Chinese dimmer just had thermal runaway and burned up

[Chuck]

I've been reading about dimmers here and thought I would try dimming my
outdoor LED lights with one of the Chinese 12-24VDC 30A PWM dimmers
found on eBay and elsewhere. The lights are running at 12VDC and
consume 8.5 A. Dimmer was installed, but noticed right away that it was
very warm. In an hour, almost too hot to touch. Should not have been,
not at the current levels I noted. After several hours, it began to
smoke and burn out. In the meantime, lights went to full brightness and
probably then some. Needless to say, the only way I'll be using any
more of these is with an in line fuse as well. Of course, the dimmer
doesn't have one inside.

[Phil Hobbs]

I sure wouldn't use one even with a line fuse.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

[ohg...@gmail.com]

I'm sure it's capable of 30 amps - for a minute at most. Sounds like typical Chinese overestimation. I remember a guy who brought what he insisted was a 1000W amplifier in for repair (said so on the box). I showed him how it drew 125W max off the line. I guess maybe it could do that 500W for a thousand of a second as the rail filters discharged into a 2 ohm speaker.

[Chuck]

I did a little research today. I actually have/had two of these
dimmers. They're all over the net. I had one that seemed to work fine
(also claimed 30 A) and then I just got this other one I had all the
trouble with. They look almost identical except the most recent one has
an amber plastic cover that covers the screw inputs. I decided to
disassemble them both. Circuit boards are different. With the one that
never heats much, there is a much larger transistor than the one that
burned. There are other differences too, but really don't know without
going back to the images I took. So, even though they looked nearly
identical, they weren't. Why would they decide to change something to
the inferior when they had a working unit that was more capable beats me
unless they were trying to save a few cents.

I've never trusted the Chinese stuff. I've unknowingly had their
transistor substitutes in the past that never lasted as long as a
Japanese equivalent. I also see 30V, 20 A switching supplies with
variable voltage all over the place too, but darned if I'm ever going to
buy one.

[Peter W.]

Coming in late on this.

30A @ 24V = 720 watts. Unless the dimmer weighs as much as a standard brick, it is not going to pass that much current for more than a very few microseconds. So much for the "Rating".

Now, 8.5A at 12V = 102 watts. So, using an average of 15ma/led, that is something like 560 typical LEDs. Allow 450 for standard losses. So, any number substantially fewer than 450 LEDs in the string will represent current going up in heat. Think of it as 0.23 watts per LED. So, if there are only 200 LEDs in the string, over 50 watts is going up in heat - somewhere - as you experienced.

These are very rough 'back of the envelope' calculations, involving a S.W.A.G. or three. But, when considering such devices for such uses, common-sense basic calculations can avoid very unfortunate down-line results.

Peter Wieck
Melrose Park, PA

[Phil Allison]

Peter Wanker the PITA TROLL. wrote:
==========================

> Coming in late on this.
>

** FFS Stay away, you imbecile.

> 30A @ 24V = 720 watts. Unless the dimmer weighs as much as a standard brick, it is not going to pass that much current for more than a very few microseconds. So much for the "Rating".

** Fucking hell, wot crap.

[Erick]

I've been using one for two years to brighten and dim about 10 amps
worth of LED lights. It burned out, most likely from a power outage
where the electricity kept going on and off rapidly for a few seconds
last year. I always worry when that happens because it can ruin
anything connected and running at the time. Anyway, just after that the
lights didn't come on that night. When I checked the fuses, both were
blown. I had two fuses ahead of the dimmer, one in each line. Replaced
those and still nothing from that dimmer. So I think it was that power
surge that did the damage. Second one has been going strong for 18
months now.

[Chuck]

On 11/16/20 1:50 PM, Chuck wrote:

That's it, no more Chinese dimmers! I just can't trust them. This
week, I managed to pick up a linear variable voltage and current Astron
12 amp power supply. It won't be as efficient as switching units, but
Astron is apparently a winner with amateur radio folks and reviews tout
its reliability. I looked at the schematic and it seems that all of
their units use the same general design, just different transformers and
components of course as size increases. I like the fact that the
schematics are readily available unlike this Chinese stuff where it is
next to impossible to find one! I have even been able to peek at
several internally online of course, but apparently people often tweak
and modify them and post images and such online. Nice to see the innards.

[Ralph Mowery]

In article <rpe4qj$42v$1...@dont-email.me>, chuc...@yahoonospam.com
says...

>
> That's it, no more Chinese dimmers! I just can't trust them. This
> week, I managed to pick up a linear variable voltage and current Astron
> 12 amp power supply. It won't be as efficient as switching units, but
> Astron is apparently a winner with amateur radio folks and reviews tout
> its reliability. I looked at the schematic and it seems that all of
> their units use the same general design, just different transformers and
> components of course as size increases. I like the fact that the
> schematics are readily available unlike this Chinese stuff where it is
> next to impossible to find one! I have even been able to peek at
> several internally online of course, but apparently people often tweak
> and modify them and post images and such online. Nice to see the innards.
>
>
>

Astron has been using the same basic design for many years for their
linear supplies. There is almost no difference in any of them, just
more pass transistors and bigger transformers. That same circit has
been used in many other power supplies with minor variations. All
designed around the 723 voltage regulator. It is almost like a
cockroach and the circuit will not die as it is very reliable.

I have a 50 amp one that has been on 24/7 for around 30 years. Only cut
off when I moved and to rearange the equiipment.

They do have two weakness in that if you push their ratings the
transistor socket pins get loose and do not make good contact.
If the power is cut off and right back on say as can hapen during a
storm the over voltage protection will trip and you have to cut it
off,count to about 10 slow and then turn it back on.

I have another supply of no name that uses the same basic circuit and it
has been on over 40 years.