LED Electrical question

[laimeduck]

Theoretical question ref LED lights.

 

I have a little electrical knowledge, but it's very basic eg V=IR, Watts = Amps x volts etc

 

We mainly use campsites in our van so usually have EHU.

The fitted internal lighting of the van is 12V, and is run from the 2 habitation batteries which are charged via a solar panel and the EHU. I have installed LED's throughout.

 

However, If I want to add say some 12 volt LED reading lights in our raised bedroom, or outside under the awning, powered by a transformer plugged in to the mains, what will the power usage be?, eg if I use 12 watts of LED, is that simply 12 watts, or will the transformer also use some watts? I assume it will as it will get hot, but how do I work out what it's using?

 

The question is not why do it - I have my reasons - it is simply how do I calculate the usage?

 

We often trip the site electrics because we forget to turn the electric fan off when we boil an electric kettle, so I would like to be able to calculate what each piece of equipment uses in terms of wattage.

 

Thanks in advance

 

[colin]

The only way you will be 100% certain is to measure it as not all transformers have the same efficiency. Personally I'd add at least 10%.

[StuartO]

LED lamps (i.e. lighting appliances, not just led bulbs) designed for the domestic market often have built-in transformer low voltage power supplies and these could be used in a MH plugged into an EHU simply by plugging them into a mains socket. But a MH, unlike a house, also has a separate low voltage (i.e. 12 volt) power circuit which will be suitable for led lighting purposes so it will usually make sense to connect things like new or extra reading lamps to that circuit instead. LED lighting invariable uses relatively little power so it can be fitted by “tapping into” an existing 12v circuit rather than having to route power cables all the way back to the EBL or leisure battery.

 

LED lighting units are often labelled with the their lighting brightness rather than their power consumption so might see brightness quoted either in lumens or in the power consumption of the equivalent incandescent light bulb they are comparable to, rated in watts. Rarely are LED labelled with their actual electrical power Consumption because it’s not big enough to worry about for purposes of circuit design.

[Brian Kirby]

As you have (presumably) replaced original halogen lights with LED, you should be quids in. The LEDs should be using only a fraction of the power of the original lighting. Do you know the Wattages of the (presumed) original halogen lamps and the new LED lamps? Multiply the number of fittings by the Wattage of each lamp in both cases, and then deduct the total LED Wattage from that of the original lamps. That should tell you how much you have to play with for new LED lighting. The installed 12V power pack transformer should easily cope, unless you intend making a light show of your van! :-)

 

Tripping the 230V supply is far more likely to be due to the Wattage of the kettle. A lot of electric kettles are 2.5 - 3KW, which alone exceeds the limit on quite a lot of site feeders, often around 10A in UK, usually less (even down even to 3A, though 6A is more common) elsewhere. We have a low Wattage (650W / 3A) kettle we carry with us in the van for just that reason.

 

Both fan, and kettle, should have a rating plate on them that will give you the Wattage of each. So, too should the fridge and the power pack. If you can find all the rating plates and then add together all the Wattages, that will give you a fairly good guide to how much 230V power you are trying to draw in Watts. If the answer is much over 9A / 2,100W you need to change the kettle! :-) Then compare that to the site feeder pillar Amperage. The only item we have to watch is Carole's hairdryer!

 

If you want LED external light, and if your awning is Omnistor (now Thule), there is a kit for installing self adhesive flexible LED strips at the base of the awning box. I added one to ours and fed the 12V supply via the step fuse, with a separate fuse and holder next to the switch for the light. They give excellent light for very little consumption. Rated 340-380 mA per metre, so under 2.4A for a 6.0 metre strip. Needs an aluminium carrier strip to fit, which may limit which awnings can be retro fitted.

[laimeduck]

colin - 2021-01-05 2:19 PM

 

The only way you will be 100% certain is to measure it as not all transformers have the same efficiency. Personally I'd add at least 10%.

Thanks Colin, that's the sort of answer I was looking for.

 

Brian & Stuart, thanks also, but I do not want to connect to the existing 12V circuit, I want to use a transformer down to 12V plugged into the EHU circuit.

