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Why do my power adapters keep failing?
Old 30th November 2009
  #31
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brianroth's Avatar
 

Over the Holidaze <g> I did a totally informal, non scientific survey.

I asked my Dad and Mom about wall warts, and a random sampling of friends who own gear or studios....or consumer gear.

Perhaps Oklahoma has AC Mains "issues", but the consistent thing is China-made wall warts that crap out.

Frequently.

UL listings mean nothing.

No fires reported, but PLENTY of "hmmmm...this no longer works...and it smells funny....."

Chinese wall warts = junk = a trip to Radio Shack/wherever....or as my parents typically do....chunk the gear and buy some other piece of chinese junk.

Bri
Old 1st December 2009
  #32
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2N1305's Avatar
 

Quote:
Originally Posted by JohnRoberts View Post
Ok.. How bright are you light bulbs?

UK changing from nominal 240V to nominal 230V should result in soft if anything mains for older gear, but newer (230v) gear connected to a mains supply that is still old school 240V will be slightly hot.

...
I had a situation at my home several years back where my nominal 240V mains drop had crept up to 260-270V and was still rising, because my local power distribution station had a stuck boost winding switch. I called my power company, and they whacked it with a spanner, or whatever they do to get it unstuck. I don't expect this to be your problem either, but do recall after the 230v transition, there were reports of power stations dragging their feet, because lower mains voltage meant lower revenue.

..

JR
Maybe that's what is happening around his neighborhood. The nly way to know now is have him call an electrician s he can measure the voltage. As you so simply put it: If you don't feel comfortable doing it, don't.
Old 1st December 2009
  #33
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2N1305's Avatar
 

stupd keybard!
Old 1st December 2009
  #34
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JohnRoberts's Avatar
 

In my case the incandescent lamps were so bright it got my attention and I dusted off my VOM to test the voltage. When the VOM confirmed too much voltage, I went to my fuse box to make sure I didn't have a flaky center tap ground causing my 240 to not split evenly across the branches (a US problem). When I saw 270 at my fuse box I called the power company, who didn't believe me, but since it was a slow night they drove 25 miles to check it our, and were rewarded with a real problem.

This was in the evening, and these step up transformer windings are supposed to automatically release as load drops off. In this case, as load dropped off, the mains voltage kept creeping up... If I didn't get them out there to fix it, who knows how high it might have gone as more folks went to bed and more load dropped off...

I suspect my situation was pretty rare, but it is not uncommon for people to have hot or cool mains feeds depending on where they are on a distribution line. And UK had the legacy 240/230 issue.

JR
Old 3rd December 2009
  #35
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Here in Ye Hacienda, I frequently check the AC Mains...I guess I am either paranoid or bored...LOL! During my frequent checks (OK...NOT 10 times a minute....but every few days, and during various seasons) I see it wander from maybe 119 VAC to 121 VAC, according to my RMS reading Fluke. The OG+E step-down tranny is on a concrete pad in my backyard...and the secondary is shared with ?? numbers of neighbors.

Incandescent bulbs seem to last a reasonable length of time here....no frequent blow outs. Yet, I've had more than a few chinese wall warts crap out. The wart for my HP scanner died a couple years ago (which made me interested in the topic..). I had a Rat Shack analog/regulated PSU which I tweaked from 13.whatever V (it was intended to run auto electronics) down to 12V and it's been perfect.

Since that time, I've had several other "warts" for cordless phones, etc die here as well. My clients all over town are constantly finding dead warts, and yet I cannot say I've ever detected AC mains much over 122VAC.

I still say...Chinese warts are junk.

Bri
Old 3rd December 2009
  #36
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Making wall warts cheap and reliable are two conflicting goals. They don't have an option about making them safe so they are typically double insulated and thermally fused. How many people do you hear about who have been killed or even shocked by Chinese wall warts???? None that I know of personally. I can't say that about internal PS.

