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smps for dc motor
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Zero999:

--- Quote from: beanflying on July 28, 2019, 09:21:09 am ---
--- Quote from: Zero999 on July 28, 2019, 09:10:49 am ---But the original poster doesn't want to run the motor at full power, otherwise I would have suggested the old fashioned approach of a buck/auto-transformer and rectifier.

I suggest they actually measure the motor current, when the motor is driving the expected mechanical load, to get an idea of the actual power consumption, before selecting an appropriate power supply. Note it's very important to measure the current, whilst the motor is loaded, as the no load current could be an order of magnitude less.

--- End quote ---

What does full load at 180V have to do with 15V 'full load' based on a likely BS power claim it is still BS. Any figures will be rubbery at best to just wrong. Taking a 'best guess' and keeping an eye on temperature is about as good a plan as any to setting a safe load point at 10% of the rated voltage.

Best '[guess' would see the motor needing to be derated to 1-200W providing the brushes will handle the higher current.

--- End quote ---
Where did I stay full load at 180V? It should have been obvious I meant full load at whatever voltage, the original poster is intending to power the motor with.
Siwastaja:
The very first words were, "a quick approximation".

Why do you think the motor ratings are bullshit? If they are, the math is garbage in, garbage out, indeed.

Yes, the most practical answer is, just try it, it's likely to work just fine with no engineering whatsoever. I said that, too.

But I'm trying to be educative. Don't belittle others, people are not stupid. They are capable of putting their own numbers in! Not limited to this grinding application. The concepts and formulae are important here, and they are correct. If not, please show a non-fact, instead of attacking and derailing.


--- Quote ---
--- Quote ---What does full load at 180V have to do
--- End quote ---
Where did I stay full load at 180V?
--- End quote ---
I said that, and he's referring to me.

It was used to calculate a meaningful parameter, in this case, stall current at 15V.  It's an approximation (neglecting non-linearities such as core hysteresis loss, friction...), and assumes that the specification is not bogus, of course.

This is because motors are very often rated by simply giving a full load voltage, rpm, power and/or current ratings. You often need to derive the relevant parameters from the parameters you have!
beanflying:

--- Quote from: Zero999 on July 28, 2019, 09:28:06 am ---
--- Quote from: beanflying on July 28, 2019, 09:21:09 am ---
--- Quote from: Zero999 on July 28, 2019, 09:10:49 am ---But the original poster doesn't want to run the motor at full power, otherwise I would have suggested the old fashioned approach of a buck/auto-transformer and rectifier.

I suggest they actually measure the motor current, when the motor is driving the expected mechanical load, to get an idea of the actual power consumption, before selecting an appropriate power supply. Note it's very important to measure the current, whilst the motor is loaded, as the no load current could be an order of magnitude less.

--- End quote ---

What does full load at 180V have to do with 15V 'full load' based on a likely BS power claim it is still BS. Any figures will be rubbery at best to just wrong. Taking a 'best guess' and keeping an eye on temperature is about as good a plan as any to setting a safe load point at 10% of the rated voltage.

Best '[guess' would see the motor needing to be derated to 1-200W providing the brushes will handle the higher current.

--- End quote ---
Where did I stay full load at 180V? It should have been obvious I meant full load at whatever voltage, the original poster is intending to power the motor with.

--- End quote ---

What would 'measuring' a current that is going to smoke the brushes achieve? Points of failure on the motor exist as does the PS. Running a motor at circa 10% nominal voltage without the data, best guess is in this case all you can do without creating a motor power curve at that voltage.

I have done this a lot with R/C motors over the years looking at BEP and performance but this is OTT for most without the gear to do it.

My main point here is you can't simply look at the PS but the motor under running load is likely the weak point with brush failure or overheating.
daniel444:
thanks for all the responses
now im thinking i might go for 24v 14A version of the same line of power supply to get a bit more torque , it has a cast iron flywheel so there  is energy stored in that too

im  spinning these diamond discs i bought off ebay , i stuck them to the flywheel with magnets for testing and was able to grind the tips of a screwdriver flat again , i dont want it to spin to fast , its for fine wet grinding and sharpening

i have another power supply that can run it at full speed but it would throw water everywhere and you couldn't get as close to it. so i want to get a dedicated lightweight power supply like the mean-well

i got the motor from a used  treadmill , took out and cleaned the brushes , they are only 30% used
Benta:
Make it simple:
just measure the resistance of the motor (I assume it's a PMDC type), moving the armature until you have the lowest resistance. This will tell you the maximum current the motor is ever going to draw, at startup or under load.
Design accordingly.
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