Why is this replacement power supply not working? - Page 1
Forum section: electronics / beginners

author: The Shadow
author_rank: Newbie
timestamp: November 01, 2016, 06:36:13 pm
content: Hi everyone!I stumbled upon this forum when a Google search for my problem turned upthis old thread, which may be similar to my issue. So I figured I'll sign up and ask my question; so please go a little easy on me if I'm in the wrong place, or otherwise out of line.I have an electric flour sifter (something like this:http://amzn.to/2fBtp3X). It has a motor that vibrates the entire unit continuously, until all the flour passes through the sifter.The other day, the power supply seemed to have burnt out. So I went and bought an identical one (well, one that seemed identical to me in terms of specs, anyway) and connected it; but the damn thing won't work.I've attached a photo of the two power supplies to this message. The one on the left is the original, the one on the right is the replacement. Both appear to be 12-volt, 1-amp supplies. Yet the new one barely moves the motor at all! There's the tiniest bit of movement, then a delay, then another tiny pulse, then another delay, then another tiny pulse, then another delay... but the motor never actually spins continuously.The only difference I see (besides the "for I.T.E. use only" designation on the old one) is that the new one says"SWITCHING ADAPTOR". Could that somehow be the cause of my issue? If not, then what else could it be?Thanks in advance!

author: Photon939
author_rank: Regular Contributor
timestamp: November 01, 2016, 06:40:18 pm
content: Sounds like the power supply is overloading, shutting down and attempting to restart (I believe this is called hiccup mode)The sifter probably uses a DC brushmotor that can draw a lot of power on startup that the old linear plugpack handled without issue. Unless the old plugpack is also switchmode, in which case you may have just gotten ripped off and it is not capable of 1A.

author: The Shadow
author_rank: Newbie
timestamp: November 01, 2016, 06:45:38 pm
content: Quote from: Photon939 on November 01, 2016, 06:40:18 pmWhy would it overload, if the new power supply has theexactsame specs as the original? Same voltage, same amperage, same everything...Quote from: Photon939 on November 01, 2016, 06:40:18 pmSo in other words... do you think the issue is indeed that the new one is a "switching adaptor" and the old one is not? And that if I manage to procure an identical adapter that isnot"switching", then it should work fine?

author: Farley
author_rank: Regular Contributor
timestamp: November 01, 2016, 06:54:01 pm
content: Could the motor itself be stuck/binding?

author: The Shadow
author_rank: Newbie
timestamp: November 01, 2016, 07:11:35 pm
content: Another data point: I tried it with another adapter, a "universal" one (see attached photo) - which is only rated for500 mA, mind you - and it worked like a charm. The motor sprang to life instantly! So does that prove that "switching" is the issue? The universal one doesn't say "switching" anywhere.Quote from: Farley on November 01, 2016, 06:54:01 pmNope. Works with the universal adapter.

author: Twoflower
author_rank: Frequent Contributor
timestamp: November 01, 2016, 07:23:07 pm
content: Is the 500mA a transformer based supply (heavy and is getting warm)? If yes this could explain why it works. The others are electronic (switching) supplies. They switch off under overload. The transformer based usually don't supply the rated voltage and may break down due to overheat protection if you overload them.I would also assume that the motor is either damaged or the bearings are dirty. This may also explain the damaged original power supply.

author: edavid
author_rank: Super Contributor
timestamp: November 01, 2016, 07:32:21 pm
content: The old 1A supply is also a switching supply (you can tell from the input voltage range). The new 1A supply is probably defective.

author: Twoflower
author_rank: Frequent Contributor
timestamp: November 01, 2016, 07:42:27 pm
content: And the 500mA is it transformer based?If yes that might indicate that the motor or the mechanic, if any, in the sifter does not run freely or a burnt motor which causes to overload the supplies.Probably the new 1000mA supply is not defective, it just shuts off because of the overload.

author: The Shadow
author_rank: Newbie
timestamp: November 01, 2016, 08:28:31 pm
content: Quote from: Twoflower on November 01, 2016, 07:23:07 pmQuote from: Twoflower on November 01, 2016, 07:42:27 pmMakes sense... the 500 mA transformer is indeed much bigger and heavier than each of the 1000 mA units.Quote from: edavid on November 01, 2016, 07:32:21 pmQuote from: Twoflower on November 01, 2016, 07:42:27 pmHow would I test these?

author: Brumby
author_rank: Unknown
timestamp: November 02, 2016, 04:57:25 am
content: The 12V 1A rating for the old and new supplies (which are both switching types) is theircontinuousrating. How they handle a much higher demand in the short term might well be a different story.....This is important because you are talking about motors.A motor has to start from stationary - and at that moment, it requires a good whack of current to get it moving. Once it gets going, though, the current drops back to what it needs to maintain its speed.The old supply could obviously handle that, perhaps through having a decent enough capacitor across the output. Assuming the new supply is not faulty, it may not be strong enough to deliver this start-up current and the protection circuit just jumps in immediately - causing the hiccuping.The 500mA supply would be a transformer type - and they just don't have fancy protection that jumps in so quickly. Rather what occurs is that the current is just taken and the overload happens. Fortunately, overloads usually cause problems by overheating - and this one is over in less than a second, where heating has barely begun, so it will kick off the motor and run for a while. However, by keeping the motor running on a 500mA supply, it'scontinuousrating will be exceeded. The temperature will rise and you will be heading for a supply failure.The new supply might be faulty - but, then again, it might just need a bit of extra capacitance to store enough energy to get the motor moving.

