# Building a 24v dc power source



## Cadillac (Jan 21, 2019)

I'm trying to power up a 3stage vacuum motor that is 24v dc. I'm in need of sourcing,making a reliable 24 volt power source. I don't know enough about bridges and rectifiers to make my own. The motor specs say 25amps so I know it needs to handle that. Is it possible to convert 120 ac voltage easily to 24 dc? The motor is for a vacuum system I'm trying to make for my surface grinder so it will need to be able to be on for lengths of time. Any help would be appreciated.


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## mksj (Jan 21, 2019)

Building you own would probably not be cost effective, you would need a big transformer (120Vac step down),  bridge rectifier, fusing, wires, eclosure etc. It would be even more expensive to make it regulated.   I would suggest buying a switching power supply which are much more compact and protected from overload.

You can get a new switching supply type 24VDC, probably something in in the 27-35 A range (600-750W).  They should be able to run off of 120VAC, most are universal voltage. and are around 88% efficient. I like MeanWell power supplies, good quality and price. See HRP-600-24 below about $110, the RSP-750 is a bit more.
https://www.mouser.com/ProductDetail/MEAN-WELL/HRP-600-24?qs=l0g2inPJSHOJl3uJKxo6pw==
https://www.mouser.com/ProductDetail/MEAN-WELL/RSP-750-24?qs=sGAEpiMZZMsPs3th5F8koCgtkdmauKZkPQnGfuImKxQ=


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## Briney Eye (Jan 21, 2019)

Check this one out.


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## eugene13 (Jan 21, 2019)

Use two car batteries and a charger.


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## RJSakowski (Jan 21, 2019)

I would go with the switching power supply.  Keep in mind though that motor starting current usually exceeds the run current and your choice should make provisions for that.  The first Mouser supply mentioned has a potential 135% overload which should be sufficient.


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## ttabbal (Jan 21, 2019)

I have a stupid stiff 12V supply. Server power supply with a couple wire jumpers to enable it. Needs 220V, but can deliver 180A all day. Of course, it sounds like a jet engine..  I believe 24V units are available.


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## Bi11Hudson (Jan 21, 2019)

If you get* really *creative, you could rewind a transformer to give the 24 volts you need. The first, and most important, step would be "_does it need *regulated* power_"? It sounds like it doesn't, what scanty description you give. Like a marine or truck electrical system. Or HVAC system...... A good source for me is a high voltage transformer from a dead microwave oven. It doesn't take a lot of electrical knowledge, just a lot of work and being careful. If it *must* be regulated, just buy one, they're not *that* expensive.

Using a hacksaw, remove the high voltage winding but leave the line volage winding. Use some sort of insulating layer to protect the wiring from the core. Milk jug plastic will work. Fische paper is the correct item but may be hard to come by. Cardstock from a shoe box will do if you can't find something better. The nice thing about the microwave transformer is that if you screw up and scratch or cut the wrong wires, just chunk it and start over.

Take a piece of AWG 14 or AWG 12 and take a half dozen wraps on the core. The exact number will vary a turn or two. Read AC volts and shoot for 21 volts(+/-) or so. DC voltage will actually be somewhat higher. Now, that gets into electrical theory and does get complicated. Just shoot for a couple of volts AC less that what the desired DC is.

The "*electric brick*" you need is a bridge rectifier. They are available for 30 to 40 amps at 300 volts for a couple of bux. Some Chinese suppliers for less. Some US suppliers for more. Under $10 though, anywhere. About 1-1/4 inches square, 5/16" or so, thick. With four 1/4" stabs sticking up, and usually with a 5mm or 3/16" hole in the middle. A heat sink isn't necessary at your ampere rating, just a way to mount the brick. The metal is not *hot*.

I highly recommend you use the quick disconnects that fit. They're cheap enough... ... Look for the two connectors that have the symbol (~) on opposite corners. Connect those to the transformer. The other two, (+) and (-) are the DC lines. Sometimes there is only a corner notched or a paint splotch to indicate the (+) line.The diagonal opposite is the (-) and the two others are the AC, the two (~).

Fuse the *line* side about 5 amps, every one I've ever dealt with was 6 amps or better. So with 5 amps, you're safe. Rig a line cord, switch, and some sort of enclosure and you have an *unregulated *24 volt supply.

Bill Hudson​


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## cathead (Jan 22, 2019)

You said it well Bill Hudson.  I have done the same using old television transformers some of which are pretty heavy duty and still not
that hard to find.  An older colored TV with tubes is where you can find these transformers.  It's also environmentally friendly since
it would be recycling at it's best.  A filter can be added to the supply by adding a couple hundred or more microfarad 
electrolytic capacitor across the  output for voltage stabilization and ripple control.   To be prudent, I would mount the bridge rectifier
on a suitable heat sink to keep it safe from overheating.


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## Cadillac (Jan 22, 2019)

I thank everyone for your responses. I am familiar with mouser electric thanks. I would like to learn how to build the power source. I seem to be building a lot of things that need its own power supply so I need to start sometime. I have many transformers and electronic parts. I’ve seen people make a power supply out of a computer power source. Would that have the right amperage I believe it has 24v?
   The one reason why I don’t want to drop 100 bucks on the power source is that I’m still in the experimental stage of the vac system and I don’t know if the motor I have already will be sufficient for the task. 
 I’m gonna scrounge up some parts and see what I can do I’ll keep ya posted thanks.


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## markba633csi (Jan 22, 2019)

Hi Cadillac, I too was wondering if your 24 volt motor would be suitable- maybe a 120 volt AC motor would be better- just plug it in. 
mark


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## mksj (Jan 22, 2019)

You are looking at a very large transformer (650-800VA) to put out 25-30A rectified DC at the other end, most computer chargers are 1-2A (maybe 30VA). A transformer of this size would be very heavy, shipping alone would be expensive, not something you have laying around.  Just being practical, I think you are better off with a switching power supply at the end of the day. As mentioned you want fusing, power switch, enclosure, etc. which is going to add up. 30A is a lot of current, if you want to pursue a transformer design I would fuse both the input (6A) and output (30A). A DC motor would not typically need a regulated output, but may benefit from some filtering (RC), you would need very robust capacitors and resistors for this level of current. This is an 800VA 20VAC output that once rectified will be in the 24VDC range.
http://www.antekinc.com/an-8420-800va-20v-transformer/

If you just want to see if it works, get/borrow two car batteries and connect them in series with some jumper cables.

This one on eBay is $35 + FedEx shipping is $14.40, total under $50 is a deal, these normally sell for $250+.
https://www.ebay.com/itm/ARTESYN-Power-Supply-LCM600Q-Out-24VDC-27A-Max-4B/163146238161


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## derf (Jan 22, 2019)

Why not just use a Shop Vac and uncomplicate things...


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## Cadillac (Jan 22, 2019)

I looked into a 120 motor in that style it goes for 359. The motor I’m using is a ametek 3stage vac motor. It says they are used for central vac systems which has the lift I need. 
 A shop vac is annoying loud. I have one now dedicated for the SG but it’s loud. 
 I already had mounted a squirrel cage  type fan which is rated at 650 cfm and it works but does not have the suction I’m after. The motor only spun to 1500rpm so I replaced with a 3000rpm motor and it works better but not what I need. I figured I had the vac motor on hand brand new let’s see if I could make it work. I’ll figure something out eventually.


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## rgray (Jan 22, 2019)

Is there a lot of leakage on these vac chucks? Would a A/C vac pump do any good. Makes very high vacuum but not large quantity if there is leakage.
Not real expensive these days and way quiet compared to centrifugal vacs.

For one of my 24v power supplies that runs my Z axis and a tool post grinder i used an old wire feed welder (130amp)  I took excess parts out and cut down the chassis. (Don't need feed motor or space for wire roll)  
The transformer  has multiple windings so voltage is selectable.


