Michael Kellett <mk@mkesc.co.uk> wrote:>On 03/03/2020 12:17, Terry Pinnell wrote: >> 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 >> >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. > >MKAs described earlier, it's an old 2.4V ex-screwdriver motor, and I don't know its rated stall current. FWIW the last time I took a meter to it and deliberately stalled it think I saw about 4.5A from the batteries. I have just noticed a data sheet link for the adapter/wart on the Farnell page I referenced and in that PDF https://www.dropbox.com/s/2shohl2zekvpe62/2871891.pdf?dl=0 I see "Over Current Protection: >3.6A with auto-recovery function". Does that imply that said recovery function is not working in this case?
Adapter fails to power DC motor
Started by ●March 3, 2020
Reply by ●March 4, 20202020-03-04
Reply by ●March 4, 20202020-03-04
jlarkin@highlandsniptechnology.com wrote:>On Tue, 03 Mar 2020 16:48:57 +0000, Terry Pinnell ><me@somewhere.invalid> wrote: > >>jlarkin@highlandsniptechnology.com wrote: >> >>>On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson >>><jj@franjam.org.uk> wrote: >>> >>>>On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote: >>>>> 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. >>>>> >>>> >>>>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 >>> >>>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. >> >>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 > >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.Thanks, understood. I have a few of these on order to play with: https://www.ebay.co.uk/itm/Cylinder-Farad-Capacitor-2-7V-500F-Electrical-Component-Super-Capacitor-Black/163826403836?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649
Reply by ●March 4, 20202020-03-04
Reply by ●March 4, 20202020-03-04
DemonicTubes <tlackie@gmail.com> wrote:>On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote: >> On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote: >> > On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote: >> > > Terry Pinnell <me@somewhere.invalid> wrote: >> > > >> > > >jlarkin@highlandsniptechnology.com wrote: >> > > > >> > > >>On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson >> > > >><jj@franjam.org.uk> wrote: >> > > >> >> > > >>>On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote: >> > > >>>> 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. >> > > >>>> >> > > >>> >> > > >>>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 >> > > >> >> > > >>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. >> > > > >> > > >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. >> > >> > You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not? >> >> Doesn't even need the temperature coefficient. The NiMH batteries power 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 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? Maybe 2.4 revision??? >> >> Anyway, a quarter ohm or maybe a bit more resistance should be added 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 tenth ohm resistor. >> >> I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply. >> >> -- >> >> Rick C. >> >> - Get 1,000 miles of free Supercharging >> - Tesla referral code - https://ts.la/richard11209 > >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 resistor 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 start out at a few ohms, but quickly drop to almost nothing after a moment of current flow.Thanks a bunch, that fixed it! With a series resistance of two 0.5 R in parallel, plus some croc-to-crocs and other wires, it starts at once. With no load quickly settled at 2.7A and 3.9V. I couldn't quite stall it but got close, when those became 5.1A and 2.0V. That was with an identical but little used motor, but I'm fairly confident the installed motor will behave in similar fashion. Terry, East Grinstead, UK
Reply by ●March 4, 20202020-03-04
George Herold <ggherold@gmail.com> wrote:>On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote: >> On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote: >> > Terry Pinnell <me@somewhere.invalid> wrote: >> > >> > >jlarkin@highlandsniptechnology.com wrote: >> > > >> > >>On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson >> > >><jj@franjam.org.uk> wrote: >> > >> >> > >>>On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote: >> > >>>> 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. >> > >>>> >> > >>> >> > >>>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 >> > >> >> > >>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. >> > > >> > >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. >> >> 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.Thanks George. That fix from you and DemonicTubes gets the seegar! See also my more detailed reply a minute ago. Terry, East Grinstead, UK
