voltage is much higher. It seems to run at just over 15 V, more or less, under "real life" conditions and never gets down to 12 V with the radio as a load. Apparently here the PSU has just a transformer, a bridge rectifier and a cap - nothing else, all the regulation is done in the radio. Yours may be similar. Btw, was yours also rated for 100 V and did you plug it into 115 V by any chance? If so, consider getting it a "properly" rated supply. The Japanese have a 100 V mains, so when they write 100 V, they actually mean it. Using the PSU on 115 V may work, but it could likely stress components in the radio if connected like this for a significant period of time. Regards Dimitrij |
PSU gone awry
"Cursitor Doom" wrote in message ... Hi all, Just before I connected up the PSU to this AOR comms rx I'd bought, I thought I'd best double check the polarity was right, because someone for some reason had spliced the cable at some time and put a new plug on it. ON checking, I noted that though the polarity was correct, this psu was putting out 19.33V - whereas it's rated output was stated as 12V! This is not some cheap Chinese psu; it's the original AOR Japanese psu made by them (or at least badged by them) for this receiver. What could cause it to go from 12 to more than 19V? Don't these wall-wart style supplies have over-voltage protection/crowbars, FFS?? Just curious... Just curious, is this Wall Wart just a transformer in a plastic case? Any 12v transformer unloaded will put out a lot more than its rated voltage. 19v doesn't sound that unlikely to me if that is what it is. Gareth. |
PSU gone awry
Dimitrij Klingbeil expressed precisely :
On 11.07.2015 19:43, Cursitor Doom wrote: On Sat, 11 Jul 2015 10:10:40 -0400, Pat wrote: Some supplies will not regulate voltage without a load. Try measuring it again with a small load (eg, a 1K resistor) across the supply. Good point! Still doesn't check-out, though. Rated current at 12V is 500mA, so a 50 Ohm resistor would be more appropriate. Managed to find a 47R power resistor and connected across supply. Now reading 14.45V, so deffo not right... AOR Japan - that supply is for a radio, right? That reminds me of the (maybe similar) power supply of another radio. Last year I bought a Yupiteru MVT-7500. It's a small handheld radio with a 100 kHz to 1.3 GHz continuous frequency range, operable from either 3 AA cells or an external power supply. It came with a linear PSU, rated for a 100 V AC mains input (Japanese) and a 12V DC output. At least, 12V DC is what's printed on it. Since I don't have a 100 V mains socket at home, I couldn't test it right away - had to get a 230 to 2x48 V transformer first, and use the secondaries in series (96 V nominal) as a practical approximation. Unloaded it happens to be slightly over 100 V, but should be within usual tolerances. When I plugged the Yupi's power supply into it and checked the output with a multimeter (unloaded), it went up over 17 V! At first I thought my improvised primary supply was iffy, but nope, the primary was OK. Then I tried loading it and it just barely got near its rated output under maximum rated load of 200 mA. But since the radio never really uses the full 200 mA anyway - either 80 or 150 mA depending on the state of the LCD backlight - the power supply voltage is much higher. It seems to run at just over 15 V, more or less, under "real life" conditions and never gets down to 12 V with the radio as a load. Apparently here the PSU has just a transformer, a bridge rectifier and a cap - nothing else, all the regulation is done in the radio. Yours may be similar. Btw, was yours also rated for 100 V and did you plug it into 115 V by any chance? If so, consider getting it a "properly" rated supply. The Japanese have a 100 V mains, so when they write 100 V, they actually mean it. Using the PSU on 115 V may work, but it could likely stress components in the radio if connected like this for a significant period of time. Regards Dimitrij And isn't the nominal in USA 120volts these day? :-Z The Japanese 100Volts was a problem in the early days of PCs as many people thought it was the same as USA whereas only military bases had USA power. Some of Japan is 60 hz and some is 50Hz -- John G Sydney. |
PSU gone awry
On Sat, 11 Jul 2015 22:42:47 +0100, Gareth Magennis wrote:
Just curious, is this Wall Wart just a transformer in a plastic case? Eh?? Have you actually read the thread? |
PSU gone awry
On Sat, 11 Jul 2015 22:40:48 +0200, Dimitrij Klingbeil wrote:
AOR Japan - that supply is for a radio, right? Correct. A "communications receiver" so-called, though it's only the size of a half a shoebox. I'm more accustomed to rack-mounted Racals so please forgive my cynicism. ;) That reminds me of the (maybe similar) power supply of another radio. Last year I bought a Yupiteru MVT-7500. It's a small handheld radio with a 100 kHz to 1.3 GHz continuous frequency range, operable from either 3 AA cells or an external power supply. It came with a linear PSU, rated for a 100 V AC mains input (Japanese) and a 12V DC output. This one is specifically made for this receiver. It even has the pin-outs for the rx's power socket printed on it. And it's been manufactured for the UK market. It states 230VAC input; 12VDC @ 500mA output; 12VA rating. And, "Made by AOR Communications, Tokyo, Japan" under the spec. Could not be clearer! |
PSU gone awry
"Cursitor Doom" wrote in message ... On Sat, 11 Jul 2015 22:42:47 +0100, Gareth Magennis wrote: Just curious, is this Wall Wart just a transformer in a plastic case? Eh?? Have you actually read the thread? OK, so just a transformer with rectifier diodes and a cap, i.e. not regulated, and not an SMPS. Gareth. |
PSU gone awry
