Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old November 24th 20, 04:18 PM posted to sci.electronics.repair
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Default another dimmer smoked today outside thank goodness!

On 11/24/20 10:05 AM, Peter W. wrote:
https://www.cpumedics.com/dell-cpb09...xoCAlsQAvD_BwE


https://www.cpumedics.com/dell-dk87p...hoCExQQAvD_BwE

If sold in the United States:

There will not be a UL mark on a computer power supply.
There will be a UR mark on a computer powers-supply.
If there is neither, it is a knock-off.

The power-supply is a sub-assembly. Not the main event.

Peter Wieck
Melrose Park, PA


Interesting

https://www.pcscsecurity.com/wp-cont...susUR_PCSC.pdf

Any external supplies I have do have the UR mark.

Well, thanks for the info. Nice to learn something new everyday. I
will no longer be tempted by the lure of the cheap Chinese eBay junk.

I will say that, by all accounts, this should have been a decent dimmer
judging by the components within but I now believe the lack of
heatsinking was the reason for the failures. The internal design looks
simple enough that, before I trash it, I may try and draw out a
schematic since most of the schematics for this junk don't exist.

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Old November 24th 20, 08:36 PM posted to sci.electronics.repair
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Default another dimmer smoked today outside thank goodness!

On 2020/11/24 6:42 a.m., Peter W. wrote:
https://www.cui.com/blog/what-is-the...-ul-recognized

https://store.intellaliftparts.com/b...abbreviations/

Per the NEC and various codes, powered item permanently installed (in the USA) is required to carry a UL/ETL listing.
Technically, any mains-attached (plug-in) item sold to the public (in the USA) is also required to carry a UL/ETL listing. At whatever operating voltage.
UL Listed items made up of sub-assemblies will typically carry UR symbols on those sub-assemblies. Repairs made to such items must be with UR components.

Where this gets cute: That junk from China is sold from, and originates in China, is typically shipped via subsidized Chinese Post, and directly to the consumer - thereby avoiding the letter of regulations and codes. And then there are here-today-gone-tomorrow resellers that get around the code by simply ignoring it. Making their consumers potential victims.

https://www.galco.com/buy/Staco-Ener...xoCQPcQAvD_BwE This device carries a CSA mark.

https://www.ebay.com/itm/20Amp-Varia...V/124023830503 This device does not. Note the difference in cost. That cost is not only for those obscene profits on the part of the manufacturer, but also for proper design, proper testing, basic quality control, insurance and all the other unnecessary niceties avoided by the resellers and their suppliers. So, the bottom line is that you get what you pay for, with all the consequences attached thereto.

Peter Wieck
Melrose Park, PA


Thanks for taking the time to reply to such depth. I will be flagging
this so it is easily retrieved in the future!

John :-#)#

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Old November 24th 20, 10:05 PM posted to sci.electronics.repair
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Default another dimmer smoked today outside thank goodness!

On 11/24/20 2:36 PM, John Robertson wrote:
On 2020/11/24 6:42 a.m., Peter W. wrote:
https://www.cui.com/blog/what-is-the...-ul-recognized


https://store.intellaliftparts.com/b...abbreviations/

Per the NEC and various codes, powered item permanently installed (in
the USA) is required to carry a UL/ETL listing.
Technically, any mains-attached (plug-in) item sold to the public (in
the USA) is also required to carry a UL/ETL listing. At whatever
operating voltage.
UL Listed items made up of sub-assemblies will typically carry UR
symbols on those sub-assemblies. Repairs made to such items must be
with UR components.

Where this gets cute: That junk from China is sold from, and
originates in China, is typically shipped via subsidized Chinese Post,
and directly to the consumer - thereby avoiding the letter of
regulations and codes. And then there are here-today-gone-tomorrow
resellers that get around the code by simply ignoring it. Making their
consumers potential victims.

https://www.galco.com/buy/Staco-Ener...xoCQPcQAvD_BwE
This device carries a CSA mark.


https://www.ebay.com/itm/20Amp-Varia...V/124023830503
This device does not.¬* Note the difference in cost. That cost¬* is not
only for those obscene profits on the part of the manufacturer, but
also for proper design, proper testing, basic quality control,
insurance and all the other unnecessary niceties avoided by the
resellers and their suppliers. So, the bottom line is that you get
what you pay for, with all the consequences attached thereto.

