Anyone have a good suggestion for a 12V step-up regulator? I am planning to use the Moteino to control a 12V 250mA stepper motor, and it's working fine right now using a wall wart 12V supply. I want to end up using AA batteries, though, and 8 is a little much. 4xAA@6V is more reasonable and probably makes the Moteino regulator a little happier, but I need a step-up for the stepper (heh). I am considering http://www.digikey.com/product-detail/en/texas-instruments/TPS6734IP/296-3226-5-ND/370118 (http://www.digikey.com/product-detail/en/texas-instruments/TPS6734IP/296-3226-5-ND/370118) but wondered if anyone else had a favorite. The TPS6734IP includes a logic-level switch to control whether the regulator is enabled or not, which is nice since I use a FET for that currently.
Quote from: snorp on March 25, 2016, 04:45:43 PM
Anyone have a good suggestion for a 12V step-up regulator? I am planning to use the Moteino to control a 12V 250mA stepper motor, and it's working fine right now using a wall wart 12V supply. I want to end up using AA batteries, though, and 8 is a little much. 4xAA@6V is more reasonable and probably makes the Moteino regulator a little happier, but I need a step-up for the stepper (heh). I am considering http://www.digikey.com/product-detail/en/texas-instruments/TPS6734IP/296-3226-5-ND/370118 (http://www.digikey.com/product-detail/en/texas-instruments/TPS6734IP/296-3226-5-ND/370118) but wondered if anyone else had a favorite. The TPS6734IP includes a logic-level switch to control whether the regulator is enabled or not, which is nice since I use a FET for that currently.
Since Mother Nature is such a 'b***h', if you want to get 12V 250mA out of your 3V 3000mAH AA, you will need to produce something in the order of 250mA x 12V/3V /0.8eff or 1.250A @ 3V for as long as you are stepping the motor at full power. It will work, but not for very long.
What duration to you need to run it and what is the interval between running it and sleeping?
Tom
Any boost regulator will need to be able to handle at least 3.75W of power to get 250mA at 12V (assuming 80% efficiency), the TPS6734IP you quoted isn't really close. Those regulator datasheets with internal FETs can be misleading, often the limit current is quotes as a typical value but you need minimum values, and those tend to be significantly less than typical values. I'd suggest using TI's web based Webbench Designer to select a suitable part e.g. LM3488, which uses an external FET. Also there can be peaks of current with any motor when starting from a stopped position (rather like a stall condition) so make sure your power supply can handle those peaks.
Mark.
Quote from: TomWS on March 26, 2016, 04:48:46 PM
Quote from: snorp on March 25, 2016, 04:45:43 PM
Anyone have a good suggestion for a 12V step-up regulator? I am planning to use the Moteino to control a 12V 250mA stepper motor, and it's working fine right now using a wall wart 12V supply. I want to end up using AA batteries, though, and 8 is a little much. 4xAA@6V is more reasonable and probably makes the Moteino regulator a little happier, but I need a step-up for the stepper (heh). I am considering http://www.digikey.com/product-detail/en/texas-instruments/TPS6734IP/296-3226-5-ND/370118 (http://www.digikey.com/product-detail/en/texas-instruments/TPS6734IP/296-3226-5-ND/370118) but wondered if anyone else had a favorite. The TPS6734IP includes a logic-level switch to control whether the regulator is enabled or not, which is nice since I use a FET for that currently.
Since Mother Nature is such a 'b***h', if you want to get 12V 250mA out of your 3V 3000mAH AA, you will need to produce something in the order of 250mA x 12V/3V /0.8eff or 1.250A @ 3V for as long as you are stepping the motor at full power. It will work, but not for very long.
Ah, I wasn't really sure how to calculate what the supply current would end up being, so that's good to know. I want to use 4 AA, though, so presumably that would be 12V/6V/0.8 or 625mA. That's a little easier to stomach.
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What duration to you need to run it and what is the interval between running it and sleeping?
I only need to run it for 5s twice a day, and the Moteino will be in low power listen mode otherwise. I figure I should be able to get a couple years out of the 4xAA with that kind of usage. Choosing a component for this regulator is a PITA, though. The datasheets are often not very clear about maximum load, though I guess I should take a hint when the typical load listed is like 120mA.
Quote from: perky on March 26, 2016, 06:37:35 PM
Any boost regulator will need to be able to handle at least 3.75W of power to get 250mA at 12V (assuming 80% efficiency), the TPS6734IP you quoted isn't really close. Those regulator datasheets with internal FETs can be misleading, often the limit current is quotes as a typical value but you need minimum values, and those tend to be significantly less than typical values. I'd suggest using TI's web based Webbench Designer to select a suitable part e.g. LM3488, which uses an external FET.
