Lithium & LED Lighting Voltages

[Kannon Fodda]

Having had a 120Ah Sterling Lithium battery in my van for over a year, replacing a rather inadequate 72Ah lead-acid thing, I am seeing a problem where the LED striplights are starting to fail. I suspect problems with the 12V voltage.

In vehicles 12V DC seems to be a rather loose target. Most systems will run with voltages a tad higher. Traditional lead-acid batteries gradually lose the voltage they generate as they run down, perhaps 12.6V if fully charges, yet 12.0V is probably below 50% capacity, and the voltage generated even if full charge might only be 12.2V if you tried to draw off a heavy current. Lithium however seems to have a much higher voltage range, the Sterling manual suggests full charge resting would be 13.6V, certainly my Victron Smartshunt normally shows voltages in the region of 13.2V (which might suggest poor quality wiring creates a tad of resistance somewhere. Problem is that even 13.2V compared to 12V is a 10% excess.

I believe LED lighting is often particularly vulnerable to damage by over voltage. Many systems if they are designed for 12V, mean 12V and the tiny electronic components start to overheat quite quickly. Other electronics such as TV's may also be at risk.

Am I alone in experiencing lighting failures that I should attribute to cheapo kit of the motorhome manufacturer? Has anyone replaced any of the Autotrail LED striplights and knows what I might need to be compatible?

Has anyone installed some stabilisation or regulator kit to control the voltages, and if so what would they recommend and how / where to fit it? Most of the wiring for lighting doesn't have any easy means of access, being ceiling mounted with cables routed nicely tucked away in inaccessible places.

 

[DuxDeluxe]

Hi Rob…… not had that problem in my van…. Yet!

Dare I say it, but I found that some cheap LED’s I have used can fail and it may be a quality issue rather than a voltage one.

 

[autorouter]

In vehicles 12V DC seems to be a rather loose target. Most systems will run with voltages a tad higher. Traditional lead-acid batteries gradually lose the voltage they generate as they run down, perhaps 12.6V if fully charges, yet 12.0V is probably below 50% capacity, and the voltage generated even if full charge might only be 12.2V if you tried to draw off a heavy current. Lithium however seems to have a much higher voltage range, the Sterling manual suggests full charge resting would be 13.6V, certainly my Victron Smartshunt normally shows voltages in the region of 13.2V (which might suggest poor quality wiring creates a tad of resistance somewhere. Problem is that even 13.2V compared to 12V is a 10% excess.

There are recognised standards for any electrical device in a motor vehicle. Safety-critical devices must function with a supply of about 8 to 32V, and occasional bursts of up to 60V. Other devices, like the radio, must tolerate these voltages but maybe not function at the extreme ends of the range.

Not only that, but even standard smart chargers have voltages of 13 to 15V, some even going to 16V in equalisation mode. So you can see that to say that 12V is a loose target is an understatement.

You are right that some appliances like TV and lights are designed for a stable 12V supply, and don't like direct supply from the '12V' battery. Since the supply voltage goes both below and above 12V, a 'voltage stabiliser' is required, that will put out a stable 12.0V when the input is 10 to 30V. If it has a brick-type supply with a 12V cigarette-lighter plug on it, it will probably be stabilised already. But if you just plug it directly into the battery supply there might be a problem.

You may think that a voltage reducer (also called a step-down or buck supply) will be OK, but you'll find that inside the reducer there's a voltage drop of 3 to 5 volts, so 12.0V out requires an input of at least 15.0V.

After a couple of pump failures and noticing a very variable pump output, I decided to fit a 12V stabiliser to the pump. It now gives a constant output, and hasn't failed for a couple of years, so far.

I used something like this:
Amazon product ASIN B06Y5JHZG2

 

[EML]

The quality of your 12V supply is unlikely to be an issue for a LED strip. Diodes (including LEDs) set a (more-or-less) constant voltage across themselves when they're on, so diode circuits are generally very resilient to supply circuit variations. If you have a fancy dimmable strip then it will contain a lot of extra electronics beyond the LEDs themselves, and this will already be regulated. OTOH, if you've just got a plain lighting strip, then I wouldn't bother regulating it.

If you actually are seeing a problem, then it's more likely that you have a bad contact, or a loose surface-mount solder connection.

The plain strips probably have 3 diodes and a resistor in series across the supply. The 3 diodes will drop maybe 6V in total between them, and the resistor handles the rest, setting a constant current through the diodes. If you supply more than 12V you get some more current through the diodes, which get brighter, and vice-versa. Unless you've got a really bad 12V supply it's pretty unlikely that you could up the 12V enough to make a LED burn itself out.

 

[Kannon Fodda]

It's odd as I'm seeing the problem on three separate strips. Two are switched together as a pair, and are about 1.2m length each, the other is switched separately and about 0.75m length (guesstimated as I haven't got the tape measure out). Through the diffuser I can see these LED strips are a series of individual small LEDs, each probably a couple of cm apart, to make one longer luminaire, and random LEDs have gone out. Other individual LED bulbs in the van are OK, although occasionally there can be minor flickering. None of the fittings and lights are dimmable.

It's worth noting that the electronics generally are really basic in terms of very thin wires, a combined EHU consumer unit 12V charger 12V distribution PSU thingy that does a flat max 12A 13.8 old school all or nothing charging with no smart /float charge capability, single USB outlet and before I upgraded a pants 72Ah lead-acid battery despite it all being built 2019. The "extra electronics", "plain strips probably have 3 diodes" assumption is I suspect incorrect when the wiring system was clearly designed as the cheapest stuff possible to be all bling (the one thing it does have is lights everywhere) yet no substance. Given the articles I do see on the web of 12V overvoltage being an issue with cheap components, and not having a degree in electronics to be able to open stuff up and know what standard the components are, cheap quality and poor connections may be a contributing factor, but still leaves me with a problem for which I need a solution, unless I am going to revert to torchlight.

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[EML]

Well... difficult to say anything useful without a datasheet for your specific strip. It is odd though that you're seeing random LEDs out. LEDs fail by:

1. The normal failure is to dim over time - are the 'out' LEDs actually on but dim?
2. If a LED has completely failed, it will normally go open-circuit, so all the LEDs in that particular series section (normally 3) will go out
3. A LED can occasionally fail by shorting. If this happens, the other 2 LEDs in that section will get brighter and will probably fail soon

Will a 12V supply that spends a lot of time at 12.8V (4 cells LiFePO4) or 13.2V cause a cheap LED strip to fail prematurely? It might, if the strip is badly designed.

If you really want to spend more money, don't regulate the 12V supply, or buy a kit which is a 12V regulated power supply which drives a strip with the conventional series arms (3 LEDs plus a resistor). The 12V supply isn't the problem: the problem is that you want a constant current (not voltage) in each series arm, so every series arm must have a constant current source (not just a resistor) plus the 3 LEDs. The constant-current source will automatically be able to cope with a wide range of battery voltages. I'm pretty sure that these strips don't cost a huge amount, but don't have the time to look right now.

A constant-current source will also ensure that all LEDs have the same brightness, so may look more professional. In my case, I don't care, because the strips are hidden.