remove resistors on LEDs for battery use?

Engineer-Joe posted:

 

Should I remove the resistors at each LED to make the batteries last longer? They seem like a waste if the battery power won't spike and will only go down over time? Should they remain to protect the LEDs?

You should leave them in place - they are there to limit the current that would otherwise flow through the LED once the necessary forward voltage is reached.  Once the forward voltage of an LED (or any diode) is achieved, they essentially have no resistance and thus would then draw more current than they are designed for.  And your LEDs won't be long for this world.  Plus, it's be a pain to remove them all.

What kind of battery pack (voltage, mA-Hr capacity)?  If your strips were meant to run on track voltage, each resistor will consume more power than the LED it's meant to "protect"!  Albeit some extra soldering, but I'd change the resistor values to match your battery...this should, say, double your battery life.

Also, the top strip looks to be 3mm diameter dome-lens?  Those have narrow conical output beam.  If good enough, then so be it.  But the wide-angle LEDs found on the light-strip rolls might be a better choice.  Again, extra soldering and such.

Final thought.  The cost of the 12V LED strips are, say, 25-50 cents per car.  You can buy a DC-DC boost (steps up voltage) converter on eBay for less than $1 (free shipping from Asia).  Example:

As a regulator, it will maintain the output voltage as the battery voltage droops.  It also has adjustment so you can set the brightness to your liking.  Of course the 12V LED strips have their own resistors.  The input voltage range on these are fairly wide so more options on battery selection.

Just reg double AA or triple if needed.

I thought it was redundant to have all those resistors.

I have extra LEDs that match the bottom 3rd Rail strip I believe. I thought about just having one resistor at the battery?

I didn't consider the convertors with the 12 volt strips.

The LEDs in your top strip look amber/yellow so operate at full nominal brightness at less than 3V.   But the whites need just over 3V at full nominal brightness.  So 2x AA or 3V is not enough.  Plan on 3x AA  or 4.5V if going the step-down approach.

If you know your application and have control over the components and operating parameters, there's nothing wrong with the one resistor approach.  To wit, here's the "Free" Harbor Freight LED worklight - photo recycled from a previous OGR thread.  Note a single resistor "protecting" 24 white LEDs in parallel, powered by 3x AAA batteries. 

Resistors are a penny a piece.  You have to de-solder and re-solder something for each of the existing resistors - whether it be a "0 Ohm" wire or a different, lower-valued resistor.  If you use one of those "LED calculators" you'll end up with something like 50-100 Ohms if you use one-resistor-per-LED...and something like 5-10 Ohms if you use the single-resistor approach.

If I were doing it, I'd try to figure out how to use the 12V LED-strips but I realize that can set you back $2 or so extra per car.  If these cars are in a consist, I'd also ponder how to tether the cars (arguably easier to do in G than O gauge) so that there's just one battery, one on/off switch, etc..  I'd also ponder how to add a charging plug and use re-chargeable batteries so as not to have to open up the car even if it only needs to be done once per month or whatever. 

Hmmm, rechargeable batteries?

I like to follow your advice Stan so I'll be looking back at my LED 12v strips.

Someone mounted the control box with the AA batteries for the dollar store lights under the car. Of course right now I can't find that pic.

To be sure, your original plan to mess with just the resistor values is the expedient solution.

But if you're seriously contemplating using 12V LED strips with a DC-DC boost converter, I will provide additional thoughts.  I suggested rechargeables with a charging port because of access issues.  But if you're saying the battery pack is external/under the car and easily accessible, then I guess not so much an issue?

I think the next step is to ballpark some operating parameters to see if the numbers add up.  If you've messed with the 12V LED strips you probably have an idea of what voltage you need to drive them for reasonable passenger car brightness.  12V will be way too bright.  Seems most guys end up driving them around 10-11 Volts.  Stated in terms of current, driving each LED at the "nominal" 20 mA will be way too bright.   Seems passenger cars using LED strips end up around 5 mA per LED.  How many inches of LED strip do you figure?

