DC step down transformer

Farmer

Has anybody installed a DC step down transformer before the inverter on grid tie??

Cariboocoot

Re: DC step down transformer

There's really no such thing as a DC transformer. What is sometimes called one is a DC to DC converter.
But why would you want to do such a thing? A GTI has minimum and maximum input Voltage, and the array should be sized to meet those needs.

niel

Re: DC step down transformer

if you need a lower voltage then take out the appropriate number of pvs to get the voltage right.

john p

Re: DC step down transformer

Farmer just out of curiosity what ever made you come up with the idea of even using some device to reduce the input voltage to a GTI?
As others have said there no such thing as a high to low voltage DC transformer. And also no such thing as a low to high voltage DC transformer.
If you connect DC to the input of a transformer all you get is a hot transformer, but NO output.

Farmer

Re: DC step down transformer

I was thinking of when they install AC step up and step down for long distance runs it changes the voltage so I assumed that dc was the same if you have too much voltage you can increase the amps and lower the voltage. Just asking and thank for the replies.

Cariboocoot

Re: DC step down transformer

Farmer wrote: »

I was thinking of when they install AC step up and step down for long distance runs it changes the voltage so I assumed that dc was the same if you have too much voltage you can increase the amps and lower the voltage. Just asking and thank for the replies.

Depending on the application, you really shouldn't have to.

Central GT inverters tend to run 250 to 500 Volt arrays, which is plenty of Voltage to go quite a long distance.
Micro-inverters are attached at the panel and output 240 VAC, which again is plenty to go a long ways.
Hybrid battery-based GTI's can make use of charge controllers like the MidNite Classic 250 or Xantrex XW 600 80 MPPT; the former allowing up to 250 Volt array and the latter up to 600.

If the high Voltage is needed to overcome long wire runs there are ways to deal with it.

waynefromnscanada

Re: DC step down transformer

Farmer, transformers are able to do what they do because the input voltage is constantly changing, which results in an ever changing magnetic field. It's that ever changing magnetic field that induces voltage in the secondary windings of the transformer. Unfortunately with DC, there is normally only a more or less constant voltage, thus a constant unchanging magnetic field, which therefore cannot induce a voltage in the secondary windings.
You didn't know that, so you asked the question. Only those who ask questions get answers.

Cariboocoot

Re: DC step down transformer

Okay, nobody bring up "induction coil" unless someone asks.

waynefromnscanada

Re: DC step down transformer

Cariboocoot wrote: »

Okay, nobody bring up "induction coil" unless someone asks.

And don't ask unless you want to get jumped on. Hahahahaha Just kidding. Go ahead and ask

john p

Re: DC step down transformer

How does a quality induction coil get inducted into the inductors hall of fame?

niel

Re: DC step down transformer

by winding up in the right place.:p ducking.

ggunn

Re: DC step down transformer

niel wrote: »

by winding up in the right place.:p ducking.

I was going to say by having a magnetic personality.

waynefromnscanada

Re: DC step down transformer

ggunn wrote: »

I was going to say by having a magnetic personality.

Don't know why, but the word "interruptus" comes to mind. Hahahaha

glenn allen

Re: DC step down transformer

sorry, can't resist

An transformer can be used. It gets a little complcated. If you cycle the DC 60 times a second ( an electronic switch comes to mind) then you will get a secondary output, then filter it and you get DC again. There are losses both going in and in the output side of this type of circuit. Those losses have to be considered when computing the ratio of the transformer windings.

Used to use this type of circuit in old tube type radios in cars. 6 or 12 volt car voltage was bumped up to 350 vdc or so to power the radio. A 4 pin vibrator that pluged into a tube socket was used to turn the primary side on and off. Its current ability was less that 2 amps normally.

The second approach that was used in systems that needed more current ability was a combination motor/generator. Millitary used this the most. Some of them were wound into the same frame others were build on a common shaft. Motor would maybe run on 12 vdc and generator would put out 24 or 48 volts dc. One of the ear marks on the ones that I have seen was that as set of brushes could be found on both ends of the shaft.