Peter Wieck
Melrose Park, PA


Thanks for taking the time to reply to such depth. I will be flagging
this so it is easily retrieved in the future!

John :-#)#


I appreciate this too. Further investigation on my part might shed
light on a cause for both of my dimmer failures: too high of input
voltage! Even though advertised as 12-24VDC input, I tend not to trust
this figure and, after looking at the components inside, I think it's
12V, period! Unfortunately, the driving supplies I had been using for
this were more like for standard Ham radio, 13.8 VDC. Perhaps this
higher voltage could not be handled by the dimmer components.

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Old November 24th 20, 11:07 PM posted to sci.electronics.repair
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Chuck wrote:
============

I appreciate this too. Further investigation on my part might shed
light on a cause for both of my dimmer failures: too high of input
voltage! Even though advertised as 12-24VDC input, I tend not to trust
this figure and, after looking at the components inside, I think it's
12V, period! Unfortunately, the driving supplies I had been using for
this were more like for standard Ham radio, 13.8 VDC. Perhaps this
higher voltage could not be handled by the dimmer components.


** You have an obvious overheating failure of one mosfet in a parallel pair.
As mosfets heat up, the on resistance increases by a factor of 2 or more.
So the temp rise does as well.
Having no heatsink at all in that device is nuts.
Bad design, buy something else.


....... Phil



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Old November 24th 20, 11:38 PM posted to sci.electronics.repair
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Default another dimmer smoked today outside thank goodness!

Chuck wrote:


I appreciate this too. Further investigation on my part might shed
light on a cause for both of my dimmer failures: too high of input
voltage! Even though advertised as 12-24VDC input, I tend not to trust
this figure and, after looking at the components inside, I think it's
12V, period! Unfortunately, the driving supplies I had been using for
this were more like for standard Ham radio, 13.8 VDC. Perhaps this
higher voltage could not be handled by the dimmer components.


** You have never posted what PSU voltage you have been using ???

The rating of 12-24V applies to the LED array it is driving.

You cannot use a 24V supply, connect a 12 V LED array and set the control half way.


...... Phil



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Old November 25th 20, 01:35 AM posted to sci.electronics.repair
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Default another dimmer smoked today outside thank goodness!

On 11/24/20 5:38 PM, Phil Allison wrote:
Chuck wrote:


I appreciate this too. Further investigation on my part might shed
light on a cause for both of my dimmer failures: too high of input
voltage! Even though advertised as 12-24VDC input, I tend not to trust
this figure and, after looking at the components inside, I think it's
12V, period! Unfortunately, the driving supplies I had been using for
this were more like for standard Ham radio, 13.8 VDC. Perhaps this
higher voltage could not be handled by the dimmer components.


** You have never posted what PSU voltage you have been using ???

The rating of 12-24V applies to the LED array it is driving.

You cannot use a 24V supply, connect a 12 V LED array and set the control half way.


..... Phil


So, it could have been either lack of heatsinking, my 1.8V overvoltage,
or both?

Thanks for the clarification on the 12-24V. I certainly didn't know this!
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Old November 25th 20, 02:04 AM posted to sci.electronics.repair
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Default another dimmer smoked today outside thank goodness!

On Wednesday, November 25, 2020 at 11:35:21 AM UTC+11, Chuck wrote:
On 11/24/20 5:38 PM, Phil Allison wrote:
Chuck wrote:


I appreciate this too. Further investigation on my part might shed
light on a cause for both of my dimmer failures: too high of input
voltage! Even though advertised as 12-24VDC input, I tend not to trust
this figure and, after looking at the components inside, I think it's
12V, period! Unfortunately, the driving supplies I had been using for
this were more like for standard Ham radio, 13.8 VDC. Perhaps this
higher voltage could not be handled by the dimmer components.