The poor reliability of these are the consequence of engineering decisions, not some cultural artifact of where they were made. As we become more comfortable with disposable consumer electronics, this will just get worse as sharp pencil accountants minimize expensive copper and iron used.

That said, there is at least some modest expectation of service that seems to be lacking in this example, so there may be some contributing factor that is taking out these weak sisters.

JR
Old 5th December 2009
  #37
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John...all I WAS trying to say is the "local fact" of the dead wall warts....

100 percent came from china.

China junk is junk.

Period!!

Bri
Old 5th December 2009
  #38
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Hi
What else is in your rack?
If it happens you have a decent size power amp or desk power supply it could be the 'kick' when you power the rack down which is 'spiking' your little supplies.
Other units with 'real' transformers tend to only fail due to overheating which is a function of overload, temperature and time.
I have seen this if you have an old type flourescent tube in parallel with a 'low energy' type lamp. You know the ones, hardly any light and 8000 hours use that somehow fail quite quickly! When you power off the kick from the flourescent kills the transistors in the low energy lamp.
While not exactly safe, if done carefully you could use an IEC cord to measure the mains.
With it completely disconnected, put the probes into the 2 smaller socket holes of the female end. Maybe use a bit od pvc tape top hold them in place. DO NOT TOUCH THE CABLES NEAR THE CONNECTION.
Make sure the meter is set to be able to measure 250 Volts AC, then switch on.
The mains in the UK should be between 218? and about 253 but most places I have measured across the UK are between 230 and 240. I don't think I have ever found any more than 250 Volt.
A good quality surge / spike protecting unit OUGHT to be able to sort this out but may not.
Powering your 'wall warts' off BEFORE anything else may also be a solution, but it is a bit dependant on remembering to do this.
Matt S
Old 5th December 2009
  #39
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Thanks Matt

Quote:
Originally Posted by Matt Syson View Post
Hi
What else is in your rack?
If it happens you have a decent size power amp or desk power supply it could be the 'kick' when you power the rack down which is 'spiking' your little supplies.

Quote:
Originally Posted by Matt Syson View Post
A good quality surge / spike protecting unit OUGHT to be able to sort this out but may not.
Powering your 'wall warts' off BEFORE anything else may also be a solution, but it is a bit dependant on remembering to do this.
I will make sure that I keep this in mind as this would make sense and certainly seem to relate to when the last power supply failed. I connected the power supply to a relevant device and the unit remained powered up for around 15mins before the whole studio was shut down and powered off. The next day when i powered the studio up the power supply was dead so it is quite possible that it was damaged by the powering down/up procedure. In addition to this, the units that appear to be more prone to having the power supplies fail on them do not have a power on/off switch and rely purely on being turned on/off by the mains.

UPDATE - My mains output has been checked and appears to be fine.

It appears that it's quite possible that a number of issues are contributing to my problem but judging by the feedback you guys have given me it appears that my most likely suspects are:

1. The units are drawing a little too much power than the wall warts can supply and causing them to overheat, burn out and fail.
2. The powering up/down procedure is spiking the supplies and damaging them.

I have ordered some new power supplies of the same spec (AC/AC 9V) which I hope to be of better quality and also have a slightly higher 'ma' rating than the original Alesis wall warts. I believe that the original Alesis power supplies are of 800ma and these ones i have being sent to me are 1000ma. From what i understand it doesn’t matter if the 'ma' is higher than the device needs as it will simply draw what it required.

I'm thinking that by going a little higher with the 'ma' rating then this will give that extra headroom which is required?

I will also try keeping all the relevant power supplies on the same power strip and power these down separately and before the rest of my rack gear.
Old 5th December 2009
  #40
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I give up.....no one believes me.

Bri
Old 5th December 2009
  #41
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Quote:
Originally Posted by brianroth View Post
I give up.....no one believes me.

