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Reduce 37VAC to 36VAC

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goofeedad

New Member
I know this is probably too simple for this forum but......

I need 36 VAC (actually I need a good 36 VDC). I found a supply of 37VAC and want to reduce it to a good / constant 36VAC (36 VDC is what I'm finally aiming at, with a minimal voltage variation at the output).

Can this be as simple as a resistor / voltage redction? I would like to do this without a high heat dissipation (I don't imagine that the heat would be great)?
 

goofeedad

New Member
I am actually powering a 36VAC/VDC (manufacturer states output can be VAC or VDC for circuit to operate) circuit for a 1.6MHz water piezo transducer. I found a 37VAC transformer and I think that is my quickest way to get a supply voltage. What I want to end up with is a compact (probably a switching power supply) DC power supply.

I also have a 12 VDC need for some of the other components in my prototype. I know that I can buy a 12VDC power supply but, I need / want to keep my size down. I am hoping that I can eventually make a final product that puts out the VDC voltages of 36 and 12 without the drastic ppv's that a simple AC / DC converter gives.
 

Willbe

New Member
A series silicon diode will drop between 0.7 and 1.0 v. Put two or three in series.
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
You're worrying over nothing - use your 37V transformer, it's well within any tolerance for the unit, and much less than any mains variations is going to cause with an actual 36V transformer.
 

hv addict

New Member
If you are still worried then just take a couple secondary windings off until you get 36v. As a rough estimate, those transformers have about .2v/turn
 

Hero999

Banned
Are you measuring the voltage off or on load?

If it's off load, the on load voltage will probably be much lower than 36VAC.
 

goofeedad

New Member
Please excuse my ignorance but, all I can tell at this point is that one of the circuits I purchased states that it requires 36VAC supply. The circuitry is pretty complex, no IC's but alot of cicuitry to get a 1+MHz piezo working with a variable piezo output.

Thanks for the responces so far, I will no doubt try them all until I find what works.
 

Hero999

Banned
Do you require AC or DC?

You've confused me because sometimes you've dais AC/DC and others you've said 36AC.

If it'll run of either AC or DC then it has a rectifier circuit built-in to it to convert it to DC.

If it only runs off AC then it probably has some sort of voltage doubler that requires an AC input.
 

crutschow

Well-Known Member
Most Helpful Member
A series silicon diode will drop between 0.7 and 1.0 v. Put two or three in series.
That will, of course convert the AC to half-wave rectified DC. But you could put one or more in series-reverse-parallel to reduce the voltage in both directions.
 
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goofeedad

New Member
At this point I am planning on the circuits requirements to be AC. While on the phone with the manufacturer, I believe he stated 36VAC or 36VDC. This morning I received the actual circuitry, the circuit board has printed on "AC36V". That's what I'm planning on until I can talk to the manufacturer tomorrow.

I have found 2 - 18VAC / 24VAC power adapters at Radio Shack. I plan on combining them, ( the 2 - 18VAC outputs to get my 36VAC, or maybe later combine 1 - 24VAC with 1 - 12VAC ) is this going to cause some problems that would affect my output?


Also, Hero999, stated that the circuit likely has a voltage doubler if it is using AC. Why is that?

Again thanks for the comments.
 

Tesla23

Member
If you are still worried then just take a couple secondary windings off until you get 36v. As a rough estimate, those transformers have about .2v/turn
Or if you don't want to pull it apart, add a few turns of your own until you get 1V, then connect this winding in series with the 37V winding. There are two ways to connect it, one will give you 36V and one 38V.
 

Tesla23

Member
The 38V I understand. How can adding more windings in series give me a lower voltage?
If you connect it the other way around the voltage will be opposite and subtract.

Think in terms of the windings. If you take the 37V winding and keep winding the same way for a few more turns then you get more volts, on the other hand if you wound the next few turns backwards you cancel the voltage from some of the turns already on the winding.
 

goofeedad

New Member
Sounds just too simple, thanks. How close to the original type of wire does the new wire have to be? I'm worried it will burn out.
 

Tesla23

Member
Sounds just too simple, thanks. How close to the original type of wire does the new wire have to be? I'm worried it will burn out.
As long as it can carry the current, pretty much anything will do (insulated of course).

Of course, Nigel's probably right and the 3% voltage change you are worried about is probably more than compensated for in the in-built allowances for mains tolerance, but there's always that chance I suppose...
 
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