Reply by ●March 4, 20202020-03-04
On Wednesday, March 4, 2020 at 10:58:27 AM UTC-5, Terry Pinnell wrote:> DemonicTubes <tlackie@gmail.com> wrote: > > >On Tuesday, March 3, 2020 at 2:14:00 PM UTC-7, Rick C wrote: > >> On Tuesday, March 3, 2020 at 3:40:56 PM UTC-5, DemonicTubes wrote: > >> > On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote: > >> > > On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote: > >> > > > On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote: > >> > > > > Terry Pinnell <me@somewhere.invalid> wrote: > >> > > > > > >> > > > > >jlarkin@highlandsniptechnology.com wrote: > >> > > > > > > >> > > > > >>On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson > >> > > > > >><jj@franjam.org.uk> wrote: > >> > > > > >> > >> > > > > >>>On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote: > >> > > > > >>>> 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. > >> > > > > >>>> > >> > > > > >>> > >> > > > > >>>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 > >> > > > > >> > >> > > > > >>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. > >> > > > > > > >> > > > > >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. > >> > > > > >> > > > You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not? > >> > > > >> > > Doesn't even need the temperature coefficient. The NiMH batteries power 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 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? Maybe 2.4 revision??? > >> > > > >> > > Anyway, a quarter ohm or maybe a bit more resistance should be added 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 tenth ohm resistor. > >> > > > >> > > I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply. > >> > > > >> > > -- > >> > > > >> > > Rick C. > >> > > > >> > > - Get 1,000 miles of free Supercharging > >> > > - Tesla referral code - https://ts.la/richard11209 > >> > > >> > 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 resistor 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 start out at a few ohms, but quickly drop to almost nothing after a moment of current flow. > >> > >> Trouble is he needs to waste power anyway. He is mismatching a 5 volt supply to a 3.8-4.0 volt motor. So the NTC will only set him up for a future motor failure. > >> > >> -- > >> > >> Rick C. > >> > >> + Get 1,000 miles of free Supercharging > >> + Tesla referral code - https://ts.la/richard11209 > > > >Ah. Sorry, it wasn't clear to me that it is a 4 V motor. If that is the case, a proper supply is a better solution. > > 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.You state two batteries provided insufficient current so you upped the number 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 of 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 was 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 enough to power the curtain with the original charging current. So you pick a power supply to directly drive the motor, but at more than twice the rated voltage. 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 supply that puts out the correct voltage at the correct current. To charge a battery 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 recharge 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 doubler/halfing circuit you could use to charge caps to 2.5 volts from your existing 5 volt supply. It is a simple circuit and would only require some FETs and a 555 timer chip. -- Rick C. -- Get 1,000 miles of free Supercharging -- Tesla referral code - https://ts.la/richard11209
Reply by ●March 4, 20202020-03-04
On Wednesday, March 4, 2020 at 12:45:12 PM UTC-5, Terry Pinnell wrote:> George Herold <ggherold@gmail.com> wrote: > > >On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote: > >> On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote: > >> > Terry Pinnell <me@somewhere.invalid> wrote: > >> > > >> > >jlarkin@highlandsniptechnology.com wrote: > >> > > > >> > >>On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson > >> > >><jj@franjam.org.uk> wrote: > >> > >> > >> > >>>On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote: > >> > >>>> 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. > >> > >>>> > >> > >>> > >> > >>>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 > >> > >> > >> > >>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. > >> > > > >> > >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. > >> > >> 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. > > Thanks George. That fix from you and DemonicTubes gets the seegar! See > also my more detailed reply a minute ago. > > Terry, East Grinstead, UKExcellent. thanks for the update. George H.