 

I am aware what trips the circuit - and can calculate the Amps required in the hook up, eg 6 Amps will give me the ability to use 6 x 230, = 1380 Watts max at any one time, 8 Amps, 8 x 230 = 1840.....etc etc

We use an 800 Watt travel kettle, and have a 1 KWatt fan heater, ie 1800 watts, so we know we can't use both together.

 

What I want to do is to be able to work out theoretically what bit of kit uses what wattage.

 

Hence my question about the transformer itself - AFAICS there is no data on the labels of the transformers I have.

[Brian Kirby]

Ah! so the "fan", is in fact a 1KW fan heater! That makes a bit of a difference! :-)

 

But as you already have a transformer (your power pack), and 12V circuitry, I'm puzzled as to why you'd want to install another transformer, with additional losses, to run (I assume) just a few more, very low Wattage, LED lights. Were the original lights in the van halogen or LED? Whose 12V electrics have Benimar fitted? Most are fairly standard devices with known characteristics. It just somehow seems like the hard way of doing something that should be simple. But perhaps I'm missing the point? :-)

[laimeduck]

Brian Kirby - 2021-01-05 6:04 PM

 

Ah! so the "fan", is in fact a 1KW fan heater! That makes a bit of a difference! :-)

 

But as you already have a transformer (your power pack), and 12V circuitry, I'm puzzled as to why you'd want to install another transformer, with additional losses, to run (I assume) just a few more, very low Wattage, LED lights. Were the original lights in the van halogen or LED? Whose 12V electrics have Benimar fitted? Most are fairly standard devices with known characteristics. It just somehow seems like the hard way of doing something that should be simple. But perhaps I'm missing the point? :-)

Brian hi and thanks again.

 

The rear bed is above the garage and the bed can be raised or lowered using several clip on supports around the frame. We run the bedroom/garage set up with a motorbike in the garage, so the head clearance in the bed area is not very large.

The existing tungsten lights are inset in a large un-movable decorative curved wooden panel in the roof and are in the wrong place and are pretty pathetic.

I have a 230 volt double plug socket in the garage directly below the head end of the bed.

 

I solder up my own LED's from long strips and can make a simple mount running along above the head end window. I simply plug a transformer into the 230V socket and lead the wires about 3-4 feetup to the LEDs. I cannot easily connect it to the existing 12V lighting circuit as it's set into the ceiling and that would entail dangling wires in the low cieling. Being removable, If I want I can also use the LED bed head light outside in the awning or elsewhere.

 

The Control panel of the Benimar is an "Own Make" badged Benimar. I have no idea what component is behind the panel, and the handbook does not say. (In fact it explains a completely different panel!).

The original light bulbs were a mixture of strip and halogen and tungsten.

I have installed 230 volt Halogen spots in the Kitchen & Lounge area and also changed all bulbs/tubes to LED (except the bedroom).

We have no intention of selling our van so will run her til we drop, so we have adapted her to OUR needs, all very bespoke!

 

It all sounds complicated but it really isn't ! I simply wanted to know what wattage a transformer was so I can run the LEDs from a 230v plug and know that it won't trip the EHU, while other stuff is in use?

[plwsm2000]

Jeremy,

In the grand scheme of things, the Watts drawn by the LED transformer will be insignificant compared to a kettle, fan heaters etc. You will find that the actual power drawn by the kettle etc. will vary by much more than what the LED transformer draws in any case.

 

Anything with a 230V heater element almost acts like a big resistor (in terms of ohms law) and the mains voltage can vary +10% to -6% (and probably lower on some camp sites). A 800W kettle will draw something like 3.48 Amps at 230V (resistance is about 66.1 ohms). The same kettle at 216.2V (230V less 6%) will only draw about 710 Watts but close to 970 Watts at 253V (230 +10%). 12W for your LED light will not be significant when calculating the total power draw.

 

That said, 12V mains transformers with a 12Watt output can come in two types - Either simple "linear" or "switching". The linear types tend to be bigger and heavier that switching supplies with efficiencies around 70% (which also vary with mains voltage). So the 12Watt output will draw about 17W from the mains (the extra 5W goes in heat so they will be quite warm to the touch).

 

A switching supply can be much more efficient (90% or greater) and will not be as dependent on the incoming mains voltage. For 12Watt output, you probably will only draw 13W from the mains.

