LED dimmer warning

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PaulRainbow

PaulRainbow

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Another close shave for some wiring. I was asked by someone to connect a key fob remote LED dimmer to some LED lights he'd fitted. He'd purchased the dimmer from a seller on Amazon, looked like this one on Ebay :

https://www.ebay.co.uk/itm/Wireless...m=162810124469&_trksid=p2060778.c100290.m3507

Simple job to fit. Turned the LEDs on and they seemed fine. Turned them up, they were very bright. After a few seconds, the smell of hot electrics. Switched the power off and the LEDs were very hot. Pulled the supply cables and connected them to a voltmeter, at full brightness the dimmer was putting out 27 volts, from a 12 volt input !!!

There is obviously a reason they cost about three quid delivered. Some Chinese electrics are fine, but i'd suggest checking everything before installing. A multimeter is worth its weight in gold.
 
I have installed one of those on-board :( I didn't check the volts but it's not over bright at full setting so probably OK. A bit academic actually as the LEDs are usually run well dimmed down.

Thanks for the warning!
 
PaulRainbow said:
Another close shave for some wiring. I was asked by someone to connect a key fob remote LED dimmer to some LED lights he'd fitted. He'd purchased the dimmer from a seller on Amazon, looked like this one on Ebay :

https://www.ebay.co.uk/itm/Wireless...m=162810124469&_trksid=p2060778.c100290.m3507

Simple job to fit. Turned the LEDs on and they seemed fine. Turned them up, they were very bright. After a few seconds, the smell of hot electrics. Switched the power off and the LEDs were very hot. Pulled the supply cables and connected them to a voltmeter, at full brightness the dimmer was putting out 27 volts, from a 12 volt input !!!

There is obviously a reason they cost about three quid delivered. Some Chinese electrics are fine, but i'd suggest checking everything before installing. A multimeter is worth its weight in gold.
Click to expand...

Was that 27V under load or o/c?
 
PaulRainbow said:
Another close shave for some wiring. I was asked by someone to connect a key fob remote LED dimmer to some LED lights he'd fitted. He'd purchased the dimmer from a seller on Amazon, looked like this one on Ebay :

https://www.ebay.co.uk/itm/Wireless...m=162810124469&_trksid=p2060778.c100290.m3507

Simple job to fit. Turned the LEDs on and they seemed fine. Turned them up, they were very bright. After a few seconds, the smell of hot electrics. Switched the power off and the LEDs were very hot. Pulled the supply cables and connected them to a voltmeter, at full brightness the dimmer was putting out 27 volts, from a 12 volt input !!!

There is obviously a reason they cost about three quid delivered. Some Chinese electrics are fine, but i'd suggest checking everything before installing. A multimeter is worth its weight in gold.
Click to expand...

Hoolie said:
"Very bright LEDs" and a "smell of hot electrics" suggests quite strongly it was under load :)
Click to expand...

PaulRainbow said:
All the clues are in post #1. 27 volts, red hot LEDs, smell of burning..............
Click to expand...

Might. I point out a stated sequence of events...
"Pulled supply cables and connected them to a voltmeter".

So I think it valid to ask for clarification of the test configuration!
 
Last edited:
Lon nan Gruagach said:
Might. I point out a stated sequence of events...
"Pulled supply cables and connected them to a voltmeter".

So I think it valid to ask for clarification of the test configuration!
Click to expand...

It was a simple post, a warning to anyone who might have bought one of these to maybe check its output at full brightness. It doesn't matter whether the voltage reading was taken under load or not, 12v into the device should not result in 27v out, either way. The fact the LEDs where red hot and there was a clear smell of burning electrics was enough to know something was wrong.
 
Our LED ribbons are of the usual groups of 3 LEDs wired in parallel, a total of about 8m of lights. The dimmer we have is exactly as described by PR and actually works very well and even remembers its setting when turned off. It seems to be a PWM system so I can't see how it could produce 27v? I will certainly disconnect and check when I next have the chance.
 
