Battery Backup Module for LED Passenger Car Lighting

Wouldn't a supercap do the trick for 5V LED strips and be more compact?

I had a brainstorm.  My YLB supplies voltage down to below 5VAC on the input all the way up to full 18 volt track voltage.  A few changes to the circuit to add a pot that adjusts the output voltage between 8 volts and 12 volts, and you have a power module that will hold a passenger car strip of 12V LED's up for about a minute at typical lighting levels.

1"L x .8"W x 1"H

@gunrunnerjohn posted:

I had a brainstorm.  My YLB supplies voltage down to below 5VAC on the input all the way up to full 18 volt track voltage.  A few changes to the circuit to add a pot that adjusts the output voltage between 8 volts and 12 volts, and you have a power module that will hold a passenger car strip of 12V LED's up for about a minute at typical lighting levels.

1"L x .8"W x 1"H

OK that looks pretty interesting. Can you tell us more about it?

Rod

Basically, what the YLB does is first regulate the track power to a bit over 5V and charge a 5V supercap.  Then it uses a boost switching regulator to boost the voltage up to 8 volts to simulate the 9V battery.  The boost regulator can be made variable with just a single pot, so if I made it output from 8V to 12V, you'd have an LED module with a supercap and variable intensity that will run on any power from around 5VAC and up.

I actually was thinking of a simpler method with less components, I'll have to think on that a bit.

Here's a better idea!  This module is 1.2" x .8" x 1.0" and does the whole job.

Dirt simple, the power comes in, get half-wave rectified, then fed into a Recom 5V switching module.  The ouput goes through an inrush limiter to limit the current demand when first chargig the 1.5F supercap.  The intensity is simply controlled using a standard pot since the currents are well below what the pot can handle.  The pot is specified at 500 ohms, but if you wanted to use this to control only three or four LED's, then the pot could be 1K or more.

I did use a couple of SMT components, but in looking at the layout now, I think they could be thru-hole as well if you desired.

This looks like a nifty idea John. I like the simplicity of it all. Can I purchase one to try it out?

Rod

@gunrunnerjohn posted:

Here's a better idea!  This module is 1.2" x .8" x 1.0" and does the whole job.

Elegant solution, GRJ! I run entirely conventional rolling stock, and one of the minor irritations I have is the lack of realism when all the passenger car lights go out every time the throttle is closed. With your module design, it sounds like there might be a few seconds (with incandescent bulbs) to a minute or so (for LEDs) of passenger car (or other) lighting after power is cut. Have you given any thought to selling those modules, or at least assembling DIY kits for sale?

@Steve Tyler posted:

Elegant solution, GRJ! I run entirely conventional rolling stock, and one of the minor irritations I have is the lack of realism when all the passenger car lights go out every time the throttle is closed. With your module design, it sounds like there might be a few seconds (with incandescent bulbs) to a minute or so (for LEDs) of passenger car (or other) lighting after power is cut. Have you given any thought to selling those modules, or at least assembling DIY kits for sale?

Well, getting the modules assembled would require a considerable up-front investment, the minimum they'll do is 100 modules  Parts for each module are around $5-6, the little switcher is $3 and the supercap is around $2.  Add to that the other parts, the PCB boards, and the assembly costs, and I'm into it for probably around $1500. I also don't know how many people would spring for the solution given the selling costs.

I also hasten to add, this really only works for lower power consumption of LED lighting, it's designed to deliver around 50-60 milliamps maximum.  For LED lighting, the supercap would probably keep them lit for quite some time.

I'm going to get a few prototype boards and tinker with it a little and see how well it works out.

I could probably give some thought to kits.

I like these new ideas from Rod and John. I wish I would have waited 4 months to start my project for 30 cars. I have added 2 - 4700mfd 35v caps in parallel with the 1000 mfd cap on the board to the v2.2 DIY kit which will keep the LEDs steady to the naked eye while crossing back to back O22 turnouts at low speed, that is $4 per car though. I will keep watching the progress on the new design.