Bri
So what non 'made in China' AC power supplies do you recomend?
Old 5th December 2009
  #42
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Quote:
Originally Posted by brianroth View Post
I give up.....no one believes me.

Bri
I'm not sure what your point is?

Yes, Chinese wall warts are engineered with a sharp pencil to be as cheap as possible and still work well enough to not lose business because they don't meet spec. I may be unusual but I happen to have some Chinese wall warts laying around that outlasted the appliances they came with.

I have also used very large numbers (trust me) of one Chinese wall wart on numerous similar but different finished products at my old day job. Not strangely only the units with the heaviest current draw, had any noticeable field failure rates. It was not random and I never had a problem with any of my products. Some engineers in other departments, using "my" WW transformer, were not as conservative as I was. I used to get all the complaints from the service department, because I was the engineer who brought the part into our system, even though I couldn't make everybody use it responsibly (it has a thermal fuse DOH).

I brought in a 1A WW and used it in applications from <100mA and up. Only one finished product I designed was capable of killing that WW (A headphone amp that could drive loudspeakers.) So I current limited the PS draw inside the SKU, and it was reliable after that (while still capable of melting ear wax with cans).

I guess what I am saying is that thermal fuses are required safety components, and real world reliability depends on how much headroom the product engineers are willing to pay for and design in.

What may perhaps never be answered is whether this is a case of a design engineer not providing adequate headroom in the original specification, or a Chinese manufacturer delivering less that he contracted to. If the latter, I would expect the product company to be more forthcoming with free replacements. if the former, they could be less helpful.
======

I am not sure how any of this is helpful to the OP, but yes, upgrading to a 1A WW from 800 mA should help, if it is a marginal thermal capacity like I suspect. If the product is drawing more than design current due to some soft failure, maybe this will push it over the edge.

I would still be inclined to measure the actual product current draw. Since this could be on the low voltage secondary, no life threatening voltages are involved.


JR
Old 6th December 2009
  #43
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Hi
I must admit AC to AC WW failing due to 'spikes' would strike me as odd as a bit of copper wire and an iron core tend to be quite reliable. I suppose if they were slightly 'up market' units they could have varistors in them which are failing when 'spiked'.

Checking the ACTUAL AC drawn by the unit's in question would be interesting for this discussion, as would checking how warm they are actually running.
Despite having been to the USA a few times, whenever people refer to 'made in USA' I do tend to think of the 1950's old time movies with a bloke with a black hat and long coat standing on a horse drawn waggon promoting 'snake oil', ready to shoot his way out of having to deal with 'warranty' issues.
Gear made cheaply AND badly can come from anywhere.
Matt S
Old 8th December 2009
  #44
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Mylithra's Avatar
 

Is it possible you're getting too much DC on your AC line? Could cause some interesting problems with power Transformers. I dont know about blowing them up, but if its really high, I suppose it could.
Old 8th December 2009
  #45
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Hi
I would doubt high DC as the primary resistance of a wall wart is pretty high so it's heating effect would be small. Other gear with bigger transformers are more likely to take the hit if this were the case.
Matt S
Old 8th December 2009
  #46
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Quote:
Originally Posted by Matt Syson View Post
Checking the ACTUAL AC drawn by the unit's in question would be interesting for this discussion.
Matt S
May seem like a silly question to any professional techies round here, but could you explain in basic terms how I can check this?

Quote:
Originally Posted by Mylithra View Post
Is it possible you're getting too much DC on your AC line? Could cause some interesting problems with power Transformers. I dont know about blowing them up, but if its really high, I suppose it could.
What exactly do you mean by this?
Old 8th December 2009
  #47
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Hi
To check the current taken by your gear you would have to 'break' one of the 2 wires going into the unit (one of the wires on your wall wart) and fit an ammeter in the circuit.
This is of course a complete 'pain' as you have to cut one of the wall wart wires and then 'stick it back together again' after you have made the test.
Your multimeter's instructions should tell you how to go about this.
Regarding DC on the mains supply. Although there may be some DC superimposed on the AC mains I would not expect this to be the issue. Basically the AC mains SHOULD be a sinewave whose 'zero' point in the wave is at 'ground' level. It is possible that due to other gear with half wave rectifiers or dimmer circuits that the reference point is actuallt 'offset' by a constant DC level. Unless this were to be more than a volt or two then it would not upset your wallwarts.
Matt S
Old 9th December 2009
  #48
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brianroth's Avatar
 

I've opened multiple "junk" "chinese" warts.

