Adapter fails to power DC motor

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I bought the following 4A 5V supply adapter:  
https://cpc.farnell.com/stontronics/t6819st/ac-dc-power-supply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
with the aim of trying it as an alternative supply for my 16 year old
curtain controller circuit. At present I successfully use 3 x AA Nimh
batteries, delivering a voltage of about 3.8 to 4.1 V (measured at the
battery terminals). Current consumption varies from about 2.6A to
stalled at 4A or so.  

I was surprised to find that the adaptor does not work with the
circuit's ex-screwdriver 2.4 motor. It delivers the 4 A to a resistor
*and* to the only other DC motor I have at hand, a 12V miniature drill.

Here's my 'scope showing the adapter's bursts of brief action:
https://www.dropbox.com/s/i2lu9z38s2fgzd3/AdaptorWithDrillMotor.jpg?raw=1

I can find other uses for this, but I'm curious to discover why it
doesn't work for the intended purpose.

Terry, East Grinstead, UK

Re: Adapter fails to power DC motor
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I was interested in the product, so looked at the datasheet, where it says

   Over-Current Protection        >3.6A with auto-recovery function

Could it be that the protection kicks in on start current, likely to be  
the full stall current of aprox 4A, recovers, kicks in again, recovers,  
etc,etc?

Jim

Re: Adapter fails to power DC motor
On Tuesday, March 3, 2020 at 7:32:36 AM UTC-5, Jim Jackson wrote:
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Huh, 3.6 A over current on a 4 A supply is a little sneaky.

Terry, I've used a bunch of Phihong power supplies... I abused 'em  
but only with a resistive load.  I guess you need a 'bigger boat'
maybe look for a 25 or 30 W supply..  
(find another 5V supply in your scrap box and put two in parallel?)  

George H.

Re: Adapter fails to power DC motor
On 3/3/2020 6:32 AM, Jim Jackson wrote:
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Sounds like it to me. I think the stalled motor inrush is causing it.

Re: Adapter fails to power DC motor
On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson

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Yes. The current limit on many warts is to quickly sense over-current,
1.5x rated maybe, shut down for some fraction of a second, and try
again. The average current into a short is low.

There can be problems with a wart trying to bring up an electronic
device too, like a negative-input-impedance switcher, or something
with big input caps. I design soft-starts into my stuff to allow the
wart to get up to voltage.



--  

John Larkin         Highland Technology, Inc

The cork popped merrily, and Lord Peter rose to his feet.  
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Re: Adapter fails to power DC motor
snipped-for-privacy@highlandsniptechnology.com wrote:

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Prompted by Jim's suggestion I tried some hefty electrolytics in
parallel, thinking they would assist startup. For example: 100,000
uF/10V, 25,000 uF/50. But same result. They were of course at the
adapter's 5.1 V when I applied the motor load.

Terry, East Grinstead, UK


Re: Adapter fails to power DC motor

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Meant to add: while fiddling with this, tapping wires at various
intervals, there was just *one* instance when the motor *did* start
running at what appeared full speed. Spent another few minutes trying in
vain to reproduce that.

Re: Adapter fails to power DC motor
On Tuesday, March 3, 2020 at 11:53:11 AM UTC-5, Terry Pinnell wrote:
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Are you switching the power at the AC input or DC output?  

George H.  

Re: Adapter fails to power DC motor

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Tried both. On the occasion I got the full power, I was tapping the 5V
connecting wire onto the motor's +ve input.


Re: Adapter fails to power DC motor
On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote:
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You could always try putting an NTC resistor in series as an inrush current limiter.  Cheap, easy, probably works...why not?

Re: Adapter fails to power DC motor
On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
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Oh!  So this is a hack and the best bet will be a bigger power supply.  
but as long as the DC motor isn't starved for torque, then you just need  
to limit the current some.. so how about a series resistor, ~0.1 ohms?  

George H.  

Re: Adapter fails to power DC motor

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Thanks George. That fix from you and DemonicTubes gets the seegar! See
also my more detailed reply a minute ago.

Terry, East Grinstead, UK

Re: Adapter fails to power DC motor
On Wednesday, March 4, 2020 at 12:45:12 PM UTC-5, Terry Pinnell wrote:
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Excellent.  thanks for the update.
George H.  