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## Cadillac (Jan 22, 2019)

Rgray thanks I’m building a metal dust vacuum system for the surface grinder not a vacuum table at least not YET. 
I’m gonna see about one of those blow up jump house blowers. I have one and if I remember right it has a nice impeller on there so it might be the ticket. I’m trying to keep as compact as possible and as quiet as a machine running and as much suction as possible. Tall order but doable I think. Will see


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## Mark Needham (Jan 22, 2019)

Your 24v motor is over 3/4 HP.
Buy a switched power supply, but provide "spike protection".
Rots of Ruck.


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## Cadillac (Jan 22, 2019)

Thanks for the response bill. I wish you were my neighbor! I’m sorry I don’t know what you mean by regulated or not. I can guess but that’s why I’m in the situation I’m in. I have a lot to go over and think about I’ll look into the transformer build. Thanks again


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## tq60 (Jan 22, 2019)

A brute force 24 volt supply is stupid simple.

If you do not understand some basics then forget about building something.

25 amps at 24 volts is not enough information.

Duty cycle and run time may be helpful.

If prototyping and project is not finished just pick up a couple car batteries or alarm garden tractor batteries and some elcheapo battery chargers as dofur and work on what you know.

There are many basic led power units of varying voltages and currents and a "switch mode" is common design that outputs good current in a small package.

Is your project a one of a kind for personal use or are you planning on making for others.
.if making for others place a call to a parts house like digi-key and they can offer many units to meet your need and as such you have a reliable source for replacements.

Sent from my SAMSUNG-SM-G930A using Tapatalk


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## homebrewed (Jan 23, 2019)

I'm an electrical engineer by training, and have designed/built linear and switching power supplies for various projects, but these days I wouldn't take the DIY route for a PSU.  I'd rather buy an off-the-shelf switcher and get on with what I really want to do (and get there sooner with less money spent IMHO).  

For the price you get V+/Ground sensing, fault protection and high efficiency.  But that's just me.  Good luck with whatever route you decide to take!


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## akabud (Jan 23, 2019)

I have one I don't need any more. It's two server switching power supplies in series to output 24V.
75 amps each so 150 total. Has 4 taps you can pull 12V or 24V. $50 shipped to your door.


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## homebrewed (Jan 24, 2019)

akabud said:


> 75 amps each so 150 total.



If they're in series BOTH will "see" 75 amps so that's the max you will get.  Still sounds like enough for sure!


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## akabud (Jan 24, 2019)

That's correct.


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## ericc (Jan 24, 2019)

We went the cheap Chinese power supply route.  These are inexpensive, turn-key, run right out of the box.  I have, however, found that all of our spares are dead.  Unfortunately, I found this out when we needed to install one at short notice.  I later on saw on the Internet that you have to test and burn these in, and discard the rejects before you need one.  I had four spares, and I still came up short when they just asked for one.  And, they failed in different ways, just sitting there.


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## ttabbal (Jan 24, 2019)

One thing I learned working on computers is that you do not want to go cheap on the power supply. They fail in various ways and I've seen them take out everything attached to them when they do. It's more likely they just stop working, but when you have expensive equipment connected to them, you're always better off getting at least a mid-grade unit. 

This is less of an issue with the old school transformer based supplies. The isolation helps. But they can have filter components fail, usually cheap capacitors, that then feeds all kinds of noise into the circuit. How much that matters depends on what you have connected. 

Both cases are annoying, as the manufacturer might have saved a couple bucks at most. I understand that's then over millions of units, but it is still annoying. Particularly as the savings don't filter to the customer.


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## Bi11Hudson (Jan 24, 2019)

An after-thought to maybe clear up some confusion.

A *filtered* circuit is simple. A capacitor of 1000 microFarads(uF) per amp will filter 60 cycles to about 5%. Sufficient on non-critical loads. But doesn't control the actual voltage. That's a function of the homebrew transformer I described earlier. For a motor load, filtering really isn't necessary. Maybe a few mics to keep down electrical noise, but even then no big deal. If the winding comes out to 23 volts or 26 volts, the filtering has no effect.

A *regulated* circuit is much more complicated and you would be advised to purchase one. I have been an EE for many years, longer than some of your responders have been alive. If I need a *regulated* supply, I won't build anything larger than an amp or so. Just buy one and be done with it.