Some how I have messed up the soldering on the last 3 boards. None of them work. I can get ~ 19v DC out with 15v AC in, but the LED strips don't come on. The pot is at full CW. Any suggestions on what I have messed up? The first ~ 10 cars came out fine.

I ordered some prototype boards for my supercap based board, we'll see if it is as good as I think it should be.  This is specifically designed to run for both conventional and command operation, there's no difference in operation or power dissipation since it uses a switching power supply instead of a linear supply.

This is a design for the 5V LED strips, and it is a constant voltage design, unlike my earlier constant current designs.  The supercap on the back of the PCB will be folded down against the board to minimize the height of the board, my 3D design view doesn't allow me to do that.  I estimate the whole package will be 1.2" L, .85" W, and about 1" tall.

It has an intensity control for the lighting and runs off track power directly.  The output is a maximum of 5V at full intensity, so the 5V LED strips will be called for.  Of course, it can also be used for individual LED's in parallel if desired.  The design can output up to several hundred milliamps, so there will be no issue lighting a lot of LED's!

I'm making it an all thru-hole design so it can be offered in kit form.

@Santa Bill K posted:

I like these new ideas from Rod and John. I wish I would have waited 4 months to start my project for 30 cars. I have added 2 - 4700mfd 35v caps in parallel with the 1000 mfd cap on the board to the v2.2 DIY kit which will keep the LEDs steady to the naked eye while crossing back to back O22 turnouts at low speed, that is $4 per car though. I will keep watching the progress on the new design.

Some how I have messed up the soldering on the last 3 boards. None of them work. I can get ~ 19v DC out with 15v AC in, but the LED strips don't come on. The pot is at full CW. Any suggestions on what I have messed up? The first ~ 10 cars came out fine.

Bill if you could shoot me a couple of pix of the problematic boards I may be able to spot the problem. Something must be different than the first bunch. My email is in my profile, or you may still have it around. Or you could post a pic or two here on the forum.

Rod

@gunrunnerjohn posted:

I ordered some prototype boards for my supercap based board, we'll see if it is as good as I think it should be.  This is specifically designed to run for both conventional and command operation, there's no difference in operation or power dissipation since it uses a switching power supply instead of a linear supply.

This is a design for the 5V LED strips, and it is a constant voltage design, unlike my earlier constant current designs.  The supercap on the back of the PCB will be folded down against the board to minimize the height of the board, my 3D design view doesn't allow me to do that.  I estimate the whole package will be 1.2" L, .85" W, and about 1" tall.

It has an intensity control for the lighting and runs off track power directly.  The output is a maximum of 5V at full intensity, so the 5V LED strips will be called for.  Of course, it can also be used for individual LED's in parallel if desired.  The design can output up to several hundred milliamps, so there will be no issue lighting a lot of LED's!

I'm making it an all thru-hole design so it can be offered in kit form.

Looking forward to seeing how this works John. Looks like it should be better and simpler.

A thought; perhaps the centers of the supercap and D1 could be shifted to align laterally? That way the supercap could be mounted on top of D1 on the board topside. That may work better in some installations? Just saying.

Rod

I thought of trying to put it on top, but it's a lot longer than the space, so it would be sitting on top of the taller switching power module.  It would also cover half of the intensity pot.  I agree it would be great if all the components were on one side.  I did also think of just having the supercap stick straight up and not fold, I may still explore that option.

I did a trial fit, here's the layout with all components on one side.  The supercap is the larger size 1.5F 5.5V one, some are smaller.  That's also why there are two sets of holes, one set is 11mm, the other is 15mm.  That matches the two styles of supercap I commonly see.

The board is 1.35" x .85" and the height remains at 1" for the tallest component, the larger of the supercaps.