They are actually a complex batch of circuit boards (aka..a "switcher") power supply.


Junk junk junk

Bri
Old 9th December 2009
  #49
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Quote:
Originally Posted by Matt Syson View Post
To check the current taken by your gear you would have to 'break' one of the 2 wires going into the unit (one of the wires on your wall wart) and fit an ammeter in the circuit.
This is of course a complete 'pain' as you have to cut one of the wall wart wires and then 'stick it back together again' after you have made the test.

Matt S
I am surrounded by so many broken power supplies at the moment that I must admit that I am kind of reluctant to purposely go breaking any more. Maybe I will have to though for the greater good!

Quote:
Originally Posted by brianroth View Post
I've opened multiple "junk" "chinese" warts.

They are actually a complex batch of circuit boards (aka..a "switcher") power supply.


Junk junk junk

Bri
Amongst the various power supplies that I have running in my home studio there are a number of cheap Chinese made ones which have been working perfectly well for many years. Out of the numerous power supplies that I’m currently using ONLY the official Alesis power supplies seem to be failing on me! They are not of the same batch as were purchased over a period of many years, are failing on various pieces of gear so it’s not being caused by one particular piece of faulty equipment and they have all been running fine with no problems for many, many years up until now. The mains output was tested and appear to be normal.

Judging by the advice that I have been given on these pages it seems that I currently have two options:

· To try replacing the Alesis power supplies with ones of a slightly higher 'ma' (1000 instead of 800) to give a little extra headroom. Who knows it may just work?
· It has been suggested that it is possible that there could be some kinda ground loop introducing a voltage differential somewhere in my studio wiring, adding to the voltage and causing the power supplies to fail. It may be worth me exploring this for reasons outlined below.

As I have mentioned in previous posts, the issue that I have with the Alesis power supplies does appear to coincide with when I had some serious ground hum issues in my home studio. Coincidence? Maybe, maybe not. However, I spent weeks trying to eliminate some serious hum/noise and finally managed to eliminate it but could there still be some kind of ground loop occurring that isn’t being picked up on the audio path but instead is now playing havoc in other areas and damaging certain power supplies?

I am keen to hear if anyone has ever encountered such a problem.

Would the 'AC' power supplies be more prone to being damaged in this scenario as that’s the only thing that seems to separate the Failing Alesis power supplies and the numerous other 'DC' type that are running perfectly well.
Old 9th December 2009
  #50
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Hi
I have not looked at the Alesis WW's but typically they don't have a ground connection so all of the 'ground loop' speculation is nonesense.
IF the Alesis units do have a 'ground' connection from the earth pin to it's output wiring then these is SOME possibility.
Are your supplies AC out or DC out units? You said AC in the past and in this case they will not be 'switcher' type units.
Matt S
Old 9th December 2009
  #51
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This is speculation on my part, while informed by experience designing with WW.

If you are having a problem with just one product, either that WW is marginal in design specification, improperly built, or the product is demanding more current from the WW than the design target (faulty).

While mains voltage waveform, and/or nominal voltage is a less likely but still possible explanation (because other gear is not failing).

-------

I have probably said this before, I would be inclined to measure the current draw of the product that is eating WW. While rare, it is always possible that there is some soft failure mode.

You say your get hum coincident with WW failures? Unusual high current draw in the product could be causing hum, most likely isolated in the product, but if unbalanced wiring is involved it could corrupt other audio paths.

