LED Array Question

[tmort]

I have an EVGlobal 36V ebike. It comes with an LED array for the tail light and a 12V 35 watt H3 automotivde halogen foglight bulb for the headlight. I find that the lights drain the batteries faster than I would like and rob some power. I found a 12V 5 watt MR16 base LED array for track lighting. with the proper base and little cobbling I can get it to physically mount quite nicely in the headlight reflector and housing.

However when I go to turn it on I am blowing the 5 amp fuse for the lights, horn, controller, etc. It is doing this after being on just a few seconds with nothing else running. It is supposed to draw under 500 mA's.

The resistance of this array with my cheap analog meter is about 100K while the original halogen is about 0.5 ohm.

Can anyone shed some light on why this isn't working as it seems like it should to me?

I also checked the resistance of the base with no lamp attached and it was infinite so there is not a short.

Thanks

 

[fechter]

Does it light up before it blows the fuse?

Some LED's don't have a built-in resistor to limit the current, but I would assume anything in a MR16 base would have one.

To measure a LED, you need a diode check function on your meter.

 

[tmort]

Yes, it lights up for a few seconds before the fuse blows.

It also is set up with polarity reversal protection.

 

[gmouchawar]

But isn't it applying 36V and not 12V. That may be well beyond what the led will take. Please measure the voltage at the terminals.
With a pure resistive load the filliment heats up increases its resistance and limits the current to the bulb. That is why it can take
36V and not burn.
However, LEDs are constant voltage devices. So the just keep taking more current till they melt and short. Aparently your fuse protects them.
You need to increase the series resistance to account for the 36V.

 

[dnmun]

put 3 lights in series, 15W LED's will be 2X your halogen. bill bates used a reflector with lens cover from harbor freight for swimming pool lights. add one to each side of the main light, maybe you can find a reflector with 12V led already mounted.

 

[tmort]

I'll check the voltage at the terminals but I thought I read i n the specs that it was 12 volt

 

[tmort]

You're right, I do have 36 volts at the terminal.

The LED array is supposed to draw 380 mA at 12 volts. So if Ohm's law is amperes = Voltage/Resistance, then .388 = 36/R or R = 95 ohms ???

Am I doing this correctly?

Thanks

 

[fechter]

Ooo! 36v into a 12v bulb, that explains the blown fuses.

On the calculation, you need to drop the voltage by 24v to go from 36v to 12v.

That works out to about 62 ohms, 10W. That's going to be a toasty hot resistor.

A small dc-dc converter would generate much less heat.

 

[tmort]

Thanks,

I have a switching regulator that I can use. I'll have to read up on how to make it work.

 

[gmouchawar]

Hi,

Ohms law doesn't hold up with LEDs. These are diodes and have a pretty constant VF with a small series resistance.
The DC/DC converter is a good idea.

 

[trappermike]

I run 2 led headlights,tail light and 4 side marker lights on 12v Led,and my battery does not seem to complain,or even notice.
Of course I reduce 48v to 12v which some to vehemently oppose ,but why???? :?

 

[trappermike]

I think when someone figures out how to wire my $1 per amp output regulators we will be ok.

 

[johnb]

I use 2 MR16s in series and a cheap LM317 voltage regulator to drop the voltage to 24V. No need for an expensive DC-DC converter.