Go Down

Topic: Power supply (Read 6812 times) previous topic - next topic

dze

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

Grumpy_Mike

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.

UltraMagnus

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.

Grumpy_Mike

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.

mpeuser

#4
Sep 01, 2010, 04:19 pm Last Edit: Sep 01, 2010, 04:21 pm by mpeuser Reason: 1
- 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....

UltraMagnus

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.

Grumpy_Mike

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.

UltraMagnus

Quote
See what I mean.


No, I don't, why don't you explain rather than gloating.

mpeuser

#8
Sep 02, 2010, 12:53 am Last Edit: Sep 02, 2010, 01:47 am by mpeuser Reason: 1
;) 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??

Lyght

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.

mpeuser

@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  ;)

billhowl

dze@: May be you can try to get from eBay like this 350W 5V DC 50A Regulated Switching Power Supply , it can adjust to 5.6V,  or you get this 350W 7.5V 46A Regulated Switching Power Supply  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.

mpeuser

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!

Grumpy_Mike

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.  ;)

Homer_Manalo

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.

Go Up