Hoolie said:
Our LED ribbons are of the usual groups of 3 LEDs wired in parallel, a total of about 8m of lights. The dimmer we have is exactly as described by PR and actually works very well and even remembers its setting when turned off. It seems to be a PWM system so I can't see how it could produce 27v? I will certainly disconnect and check when I next have the chance.
Click to expand...

I have to replace the faulty one, i'll carry out some more tests when i do so.
 
PaulRainbow said:
Another close shave for some wiring. I was asked by someone to connect a key fob remote LED dimmer to some LED lights he'd fitted. He'd purchased the dimmer from a seller on Amazon, looked like this one on Ebay :

https://www.ebay.co.uk/itm/Wireless...m=162810124469&_trksid=p2060778.c100290.m3507

Simple job to fit. Turned the LEDs on and they seemed fine. Turned them up, they were very bright. After a few seconds, the smell of hot electrics. Switched the power off and the LEDs were very hot. Pulled the supply cables and connected them to a voltmeter, at full brightness the dimmer was putting out 27 volts, from a 12 volt input !!!

There is obviously a reason they cost about three quid delivered. Some Chinese electrics are fine, but i'd suggest checking everything before installing. A multimeter is worth its weight in gold.
Click to expand...

There isn't a chance that the victim's boat was wired with 24V and you reasonably assumed it was a 12V supply, is there? 27V/2 = 13.5V which is about what you'd expect on each of two power batteries. So you'd have been varying the controller up to 24V (nominal), not up to 12V (nominal)?
 
Now then, pin back yer lug oles and prepare to learn a thing or 2.
Let's start with the device. If it is indeed the same functionally as the one in the link..
It is no more than a power supply chopper, it actives dimming by pulse width modulation.
The control side needs at least 5V and not more than 24V. The output side will only chop the incoming supply, it will not boost or convert the voltage. The output circuit has a maximum capability of 8A, thus he specification that it can control 40W from a 5V supply, 92W from 12V and 192W from 24V.

So, where did 27V come from and is it significant?
Being a square wave chopper any parasitic inductance in the circuit could easily provide 27V into a high impedance such as a multimeter. When any significant load is applied a more sensible and relevant reading would be obtained.

So why bother with all this electronic mumbo jumbo... If I am right about the device, it's function and operating principal (and, given my knowledge of electronics and chinglish, I am right) then there is another problem that won't be solved by removing the unit.

Which all comes back to was the 27V measured under load? And instead of misguided glib cheeky replies, just answer the question if you want any help with not misdiagnosing the problem and misleading the forum about the dimmer.
 
Lon nan Gruagach said:
Now then, pin back yer lug oles and prepare to learn a thing or 2.

<snip>

And instead of misguided glib cheeky replies, just answer the question if you want any help with not misdiagnosing the problem and misleading the forum about the dimmer.
Click to expand...

Who the hell do you think you are ?

I didn't ask for your help and i don't need it either. I'm perfectly capable of working a multimeter, thanks.
 
BelleSerene said:
There isn't a chance that the victim's boat was wired with 24V and you reasonably assumed it was a 12V supply, is there? 27V/2 = 13.5V which is about what you'd expect on each of two power batteries. So you'd have been varying the controller up to 24V (nominal), not up to 12V (nominal)?
Click to expand...

Having had a chance to get back onboard and finish testing, the issue was that the supply on the boat was indeed 24v, although it was clearly marked as being 12v. The 27v would be due to the mains charger being on.

To answer another question that was raised, some devices will produce voltages higher than the input voltage, for instance, i have a variable converter that runs my 19v laptop from the 12v input.

These things are advertised with varying descriptions and this one came with data. Advertising it as a LED dimmer with 12-24v input is misleading, one would tend to assume there would still be a maximum output of 12v, or it will burn the LEDs out in a short time.

I still think it's a good bet to check the output of any cheap Chinese electrics.
 
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