28BYJ-48 12V help

Two things,

I've converted it to bipolar mode, would this change the amount of steps per one revolution?

What's the maximum current i should be running at like 18V on this motor?

After converting the motor into a bipolar mode, every two halves of the winding are connected in series. The current through the winding should remain the same. If one half of the motor winding runs at 12 V, then after the rework, the two halves should run at 24 V.
Unfortunately, it is not possible to find a good datasheet where the maximum rated winding current would be given.

So you've deleted the red wire going to the middle of both coils?

Well, I guess you just need to cut one or the other really.

I've never seen a more detailed datasheet than this.
You can measure the resistance from pink to orange, and from yellow to blue, to get an idea of much current flow you might see worse case:
18v/resistance = current.
I measure 44 ohm on a 5V motor which would suggest ~114mA.
Running 12V yields 272mA
18V yields 409mA.
You need to pulse one coil, than the other, to spin the motor.

Measure yours, see what you get.

Thanks for that, I'm running 16V just fine with a current draw of 60 ma right now.

I'm not so sure I've got a 64 steps per rotation model though. Unless that changes in a bipolar conversion? it's taking me about 2020 steps to rotate all the way and thats with a large delay between pulses.

edit: I worked it out wrong my bad

I've been rotating the motors with this sequence, and getting close to 8 RPM I think.

0110, 1100, 1001, 0011
so there are effectively 4 coils.
With just 2 coils, I don't know how to mimic that.

getting roughly 12.5 rpm with mine. Sorted everything out.

Cool. What are you using for a driver? And how warm do they get?

I'm using a drv8825, I don't have a thermometer or temperature probe or anything but it's not too hot to pick up after constantly spinning for about 10 minutes, so I think for my use case its okay. They should be alright up to like 80C right?

If it gets too hot to touch without burning yourself, that's probably too hot.

Did you set the current on the DRV8825.
A current controlled driver is a poor choice if you just use it as a H-bridge (full voltage all the time).

A 5volt motor could be a better match for a current controlled driver on a 12/18/24volt supply.

I could get 16RPM (unloaded) with basic ramp-up/down, without modification of the 12volt motor.
With a TPIC6B595, used like the standard/supplied ULN driver.
Not sure why you want to go the DRV8825 way.
Leo..

Yes I've set the current limiter, but idk what you mean by just using it as a hbridge?

Like if your asking if my use case is just to spin it all the time constantly of course it's not otherwise I wouldn't have got a stepper. I was just testing how hot it'd get.

I need to turn something precisely with a decent amount of torque.

Also the TPIC6B595 is literally as expensive as a 4988 or drv8825 and I've converted the stepper motor to bipolar mode anyway.

The DRV works as a common H-bridge if current is set above what this high-impedance stepper naturally draws. Then it does not make any difference if you use a DRV or a standard ULN board or a TPIC chip.

Don't know what your application is, but if you need something precise, then a 28BYJ-48 is probably the wrong choice. It's gear train has a lot of backlash.
Leo..

And again, please explain to me the difference between any of these driver boards and an h bridge because it honestly sounds like you'd recommend a h bridge for any type of stepper motor application.

Also I converted it to bipolar for the extra torque. I don't need or want to use a uln or tpic when I can do the conversion and double the voltage

And I need it to be "precise enough" just to turn a thumb screw that has 12 "clicks" per revolution one for each setting

As you've converted to bipolar, an H-bridge, or controller/H-bridge (A4988 and DRV8825) , is really the only way to go. TPIC6x595 only works now if you have a way to supply voltage from one end of the coil, or the other - which is what an H-bridge provides.

A DRV contains four two H-bridges. One half-bridge for each of the four wires of your converted motor.
The function of this specialized stepper driver is to keep motor current (torque) the same at higher motor speeds (if used right).
Leo..

Not according to the datasheet.
"The device has two H-bridge drivers and a microstepping indexer, and is intended to drive a bipolar stepper motor"

Duh.. Page 11 of the datasheet.
Four Half-bridges makes two H-bridges.
Leo..

Yes, I was looking to see what they called the 4 output drivers. You beat me to it.

(How is your kinetics display going? I've been waiting for my wife & son to move their starter plants (tomatoes and peppers mostly) out of the basement and outside into the garden to get some room back to move around in the basement again.)

Ok so why do you keep telling me not to use the driver. You're pretty confusing lol