12v LED reflector bulbs

[Capt Slog]

I recently bought some LED reflector spot light bulbs.  They were fairly cheap compared to most I've seen around in other places, I paid £3.50 a bulb.  The only problem is, I don't have very much information on them.

They are marked:-

MR16+c  (which is miniature reflector, the size, + cover)

12. Vdc white
    
15000. mcd.
       
       

They draw around 75mA at 12V and there are 20 LEDs in the case. I've taken one up to 15v briefly, it does brighten, and draws 180mA.

 BUT, and here is the important bit, there is NO polarity on the pins. Yup, they go in either way to a DC power source.

I know that there is some electronics inside the casing, but I can't see it, and I'm not about to sacrifice a bulb (yet) to have a look.

Has anyone used these or know anything about them, I was hoping some clever person on here could shed some light on these (groan!).  I'm particularly interested to know if there is some form of overvoltage protection built in. I'm intending to run them from my battery which is being charged by the windmill.

[Capt Slog]

The board has done something strange to the info I posted, it should say 15000 mcd.

[WindJuggler]

Hello,

The reverse polarity system is made by a bridge rectifier. Either what polarity you put on the leads it will be corrected.

For the overvoltage part it would be OK to go a little over 13.8V.

If you would go to a higher voltage for a long time or constantly you could damage the electronics on the inside.

You can do a current calculation to see how high they would go.

Lets say 20 LEDS at In=20mA each you would be able to go to 400mA.

But be carefull I think the leds are driven by a MOSFET or something like it.

You can see this by the fact that the current has no linear regression compared to the voltage.

Good luck,

[DamonHD]

Yes, these seem to be designed to be run from 12V AC from a main step-down transformer, so they should work fine from DC.  The only downside is a little more power loss than strictly necessary in the bridge rectifier.

The MR16 LED bulb that I bought recently explicitly said on the box that it was for DC or AC as I recall.

Rgds

Damon

[Capt Slog]

These definitely say DC.  I bought them from the REUK shop.

Would I benefit by putting a resistor in series when I come to use them?  I'm intending to use them as house lights, I don't want them to start failing as it makes the system look bad.

I'm concerned that they might be damaged when the battery voltage goes high in gusts.

[ghurd]

Try to keep it under 100ma, which is probably around 13.8V.

Might add a resistor in the socket to keep it under a bit of control.

G-

[richhagen]

Systems designed to use MR16 bulbs may be both AC or DC powered.  They often are supplied by a simple transformer from mains power.  As a result many of the LED ones, and all of the LED ones that I have seen, incorporate a bridge rectifier, which means that they will run off of DC with either pin as the positive lead.  

Most of the bulbs I have seen are designed to survive up to about 14 volts or so, but that doesn't mean that your particular one is.  If you are comfortable with fiddling with it then if you are running it from a DC source, and are comfortable with opening it up and a bit of soldering, you could bipass the bridge diodes and improve the efficiency a bit with a lower supply voltage, or if you limit the current to the LED's - which may already be done via the circuit on some of the boards.  You would just have to make sure that you did not over current the LED's if the supply voltage varies such as when charging the battery that they are running from.  Rich

[Capt Slog]

Thanks for that Rich.

I'm not able to get into the bulbs though, they are very well made and sealed, so I'll be using them as bought with a resistor to add a bit of protection.  As you say, it's the charging voltage to the battery that is the worry.  I have one of Ghurds excellent contollers built into the system, and I'm hoping that this will also help keep the voltage down when it cuts in to dump.

It's all quite a step going from having mains lighting to battery powered LED.  Exciting too though.  It's come at a time when Mrs Slog is under the opinion that the existing lights are starting to look a bit tired (read:- Mrs Slog cleaned them and provoked bits to start falling off), so if I can buy some nice MR16 units, I'll probably get away with it!  

[Electron Skipper]

They sound like a Lumex product repackaged.

With that assumption, www.lumex.com is thier website, and you can pull the spec sheet.  They were intended as direct replacements for the low voltage halogen light bulbs.

Chances are good the ones you have, marked as "DC" with no polarity are containing an internal bridge rectifier, which protects against reverse polarity  and simplifies and reduces the chances of returned product because the consumer was ill informed.

If concerned about over voltage, if their location will see only a maximum of 15 volts, they should be fine.  If that is a concern still, wire in a 1N400x or 1S400x series rectifier, which will drop the voltage slightly due to it's internal resistance.