Author Topic: How to Make a Power Supply (Read 94577 times)

Bernd · « **Reply #50 on:** May 18, 2009, 01:37:12 PM »

Darren,

You might want to add a fuse on the mains side of the tranny for saftey sake. Other than that it looks OK.

Bernd

Darren · « **Reply #51 on:** May 18, 2009, 01:43:54 PM »

Good point Bernd,

It easy to forget what comes without question for some of us could be missed by others

You could also add a fuse after the transformer, say 5A or if you know you current demand is low like these motors then a 3A would be better.

But, DO fit a mains fuse as Bernd suggested.

Bernd · « **Reply #52 on:** May 18, 2009, 02:04:33 PM »

As far as I know and have seen in electrical magazines in the US all such projects have a fuse in line on the incoming voltage to the transformer.

Seems each country has different electrical codes for such devises.

Looking good Darren. Carry on and sorry for the interruption.

Bernd

Darren · « **Reply #53 on:** May 18, 2009, 02:08:14 PM »

In the UK many electrical goods do not have an internal fuse.

This is because our wall socket plugs have internal fuses. This makes it quite hard to connect anything to the mains supply without a fuse.

Do I understand from your post that US plugs don't have internal fuses?

Divided he ad · « **Reply #54 on:** May 18, 2009, 02:29:50 PM »

Thank you for the parts list Darren

I'll get figuring out the stuff and where to buy it ASAP

Got to get my mill powered

The plug thing.... Odly the other side of the pond do not have fuses in the plugs.... like the French (And I suppose other European countries?)
It seems a little under protected to me..... But hey, someone must know what they're doing? right?

Ralph.

Bernd · « **Reply #55 on:** May 18, 2009, 03:22:16 PM »

Darren,

Here's a quick run down of how the power gets into the house. 220v to outside meter. From meter to panel box. Panel box has the circuits for all the rooms. Power is run through a circuit breaker, usally 15 to 20 amps. Then the wire is run to the room plugs. No fuses in the plugs themselves, except for any outlet near water supply, usally kitchen and bathroom. These plugs have ground fault interupt circuits in them and will shut power off to the wall outlet.

Usally when somebody shows a diagram of a circuit they include a fuse and power light on the mains side of the transformer for saftey reasons. A majority of the applances do have an interanl fuse. Just today the microwave oven blew the internal fuse. It is a 15amp fuse. The power line it's connected to has a 20 amp circuit breaker. A dead short would probably open both fuse and breaker.

I don't know if all electrical appliances have internal fuses or not. Rather confusing, I know.

You won't want to look through the electrical code book, it's quite thick.

Probably hasn't helped any but you get the idea.

Bernd

Bernd · « **Reply #56 on:** May 18, 2009, 07:03:29 PM »

Darren,

I've done a bit more research on published power supplies, but couldn't find some of my electronic books. I did a google search and came up with this PDF file. It's call Power Supply Design Basics.

I don't see any fuse, on/off switch or power on indicator on the mains line in their example. I still think it's good practice though.

Hope you don't mind me adding this to your thread.

Bernd

Darren · « **Reply #57 on:** May 18, 2009, 07:16:28 PM »

Bernd I can't see that page for some reason, must be the US anti terrorist action coming into play, must think I need it to do some bad things

Generally if you need telling that you need a fuse in a mains circuit then you shouldn't be playing with this stuff anyway.

As a rule, people showing other people electronic circuits do not include the peripherals.

It would be a bit like me giving you a slap on the wrist for showing someone how to mill a chunk of metal and not mentioning that they need to wear safety glasses.

Bernd · « **Reply #58 on:** May 18, 2009, 07:49:54 PM »

Quote from: Darren on May 18, 2009, 07:16:28 PM

Bernd I can't see that page for some reason, must be the US anti terrorist action coming into play, must think I need it to do some bad things

Interesting. It's an app note on basic power supplys from the SGS-Thomson Microelectronics.

All right I'm giving up on this while I'm still somewhat sane.

Must have been to many of these

when I was younger.

Bernd

Alan Haisley · « **Reply #59 on:** May 21, 2009, 10:11:14 PM »

Quote from: Darren on May 18, 2009, 02:08:14 PM

In the UK many electrical goods do not have an internal fuse.

This is because our wall socket plugs have internal fuses. This makes it quite hard to connect anything to the mains supply without a fuse.

