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Hello all!
I'm working on a one off prototype of a project - nothing serious, just for personal use. I'm making a pan/tilt/slide rig for my camera, and I need to be able to run up to four stepper motors at once (pan, tilt, slide, and focus/aux motor). As the project is geared down 50:1 and I would like to be able to run video runs on it as well, I need a high voltage for my steppers to run off of (allows faster stepping time). Running off of a 12v input.
So this means I need a source capable of running 4 motors at 0.64A each (2.54A, thus 3A capability for some overhead).
If it matters, I am running using StepStick A4988 drivers.
I have done absolutely nothing using boost circuits, and have relatively small knowledge of engineering my own stuff, due to limited experience (I've only got a year of electronics class in high school).
I wouldn't want to burden anyone on here excessively trying to figure out a design, so if someone has any material that would help me figure out just what I am doing that would be great (webpages, books, et cetera).
Right now I am looking at using either of these to run the boost portion of the circuit, and have no idea if they will work, or if one is better than the other. I do like keeping it in a TO-220 package simply because it is easy to find a heatsink for a chip (and this is likely to produce a lot of heat). Willing to consider other chips though, if they would work better.
http://www.digikey.com/product-detail/en/MC34166TG/MC34166TGOS-ND/919095
http://www.digikey.com/product-detail/en/LM2596TVADJG/LM2596TVADJGOS-ND/2003293
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30v is somewhat strange voltage for motors? You sure they need 30v? You're looking at 90 watts of power... that's quite a few amps at 12v.
Both of those ICs aren't capable to produce 3A when boosting voltage. The internal current on the mosfet is much higher than 3A when boosting voltage so you can't reach that 3A the parts are rated for.
My advice would be to create an account on ti.com (it's free) and then use the Webbench tool they have to see a bunch of designs. You need to login to see the schematic, list of parts and so on... once you select a design you can then click on parts and select from a list alternative, for example to change from a surface mount to254 to a to-220 that's through hole.
Here's for example a simple circuit they recommend, using LM3478.. if you login and enter the parameters in the software, you can also see the part numbers and what parameters are important (so you can find alternatives manually or pick something the software suggests):
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Another solution is a pre-made module off eBay for less than $10. Look for "boost converter".
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The May 2011 Silicon Chip features an adjustable boost converter circuit for applications such as in-car laptop charging; its voltage and power levels are comparable with what you want.
http://archive.siliconchip.com.au/static/images/articles/i1124/112454_8mg.jpg
http://archive.siliconchip.com.au/static/images/articles/i1124/112454_5mg.jpg
You don't need to choose a fancy expensive chip, your good old cheap jellybean 34063 will do it, with a suitably chosen external MOSFET and beefy inductor and diode etc.
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I have used these modules with pretty good success.
http://www.ebay.com/itm/DC-DC-100W-Constant-Current-Boost-Step-up-Module-Mobile-Power-Supply-LED-Driver-/300925643943?pt=LH_DefaultDomain_0&hash=item461090eca7 -
Or maybe its bigger brother, from the same store.
http://www.ebay.com/itm/New-800W-Boost-DC-DC-Converter-Power-Supply-Step-up-Module-10A-12-80V-to-12-80V-/281166293173
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I have used these modules with pretty good success.
http://www.ebay.com/itm/DC-DC-100W-Constant-Current-Boost-Step-up-Module-Mobile-Power-Supply-LED-Driver-/300925643943?pt=LH_DefaultDomain_0&hash=item461090eca7
My personal experience, I have something similar (no constant current though)
http://www.ebay.com.au/itm/351023576452
It seemed fairly happy giving 28volts at 2.3amps (65watts) with a 12volts input but I did get the heatsink to 90 degrees with no active cooling :p
So if you NEED a constant 90watts, I'd be looking for something bigger
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LT1270 or LT1270A, if you need a single chip solution, else fashion a boost using a small controller IC (3842?)
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Thanks for all the replies. I looked around a bit on TI's site and am still working stuff out there- but a cheap module might be a workable solution.
