Author Topic: Post a guess on the min starting voltage for this brushed DC motor  (Read 2377 times)

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Online Psi

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So i found this old motor in my junk draw and was quite impressed how little voltage is required for it to start moving.
It's a 5-12V DC brushed motor and has no gearing (1:1)

To win respect from your fellow forum users post a guess for the starting voltage.

I'll post a video showing the min voltage in a few days.

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Offline tautech

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #1 on: May 19, 2018, 07:57:05 am »
And why not: 0.3V
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Offline Gyro

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #2 on: May 19, 2018, 10:15:15 am »
Those Escap coreless motors with precious metal brushes aren't a million miles off being moving coil meter movements - I'll go for 75mV.
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Online Electro Detective

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #3 on: May 19, 2018, 10:29:02 am »
What are the prizes for the winning guess and runner ups?

Rigol/Siglent DSO,

EEVblog meter,

Audiophool Convention tickets  :scared:


No gearing? I'm buying in with 50 microvolts to get that motor cranking btw

« Last Edit: May 19, 2018, 10:30:38 am by Electro Detective »
 

Online Psi

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #4 on: May 19, 2018, 11:34:04 am »
I'm buying in with 50 microvolts to get that motor cranking btw

0.00005V ? That's a bit crazy,  Gyro is pretty close
« Last Edit: May 19, 2018, 11:37:13 am by Psi »
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Offline Ampera

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #5 on: May 19, 2018, 02:47:01 pm »
50mV

Just from a physics perspective, it wouldn't take much energy to get that small shaft moving. It wouldn't move much, but it just needs to break the friction of the stuff around it.
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Online Brumby

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #6 on: May 19, 2018, 02:50:19 pm »
I'll throw up a number: 82mV

No particular reason.
 

Offline schmitt trigger

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #7 on: May 19, 2018, 04:18:00 pm »
Me too

94.5 mV

Because why not
 

Online NiHaoMike

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #8 on: May 19, 2018, 04:30:21 pm »
0.1337V
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Offline Zero999

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #9 on: May 19, 2018, 04:48:36 pm »
There will be some hysteresis. It will probably start moving at 40mV and once moving, will continue to work down to 20mV.
 

Online amyk

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #10 on: May 19, 2018, 04:57:55 pm »
67mV.

Here's a 120V brushed AC motor starting at less than 9V:

That one is more surprising since the brushes on those motors have a lot more friction, being designed for many amps.
 

Online Tomorokoshi

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #11 on: May 19, 2018, 05:13:48 pm »
42 mV.
 

Offline Gyro

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #12 on: May 19, 2018, 05:53:06 pm »
.... Gyro is pretty close

Hey, no fair!  :scared:
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Online Psi

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #13 on: May 19, 2018, 11:55:48 pm »
.... Gyro is pretty close

Hey, no fair!  :scared:

yeah sorry, that did occur to me, 4 hours after i posted it.
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Online Tomorokoshi

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #14 on: May 19, 2018, 11:59:23 pm »
.... Gyro is pretty close

Hey, no fair!  :scared:

yeah sorry, that did occur to me, 4 hours after i posted it.

If that's the case, then perhaps a second guess is in order: 88 μV.
 

Offline JohnnyMalaria

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #15 on: May 20, 2018, 02:02:33 am »
Zero
Tell me it can't be done and I'll do it. Or give it a damned good try.
 

Offline Ampera

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Online Brumby

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #17 on: May 20, 2018, 03:18:22 am »
.... Gyro is pretty close

Hey, no fair!  :scared:

yeah sorry, that did occur to me, 4 hours after i posted it.

I think, therefore, that Gyro should be given first acknowledgement for a good answer.  I will admit I based my guess on his figure.


Reminds me of a guessing competition many years ago at a place I once worked - how many grains of rice were in the jar.  I took some measurements of the jar and some grains of rice (of the same type) and did some volume and packing calculations.  Yes, I did get a few eye rolls.

I came up with a number that was far higher than any other guesses, so even with some significant error on my part, I felt confident I was in the right ball park for a win.  Each person's entry consisted of 5 guesses, so I took my calculation as my middle guess and picked two more higher and two more lower, spaced about 1,000 apart.  Someone after me picked numbers halfway between my guesses, so my coverage was now cut in half.  That was annoying.  Nevertheless, it turned out that my coverage included the number the judges came up with - and I won the tea set.
« Last Edit: May 20, 2018, 03:28:04 am by Brumby »
 
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Offline ez24

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #18 on: May 20, 2018, 07:30:28 am »
1.55 v
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Online Electro Detective

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #19 on: May 20, 2018, 09:34:11 am »

So because of the confusion Gyro is in the lead to win the DSO ?   |O

 ;D
 

Offline Gyro

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #20 on: May 20, 2018, 12:24:31 pm »
Just because you got it horribly wrong.  :P

So there's a DSO up for grabs now? I was just starting to get my hopes up for Brumby's tea set!  Worst case, I'll settle for 'frank admiration'*.  :D

I used one of those motors many years ago (think it was a 12-24V one) as a replacement for a synchronous motor on a belt-drive turntable. I mounted it straight to the chassis (no vibration damping) and fed it with an regulated supply from an LM317 and multi-turn pot. I think it took about 1.5V for 33-1/3 RPM and was perfectly speed stable and silent without any additional feedback - just its own inherent back emf/current draw.


* Think that's a Douglas Adams quote, as in signed "Yours, with frank admiration".
"FORD: Yeah. Where’s Zaphod?
ARTHUR: He… well… he’s in his cabin signing photographs of himself: “To myself with frank admiration.” But why are the Vogons following us?"
« Last Edit: May 20, 2018, 01:23:32 pm by Gyro »
Chris

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Offline BrianHG

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #21 on: May 20, 2018, 10:32:39 pm »
-65mv
Yes, negative...
The title topic says minimum, and everyone here guessed a positive voltage.  :P
« Last Edit: May 21, 2018, 07:52:51 pm by BrianHG »
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Online Gregg

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #22 on: May 21, 2018, 07:08:09 pm »
It depends on how much your power supply overshoots on startup.
 

Offline ez24

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #23 on: May 21, 2018, 08:15:44 pm »
It depends on how much your power supply overshoots on startup.

I think overshoot counts thus I have a better chance with 1.55v   :-DD
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Online james_s

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Re: Post a guess on the min starting voltage for this brushed DC motor
« Reply #24 on: May 23, 2018, 01:19:57 am »
I've found most 120V universal motors will run on less than 12V. Not very fast, but they will start up and run. The 240V motor in the air blower in my spa will also run on 12V.
 


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