# Thread: Power Supply Suggestions please..

1. Originally Posted by Ricardoco
The other things range from 12v to 32v but the contactors can be what ever i want when i order them.
Presumably the contactors are just to switch these other things on and off?
The absolute minimum you can get from the transformer you have bought is by using one 24v winding, which when rectified will give 24*2^0.5-1.1=32.8V which is clearly above 32V so probably not much use. Also the tolerance on the mains voltage (230V +10% - 6%) means that it could be up to 32.8*1.1=36.1V.

How much power do these other things need? Can you provide a list of voltage and current or power that each device uses so we can work out the best transformer? It sounds like you'd be much better off with a separate transformer, perhaps 16V.

2. Originally Posted by Jonathan
Presumably the contactors are just to switch these other things on and off?
The absolute minimum you can get from the transformer you have bought is by using one 24v winding, which when rectified will give 24*2^0.5-1.1=32.8V which is clearly above 32V so probably not much use. Also the tolerance on the mains voltage (230V +10% - 6%) means that it could be up to 32.8*1.1=36.1V.

How much power do these other things need? Can you provide a list of voltage and current or power that each device uses so we can work out the best transformer? It sounds like you'd be much better off with a separate transformer, perhaps 16V.
If i was comming out and used non regulated that would be a problem but i will build a circuit to give me all the voltages i will ever need. Besides which they are on their way to me this moment.

rick

3. Originally Posted by Ricardoco
If i was comming out and used non regulated that would be a problem but i will build a circuit to give me all the voltages i will ever need. Besides
The problem is unless it's less than a couple of amps it's hard to regulate the voltage, since linear regulators are extremely inefficient so you can only use them for quite small currents, SMPS's are quite difficult to design and adding more transformers is rather illogical, so I'll be interested to see how you plan to change the voltage. Also if the other appliances only use a small amount of current (making it reasonable to use linear regulators), then the transformers are probably several times bigger than they need to be.

4. Originally Posted by Jonathan
The problem is unless it's less than a couple of amps it's hard to regulate the voltage, since linear regulators are extremely inefficient so you can only use them for quite small currents, SMPS's are quite difficult to design and adding more transformers is rather illogical, so I'll be interested to see how you plan to change the voltage. Also if the other appliances only use a small amount of current (making it reasonable to use linear regulators), then the transformers are probably several times bigger than they need to be.
So you really think that they will be too much for 5 steppers and a few low amp (Less than 5A) power supplies providing 12V 18V 24V and maybe even 36v. I will be using circuits based on LM317's (or equiv) driving 2n3055s...

Rick

5. Jonathan, Check your mail..

6. Originally Posted by Ricardoco
So you really think that they will be too much for 5 steppers
There's nothing wrong with having too much power available - it's just generally doesn't make economic sense.

Originally Posted by Ricardoco
and a few low amp (Less than 5A) power supplies providing 12V 18V 24V and maybe even 36v. I will be using circuits based on LM317's (or equiv) driving 2n3055s...
Earlier you said you didn't want to make a power supply when it was just a transformer, rectifier and capacitor, but now you're suggesting a lot more components to get what you could have made for less money by just using the correct voltage transformers. For the 12V and 24V you could have used a transformer with two 9V secondaries, which would be much cheaper, easier and more compact. 36V can be had from the stepper motor transformer. 18V from a 12V transformer.

A linear PSU made with LM317's and 2n3055 transistors may work, but the power it dissipates will be huge. Say you're using 12V at 5A - the voltage across the transistor Collector-Emitter junction is 32.8-12=20.8V. At 5 amps that means your transistor has to dissipate 20.8*5=104W. The absolute maximum rating for that transistor is 115W (TIP3055 only 90W), but that's not enough since as the transistor junction to case thermal resistance is thermal resistance is 1.5°C/W, even with a perfect heatsink it can only dissipate (150-25)/1.5=83W at 25°C ambient. Add to that another few of these circuits and your control box is going to turn into an oven unless you're planning on linking it to the spindle water cooling!

This concept is workable if the power dissipation is less, which is likely to be the case for the 24V output, but it seems a lot of hassle and expense when you could have just got a transformer, or two, with the right voltages and VA rating to start with. The only reason I'd do it is if the devices you're powering need the high power quality (low ripple in particular) delivered by a linear supply, which seems unlikely.

