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Forum 2005-2010 (read only) => General => Frequently-Asked Questions => Topic started by: dze on Sep 01, 2010, 09:07 am

Title: Power supply
Post by: dze on Sep 01, 2010, 09:07 am
Hi there,

I found (maybe) the right motor for my needs. The DC motor is running at 6 volts but max 12 amps. This kind of power  supply is really hard to find. What I've found so far is 12 volts 10 amps. I guess i can run the motor that i'm going to use at 10 amps but how do i lower the 12 volts to 6 volts. I understand that there's a way to voltage divide like adding a resistor in parallel, is this the way around it?

Bascially i would need a total of 6 of these motors to realise my project. Can anyone give me some advice on how i can meet the requirement of the power supply? What i have found so far are power supply for leds giving 12 volts 10 amps and even up to 25 amps. How could i use these?

any advice would be greatly appreciated.

thanks
best
dze
Title: Re: Power supply
Post by: Grumpy_Mike on Sep 01, 2010, 10:08 am
Quote
I understand that there's a way to voltage divide like adding a resistor in parallel, is this the way around it?


No using resistors only works for low currents.

Quote
I guess i can run the motor that i'm going to use at 10 amps

So how is that going to happen?
Given 6V the motor will take 12A if your power supply can only provide 10A it will go into overload and probably shut down if you are lucky or burst into flames if you are not.

You can reduce the voltage to 6V using a 6V regulator but you will be burning off vast amounts of power, a full 60W and that is too much for a simple regulator.
You need a DC/DC converter but these are not cheap.
http://uk.farnell.com/jsp/search/browse.jsp?N=500006+1004234+5054171&Ntk=gensearch_001&Ntt=DC%2FDC&Ntx=mode+matchallpartial&No=0&getResults=true&appliedparametrics=true&locale=en_UK&catalogId=&prevNValues=500006+1004234&filtersHidden=false&appliedHidden=false&originalQueryURL=%2Fjsp%2Fsearch%2Fbrowse.jsp%3FN%3D500006%2B1004234%26Ntk%3Dgensearch_001%26Ntt%3DDC%252FDC%26Ntx%3Dmode%2Bmatchallpartial%26No%3D0%26getResults%3Dtrue%26appliedparametrics%3Dtrue%26locale%3Den_UK%26catalogId%3D%26prevNValues%3D500006%2B1004234

My advice is what I said last time, give the motor 5V from a computer PSU.
Title: Re: Power supply
Post by: UltraMagnus on Sep 01, 2010, 02:38 pm
5V from a computer PSU should do it.

you could make your own power supply too, get a big transformer, some big diodes, and a big capacitor.
Title: Re: Power supply
Post by: Grumpy_Mike on Sep 01, 2010, 03:59 pm
Quote
you could make your own power supply too,

Do you think someone who is asking such questions is at a level where he can make his own power supply.

Constructing power supplies can be tricky as you are dealing with mains and with a 10A current it is not the easiest of things to make.
Title: Re: Power supply
Post by: mpeuser on Sep 01, 2010, 04:19 pm
- 6V transformers are not common above  48VA (around  8A).
- I doubt that there are "LED supplies" @12V 10A... You might have seen Halogen transformers, which are generally 50 to 500 VA (= 4 to 40A). They indeed can be a bargain... The old ones contain a heavy transformers, modern ones are extremely small and "switched" (and might have issues with motors...)

Both output AC of course.

Outfashioned AT power supplies for 300 W schould be available for <10$ you might even get some for free, if you are lucky. Their interfacing is well documented in the web....
Title: Re: Power supply
Post by: UltraMagnus on Sep 01, 2010, 06:05 pm
Quote
Do you think someone who is asking such questions is at a level where he can make his own power supply.

Anyone that can wire up a motor to run from an arduino should be able to wire a transformer, four diodes, and a capacitor together, yes.

Quote
- 6V transformers are not common above  48VA (around  8A).

They can be used in parallel without issue.
Title: Re: Power supply
Post by: Grumpy_Mike on Sep 02, 2010, 12:19 am
Quote
Anyone that can wire up a motor to run from an arduino should be able to wire a transformer, four diodes, and a capacitor together, yes.

Oh dear you have a lot to learn.

Quote
They can be used in parallel without issue.


See what I mean.
Title: Re: Power supply
Post by: UltraMagnus on Sep 02, 2010, 12:24 am
Quote
See what I mean.


No, I don't, why don't you explain rather than gloating.
Title: Re: Power supply
Post by: mpeuser on Sep 02, 2010, 12:53 am
;) We had had this for batteries already.
But it is worse for transformers.

As with batteries, they have to be absolutely identical...
But there are high risks involved.
- you can mess-up the phases ;D
- When a connection at the mains side fails, this transformer willl work in the other direction  ;D

Yes, there can be a lot of fun...