On Saturday, July 11, 2015 at 1:45:09 PM UTC-4, Cursitor Doom wrote:
On Sat, 11 Jul 2015 10:10:40 -0400, Pat wrote: Some supplies will not regulate voltage without a load. Try measuring it again with a small load (eg, a 1K resistor) across the supply. Good point! Still doesn't check-out, though. Rated current at 12V is 500mA, so a 50 Ohm resistor would be more appropriate. Managed to find a 47R power resistor and connected across supply. Now reading 14.45V, so deffo not right... If the supply is rated at half amp at 12V, a 27 ohm 10 w resistor will give you a better idea of the supply. As Gareth pointed out, this is probably just an AC xfr, rectifier, filter. Not a smps and not regulated. If you're unsure about the radio's capability of internally regulating the input or not loading the supply down sufficiently to keep the voltage in the 12-14v range, then replace it with something more appropriate or add an external series pass 12V regulator IC. |
PSU gone awry
On Sun, 12 Jul 2015 06:21:15 -0700, John-Del wrote:
If the supply is rated at half amp at 12V, a 27 ohm 10 w resistor will give you a better idea of the supply. I used 47R because it gives rise to half the rated output current, which I thought would be about right for a conservative design POV. No decent designer, surely, is going to specify a 500mA PSU for a load requiring 500mA of current. Absolutely maxed-out! As Gareth pointed out, this is probably just an AC xfr, rectifier, filter. Not a smps and not regulated. If you're unsure about the radio's capability of internally regulating the input or not loading the supply down sufficiently to keep the voltage in the 12-14v range, then replace it with something more appropriate or add an external series pass 12V regulator IC. I've got it running off a big ol' linear supply at the moment. Just out of curiosity I'll see how much current it's drawing. Should it turn out to be only around 150-250mA - as I suspect - then we'll know for sure that wall wart is f*cked. I reckon if I scoped the PSU output I'd see pure sine waves! |
PSU gone awry
On Sunday, July 12, 2015 at 10:30:45 AM UTC-4, Cursitor Doom wrote:
On Sun, 12 Jul 2015 06:21:15 -0700, John-Del wrote: If the supply is rated at half amp at 12V, a 27 ohm 10 w resistor will give you a better idea of the supply. I used 47R because it gives rise to half the rated output current, which I thought would be about right for a conservative design POV. No decent designer, surely, is going to specify a 500mA PSU for a load requiring 500mA of current. Absolutely maxed-out! Yeah, but you're missing the point. An unregulated wall wart is rated for the max current that the supply will output no less than 12V. If your radio has regulators inside that can handle an input of 19.33 volts, then there's no problem. If the radio was designed to run on batteries and/or a regulated supply, then you should definitely go to a regulated supply, or add a post regulator to the wall wart. |
PSU gone awry
On Sun, 12 Jul 2015 08:17:38 -0700, John-Del wrote:
Yeah, but you're missing the point. An unregulated wall wart is rated for the max current that the supply will output no less than 12V. If your radio has regulators inside that can handle an input of 19.33 volts, then there's no problem. If the radio was designed to run on batteries and/or a regulated supply, then you should definitely go to a regulated supply, or add a post regulator to the wall wart. The radio at the power connection states it accepts 12VDC and has a little diagram of the three hole pin-out for polarity/orientation. I find it absurd that one should expect such a device to be able to cope with 19V in. Call me old fashioned if you like, but that's my mindset. If it says it requires 12V I'm not going to stick 19V unreg into it. Just doesn't sit right with me. I've checked the current this radio draws when supplied with 12V regulated on full volume with the display on max. etc., etc., and it's 275mA, so a little higher than I expected but not enough to make any material difference. *If* that PSU is working as it should then my opinion of Jap design has just taken a big hit. |
PSU gone awry
On Sun, 12 Jul 2015 06:21:15 -0700, John-Del wrote:
As Gareth pointed out, this is probably just an AC xfr, rectifier, filter. Not a smps and not regulated. Damn thing's linear! I just took it apart to see and there's only a trannie, a little full wave rect. and a 25V/1000uF electrolytic in there. That's all! First thing to do is check that cap.... |
PSU gone awry
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PSU gone awry
"John-Del" wrote in message ... On Sunday, July 12, 2015 at 10:30:45 AM UTC-4, Cursitor Doom wrote: On Sun, 12 Jul 2015 06:21:15 -0700, John-Del wrote: If the supply is rated at half amp at 12V, a 27 ohm 10 w resistor will give you a better idea of the supply. I used 47R because it gives rise to half the rated output current, which I thought would be about right for a conservative design POV. No decent designer, surely, is going to specify a 500mA PSU for a load requiring 500mA of current. Absolutely maxed-out! Yeah, but you're missing the point. An unregulated wall wart is rated for the max current that the supply will output no less than 12V. Further to that, it will (should) be rated to supply at least 12v @ 500mA when the mains supply voltage is at the legal minimum (not that it is likely to ever reach that value in the real world). Currently that is 216.2v. (legal requirement = 230v +10% / -6%) 12v is just the lowest guaranteed voltage this unregulated PSU will deliver at 500mA, it is not what is normally expected to come out of it. Gareth. Gareth. |
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