Reply by ●March 5, 20202020-03-05
On 2020-03-04, Terry Pinnell <me@somewhere.invalid> wrote:> Michael Kellett <mk@mkesc.co.uk> wrote:> As described earlier, it's an old 2.4V ex-screwdriver motor, and I don't > know its rated stall current. FWIW the last time I took a meter to it > and deliberately stalled it think I saw about 4.5A from the batteries.You can use Ohm's law to determine stall current. At 5V it'll be more than twice what it was at 2.4V> I have just noticed a data sheet link for the adapter/wart on the > Farnell page I referenced and in that PDF > https://www.dropbox.com/s/2shohl2zekvpe62/2871891.pdf?dl=0 > I see > "Over Current Protection: >3.6A with auto-recovery function". > > Does that imply that said recovery function is not working in this case?From your description it sounded like it was working as designed: the 5V comes back when the load is removed. -- Jasen.
Reply by ●March 5, 20202020-03-05
On 3/4/2020 10:03 AM, Terry Pinnell wrote:> Jasen Betts <jasen@xnet.co.nz> wrote: > >> On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote: >>> 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. >> >> overcurrent... a fairly common problem when tyrying to run motors off >> switching powersupplies. >> >> adding large capacitors may help. > > 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. >100,000uF is .1F. If you use two of those supercaps in series, you'll have 250F. That would be 2500 times more than the 100,000uF you tried. A considerable difference. However, equalizing the voltage across the series arrangement remains a problem for you.
Reply by ●March 5, 20202020-03-05
On Wednesday, 4 March 2020 15:58:27 UTC, Terry Pinnell wrote:> DemonicTubes <tlackie@gmail.com> wrote: > > >On Tuesday, March 3, 2020 at 2:14:00 PM UTC-7, Rick C wrote: > >> On Tuesday, March 3, 2020 at 3:40:56 PM UTC-5, DemonicTubes wrote: > >> > On Tuesday, March 3, 2020 at 12:17:29 PM UTC-7, Rick C wrote: > >> > > On Tuesday, March 3, 2020 at 1:11:09 PM UTC-5, DemonicTubes wrote: > >> > > > On Tuesday, March 3, 2020 at 9:53:11 AM UTC-7, Terry Pinnell wrote: > >> > > > > Terry Pinnell <me@somewhere.invalid> wrote: > >> > > > > > >> > > > > >jlarkin@highlandsniptechnology.com wrote: > >> > > > > > > >> > > > > >>On Tue, 3 Mar 2020 12:32:31 -0000 (UTC), Jim Jackson > >> > > > > >><jj@franjam.org.uk> wrote: > >> > > > > >> > >> > > > > >>>On 2020-03-03, Terry Pinnell <me@somewhere.invalid> wrote: > >> > > > > >>>> 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. > >> > > > > >>>> > >> > > > > >>> > >> > > > > >>>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 > >> > > > > >> > >> > > > > >>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. > >> > > > > > > >> > > > > >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. > >> > > > > >> > > > You could always try putting an NTC resistor in series as an inrush current limiter. Cheap, easy, probably works...why not? > >> > > > >> > > Doesn't even need the temperature coefficient. The NiMH batteries power 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 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? Maybe 2.4 revision??? > >> > > > >> > > Anyway, a quarter ohm or maybe a bit more resistance should be added 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 tenth ohm resistor. > >> > > > >> > > I'm not at all surprised he is getting an overload driving a 4 volt motor from a 5 volt supply. > >> > > > >> > > -- > >> > > > >> > > Rick C. > >> > > > >> > > - Get 1,000 miles of free Supercharging > >> > > - Tesla referral code - https://ts.la/richard11209 > >> > > >> > 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 resistor 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 start out at a few ohms, but quickly drop to almost nothing after a moment of current flow. > >> > >> Trouble is he needs to waste power anyway. He is mismatching a 5 volt supply to a 3.8-4.0 volt motor. So the NTC will only set him up for a future motor failure. > >> > >> -- > >> > >> Rick C. > >> > >> + Get 1,000 miles of free Supercharging > >> + Tesla referral code - https://ts.la/richard11209 > > > >Ah. Sorry, it wasn't clear to me that it is a 4 V motor. If that is the case, a proper supply is a better solution. > > 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.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 any battery. I've not measured anything but suspect the motor is likely drawing way above 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