It MIGHT work to connect the DC lines AFTER each rectifier.. Not perfect but also not really dangerous....

And - BTW - what has this  "capacitor" to do with it??
Title: Re: Power supply
Post by: Lyght on Sep 02, 2010, 01:44 am
First i'd like to say, i can wire up an ARDie, and i've become very successful recently at my own scripting.
However i dont think i could physically do a transformer... so i'm an example of someone who can wire stuff up, but dont even understand the "In line" stuff quiet yet.

However on the second hand i can say that i havnt posted on these forms in a while because instead of getting decent objective responses... except in specific occassions and here i'll say Andrew thank you, your replies on my post have helped me help myself, at least you point me in the right direction.
However to others here, seems like you forgot where you came from... I came on here not knowing anything except insert tab A into slot B... and still have tons to learn, but seem to not get a newbie hand very often... You post stuff so technical in response you expect us to know what you mean, when in reality we dont.

You say oh well just you just define this here, subtract and multiple this here... if you dont believe me, do a search on your own posts.. see how it's progressed....I try to search posts on "God members" because i figure if anyone is posting learning oppurtunities it you guys.

And trust me on alot of the "God members" i have done searches on your posts and some of them just seem to be snotty...

and i mean no disrespect i'll state that now..... just an observation... I'm here to learn, and i've pulled back alot from posting. Since my last post i've actually completed 5 decently sized projects, and all thanx to Andrew's posting me in the right direction, with multiple examples and situtations... But if you read my post you can feel the frustration in the posting, but andrew stuck with me and i ended where i needed to be.

Like i said all just observation, and not ment to be disrespectful, all i ask is remember some of us do have alot to learn, and want too... just be patient and some of us do require pretty pictures to grasp concepts you understand readily...

So sorry for long post and i know has nothing to do with voltage, but i just thought with previous posts i might voice a small opinion, but it's only mine i'm sure.
Title: Re: Power supply
Post by: mpeuser on Sep 02, 2010, 01:59 am
@Lyght: Yes I see your point. However I cannot really see it with this thread. And please understand that there is sometimes a small friendly in-fight between us "god members", so don't get confused. Please also understand - as Ptolemy the Pharao had to 2300 years ago - that there is no king's road to microcontrolling. There are not always simple explanations, and the road is not only narrow and twisted but also long and  bumpy...

Just stay tuned  ;)
Title: Re: Power supply
Post by: billhowl on Sep 02, 2010, 03:16 am
dze@: May be you can try to get from eBay like this 350W 5V DC 50A Regulated Switching Power Supply (http://cgi.ebay.com/350W-5V-DC-50A-Regulated-Switching-Power-Supply-K001-/170431324065?pt=LH_DefaultDomain_0) , it can adjust to 5.6V,  or you get this 350W 7.5V 46A Regulated Switching Power Supply (http://cgi.ebay.com/350W-7-5V-46A-Regulated-Switching-Power-Supply-K302-/170528987317?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item27b451d8b5)  adjust to 6V.
the motor max current of 12A I think is the stall current, so 50A will be able to operate all 6 motors.
Title: Re: Power supply
Post by: mpeuser on Sep 02, 2010, 08:31 am
Similar switched DC power supplies are available from  e.g. MW ("Mean Well") :-)

The rule seems to be $20 per 100W, which makes those eBay things quite a bargain. Note you definitely need a fan above 150W!!

Though they are generally 12, 24, 48 volts you will sometines find 5 or 7.5 volt versions, as above.. If you have the choice, prefer 7.5 volts over 5. The motors will like it!
Title: Re: Power supply
Post by: Grumpy_Mike on Sep 02, 2010, 10:10 am
Quote
You say oh well just you just define this here, subtract and multiple this here..


Yes we do. The problem is that there are many people asking advice and they all have different ability levels. To address each one as a complete beginner would be time consuming, patronising and wasteful.
Once when I was very young I was on an exhibition stand in London showing off some active filters we had been working on at the Admiralty Underwater Weapons Establishment. I explained what the filters did to one person and he said "what's frequency". I was a bit shocked so the very next person to come to the stand I said "do you know what frequency means". He was very cross and said he was the professor of Electronics at Imperial Collage and stormed off.

Quote
all i ask is remember some of us do have alot to learn, and want too..


