Puzzler for you electrical gurus....

[deserteagle56]

A year ago I bought a 12v LED light strip (18" long) and mounted in the van I use an another RV. I like it so much I bought a couple more of them to use to mount in my Bigfoot pictured below. These light strips are specifically designed to use as under-counter lighting in RVs. This morning I tried to mount one of the light strips in the Bigfoot but I cannot get it to come on and cannot figure out why. I removed the OEM light fixture (designed to use a #1141 12v bulb) to access the wiring and spliced into it. Nothing. My test light tells me there is power and the OEM fixture works fine. If I connect the light strip directly to a 12v battery just by touching the wires to the battery posts it works fine. So what is different with the power going to the original light fixture?? What do I have to do to make this thing work?

Thanks in advance!

[NRALIFR]

fishing2 wrote:
Maybe the inverter is putting out some AC. I don't know how much it would take to make it not work but you can test it by putting the voltmeter on AC.

That's what I suspect. The converter is putting out a "noisy" 12v.

Put your Digital VOM on an AC scale and measure the 12v when shore power is plugged in, to see how much ripple is coming from the converter. Just for grins I measured mine, and was seeing about 50 millivolts of AC on the 12v from the converter. Voltage is stable on a D.C. scale. I don't have any LED lights in my camper though.

If I remember right, D.C. ripple is an indication of a bad capacitor. On the ancient stuff I used to work on, we'd tighten all the capacitor screws on the power supplies and look for bulging or leaking caps. Those caps were huge and were screwed on, yours are much smaller and will be soldered.

:):)

[SidecarFlip]

Reading and learning about LED's. I converted all my external clearance and tail lights to LED's and have had no issues....yet.

I didn't buy the cheap ones though. Everything is CREE, which I'm told is the best available.

I also went to LED lights on my Farm Tractors for the amp draw. My field lights 4 front facing and 2 rear facing plus one side facing on the right side (to watch side mount implements with) are all multiple LED spot and flood, CREE again.

Prior to, I ran halogen spot and floods and it was all my tractor alternator could do to keep up and my front facing lights now have a 3/4 mile illumination range (depending on bug concentration)...lol

[fishing2]

Maybe the inverter is putting out some AC. I don't know how much it would take to make it not work but you can test it by putting the voltmeter on AC.

[Eric_Lisa]

HMS Beagle wrote:
It is possible that it considers 13.4V to be over voltage...

I'm with this answer. Light emitting diodes are VERY sensitive to voltage. White LEDs themselves operate from 2.9 - 4.2 volts (source: Wikipedia). They do not run at the voltage your camper runs at. They are not like incandescent bulbs which can run at a wide range of voltages (though too high of a voltage causes a short life). Connecting an LED (just an LED, not a 'LED bulb') to 12V power will immediately burn it out.

That is why LEDs have been so difficult to get into the marketplace. Our home fixtures run at 120V AC, and automotive (including campers) are all over the board from 10V to 15V at the extremes. Within each bulb is technology to adjust the voltage so that the LED is happy with the voltage it receives.

If that technology is good, then an under/over voltage will shut off the power to prevent damage to the LEDs. If it is cheap technology, then it will allow a shift in supply voltage to exceed the capabilities of the LED and damage it. And that is the reason why some of the LEDs on my camper bulbs have gone dark - I bought the cheap ones!

For the OP, I think the charging voltage it too high for the LED bulb to handle, so it is shutting itself off to protect its LEDs from an over voltage. The on-battery voltage is within spec, however. See if your battery charger has different power modes. Mine has a 'quick charge mode' and a 'maintenance mode'. Switching between them changes the voltage reading of the 12V circuits. I'll bet plugged in, set to maintenance mode will do the trick.

HTH,
-Eric

[mkirsch]

This puzzles me

Same here. I would think the voltage would DROP when shore power is removed.

13.23V from a 6-cell lead-acid battery is seriously overcharged.

I suspect he got his figures crossed. If that is indeed the case, then the reason the LED won't light is due to excessive voltage. Those LED fixtures generally operate on a range of voltages, so a diode won't affect operation when the camper isn't connected to shore power.

