Boost-Buck Switch

[Joethemechanic]

I had this idea, but I'm thinking it might be a problem. This is for a piece of test equipment. 120V in with a 32 volt boost.

The reason I wanted to put the switch there is because it is a low current portion of the circuit

What I'm worried about is , it the switch is thrown under load, the primary windings could end up with a voltage of almost 4 times the 120 volt line imposed on them. Possibly damaging the transformer and requiring a 480 V rated switch.

Do you think I'm worrying needlessly?

And this was the original question. I already scrapped the idea of a switch on the primary side almost a day ago. I just wanted to see who was on the ball,,,,,,,,,,,,,,,

 

[jim dungar]

I'm not sure you are comprehending at all.

I have more confidence in my comprehension than i do yours.

It's a boost buck, the secondary is in series with the load,

That is the way a boost buck is connected

Technically there is no secondary when it has been connected as an autotransformer, there is a high voltage and a low voltage. There are several ways to create buck-boost winding arrangements, but all of them do involve connecting the high voltage and low voltage indings in some sort of series connection.

If I open the primary under load it goes overvoltage just like when you open up a CT circuit

No it doesn't. there is a big difference between the performance of on open circuited power transformer and a current transformer. Among other things, there is the internal impedance of the transformer.

You never hooked up a boost buck?

Why, yes I have. In fact I have been involved with 1000A 600V-480V three-phase transformers feeding an entire glass making assembly line.

The low voltage secondary is always in series with the load. That is not a disregard of voltage ratings.

The disregard of voltage ratings has to do with series connecting a 32V device and a load and then connecting the combination to 120V. You are creating a voltage divider, depending on the impedances of these devices, it is possible for the 32V device to be exposed to more than 32V.

 

[Joethemechanic]

Where is that cute Lady Engineer from Jersey? I want her perspective on this.

 

[kwired]

It's been done and in operation for hours

I bolted a 1900 on it to make room for the larger switches. I used a 3 way to take the 32 volt winding in and out of the secondary, and I used a 4 way to be able to reverse the secondary for when I want to operate in buck mode.

What kind of voltages are you seeing in the areas you were concerned about?

What voltages are you seeing at the load? Try loads with different impedances.

 

[Joethemechanic]

I don't know where the voltage on the primary would go because I never open circuited it. As a boost buck, depending on switch position, it's either 88, 120, or 152 V


But with a shorted primary it has a current of 3.30 Amps, when I apply a load of 12.50 amps through the the secondary. That is exactly the 3.78/1 ratio of turns. So it does indeed function as a current transformer when hooked up as such.

 

[kwired]

I don't know where the voltage on the primary would go because I never open circuited it. As a boost buck, depending on switch position, it's either 88, 120, or 152 V


But with a shorted primary it has a current of 3.30 Amps, when I apply a load of 12.50 amps through the the secondary. That is exactly the 3.78/1 ratio of turns. So it does indeed function as a current transformer when hooked up as such.

In that example what is the connected load and what are voltages at different key points?

 

[Joethemechanic]

That is with a resistive load (heater). I didn't measure voltages yet, Still making breakfast for me and mom, having some coffee, feeding the cats,,,,,,

 

[Joethemechanic]

Ok made a couple of mesurements

 

[kwired]

Ok made a couple of mesurements

Now do same thing with only a 5-25 watt load and see what you get. I'm a little curious what happens to the voltages in the transformer and voltage across the load. I think I know about what results will be.


Can you also either hold your switch in mid position or somehow open circuit both sides and see if you get the high voltage you were concerned with - with both a heavy and light load connected?

 

[cadpoint]

I'm not a transfomrer groupie by any means, I frankly had to go to google and use image and the phrase "diagram 32V buck booster", to get a taste of this.

I would go search GE.com, Squared.com and midwest.com(http://www.swgr.com/-frankly this is a supplier site and not midwest), or anyone that builds this type of transformer to get the proper wiring diagram, I'd be a mess to suggest anything else!

Frankly, the diagrams I've seen are flat out scarey! JMO...

 

[kwired]

I'm not a transfomrer groupie by any means, I frankly had to go to google and use image and the phrase "diagram 32V buck booster", to get a taste of this.

I would go search GE.com, Squared.com and midwest.com(http://www.swgr.com/-frankly this is a supplier site and not midwest), or anyone that builds this type of transformer to get the proper wiring diagram, I'd be a mess to suggest anything else!

Frankly, the diagrams I've seen are flat out scarey! JMO...

They are all going to have exactly what OP drew - until he introduced the switch. A buck - boost is just an autotransformer.

 

[Besoeker]

I had this idea, but I'm thinking it might be a problem. This is for a piece of test equipment. 120V in with a 32 volt boost.

The reason I wanted to put the switch there is because it is a low current portion of the circuit

What I'm worried about is , it the switch is thrown under load, the primary windings could end up with a voltage of almost 4 times the 120 volt line imposed on them. Possibly damaging the transformer and requiring a 480 V rated switch.

Do you think I'm worrying needlessly?

Wouldn't a simpler arrangement be better and avoid your worries?

 

[kwired]

Wouldn't a simpler arrangement be better and avoid your worries?

I think that has been suggested but not been drawn out so well. (nice drawing BTW) I even mentioned it in a PM but not sure if it was clear enough. Or maybe we are not clear on OP's intentions.

 

[templdl]

Yes, it was suggested back on post #9 with a hand draw schematic which was a good piece of art.
This one is a fancier version.

 

[Besoeker]

I think that has been suggested but not been drawn out so well. (nice drawing BTW)

Just keeping my hand in....but thank you for your kind comments.

 

[Besoeker]

Yes, it was suggested back on post #9 with a hand draw schematic which was a good piece of art.
This one is a fancier version.

Tidier maybe.
But no fancier.

 

[Joethemechanic]

Can you also either hold your switch in mid position or somehow open circuit both sides and see if you get the high voltage you were concerned with - with both a heavy and light load connected?

I can open circuit anything the cover is off and almost everything is together with spade connectors.

The smallest bulb I have is a 60 watt (marked) although hooked across the line it seems to be using somewhere around 50 watts (measured) Cheap Chinese bulb I guess :happyno:

 

[Joethemechanic]

I think that has been suggested but not been drawn out so well. (nice drawing BTW) I even mentioned it in a PM but not sure if it was clear enough. Or maybe we are not clear on OP's intentions.

Yes, that is pretty much what I built 27 hours ago Saturday around lunch time

 

[Joethemechanic]

I'm not a transfomrer groupie by any means, I frankly had to go to google and use image and the phrase "diagram 32V buck booster", to get a taste of this.

I would go search GE.com, Squared.com and midwest.com(http://www.swgr.com/-frankly this is a supplier site and not midwest), or anyone that builds this type of transformer to get the proper wiring diagram, I'd be a mess to suggest anything else!

Frankly, the diagrams I've seen are flat out scarey! JMO...

Scary, huh?

I'm a guy that moves and connects 500 KW and 1 meg generator sets, hooks up huge 100 HP and better machinery floating on barges thousands of feet away from their power source. I move 100,000 pound machines in Manhattan. This is child's play

Call the manufacturer? What kinda data am I going to get out of that?

Who besides a first year apprentice can't draw up a schematic for a standard boost- buck connection.

I think if that gave me difficulty, I'd go stick my head in the oven

 

[Joethemechanic]

Hey Kwired,

Same small bulb as a load. Open primary