LION is still working on the lighting problem of him. LION will be using one 3 unit LED circuit (12 v dc - resistor etc built in) in each of 6 cars on the subway trains of him. This will be (I hope) a single train line with one rectifier and battery for all of the LED units.
LION wants to know about connecting the red (positive) leg to the Battery. Obviously it will work if I just do it. (After all, I just did it!) But obviousl when the train stops for the day, the battery will be discharged.
I am hoping that the circuit will charge the battery to about 7 volts which will provide sufficient light. What can I do to limit the discharge of the battery. Someone mentioned zener diodes, but LION knows naught about them. If I drop one between the battery and the positive bus, can it stop the flow of electrons when the system reaches say 5 volts. Thus the battery will not completely discharge, but will be ready to take a charge onee the train begins to move.
What do youse guys think? will it work?
OPTION #2:
About halfway down on this page is a diagram for using RF transmission of power to devices. Now THAT would really work. The lighing circuits would be fully independant of the tracks and would get all of its power from the RF transmitter. It looks like this technology is either already available for WiFi devices, or soon shall be. What does anybody know about this?
ROAR
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No, do not connect the battery directly. You need a smooth filtered DC to charge a battery, plus the correct voltage and the current needs to be limited, to what depends on the type of battery (NiCad, NiMH, Li-Ion, Lipo).
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Is NiMh battery. LION knot know the curent off hand. Him will go upstairs and look at object. Is 9v Battery. I assume I can charge it to a lower voltage. My track power is 10.2V dc, the full wave restifier eats some of that. LION figures about 8 volts into the battery.
The Battery claims to be a 9 volt battery, but in the small pring it says it is really 8.4 volts, and 200 mA.
The supply to the rectifier is already DC, filtered and regulated, the rectifier is there since the equipment can move in either direction. It also isolates the lighting bus from the track bus.
The power supply is able to put out 12 Amps to the tracks.
the schematic illustrates how a resistor and zener diode can limit the voltage across some load. I don't believe you need the capacitor since you're using the bridge to simply correct the polarity of the DC track voltage.
i think the way to look at this is the LED circuit is always powered by the battery, 9V, and the battery is charged by the track voltage when it is high enough.
the resistor between the bridge and zener needs to be low enough to allow sufficient current for the LEDs and to charge the batter, but not too low to cause excessive current through the zener that may damage it.
I think you need to be very careful about overcharging a NiMh battery. And this may complicates things.
an undercharged battery won't last very long. There's a particular voltage that it operates at and once below it, the battery is nearly discharged. It will exceed the operating voltage when it it fully charged and this must be managed carefully.
the zener voltage should be just about (i.e. ~ the same) the battery voltage. A difference of less than 0.1V may will determine how fully charged the battery ever gets (see red curve). For this reason, the super-caps would be less critical.
As for preventing the battery from discharging. Like all diodes, LED current increases exponentially with the voltage across them. Once the supply voltage drops below some minimum, the current should be very small.
best of luck - i like your approach to model railroading
greg - Philadelphia & Reading / Reading
LION *was* looking at Super Caps. Him has 2.5 Volt caps at 4.7F.
Him figured to put two caps in series for a 5V, 2.3F device. This works when tried on the bench, but when passing it through the bridge rectifier is stops dead and does not appear to be charging. It seems to discharge at a higher rate than I expected, and the lights noticably dim in the 30-40 seconds that the train is stopped in the station.
LION bought four caps in the event that him would have to put two pair in paralel. Would that give me 4.7 F at 5 V?
gregcI think you need to be very careful about overcharging a NiMh battery. And this may complicates things.
Lion, I mistook NiMh for LiPo batteries which can be hazardous if overcharged. I believe NiCads are less susceptable to overcharging problems.
Supercaps can only provide a useful voltage (80%) for a limited time (1F, 10 ma, ~20 sec). A 120 maH 9V can supply 10 ma for ~12 hours.
curious about your problem. Purchased some supercaps and considering building a keep alive for my loco.
Lion
here's a schematic of what I think you're trying to do using super-caps and LM317s as current regulators. (LM317s come in TO-92 plastic packages smaller than to-220 package)
while resistors will certainly limit current, current will vary with voltage. The lm317 output is 1.25V above the adj pin. If R is 125 ohm, the output will be whatever is needed to drive 10ma thru R and whatever it is connected to.
one regulator limits the current into the caps which will charge from 0V to something close to track voltage. A resistor would have to be the sized for the max voltage and current would drop as the voltage rises. A regulator will allow a constant current no matter what the cap voltage is, allowing it to charge at the same rate when near 0V as well as near max voltage.
likewise, a current regulator maintains a constant current (LED brightness) thru the LEDs as the cap voltage drops until the cap voltage drops below the total min voltage of the LEDs + the drop across the LM317.
both regulators are tied to track voltage. The diode passes current to the LED path whenever the cap voltage (+0.7V) exceeds the track voltage.
If a NiCad battery were used in place of the caps, an LM317 could be used to provide a regulated voltage just above the full charge voltage of the battery thru a current limiting resistor. The LM317 is adjustable and that voltage can be adjusted precisely.
And since the battery voltage is relatively constant, a resistor can replace the LED current regulator. I assume there can be multiple strings of LEDs
others can check me on this
Track voltage is a constant 10.2 volts except when entering or leaving the stations where it tapers off to zero. There is a full wave rectifier between the track and the lighting circuit to assure the correct polarity on the lighting circuit, but this will lower my bus voltage to what? about 8 volts? If I use the power regulator to bost the voltage to say 12 volts that will then charge the battery.
What are those resistors and that diode between the battery and the light bus? What do they do for me, what values to they have? what voltage will be on my lighting bus?
Here are the LEDs I was thinking of using.
