120VAC to 80VDC for a portable DC power supply

Thread Starter

Tin_Man_0

Joined Jul 27, 2019
8
Ok, so I bought this DC buck reducer and connected a torridal tranformer to a rectifying bridge to get my 80vdc to power this thing and it's been working beautifully. My current configuration is as fallows:

AC Mains ---> Primary on Marantz toridal power tranformer --> rectifying bridge --> Variable voltage device.

Here are some not so pretty pictures, but trust me, it works....




So, like I was saying, this super simple configuration is working beautifully, I've been using this thing as my benchtop power supply to power or charge anything that falls within it's 80v 5a limit. however! the damn Marantz toridal transformer part weighs about 40lbs! It's big, it's bulky and I want to get rid of it for something much smaller. I currently have the voltage regulator mounted to a face plate on an electrical outlet box as well as the rectifying bridge inside it mounted in such a way as to use the box itself as a heat-sync. I'm hoping to drastically reduce or eliminate the transformer to something more reasonable, preferably something that will fit inside the electrical box. The regulator says the input can be anywhere from 10v to 90v DC, I'm hoping to get somewhere in the 80v range to power it as that's what I'm currently getting out of the Marantz. Any suggestions?

P.S, by portable, I just mean not 50lbs, AC mains will continue to be the power source.
 

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dendad

Joined Feb 20, 2016
4,452
It looks like one of these...
https://www.ebay.com.au/itm/192903866533?var=493070196001&ssPageName=STRK:MEBIDX:IT&fromMakeTrack=true

For a start, 80V at 5A = 400W. So, if you need the full power, your supply will have to be at least that. Maybe go for a 500W version.
What actual output voltage and current are you after? A switch mode power supply may be smaller than the transformer but getting an 80V one may be hard and expensive.
A 48V10A 480W = 214*113*49mm, and a bit over $50AU...
https://www.ebay.com.au/itm/Transfo...hash=item520f536642:m:mGcV6VW2C2KorMOEex-tJ6g
If you do not need 400W, a smaller transformer could be used.

So, first off, please let us know your actual output power requirements of your regulator to your load. Max voltage and current.
 
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Thread Starter

Tin_Man_0

Joined Jul 27, 2019
8
It looks like one of these...
https://www.ebay.com.au/itm/192903866533?var=493070196001&ssPageName=STRK:MEBIDX:IT&fromMakeTrack=true

For a start, 80V at 5A = 400W. So, if you need the full power, your supply will have to be at least that. Maybe go for a 500W version.
500w might be overkill. From what I've seen, this thing's max are 5A and 80V but not together. As I approach 80V, my max amps starts to drop.

...What actual output voltage and current are you after? A switch mode power supply may be smaller than the transformer but getting an 80V one may be hard and expensive.
If you do not need 400W, a smaller transformer could be used.
So, first off, please let us know you actual output power requirements, max voltage and current.
I plan on getting the most out of this box. I currently use it to charge 18650 batteries, power laptops, charge my ebike, power my digital camera (no more batteires), you name it. It's very much like I said, I use it like a benchtop power supply but now I need it to be a little more portable.
 

dendad

Joined Feb 20, 2016
4,452
What max volts out do you need?
As long as you have a few input volts more then the output you require, it will work ok. So, for example, if you just want 15V max out, try using an old laptop 19V power supply. Or for 24V out, an old HP printer supply of 32V
 

Thread Starter

Tin_Man_0

Joined Jul 27, 2019
8
What max volts out do you need?
As long as you have a few input volts more then the output you require, it will work ok. So, for example, if you just want 15V max out, try using an old laptop 19V power supply. Or for 24V out, an old HP printer supply of 32V
You're two steps behind me brother. Already thought of that. You see, the problem is the Volts/Amps combo here. I'm guessing there's some law of physics or legal law as to why wallworts or DC power adapters seem to top out at max 48v, and even at 48v you won't see anything past 1 amp. The next thing I was looking at was transformers. Stupid me thought that with today's technology I would just be able to go to a site type in my voltage and amperage requirements and my primary and secondary wingdings with any desired taps would just be calculated and a custom transformer would just be spit out and mailed to me. Wishful thinking. What I'm now hoping for is maybe some sort of transformerless solution using capacitors or resistors, although I hear that's kinda dangerous. So Here I am, asking you fine folks.

I must have gotten lucky with coming across that Merantz transformer I pulled out of an audio amplifier to do the job it's currently doing so well.
 

dendad

Joined Feb 20, 2016
4,452
You still have not mentioned the max voltage you need for your load.
Are you after 75V out?
Some HP printer power supply bricks are 32V or 3 or 4 Amps.
Do you need more that 28V out?
And yes, transformer less operation is a big no-no!
 

Thread Starter

Tin_Man_0

Joined Jul 27, 2019
8
You still have not mentioned the max voltage you need for your load.
Are you after 75V out?
Some HP printer power supply bricks are 32V or 3 or 4 Amps.
Do you need more that 28V out?
And yes, transformer less operation is a big no-no!
I'm not sure why you're having a hard time understanding. The variable buck converter is there for a reason. If i had a need for fixed voltage, then id just skip the variable buck and just power my "load" directly from whatever my solution. My "load" is many devices, all with different needs of voltage and amperage. my only restriction is the 80v 5 am max of the buck at the moment.
 