So what is the best way to learn. To point someone in the right direction and let them get on with things or to spoon feed and do it all for them. It's a fine judgement and to some extent decisions will be based on a gut feel. I don't know about others who spend time posting here ('other Gods' although I don't particularly like the term) but there are few names that stick in the mind and so it is difficult to remember past posts, although not past post topics. I even answered a post from my own Son without realising who he was despite having his real name as a user name. (my excuse was that all the names were rolled into one word with no spaces and I am dyslexic)

Quote
just be patient and some of us do require pretty pictures to grasp concepts you understand readily

That's one failing of this forum, the difficulty of posting pictures. Pictures are quite time consuming to produce and it is often easer to describe a simple circuit in words. However, it should be easy to take the words and produce a sketch.
Some pictures are very useful in understanding basic concepts. I spent a lot of time producing the animated picture of a PWM signal for this page:- http://www.thebox.myzen.co.uk/Tutorial/PWM.html

However, if you feel that something has been "explained" and you don't understand it then please ask again, and again and again until you get an explanation that you feel happy with. There is always someone willing to answer you, that's the beauty of this forum.

As to your specific question what you are asking for is something that is out of the ordinary. It pushes the limits of what is readily available. So there are two possible solutions, one is that you don't actually need what you are asking for and can get away with something more readily available. The other is that you will have to custom make what you want. Now I know I would find making a power supply of your specifications quite daunting. In a conventional power supply the transformers are large and heavy, the capacitors are physically large, expensive and possibly prone to exploding if you don't get it right. There are different problems you need to cope with when handling large currents that simply are not an issue at say 1 to 3 amps. So I make the judgement if I don't fancy making one then you probably won't.

I feel we have a degree of responsibility not to lead a beginner astray and to point out the pit falls and maybe unforeseen difficulties. It is all too easy in electronics to imagine you can do anything you can imagine. Hence the beginners that regularly want to connect hundreds of LEDs to an arduino.

Then there are people who, while not having done much practical themselves are convinced it is all easy and hand out advice that is wrong or potentially dangerous.

Finally there is the point that given N engineers there will always be at LEAST N+1 strongly held opinions.

It's free advice and if you don't like it then you can always have your money back.  ;)
Title: Re: Power supply
Post by: Homer_Manalo on Sep 02, 2010, 01:12 pm
Sorry dze but I don't want to post another power supply thread. And since this is a power supply thread here is a list of power supply manufacturers. You might want to check them out: http://www.interfacebus.com/Power_Supply_Manufactures.html

Well, I have a question too about power supply. If I have two 12V(25A) power supplies connected in series and the 24V has a load, can I tap the 12V with a load of different current rating? Thanks.
Title: Re: Power supply
Post by: mpeuser on Sep 02, 2010, 01:14 pm
Of course you can!
You can pile up any number of any kinds of power supplies (well within some range..), and all of the will do the best to contribute a little bit of current and a little bit of voltage.

Mind that you do not connect their (secondary) grounds.
Also they might have small resistors in them that would only only allow a certain amount of current, and might also be used for current limitation.


The best rule ist to pile them from ground, starting with the highest current capabiliy... This however is somewhat logical...
Title: Re: Power supply
Post by: Homer_Manalo on Sep 02, 2010, 01:17 pm
Quote
Of course you can!

Referring to my post? If you are then how is that possible since current in series is supposed to be equal?Thanks.
Title: Re: Power supply
Post by: Grumpy_Mike on Sep 02, 2010, 01:23 pm
Quote
since current in series is supposed to be equal


That is only for a load, you have a generator, the current depends on the load each generator sees.
Title: Re: Power supply
Post by: dze on Sep 02, 2010, 07:46 pm
hi there!

thanks for all the helpful replies.

regarding soldering, yes i think i can manage without frying myself connecting some components along with a schematic.

i feel that the way of leading a newbie along the right path, giving both pratical(buyable) solutions and a diy or hacking solutions are both good. then i can see how much i want to delve into what possibilties i have or start looking for others.

A better way is to get a ready for use powersupply which suits my needs and I hope that i can find such. Well what i have found out so far is that 'Mean Well' sell a particular powersupply for my needs; 5.5v 75 amps. that way i can connect up all six motors and run them from the same power supply.

currently i'm working with adafruit motorshield and a 12 volt motor. this is not my ideal combination, cause i would need to control 6 motors with pwm controls  and to run in sync. So after all the testing, i would be using just the arduino.

so here goes some really simple but for me mindblogging questions;

How would i connect each motor running at 5, 6 or 7.5v 12a (total 6 motors) to arduino each with it's own pwm control? say i'm using a 5.5v 46a power supply (which means i would need a 2nd one)

I'm refering to http://itp.nyu.edu/physcomp/Labs/DCMotorControl as my reference. The datasheet for L293 says it handles max 1amp, what should i use instead to handle 12amp per motor?

any advice.



Title: Re: Power supply
Post by: UltraMagnus on Sep 02, 2010, 09:01 pm
Quote
And - BTW - what has this  "capacitor" to do with it??


you need to smooth the supply after rectification.
Title: Re: Power supply
Post by: mpeuser on Sep 02, 2010, 09:09 pm
You will encounter a noticeable voltage drop from the H-bridge transistors at higher currents; that is why I still recommend the 7.5 volt supply....