@gunrunnerjohn posted:

I did a trial fit, here's the layout with all components on one side.  The supercap is the larger size 1.5F 5.5V one, some are smaller.  That's also why there are two sets of holes, one set is 11mm, the other is 15mm.  That matches the two styles of supercap I commonly see.

The board is 1.35" x .85" and the height remains at 1" for the tallest component, the larger of the supercaps.

John I think you nailed it! That looks like the best of all worlds to me. And it should fit into most any passenger car. Bravo

Rod

@gunrunnerjohn posted:

I did a trial fit, here's the layout with all components on one side.  The supercap is the larger size 1.5F 5.5V one, some are smaller.  That's also why there are two sets of holes, one set is 11mm, the other is 15mm.  That matches the two styles of supercap I commonly see.

The board is 1.35" x .85" and the height remains at 1" for the tallest component, the larger of the supercaps.

Nice reconfig, GRJ! I think that'll make it easier to shoehorn into available space, and enable the installer to stick it down on the 'flat' side.

Just curious -- I know it's intended for low-draw LEDs, but wouldn't incandescent bulbs just discharge the supercap quicker, or is there some other limitation? I suppose I could swap in E10 base LEDs, but it would be nice to stay with the OEM bulbs and sockets.

@Steve Tyler posted:

Just curious -- I know it's intended for low-draw LEDs, but wouldn't incandescent bulbs just discharge the supercap quicker, or is there some other limitation?

Well, first off, the switching module outputs 5VDC at up to 500ma.  However, the incandescent bulbs are rarely 5V bulbs, so they would hardly light at all on 5VDC.  I could have designed for a different voltage output, but the object of the exercise was to do an LED lighting board for conventional and command operation.  I truthfully don't see much point in trying to arrest the flicker of incandescent bulbs, it's just to limited of an audience.

With this layout and provisions for the larger supercap, you can also put a larger value supercap on the board in the space provided if you want even longer holdup times.  If my experience with lighting passenger cars with the 12V strips are any guide, I expect it to be more than sufficient for any reasonable power interruption.

Obviously, for the same illumination with the 5V strips as you'd get with the higher track voltage feeding 12V strips, the illumination will take about three times the current, so I'm thinking 60-70 milliamps for a typical brightness.  For 67ma (75 ohm load), using a 1.5F supercap I get over ten seconds of almost steady light before the LED's start fade, more than sufficient for the task.  The board will run on around 6-6.5 to 18 VAC from the track, so virtually any operating environment is supported.

Here's a 3D representation of the board with the larger supercap installed, note it's fills the space at the end of the board, that's the limiting factor here.  However, the larger form factor caps are frequently the cheaper ones, so I wanted the board to be able to use them.

@gunrunnerjohn posted:

Well, first off, the switching module outputs 5VDC at up to 500ma.  However, the incandescent bulbs are rarely 5V bulbs, so they would hardly light at all on 5VDC.  I could have designed for a different voltage output, but the object of the exercise was to do an LED lighting board for conventional and command operation.  I truthfully don't see much point in trying to arrest the flicker of incandescent bulbs, it's just to limited of an audience.

Fair enough, and yeah, I was overlooking the module's lower output voltage, so it appears some sort of bulb change would be in order in any event. I suspect there *are* 5-6 volt E10-base incandescent bulbs out there, but if I'm swapping bulbs anyway, I see no advantage to *not* going to LEDs.

In fact, if you could offer a stick-on strip of compatible LEDs with your kit, I could just bypass/replace the current lighting entirely, using the existing track pickup to power the strip through your module. Any thought to offering an option to add LEDs to your kit, to make a soup-to-nuts solution for us conventional codgers?

Anything's possible Steve.   I did do a little bench test to verify the current draw and longevity of the cap charge.  It appears with a 1.5F cap, it'll hold up full brightness for around 10 seconds and then slowly start fading.  This is assuming a fairly bright setting on the intensity.  Should be more than sufficient for conventional, even reversing directions.