Thanks. I agree the datasheets seem pretty misleading. Even the LM3488 you reference only mentions a peak current (< 10us) of 1A, and no mention of what a nominal maximum is. Frustrating. I need a through-hole package anyway.
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Also there can be peaks of current with any motor when starting from a stopped position (rather like a stall condition) so make sure your power supply can handle those peaks.
Do steppers behave similarly to a traditional DC motor wrt inrush, though? My understanding was that they do not, but maybe it still makes sense to spec a regulator with some head room.
You're right, steppers have a resistance per phase which can be used to calculate the current. Assuming this is 250mA at 12V maybe you could use an LM2577T-12/NOPB, this is a TO-220 formed lead through-hole package but has a 3A internal switch rather than the lower 1.5A from DIL devices. There's an application circuit showing 12V out at 800mA from 5V input:
http://www.farnell.com/datasheets/1992141.pdf
Mark.
Quote from: perky on March 27, 2016, 04:35:27 PM
You're right, steppers have a resistance per phase which can be used to calculate the current. Assuming this is 250mA at 12V maybe you could use an LM2577T-12/NOPB, this is a TO-220 formed lead through-hole package but has a 3A internal switch rather than the lower 1.5A from DIL devices. There's an application circuit showing 12V out at 800mA from 5V input:
http://www.farnell.com/datasheets/1992141.pdf
Mark.
This is a good choice except that it doesn't have an enable input. However, if you power it from a load switch then you'll be able to completely turn it off when you're not using it. Good suggestion perky.
What kind of stepper driver are you using? The Allegro A4988 will drive this motor directly and comes in a wide variety of breakout boards. With this driver the current is ramped up so that you won't have any inrush issues. These are selling on eBay for about $1.50.
Tom
Thanks Tom. With most boost regulators there's a DC path from the input through the inductor and diode to the output, so even if they have an enable pin the output can never go below a diode drop of the input voltage. It's best to use a high side load switch (i.e. a P channel FET) on its input voltage if you want to isolate the circuit from taking any current.
Mark.
Quote from: perky on March 27, 2016, 07:19:41 PM
With most boost regulators there's a DC path from the input through the inductor and diode to the output, so even if they have an enable pin the output can never go below a diode drop of the input voltage. It's best to use a high side load switch (i.e. a P channel FET) on its input voltage if you want to isolate the circuit from taking any current.
Mark.
Mark, Good observation. Thanks.
@snorp, a 'back of the napkin' calculation tells me that your optimum setup would be three Lithium AA batteries giving you a nominal voltage of 5.4V, Mark's Boost Circuit (which will probably give you about 70% efficiency), and your Moteino running an average current of about 60uA. Obviously improving on anything will help. Ex: getting better than 60uA current on your Moteino (which is fairly easy if you follow good practices, hard to do if you don't) will allow a more optimum solution with a higher voltage battery pack. However, this mix should give you over a year and a half of battery life.
Tom
Quote from: TomWS on March 27, 2016, 06:01:33 PM
Quote from: perky on March 27, 2016, 04:35:27 PM
You're right, steppers have a resistance per phase which can be used to calculate the current. Assuming this is 250mA at 12V maybe you could use an LM2577T-12/NOPB, this is a TO-220 formed lead through-hole package but has a 3A internal switch rather than the lower 1.5A from DIL devices. There's an application circuit showing 12V out at 800mA from 5V input:
http://www.farnell.com/datasheets/1992141.pdf
Mark.
This is a good choice except that it doesn't have an enable input. However, if you power it from a load switch then you'll be able to completely turn it off when you're not using it. Good suggestion perky.
Yeah, and at $6.50 a piece + the cost of a FET to switch, it's kind of expensive. Will consider, though.
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What kind of stepper driver are you using? The Allegro A4988 will drive this motor directly and comes in a wide variety of breakout boards. With this driver the current is ramped up so that you won't have any inrush issues. These are selling on eBay for about $1.50.
I'm using one of those ultra-cheap 28BYJ that come with a board containing a ULN2003A. The ULN2003A is in a DIP socket that I can easily remove and slap into my own PCB. Since the 28BYJ is unipolar, I don't need a H-bridge or anything.