But not for a motor load. Just build a transformer supply and use a speed control, usually a duty cycle controller. The supplier I often use (Marlin P Jones Surplus) has them for 10 or 15 bux or so. Several other sources have similar availability. They are not uncommon, albeit usually Chinese.

A regulated supply, on the other hand, will supply the rated voltage within a very tight tolerance, something as tight as +/- 0*.*24 volts or less. That's 1%, 1 in 100, and I don't see any reason for that sort of control. Two batteries in series will provide from 26+ at full charge to 20 volts or less at discharged. That's all you need for a motor load.

The *transformer *I suggested is a home brew job. It is not an accurate or precise device, but it is *cheap*. Not just in-expensive, cheap. Low end, no safetys, no enclosure, usually aluminium windings, but ok for testing. The prinary, at 120 volts, is rated for 6 amps or more. Therefore, the proposed secondary, at 24 volts, will be good for 4 to 5 times that. 24-30 amps. 

The bottom line here is that you are dealing with an *electric* load, not an *electronic* one. The two are distinctly different fields. Many modern pursuits mix the two indescriminately, often to their and other's, despair. My TV, computer, and stereo are *electronic*. My machine motors, old ('68 Chev) truck, and most older equipment is *electrical*. The two are destinctly different. Your project seemsw to fall in the latter.


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## Cadillac (Feb 13, 2019)

So Ive still been searching for a 24v power supply. We have these battery chargers at work for a 48v vehicle that has different rating on the label for different applications. It shows from 12-60 volts with corresponding amperage.






I’ve fixed some of these but admittedly don’t understand it like I should. Opening it up I see adjustable mosfets I think? the little blue boxes with screw. I’ve tried adjusting screws and I can change voltage but only down to like 37 volts with adjusting one box. I haven’t been able to figure what the other two do. There is a switch on the side of unit for 110 or 220 which we have set to 110 and my output is 50.4volts. Doesn’t anyone have a clue how to set this unit to 24volts the label looks like it would have 15a which would be close to what I need. Is this the wrong application for a charger? Any thought would be appreciated thanks.


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## markba633csi (Feb 13, 2019)

The red mark means It's for 50 volts only, lithium polymer batteries.  It's not made to have a wide range adjustment- those other numbers are all the different models they make
The blue boxes are trimpots. One is for voltage trim, the others are current limit and so forth
They probably use different transformers for the lower voltage models


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## sixball (Feb 13, 2019)

This is all very interesting to me because my house and shop run through an inverter from a 24v DC battery bank charged by solar panels and I've never seriously thought much about DC power except for a few lights. I should think more.


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## Latinrascalrg1 (Feb 13, 2019)

Bi11Hudson said:


> The bottom line here is that you are dealing with an *electric* load, not an *electronic* one. The two are distinctly different fields. Many modern pursuits mix the two indescriminately, often to their and other's, despair. My TV, computer, and stereo are *electronic*. My machine motors, old ('68 Chev) truck, and most older equipment is *electrical*. The two are destinctly different. Your project seemsw to fall in the latter.



First off Please do not take my Questions like I'm telling you the answer!   My only motive is to gain more Knowledge here and Sentiment is easily lost over the inter-web! 

With that said,
Going by your definitions Could this Difference be better described as.... 
Electronic- TVs, Computers, stereo etc... as Being "Digital electronic components."  Where as Electrical- Machine motors, old ('68 Chev) truck, and most older equipment, etc...as being "Analog electronic components?"


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## Cadillac (Feb 13, 2019)

Thank u. I just know I have something laying around that can do the job. I just don’t know half of what I’m looking at. 
 I did try using 2 12v batteries I had laying around. They were from emergency lights so they were smaller like motorcycle size. They worked but the motor drained them Pretty quick. 
 I keep running in to road blocks with every motor I find. To big,wrong direction,to slow,different voltages. It just doesn’t want to cooperate. I’ll get it eventually being cheap has its drawbacks.


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## Bi11Hudson (Feb 21, 2019)

In the middle of making the transition from a very old W-XP to W-10. I got to *un*-learn just about everything I *knew* about the Internet. Been off-line for over a week, so far. Sorry 'bout that.

