Time for a stupid power supply question

[sdantonio]

my proposed system will be as follows (sort of)

Breakout board
3 driver boards 0-35VDC (0-35VDC chopped output and 12VDC fixed output)
3 motors 4VDC, 2.8A

now it seems logical to me that I could get away with a minimum power supply of 12VDC, 9A.

My tristed view of potential and current

I view potential like a waterfall. If you stand under the waterfall then the power with which the water hits you is a function of the height of the waterfall. But in any case the water is forced upon you by gravity like a power supply forces the system to take whatever voltage it puts out (i.e. the reason to chop the voltage down to 2.8VDC per motor).

I view current like a large quiet lake. I (the motor) can go down to the lake and take a teaspoon full of water and use it if that is all that I need, or I can go and get a 5 gallon container full if I need that much. The currect is not forced on the motors, but is there as a reserve that the motors can draw on when they need it.

So, applying this analogy I should be able to use any power supple from 12VDC, 9A up to 35VDC, 9 billion Amps (assuming one exists that big).

So something like a

12VDC, 20A,
or 12-15V 30A (my first choice so far)

supply would be just great for the application,

But

13.8 VDC, 8A

would be a bit small.

Thanks
Steven

[CJL5585]

Well, I read your post, but there is something you failed to consider: The top speed of the machine is somewhat determined by the driver voltage.

I would recommend that you use a power supply voltage between 24 and 30 Volts DC.

Hope this helps,
Jerry

[pminmo]

Steven,
Lake, almost. motors are inductive, they have a charge/discharge rate. Rule of thumb, the faster the rate the faster they can step. Same motor and driver will step faster under load on a higher power supply. i.e. faster IPS.

BIG HINT, stepmotor manufacturers typically do their torque/speed curves at many times higher than the coil rating.

[sdantonio]

I would recommend that you use a power supply voltage between 24 and 30 Volts DC.

hi Jerry,

Now I'm confused. If my motors are rated at 4VDC, then, I was under the belief that they would burn out at anything over 4V, and at 4V they would be running at top speed. Or is that taken care of by the chopper? Do I need about 12V per motor to power the whole thing?

If I go 24 to 30V then what value would you recomend for amperage?

Is there any tutorials online that anyone is aware of that describes how to size a power supply to a set of motors?

[sdantonio]

Hi Phil,

I think this discussion is going to bring me back to your spmpleps using the 24VAC 10A Transformer (and I will have to ask a few questions about that schematic).

Small setback. I opened the digikey box this weekend to start etching my boards and found they they sent me the wrong copper, so I ordered another piece from mouser. They also found the 330ohm 5 pin resister network for me (and then mouser called Bourns and struck a deal so I don't have to order the minimum of 2000 since it's a non-stock special item). If you would like to check this number to see if it is the right one I would be very greatful.

(Mouser #) 652-4606X-101-330 6 0.190 1
(Bournes #) 4606X-101-331
Bourns SIP Conformal Coated Resist

Thanks,
Steven

[erase42]

hi steve,
you didnt mention if it is steppers or servos. in the case of steppers at least, the rule of thumb is to run them at 4 to 5 times the rated voltage. my machine has 4 steppers that all run at the same time. ive got a 24 v 12 a power supply and im probably a little underpowered especially on motions requiring all 4 motors.

[ger21]

I'm guessing your building the Allegro based board? 3977 or something like that? Ideally, you want to run the motors at 10-20 times the rated voltage. That chip has a Max rating of 35V, and you should probably stay around 30V to be safe. So you can get about 7x the rated voltage, which isn't too bad. 12V will severly limit your speed.

As for current, because of the way a chopper drive works, the most current you're likely to need is about 2/3 the motors rated voltage, or 1.87A, time 3 motors = 5.6A, so a 6 amp supply will work. The Xylotex boards are based on the same chip, and are for all practical purposes the same drive, and they say a 4.5A supply is sufficient. But I'd go with at least 6A. More won't hurt, but you really shouldn't need it.

So, bottom line, is get a 24V-30V supply, 6A or higher. This will run all 3 motors no problem.

[pminmo]

Steve,
Help the old grey matter out here. 330 ohm network, for what board?

[sdantonio]

I just found this writeup online (one of the Computer Science guys at Murray State College.

I assume that if I do something like this and run between the -12 ans +12V terminals (giving me 24V total), and if I use a big power supply like a 475watt one I should be able to get around 30 amps.

And there are a ton of them on ebay for about $6 (and probably more at my local dump, especially after all the kidies got their new christmas computers).

For some wierd reason I have no problem building driver boards, but I would rather leave the power supplies to the experts.

Steven

[CJL5585]

Originally Posted by sdantonio I just found this writeup online (one of the Computer Science guys at Murray State College. I assume that if I do something like this and run between the -12 ans +12V terminals (giving me 24V total), and if I use a big power supply like a 475watt one I should be able to get around 30 amps. And there are a ton of them on ebay for about $6 (and probably more at my local dump, especially after all the kidies got their new christmas computers). For some wierd reason I have no problem building driver boards, but I would rather leave the power supplies to the experts. Steven

Sorry to be the messenger of bad news:
On the 475 watt supply if you look at the specs you will see that:

The +12 Volt side specifies it is good for 20 Amps.
The -12 Volt side specifies it is good for 2.0 Amps.

In order to use the +12 and -12 to get the 24 Volts for your project, both sides of the supply will have to be rated for the same amount of current.

So, the -12 Volt side would also have to be capable of producing 20 Amps. In the present configuration the 24 Volts would have a max current rating of 2 Amps. THE CURRENT THAT FLOWS IN ONE SIDE MUST FLOW OUT THE OTHER SIDE.

Oh, by the way, power supplies are easier to build and troubleshoot than driver boards any day.

Jerry

[sdantonio]

Well, I tried anyway. May be I should have paid more attention in the one electronics class I was forced to take 10 years ago

And I thought I was onto something here .

Steven