Then you fuss with battery capacity.  A typical 1.5V AA alkaline might be, say, 2500 mA-Hr.  For back-of-envelope purposes, that means 25 mA for 100 Hours, or 50 mA for 50 Hours, etc.  A typical AA NiMH rechargeable might be, say, 2000 mA-Hr but only 1.2V.  I figure you probably have a number in mind for operating hours before battery change.  What might this be?

 I hate to say this but someone posted that the small battery LED lights seem to last about a month or more of use? I really hate having to change out batteries and that was a huge reason I went to track power in the first place. So I'd like to go rechargeable here. 

 It would be cool if I could plug the MTH battery charger into these to re-charge. So now I'm wondering about a spare MTH 3 volt battery pack? I don't know the  did-charge curve on those? I believe they are at around 2.5 volts average?

 If not, I have a wall charger for AA and AAA types. 

It appears that with the self stick 12 volt strips, around 36 LEDs equal the length of what should be lit in the car. I don't think they need that much light though. Probably half of that would work. so while I'm soldering stuff what's a few extra joints?

Engineer-Joe posted:

 I hate to say this but someone posted that the small battery LED lights seem to last about a month or more of use?  

Wishful thinking!    Let's do the math.  Supply and demand.

Demand: 36 LEDs.  Say each LED draws ~10 mA.  At that current, the Voltage across the LED will be ~3V.  That's 3V x 10mA = 30 mW per LED, or total demand of 36 x 30mW = 1080 mW.  Call it 1 WATT of demand.

Supply:  I got these images from the MTH web site picking off the numbers from the pictures.

Let's say we use the MTH PS2-3V 2x AA battery pack.  As printed on the wrap, it's 2.4V x 700 mA-Hr = 1680 mW-Hours = 1.7 Watt-Hours of supply.

So even if we could transfer all the stored battery energy (with 100% efficiency) into the LEDs, that's only 1.7 Hours operating time.     For back-of-envelope calculations, let's just say 50% efficiency due to losses in converters, resistors, etc.. so now down to say 1 Hour of realistic operating time.

As an aside, a fully charged supercap battery-replacement for the PS2-3V stores less than 0.01 Watt-Hours.  So some 100 times less energy than the charged battery!

So what to do?!  Not rocket science.  Lower demand or increase supply.  To get anywhere near a month (720 Hours) or even a week (168 Hours) of operating time, we're talking huge changes.  Say revised goal is 4 hours per day for a week = 28 hours of operating time.   So we need a battery with 30x more capacity.  Or cut LED brightness in half and a 15x "bigger" battery.  Or cut LED brightness to 1/4 and a 7.5x battery.  Etc.

If I were proceeding, I'd start with a 4x AA (4.8V) battery pack using ~2000 mAh NiMH rechargeables, followed by the $1 DC-DC boost converter.  The supply is then 4.8V x 2000 mAh = 9.6 Watt-Hours.  Then I'd cut the LED brightness in half (adjusting the DC-DC converter output voltage) lowering demand to 1/2 Watt.  The combination of demand reduction and supply increase would provide at least 10 Hours of operating time before re-charging.

Thank you for the patience! I appreciate the help. I only understand the basics. I always look at resistors as wasted energy and can't get away from what I think about them.

 I can easily have 2 sets (or more) of AAs wired together under the coach cars to spread out the weight and still hide them. I can also easily lower the number of LEDs and the brightness. I had thought about the baggage car for a battery car with connections to trailing coaches. If I go that route, I could easily have many more chargeable batteries and easily recharge them using just that car at the charging station. That car is going to be empty inside so think of all the room! I could also put an extra battery pack from my 12 volt Milwaukee cordless drills inside. I didn't like the load weight's center of gravity being so high from the ground. So I think going with AA batteries laying flat against the floor would be better? Having the baggage car heavier might help with tracking anyways.

 The MTH pack is out. I didn't realize how low it's output capacity was.

FWIW, I run 18" passenger cars on around 25ma for the entire warm white strip of LED's in the car using my constant current regulator module.  When I turn it up to the full 45ma, the lights are way too bright for my taste.  If you use those numbers, Stan's estimate of 10 hours is pretty close as you'll have converter efficiency to work with.

gunrunnerjohn posted:

FWIW, I run 18" passenger cars on around 25ma for the entire warm white strip of LED's in the car using my constant current regulator module.  When I turn it up to the full 45ma, the lights are way too bright for my taste.  If you use those numbers, Stan's estimate of 10 hours is pretty close as you'll have converter efficiency to work with.

Joe, that's the data sheet efficiency, but remember that's the maximum under ideal conditions.

Well in the large scale world I use these to power whole passenger train interior & exterior lighting. Battery is usually in a headend baggage car, rpo or combine along with Buck Converter etc. Easily removable for charging. All cars daisy chained together.

This charger works great!

Can use same charger for this loco battery...

I just threw out 10mA operating LED current as a starting point.  As GRJ says, it's a matter of preference.  In his case, let's say his 18" car uses a 16" LED strip which is 8 sections of 3-LEDs (2" per section).  That means his 25 mA overall strip current is divided 8 ways so that each section gets 3 mA of current; each LED is operating at about 3 mA.  But that's only a factor of 3 reduction in demand... whereas you are after something like a 100 times or more!

The other wildcard which I'm curious about if you proceed is the scale-factor.  So a typical G-gauge car is around 1:24 scale vs. O-gauge 1:48 scale.  That means you are illuminating a volume not 2 times larger but 8 times larger; length, width and height are all doubled!  You will have a longer LED strip, but that is on the length dimension so you might have, say, 2x the number of LEDs.  Does this mean you need to operate the LEDs 4 times brighter than an O-gauge car to compensate for the 8x volume difference?  Or is it something less since you're only trying to illuminate a 2-dimensional surface (the windows).  Not obvious to me.

As per efficiency, I toss in the 50% number as a placeholder.   Note that with the 12V LED strips, most have 3 LEDs in series with a 150 Ohms resistor.  That resistor dissipates about 20-25% of the power going into each section.  So each LED section operates at only 75-80% efficiency to start with!  As GRJ says, converter datasheet specs touting conversion efficiencies over 90% are cherry-picking the operating conditions.  For the $1 eBay converters, the passenger car application is operating at the low-end of the power curve so I'd expect efficiencies of, say, 75%.   Efficiencies cascade...so if the converter is operating 75%, following by LED sections operating 75%, the combination is operating at 75% x 75% = 56%.  Again, even if you could operate at 100%, that's still only a 2x factor compared to 50% efficiency.  We're looking for 100x improvements.

I like the baggage car idea (with tethers) if that's practical - especially if you use an off-the-shelf power-tool battery pack for which you have a charger.  Seems a hassle to remove 4, 8, or whatever 1.2V batteries, individually charge them, and re-install.

Joe, I always enjoy your projects. We all learn so much from all the input you receive. Thanks for posting the road blocks you encounter along the way. You help the whole brotherhood who lack the education to accomplish what we wish to achieve.

Joe - this looks like an interesting project and the advice from Stan and GRJ is always spot on...  One thing you might consider - as you think about going the route of having one battery and a set of tethers to all the cars - would be to set it up so the battery pack doesn't have to be removed to be recharged.  It sounds like, in your case, that the baggage car might be a good choice because you can install a larger battery pack inside the car (I assume that the passenger cars all have interior detail so finding a place to hide a battery isn't easy).  The advantage of being able to recharge the battery pack without having to remove it is two-fold - one, it avoids having to mess with taking the shell off the car every time, which also avoids the problem that eventually something will break or wear-out.  Second, it also means you would be able to recharge more often (by virtue of being easier to recharge), and thus not have to make all the compromises Stan outlines as a way of maximizing battery lifetime.  Just a thought...

stan2004 posted:

The LEDs in your top strip look amber/yellow so operate at full nominal brightness at less than 3V.   But the whites need just over 3V at full nominal brightness.  So 2x AA or 3V is not enough.  Plan on 3x AA  or 4.5V if going the step-down approach.

If you know your application and have control over the components and operating parameters, there's nothing wrong with the one resistor approach.  To wit, here's the "Free" Harbor Freight LED worklight - photo recycled from a previous OGR thread.  Note a single resistor "protecting" 24 white LEDs in parallel, powered by 3x AAA batteries. 

Resistors are a penny a piece.  You have to de-solder and re-solder something for each of the existing resistors - whether it be a "0 Ohm" wire or a different, lower-valued resistor.  If you use one of those "LED calculators" you'll end up with something like 50-100 Ohms if you use one-resistor-per-LED...and something like 5-10 Ohms if you use the single-resistor approach.

If I were doing it, I'd try to figure out how to use the 12V LED-strips but I realize that can set you back $2 or so extra per car.  If these cars are in a consist, I'd also ponder how to tether the cars (arguably easier to do in G than O gauge) so that there's just one battery, one on/off switch, etc..  I'd also ponder how to add a charging plug and use re-chargeable batteries so as not to have to open up the car even if it only needs to be done once per month or whatever. 

I have two of these lights. One of them is at least a year old now + and I use it when looking for things or when the power goes out. I never even looked at the batteries, let alone change them.

Casey Jones2 posted:

Well in the large scale world I use these to power whole passenger train interior & exterior lighting. Battery is usually in a headend baggage car, rpo or combine along with Buck Converter etc. Easily removable for charging. All cars daisy chained together.

Engineer-Joe posted:

...I could also put an extra battery pack from my 12 volt Milwaukee cordless drills inside. I didn't like the load weight's center of gravity being so high from the ground. So I think going with AA batteries laying flat against the floor would be better? Having the baggage car heavier might help with tracking anyways.

Right.  The problem with many power-tool battery packs for the application at hand are their awkward shapes which work fine to snap into the power tool...but not so good for laying low and flat on a baggage car floor.  Add to that the battery chargers for power-tool packs are usually cradles that means you pretty much need to extract the pack from the battery car to charge it. 

In a cursory search for rechargeable packs on eBay, it seems toy cars/planes/copters have battery packs with 2-wires to a connector.  And they sell corresponding chargers once you settle on a voltage, battery technology (NiCd, NiMH, LiPo), a connector type.

The LiPo packs seem to offer the best energy density, but they tend to cost a bit more and the mating chargers are also more expensive.

Seeing as this is a one-off, I'm not sure it will be easy to come up with a simple mechanism/method to select between 1) off, 2) on, 3) charging.  We have come to expect the ability to operate & charge at the same time thanks to smartphones and such, but the technology to do this can be surprisingly tricky especially with Lithium batteries.  So it may be as "dumb" as a 3-position slide switch to select between the 3 modes. 

To be clear, I'm assuming you will want to get lucky and stumble on some off-the-shelf (co-opted from the toy industry, power-tool industry, whatever) rechargeable battery "system" rather than a roll-your-own.  By "system" I mean that to include both the battery pack, mating charger, and a connector style that easily integrates into a piece of rolling-stock.

In any case I think you need to settle on an operating-time measured in tens of hours...rather than hundreds of hours.

Stan (& Joe), what about the battery packs for extra power for your phone or other devices that make them more portable and last longer while you are away from a charger? I know they are only 5 volts, but they have some with very high mAh ratings and they usually are not terribly expensive. Could these be made to work somehow? First one I found: Power Bank USB Pack Portable Rechargeable Battery Charger 10400mAh 1A & 2.4A New Edit: After more looking these are available in several (and multiple) voltages as well. Thought I had seen those somewhere.

I tried to make a picture like you posted above showing the details on the batteries, but mine was with zero success.

My grandson has a similar one for his iPhone, that would probably work well if you find one that fits into the car. 

Here's one on eBay: 301961500010, 20000mAh Dual USB External Power Bank Pack Portable LCD Charger for Cell Phone, $15.99 shipped free from the US.  You can put the charger in anytime, running or not, and all the electronics if figured out for you.  20AH should power the lights for a decent amount of time, maybe not 100's of hours, but don't get greedy.

I don't have any with that high of a mAh rating, but I have a few smaller ones. On youtube I have seen some pretty high mAh ratings on some that looked to be pretty small. Compared to the person's hands using them and other stuff on their workbenches. Youtube is also where I saw the selectable/multiple voltage models, like 3, 6, 9, 12v etc. Pretty neat little devices that I never saw a need for until I finally got one. 

The good thing about these products is they've already figured out the charging and switching seamlessly from charge to discharge, or even doing both at the same time.  All you need to do is provide a filtered 5VDC to the charging port for the charge.

The output of this would logically be fed into a boost regulator for this application with the LED strips.

stan2004 posted:

Casey Jones2 posted:

Well in the large scale world I use these to power whole passenger train interior & exterior lighting. Battery is usually in a headend baggage car, rpo or combine along with Buck Converter etc. Easily removable for charging. All cars daisy chained together.

What is the lighting configuration and what kind of operating times are you seeing?

 

Also, have you settled on a tether connector type/style that works for daisy-chaining large-scale?

Well one of my personal trains is 7 heavyweight passenger cars using the Led peel n stick strips. Using the standard group of 3 Led's per piece some cars have 3 pieces and some have 4...depends on the lighting mood of the particular car. What I mean is baggage, rpo & combine don't need to be lit as bright as say a coach or Pullman. Then to make things worse in the diner car the tables have Led's and no overhead lighting in that area. The observation car is using incandescents for the marker lights. 

I get about 12 hours lighting out of the 2,200 mah battery and that's with the Buck output set at like 11.5V.

Car interconnects are the JST SM connectors as that style is used a lot in G scale locos & car wiring..so just used what I already had plenty of stock...connectors and contacts then make my own wiring harnesses.

gunrunnerjohn posted:

The good thing about these products is they've already figured out the charging and switching seamlessly from charge to discharge, or even doing both at the same time.  All you need to do is provide a filtered 5VDC to the charging port for the charge.

The output of this would logically be fed into a boost regulator for this application with the LED strips.

I went looking the other day on ebay for the boost boards and some had mini usb type(phone) connectors on the input.

I had pondered using either a three wire connector that when plugged in the opposite way, the polarity could remain the same?

(for example use the center pin for pos., and either of the outside pins for neg.)

Or actually have single wire pins that could plug into the appropriate sockets to keep the polarity?

I think I need to research it to make sure it's easy. Maybe I'm overthinking this? The cars will probably always face the same direction.

You can just provide a connector to charge it when you desire, I think you're overthinking it.

rtr12 posted:

Stan (& Joe), what about the battery packs for extra power for your phone or other devices that make them more portable and last longer while you are away from a charger? I know they are only 5 volts, but they have some with very high mAh ratings and they usually are not terribly expensive.

The one GRJ shows is 20,000 mA-Hrs or 100 Watt-Hrs for only $16 - only 16 cents per Watt-Hr.  Nice.   It appears there are some that have the USB connector on the side (vs. on the ends) so if the pack can fit in a baggage car, RPO, whatever, then the charging plug would be accessible by sliding the car door.

And the charger can be a $1 wall-wart USB charger.

I think we have a winner! 

Engineer-Joe posted:

I had pondered using either a three wire connector that when plugged in the opposite way, the polarity could remain the same?

...

Maybe I'm overthinking this? The cars will probably always face the same direction.

