[NC Cams]

It means that you can possibly and eventually boil water (155 deg C = 311Deg F) or bake a cake with it if you try to draw 0.75 amps on the primary side for long enough time without forced air cooling....

0.75 amps at 120volts is only 90 watts - about as much power as a decent light bulb.

[BCwanderer]

Hey all. Im looking for a good regulator circuit. I have a 52 V and want to drop it to 40 Vdc. Of course it will need to handle 20 amps.

You can use High current FET transistors on the high side with a (approx) 38 volt Zener diode to bias the load FET transistors.

You may have to adjust the FET gate voltage to find the right setting as the FETs will be operating in the linear portion of the outut curve.
Hook the FETs up on the high side and the FETs will limit the voltage.
Use multiple FETs to spread the heat.
eg- running a 75 watt TO220 FET at 50% you would drop 35 watts per FET
Dropping 52 volts to 40 volts is 12 volts load so you could pull 3 amps per FET.
Adding load resistors can reduce the load on the FETs also

This setup will give you good current with fast response.
Good fat capacitors to soak up pulses will also help your regulation and absorb back emf from the motors switching off.
As it is a motor driver, you don't need exact regulation.

Your voltage from the transformer will not always stay at 52 volts because the load will cause voltage drawdown when it is drawing the max current.
This reduced transformer voltage will reduce FET wattage load as well.

FETs on E-Bay can be bought for less than a buck.
Heatsinks would be needed.

[jwstolk]

instead of removing a couple of windings, you can add some (in the opposite direction).
connect the original and the added secondary windings in series and measure the voltage. if it is higher instead of lower, swap the wires of the added windings.

[jwstolk]

Hi,
Welcome to my forum to discuss about electric motors.
http://groupyahoo.com/group/Stevenmotors
Steven

If you add "s." between "group" and "yahoo" you will find it has nothing to do with transformers at all :-)

[NC Cams]

Using fets to serve as linear regulators may not be quite as simple as suggested in post 22.

We played around a lot with fets several years ago with regard to constructing fet based linear regulator circuits. We found that they would/could oscillate wierdly at times and voltage regulation could suffer under rapidly varying loads.

This was especially true if you tried to parallel them to get adequate power dissipation capability.

Ultimately I learned/was told that clunky old darlingtons make the best pass elements for linear regulators - they work better as power dissipators that carry large current...

Fets do work EXTREMELY well as switch mode regulators which is one reason why they were developed. We found that they did EXCELLENT motor speed regulation when used in pulse width modulation (PWM) mode - a true voltage regulation methodology.

Rather than use fets as linear regulators, I'd consider the use of a switching regulator IC (SG3526 or LM3526), some fets, capacitors and perhaps an inductor to increase efficiency.

We used a variation of this voltage regulator chip to make a constant current battery charger (2 IRLZ44 fets in parallel pulsed at 40-50hz) as well as a "chopper" style motor speed control (6 IRFZ40's in parallel pulsed at 3-4Khz).

You may actually be better off reading the following article:

http://www.elecdesign.com/Articles/A...7635/7635.html

It is better to design/build what you need/want that to try to cobble together something that was ill suited in the first place, especially if it involves trying to get rid of surplus power...

Since you're regulating voltage via PWM with the 3526, you DON'T waste the power as heat and you retain high current potential if you have sufficient pass element capability. You'll be amazed at the voltage regulation capability of the 3526 once you understand how to use it's full capabilities.

TI used to have a neat manual on the design and construction of switch mode regulators. The manual would be handy to have/find should you chose to make a PWM type voltage regulator....

[jwstolk]

You may actually be better off reading the following article:
http://www.elecdesign.com/Articles/A...7635/7635.html

Is anyone getting past the "wait 20 seconds" message on www.elecdesign.com?
In my FireFox it just reloads each 20 seconds :-(

[Al_The_Man]

I am using Firefox with no problem, I just click the immediate link.
If I were you I would forget the Regulator idea, they are big heat wasters.
There are plenty of detailed posts here by myself and others for modifying Transformer winding on Toroid, and even a detailed one on MicroWave Tfmr mod. but more involved.
Personally what I do is to obtain a Toroid from the guy on eBay that winds them, that is closest or above the voltage I need and reduce the turns accordingly, this leaves enough room for another layer of turns for a 24v or 5v supply.
Al.

