another dimmer smoked today outside thank goodness!

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

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.

Reply to
Chuck
Loading thread data ...

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.

Reply to
ohger1s

I think that's why they are burning up, then. Nothing else on the board was fried, only the one Mosfet.

Reply to
Chuck

ng

in

the

ut

d
/

tal tab is

board

Going back to my ham radio days, my 2 meter amps of 100 W had heatsinks of probably 4x6 and an inch or two thick, IIRC. Sometimes even a fan too. My guess is that would at the very least be needed for these dimmers and even that heatsink size will get it no where near say 300 W+. Shame on them.

Reply to
Chuck

did

good

n

hers

e

urnout

stead

tage/

rust

No UL approval I'm sure.

Why would you trust it then?

Unregulated electrical junk sold on Amazon can be hazardous to your house or your family.

John :-#(#

Reply to
John Robertson

John Robertson wrote: ================== >

** What standard is there for such a device the runs on 12- 24V DC ??

** UL does not check for good design or reliability.
**True - but this is not a good example for that.

..... Phil

Reply to
Phil Allison

Fair enough, under - what is it - 32VAC is unregulated...

John ;-#)#

Reply to
John Robertson

formatting link
cognized

formatting link

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

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 th e consumer - thereby avoiding the letter of regulations and codes. And then there are here-today-gone-tomorrow resellers that get around the code by s imply ignoring it. Making their consumers potential victims.

formatting link
This device carries a CSA mark.

formatting link
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, basi c 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

Reply to
Peter W.

Yes, I definitely see that now. Unfortunately, I had really hoped to be able to use one of these dimmers because the linear supply is going to take up more space, but I will not sacrifice my safety for space. I do wonder about something like PC power supplies. I have some old Dell ones, many times used for other purposes (those three voltage rails sure come in handy sometimes), but none that I can see have any UL listings. I've had desktop PC's run for years 24/7 without incident. Anything that ever went bad was usually memory or hard drives and such. I've had a lot more trouble with laptops (but still not laptop power supplies... motherboards!), but that's a story for another day.

Reply to
Chuck

formatting link

formatting link

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

Reply to
Peter W.

Interesting

formatting link

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.

Reply to
Chuck

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

John :-#)#

--
(Please post followups or tech inquiries to the USENET newsgroup) 
                      John's Jukes Ltd. 
 Click to see the full signature
Reply to
John Robertson

ul-recognized

is not

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.
Reply to
Chuck

Chuck wrote: ============

** 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

Reply to
Phil Allison

** 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

Reply to
Phil Allison

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!

Reply to
Chuck

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

** 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

Reply to
Phil Allison

non inductor ???

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
Reply to
antispam

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

** Some uniwanker dope

** It will be much higher in practice.
** The OP's rms current is way higher than 7A.
** 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

Reply to
Phil Allison

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
Reply to
antispam

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.