Re: Adapter fails to power DC motor
On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote:
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4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
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old
imh
 the
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tor
rill.
g?raw=1
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t says
 be  
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rs,  
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,
n
nt limiter.  Cheap, easy, probably works...why not?

Doesn't even need the temperature coefficient.   The NiMH batteries power t
he motor at '3.8 to 4.1 V".  This supply runs at 5 volts and he has not sai
d anything about reducing that voltage that I saw.  They guy is not very pr
ecise in his description of the circuit though.  I don't know what he means
 by "ex-screwdriver 2.4 motor".  Is that 2.4 volts?  2.4 amps?  Maybe 2.4 r
evision???  

Anyway, a quarter ohm or maybe a bit more resistance should be added betwee
n the motor input and the PSU output.  That would drop the volt at full pow
er.  Or maybe use a smaller resistor (~0.1 ohm) and a diode drop.  Or maybe
 two diode drops, one silicon and one Schottky plus optionally a tenth ohm  
resistor.  

I'm not at all surprised he is getting an overload driving a 4 volt motor f
rom a 5 volt supply.  

--  

  Rick C.

  - Get 1,000 miles of free Supercharging
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Re: Adapter fails to power DC motor
On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote:
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v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
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r old
 Nimh
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at the
o
istor
 drill.
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jpg?raw=1
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it
 it says
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n
to be  
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vers,  
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nt,
e
 in
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rent limiter.  Cheap, easy, probably works...why not?
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 the motor at '3.8 to 4.1 V".  This supply runs at 5 volts and he has not s
aid anything about reducing that voltage that I saw.  They guy is not very  
precise in his description of the circuit though.  I don't know what he mea
ns by "ex-screwdriver 2.4 motor".  Is that 2.4 volts?  2.4 amps?  Maybe 2.4
 revision???  
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een the motor input and the PSU output.  That would drop the volt at full p
ower.  Or maybe use a smaller resistor (~0.1 ohm) and a diode drop.  Or may
be two diode drops, one silicon and one Schottky plus optionally a tenth oh
m resistor.  
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 from a 5 volt supply.  
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Certainly a normal resistor would most likely work.  The reason I suggested
 an NTC ('thermistor' as they are commonly known) is to avoid wasting power
.  They are readily available and dirt cheap...of course if you don't have  
one on hand and need to get it working now, yeah just throw a low value res
istor on there and go for it.

I'm sure you know all this, but this is for OP's benefit.

Those NTC thermistors are often called 'inrush current limiters'.  They sta
rt out at a few ohms, but quickly drop to almost nothing after a moment of  
current flow.


Re: Adapter fails to power DC motor
On Tuesday, March 3, 2020 at 3:40:56 PM UTC-5, DemonicTubes wrote:
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-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
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ear old
AA Nimh
d at the
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 to
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e
esistor
re drill.
r.jpg?raw=1
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y it
re it says
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ion
y to be  
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covers,  
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rent,
y
c
g
the
ng in
urrent limiter.  Cheap, easy, probably works...why not?
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er the motor at '3.8 to 4.1 V".  This supply runs at 5 volts and he has not
 said anything about reducing that voltage that I saw.  They guy is not ver
y precise in his description of the circuit though.  I don't know what he m
eans by "ex-screwdriver 2.4 motor".  Is that 2.4 volts?  2.4 amps?  Maybe 2
.4 revision???  
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tween the motor input and the PSU output.  That would drop the volt at full
 power.  Or maybe use a smaller resistor (~0.1 ohm) and a diode drop.  Or m
aybe two diode drops, one silicon and one Schottky plus optionally a tenth  
ohm resistor.  
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or from a 5 volt supply.  
Quoted text here. Click to load it
ed an NTC ('thermistor' as they are commonly known) is to avoid wasting pow
er.  They are readily available and dirt cheap...of course if you don't hav
e one on hand and need to get it working now, yeah just throw a low value r
esistor on there and go for it.
Quoted text here. Click to load it
tart out at a few ohms, but quickly drop to almost nothing after a moment o
f current flow.

Trouble is he needs to waste power anyway.  He is mismatching a 5 volt supp
ly to a 3.8-4.0 volt motor.  So the NTC will only set him up for a future m
otor failure.  

--  

  Rick C.