Now to answer your query: You got things headed in the right direction, just a little shy of the point. 

There was a time that telephones were "land line" only. If you wanted to communicate across the air waves, you used a radio. The phone was electrical, the radio was electronic. A motor is electrical, specifically as a "magnetic" way to convert electrical energy into mechanical (rotation) energy. A  generator is electrical, rotating magnetism. That old truck is electrical, the spark plug firing by the (collapsing) field of the coil, powered by a battery. Late model trucks (Ford V-10) use electronics to select which of 10 different coils to fire. 

A radio, television, many (most) modern appliances, whatever, have active components, amplifiers, transistors, vacuum tubes, things of that nature. There are still vacuum tubes in use, though rare. Talk to any serious HAM, the ones that do code transmission. (I don't, BTW). 

Look at www.hudsontelcom.com, for the article on "Home Shop Electrics". That's pure electrical. I cover magnetic theory to a mild extent, it's not _too_  heavy. As in *no math*. There's no electronics there, strictly magnetic theory. There is a *vast *difference between electronics and electricity. The two are related only at the level of *basic* theory. While electricity is fairly easy (?) to grasp, electronics is much more difficult. But to understand one doesn't mean automatic comprehension of the other. In my day, grasping electricity, there were very few to grasp electronics. Today, it's the other way around. Most everybody grasps electronics, to grasp electricity is rare.

In its' simplist form, try to understand grounding against EMP. Or, perhaps arc welding. Old style, with a rod. Those are both pure electrical. As stated, I am (was) an EE, from way(!) back. I learned my craft on an old ship, WW-2 vintage. We had _radar _and _radios_, yes. But, to make the ship move took *electricity,* not *electronics*. The electronics people were "operations" division, electricians were snipes. (engineering division) Because we each saw the world from vastly different perspectives.

I know the above was about as clear as mud. Look up the web site, it'll help. Just enough to get started, true. But, a start.

Bill Hudson​


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## Bi11Hudson (Feb 21, 2019)

An adder, if I may. 

Analogue is a smooth curve that can have an infinate number of points. Digital is fundamentally on and off.  Only two points. Like a light switch, on and off. Digital actually predates analogue with many products. Such as telegraph with morse code. And the spark for an automotive engine.

In its' simplist form, take the number 31. This in the "people" form, base 10. Now, with the fingers on one hand (5), I can count in binary to 31. That is "machine" speak, such as your computer. A 5 bit word, like the ancient ASR-19 teletype. A purely electrical device. Just the timing of 5 bits within a tightly controlled timeframe. Think back to the "clacking" in an old timey newsroom. That was the teletype. 

In 1984, when I was traveling for Wang Computers, there was a time an ASR-19 ran right alongside the current Wang "super-mini", before the IBM PC became the defacto standard. The teletype had two wires in an undersea cable. Out of ?who knows? total. Not very many, it was in the middle of nowhere in the South Pacific. Knowing the users, it probably was multiplexed, shared by several users. But, still electrical. Sensitive electrical, but electrical. The Telex people had an ASR-43, still electrical. But, a very nice typewriter as well as a paper tape reader. Electrical... ...

I suppose the basic question is whether the machine has a relay or a transistor (or thyristor). And if the relay is turned on by another relay or a low level electronic device. 

Again, it's difficult to draw the line. I recently saw an ad for "large" motor training. The photo had a fellow holding a 1/4 HP motor in one hand. I thought it funny, having worked on the main hoist of a bridge crane with* two * 350 HP motors in shunt.(parallel) 700 HP total. That on a 310 *ton* bridge crane. Big enough to deadlift a small ship, in one lift.

On the wonders of modern technology, I had WinDoze XP. Now, I'm trying to relearn so I will have WinDoze 10. Ii's been a week and I still don't have my eMail back up. Driving me nuts. Makes me wish for the C/PM 16 bit days again. Where MS-DOS was copied from, by the way. Long before Winderz. Bill Gates was a hell of a salesman, but never that much of a computer man. I look to An Wang for that. Just a rant about "modern" technology. Forgive me, please.
Bill Hudson​


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