30v is somewhat strange voltage for motors? You sure they need 30v? You're looking at 90 watts of power... that's quite a few amps at 12v.
I'm looking for 24-30v. It is a rather high voltage for the motors (they are rated at 12v) but from my understanding the voltage determines the speed of the motor (to some extent) while the current mainly affects the torque output.
Both of those ICs aren't capable to produce 3A when boosting voltage. The internal current on the mosfet is much higher than 3A when boosting voltage so you can't reach that 3A the parts are rated for.
This is due to the inductance of the coils, as it takes a certain time for the coils to produce their full torque at any given voltage.
But you probably know all that...
Since it is geared pretty high (I plan on using it for videos as well as time lapse photography) I need quite a range of speed, from a few degrees a second to hundredths of degrees a minute. Higher voltage = higher speed.
It is some pretty crazy amperages, and will likely pull near 10A @ 12v when all is said and done - but that is a maximum. I doubt that 4 steppers will be running 100% at any given time but will design with that in mind. Pretty scary dealing with all those amps with little training, but I'll learn.
Thanks for the heads up on the chips. Figured I'd ask. Totally worth it!My personal experience, I have something similar (no constant current though)
Constant current is not an issue, the stepper drivers have current limiters.
It seemed fairly happy giving 28volts at 2.3amps (65watts) with a 12volts input but I did get the heatsink to 90 degrees with no active cooling :p
So if you NEED a constant 90watts, I'd be looking for something bigger
90 degrees C is a bit concerning though as the project will be encased in a metal box. I might just have room for active cooling, though I was not planning on it. Regardless I think the only time all 4 motors will be running is doing a video run, which will mostly be short clips. I just need something that can handle the current if the need arises for a short period of time - that might just be it.
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Id be more worried about the temperature of the motors than the temp of the boost regulator if you're planning to run 12volt motors at 30volts
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Id be more worried about the temperature of the motors than the temp of the boost regulator if you're planning to run 12volt motors at 30volts
I believe that it is fine for the motors as long as I have a current "chopping" driver (which I do). This should limit the motors to their max of .64A regardless of the voltage.
From a Pololu pageQuoteTo achieve high step rates, the motor supply is typically much higher than would be permissible without active current limiting. For instance, a typical stepper motor might have a maximum current rating of 1 A with a 5? coil resistance, which would indicate a maximum motor supply of 5 V. Using such a motor with 12 V would allow higher step rates, but the current must actively be limited to under 1 A to prevent damage to the motor.
I borrowed a power supply a while back and did a test at 30v and ran everything for about 20 minutes without ill effect, everything seemed normal. However once I did set the current limiter at .8A or some such, and the motors very quickly got hot.
That part was exciting
Of course, if I am misinformed, please let me know before I blow more stuff up
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Well, now I feel stupid
If I wire the motor in a half-coil bipolar configuration, it will be able to achieve higher speeds, but at a lower torque. I'll have to do some torque testing, but this would reduce my power needs by half! -
Or maybe its bigger brother, from the same store.
http://www.ebay.com/itm/New-800W-Boost-DC-DC-Converter-Power-Supply-Step-up-Module-10A-12-80V-to-12-80V-/281166293173
No constant current capability though. -
I have used these modules with pretty good success.
http://www.ebay.com/itm/DC-DC-100W-Constant-Current-Boost-Step-up-Module-Mobile-Power-Supply-LED-Driver-/300925643943?pt=LH_DefaultDomain_0&hash=item461090eca7
My personal experience, I have something similar (no constant current though)
http://www.ebay.com.au/itm/351023576452
It seemed fairly happy giving 28volts at 2.3amps (65watts) with a 12volts input but I did get the heatsink to 90 degrees with no active cooling :p
So if you NEED a constant 90watts, I'd be looking for something bigger
Just an update for anyone playing along at home.
I bought some of the constant current versions, and the heatsinks are about twice the area to the cheaper, non constant current versions I linked to, So I assume they'd handle 65watts with just passive cooling without issue
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Buy a second 12 volt battery,connect them in series,& you have 24 volts with no silly Electronics!