There are 5V versions of the 28BYJ, but it doesn't seem to have enough torque to do the job. There are so many variations of this motor, though, who knows what I really got. The 12V 1/64 I have works well, though, so I'm going with that.
Quote from: TomWS on March 28, 2016, 06:35:54 AM
@snorp, a 'back of the napkin' calculation tells me that your optimum setup would be three Lithium AA batteries giving you a nominal voltage of 5.4V, Mark's Boost Circuit (which will probably give you about 70% efficiency), and your Moteino running an average current of about 60uA.
Hmm, Google and forum search aren't finding anything for Mark's Boost Circuit. Do you have a link? (EDIT: perky is Mark, whoops)
Right now the Moteino uses about 100uA while in listen mode (~1000ms idle with ~4ms rx, and I have a pullup enabled for a button). I could probably improve that some more. It's possible a 2ms rx may work which would let me keep the responsiveness. BTW, Tom, I've done a lot of work on RFM69_WL to expose more listen mode stuff. It chooses the closest coefficient and resolution for any listen/rx values you want. I'll send that to you at some point soon-ish.
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Obviously improving on anything will help. Ex: getting better than 60uA current on your Moteino (which is fairly easy if you follow good practices, hard to do if you don't) will allow a more optimum solution with a higher voltage battery pack. However, this mix should give you over a year and a half of battery life.
Hmm, I'm totally off on my battery life math somehow. 3 x Energizer L91 should be 5.1V (3 * 1.7) and at least 3Ah per battery for a total of 9Ah total according to the datasheet here[0]. If we estimate 840mA for the motor (12 / 5.1 / .7 * 250), we have about 100uA to run it for 10s (10 / 86400 * 840). Add to that the 60uA for the Moteino and we're at about 160uA total average consumption, so 9000 / .16 = 56250 hours or 6.4 years! That's...slightly different than your estimate of 1.5 years. What did I do wrong?
If I do find some way to use 8xAA to get 12V to both the motor and Moteino, do you see any major problems with that? Obviously the motor is happy, but driving the Moteino at 12V? The datasheet says it should be fine, but Felix has warned before that anything above 9V will generate some heat. How much heat exactly, and how much energy is wasted? I am not having a good time with the MCP1703 data sheet there. I think it will need to dissipate ~500mW which seems like a lot...
Thanks Tom and perky for your help, I really appreciate it.
(0) http://data.energizer.com/PDFs/l91.pdf (http://data.energizer.com/PDFs/l91.pdf)
OK, another (significantly cheaper) suggestion, the MC33063APE4 which has a quoted max switch current of 1.5A. This is probably still too low to get 250mA out at 12V though, so it can be boosted with a cheap NPN transistor.
http://www.farnell.com/datasheets/1974516.pdf
Mark.
Quote from: perky on March 28, 2016, 11:47:14 AM
OK, another (significantly cheaper) suggestion, the MC33063APE4 which has a quoted max switch current of 1.5A. This is probably still too low to get 250mA out at 12V though, so it can be boosted with a cheap NPN transistor.
http://www.farnell.com/datasheets/1974516.pdf
That does look significantly cheaper. I'm confused about why 1.5A switching isn't enough, though, if Vin is ~6V (4xAA). Even at 70% efficiency (might be a little worse than that with this regulator?) that's only 715mA. Sorry if I'm being thick, just trying to better understand how to spec something like this.
Let's say for arguments sake you were converting 6V to 12V and you need 250mA output current. This means the inductor will be ramping up from 0 to Ipeak for the first half of a cycle, then ramping down from Ipeak back to 0 for the second half as it dumps it's current to the output. Note that the inductor only supplies current to the output for the second half of the cycle, that's important later.
Now the average current from the source, multiplied by the source voltage, is the power. If we assume 100% efficiency that's the same as the output power. The input current has to be double the output current in this example, so the average input current has to be 500mA. That's the average across the whole cycle.
The current waveform in the first half of the cycle looks like a saw tooth, it ramps up linearly from zero to Ipeak. The average of this is Ipeak/2. Similarly the output current ramps down from Ipeak to 0. The average of this is also Ipeak/2 , but since the inductor only provides current to the output in the second half of the cycle the Ipeak actually has to be *four* times our average output current, in our case that's 1A. This also works with the input as this supplies current over the whole cycle, and it's average is Ipeak/2 which is 500mA.
So on the face of it we should in theory get satisfaction with this. Efficiencies and component tolerances will eat into this, and you'll need some design margin, but I've changed my mind - this is probably going to be OK without an external NPN transistor.