Darren,

Does UK house wiring include fuses or circuit breakers at the service point in addition to the plug fuses? If not I'd worry about a broken wire short in the wall.

Alan

Darren · « **Reply #60 on:** May 22, 2009, 05:29:32 AM »

Yes we have one of the highest safety standards in the world I believe.

Don't worry about us Brits

raynerd · « **Reply #61 on:** May 30, 2009, 02:28:35 AM »

If I want to run a driver at 2.5A and 3.75V but ulimately I have three boards to drive 2.5 x 3 = 7.5A - will my PS have to be rated 7.5A or above? It is this link between voltage and current that confused me and the requirements to power components I don`t get. When selecting a power supply to drive the above, am I just interested in the ampage that it can draw and the fact that it needs to draw 7.5A maximum. The voltage will just be adjusted to achieve this current right?

The power supply that they actually sell for this setup is rated:

Quote

Small Power Supply for our 2.5A 3 Axis Driver Kit.
Input voltage of 100-240V; AC 50-60Hz; 1.5A
24V DC Output
Short circuit, over voltage and over current protection.
24 Volt Power Supply £33 Each + £6.50 P&P

One last thing, to throw a spanner in the works, if I only wanted to run one 2.5A driver would this need to be a variable supply or would it be suitable to plug into one driver as it is?

Any help appreciated.
Chris

John Hill · « **Reply #62 on:** May 30, 2009, 03:56:40 AM »

Chris, when that power supply is outputting 7.5 amps at 24 volts thats 180 watts but you say your load voltage is only 3.75 volts? 3.75*7.5 =28.125 watts, more than 150 watts going 'somewhere'. I dont think we have the fully story here but at least we can be confident the 24volt power supply can supply the 10 amps just by doing a check that the power supply input watts is comfortably more than the required power supply output watts.

I assume this is a controller board to drive three stepper motors? Can you provide a link to a description of these controller boards?

No, you would not have to change the supply if you reduce the number of drivers. Assuming the voltage stays the same the amount of current that will flow will increase as the load units are increased up to the maximum current available from the supply.

Bluechip · « **Reply #63 on:** May 30, 2009, 05:12:18 AM »

Chris

I would suggest that a 24V PSU for a 3.75V motor is not suitable. You can put dropper resistors in series, but is is a very inelegant way to go about it.

There is not enough info. on the stepper motor, but here's a quick ball park guess .. lot of assumptions tho'

24 - 3.75 = 20.25 V to be lost.

Assume motor load = 2.5A ( & constant, which it won't be)

Series resistor = ( R = ( E / I ) 8.1 R

Power to dissipate = I^2 x R = 50W
Thats a lot, it will get hot.
If I were doing this, I would not go with that PSU. It doesn't really come close to what is reqd.

John. If the PSU has effective current limiting, you wont get 7.5A out of it. I presume if it's designed for 2.5A, the internals would be stressed at 7.5A.

I would make my own PSU, (do a Darren

, )with my favourite Reg. ic, the L200, with a series pass transistor.

This chip is a variable output from 2.7V to 37V at 2A, more with a pass transistor.

Try looking for L200.pdf

Lots of circuits thereon..

Dave

raynerd · « **Reply #64 on:** May 30, 2009, 05:30:47 AM »

Ok - I`m sorry but still some of this is going over my head:

The driver:
http://www.routoutcnc.com/singlesmall.html

The motor:
http://web.archive.org/web/20050318040147/http://www.homeshopcnc.com/page3.html first one on that page but now wired 4 wire bipolar.

The ""available" power supply -
http://www.routoutcnc.com/hardware.html - down at the bottom - the 2.5A kit PS, not the others.

I don`t want to go with their power supply because I have a feeling that this driver, and I only have one at present just to try it, won`t be good enough to drive my motors or it will be good enough but the motor won`t be! Basically, I think I`ll end up upgrading! I want to make a PS so that I know how to go about upgrading in future, to save money (hopefully) and also so that I have a better understanding...

So i I had a go at making Darrens power supply - would it work as it and what "settings" would I need it on to power first of all just one motor and driver and then eventually 3 motors?

Chris

Darren · « **Reply #65 on:** May 30, 2009, 06:41:22 AM »

Chris, I think you mean you want 2.5A @ 37.5V?

But really if you read the instructions 24V output is ideal.

Yes this power supply would do that, but it's not the type I would use as you don't need the variable voltage facilities.

In all honesty at 33 quid each I would use theirs.