author: Twoflower
author_rank: Frequent Contributor
timestamp: November 02, 2016, 09:13:15 pm
content: Quote from: The Shadow on November 01, 2016, 08:28:31 pmHmm after re-reading your initial post and some answers again: Is the motor encapsulated and really just make the part vibrate? This would mean that the motor/mechanic can't collect dust. Which would probably more pointing to the description Brumby mentions.The old supply might handle a short overload caused by the standing motor much better than the new one. Also the motor might not be an easy load to drive from a switching power supply. Probably the easiest solution would be to see if you can get a transformer based 12V 1A supply.

author: neko efecktz
author_rank: Regular Contributor
timestamp: November 03, 2016, 01:18:53 am
content: There is the possibility of the connector.If using a Barrel Plug. Compare the size of the pins.If the new Adaptor, Plug Pack, Wall Wort has a 1.2mm barrel type plug and the machine has a 2.5mm barrel socketthe new plug would not be contacting and therefore no power to the machine.Just a thought.Bill.

author: The Shadow
author_rank: Newbie
timestamp: November 03, 2016, 11:06:21 pm
content: Quote from: neko efecktz on November 03, 2016, 01:18:53 amIt's a directly soldered connection, not a barrel connector.

author: The Shadow
author_rank: Newbie
timestamp: November 03, 2016, 11:08:15 pm
content: Quote from: Twoflower on November 02, 2016, 09:13:15 pmYes, basically.

author: The Shadow
author_rank: Newbie
timestamp: November 03, 2016, 11:15:45 pm
content: Quote from: Brumby on November 02, 2016, 04:57:25 amI appreciate your thoughts, and explanation. But what I'm really struggling to figure out is... what is the difference between the old and new power supplies? I mean, to the naked eye, the specs look exactly the same. So why/where would there be a difference?

author: Brumby
author_rank: Unknown
timestamp: November 04, 2016, 12:30:36 am
content: Specifications are given to inform you what the product isdesignedto provide - and that if used within those specifications, the unit will deliver the expected performance for a reasonable time. The manufacturer hopes this will be at least the warranty period plus a day.But there are two more things you need to understand.The first being this: The specifications given - 12V 1A DC do notfullydescribe the capability of the supply. These 3 are the basics - ones you have to get right for the fundamental idea of getting a supply that's "in the right ballpark". There is alotmore information about the unit that may affect your ability to use it in a specific application, that is simply not provided. Examples are: What is the ripple for various load currents? What is the current capability for transient loads of various magnitude and duration? What is the temperature rise over time for various currents?These factors can vary significantly for different supplies - and if you were to take a dozen different supplies with the same basic specifications, I will just about guarantee you that they will vary - possibly significantly - on these three questions alone. In your situation I'm thinking the transient capability is one aspect of the old and new supplies that is so different - the new supply being less capable and, thus, being unable to deliver the short term requirement to supply the "stall current" - which happens at switch on, but only for a short time - to overcome the mechanical inertia of a stationary rotor.The second is that, sometimes the final product is capable of more than it was originally designed. A supply specified at 1A continuous might be physically capable of delivering 1.3A, due to the components used. One supply might be able to do that for 10 minutes, another for six months and another for 20 years - but they will all have the same basic specification.The question as to why one supply worked and the other doesn't is exactly the same as asking why, from two 60V 1A NPN transistors, one works in a circuit and one won't. The differences in supplies would become immediately obvious if you were to get the full detailed specifications - just like a transistor datasheet.That is just too complicated for the average consumer and the basics will be enough for most situations. In those instances where the basics don't tell you something that will affect whether a given supply will be suitable (as in your case) the general public are given guidance by those who have experience through the "school of hard knocks" (usually) that "these one's won't work - but this one does" ... with an explanation of "It's just one of those things" and the reasons attributed to the mystery and magic of electrical stuff.

author: Seekonk
author_rank: Super Contributor
timestamp: November 04, 2016, 02:16:31 pm
content: I sense that you really don't have any equipment to teat these like a voltmeter and fixed resistance load. A supply going bad may be an indicator if the motor drawing excess current. I would try an automotive lamp. That would likely be a 13-15 watt lamp drawing about one amp and provide a visual indication of what the supply is doing. A lamp also draws a substantial amount of current when first powered on the order of 7 times more than when hot. Without numbers or a known load further discussion is worthless.

author: The Shadow
author_rank: Newbie
timestamp: November 30, 2016, 07:33:45 pm
content: Update: I resolved the problem by simply paying a few bucks more for a 2.5 A power supply. Thanks for all your help, everyone!

author: metrologist
author_rank: Super Contributor
timestamp: November 30, 2016, 08:49:34 pm
content: bigger hammer usually works, for a while...

author: The Shadow
author_rank: Newbie
timestamp: December 01, 2016, 07:36:28 am
content: Quote from: metrologist on November 30, 2016, 08:49:34 pmMeaning?

author: wraper
author_rank: Unknown
timestamp: December 01, 2016, 09:45:19 am
content: Second PSU is should be counterfeit, therefore good luck getting 1A out of it.Looks like they ripped off TUV mark (in bad quality) from this pic: