Running pixel from a car 12v battery.

[davenmarcia]

Hi I am looking at running some pixels from a caravan 12v system it sits at about 13.2v and wondering if this would be the go for dropping it to 11.9v to safely run the pixels.

DC-DC Adjustable Step-down Module 5A 75W

DC-DC Adjustable Step Down Module 5A 75W XL4015

core-electronics.com.au

The pixels will be controlled by a wemos d1 mini running wled and about 4m of 30led/m strip (I know strip is bad lol thats why its not in a prop).

Thanks in advance Dave

 

[David_AVD]

Most regulators (step down converters) need a few volts headroom to operate correctly so that may not work very well.

If you only want to drop 1V - 2V, you could use one or 2 diodes in series with the voltage supply. They will need to be rated for the current, but one way to do it cheap is use half of a 25A diode bridge. Easy to connect to and bolt down. I can give more details if needed.

 

[davenmarcia]

Thanks more info would be great. I just want to safely run the led's without going over the voltage and risk them burning out.

Dave

 

[Notenoughlights]

Could always go to 5V pixels, a 5V regulator should work fine from a car battery, as David mentioned you require a few volts head room.

 

[David_AVD]

Going with 5V strip would in some ways be better as then you can regulate it properly.

Do you already have the 12V strip? (I assumed you did)

 

[davenmarcia]

Yep already have the 12v strip or i would just go the 5v route

 

[TerryK]

What kind of strip? WS2815s are rated up to 13.5 Volt. Also curious if the vehicle would be running or not (how good is the regulator?). As David mentioned, a diode or 2 would give you a bit of 'headroom'.

 

[David_AVD]

If you want to use a high current diode bridge to drop the voltage a little, run the battery + into the diode bridge - terminal.

The diode bridge + terminal will be the output to your 12V LED strip. This will give 2 diode voltage drops.

 

[davenmarcia]

What kind of strip? WS2815s are rated up to 13.5 Volt. Also curious if the vehicle would be running or not (how good is the regulator?). As David mentioned, a diode or 2 would give you a bit of 'headroom'.

they are 2811s and the vehicle is a caravan with solar input so at night it will have no charge and sits around the 13.2v maybe down to 12.8v depending on what is running at the time.

 

[Elecgreg]

you could look into a DC-DC converter input side to a 12V output they are available and will ensure as the 13.2 falls to 11.8V during discharge that the 12V output will be maintained however it may take some searching to find a suitable current carrying capacity for the light strings.

The input can be variable however the out put is what is important for you application

 

[TerryK]

A WS2811 strip? Almost certainly 12 Volt resistor in nature. If you are feeling adventurous connect a half dozen or so and run up and down the road for a spell and see how they hold up. Fusing would be advisable I think. Unless the regulator messes up most automotive systems don't go above 13.8 VDC. Electrical noise may be more of an issue than the voltage and that would be only when running.
If you plan on powering them only when parked I would connect them directly. If you remain cautious, David's idea is what I would do. A silicon diode will give you a voltage drop of approximately .6 volt; 1.2 for a pair in series.

 

[davenmarcia]

Yep a 2811 strip it's a few years old and might try the test with a small section that I'm not going to use.

 

[Old Salt]

These are also available: Automatic buck-boost power supply 8-40V to 12V from Amazon or eBay.

If the volage is too high they drop it, too low and they boost it. David's diode bridges are a lower cost solution.

 

[BRW]

A note on auto voltage, I was just working on a Subaru (US) and it was charging at 14.6 VDC at the battery terminals. I don't know if that is high for Subaru, I always think of charging voltage as about 13.7/13.8. The battery is 6 yrs old so it hasn't been too hard on it.

The car is a covid victim, it is her family's second car and has not be driven since March, so the focus wasn't on the charging voltage.

You might discharge the battery some then check voltage while charging if there is any concern.

 

[TerryK]

A note on auto voltage, I was just working on a Subaru (US) and it was charging at 14.6 VDC at the battery terminals. I don't know if that is high ...

My concern as well. Over the years I've seen low 14s while charging; some regulators seem to run high. WS2811s are rated at 6.0 to 7.0 and for 12 Volt manufacturers add resistors to get down to the 6/7 window. Not knowing how the strip is built it's a best guess how it would like the automotive 13.8.