SCR series regulator

[sndscientist]

ok before i begin i am very well aware of hazardous voltages and i use isolation transformers for all of my HV projects so please don't preach to me about the dangers of what i am asking. Having said that, my question;

i am considering a new project using an scr series regulator (not shunt) to obtain roughly 48 volts @ about 7 amps from a 110v main (via isolation transformer). my problem is i don't know enough about SCR control circuits or the way SCR's clip the wave form to know if it is feasible to regulate down that low. after the scr i intend to toss in a full wave bridge and filter capacitors to stabilize it. i have done similar things with triacs in the past by running 12 volt lamps directly from triacs connected to the wall outlet so i understand that those devices clip the wave giving me 110 peak and if done right about 12v average similar to a PWM.

i had tried doing a PWM supply with a rectified 170vdc (us mains) but the harmonics were giving me a major problem.causing all sorts of gremlins.

so the basic question is does anyone have any experience with the SCR controllers, can i successfully regulate 30-33 volts (rectified 42-46vdc) from the 110 mains

 

[(*steve*)]

SCR regulation introduces a lot of ripple. In most cases it is effectively a mains frequency switch mode power supply.

I have seen it used as a pre-3V or, but I doubt it is very good on its own.

Do you have a circuit diagram?

 

[Bluejets]

7 amp is a pretty tall order. Why not use a conventional switch mode power supply?

 

[ramussons]

If you need about 48 VDC @ 7A from 110 VAC, the best is to use a SMPS as Bluejets suggested.
If you still want to use a SCR type regulated supply, you need to, first of all, get a 110 V - 48 V transformer rated at about 500 VA. Communication equipment used these type of Power Plants during the 70's. You will not need Bridge rectifiers since the SCR itself is a rectifier.

 

[BobK]

Agree. If you are going to use an isolation transformer, why not a stepdown instead?

Bob

 

[sndscientist]

sorry for the late replies, i've been very busy this week, in order

"*Steve*", no i don't have a circuit diagram as i was planning on buying a cheap e-bay chineese one to test the concept before i decide what route to to take. i figure i would rather burn out a 99 cent e-bay board than spend an hour gathering parts and building one myself.

"Bluejets & ramussons" i would love to use a smps but they are cost prohibitive and space requirement is an issue. if i decide to use an scr or triac i can fit the circuit in a space about the size of a postage stamp solid mounted to the side of a metal box for heat dissipation.

"Bobk" the isolation transformer is only used so i don't electrocute myself during building and designing. the only reason i mentioned it is because typically people don't like to give advice on the internet when dealing with high voltage (over 36 VDC) and people outright refuse to give advice when someone is attempting to do what i am doing build power supplies with mains potential even though i deal with 110, 240 and 208 vac as well as 170vdc (F.W.B. on 110vac mains 169.97vdc ) on a daily basis and know the safety procedures when dealing with it.

 

[BobK]

If you are trying to get a regulated 48V a triac circiut is not going to do it. It will be much worse than an SMPS which starts with DC and uses a high frequency so the required inductors and capaciitors can be small. At 60 Hz, you would need at least 10000 ufd to smooth it. That is not going to be small.

Bob

 

[(*steve*)]

I have a power supply which uses an SCR as the main regulating element.

It is a 0-40V 0-30A power supply. It weighs almost 80 lbs.

It has the biggest transformer that I've ever seen in a power supply, combined with an absolutely huge set of filter caps. In addition, it has a pretty massive "traditional" series regulator to smooth the output.

Electrically it's really noisy in operation.

I'm pretty sure it's a design from the late 60's.

It can be done, but an scr used in this manner is really only going to be a pre-regulator, and the weight and expense you save is pretty much made up by the weight and expense of the transformer and filtering.

Also note that the power factor is abysmal. This power supply is labeled as 2850VA whilst supplying only a little in excess of 1200W. And let me tell you, the power supply itself is reasonably efficient, the overhead for the linear regulator is a relatively constant 6V or thereabouts, so that's not the reason...

If you're curious, Google HP6268B.