  + Get 1,000 miles of free Supercharging
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Re: Adapter fails to power DC motor
On Tuesday, March 3, 2020 at 2:14:00 PM UTC-7, Rick C wrote:
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ly-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
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 year old
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x AA Nimh
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red at the
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6A to
the
 resistor
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ture drill.
n:
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tor.jpg?raw=1
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why it
here it says
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ction
ely to be  
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recovers,  
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urrent,
try
nic
ing
w the
00
e
rt
ying in
 current limiter.  Cheap, easy, probably works...why not?
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ower the motor at '3.8 to 4.1 V".  This supply runs at 5 volts and he has n
ot said anything about reducing that voltage that I saw.  They guy is not v
ery precise in his description of the circuit though.  I don't know what he
 means by "ex-screwdriver 2.4 motor".  Is that 2.4 volts?  2.4 amps?  Maybe
 2.4 revision???  
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between the motor input and the PSU output.  That would drop the volt at fu
ll power.  Or maybe use a smaller resistor (~0.1 ohm) and a diode drop.  Or
 maybe two diode drops, one silicon and one Schottky plus optionally a tent
h ohm resistor.  
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otor from a 5 volt supply.  
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sted an NTC ('thermistor' as they are commonly known) is to avoid wasting p
ower.  They are readily available and dirt cheap...of course if you don't h
ave one on hand and need to get it working now, yeah just throw a low value
 resistor on there and go for it.
Quoted text here. Click to load it
 start out at a few ohms, but quickly drop to almost nothing after a moment
 of current flow.
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pply to a 3.8-4.0 volt motor.  So the NTC will only set him up for a future
 motor failure.  
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Ah.  Sorry, it wasn't clear to me that it is a 4 V motor.  If that is the c
ase, a proper supply is a better solution.

Re: Adapter fails to power DC motor

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It's not, it's a 2.4 V ex-screwdriver motor, originally powered by two
1.2 V NiCads.

For the last 16 years, as I mentioned, it's been powered by three Nimh
batteries (C-type, not AA, another typo, sorry), "...delivering a
voltage of about 3.8 to 4.1 V...". A lower voltage of 2.5 V or so from
two such batteries delivers insufficient current to open and close the
quite heavy curtains. It's running well at present, closing smoothly in
just over 2 secs:
https://www.dropbox.com/s/b96xyihr4ustgjq/Curtains-1.mp4?raw=1
but I'd rather like battery independence.

Re: Adapter fails to power DC motor
On Wednesday, March 4, 2020 at 10:58:27 AM UTC-5, Terry Pinnell wrote:
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te:
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upply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
Quoted text here. Click to load it
 16 year old
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 3 x AA Nimh
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asured at the
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 2.6A to
Quoted text here. Click to load it
th the
o a resistor
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niature drill.
tion:
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lMotor.jpg?raw=1
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er why it
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, where it says
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function
likely to be  
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n, recovers,  
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r-current,
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nd try
tronic
ething
llow the
 in
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0,000
 the
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us
start
 trying in
Quoted text here. Click to load it
ush current limiter.  Cheap, easy, probably works...why not?
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s power the motor at '3.8 to 4.1 V".  This supply runs at 5 volts and he ha
s not said anything about reducing that voltage that I saw.  They guy is no
t very precise in his description of the circuit though.  I don't know what
 he means by "ex-screwdriver 2.4 motor".  Is that 2.4 volts?  2.4 amps?  Ma
ybe 2.4 revision???  
Quoted text here. Click to load it
ed between the motor input and the PSU output.  That would drop the volt at
 full power.  Or maybe use a smaller resistor (~0.1 ohm) and a diode drop.  
 Or maybe two diode drops, one silicon and one Schottky plus optionally a t
enth ohm resistor.  
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t motor from a 5 volt supply.  
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ggested an NTC ('thermistor' as they are commonly known) is to avoid wastin
g power.  They are readily available and dirt cheap...of course if you don'
t have one on hand and need to get it working now, yeah just throw a low va
lue resistor on there and go for it.
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hey start out at a few ohms, but quickly drop to almost nothing after a mom
ent of current flow.
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 supply to a 3.8-4.0 volt motor.  So the NTC will only set him up for a fut
ure motor failure.  
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e case, a proper supply is a better solution.
Quoted text here. Click to load it

You state two batteries provided insufficient current so you upped the numb
er of cells which provided more voltage.  Do you see the problem with that?
  