Of course I have individual LEDs and can make my own as I have been doing. These require 12 volts, but will work fine at 8 or even 5 volts. I do have a set of six units, and will put one in each car on my train. I was indending to power the train-line from a single electronics package in one car.
The only specs I can find on this lighting unit are:
Bright white 3-led modules. Operate on 12Vdc. Each weather-resistant epoxy sealed module is 0.55" wide with mounting holes at each end on 3.3" centers. 3.5" wire leads connect the modules. Very bright, but not as bright as our LS-123WW modules. Suitable for shelf lighting and displays. Dimmable. String of 20 modules. Power: 0.72W per module Viewing Angle: 140-150° Luminous Flux: 18-20lm
Thanks for your thoughts.
Elias
BroadwayLionTrack voltage is a constant 10.2 volts except when entering or leaving the stations where it tapers off to zero. There is a full wave rectifier between the track and the lighting circuit to assure the correct polarity on the lighting circuit, but this will lower my bus voltage to what? about 8 volts?
The forward voltage across a diode is typically 0.7 volts. So I would expect a drop of 1.4V across the bridge and only 8.8V after the bridge.
This may be too low to fully charge a nominally 9V battery (NiCad cells are 1.2V, 8 would be 9.6V). Is a 9V NiCad 9.6V, 8.4V, or ???
BroadwayLionIf I use the power regulator to bost the voltage to say 12 volts that will then charge the battery.
i don't understand why you think the voltage would be greater after a regulator. A conventional voltage regulator (e.g. lm317, lm340, 7805) regulate the a varying input to a lower constant voltage. The input to a 5V regulator might typically be 8V.
BroadwayLionWhat are those resistors and that diode between the battery and the light bus?
I think you know that the resistor in series with the LEDs limits the current thru the LEDs. However, you're LED assemblies look like they may already have resistors. I was thinking higher track voltage and DCC system with current limits.
in the capacitor circuit, the diode isolates the capacitor from the LEDs, allowing the capacitors to charge independently and only supply current when the track voltage is less than the capacitor voltage (see below).
in the battery circuit the LEDs could be connected directly to the battery but would "leach" charge current when the batter is charging (see below).
BroadwayLionWhat do they do for me, what values to they have?
either limit current or determine the current in the lm317 current regulator.
BroadwayLionwhat voltage will be on my lighting bus?
for the capacitor circuit, i'll guess at 6V less than track voltage.
battery voltage less 0.7V diode drop in the battery circuit (but see below)
BroadwayLionThese require 12 volts, but will work fine at 8 or even 5 volts.
i'm surprised that they can work over such a large voltage range. perhaps they have a current regulator circuit such as i described. Those may not be resistors in your photo, but 20 ma current limiters chips
is there any reason to run them at a higher voltage if they are just as bright at 5V?
BroadwayLionI do have a set of six units, and will put one in each car on my train. I was indending to power the train-line from a single electronics package in one car.
if the 8.8V after the rectifier is close to the battery voltage a current limiting resistor may not even be needed. I think (!) the battery will have internal resistance that limits the charging current.
in this case, the LED circuit will operate at the track/battery voltage.
if you have a battery, measure its fully charged voltage. Is is close, hopefully just below track voltage.
also with a discharged battery, put an ammeter between it an the track and measure what the peek charging current is when initially attached to the track. An analog meter may be easier to read.
I also forgot that your throttle is probably less susceptable to current loads. For the capacitor circuit, your supply can probably handle larger (?) initial charging currents allowing smaller valued current limiting resistors and there is less need to limit the current as on a DCC system.
8.8V / 50 ohm = 176ma that quickly drops as the capacitor charges, but is only 36ma when the capacitors are at 7V. With just a current limiting resistor, the capacitor can eventually fully charge to the 8.8V
the diode is needed if you want the LEDs to light at full brightness right away. If you can wait, the diode can be eliminated and they will only light after the capacitor voltage reaches the LED turn-on voltage (5V?)
of course all this needs to be verified on the bench.
gregcThis may be too low to fully charge a nominally 9V battery (NiCad cells are 1.2V, 8 would be 9.6V). Is a 9V NiCad 9.6V, 8.4V, or ???
It is a "9 volt" NiMH battery, the small print says it is 8.4 volts.
gregci'm surprised that they can work over such a large voltage range. perhaps they have a current regulator circuit such as i described.
The light over that rang, but full brightness is at 12 volts, acceptable illumination is also provided at 5 volts, but 12 volts, or maybe 8 volts is better.
gregcI also forgot that your throttle is probably less susceptable to current loads. For the capacitor circuit, your supply can probably handle larger (?) initial charging currents allowing smaller valued current limiting resistors and there is less need to limit the current as on a DCC system.
Ahem... What Throttle. LION has no throttle. Power supply puts 10.2 volts on the tracks, with 10 Amps available current. Resistors embedded across track gaps slow the train as it approaches or leaves stations. Reverse is not possible on a subway : fhe folowing train is only 240 seconds behind your.
Thanks. It is off to the bench we go!
is it really that simple?
presumably you already have the LEDs tied across the bridge rectifier and they work fine as long as there is track voltage (w/o resistors).
since the bridge output is presumable 8.8V (have you checked this?) and the NiMH battery is actually 8.4, is seems that simply adding it to the circuit across the bridge output is ok!
8.8V is above the operating voltage of the battery but not excessively above it and certainly not high enough to overcharge and damage the cells. But I wonder how long it would take to sufficiently charge the battery after not being charged.
gregc But I wonder how long it would take to sufficiently charge the battery after not being charged.
There is only one way to find out.
The fly in the ointment is that the battery will still power the lights even when the trains are not running, and thus running itself down. I'll have to make a shut-off of some sort.