Originally Posted by Ricardoco
Jonathan, Check your mail..
I have...

7. Originally Posted by Jonathan
There's nothing wrong with having too much power available - it's just generally doesn't make economic sense.

Earlier you said you didn't want to make a power supply when it was just a transformer, rectifier and capacitor, but now you're suggesting a lot more components to get what you could have made for less money by just using the correct voltage transformers. For the 12V and 24V you could have used a transformer with two 9V secondaries, which would be much cheaper, easier and more compact. 36V can be had from the stepper motor transformer. 18V from a 12V transformer.

A linear PSU made with LM317's and 2n3055 transistors may work, but the power it dissipates will be huge. Say you're using 12V at 5A - the voltage across the transistor Collector-Emitter junction is 32.8-12=20.8V. At 5 amps that means your transistor has to dissipate 20.8*5=104W. The absolute maximum rating for that transistor is 115W (TIP3055 only 90W), but that's not enough since as the transistor junction to case thermal resistance is thermal resistance is 1.5°C/W, even with a perfect heatsink it can only dissipate (150-25)/1.5=83W at 25°C ambient. Add to that another few of these circuits and your control box is going to turn into an oven unless you're planning on linking it to the spindle water cooling!

This concept is workable if the power dissipation is less, which is likely to be the case for the 24V output, but it seems a lot of hassle and expense when you could have just got a transformer, or two, with the right voltages and VA rating to start with. The only reason I'd do it is if the devices you're powering need the high power quality (low ripple in particular) delivered by a linear supply, which seems unlikely.

I have...

OK i did ask about off the shelf din solutions giving me the ability to simply add extra units as and when i needed them and it seemed that opinion was against that, so as this isnt going to just look like a box of spagetti like a lot of projects i see turn out, i had to factor in not only what i want now but also guess what i may need in the future, the last thing i want is to keep stripping the damn thing down to do mods. I want to wire the Box, take into consideration what i need at the time of building and build it, and if that includes a 6" fan or two for cooling then so be it, shut the door on the cabinet and dont open it till the warning light and buzzer comes on, Yes there may be a heat dissaption requirement by the multiple 2n3055's but it wont be the first successfull supply ive build by any means, i think i build my first one when i was 12 and although that is long since been stripped for bits my current dual 0-30vdc supply was built by me 25yrs since, and im still very happy with it, although im always happy to try new ideas.

So You know what i have get your thinking head on and show me a better circuit solution. That would be magic

Rick

8. What wrong using directly an AC Source? for example use directly an transformer 220AC to 110AC?

Is better to use DC Instead AC?

Thanks

9. Originally Posted by Ricardoco
OK i did ask about off the shelf din solutions giving me the ability to simply add extra units as and when i needed them and it seemed that opinion was against that
Yes, since at the time there was no mention of powering other things. Still, I wouldn't use them for powering the other things or stepper motors since they're so much more expensive.

Originally Posted by Ricardoco
if that includes a 6" fan or two for cooling
My point is that may not be enough - if the transistors aren't rated for the power dissipation required it doesn't matter how big the fans are, it's not going to work (unless you split the power between multiple transistors).

Originally Posted by Ricardoco
So You know what i have
No, I don't know since you've not said exactly what current each of the other devices require and without that there's no point in further speculation.

Originally Posted by samsagaz
What wrong using directly an AC Source? for example use directly an transformer 220AC to 110AC?

Is better to use DC Instead AC?
This thread started by discussing which PSU is most suitable for powering stepper motor drivers, which in general run from a DC source so you have to rectify the transformer output to obtain that.

10. Ok, Ive recieved My toroidal which is 4x24 1200VA so using a series arrangement i will have the 50-80vac I require for the Drivers/steppers i will also have 1 or 2 free windings at approx 24vac which is what the contactors require, I will be using an ATX power supply for the smaller relays and the indicator 3v LED's and 5v for the bob as i have one and its easy, im still waiting for the Enclosure which should be here in the week sometime, and the caps im sure i have beneath a few cob webs somewhere.

Looks Like she will be getting that bigger coffee table she has been asking for. cos there wont be room on this one for the rest of the stuff by the end of the week...

Rick

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