Large Scale Central

Ned LED Re-wiring help

Electronics
#1

OK guys… ISO some help to re-wire three of these HF battery lights… into A strip of 6 of the LED strips wired end to end, [ linear strip ].

Powered by 4ea AAA batteries ( comes with the worlds worst cheap batteries).

Opening it up shows this:

and inside…

And the bottom of the switch circuit board…

So I traced out a schematic … pertty simple,but I don’t understand how to cut out the resistors or add enough, or what happens to put the six light strips in a long row.

I believe the 2 Led strips are wired in parallel …

I have 3 ea. 4 up AA battery cases [6VDC] output, that matches the 6VDC of the original light case, to use as a larger Mhr power source.

So could someone help me out in what I need as a wiring diagram, and what to do about the resistors in each of the original circuits , or how to wire up the lights…

I have lots of resistors and stuff to get it wired up, just don’t know what to do, to not burn the LED’s up…

#2

From Dave Bodnar’s site …http://www.trainelectronics.com/LED_Articles_2007/LEDs_for_Coaches/index.htm

#3

The key here is to understand why 2 red wires between the modules, and what the resistance is.

Those are 6.2 ohm resistors, and 6 in parallel (to handle the current) is 1/6 of 6.2 ohms, i.e. 1.03 ohms… just enough to limit the current a bit…

Most likely each of those arrays are leds in parallel, so nominally they would take 3.6 volts each, thus the 6v supply.

at so low a resistance, the numbers are pretty impossible to work without knowing the voltage drop across the resistors or the leds.

if you can measure the voltage across the resistors with an accurate meter, we can calculate the current drawn and then proceed.

The other way is to get a large 1 watt 1 ohm resistor, cannot think that you need anything higher wattage.

Greg

#4

Thanks Greg…When I get home today I’ll measure the R on the resistors…

My ignorance here… When I measure across, Do I have the batteries in, and or the LED’s burning?

Dave

#5

Dave,

Batteries in, power on.

#6

Back home and at it…

Took the LED strips off the mount, And sure enough they are wired in Parallel.

Here is a composite of the 4 end wiring of the LEDs. Maybe the printouts on the board ends will mean something. L to R of the LED ends.

Made the R readings, I don’t know if my meter is accurate enough, it’s the best one I have.

1st: Batteries in, no power to the LEDs. 1.1 Ohms

2nd: Batteries In, LEDs Lit. 7.55 M Ohms.

I hope that this helps to come up with an answer… If I need to do or provide anything else, just ask…

Dave

#7

Dave,

What Greg was asking is for a DC VOLTAGE reading across the resistors. With that reading and knowing the resister value it is an easy ohms law calculation to get the actual current draw. Where the heck is Greg !

#8

Oh Oh., See why I ask before I let the magic smoke out?

OK… I get right on it and get that measurement. DC VOLTAGE, using the same test setup…

Dave

#9

OK …Here is second try…

First is VDC straight across the leads off 4 fresh re-charged Ni-Mh batteries. 5.75 VDC

And then with LEDs lighted VDC thru the Resistors… 3.211 VDC.

BTW: The resistors got HOT… after only 3-4 min of the LEDs on, they got so hot that that they blistered my finger when I touched them…

Just seems that they were using up a lot of energy as heat… is that normal?

Hope that this gives enough info to help.

Dave

#10

As Greg has said they are composed of 10 LEDs in parallel (the little dark strips are the LEDs).

Here is how I would do it; cut all the El Cheapo crap out and bin it then use an LED calculator to figure out the value of a current limiting resistor using the voltage that will be connected and 10 LEDs in parallel

From a calculator using 6V supply, 3.6V LED voltage (white LED supplied by calculator), 30mA ( just plucked it out of thin air), 10 LEDs in parallel gives a resistor value of 8 ohms. (8.2 ohms closest value that is readily available)

Link to calculator I used to get those figures. https://www.easycalculation.com/physics/electromagnetism/led-parallel-resistance.php

When you say 6 strips are you talking about connecting 6 LEDs strips in parallel that is one hell of a lot of LEDs? I have one of these in my shed and it lights it up like Vegas.

#11

Dave,

Something is really wrong with that light. No way those resistors should get that hot. If your readings are correct, then the current is 3.11 amps and 9.99 watts on those resisters!

#12

OK gang… I do know that the resistors should not be getting that hot…

So I opened up a different light, all the same guts inside, to be sure that I hadn’t messed something up, or that one was jus faulty.

Again Freshly re-charged set of Ni-MH batteries, turned on the light, and waited 2 minutes, and took a reading with my infrared Thermoter.

SUPRIZE, SUPRIZE…

Thats the reading when my phone snapped the pic. Highest I read was 214 deg.

That has to be drawing a lot of amps to generate that much heat in such a short time… Is this whole system designed that poorly, that I should just give up, or strip it all down and try my hand at a better design?

#13

so the 6 resistors in parallel give you 1.03 ohms. You measured the voltage across them as 3.211 volts.

From ohms law V=IR we can solve for current I=V/R or 3.211/1.03 = 3.11 amps if your measurement is truly across the resistors. (now you see why they are in parallel, to be able to handle all that current and spread the power/heat)

Power in watts is P=V*I or 3.211 * 1.03 = 3.3 watts… and that would make a lot of heat, which corresponds to your measurements of over 200 degrees.

By the way, notice the “2w” on the led strip, maybe 2 watts? 2 of them lit up at max power would be 4 watts total, so numbers seem right.

Yes, you are basically using a LED strip wayyy too powerful for what you want I believe, too many LEDs in the same housing, overkill in my opinion…

Greg

#14

Greg,

Check your math. I = 3.11 x V= 3.211 = 9.99 watts. I think you used the resistor value in your calculation.

#15

Thanks for catching my mistake Paul, was a little dopey… I am not confident that the voltage across the resistors is right.

In the picture I see the red probe, but not the black, which should be on the other side of the parallel array.

Something is not right, no way that is 10 watts.

Greg

#16

Greg,

If it is almost 10 watts that sure would explain why the resistors get so hot! Those batteries won’t last long.