EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: I_Saldana on May 27, 2021, 08:37:33 am
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I was wondering what the snags are when doing the following:
I am considering buying a 60A 12VDC transfo on a chinese store at random then buy an american car/mobilehome 12VDC to mains converter to power potential future american imported low power vintage electronics audio equipment, random devices like clocks. Attach both with a couple of 6mm² + cables.
The things available on the market are usually straight coil transfo's that don't change the frequency. Then there's kit that does change the frequency but is sold at a premium in audio stores, sometimes hundreds of euros. Then there's the huge industrial racks that I presume are used for motors and stage equipment.
Please tell me what the caveats are here.
Thnx in advance.
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Among the shortcomings would be the "Made in China" part of the equation as well as the inverters that are affordable generate an almost square wave which audio gear would hate as well as the noise that would get coupled in from the sharp edges of the waveshape. Also the frequency stability would be horrible for synchronis motor clocks, turntables and so forth. If you do it you will need a true sinewave frequency controlled inverter.
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I am considering buying a 60A 12VDC transfo on a chinese store at random
Buy a surplus server power supply instead, it will be cheaper and be of top notch quality.
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Go for as higher DC link voltage, as possible. 12V is far too low. The current will be insanely high. Try to get hold of a 48V PSU and inverter, if possible. Only a quarter of the current is required, so much thinner cables can be used, with lower losses.
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Go for as higher DC link voltage, as possible. 12V is far too low. The current will be insanely high. Try to get hold of a 48V PSU and inverter, if possible. Only a quarter of the current is required, so much thinner cables can be used, with lower losses.
He's only looking at 600W or so, 12V is perfectly fine. About the only high power loads that care about frequency would be motors in which case VFDs would make a lot more sense.
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In any event you definitely want a "pure sine wave" inverter. The cheaper ones just output a short duty cycle square wave to give the same peak and RMS value as a sine.
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First,
Thank you all for the quick replies.
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@CaptDon
I'm not very chauvinistic tbh buy your "made in china" products locally instead of buying them in china? I bought some real crap from china in the last decade but also some pretty good gear. My oscilloscope is a Siglent, my multimeter a uni-t .. you do get what you pay for and all in all sometimes people pay way too much of a premium for things these days. People used to pull up their nose for "made in japan" products, now most can't afford them. Like with everything its a matter of doing a bit of research, this is where forums like these come in handy, so even if i don't agree with the made in china blanket statement thank you kindly for taking the time to reply.
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@NiHaoMike
Yes, a pc server psu was not something I considered. In retrospect it seems like the obvious choice and also very "off the shelf" gear that's made in large quantities and thus cheap. This is what I had in mind at first:
https://www.aliexpress.com/item/32670477391.html (https://www.aliexpress.com/item/32670477391.html) it's the class of psu that I used for my Christmas lights and also gets used for those cheap RD "bench" psu's.
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@BrokenYugo
The 12V to mains US adapters advertised as "pure sine wave" seem a little more expensive but not all that. Thank you and @CaptDon for pointing out the cheap ones output square waves.
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@zero999
The audiophile gear that sells for this purpose is indeed 48v . This is what I was originally looking at and started sweating.. https://www.kccscientific.com/product-category/frequency-converter/ (https://www.kccscientific.com/product-category/frequency-converter/)
1500$ for a 500 - 1000 watt machine.. 800$ for 200 watt .. seems steep.
The prices of mains to DC PSUs at identical amperage don't seem very different at different voltages. The snag would be the DC at AC not being a product as readily available a consumer product as a mobile home converter.
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24V and 48V are also used on various servers. So all three voltages can be found on the surplus market. 12V is just the most common, easiest to find and usually cheapest.
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Go for as higher DC link voltage, as possible. 12V is far too low. The current will be insanely high. Try to get hold of a 48V PSU and inverter, if possible. Only a quarter of the current is required, so much thinner cables can be used, with lower losses.
He's only looking at 600W or so, 12V is perfectly fine. About the only high power loads that care about frequency would be motors in which case VFDs would make a lot more sense.
It's 50A plus losses in the inverter, which isn't normally considered to be a low current. Fair enough, if it's the cheapest available, but certainly wouldn't be my first choice.