Edit: Just to confirm that thinking, look at section 9.2.2.2 on page 14 of the MC33063 datasheet where you'll find some equations for a step up regulator. The ratio of ramp up to ramp down is ton/toff, and assuming Vin(min)=6, Vf=0 and Vsat=0 this gives 1:1. The equation for Ipk(switch) is 2*Iout(max)*((ton/toff)+1), i.e. 4*Iout.
Quote from: snorp on March 28, 2016, 11:39:07 AM
Hmm, I'm totally off on my battery life math somehow. 3 x Energizer L91 should be 5.1V (3 * 1.7) and at least 3Ah per battery for a total of 9Ah total according to the datasheet here[0]. If we estimate 840mA for the motor (12 / 5.1 / .7 * 250), we have about 100uA to run it for 10s (10 / 86400 * 840). Add to that the 60uA for the Moteino and we're at about 160uA total average consumption, so 9000 / .16 = 56250 hours or 6.4 years! That's...slightly different than your estimate of 1.5 years. What did I do wrong?
If your batteries are in series to add voltage, you don't get to add their charge (Ah) as well. You can have your 5.1V @ 3Ah, or in theory 9Ah @ 1.7V (parallel - not recommended), but not both.
Sigh...that makes sense.
Quote from: snorp on March 28, 2016, 08:52:26 PM
Sigh...that makes sense.
:)
Like I said Mother Nature is a ....
The good news is that Mother Nature is very 'generous' and has many choices for you to consider (as long as you recognize that 'she' has you by the... uh, well, you know...).
Hey! Your motors look like the cheapest, most effective actuators on the planet! Use them wisely! Of course, depending on your torque needs, the 5V version might be a better choice from a PS perspective. I just ordered 5 of them!
Tom
@snorp, Attached below is how I would set up the power for your stepper. I would try to run the stepper from 6V and, if that's not enough power, then put the boost circuit in.
In all cases, however, I'd run the Moteino from 2xAA without an internal VR to minimize unnecessary voltage conversion losses, then the other 2xAA provide the extra voltage for your motor. You could rotate the batteries every six months if you wanted optimum wear, but it's probably not worth it if you're diligent about low power consumption on the Moteino SW.
Tom
Worth looking into servos as well which have the DC motor, gears and electronics all in one handy package. You can get really cheap servos from places like HobbyKing, and ServoCity have app notes on how to drive them.
Mark.
Quote from: TomWS on March 29, 2016, 08:25:55 AM
@snorp, Attached below is how I would set up the power for your stepper. I would try to run the stepper from 6V and, if that's not enough power, then put the boost circuit in.
In all cases, however, I'd run the Moteino from 2xAA without an internal VR to minimize unnecessary voltage conversion losses, then the other 2xAA provide the extra voltage for your motor. You could rotate the batteries every six months if you wanted optimum wear, but it's probably not worth it if you're diligent about low power consumption on the Moteino SW.
Hmm, how much loss will there be to regulate the 6V to 3.3V? Only a few uA, surely? I'm measuring 22uA right now during the idle phase of listen mode, where most of the time will be spent. I found I can set the RX time to 1ms (which uses 17ma) and still receive my commands, so the average consumption without running the motor is a respectable 39uA. I am not sure it's worth the effort to split the batteries up like you have, but I do appreciate the suggestion. I could get it lower by disabling the pullup for a push button switch I'm using, but not sure how I would do that reliably while still allowing the button to do its thing. Maybe an external pullup with a higher value resistor would be more conservative?
I had ordered a 5V motor but got a 12V one, and it doesn't have enough torque when run at 5V. Because I'm a moron, I assumed that meant the 5V models of the motor would perform similarly, but that's almost certainly false. Ordered some 5V ones from another place, so we'll see how they do. Splitting the batteries probably makes more sense if I end up needing the 12V. Thanks for the help!
What's the normal state of the pushbutton switch? Is it normally sinking current? Is it used as a wakeup switch?
It's easy if you regularly poll it or poll it once (like a mode select switch). Basically during the polling routine you turn on the pull-up, read the status and if the input is high the swich is off and you can leave the pull-up on. if it's low the switch is pulling it to ground and sinking current, so turn off the pull-up and either ground or turn a pull-down on the pin. You don't want to leave the input floating, that'll cause excessive current by itself.
If you consider an MCU pull-up as being around 100k it would take 33uA at 3.3V.
Mark.
Quote from: snorp on March 29, 2016, 03:37:13 PM
Hmm, how much loss will there be to regulate the 6V to 3.3V? Only a few uA, surely?
