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Building a 24v dc power source

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Cadillac

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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.
 

mksj

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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=
 

RJSakowski

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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.
 

ttabbal

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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.
 

Bi11Hudson

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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​
 

cathead

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You said it well Bill Hudson.:encourage: 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.
 

Cadillac

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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.
 

markba633csi

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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
 

mksj

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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

LCM600Q.jpg
 

Cadillac

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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.
 

rgray

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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.
 

Cadillac

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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
 

Mark Needham

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

Cadillac

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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
 

tq60

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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
 

homebrewed

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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!
 

akabud

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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.
 

ericc

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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.
 

ttabbal

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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.
 

Bi11Hudson

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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.
 

Cadillac

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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.
287640
287641


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.
 

markba633csi

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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

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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.
 

Latinrascalrg1

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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?"
 

Cadillac

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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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