** You have never posted what PSU voltage you have been using ???

The rating of 12-24V applies to the LED array it is driving.

You cannot use a 24V supply, connect a 12 V LED array and set the control half way.


..... Phil

So, it could have been either lack of heatsinking, my 1.8V overvoltage,
or both?

** Was you 8A current figure when the controller was set to full ?

Thanks for the clarification on the 12-24V. I certainly didn't know this!


** Yes - it is missing data in the advertising.

A PWM controller is *not* a voltage regulator, merely a " time division" current reducer.

If the voltage is a little high, the current will be way higher.


....... Phil
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Old December 22nd 20, 12:16 AM posted to sci.electronics.repair
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Default another dimmer smoked today outside thank goodness!

wrote:
On Monday, November 23, 2020 at 3:50:47 PM UTC-5, Chuck wrote:
Well, I have one additional so called "30 amp" Chinese dimmer remaining
after the prior one smoked. This one had a circuit breaker and it did
go today, but not before it started smoking. As I said, I have a good
Astron power supply on the way to replace, but I still had the dimmer in
place until then and outdoors.

This time, I decided to open it up and see what's going on. As others
have said, the Chinese tend to exaggerate ratings so "30 amp" was
probably far from it, but I was surprised what I saw internally:

two HY1707 Mosfets
an LM358
a 78L05
a 555 timer


non inductor ???


At 12V, 7 amp load, it seems like it should have been able to handle the
load, but I am wondering that since I was driving it with a switching
supply, maybe that somehow affected the dimmer? By the way, the burnout
was one of the HY1707's. Perhaps they actually need a heatsink instead
of just being attached to the circuit board?

That's absolutely all for the Chinese stuff. I had a constant voltage/
current module on the way, but not even going to open it. Can't trust
it anymore.


A device like that needs a proper heatsink. Even if the metal tab is soldered to the PC it's still inadequate for high power applications.


For 70A mosfet 7A is light load. Estimate based on typical
values shows that it should disspate about 0.3W. For TO-220
part at that load heatsink makes little economic sense: mosfet
will run fine without heatsink and better (lower Rdson)
mosfet is cheaper than heatsink. Of course, if one wants
to handle nominal 30A, than heatsink would be necessary.

The above assumed that there is an inductor and that second
HY1707 works as synchronous rectifier. Otherwise RMS current
may be much larger than average.

--
Waldek Hebisch
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Old December 22nd 20, 12:45 AM posted to sci.electronics.repair
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wrote:

=============================

** Some uni****** dope


A device like that needs a proper heatsink. Even if the metal tab is soldered to the PC it's
still inadequate for high power applications.

For 70A mosfet 7A is light load. Estimate based on typical
values shows that it should disspate about 0.3W.


** It will be much higher in practice.


to handle nominal 30A, than heatsink would be necessary.


** The OP's rms current is way higher than 7A.

The above assumed that there is an inductor and that second
HY1707 works as synchronous rectifier.


** You on crack ???

Do you have no idea what this device is ?

It is **NOT** a power supply .

It is just an on/off switch performing PWM lamp control.



...... Phil
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Old December 22nd 20, 03:17 AM posted to sci.electronics.repair
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Phil Allison wrote:
wrote:

=============================

** Some uni****** dope


A device like that needs a proper heatsink. Even if the metal tab is soldered to the PC it's
still inadequate for high power applications.

For 70A mosfet 7A is light load. Estimate based on typical
values shows that it should disspate about 0.3W.


** It will be much higher in practice.


to handle nominal 30A, than heatsink would be necessary.


** The OP's rms current is way higher than 7A.

The above assumed that there is an inductor and that second
HY1707 works as synchronous rectifier.


** You on crack ???

Do you have no idea what this device is ?

It is **NOT** a power supply .

It is just an on/off switch performing PWM lamp control.


Well, I would prefer to put inductor in such device. But
you are right, inductor (+ good control) would be too expensive
for current market. At first I was mislead by mention of two
mosfets, but connecting them in parallel (to get higher current)
in simple PWM makes sense.

--
Waldek Hebisch


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