Techie question on lighting voltage.....?

Zerogee

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A little technical conundrum, I wasn't sure whether to post this under DCC or Battery Power, because it applies to both....

A bit of background before the question:
After much procrastination, I'm finally getting round to putting together my "multi-power" loco - the mission brief is for a loco that I can take anywhere and run on DC or DCC track power, OR battery power with full DCC sound and control. It's an OBB 2095 (a "whizzy cranks"), with a Massoth XLS for driving and sound control, plus a Tam Valley DRS receiver and a 14.8 volt Li-Ion protected battery pack on board. A DPDT centre-off toggle switch will select either track power (DC or DCC fed straight to the XLS) or onboard battery power fed to the XLS via the DRS module.

Now, the question: what to do about the lights? If I put 24 volt bulbs in the loco and leave the XLS lighting output at full value, that will be fine on track power but rather dim when only running on the 14.8 volts delivered by the battery pack. On the other hand, if I use 5 volt bulbs and set the XLS lighting outputs down to a safe value (usually "6", which means 6/32 of full track voltage) under track power, then they will again be very dim (if on at all) when on the battery, because they will only be getting 6/32 of 14.8v, which is under 3 volts....

The only way I've been able to figure out so far is to use two separate 5 or 6 volt voltage regulators (one each for front and rear lights) that are fed from the light outputs of the XLS - then if the XLS is left at full output values for the light functions, it shouldn't matter whether 24v track power or 14.8v battery power is being fed from the XLS, because in both cases the voltage regulators will step this down to a suitable level for the 5volt bulbs.

So, (a) will this work, and (b) any better and/or simpler way of doing it?
Over to you, chaps.......

Jon.
 

ntpntpntp

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Voltage regulators and 5V lights sounds like the way to go. They don't need to handle much current if just driving a couple of lights.

I've never been a fan of using the decoder CVs to set the output voltage (which is just a PWM average and still peaking at full voltage (ish)). I always leave at full output. If you ever reset or change the decoder you'd have to remember to set the lighting CVs again.
 
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Hutch

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A little technical conundrum, I wasn't sure whether to post this under DCC or Battery Power, because it applies to both....

A bit of background before the question:
After much procrastination, I'm finally getting round to putting together my "multi-power" loco - the mission brief is for a loco that I can take anywhere and run on DC or DCC track power, OR battery power with full DCC sound and control. It's an OBB 2095 (a "whizzy cranks"), with a Massoth XLS for driving and sound control, plus a Tam Valley DRS receiver and a 14.8 volt Li-Ion protected battery pack on board. A DPDT centre-off toggle switch will select either track power (DC or DCC fed straight to the XLS) or onboard battery power fed to the XLS via the DRS module.

Now, the question: what to do about the lights? If I put 24 volt bulbs in the loco and leave the XLS lighting output at full value, that will be fine on track power but rather dim when only running on the 14.8 volts delivered by the battery pack. On the other hand, if I use 5 volt bulbs and set the XLS lighting outputs down to a safe value (usually "6", which means 6/32 of full track voltage) under track power, then they will again be very dim (if on at all) when on the battery, because they will only be getting 6/32 of 14.8v, which is under 3 volts....

The only way I've been able to figure out so far is to use two separate 5 or 6 volt voltage regulators (one each for front and rear lights) that are fed from the light outputs of the XLS - then if the XLS is left at full output values for the light functions, it shouldn't matter whether 24v track power or 14.8v battery power is being fed from the XLS, because in both cases the voltage regulators will step this down to a suitable level for the 5volt bulbs.

So, (a) will this work, and (b) any better and/or simpler way of doing it?
Over to you, chaps.......

Jon.


As an ex-tekky, I agree that the voltage regulators are an inexpensive and effective way to go. There are buck-boost regulators available if you wish to have the 24 volt lamps instead of a lower voltage. I have used them successfully on Aristocraft diesel smoke units in the past so as to have smoke while running at low speed.
 
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Zerogee

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Thanks for the replies so far, chaps - couple of cheap 5v voltage regulator boards just ordered off evilBay (could have got them even cheaper from China but I want them in a couple of days, not weeks...). Got the XLS on order from Muns, already got the Tam Valley unit and the battery pack, so it's all starting to come together....... :)

Might even have it ready for touring round some of our local area GSS open garden days this summer!

Jon.
 

stockers

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Should all work Jon, but with those cheapy voltage regulators the input voltage will still effect the output to a certain extent. You also need to set them with a voltmeter. (Unless you have found something different on Ebay)
 

Zerogee

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Should all work Jon, but with those cheapy voltage regulators the input voltage will still effect the output to a certain extent. You also need to set them with a voltmeter. (Unless you have found something different on Ebay)

They are fixed 5v output, Alan, not variable ones with a control pot - so I'm assuming they don't need setting? And surely the whole point of them is that the output is the same provided the input voltage is within the range specified?
I went for a couple of these:
http://www.ebay.co.uk/itm/161798846149?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Jon.
 

Neil Robinson

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They are fixed 5v output, Alan, not variable ones with a control pot - so I'm assuming they don't need setting? And surely the whole point of them is that the output is the same provided the input voltage is within the range specified?
I went for a couple of these:
http://www.ebay.co.uk/itm/161798846149?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Jon.

