12v - 5v stepdown for usb lights in van

[chatlow]

Hi All

I've just fit some led strip lights to my campervan and face-palmed when I saw they were USB and on 5v, not 12v. I have cut the usb end off and wired to a switch panel in the van that runs off the 12v leisure battery. As a quick test, I've powered on to check all OK and fine. I can't leave them like this as they could overheat.

I purchased a 12v/24v - 5v 3a step down convertor from ebay. Connected input to van's 12v system and output to the switch (via a 5a fuse). Soon as I turn the switch on, the fuse blew.. Thought maybe a dud convertor, but same thing using a replacement sent to me.

Can anyone tell me why the fuse keeps popping and if this setup sounds ok?

Thanks a lot

 

[DPG]

Can you post some photos of how you have wired it

 

[chatlow]

Can you post some photos of how you have wired it

I didn't take any unfortunately. As follows:

Convertor input: Van's switch (panel) 12v live connected to the convertor input live (with 5amp fuse built into this switch), then neutral on converter connected to earth bus bar in van.

Then for the convertor output; live to live of led lights and neutral to neutral of led lights.

Any thoughts on this would be very much appreciated!

 

[Lucien Nunes]

Does the fuse blow with the LEDs disconnected from the converter? If not, can you measure the output voltage of the converter?

You might have damaged the LEDs already. A 5V string will take anything up to 10 times its normal current at 12V because the current is not proportional to the voltage, only to the small fraction of voltage dropped in the ballast resistors. So a USB LED product will seriously fry when connected directly to 12V.

 

[telectrix]

USB socket in smoke lighter. simple fix.

 

[chatlow]

Does the fuse blow with the LEDs disconnected from the converter? If not, can you measure the output voltage of the converter?

You might have damaged the LEDs already. A 5V string will take anything up to 10 times its normal current at 12V because the current is not proportional to the voltage, only to the small fraction of voltage dropped in the ballast resistors. So a USB LED product will seriously fry when connected directly to 12V.

The fuse is attached to the switch, so yes, can link it up to the main feed without connecting the LEDs at all and test the output. I tested the LEDs quickly again at 12v and they are still operating fine. They actually dont heat up at all when powered by 12v

 

[Lucien Nunes]

Might have onboard voltage converter / regulator then, which would still be vulnerable to overvoltage, but I get that the LEDs appear unharmed. Last time I accidentally connected 5V devices to 12V (I had picked up the wrong voltage converter, I thought it was 5V but didn't read the label) I did £3k of damage in under a second.

 

[chatlow]

Might have onboard voltage converter / regulator then, which would still be vulnerable to overvoltage, but I get that the LEDs appear unharmed. Last time I accidentally connected 5V devices to 12V (I had picked up the wrong voltage converter, I thought it was 5V but didn't read the label) I did £3k of damage in under a second.

I'm such an idiot. I just realised there's a positive/negative section at the bottom of the strip so I'm able to check the voltage when on. I have just tested when they are connected directly to 12v and they're only drawing 4.79!

Is it safe to say there's a built in regulator or should I try some other test? Excuse the lack of experience showing

Thanks again

 

[DPG]

I'm such an idiot. I just realised there's a positive/negative section at the bottom of the strip so I'm able to check the voltage when on. I have just tested when they are connected directly to 12v and they're only drawing 4.79!

Is it safe to say there's a built in regulator or should I try some other test? Excuse the lack of experience showing

Thanks again

It sounds like there might be. What made you think they were 5V? Do you have any instructions /data for them?

 

[chatlow]

It sounds like there might be. What made you think they were 5V? Do you have any instructions /data for them?

They came with a USB connector which is 5v (I have chopped off the USB end to connect directly into my switch panel). Probably a very stupid question but would I see the light strip draw the entire 12v if they were being over powered with that system?

Be good to know if they are safe to leave connected directly like this

Thanks

 

[chatlow]

re-checked again. With the lights turned down to minimum, I'm reading a max of 7-7.5v, depending on what colour is coming through. The increases to around 10v when turned up to max brightness. This is the type of led strip you can cut sections and/or add if you want to. This item: https://www.amazon.co.uk/gp/product/B07XRHLVCN/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1

Given I will only be using them on low setting and not for very long periods of time, is 7.5v a definite no no for 5v lights?

Thanks

 

[DPG]

re-checked again. With the lights turned down to minimum, I'm reading a max of 7-7.5v, depending on what colour is coming through. The increases to around 10v when turned up to max brightness. This is the type of led strip you can cut sections and/or add if you want to. This item: https://www.amazon.co.uk/gp/product/B07XRHLVCN/ref=ppx_yo_dt_b_asin_title_o01_s00?ie=UTF8&th=1

Given I will only be using them on low setting and not for very long periods of time, is 7.5v a definite no no for 5v lights?

Thanks

Best to stick with the correct voltage.

To be honest it may be easiest just to buy a 12V LED strip for what they cost.

 

[chatlow]

Best to stick with the correct voltage.

To be honest it may be easiest just to buy a 12V LED strip for what they cost.

Thanks, Yeah Im trying to find any excuse not the touch these lights as they're stuck down using 3m tape. Should prob not tempt fait with electricity and get the heat gun out to remove then buy some 12v lights

 

[Lucien Nunes]

You didn't mention the dimmer / control unit. That is an electronic high-frequency duty-cycle controller that switches the LEDs on and off thousands of times a second, with the average fraction of on-time controlling the perceived brightness. Don't trust your meter to read those voltages correctly, it won't understand the waveform.

Even if the LEDs are receiving the correct average voltage, the electronics in the control box won't necessarily be OK with 12V. There will probably be 6.3V electrolytic capacitors that can't stand more than that continuously that will eventually go pop and the thing will die.

But what of the converter.? Does it work or blow the fuse? And why not use a regular 12V - USB charger or hub to feed 5V to the LED controller, as suggested by Tel in post #5?

would I see the light strip draw the entire 12v

Ordinary devices designed for a specific voltage don't 'draw' volts. You feed them with a voltage that is fixed by the source and they draw the current (amps) that they need, which depends on their power.

 

[chatlow]

You didn't mention the dimmer / control unit. That is an electronic high-frequency duty-cycle controller that switches the LEDs on and off thousands of times a second, with the average fraction of on-time controlling the perceived brightness. Don't trust your meter to read those voltages correctly, it won't understand the waveform.

Even if the LEDs are receiving the correct average voltage, the electronics in the control box won't necessarily be OK with 12V. There will probably be 6.3V electrolytic capacitors that can't stand more than that continuously that will eventually go pop and the thing will die.

But what of the converter.? Does it work or blow the fuse? And why not use a regular 12V - USB charger or hub to feed 5V to the LED controller, as suggested by Tel in post #5?



Ordinary devices designed for a specific voltage don't 'draw' volts. You feed them with a voltage that is fixed by the source and they draw the current (amps) that they need, which depends on their power.

Thank you, interesting stuff! Confirmed I'll def be replacing these with 12v then.

With regards to the 12v-5v convertor I purchased, yes, it immediately pops the 5a fuse that connected it to the light strip.
As for using a regular USB source. There isn't one on this switch panel and to be honest, I want the strip connnected to a switch in my van for ease of use.

I'll look into some 12v light strips. The ones that have a controller (for colour change and dimming) come with a standard plug which I'm hoping I can just chop off and connect the wires to my 12v panel

Appreciate the help, everyone