[NC Cams]

Click the link - don't wait....

[pminmo]

As far as a regulator, using a buck configuration switching regulator would be superior to a linear regulator. But it also is more difficult to troubleshoot if it doesn't come up working, where a linear regulator can be debugged with a voltmeter.

Al, what guy on ebay winds torrids?

[jwstolk]

Click the link - don't wait....

That's what i did first. same result, just a reload and another 20 sec :-)
same with just the domain name. no links in the page info, lot of junk in the page source.
Maybe something with cookies or adblock or something. anyway, I don't need to see it :-)

[tekno]

Is anyone getting past the "wait 20 seconds" message on www.elecdesign.com?
In my FireFox it just reloads each 20 seconds :-(

Well the transformer is center tapped for the 35V ac. so I am using the center tap for one side and the other side go through diodes it ends up being a full wave with only 2 diodes trying to get a pic of it for you all

[Al_The_Man]

You need a bridge fed from one side and centre tap, except do not ground the centre tap.
Ignore/tape up the other outer end.
If the toroid brought out all 4 ends of both secondaries, there is a way of paralleling them up, but only if all 4 conductors are accessible.
Al.

[Al_The_Man]

Al, what guy on ebay winds toroids?

This is one of his listings, I imagine if he was approached for a certain design, he may oblige?
(Item #7620127071)
Al.

[pminmo]

Thanks Al

[mayfieldt]

Pminmo touched on an often used simple method of deceasing and increasing line voltage.
That is the use of a Bucking or Boosting Transformer.

In your case, try using a 24V/10A Transformer, connect it's secondary in series with your Transformers Primary.
Measure your power supplies output. If the voltage has increased then you need to reverse either the Primary or Secondaries connections (not both) of the 24V transformer.
You should be able to expect about a 10V drop on you supply.

The 24V transformers are a common size and should be readily available. These are often referred to as ‘Control Transformers’.

What a Bucking transformer does is subtract its secondary voltage from the power line voltage.
A Boosting transformer will add its secondary voltage to the power lines voltage.
A Boosting Transformer is said to be “In Phase” and the Bucking is 180 degrees “Out of Phase”.

I once lived in a rural area where the power lines would fluctuate plus/minus 20 volts!
On any critical equipment we would use a Transformer with a switch that reversed its primary windings. This would give us either a Boost or a Buck.
The Transformer often had several taps that allowed the selection of the desired output voltage, plus, they would have an AC Meter to read the output voltage.

Tom M.

[Al_The_Man]

A couple of points on Buck/Boost transformers, They can be used on the primary and also in series with the secondary, The buck/boost winding only has to be sized to carry the same current as the winding it is operating with, in the previous example more like 1Amp should suffice as there would never be 10 amps in the primary, actually if he did intend using a 24v 10a transformer, he may as well use a 28v and use as the main supply and scrap the toroid.
I only tend to use Buck/Boost where it is either impossible/ impractical/costly to modify the existing transformer.
However is is a usefull tool.
Al.

[tekno]

A couple of points on Buck/Boost transformers, They can be used on the primary and also in series with the secondary, The buck/boost winding only has to be sized to carry the same current as the winding it is operating with, in the previous example more like 1Amp should suffice as there would never be 10 amps in the primary, actually if he did intend using a 24v 10a transformer, he may as well use a 28v and use as the main supply and scrap the toroid.
I only tend to use Buck/Boost where it is either impossible/ impractical/costly to modify the existing transformer.
However is is a usefull tool.
Al.

think I'll just look for a new transformer.

[mayfieldt]

'Al The Man': Absolutely! Modifying the Toroid would be the first thing I would try.
As for the primary current, my math must not be working.
I calculate that with a 32V secondary loaded to 18 Amperes would be a little under 5 Amps in the Primary.
Check Me...
4.92Amps = (32V * 18Amps)/117V Line

Tom M.

[NC Cams]

These links may help you in determining what size transformer to use and the more specific details involved in doing a really dead nuts package:

Linear P/S design/construction
http://www.campbelldesigns.com/files...ply-part-1.pdf

Servo amp P/S design
http://www.elecdesign.com/Articles/A...7635/7635.html