Hmmmm, good question. Let's figure it out. You say your Moteino draws 39uA average, we'll use that number.
Case 1: Running directly off 2 batteries at 39uA consumes 341mAH per year. Not bad, you'll get plenty of life with that.
Case 2: Running off 4 batteries at 39uA plus 2uA quiescent current for the VR. 359mAH, still not bad but you've consumed twice the number of batteries...
Tom
PS: Also perky's advice on the pullup unless you need it for wake on state change, in which case, you should make sure that the NORMAL, non-active state, is OPEN on the switch.
Quote from: WhiteHare on March 29, 2016, 11:02:08 AM
If torque is an issue, it's worth mentioning (in case you're not already aware) that you can get very high torques with low voltages (3v or less) and surprisingly low currents (easily 30ma or less) with just ordinary, inexpensive, low-RPM DC motors. Most projects don't need a stepper motor, which typically does require high current to get decent torque and/or holding power. Also, stepper motors tend to be noisy compared to regular motors. If you're just operating for 5 seconds twice a day (maybe to open and close some blinds for instance), most likely a highly geared regular motor will suffice, and your batteries will last much longer too.
I did briefly consider a gear motor, but I wasn't really able to find any that seem suitable. I want to turn fairly slowly (<= 5 RPM), and need to position it with a reasonable amount of precision (encoder? hall effect sensor?). I actually started with a hobby servo, but those are pretty noisy and there doesn't seem to be a good way to control the speed. The accuracy left something to be desired, too, but maybe I just had a crappy couple of servos. These 28BYJ steppers are dirt cheap (about 1/8th the cost of even a crappy servo!) and have pretty good precision.
Quote from: perky on March 29, 2016, 03:55:11 PM
What's the normal state of the pushbutton switch? Is it normally sinking current? Is it used as a wakeup switch?
It's a normally-open (Omron B3F) tactile switch. I am using the internal pullup (INPUT_PULLUP) with the switch connected to pin 3 and DN, so it should normally (EDIT: not) be sinking current.
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It's easy if you regularly poll it or poll it once (like a mode select switch). Basically during the polling routine you turn on the pull-up, read the status and if the input is high the swich is off and you can leave the pull-up on. if it's low the switch is pulling it to ground and sinking current, so turn off the pull-up and either ground or turn a pull-down on the pin. You don't want to leave the input floating, that'll cause excessive current by itself.
If you consider an MCU pull-up as being around 100k it would take 33uA at 3.3V.
I do use it to wake-up (via interrupt), because otherwise we're just waiting waiting for interrupts from the radio and the CPU is almost completely off. The button resets my stepper origin position, so it's useful for getting things set up properly.
I disabled the INPUT_PULLUP and my power consumption did not measurably change (still 22uA), so I suppose the pin itself has a lot more impedance. The doc here[0] says that input mode puts something like 100MOhm in front of the pin, so I guess that makes sense. I guess I can stop worrying about the pullup.
(0) https://www.arduino.cc/en/Reference/Constants
I should move this to a new topic, but FWIW, I received my 28byj-48 steppers yesterday and played around with one today. The motors were claimed to be 5V (see below) and I ran them off a 6V SLA battery and the supplied ULN2003 driver board.
Interesting results:
1. Current drawn when stepping at 1000 steps per second (8 step sequence) averages about 234mA in one direction, about 217mA in the reverse direction. Not sure why there's a difference, but the 'specs' do cite different 'pullin' & 'pullout' torques (whatever that is in a stepper!). And that includes the silly LEDs on the driver board.
2. At this speed there is plenty of power for my needs. Speed at this pulse rate is slightly less than 15RPM.
3. Most significantly (and I totally missed this detail looking at the ULN2003 datasheet) is that, with all the windings off (ie, the four control lines driven to ground) there is NO power drawn by the motor or ULN2003. You don't need no stinkin' load switch. This makes sense when you think that the ULN2003 is nothing but a bunch of NPN darlington transistors. Don't bias the base, there is no current. There may be some leakage, but it's below 1uA...
Re motor 'voltage'. I'll wager that there is no difference between a 12V motor and a 5V motor other than the max torque and max speed you can get out of it. Run these babies at 6V and you've got a nice little actuator...
BTW, for some reason the Arduino stepper library in my 1.6.0 IDE setup did nothing useful. I'll have to chase it down, but it was simple enough to spin a bidirectional step function (the IDE only does 4 step sequence anyway) so I'm using my own.