Lo_volt

Joined Apr 3, 2014
316
I'm not sure why you're having a hard time understanding. The variable buck converter is there for a reason. If i had a need for fixed voltage, then id just skip the variable buck and just power my "load" directly from whatever my solution. My "load" is many devices, all with different needs of voltage and amperage. my only restriction is the 80v 5 am max of the buck at the moment.
Most of us power each of our "loads" with a power supply, be it a wall wart or benchtop supply, that is tailored to the "load". We're wondering why you have set up an 80 volt power supply that you can use for many devices. It's one thing to use it for circuit design and prototyping. In the manner in which you are using it, there might be some worry as well that you'll apply 80 volts to something that's rated at a lower voltage and damage it.

As for why wall warts "top out at max 48v", it's because the safety requirements (UL and IEC) for power supplies and equipment 50 volts or higher are more stringent (See: https://en.wikipedia.org/wiki/Low_voltage). Most manufacturers won't bother. Those that do will charge more.

I did a quick search on 80 volt capable bench supplies. They're pretty pricey. It sounds like your power supply works well. Why not put it into a box with a handle such that you can carry it around?
 

dendad

Joined Feb 20, 2016
4,452
My "load" is many devices, all with different needs of voltage and amperage. my only restriction is the 80v 5 am max of the buck at the moment.
I understand. My ideas for an old power supply were to feed your variable one, in place of the transformer.
As Lo_volt mentioned, I too am wondering why you would want a supply capable of going to near 80V as a bench variable supply. It does make more sense to me to have a number of supplies. And having one capable of going so high when working on low voltage stuff is asking for trouble.
I find 99% of my work is under 24V. Admittedly, as I design and build industrial control equipment, most of that runs on 24V anyway. Just off hand, I can't think of the last time I needed a DC supply above that.
 

DickCappels

Joined Aug 21, 2008
10,152
Clearly tin_man_o wants up to 80 volts out. Asking why over and over will not change his mind.

500 Watts is a lot of watts. Looking though the Mouser website it looks like an isolated 90 volt, 450 or 500 W power supply will be very expensive. You can get around this if you are willing to undertake the rather difficult task of making your own. Not recommended for the faint of heart. It would likely be an isolated forward converter following the rectification and filtering or doubling of the 120 VAC.

That toriodal transformer sounds like a good solution at this point.
 

cmartinez

Joined Jan 17, 2007
8,220
I'm guessing there's some law of physics or legal law as to why wallworts or DC power adapters seem to top out at max 48v, and even at 48v you won't see anything past 1 amp.
It's most probably legal, since the human body begins to feel the effects of electrocution at about that voltage.
 

panic mode

Joined Oct 10, 2011
2,715
the only way to reduce weight and size is to increase frequency use SPS). there is just no way around this if you want output to be isolated.
next question is if you want to buy or build or hack existing one. good candidates may be SMPS for audio amps. They tend to provide dual output (+/-35 or 40V). Personally i would go consider hacking 500W PC PowerSupply due low cost, then rewind the secondary, and throw in pot to adjust output voltage. I am using smaller one right now to get 1-25V output and up to 30A (not at the same time). All i did was add potentiometer and output terminals.
 

crutschow

Joined Mar 14, 2008
34,285
Unless you want to spend a fair amount of money, I think you will need to stay with your large transformer setup, if that works for you.
Is there some reason you need to make it more portable?
 

panic mode

Joined Oct 10, 2011
2,715
or just try some beefy low voltage PSU (PC or those sold on Jameco or Amazon) and add adjustable boost converter. They are on amazon for $25 for units claiming 1500W. This way you get something from 50lbs to lbs for $50-60.
 

Thread Starter

Tin_Man_0

Joined Jul 27, 2019
8
Thanks for the ideas guys. The reason I'm looking for 80v is mostly flexibility. I currently use this powers supply for many devices and the demand keeps going up as I'm currently working on electric scooters and bikes. I'm currently at 53v @ 5 amps and climbing. Thanks for all the ideas but I think maybe I got a new one. Maybe you guys can tell me if this will work?

Basically I'm thinking I'm going to purchase a couple of cheap DC adapters ebike chargers and simply run them in series. I can get two ebike scooter chargers rated at 42v @ 2.5 amps each and connect them in series. I'd get my 84v @ 5 amps wouldn't I?
 

DickCappels

Joined Aug 21, 2008
10,152
If you do that its a good idea to put reverse diodes across the outputs of the power supplies to keep one power supply from drive reverse voltage into the other in case one goes into current limit.

With the arrangement you described you can probably get 84V @ 2.5 amps. The current limit on each power supply is still 2.5 amps. If you want to get 5 amps out of the arrangement, you need to add two more power supplies, but make sure they can be put in parallel without them hurting each other.
 

Thread Starter

Tin_Man_0

Joined Jul 27, 2019
8
Or! possibly you guys can help me design a circuit with multiple transformers to do this? I tried connecting a smaller transformer to AC mains.... I'm pretty sure you can guess what happened.
burn.gif
 

Thread Starter

Tin_Man_0

Joined Jul 27, 2019
8
By the way, I thought of this idea as well, but just something about using a variable power supply to power a variable power supply doesn't seem right. While this box would be lighter than the toridal transformer, it probably has a whole lot of extra that can be eliminated for a fixed voltage. But it's starting to look like maybe I don't have much of a choice, it's going to be bulky no matter what. It just seems such a big deal to go down voltage. I always thought the headaches came from trying to go up.
 
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