[Charles]

Look up LED driver on ebay there are lots of switching type power supplies. Buy bigger though, they do get hot when working close to their limit. I'd go for a 24w supply to run a 12w strip. The power usage of the actual supply is inconsequential to hook up, in fact you can safely ignore all LED lighting when calculating hook up amps.

[Derek Uzzell]

There is on-line guidance (including videos) on calculating how much power a 12V LED strip may consume:

 

https://tinyurl.com/y4fnfhxq

 

 

 

[747]

Many people change from Halogen to LED 12 volt lights but never bother to alter the fuse in the circuit to a more appropriate level.

 

If the OP is in that position then I would suggest adding the new LED lights to an existing light circuit with an on/off switch. Nothing more needs to be done.

[Keithl]

Jeremy,

 

IMO You do not really want to leave the transformer plugged in and switched on all the time even with the lights turned off as it will still generate heat and be a possible fire risk.

 

So unless you can turn it off when you turn the lights off you would be much better placed to find a 12 volt source to power your new lights.

 

Keith.

[colin]

I would note that 230v LED lamp are considerably less efficient than 12v LED. A typical 'cheap' 805lm (old 60w) lamp will be around 9w, the equivalent output in 12v will be around 6w, but will cost considerably more to buy.

[laimeduck]

Hi everyone and thanks all for your replies.

 

Phil (plwsm2000) your comment

"So the 12Watt output will draw about 17W from the mains (the extra 5W goes in heat so they will be quite warm to the touch)."

is exactly what I wanted.

 

I knew they got hot and as nothing comes free, so there had to be a watts implication. I simply didn't know how much!

 

Keithl :- As far as leaving it plugged in is concerned, we won't. We will use a remote control socket switch which we already have. That will turn off the power to the socket, so the transformer will only be "live" when the lights are on.

 

That way we can operate the lights without moving from the bed. (Only my wife will have to get up to make the tea!) Tee Hee!

[Brian Kirby]

Last thoughts :-) Have you considered leaving out the middleman (transformer), and looking into 230V LED lamps/fittings?

 

I ask, because I've been looking at swapping existing 12V transformer driven halogen downlighters for LED, and noted that a number of people have complained of flickering/intermittent light from the LEDs. This seems to happen in some cases even if LED "drivers" are used, but much more frequently if the 12V source is a normal toroidal transformer. The LEDs need a smoothed DC supply, so you need at least a 230V to 12V DC step down transformer-rectifier.

 

You could take a 230V feed off the socket in the garage through a fused spur and switch to feed the bed end 230V LED lights. The awning light could also be 230V fed using LED lamps if you already have a suitable 23V external socket. Just suggestions, of course! :-D

[plwsm2000]

Just a word of caution when using "12V" LED strips in a MH. Unless your habitation battery is virtually flat, you will never get 12V - it is more likely to be closer to 13V when fully charged and somewhere close to 14.4V when on charge (depending on battery type and if the charger is in its main charge stage).

 

This may not seem a big increase but it will give a substantial rise (more than double) in the power consumption of the LED strip light. This power increase will cause the actual LEDs in the strip to get quite hot. Although I don't see this as a fire risk, it will significantly degrade the life of the LEDS and reduce their light output over time. You might only notice this after several weeks.

 

In case anyone doubts this, I just measured the current draw on a strip of LEDs at different voltages (these were "5050" size LEDS). At 12.0V, the current was only 2.77A (=33 Watts). At 13.2V they took 3.78A (50W) and at 14.3V, it was 5.01A (72W). I had to switch off after a few minutes at 14.3V since the plastic reel they were still on started to melt!.

 

It would be best to use a dimmer and limit its output to about 90% when on EHU

 

[Derek Uzzell]

Overheating of 12V LED lighting when used in a motorhome has been discussed here in the past (example here)

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/21w-Flourescent-modified-to-2w-LED-1-50-How-to/45945/

 

On Page 2 of this thread about Fiat dashboard lighting

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/fiat-dashboard-lighting-/45838/

 

I mentioned that I had used 12V LED strp to illuminate the instrument cluster and said:

 

"When driving the LEDs are going to receive 'alternator voltage’ that will be above 14V and, consequently, the LEDs will get warm. It would be possible to regulate them down to 12V - when they would run cooler - but I didn’t bother and there haven’t been any signs of overheating.”