But as has been said no such thing as a simple DC transformer. This is why Westinghouse lost out on DC power systems and Tesla's AC system was used.

Some have said that it was the ability to increase voltage and reduce current, but this works in both DC and AC systems. But transformers only work in AC systems.

Cariboocoot

Re: DC step down transformer

glenn allen wrote: »

If you cycle the DC 60 times a second

In other words, convert the DC to pseudo-AC first and the transformer works fine. :roll:

CDN_VT

Re: DC step down transformer

Good points Glenn Allen .
I remember those tube radios , Buick Rocket(303 engine) 1955-58 had one. Can't remember the exact year we had.
It still worked in 1990 .

VT

inetdog

Re: DC step down transformer

Cariboocoot wrote: »

In other words, convert the DC to pseudo-AC first and the transformer works fine. :roll:

The best thing you can do is to reverse the DC polarity 120 times per second (which gives 60 cycles per second) in a way which will produce a square wave centered at zero volts. Or you could generate a modified square wave (MSW) to be a little gentler on the transformer. MSW output would not make full use of a current limited DC supply though, since current would only be driven half the time.
Make sure that you have some diodes or capacitors in place to carry the current through the transformer while you are switching the DC or you may develop some really high voltages.
The DC to DC ratio may not end up being exactly proportional to the transformer winding ratio the way it is with sine wave AC, so some experimenting will be needed.

Cariboocoot

Re: DC step down transformer

See CDN_VT's remarks about the old car radio.

That's what they did: a "vibrator"; a "self-unlatching" relay. Buzzed like anything, and produced a nasty saw-tooth pseudo-AC waveform that could be stepped up to the Voltage needed to power the valves (vacuum tubes). The frequency of the AC wasn't important. Some were "cleaner" than others. Your AM band came with intervals of "bzzzzzzzzzzzzzzzz". FM was practically unknown at the time.

Hurrah for transistors!

"Nail down my coffin lid, kiddo; the light hurts my eyes." - Victor R. Gook

waynefromnscanada

Re: DC step down transformer

Cariboocoot wrote: »

See CDN_VT's remarks about the old car radio.

That's what they did: a "vibrator"; a "self-unlatching" relay. Buzzed like anything, and produced a nasty saw-tooth pseudo-AC waveform that could be stepped up to the Voltage needed to power the valves (vacuum tubes). The frequency of the AC wasn't important. Some were "cleaner" than others.

ah yes, I remember them. Considering the state of electronics in those days, they were amazing little devices.
And who ever would have dreamed we'd be lighting our homes with LEDs. They hadn't even been invented yet.

niel

Re: DC step down transformer

ah yes, i remember those too. the relays inside those things had to be super tough to cycle like that and still give many years of service. think of it as for if it only was able to manage even 10 cycles per second (cps, remember that one too? not sure of the rate of switching they actually employed. anybody know?) over the course of a year with an hour's use per day is 13,140,000 switchings. how many relays and switches today can do that? some cheap switches are lucky to get 1000 switchings. these vibrators often lasted a few years before needing replaced too. nowadays that term brings something else to mind.

Cariboocoot

Re: DC step down transformer

The one in my old Borgward was still going up until the car was wrecked this past year. Might have worked even afterward. That's 50+ years of sporadic operation.
Not sure if they had caps on them to lessen the arcing, but possibly so.

waynefromnscanada

Re: DC step down transformer

As I remember, they did have arc suppression caps, and I seem to remember the contacts were supposedly tungsten.

inetdog

Re: DC step down transformer

waynefromnscanada wrote: »

As I remember, they did have arc suppression caps, and I seem to remember the contacts were supposedly tungsten.

I agree. Unlike small current, small voltage, infrequent use situations where silver alloy contacts or plating will give minimal voltage drop, the use of tungsten in this application gives far longer contact life. I would expect the mechanical mechanism of the vibrator to fail before the contacts. Does anyone have a good idea of what frequency the vibrators typically ran at?
Also note that the vibrators may only have fed the transformer with half-wave DC rather than alternating DC, so the transformer primary resistance would have to be high enough to limit the current to a value below that for core saturation. (You could get the effect of alternating DC with only an SPDT contact by driving the DC to opposite ends of a center-tapped primary winding, though.)

