Led light stack burned out on SL-10

[Edster]

The green led light on top of the control burned out. The red still works but not the green. I ordered whole new light assembly from Haas. Anyone have to put one of these in? I'm hoping I just need to remove the face of the control panel. Does the monitor stay in when I remove the face? Keyboard?

Thanks in advance.
Ed

[Geof]

Are you sure they "burnt out". It is very unusual for LEDs to burn out unless something has gone wrong in the circuit driving them. If you just replace them you may find the new ones go immediately.

Incidentally don't remove the front of the control remove the back.

[Edster]

I thought it was burned out. I found the two screws at the top that let the control panel swing out. I replaced the led circut board with the new one and I'm having the same problem. I disconnect the plug and re connect and the green light flashes bright for a second then goes dim. So dim I can barley see it. I found the cable in the control box in the back and when I unplug it it's the same thing. Do you think it could be a relay? I found the schematic with the relays on it and there are two relays for the beacon, one for green one for red. I thought about swapping them, but I can't seem to find them. The schematic shows K30 and K29, but there nowhere to be found.

[Geof]

I don't know much about electronics but if they flash bright when first connected and then fade I would suspect a power supply fault. Relays are either open or closed so the fading is not likely to be a relay fault.

[Edster]

Everything else works fine on the machine, who knows it could be a power supply problem. I was thinking the relay might be getting weak. I've got one on my fadal that triggers the y delta switch that's weak. It's causing the y delta contactor to buzz a little. If I tap on the cabinet the buzzing stops. The service guy didn't have one on the truck when he was here replacing the contactor that we originally thought was bad

Oh well the next time the service guy is out I'll have to have him look at it.

[gar]

0701005-1030 EST USA

Ed:

If the light actually has an LED, then the following are the general characteristics:

An LED somewhat approximates a constant voltage device with some internal series resistance. Light output is proportional to current to some extent. The said constant voltage device is quite sensitive to temperature. An LED is a solid-state diode and has its general characteristics.

If you want to supply power to a constant voltage device with a low series internal impedance, then you need to use a constant current source. Under some conditions a resistor can approximate constant current.

Suppose at the brightness you want the LED voltage drop is 2 V and at that voltage and room temperature the current is 20 MA. If the source to power this is 24 V, then a series resistor of R = (24-2)/.02 = 1100 ohms is required. It should be obvious that a 50% drop in the source voltage will drop the current to slightly less than 10 MA. About 1/2 brightness.

Next. Let's assume the LED internal resistance is Ri = (2-1.5)/0.02 = 25 ohms, and for 20 MA we connect a voltage source directly to the LED it has to be Vs = 2 V. Now double the 2 V source to 4 V. The LED current becomes In = (4-1.5)/25 = 2.5/25 = 0.1 amp = 100MA. This is a 5 times increase in current. At 2 V input the LED dissipates 0.04 W a satisfactory value for a small LED. At the 4 V input the power dissipated in the LED is 4 * 0.1 = 0.4 W or 10 times that of a 2 V source. Probably will burn out a small LED.

It should be noted that flourscent lamp bulbs, neon bulbs, voltage regulating tubes, arc lights, and welding arcs are all essentially constant voltage devices and therefore need to be driven by an approximation to a constant current source.

Back to your problem. If you actually have an LED light, then where is the current limiting element that controls the LED current. You need to find it.

HAAS probably uses solid state relays to control the lights and therefore they won't look like ice cube mechanical relays.

HAAS might use a solid-state device with constant current characteristics as the relay to switch the LED light. If this was the case and it was faulty that could explain what you have observed. But the mostly likely case is that an external to the LED series resistor is used for current limiting. This will be the most reliable method.

You did not want to read all this, but if you understand the characteristics of an LED, then in the future you can solve your own problem.

.

[Geof]

Originally Posted by gar 0701005-1030 EST USA ....If you actually have an LED light, then where is the current limiting element that controls the LED current. You need to find it....

I just had a look at the LED lights on one of my machines. There are additional components besides the lights including a capacitor. I wonder if these things are built to simply plug in place of the old style with incandescent lights so they have everything included. I guess the way to check is find out what voltage is applied to the connectors on the unit.

[gar]

071005-1819 EST USA

It makes sense that HAAS might go to an LED light and still power it from the same AC supply that was used for an incandescent.

The LED probably can be run at a lower current than the incandescent. Depending upon the driver switch (relay or whatever) there may be some special requirements of the load.

Assuming no special requirements and there is no switching type current regulator, then there is no need for a capacitor. All you need to run an LED on AC is a current limiting resistor, a reverse biased diode in parallel with the LED, or the LED at the center of a bridge rectifier. No filtering is required.

One could use a capacitor as a current limit in the steady state condition, but this could have high initial inrush current. That inrush could be limited with a series resistor, maybe better with a negative coefficient thermister.

.