NiMH cells have a higher internal resistance than do NiCd or Li-ion cells o
f similar size.  So when trying to open the curtain with two NiMH cells you
 were losing voltage in the series resistance and so the delivered power wa
s too low.  By adding a third cell the voltage increased to where it should
 have been and were able to get sufficient power to open the curtain.  

Now your cells are showing their age and no longer hold a charge long enoug
h to power the curtain with the original charging current.  So you pick a p
ower supply to directly drive the motor, but at more than twice the rated v
oltage.  So the peak current is far higher than either required or allowed  
by the PSU and it doesn't work.  

No, a couple of series diodes are not going to work.  You need a power supp
ly that puts out the correct voltage at the correct current.  To charge a b
attery power source at 2.4 volts seems problematic since you don't want to  
use a proper system to do this.  I think I would go with a capacitor/super  
capacitor based system.  They can be charged at a higher rate for quick rec
harge and are resistant to overcharging as long as your power source doesn'
t drive them to an excessive voltage.  In fact, there is a capacitive doubl
er/halfing circuit you could use to charge caps to 2.5 volts from your exis
ting 5 volt supply.  It is a simple circuit and would only require some FET
s and a 555 timer chip.  

--  

  Rick C.

  -- Get 1,000 miles of free Supercharging
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Re: Adapter fails to power DC motor
On Wednesday, 4 March 2020 15:58:27 UTC, Terry Pinnell  wrote:
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te:
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upply-5v-4a-2-1mm/dp/PW04378?st=5v%20power%20adaptors
Quoted text here. Click to load it
 16 year old
Quoted text here. Click to load it
 3 x AA Nimh
Quoted text here. Click to load it
asured at the
Quoted text here. Click to load it
 2.6A to
Quoted text here. Click to load it
th the
o a resistor
Quoted text here. Click to load it
niature drill.
tion:
Quoted text here. Click to load it
lMotor.jpg?raw=1
Quoted text here. Click to load it
er why it
Quoted text here. Click to load it
, where it says
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function
likely to be  
Quoted text here. Click to load it
n, recovers,  
Quoted text here. Click to load it
r-current,
Quoted text here. Click to load it
nd try
tronic
ething
llow the
 in
Quoted text here. Click to load it
0,000
 the
Quoted text here. Click to load it
us
start
 trying in
Quoted text here. Click to load it
ush current limiter.  Cheap, easy, probably works...why not?
Quoted text here. Click to load it
s power the motor at '3.8 to 4.1 V".  This supply runs at 5 volts and he ha
s not said anything about reducing that voltage that I saw.  They guy is no
t very precise in his description of the circuit though.  I don't know what
 he means by "ex-screwdriver 2.4 motor".  Is that 2.4 volts?  2.4 amps?  Ma
ybe 2.4 revision???  
Quoted text here. Click to load it
ed between the motor input and the PSU output.  That would drop the volt at
 full power.  Or maybe use a smaller resistor (~0.1 ohm) and a diode drop.  
 Or maybe two diode drops, one silicon and one Schottky plus optionally a t
enth ohm resistor.  
Quoted text here. Click to load it
t motor from a 5 volt supply.  
Quoted text here. Click to load it
ggested an NTC ('thermistor' as they are commonly known) is to avoid wastin
g power.  They are readily available and dirt cheap...of course if you don'
t have one on hand and need to get it working now, yeah just throw a low va
lue resistor on there and go for it.
Quoted text here. Click to load it
hey start out at a few ohms, but quickly drop to almost nothing after a mom
ent of current flow.
Quoted text here. Click to load it
 supply to a 3.8-4.0 volt motor.  So the NTC will only set him up for a fut
ure motor failure.  
Quoted text here. Click to load it
e case, a proper supply is a better solution.
Quoted text here. Click to load it

Long ago I learnt that mains power was far more reliable than any battery.  
The ability to manually open & close will also be far more rleiable than an
y battery.

I've not measured anything but suspect the motor is likely drawing way abov
e 4A for tiny fractions of time. A 2.4v screwdriver motor that self limited
 to 4A on 5v wouldn't be a lot of use.


NT

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