Modification of Backlit panel help....

[Mach7]

Hello All,

Looking at replacing my 'grain of wheat' lights with LED's for back light operation.

I find that the incandescent bulbs are putting me over budget in amps. The attachment alone takes 35 bulbs and at .060 ma/per it adds up.

Has anyone found a solution around this? In other words what are my options using the existing bulbs? In my mind I am stuck with the same high ampere draw as there are about 300 of them total in the entire overhead panel.

My (present) solution is to change them out with small LED's as they draw only .20 ma/per to reduce my amp requirement.

any and all suggestions are welcome!

Jim

[Joe Lavery]

The bigger problem you will have is that LEDs require two connections, you can't daisy chain them as you would bulbs. They also need current limiting resistors, so you would probably need to design and make new PCBs.

Another option would be to use LED strips, but this is not very flexible for the type of panels you have.

Joe.

[ame]

What power supply are you using? Is it 12Vdc, for example? Do you want dimming control?

Single white LEDs generally have a forward voltage of about 3V and consume about 20mA at full brightness. They are available in warm white and cool white, and in a variety of packages, e.g. 3mm, 5mm, SMD.

If you have a 5V supply for your panel lights then you must power each LED individually, and each must have its own dropper resistor. The resistor must dissipate the excess power and limit the current to protect the LED.

For a 5V supply and a 3V LED the excess voltage is 2V. To limit the current to 20mA the resistor value will be 2V/20mA, which is 100 ohms.

You can buy LEDs with dropper resistors and wires pre-attached.

For LEDs you can calculate the resistor value with the simple formula

R = (Vs - Vf) / If

Where Vs is the supply voltage, Vf is the forward voltage of the LED, and If is the desired current.

If you have a 12V supply you can generally feed groups of three LEDs in series with a single dropper resistor.

Three LEDs in series will have three times the forward voltage, but the current through them will be the same. So, a string of three white LEDs will have a forward voltage of 9V, and with a 12V supply the dropper resistor must dissipate 3V at 20mA. Its resistance is:

R = (Vs - Vf) / If

= (12 - 9) / 0.02

= 3 / 0.02

= 150 ohms

That's in general.

Your specific situation may require something different, or a combination of different solutions.

For dimming, you have two choices. A current-limited supply, or PWM.

The current-limited supply needs no dropper resistors. The supply limits the current to, say, 20mA to avoid damaging the LEDs. Varying the brightness means varying the current limit on the supply. Less current means less brightness.

PWM varies the brightness by providing 100% of the voltage for some % of time. Dropper resistors are required. The PWM controller will turn the power on and off very rapidly, so the LEDs don't seem to flicker. If it's on 100% of the time you get full brightness. If it's on 50% of the time you get less. If it's on 10% of the time you get even less.

[fordgt40]

I had similar problems when backlighting my overhead. How I solved it is documented in this link. Hope this helps


http://www.737ng.co.uk/djb/Overhead%20Article.pdf

[Mach7]

@fordgt40

Thanks for the information...unfortunately I am trying to modify existing OEM panels by changing out the lamps and doing a straight replacement with 1.8/2mm LED bulbs.

I have had great success with some of the smaller panels that only accommodate 4 or 5 LED, but my problem will be the larger panels as I will not be able to use the same PCB board to wire multiple lights in series due to the voltage requirement.

Some panels have up to 35 lights, so I might take a page from your PDF design and modify/construct a PCB board that breaks up the light strings every 8 LEDs or so (using 24 volts)...so in essence I am layering my power LED strings, but more stacking them on the same board rather than layering them.

I have attached a rough idea on how to do this. The OEM boards are about 2 mills thick and screw to the back of the actual panel.

I might be able to duplicate this board with my 3D printer and then recessing wires in the material for my (a) and (k) runs to each of my led clusters.

any thoughts are welcome

-Jim

[jackpilot]

Jim
Are you sure you cant get enough amps from a solid PSU.
I use a 1200 Watts computer PSU to feed 5V to my complete 737 Overhead backlighting (FDS IBL bulbs) + a few cards and lights.
Changing to leds is (IMHO) a mammoth project.
Jack

[Garys]

I agree Jack. Buy something like this https://www.meanwell.com/productPdf.aspx?i=469 and never worry about 5v amps again - for most of us anyway.

Nice overhead Dave.... The backlighting looks awesome.

Mach7 - Try getting in contact with Phil Lambert @ simvionics. This is his area of expertise. He will be able to help you decide what is the best way to make the conversion

[bernard S]

emmm   just a thought  since using real  would the aircraft master dimmer box be of any help ?

[ame]

@fordgt40

Thanks for the information...unfortunately I am trying to modify existing OEM panels by changing out the lamps and doing a straight replacement with 1.8/2mm LED bulbs.

I have had great success with some of the smaller panels that only accommodate 4 or 5 LED, but my problem will be the larger panels as I will not be able to use the same PCB board to wire multiple lights in series due to the voltage requirement.

Some panels have up to 35 lights, so I might take a page from your PDF design and modify/construct a PCB board that breaks up the light strings every 8 LEDs or so (using 24 volts)...so in essence I am layering my power LED strings, but more stacking them on the same board rather than layering them.

I have attached a rough idea on how to do this. The OEM boards are about 2 mills thick and screw to the back of the actual panel.

I might be able to duplicate this board with my 3D printer and then recessing wires in the material for my (a) and (k) runs to each of my led clusters.

any thoughts are welcome

-Jim

If you have a 24V supply then you should probably limit your LED string length to seven LEDs. Each LED drops about 3V, as stated, so if your power supply is marginal then you may not have enough voltage to light any of them. Also, you have no headroom for your current limiting (dropper) resistor.

If you have seven LEDs then the total forward voltage (Vf) is 21V, leaving 3V to drop in the resistor. The resistor value (at 20mA) is then 3/0.02 = 150 ohms.

If you are lucky you can spread seven LEDs around the same area as eight in your original drawing. The power consumption per string is P = I x V, which is 20mA x 24V, 0.48W. So four strings consume about 2W. Or alternatively, each string needs 20mA, so four strings need a total of 80mA.

You could have varying numbers of LEDs per string (up to seven), and calculate the specific dropper resistor value for each string.

[ame]

I agree Jack. Buy something like this https://www.meanwell.com/productPdf.aspx?i=469 and never worry about 5v amps again - for most of us anyway.

Wow! 500W! That's enough for over 8000 LEDs.

[Mach7]

Thank you everyone for you input so far. I think I am getting close to a solution with all of your input(s)

@Gary & Jackpilot...
 I am leaning towards the regulated power supply...that might me the best idea as all I would have to do is change out some burnt bulbs and be on my way.

So...im going to ask a really dumb question with respect to the power supply.

This meanwell SE-600 unit will provide 5 volts with a rated current of 100 amps...plenty enough power for what I need.

So my question is this...with this type of unit, using the existing (incandescent)  bulbs in the panels, my amp requirement will be approximately 18 to 20 amps. Although the unit can deliver up to 100 amps, will this not trip the  outlet plug breaker as its rated at 15 amps?

[ame]

Thank you everyone for you input so far. I think I am getting close to a solution with all of your input(s)

@Gary & Jackpilot...
 I am leaning towards the regulated power supply...that might me the best idea as all I would have to do is change out some burnt bulbs and be on my way.

So...im going to ask a really dumb question with respect to the power supply.

This meanwell SE-600 unit will provide 5 volts with a rated current of 100 amps...plenty enough power for what I need.

So my question is this...with this type of unit, using the existing (incandescent)  bulbs in the panels, my amp requirement will be approximately 18 to 20 amps. Although the unit can deliver up to 100 amps, will this not trip the  outlet plug breaker as its rated at 15 amps?

It's not a dumb question. But the answer is no.

The key is power dissipation. Ignoring conversion losses you can calculate the current draw for any given voltage and power. It's just P/V.

So, a 5V 100A PSU can feed a 500W load.

That 500W comes from the wall outlet. However, the outlet has 110V available. Therefore the current draw at the outlet is 500W/110V, or about 5A. Well within the breaker's safe operating zone.

I assume you are in the US, with 110V circuits. If you were in the UK then you'd have 240V available, so your current draw from the wall would be around 2.5A. Still the same number of watts.

There are conversion losses,so your 5V PSU supplying 100A might draw 600W from the wall, but that's still manageable. And that's only if you hook up 500W of load to the PSU. Probably you'll draw a lot less.

[Mach7]

@ame

Thanks for the response...I live in Canada so our power grid is basically the same as the US.

each of My wall outlets are protected by 15 amp breaker...so with this power supply, (even though these lights will draw well over 15 amps), the outlet draw will be considerably less?

If this is the case then I might as well save the time and stick with the incandescent bulbs.

Thanks again!

-Jim

[ame]

It's all about the power dissipation. Volts and amps and watts are all related, so you can calculate the various quantities.

However, changing things has consequences. For example, the 500W power supply draws 5A from the wall socket at 110V when fully loaded, so a cable with at least 5A current capability is required for the power cord. However,the PSU can supply a load of up to 500W at 5V, so the low-voltage cable needs a 100A capability (if fully loaded). That's a fat cable!

[fordgt40]

However,the PSU can supply a load of up to 500W at 5V, so the low-voltage cable needs a 100A capability (if fully loaded). That's a fat cable!

Sorry, for a number of reasons this a red herring. You simply ensure that your downstream low voltage wiring has an appropriate in line fuse.

[Mach7]

Ok guys, just want to clarify my assumptions with respect to power supply capability etc before I decide to order one, (power supply) and move towards the incandescent bulb solution....

I have attached a rough diagram of what I think you are all trying to tell me, but will include the following questions;

SO basically the power supply will draw from the wall outlet but will not exceed a specific amp rating, (i am assuming it is anywhere from 5 to 7 amps), regardless of the amp requirement of the overhead panel lights.

Each one of my panels has a different number of lamps installed, for example, (assuming the amp draw per lamp is .050 amps, my hydraulic panel would draw 1.6 amps...fuel panel 1.75 amps, electrical panel 1.75 amps, engine start & aice panel 2.1, etc etc etc. adding up to about 20 odd amps of total draw...

