Adapter fails to power DC motor

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

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.

Sounds like it to me. I think the stalled motor inrush is causing it.

Yes. The current limit on many warts is to quickly sense over-current,

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.

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

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.

Are you switching the power at the AC input or DC output?

George H.

If there was no load on the big cap, the supply would eventually charge it. But the start current of the motor could collapse everything when it was connected. A supercap might work. Or a better power supply.

You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not?

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.

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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.

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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???

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.

from a 5 volt supply.

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.

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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???

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.

or from a 5 volt supply.

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.

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.

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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???

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.

otor from a 5 volt supply.

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.

start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.

pply to a 3.8-4.0 volt motor. So the NTC will only set him up for a future motor failure.

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.

overcurrent... a fairly common problem when tyrying to run motors off switching powersupplies.

adding large capacitors may help.

Are you quite sure that the motor stall current is only 4A with full working voltage applied ? This is quite different from stalling the motor and measuring the current (which will likely be limited by the power supply.) I would expect the rated voltage stall current of the motor to be at least 10x the full load working current.

MK

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

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

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:

I have a couple of supercapacitors on order (from China, so maybe I'll be waiting a long time) but as you see from my earlier post a 100,000uF electrolytic didn't fix it.