If I had limited knowledge of building large power inverters and wanted a continuously variable value of the mains supply, I'd opt for a variable transformer configuration. But why would I want such facilities if all I was playing with was an Arduino and PICs
177v at 10a is 1.77kVA so you're looking at something like 2kW input. That's a massive (and complex) device for a novice to attempt to build.
I think your best bet is a 2kW isolation transformer followed by a Variac type variable transformer (also rated at 2kW) which offers 0-110% fully variable output. Note that these are usually rated as x Amps so in your case 10A. But this value remains a constant limit, irrespective of the voltage output, so for example you still get just 10A with an output of 20volts.
I specified an isolation transformer as the input device because variable transformers are usually autotransformer devices which means they offer no isolation from the potentially lethal mains system.
I did not imply that 117 from an isolation wasn't potentially deadly (no pun intended). But any voltage source pushing current through the body in order to do harm requires a return path and an isolated output offers no return path, via the body, to ground if neither terminal is grounded (isolated output) - as is the case with a utility mains supply (neutral grounded). So, in that respect an isolation transformer offers a degree of protection that an autotransformer does not.
There are actually multiple planned uses of this power supply. I am trying to learn to build inverters (1 and 3ph) with PIC, and this is just part of what I'm referring to as "the learning experience". I have TONS of MOSFETs and IGBT's laying around, even some modules that have the gate drivers packaged in with 2-6 IGBTs/MOSFETs. (1 and 3ph)
I also have a 2560 Mega and a few 5v Mini Pro boards. Need to use stuff I have on hand already.
I have already reviewed the idea of a variac, but a 10A variac is about $120 on ebay (unknowing of its condition) up to $300. Lab power supplies go up to 60V@5A for ~$100, still a bit steep.
This power supply will not be used to power any micro controllers, there will be a separate section built in to power my micro controllers and that bit is already handled/assembled/tested/etc. I sourced that bit out of a bread maker I got for $5 (along with a HUGE ACIM, prob 1/3-1/2hp)
I'm fully aware I'm working with VERY dangerous voltages, and promise to hold no one accountable for stupid actions.
edit: If I can build this, I actually intend to put a piezo buzzer to sound when I am working over 35v, and to remind me to turn it off so me, partner, nor dog get zapped.
jackrae:
I did not imply that 117 from an isolation wasn't potentially deadly (no pun intended). But any voltage source pushing current through the body in order to do harm requires a return path and an isolated output offers no return path, via the body, to ground if neither terminal is grounded (isolated output) - as is the case with a utility mains supply (neutral grounded). So, in that respect an isolation transformer offers a degree of protection that an autotransformer does not.
I agree. And I knew what you meant when I read it. But someone could misread it and think that because there's no direct electrical connection to the mains supply in an isolation transformer, it is somehow not dangerous. Sure it requires you to get a hold of both circuit conductors simultaneously, which is unlikely.
To ground, or not to ground... was one of the great early 20th Century quandaries in electricity for this very reason.
Is this really what forums are about these days? Someone asks for direction on how to do something with parts they HAVE ON HAND, the first reply is "go buy something you don't have" and then the discussion gets hijacked into an argument about generally known safety concerns. (most everybody here knows that electricity is dangerous)
People that have degrees, or have invested MANY YEARS of time in the study of electronics, can sit down at their bench with the components they need and build something completely from scratch up to the level of their abilities. Atmel, Microchip, ST, NXP, Zilog, etc will all sell bare micro controllers by the millions every day to companies and then indirectly to the "experts"...
I always THOUGHT that Arduino was meant to bridge the gap from the amateur to the expert, and to make prototyping easy and efficient. It seems to have worked, seeing as Microchip has come out with their own knock off's.
so can somebody give me direction to this issue, or recommend a micro controller forum where people answer questions rather than hijack and argue?
You asked a question - I gave an answer that I felt offered the best chance of success with minimal risk - a colleague offered a helpful and realistic cautionary comment - end of story. No-one is obliged to give answers that answer your problem, merely offer suggestions that, hopefully might be useful. You are at liberty to either accept or reject as you see fit.
The fact that you haven't got a favourable response from other readers might indicate that other contributors feel you are aiming for a target out-with the capability of a typical amateur. Switch-mode supplies are a complex subject, the complexity of which probably increases exponentially with power demand.
You do have a funny way of responding through. But any way:
I have seen some circuits in the past where people used a microcontroller to control an SMPS. I have someone in Spain develop a custom variable voltage SMPS (0-450V @ 200mA max). That was without a microcontroller. Unfortunately she stopped communicating after about 3 years (just to give you some idea). I did understand though that controlling the lowest voltage was the most complex. As transformers are designed for a specific load and at very low loads there were some problem to solve.
Using a microcontroller can probably used. It is more a question what the highest frequency you can switch I suppose.
The 1,7KVA question is I suppose more a problem of feasibilitly than design. I have seen enough 1KW and 2Kw smps's around designed by hobbyists in the past. But at a lower voltage (+/ 50V).
You will still need a transformer.
The only differance is that instead of using a iron core transformer you will need a ferrite core transformer.
Such a power supply is feasable, but it sure isnt a beginners project, and a real lot can go wrong.
I would get some experiance in building small lo power switch mode power supplies first.
Theres a lot of math involved in building switch mode supplies that has to be well understood, otherwise you will end up
with a lot of dead fets.
Grabbed a few books on power electronics... doesn't seem so painfully difficult as you pointed out Jackrae. I know variac transformers are out there, and if I had $130+ to throw at the one I want I wouldn't be here asking the question.
Nicoverduin> I did find some xfmr-less power supply circuits online, but like you said they were only a few milliamps of output. I do need a bit more than that. None of the ones I found schematics for were switched mode tho. I'm still learning terminology, and my knowledge of electronics is dated. (I started in vacuum tubes, and yes, 83 is the year I was born lol) Luckily fine tuning low voltages isn't of incredible importance, there's a separate section (yes, with a transformer) for that.
This power supply is going to be used to power an SRM (switched reluctance motor) thru an inverter, and the variable voltage is basically a safety net between it, the power board of the inverter, and the electrical outlet. I guess I should've simply asked for some direction in building a SWITCHED MODE POWER SUPPLY or something similar with an arduino as the captain.
mauried: already built several low volt power supplies, just haven't run into a need to tie a micro controller into one yet.
through. But any way: