LEDs off campervan leisure battery

[Welshopen]

Hi all not sure if this is the correct area. Hopefully it is.

I'm installing some 12V LEDs in my camper and plan to run them off my leisure battery 12V.

I keep reading that i need to calculate the required resister to avoid blowing the led. however, i'm also reading that people just run them straight off battery with a fuse.

Any idea what is the correct way?

M

 

[SFK]

What type of LEDs are you looking at?
Can you show us an example?

But generally....
The little round LEDs with two wires sticking out need a resistor or they will fail.

But it is unlikely you are looking at these.

If you are looking at the long strips of LEDs that day 12V then these come with the resistors built into the strip, so no restore needed. Just cut strip to length where it is marked.

As a side note, some might worry that car battery tends to provide 14V not 12V , but this will not matter in this case (LEDs will be slightly brighter and last slightly shorter time.

Do search for (and select the better quality)
12V led strip, or 12v led and you will be okay.
https://www.amazon.co.uk/s?k=12v+led&ref=nb_sb_noss

Sfk

 

[Welshopen]

What type of LEDs are you looking at?
Can you show us an example?

But generally....
The little round LEDs with two wires sticking out need a resistor or they will fail.

But it is unlikely you are looking at these.

If you are looking at the long strips of LEDs that day 12V then these come with the resistors built into the strip, so no restore needed. Just cut strip to length where it is marked.

As a side note, some might worry that car battery tends to provide 14V not 12V , but this will not matter in this case (LEDs will be slightly brighter and last slightly shorter time.

Do search for (and select the better quality)
12V led strip, or 12v led and you will be okay.
https://www.amazon.co.uk/s?k=12v+led&ref=nb_sb_noss

Sfk

Thanks for the reply.
These are the ones I was looking at
https://www.amazon.co.uk/dp/B00YU36IPO/ref=cm_sw_r_wa_apa_i_AKWxDb65Y1F28

 

[Harry Bloomfield]

Thanks for the reply.
These are the ones I was looking at
https://www.amazon.co.uk/dp/B00YU36IPO/ref=cm_sw_r_wa_apa_i_AKWxDb65Y1F28

They will be absolutely fine.

 

[Welshopen]

They will be absolutely fine.

Excellent! Thank you

Why do these not need resisters?

 

[big-all]

keep in mind 5 or 6 off those spots will use an amp an hour allowing for a bit off loss
so 11 [2ah]running for 6 hrs a day will flatten a 60ah lessure battery in about 5 days

 

[Harry Bloomfield]

Excellent! Thank you

Why do these not need resisters?

Because rather than just being a bare LED, they are specifically designed for 12v operation - there are various ways of doing that, several LED's in series like old fashioned Christmas tree lights, or a built in power supply dropping the voltage to what the LED's need, or built in resistors. The second method being the most likely one. Just fit and enjoy.

 

[Welshopen]

keep in mind 5 or 6 off those spots will use an amp an hour allowing for a bit off loss
so 11 [2ah]running for 6 hrs a day will flatten a 60ah lessure battery will last about 5 days

Hi yes I understand that these are going to draw much from the battery. At least not before my split charger recharges it.

I just don’t get how you read about needing resisters but these don’t need them..

 

[SFK]

We know that these do not need a resistor because it says "for 12V use". This is because the manufacturer has added the correct resistirs to make the work at 12V.

Bare LEDs, to which you need to add a resistor, do not tell you what voltage they are set up for, but tell you its spec (eg 3V 20mA) so you can calculate its needed resistor using V=IR to make it work at the voltage you have.

So, because it says 12V we know it does not need an external resistor. Have a look at images of led tape for 12V and you can see the manufacturers resistors.

Sfk

 

[Keithmac]

Hi yes I understand that these are going to draw much from the battery. At least not before my split charger recharges it.

I just don’t get how you read about needing resisters but these don’t need them..

You are confusing bare led components with dedicated 12v lighting units.

 

[ericmark]

It says for Campervan, Motorhome, Caravan, Boat, Marine and Vehicle so should be OK. This firm specialises in this type of lamp, most rated as 10 to 30 volt, personally I would pay the extra and get lamps clearly marked as 10 to 30 volt.

 

[ericmark]

Hi yes I understand that these are going to draw much from the battery. At least not before my split charger recharges it.

I just don’t get how you read about needing resisters but these don’t need them..

I have found the old split charging is not really good enough to recharge a leisure battery in the allotted time when used with a caravan, they may work OK with a camper van it depends on how much it is used.

Typical a lead acid battery 80% discharged takes at float voltage around 24 hours to recharge, it will get up to 80% charged reasonably quickly maybe 6 hours, but the last 20% is slow, and if not fully charged it's capacity starts to drop. Today the battery to battery charger can speed up the process, and no real option where the cars alternator is switched off under load, it charges the battery up to 90% far faster so it then has more time to get that last 10%.

Domestic 12 volt lights are often rated 50 Hz and even if they will work on DC are rated at 12 volt not 13.8 volt found with a 12 volt battery on charge, so the extra resistance is to allow for the extra 1.8 volt. So a LED is typical 3 volt, so the lamp has groups of 3 LED's so 9 volt and a resistor to drop from 12 volt and limit current as LED's are current devices not voltage.

So 0.15 amp at 3 volt = 20Ω and 0.15 at 4.8 volt = 32Ω so resistor required = 12Ω approx. Also 1.8 volt x 0.15 amp = 0.27 watts, so would need to be 1/2 watt rated. However when running at 12 volt the lamps will be dimmer, with the 10 to 30 volt lamps the switched mode power supply keeps the current through the LED the same throughout the voltage range, so it will make no difference engine running or stopped light output is the same and also power used is the same. Using a SMPS or driver to give it proper name you get around 100 lumen per watt, with a resistor around 60 lumen per watt, so to my mind worth paying the extra in a caravan.

 

[Harry Bloomfield]

I have found the old split charging is not really good enough to recharge a leisure battery in the allotted time when used with a caravan, they may work OK with a camper van it depends on how much it is used.

My system works absolutely fine. Most installers rate the cabling along the car to the relay and from the relay into the trailer, simply on current rating. Trouble is, they ignore or are not conversant with volts drop along the cable run. Make the cable adequate, to minimise the volts drop down to a reasonable value and a secondary battery will charge. Usually the cable has the constant load of 100w fridge shared with the battery charging.

A 2.5mm cable is adequate for the current, I run a 6mm or 2x4mm.