Cariboocoot

Re: DC step down transformer

No idea what the frequency was (possibly differed from one unit to another) but you are correct about the "AC" they delivered: usually there were only three terminals on the "cans"; (+) in, "AC hot" out, and a common ground. Meaning the "AC" was just pulsed DC with very little capacitance on the circuit. Hence my earlier reference to the jagged saw-tooth waveform.

As I recall the best of these were inside sealed glass (vacuum) tubes, and isolated with rubber to reduce the noise.

Somewhere in this world there's someone who restores these radios and knows all about what went in to them. They probably have a FET circuit in a can to replace the vibrators now. And yes I know they make modern radios that can fit in to your classic car and look just like the real thing. But some folk are purists!

I also remember my dad modifying a 12 Volt CB radio to run on 6 Volt in his '58 VW bus. Had to cut the case open to fit a bigger transformer and change the vibrator.

BB.

Re: DC step down transformer

Here is a nice Youtube Video about the old radio vibrators (note, there are NSFW Youtube links there too):

https://www.youtube.com/watch?v=Fp6PkRTmb8U

-Bill

Note--From the video, they vibrate around 100-120 Hz or so...

And you may be able to find solid state replacements too:

http://www.taymanelectrical.com/vibrators.htm

-BB

niel

Re: DC step down transformer

now everybody knows that the numbers of switchings is at least 10x what i guessed at further proving my point on how much this little device goes through.

waynefromnscanada

Re: DC step down transformer

Thanks for the memories. Great video. I truly miss the vacuum tube. Sure they couldn't compare to the reliability or efficiency of modern electronics, but they were alive, they were warm, or even downright hot, and they glowed. They were alive! Not at all like the cold, inanimate little stones that power the things we have today.

Cariboocoot

Re: DC step down transformer

waynefromnscanada wrote: »

Thanks for the memories. Great video. I truly miss the vacuum tube. Sure they couldn't compare to the reliability or efficiency of modern electronics, but they were alive, they were warm, or even downright hot, and they glowed. They were alive! Not at all like the cold, inanimate little stones that power the things we have today.

If you like you could build a solid-state circuit inside a plexiglas tube-case and include an LED to give you that glow.

waynefromnscanada

Re: DC step down transformer

Cariboocoot wrote: »

If you like you could build a solid-state circuit inside a plexiglas tube-case and include an LED to give you that glow.

Hahahaha and add a good sized resistor to give it that motherly warmth.

Ken Marsh

Re: DC step down transformer

Wow! We must have a bunch of old codgers here.
Yes, I remember them well.
Most of the GM versions had double throw vibrators that were connected to a push-pull primary winding.
Some times you would have to kick them to get them going.
They would run anywhere from 60 to 100 cps (note I say cps not hertz).
It still hurts to say hertz...
But in that age automotive voltage regulators were vibrating contact.
and gensets used vibrating contact voltage regulation.

A few years back we were sitting in our cabin up on a mountain in the Rockies.
The generator with mechanical regulator (vibrating contact) was humming along.
It was Christmas and the women were complimenting us on how nice and bright the lights were.
Well, I should have caught on right then.
Then a florescent ballast erupted in smoke.
We just got straightened around from that and another one went up in smoke.
We decided to check the genset out put voltage which was 152 V.
All told we lost two florescent ballasts and three CF bulbs.

We still have the generator which works great with its new static regulator.

niel

Re: DC step down transformer

tubes are not totally doa as far as the market is concerned as there are many that are still made for radio and tv transmitters. of course the price is up there for these tubes too as the high costs set in due to smaller production needs and inflation. solid state is moving into the high powered amplifiers realm slowly but surely, but they are even higher priced than the tubes.

as far as old codgers go,
what did you say sonny as i don't hear so well any more. oh that's not my hearing, that's my eyesight. i told myself i'd remember that, but i'm not as sharp as these young whipper-snappers today.:p