Any computor/laptop telephone, printer etc supply should do somewhere near 24V, some are 19V, they would do.

Just check the Amp outputs are high enough.

Bluechip · « **Reply #66 on:** May 30, 2009, 06:44:18 AM »

Chris

Sent you a PM

dave

raynerd · « **Reply #67 on:** May 30, 2009, 06:58:13 AM »

I see Darren! I`ve just looked at the pdf spec sheet and I took this from it:

Quote

Setting the current for your stepper motors.
The formula VREF = Motor Current X 1.4 can be used to determine the Value for VREF
The most common current ratings are shown in a table below.
Motor Current
(A)
VREF Voltage
(V)
2.5 A - 3.5V
2.0 A - 2.8V
1.75 A - 2.5 V
1.5 A - 2.1 V
1.25 A - 1.8 V
1.0 A - 1.4 V
0.75 A - 1.05 V
0.5 A - 0.7 V
Note: It is normal to exceed the motors rated voltage by up to 20 times, for instance a
5V stepper motor run at 24 V would be perfectly expectable.
D Never exceed a motors rated current or the drive cards 30V DC Max. Doing so could
damage the motor and the stepper drive card.

How can a PS running 24V not blow a motor only requiring 3.75V ?

I think I understand the current a little more - is it saying that if the driver is rated 2.5A then that driver will draw 2.5A from the power supply, if your PS isn`t able to provide that current then your PS will blow as the components are drawing too much current from it - is that right? So in actual fact, to run one motor - it doesn`t matter as long as the PS is rated above 2.5A.

I still don`t get the voltage though, if the motor only runs at 3.75V how can I plug into the driver a 24v supply - surely it will blow the motor?

Chris

EDIT: the PS I have spare is a laptop 75W AC adaptor - DC output is 18-20V - 3.79A, would this be any use?

Darren · « **Reply #68 on:** May 30, 2009, 07:12:39 AM »

What does it mean by vref?

That to me is in respect to the power supply setup and not the voltage output to the motor?

I could be wrong as I do not know the full facts,

In all honesty their power supply is a good price, you'd have a job to better it if you needed to buy all the components to make one yourself.

raynerd · « **Reply #69 on:** May 30, 2009, 07:15:48 AM »

VREF = voltage reference.

I understand that their PS may be a good deal but I am interested to learn more about it myself and see if I could save money by using my own spare PS.

I appreciate your time and help.

Chris

Darren · « **Reply #70 on:** May 30, 2009, 07:20:21 AM »

Sorry Chris, yes I know what vref is, but to what is it referincing?

I guess it's to the voltage regulator chip to set the output voltage to the motor. Which is very different to vref value.

That is, do not confuse vref with the motor requirement voltage.

raynerd · « **Reply #71 on:** May 30, 2009, 04:37:55 PM »

Oh I see!! So the driver has a voltage regulator on it anyway so even though your running into it a 24V PS the regulator chip will reduce it to the required voltage to run your motor at 2.5A??

A couple of thoughts - why would it "need" to take in a 24V to throw out only 3-4V for the actual motor? Also, any 24V PS will be ok - but what current should it be rated - anything over 2.5A or should it ideally be a little higher?

All the best, I am understanding this a little more now.

Chris

John Hill · « **Reply #72 on:** May 30, 2009, 05:04:04 PM »

I do not believe this is a simple thing that can be understood by refering to Ohm's Law.

The motors are not being fed simple DC, they are being pulsed at some high audio frequence (the description refers to being able to hear the motor making a noise in the windings).

Motors winding are highly inductive and it is a common practice to feed an inductive load via a resistance where a quick reaction is required. Ancient telegraph practice in fact. The principal is that there is a high voltage across the coil when there is a low current but when the current begins to flow so the voltage drop across the resistor rises and stops the coil overheating. I am not suprised that they are proposing such relatively high voltages for nominally low voltage windings.

Any power supply Chris that can provide at least the amps at the voltage you require.

raynerd · « **Reply #73 on:** May 30, 2009, 05:11:22 PM »

Cheers for the info John - I`m going to give this spare laptop charger a go as it is rated 18-20v @3.79A. Please do tell me if this is well too low powered.
Chris

John Hill · « **Reply #74 on:** May 30, 2009, 08:52:56 PM »

Chris, I think that is a little light on capacity but it might work.

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Author Topic: How to Make a Power Supply (Read 94577 times)