 

I had asked the supplier of the LED strip (Aten Lighting) whether operating the strip at a higher voltage (eg. when a motorhome’s alternator or onboard battery charger was running) could cause overheating or longevity problems. I was told that they had not received complaints about this but, if I was concerned about it, they offered a voltage regulator that would guard against this.

 

If Jeremy uses a transformer that outputs a ‘steady' 12V, presumably overheating should not be an issue, and if he ran the strips from his motorhome’s leisure battery off-EHU it should also be OK - but on EHU with the battery-charger operating overheating of the strip could be a potential risk.

[laimeduck]

 

Derek - I converted all my lights to LED as a result of that 2017 thread by Allan of aandncaravan, but decided to go down the route of John 52 and use strips of LED which I made up from a reel. (rather than the COB units) That seems to solve the problem of overheating.

 

The strips were self adhesive and I simply stuck them onto the fluorescent tubes, 2 per tube, so I guess any heat build up (if any?) would be dissipated through the tubes.

 

I have been using them for 3 years, none have failed and I have had no overheating problems that I am aware of.

 

Concerning your last paragraph, my original question concerned 12V LED's powered from a plug in 230/240V mains transformer - the voltage will not alter on that, so there is no problem there. (And if the transformer is switched off when not in use, no heat problems there either).

[Derek Uzzell]

I used self-adhesive 12V LED strip when I illuminated my Ducato’s instrument cluster. Those LEDs are only in use when the vehicle is being driven when they get the alternator’s voltage of 14+V. As the strip is stuck on the underside of the cowl above the instruments, the LEDs do get noticeably warm.

 

I had bought two one metre lengths of different design strips and only used one type for the instrument lighting, so I installed the unused strip at the rear of the Rapido’s otherwise poorly-lit garage. That strip gets leisure-battery voltage of 12-ishV to 14-ishV depending on whether the motorhome is off or on EHU, but the garage lighting is only switched on for short periods so there’s no realistic risk of overheating.

 

As I said above, your plan to use a transformer should prevent overheating. But Phil’s caveat is valid if LED strips intended for a ‘fixed’ 12V voltage are subjected to a voltage significantly higher than that.

[gassygassy]

Derek- are you aware of the white dials you can get for the Ducato? I changed my illegible black ones to white ones and it was very worthwhile. It takes 3 minutes and a No.2 Pozi to take the speedo console out -I think there is a total of 4 screws to undo, and about ten minutes to slide off the black dials and insert the white ones. It's much better than illuminating the black dials from outside.

[Derek Uzzell]

I do know about Lockwood's white dials overlays for Ducato X290 vehicles

 

https://lockwoodinternational.co.uk/product/ducato-etc-2015-manual-part-no-8414/

 

After X290 Ducatos became available in the the UK in mid-2014 there were widespread complaints on motorhome forums (including this one) about difficulties reading the speedometer in low-light daytime conditions. Lockwood initially produced for a Ducato motorhome owner’s vehicle a one-off ‘bespoke’ set of two white overlay-dials for the speedometer and tachometer. This attracted sufficient interest for Ducato X290 speedometer/tachometer white dials to be marketed generally and, later on, Lockwood added to the set a 3rd overlay covering the fuel and coolant temperature gauges. The Lockwood white dials were discussed here in 2018

 

https://forums.outandaboutlive.co.uk/forums/Motorhomes/Motorhome-Matters/Boxer-Ducato-Relay-Speedometer-difficult-to-read-in-daylight/50814/

 

As my 2015 Ducato-based Rapido motorhome is left-hand-drive, its speedometer was less prone to the visibility issues affecting RHD equivalents. My LED approach was pre-Lockwood white dials and the exercise was more of an inexpensive ‘amusement’ project than a necessity. The effect is shown by the photo attached below.

 

In practice, to show speed I exploit the ‘data’ display of an ancient Garmin sat-nav than can easily be switched between mph and km/h and can be positioned in my sight line avoiding the need to look downwards at the instrument cluster speedometer.