Having said this, my assumption is that these amp ratings are cumulative therefore the power supply must be able to deliver hence the 100 amp rating on the power supply.

therefore is it safe to assume that, regardless of the output to the panels, the power supply will not draw more current from the wall outlet than is required to operate the panels?

In other words, lets assume the panels are drawing 21 amps from the power supply (busbar), I am assuming that the oulet will be capped at the specific power supply rating of 5 or 7 amps?

Also, I am using 22 gauge wire to each of my panels from the (diagram) busbar, as 22 gauge is rated to 6.3 amps and I will not even get close to that value per panel.

Thanks again

-Jim

[Trevor Hale]

Jim,

If the Power supply draws say 100Watts @ 5Volts = 20Amps, but you plug it into a wall outlet that is 115V as voltage goes up, current goes down.

for the same 100Watts At 10 Volts, you would draw 10Amps, at 24v you would draw 4.16Amps and at 110V you would draw 0.83 to 0.9Amps.  Effectively you could drive at 1500Watt Power Supply from a regular house outlet without issue giving you ~300Amps at 5V.

Food for thought.

Trev

[Mach7]

For sure Trev,

Leaving the mental math for a moment...I just want to make sure that when I plug this 5 volt 100 amp SE-600 SERIES power supply into my 115 volt wall outlet, that I won't be tripping my 15 amp (outlet)  circuit breaker when the aforementioned power supply trys  to satisfy the back light requirement of more than 20 amps.

I am sure you explained this in the text, but just wanted to make sure my 'coles notes' version was correct.

[jackpilot]

Just make sure the wires between the PSU and your bus are a good 10-12 Gauge (automotive)

[Garys]

For sure Trev,

Leaving the mental math for a moment...I just want to make sure that when I plug this 5 volt 100 amp SE-600 SERIES power supply into my 115 volt wall outlet, that I won't be tripping my 15 amp (outlet)  circuit breaker when the aforementioned power supply trys  to satisfy the back light requirement of more than 20 amps.

I am sure you explained this in the text, but just wanted to make sure my 'coles notes' version was correct.

It will depend on how much equipment you already have on the circuit. This power supply by itself wont trip the breaker to power your overhead, but if its on the same circuit as several pc's, projectors, monitors, sound systems etc then the power draw could tip it over the edge. That's why the majority of us spilt our simulators  power requirements over several circuits or install dedicated 20amp circuits.

[Mach7]

@Jackpilot...

For sure!..I am actually going to use 14 gauge from the PSU to the busbar, then 22 gauge branching off to each of the panels.

14 gauge is good for 32 amps, and 22 guage is good for 6.3, and I shouldn't come close to that in this setup.

@Gary's

That is a very good point...in fact I have been aware of this through the entire process. Some time ago I bought some of those volt/amp readout devices and installed them into every outlet in the room...the room was designed as an office, so each dual outlet has its own 15 amp protection breaker. Even with 8 computers computers, 10 lcd monitors, and numerous 5, 12 and 24 volt power supplies...the devices do not come off the same outlet, but rather spread around the room, so my amp draw from said outlets is well below anything to be concerned about.

With the overhead lights, I will connect an outlet that has the least amount of draw with everything up and running.

So I did a test run to better understand what you guys are trying to tell me...and thing my understanding is clear.

I hooked up a 5 volt/10 amp power supply to one of the overhead panels, (see attachment). This panel has a total of 75 lamps, which equates to an amp draw from the power supply of approx. 3.75 amps. When I looked at the volt/amp draw from the outlet, it showed .32 amps.

So my question has been answered.

Thanks guys

-Jim

[ame]

So I did a test run to better understand what you guys are trying to tell me...and thing my understanding is clear.

I hooked up a 5 volt/10 amp power supply to one of the overhead panels, (see attachment). This panel has a total of 75 lamps, which equates to an amp draw from the power supply of approx. 3.75 amps. When I looked at the volt/amp draw from the outlet, it showed .32 amps.

So my question has been answered.

Thanks guys

-Jim

Excellent.

Your PSU is supplying 5 x 3.75 = 18.75W to the lamps and drawing 110 x 0.32 = 35.2W from the wall. Your PSU is therefore around 50% efficient. The extra power drawn will be dissipated as heat.

[KyleH]

@Jackpilot...

For sure!..I am actually going to use 14 gauge from the PSU to the busbar, then 22 gauge branching off to each of the panels.

Keep in mind you are dealing with DC power on that side of the power supply which has different transmission characteristics. I would suggest using a 18AWG wire to your panels as with current levels and distances involved you will start running into voltage drop issues over the wires.

[Mach7]

@KyleH

18 gauge would be a better option, unfortunately all the panels are pre-wired with 22 gauge, so I will have to live with the voltage drop:(

[ame]

@KyleH

18 gauge would be a better option, unfortunately all the panels are pre-wired with 22 gauge, so I will have to live with the voltage drop:(

Use a fat wire to go from the PSU to nearby to the panels, then 22-ga from there over short distances?