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??
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...
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.
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
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. ;)
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!
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 th e 12-14v range, then replace it with something more appropriate or add an e xternal series pass 12V regulator IC.
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!
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!
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 a nd/or a regulated supply, then you should definitely go to a regulated supp ly, 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.
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....
Off hand i would say that most likely there is nothing wrogn with it... That is, if it's for the japanese market?
I've had a few amplifiers and such where the supply voltage was assumed to be 200 volts and 230 was being used.
Normally they supplied a version for the US market.. Maybe there is a selectable tap on the transformer inside, that was the most common way they did it.
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