UPDATE: I did get the library working (sort of). I didn't realize it was 4 stepping instead of 8 so my speed setting was twice what I expected, but, also, this motor does not like 4 stepping very much. 8 stepping is much smoother, higher torque and, as a consequence, you can get it to rotate at a faster speed.
Tom
Quote from: TomWS on March 31, 2016, 01:09:32 PM
I should move this to a new topic, but FWIW, I received my 28byj-48 steppers yesterday and played around with one today. The motors were claimed to be 5V (see below) and I ran them off a 6V SLA battery and the supplied ULN2003 driver board.
I got my 5V motor today as well, and powering with 4xAA seems to give similar torque as the 12V. Woo! I was going to turn it into a bipolar motor to get more torque if I had to (which is apparently pretty easy on these), but it's nice that I won't need to.
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<snip>
3. Most significantly (and I totally missed this detail looking at the ULN2003 datasheet) is that, with all the windings off (ie, the four control lines driven to ground) there is NO power drawn by the motor or ULN2003. You don't need no stinkin' load switch. This makes sense when you think that the ULN2003 is nothing but a bunch of NPN darlington transistors. Don't bias the base, there is no current. There may be some leakage, but it's below 1uA...
I thought I checked this before and saw some power consumption, but I checked again and you're right. Guess I don't need the FET anymore either. This is going to be a pretty boring PCB.
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BTW, for some reason the Arduino stepper library in my 1.6.0 IDE setup did nothing useful. I'll have to chase it down, but it was simple enough to spin a bidirectional step function (the IDE only does 4 step sequence anyway) so I'm using my own.
UPDATE: I did get the library working (sort of). I didn't realize it was 4 stepping instead of 8 so my speed setting was twice what I expected, but, also, this motor does not like 4 stepping very much. 8 stepping is much smoother, higher torque and, as a consequence, you can get it to rotate at a faster speed.
Yeah, also the correct sequence seems to be 1-3-2-4, which I don't believe is standard. I'm using AccelStepper with the HALF4WIRE mode instead of the built-in stepper library. Works well and provides nice smooth accel/decel.
Quote from: snorp on March 31, 2016, 04:44:31 PM
I got my 5V motor today as well, and powering with 4xAA seems to give similar torque as the 12V. Woo! I was going to turn it into a bipolar motor to get more torque if I had to (which is apparently pretty easy on these), but it's nice that I won't need to.
Since you have both motors in hand, can you measure the respective winding resistances and see if they are truly different motors?
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I thought I checked this before and saw some power consumption, but I checked again and you're right. Guess I don't need the FET anymore either. This is going to be a pretty boring PCB.
<g> They're the best kind! Very reliable...
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Yeah, also the correct sequence seems to be 1-3-2-4, which I don't believe is standard. I'm using AccelStepper with the HALF4WIRE mode instead of the built-in stepper library. Works well and provides nice smooth accel/decel.
Thanks for the lead on the AccelStepper library. I don't need it for the immediate project but could be useful if I ever try to do something more sophisticated. I didn't have an issue with the 1-2-3-4 sequence, but maybe that's why the Arduino library didn't work well. Since mine is operating smoothly and meets AQL, I'm goin' with it!
Tom
If it was purely down to power being the same for both and with 250mA at 12V I'd expect the 5V version to have a resistance of (5*5)/(12*0.250), or 8.33R.
Mark.
Just ordered five of these on Amazon for $15 http://www.amazon.com/Elego-28BYJ-48-ULN2003-Stepper-Arduino/dp/B01CP18J4A. No idea what I'm going to use them for but the price was right :)
Quote from: TomWS on March 31, 2016, 06:53:12 PM
Since you have both motors in hand, can you measure the respective winding resistances and see if they are truly different motors?
Looks like 80 ohms for the 12V and 28 for the 5V.
Quote from: snorp on March 31, 2016, 10:30:45 PM
Quote from: TomWS on March 31, 2016, 06:53:12 PM
Since you have both motors in hand, can you measure the respective winding resistances and see if they are truly different motors?
Looks like 80 ohms for the 12V and 28 for the 5V.
Thanks for taking the time to measure and report this! I'm surprised that there is a difference.
Tom
That's interesting, 80 ohms gives 150mA at 12V (1.8W), and 28 ohms gives 178mA at 5V (0.9W). If the power was the same we'd expect the resistance at 5V to be somewhat less. It's almost like it's exactly the same motor but with a additional resistors in series with the windings at 12V.
Mark.