Post a guess on the min starting voltage for this brushed DC motor - Page 1
Forum section: electronics / general

author: Psi
author_rank: Super Contributor
timestamp: May 19, 2018, 07:29:05 am
content: 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.

author: tautech
author_rank: Super Contributor
timestamp: May 19, 2018, 07:57:05 am
content: And why not: 0.3V

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2018, 10:15:15 am
content: Those Escap coreless motors with precious metal brushes aren't a million miles off being moving coil meter movements - I'll go for 75mV.

author: Electro Detective
author_rank: Super Contributor
timestamp: May 19, 2018, 10:29:02 am
content: What are the prizes for the winning guess and runner ups?Rigol/Siglent DSO,EEVblog meter,Audiophool Convention ticketsNo gearing? I'm buying in with 50 microvolts to get that motor cranking btw

author: Psi
author_rank: Super Contributor
timestamp: May 19, 2018, 11:34:04 am
content: Quote from: Electro Detective on May 19, 2018, 10:29:02 am0.00005V ? That's a bit crazy, Gyro is pretty close

author: Ampera
author_rank: Super Contributor
timestamp: May 19, 2018, 02:47:01 pm
content: 50mVJust 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.

author: Brumby
author_rank: Unknown
timestamp: May 19, 2018, 02:50:19 pm
content: I'll throw up a number: 82mVNo particular reason.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 19, 2018, 04:18:00 pm
content: Me too94.5 mVBecause why not

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 19, 2018, 04:30:21 pm
content: 0.1337V

author: Zero999
author_rank: Super Contributor
timestamp: May 19, 2018, 04:48:36 pm
content: There will be some hysteresis. It will probably start moving at 40mV and once moving, will continue to work down to 20mV.

author: amyk
author_rank: Super Contributor
timestamp: May 19, 2018, 04:57:55 pm
content: 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.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 19, 2018, 05:13:48 pm
content: 42 mV.

author: Gyro
author_rank: Super Contributor
timestamp: May 19, 2018, 05:53:06 pm
content: Quote from: Psi on May 19, 2018, 11:34:04 amHey, no fair!

author: Psi
author_rank: Super Contributor
timestamp: May 19, 2018, 11:55:48 pm
content: Quote from: Gyro on May 19, 2018, 05:53:06 pmyeah sorry, that did occur to me, 4 hours after i posted it.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: May 19, 2018, 11:59:23 pm
content: Quote from: Psi on May 19, 2018, 11:55:48 pmIf that's the case, then perhaps a second guess is in order: 88 μV.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 20, 2018, 02:02:33 am
content: Zero

author: Ampera
author_rank: Super Contributor
timestamp: May 20, 2018, 03:03:27 am
content: Quote from: JohnnyMalaria on May 20, 2018, 02:02:33 amFree energy everybody!

author: Brumby
author_rank: Unknown
timestamp: May 20, 2018, 03:18:22 am
content: Quote from: Psi on May 19, 2018, 11:55:48 pmI 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.

author: ez24
author_rank: Super Contributor
timestamp: May 20, 2018, 07:30:28 am
content: 1.55 v

author: Electro Detective
author_rank: Super Contributor
timestamp: May 20, 2018, 09:34:11 am
content: So because of the confusion Gyro is in the lead to win the DSO ?

author: Gyro
author_rank: Super Contributor
timestamp: May 20, 2018, 12:24:31 pm
content: Just because you got it horribly wrong.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'*.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?"

author: BrianHG
author_rank: Super Contributor
timestamp: May 20, 2018, 10:32:39 pm
content: -65mvYes, negative...The title topic says minimum, and everyone here guessed a positive voltage.

author: Gregg
author_rank: Super Contributor
timestamp: May 21, 2018, 07:08:09 pm
content: It depends on how much your power supply overshoots on startup.

author: ez24
author_rank: Super Contributor
timestamp: May 21, 2018, 08:15:44 pm
content: Quote from: Gregg on May 21, 2018, 07:08:09 pmI think overshoot counts thus I have a better chance with 1.55v

author: james_s
author_rank: Super Contributor
timestamp: May 23, 2018, 01:19:57 am
content: 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.

author: Brumby
author_rank: Unknown
timestamp: May 23, 2018, 01:39:57 am
content: I forgot to ask .... is this with or without a Batteriser?

author: Psi
author_rank: Super Contributor
timestamp: May 23, 2018, 10:21:42 am
content: Gyro 75mVElectro Detective 0.050mVTwoOfFive 50mVBrumby 82mVschmitt trigger 94.5mVNiHaoMike 133.7mVHero999 40mVamyk 67mVTomorokoshi 42mVJohnnyMalaria 0mVez24 1550mVBrianHG -65mVSo, results are in, and im calling it a tie between Gyro (75mV) and amky (67mV).Mainly because i stuffed up and let the cat out of the bag.BrianHG gets some points for guessing perfectly 180deg out of phase.Video

author: Gyro
author_rank: Super Contributor
timestamp: May 23, 2018, 11:22:48 am
content: Yay, thanks (congrats to amyk and BrianHG).It's still impressive to see those motors turning so slowly.

author: Psi
author_rank: Super Contributor
timestamp: May 23, 2018, 08:08:07 pm
content: Yeah.Make sure you checkout the end of the video. I included some closeup shots of the commutator rotating.

author: Brumby
author_rank: Unknown
timestamp: May 24, 2018, 02:39:22 am
content: Dang, I went high .... should have gone low.Yes, I am using Gyro's figure as my reference.

author: Ampera
author_rank: Super Contributor
timestamp: May 24, 2018, 02:47:48 am
content: I'm happy with my guess, I wasn't that far off.