[ticki2]

deserteagle56 wrote:
There is obviously something different with the power coming via inverter (shore power) versus battery power. I know I said that the voltage is the same but there is a minute difference and I wonder if that's enough to cause the problem. When on inverter the multimeter shows the voltage constantly changing a tiny amount, in a range from 12.9 to 13.1 volts. When on battery power the voltage is rock steady at 13.23 volts.

Whatever the reason, as least I'll be able to use the LED light strip on the majority of my camping trips. Thanks to all who responded.

This puzzles me , the voltage should be higher on converter than on battery alone .

[HMS_Beagle]

It is possible that it considers 13.4V to be over voltage. Most LED fixtures have a driver of some kind in them to regulate the voltage closely, and may shut down if out of range. If it is a house fixture it might be expecting 12V in a narrow range, while an RV fixture should expect anything from about 10 to 14.7V. To test this, you might try putting a diode in series with the fixture, which will drop the voltage by around 0.7V. If that works, it could be a good solution to keep the LED running while on the inverter. Just make sure the diode has a current rating greater than the draw of the fixture. You may end up with a problem on the low voltage end as the batteries discharge though.

[time2roll]

What converter is creating the 12v power in each of the RVs?

[deserteagle56]

There is obviously something different with the power coming via inverter (shore power) versus battery power. I know I said that the voltage is the same but there is a minute difference and I wonder if that's enough to cause the problem. When on inverter the multimeter shows the voltage constantly changing a tiny amount, in a range from 12.9 to 13.1 volts. When on battery power the voltage is rock steady at 13.23 volts.

Whatever the reason, as least I'll be able to use the LED light strip on the majority of my camping trips. Thanks to all who responded.

[zcookiemonstar]

You could try and connect your led to a different fixture location so you at least know if it is something with the whole camper or just that one spot.

[d3500ram]

OK... not a guru, but still feeding back to you based on your observations:

You state: "I unplugged the camper from shore power and now the light strip works! When I plugged it back in the light strip went out. Now, why would that be?"

Check the leads with the camper on shore power and use the voltmeter on the 120V AC setting to verify if it is 120A and not 12D being supplied. Perhaps there is some weird "auto switch-over" to 120 when plugged in that is not there when disconnected. Perhaps it reverts to 12DC when unplugged on that circuit.

ON EDIT-
I reread where you also state: "Voltage is the same at the leads whether or not the camper is plugged in!"
upon reading that I am stumped too!

Could there be some sort of current sensor on the LED's? That is, there perhaps is higher current available at 12V when plugged in that is not available on the house batteries??? I do not know what else could be causing an on/off switching condition between shore and 12V power inputs.

This is a good one!

[deserteagle56]

Figured it out - but still stumped!

Per the above suggestions, I went out with my multimeter and checked the wiring. As HMS Beagle said, on my Bigfoot the black is hot and the white is ground. Voltage is running 12.9 - 13.1. Just as a check, I reversed the leads (in case the light strip got wired wrong) but nothing.

Then on a hunch, I unplugged the camper from shore power and now the light strip works! When I plugged it back in the light strip went out. Now, why would that be?? Voltage is the same at the leads whether or not the camper is plugged in! And the original light fixture (has an LED bulb in it, by the way) works whether the camper is on shore power or on battery power.

[HMS_Beagle]

White wire as ground is fairly standard in an RV, a hang over from houses where white is neutral and black is PH1? Sometimes you run into black and red which would be - and + on a car or boat. It never hurts to test it.

[Powerdude]

Yep, had the same problem when I was putting LEDs in.

Don't use a test light to check the connections. A lot of RVs don't follow the standard electrical code.

On mine, + was black, and negative was white (crazy stuff).

On a standard voltmeter, the red lead is the positive, and the black lead is the negative, when plugged into the correct red and black terminals on the voltmeter (check that too !).

The red wire when connected to the positive, and the black wire when connected to the negative should give you a positive 12ish volts (depending on the battery charge).

If it is negative voltage (little - minus sign is displayed) , then you have the red wire connected to the negative, and the black wire connected to the positive. That's how you know on a voltmeter. Test lights don't tell you that.

Hope this helps !