You still have to decide for yourself, whether you want
- a simple discrete bridge
- a H-Bridge controller (+ additional transistors)
- (and that is best) a ready made board.

Here some examples of high current H-bridges
http://www.cirrus.com/en/pubs/proDatasheet/SA60U_M.pdf
http://www.pocketmagic.net/?p=508
http://www.roboticsconnection.com/p-77-10-amp-dual-h-bridge.aspx
http://www.modularcircuits.com/h-bridge.htm


BTW: I just encountered that simple explanation for H bridges:
http://www.barello.net/Papers/H-Bridge.pdf
http://www.modularcircuits.com/h-bridge_secrets1.htm
Title: Re: Power supply
Post by: dze on Sep 03, 2010, 12:45 am
deSilva@ just a short note, while reading through your links

the diy h-bridge supports up to 10A of current but the µModule supports up to 16A. the specification is still gibberish to me. what does it mean? how do i interface with the arduino through rs-232?

are there any other boards out there, which is relatively cheap <20? that could suit my needs?
Title: Re: Power supply
Post by: dze on Sep 03, 2010, 12:53 am
also i don't need the motor to run backward or forwards, it's just one direction that i need. so maybe i do not need a h-bridge.

Title: Re: Power supply
Post by: mpeuser on Sep 03, 2010, 01:06 am
I think all boards for 10 to 20 amps will be > $20... They main reason is that they contain a lot of protective means, among them stall detection...

As I said many postings ago, that what you need is just a transistor; I should recommend a logic level FET type... In some posting - maybe not in this thread - I had given a small list of inexpensive ones. There must be some tutorial explaining this most simple interface..... Note that you will need a large heatsink!

Edit
----
http://www.earthshineelectronics.com/files/ASKManualRev4.pdf
Look at project 11 (and also at the other projects....)
Title: Re: Power supply
Post by: dze on Sep 03, 2010, 12:44 pm
i'm currently looking at trying to diy me a motor driver for load up to 12 amp. Can someone recommend me some appropirate mosfet to suit my needs.

this link i find is pretty good but it's driving at 24 v 40 amps.
http://hades.mech.northwestern.edu/index.php/Driving_a_high_current_DC_Motor_using_an_H-bridge

my needs are 7.5v at 12 amps. there will be six of such motors. so i think i would build single motor drivers for each motor.

there are tons of schmectics on the net about h-bridges but can someone direct me more closely (schematics and parts) to my needs?

thanks desilva, for your links and pdf. i guess i'm skipping the chapters and working towards my concept/needs.

thanks for any advice!

Title: Re: Power supply
Post by: billhowl on Sep 03, 2010, 02:02 pm
If you are not control the speed of the motor, you can use relays to control the motor on/off like this
http://www.arduino.cc/playground/uploads/Main/relays.pdf
you must get relays that can switch 12A
Title: Re: Power supply
Post by: dze on Sep 03, 2010, 03:32 pm
i need speed control, pwm but not direction.
Title: Re: Power supply
Post by: Grumpy_Mike on Sep 03, 2010, 03:42 pm
You can use this one:-
http://uk.farnell.com/international-rectifier/irfb4228pbf/mosfet-n-ch-150v-83a-to220ab/dp/1704509

It takes at least a 10V gate signal to turn it on fully so you drive it from the arduino using a transistor with the collector resistor to 12V. It has an on resistance of 0.015R and can handle a maximum of 83A so there is plenty of margin.
Title: Re: Power supply
Post by: mpeuser on Sep 03, 2010, 05:27 pm
What Mike said had been said already sometimes in this thread. Seems we are ready for another turn of the wheel..... Is this a rat race?
Title: Re: Power supply
Post by: billhowl on Sep 05, 2010, 01:01 pm
(http://us1.webpublications.com.au/static/images/articles/i1101/110145_2lo.jpg)
This is an example of how to drive motor up to 40A using Power Mosfets (http://www.siliconchip.com.au/cms/A_110145/article.html) Q5-Q8 by using 3 transistors Q1-Q3.
12V-24V High-Current DC Motor Speed Controller (http://320volt.com/pic16f88-yuksek-akimli-gostergeli-12v-24v-motor-hiz-kontrolu/)


Title: Re: Power supply
Post by: mpeuser on Sep 05, 2010, 01:31 pm
This is a fine circuit with a lot of schnick-schnack in it. Note that it can be reduced to one single logic level MOSFET with a siffiently large heat sink!

80% of the circuit has to do with the PIC (which can be substituted by the Arduino; 10% is current sense (which is important!).