I was thinking maybe just putting, say, female 2-pin polarized connectors on both ends of each passenger car...the ones Casey shows seem reasonably priced and apparently commonly used on G-gauge already.  Then the car-to-car tethers would be 2-wire male-to-male cables.  The power car with the battery, step-up converter, on/off switch, etc. would have the 2-pin female.  In this way you can have the passenger cars facing either direction.

gunrunnerjohn posted:

You can just provide a connector to charge it when you desire, I think you're overthinking it.

I meant to connect it to the actual light circuit. Wouldn't I use the USB 5 volt output?

C'mon man! How about a recharging bumper? Just back it into a siding and you're all set.

Although electronics are generally way over my head, I enjoy reading the discussions and creativity involved in applying other products to model railroading.  I wonder if model train manufacturers would be interested in these passenger car lighting innovations in new cars in O gauge-scale if the cost/price calculus made sense.  Of course the after market retrofittting of our cars has already benefited by the electronic ingenuity of you folks.  As an aside, I decided several tears ago that lights in passenger cars was not high on my list after a few incidents with rollers hanging up on switches, so a disconnected the incandescent lights and removed the rollers for smoother rolling cars.  But I do enjoy seeing the lights on video posts on the forum.  I had read a post or two about battery powered led lights and thought about eventually installing leds in my passenger cars. I have 12 heavy weights. 3 RPOs, 1 baggage, 2 express, a dinner, a coach- baggage combo, a sleeper, 2 coaches and an observation car. I think lights would not be needed in the express cars and baggage car and probably not in the sleeper.  So my retro project would be relatively small. Thanks for an interesting thread.

Ah, the power of collective experience once again.  Nice going all. 

Now, lessee, a charging bumper - one with a button on top that when pushed deploys a charging jack (spring loaded, of course)  that mates with a receptacle built into the vestibule of the baggage car...!

You can crank up the volume, here's a 50,000mah pack, that's 50 amp hours, and it's $14.59 shipped.  Plugs on the side as Stan mentioned, but I'm not sure those are the charging plugs.  eBay: 263256534270

There are tons of cheap choices in all sorts of sizes.

LOL.  I'd take a close look at those specs.  At 50 Amp-Hours at 5V for $14.59.  That's 5V x 50 Amp-Hrs = 250 Watt-Hours...or an eye-popping 6 cents per Watt-Hour.    OK, I know prices have been coming down on these and I don't have one so maybe I have nothing to say...but geez Louise!  I also see some battery packs claiming 100,000 mAH...or a whopping 500 Watt-Hours of storage for not much more $.

As to the charging issue.  With storage capacities in the hundreds of Watt-Hours, you need to do-the-math.  So let's say you indeed have a 250 Watt-Hour battery pack.  And let's say you attempt to charge this pack with a USB 5V charger that puts out 1 Amp (typical for a $1 wall-wart USB smartphone charger).  So the charger can deliver 5 Watts.  That means it would take (at least) 50 Hours to charge a 250 Watt-Hour battery pack!  So much for the idea of over-night charging.  I guess that would be an over-weekend charger! 

OK, yes you can get 2 Amp or 3 Amp 5V USB chargers, and for all I know you can feed 12V from a car to charge these gadgets.  I also figure you probably wouldn't wait for the battery-pack to completely discharge before re-charging.  And so on.  But the point is one must do their "due diligence". 

In any case, I think rtr12 stumbled on a non-train technology which has great promise for our battery-powered applications!

Those suckers sure claim a lot of energy storage.  I'm a little skeptical of the claims, my grandson has a 12000mah one that is pretty hefty, about as large as the 50,000mah one in that ad.

Thanks Stan!

Earlier I was looking at some 12 volt battery packs and I think some are just cases for batteries and you purchase the batteries separately? Some even come with jumper cables to start your car! Anyway, watch the listings carefully.

Not enough mAh, but under the 'what will they think of next' category.

ZNTER S19 9V 400mAh USB Rechargeable 9V Lipo Battery

Also take a look at the 'Frequently Bought Together' line below the main ad. Looks like they have AA and AAA as well, plus some nifty multiple device charging cables.

I must stop looking at all this stuff!!