This high current draw might also clear when the product has cooled off.

=======

I repeat this is speculation, and if the problem is an intermittent high current fault, it will be difficult to find and correct. Another temptation is a resettable thermal breaker (fuse) added in series with the WW and sized to protect the WW. But this is getting a little Rube Goldberg. It would help identify an intermittent high current fault as the failure vector.

JR
Old 9th December 2009
  #52
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Quote:
Originally Posted by JohnRoberts View Post
I have probably said this before, I would be inclined to measure the current draw of the product that is eating WW. While rare, it is always possible that there is some soft failure mode.
So to measure the current draw of the product do I have to break open the wires of the power supply and attach a multimeter?
Old 9th December 2009
  #53
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Hi
Yes I am afraid so unless you manage to use the plug off a broken unit which you then attach carefully to your working unit with 'sticky tape' for the 'outer' connection and use the inner, via an AMMETER to measure the current. NOTE this will be only an indication as the exact current would need a high quality RMS reading ammeter.
Matt S
Old 9th December 2009
  #54
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Quote:
Originally Posted by Matt Syson View Post
Hi
Yes I am afraid so unless you manage to use the plug off a broken unit which you then attach carefully to your working unit with 'sticky tape' for the 'outer' connection and use the inner, via an AMMETER to measure the current. NOTE this will be only an indication as the exact current would need a high quality RMS reading ammeter.
Matt S
I have just dug out an AC power supply that has an interchangable barrel connector. Due to this interchangable connector i can open the connection up slightly to expose the two pins. I'm assuming that i can get the probes of my multimeter on those and get a reading while its powering the unit?
Old 9th December 2009
  #55
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Hi
Not quite!
What you are proposing is to connect a meter in PARALLEL with the unit. If using a VOLTMETER it would tell you the voltage, but you don't need to know this.
What you need to do is conspire to get an AMMETER wired in SERIES with one of the exposed pins.
Wikipedia or whatever the BOLD terms to get a grip on what you should be doing. Messing with mains connections is dangerous to you. Read up on Voltage and Current and using a multimeter before you really try this as you may damage either the power supply or your unit. The voltages here are unlikely to actually hurt you.
A silly question perhaps but I presume the Alesis unit is marked as requiring AC supply and not DC?
This will be marked on the gear and in it's handbook.
Matt S
Old 9th December 2009
  #56
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Whoa,, I am not talking about mains voltage...

Yes, in series with the WW output which will be double insulated and low voltage.

Use a end cut off from one of the broken WW you have.

Make sure your ammeter has a 1+A scale or use a very low value resistor in series and measure the voltage drop across that.. (A 1 ohm R would drop < 1V for < 1A).

As I said before if not comfortable don't mess around, but this should be relatively safe for you,, not so much for the WW if you short it's output.

JR
Old 9th December 2009
  #57
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Yes, the units are clearly marked as requiring AC. I also checked the Alesis website that confirmed that their P3 power supplies, which are the type i have been using, are the appropriate ones for the various devices I have here.

I have carried out another check on my mains outlet tonight using my multimeter and I'm still getting readings of between 231-236VAC so everything seems to be ok there.

I have obtained a replacement (non Alesis) power supply today, 9V AC 1000mA. I will run this for a few days and see how it goes. Hopefully due to the slightly higher 'mA' and possibly better quality components this type will run the units ok.

I'd like to thank you all again for your ongoing assistance, suggestions and opinions on this matter, it is very much appreciated. thumbsup
Old 10th December 2009
  #58
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dialectic,

Not to derail the thread but, if you go out to boot sales / flea markets, have a dig through the WWs that are there. I almost always find a few AC wallwarts for a euro a piece. At most, you'll have to change the gear-end plug.

Karl

w/3 RNCs, Alesis microlimiter, Lexi Alex ...all on bootsale PSU
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