Frequency is important for some appliances which use it for timing. A turntable or tape deck might turn a little slowly on 50Hz and it will cause some clocks to lose time.@zero999
The audiophile gear that sells for this purpose is indeed 48v . This is what I was originally looking at and started sweating.. https://www.kccscientific.com/product-category/frequency-converter/ (https://www.kccscientific.com/product-category/frequency-converter/)
1500$ for a 500 - 1000 watt machine.. 800$ for 200 watt .. seems steep.
The prices of mains to DC PSUs at identical amperage don't seem very different at different voltages. The snag would be the DC at AC not being a product as readily available a consumer product as a mobile home converter.
Audiophool gear is always overpriced and often isn't any better than something for a fraction of the price. You're paying for the name and asthetics. 48V is commonly used for tellecommunications. If I see the word audiophile in a product's description, it makes me more wary of buying it.
Don't worry about the DC link too much. Higher being better, is just a general rule of thumb, just get whatever is most convenient. The inverter is the most important thing. To be low noise, you need a true sine wave inverter. Don't usea modified sine, or square wave inverter for audio equipment, it can cause problems with noise.
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I was wondering what the snags are when doing the following:
I am considering buying a 60A 12VDC transfo on a chinese store at random then buy an american car/mobilehome 12VDC to mains converter to power potential future american imported low power vintage electronics audio equipment, random devices like clocks. Attach both with a couple of 6mm² + cables.
I suggest one or two sizes bigger on the wire, even though you are probably not running a long length, 6mm2 is a bit small for 60A. Also, buy a fuse.
If you do want to buy a PSU and inverter, consider at least a handy 12v inverter, sized such that it could power things from a car battery should there be an emergency.
If you are cutting it fine with power calculations and cheaper components, remember to factor in the conversion losses of both the power supply and the inverter.
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Thank you for the reply.
I was taking a margin on both, nothing with a significant load would be attached to it. Talking tape decks, clocks, a turntable maybe, a 120vac60 minidisc from Japan... etc, never an amplifier or the likes. And yes ofc a fuse.
I just want options when I see something on an auction site, not having to think "the voltage isn't adequate" and not being able to buy it because of that.
This first try/implementation/project would not be for constant use either.
Making the whole thing portable/ modular and not making it a whole has it's merits yes.
6mm2 stranded encapsulated in soft silicone ( i think it's silicone ) is what I have. I wasn't planning on making it longer than 20-30 centimetres. But sure , I can just attach two.
Don't these things usually come with 4 poles as well? 24v when used in series, 12v when used in parallel ? Or is that just for AC "bell transformers"?
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go old skool, 240V 50HZ motor driving a 110v 60HZ generator.
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Just thought I would throw this out there, and speaking as someone who has been doing this since the late 1980's - the vast majority of vintage US consumer audio equipment will run just fine on 120V, 50Hz, as long as it doesn't have a synchronous motor, and the better quality products with synchronous motors, like turntables, will have 50Hz pulleys available, although they may be difficult to find at this point in time.
Only side effect I've experienced is power transformers running a little on the warm side.
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go old skool, 240V 50HZ motor driving a 110v 60HZ generator.
You'd have to get the belt ratio correct.
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24V and 48V are also used on various servers. So all three voltages can be found on the surplus market. 12V is just the most common, easiest to find and usually cheapest.
24V is not that common (I'd imagine the few that are out there would be quickly bought by those building large 3D printers), 48V is common because it's the standard for enterprise PoE. The bigger issue is finding a small 48V inverter - all the ones I have seen are quite large of at least a few kW.
I was taking a margin on both, nothing with a significant load would be attached to it. Talking tape decks, clocks, a turntable maybe, a 120vac60 minidisc from Japan... etc, never an amplifier or the likes. And yes ofc a fuse.
For the clocks, standby power would be a significant problem for the setup. Perhaps replace the original motor with a small stepper run by a microcontroller? If that's not practical, use a small transformer to step up the voltage from a small class D amplifier with a microcontroller generating the 60Hz sine wave, that's the simplest way I know of to make a very low power sine wave inverter.
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go old skool, 240V 50HZ motor driving a 110v 60HZ generator.
You'd have to get the belt ratio correct.
It would have to be a synchronous machine. Gears would be more accurate than a belt, but a little more tricky to DIY.
I wonder if a cheap variable frequency drive, connected to a filter and transformer would work? It would have to be a dumb inverter, nothing smart, otherwise it won't work with an imballanced load, i.e. only using two of the phases.