IMHO they should be fine. Please be aware that these linear devices dissipate the excess energy in heat (as apposed to the on off approach of digital) so would reduce battery running time slightly.

I'd also like to add a caveat that will be obvious to many anyway.
In your case you'll be using the decoder output even when running analogue so the polarity won't change with direction.
If connecting directly to the track a diode bridge would be required between the track and module on both DC and DCC to get the correct polarity DC input to the module.
.
 
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GAP

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Ummm no option to replace the incandescent lights with LEDs and turn light output on or off regardless on power source.

Alternatively I would wire the LEDs across the motor lugs so no matter what the input is the lights are across the motor the LEDs will turn once the motor voltage reaches a certain point (usually not very high).
If the LEDs are wired in reverse polarity they become directional, simple solution without all that mucking about with extra electronic bits.
I do this with all my locos and really don't stress that much if the lights go out while the train is slowing down.
 

Zerogee

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IMHO they should be fine. Please be aware that these linear devices dissipate the excess energy in heat (as apposed to the on off approach of digital) so would reduce battery running time slightly.

I'd also like to add a caveat that will be obvious to many anyway.
In your case you'll be using the decoder output even when running analogue so the polarity won't change with direction.
If connecting directly to the track a diode bridge would be required between the track and module on both DC and DCC to get the correct polarity DC input to the module.
.

Thanks Neil - and a good point about the polarity issue for anyone using direct track power, as you say it won't affect my installation because I'm taking the light outputs from the XLS.

Jon.
 

Zerogee

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Ummm no option to replace the incandescent lights with LEDs and turn light output on or off regardless on power source.

Alternatively I would wire the LEDs across the motor lugs so no matter what the input is the lights are across the motor the LEDs will turn once the motor voltage reaches a certain point (usually not very high).
If the LEDs are wired in reverse polarity they become directional, simple solution without all that mucking about with extra electronic bits.
I do this with all my locos and really don't stress that much if the lights go out while the train is slowing down.

The point of this install, which is really going to be a rolling test-bed to see if it all works as I hope, is to have full DCC control over everything including the lights (except when running on track power DC of course!).
I guess I could go the LED route, but to me it's not worth replacing and re-wiring all the loco lamps on the 2095 when the already-installed incandescents will work just fine.

Jon.
 
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ntpntpntp

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1.2 amp regulator probably a bit overkill for a few lights, but should do the job.
 

stockers

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Zerogee

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Look good to me Jon. Have not seen that actual one before.

UK posted stock (apparently) so should be here in a couple of days - will let you know how well they work!

Jon.
 

Neil Robinson

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Thanks Neil - and a good point about the polarity issue for anyone using direct track power, as you say it won't affect my installation because I'm taking the light outputs from the XLS.

Jon.
Ah, I've just taken a closer look at your specific example and it has a four individual diode bridge on the board.
For directional lighting directly from DC track power a little modification would be needed.
 

Zerogee

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Well, this morning a little packet arrived with ONE of the two voltage regulators in it, no mention of whether the other is to follow (at the time I placed the order they definitely showed two available...) :mad:
Have sent them a message via evilBay, and await the response....

While I'm waiting, a quick question to Those Wot Know Stuff About Electrickery - the regulator has arrived with no instructions at all, which is pretty much what I expected, but I thought there might be at least an "in" and "out" marked on the PCB - there isn't..... Looking at the circuit board here:
http://www.ebay.co.uk/itm/161798846149?_trksid=p2060353.m2749.l2649&ssPageName=STRK:MEBIDX:IT
would I likely be right in assuming that the INPUT terminals at those on the left nearest the diodes, and the OUTPUT is the other end near the resistor and red LED?
The end that I'm assuming is the output is marked with + and - terminals, while the other end terminals are unlabelled, which would make sense as it is supposed to not be polarity sensitive and to cope with both AC and DC....

Jon.
 

ntpntpntp

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Yeah, the 4 diodes forming a bridge rectifier will be on the input side.

I wonder what the jumper pins are for? - Actually, looks like they're just a row of plus and a row of minus output pins, so for some sort of header rather than jumpers.
 

Zerogee

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Yeah, the 4 diodes forming a bridge rectifier will be on the input side.

I wonder what the jumper pins are for? - Actually, looks like they're just a row of plus and a row of minus output pins, so for some sort of header rather than jumpers.

Yes, looking at the tracks on the PCB, the two rows of pins in the yellow block seem to be directly connected to the output screw terminals.... so as you say, simply an alternative method of output connection?
Curiously, the one unit I received appears to be a mirror-image of the one in the picture in terms of component layout - and it's NOT just a case of a flipped photo on eBay, because the actual regulator chip is the same way round in both cases..... rather odd!

Jon.
 

ntpntpntp

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Curiously, the one unit I received appears to be a mirror-image of the one in the picture in terms of component layout
Jon.
So if the other one turns up built the other way round, does that mean you've got directional lighting regulators? :)

Slightly more seriously: you can get negative voltage regulator equivalents (eg LM7805 is +5V, LM7905 is -5V), I wonder if a module made for such a beast might be designed as mirror image? They have sent you the right thing?