Grain of wheat bulbs.

[jazz]

Hi. Now I'm not an electrician and need advice regarding grain of wheat bulbs.  I have 60 bulbs to wire up on the layout for street lighting and buildings.

 

I know about series and parallel wiring.  My question is, will a 3 amp 12v transformer be sufficient. Also does parallel wiring increase the wattage required or does this make no difference whether it in series or parallel.

 

Regads Ken

[Ray H]

I think I worked out that a GoW bulb draws about 30mA. Sixty times 30mA equals 1.8A so your power supply should be sufficient.

 

Wiring the bulbs in series will reduce (halve?) the brightness of each bulb, wiring them in parallel whether through a switch or not is how I would envisage they'd be wired - i.e. one wire of each bulb connected to the +ve and the other side connected to -ve. You may want to fit a switch between groups of bulbs and the +ve rather than have all of the bulbs powered at all times when the supply is turn on.

[Miss Prism]

Dropping no more than 9V or 10V across each bulb is likely to provide a more realistic illumination level, as well as greatly increasing the bulbs' lives.

[jazz]

Thanks for the replies.  I started by wiring the first set of street lights (three bulbs per lamp) to a 1amp transformer. It tripped after three minutes.

 

At first I assumed it was faulty, manufacturer said I was lucky to illuminated 21 bulbs, 14 being what could be expected.

 

Miss Prism, I was thinking of wiring in blocks of three series.  The three blocks are then wired in parallel which I thought would reduce the brightness.

 

Alternatively, I could wire in all in parallel and install a cheap panel controller. Which is going to be the best, I'm not sure.

 

What I would like is a dimish light and long lasting bulbs.

 

These are some of the lights, caught before the power tripped.

 

[Madcaravanner]

Personally I do use these by wiring groups in series switched - -  so they can be independently controlled 

then

I connect to an independent power supply in parallel to maintain the brilliance I want - obviously the more bulbs you use the dimmer the light so on some sets I have a small variable resistor to bring the brilliance down where I can only use one or two bulbs

[jazz]

Gray, I still unclear on the amps issue. I have been told I will be drawing 4.8 amps on 60 bulbs. I also have been told each pair of lamps in series wil reduce the amps required by half, so theoretically that would bring it down to 2.5 amps assuming each is pair wired in parallel. Is this correct.

 

Now reverting back to the idea of using a 1.5 amp controller on all 60 lamps to bring the brightness down to a dim prototypical glow may not be advisable on a 16v AC 3 amp transformer. Plus it may not resolve the proble of tripping out with overload.

 

So I'm still confused what to do as I am reluctant to purchase multiple transformers when there may be a way of doing it with one transformer.

[Miss Prism]

Ken - are the bulbs in the '3-bulbs per lamp' units internally wired in parallel or series?

 

Do you have a meter?

[jazz]

Ken - are the bulbs in the '3-bulbs per lamp' units internally wired in parallel or series?

 

Do you have a meter?

 

Hi. Don't know to the first, no to the second.  The lamps were purchased assemble, on two wires protude from the base. Ken

[Madcaravanner]

Gray, I still unclear on the amps issue. I have been told I will be drawing 4.8 amps on 60 bulbs. I also have been told each pair of lamps in series wil reduce the amps required by half, so theoretically that would bring it down to 2.5 amps assuming each is pair wired in parallel. Is this correct.

 

Now reverting back to the idea of using a 1.5 amp controller on all 60 lamps to bring the brightness down to a dim prototypical glow may not be advisable on a 16v AC 3 amp transformer. Plus it may not resolve the proble of tripping out with overload.

 

So I'm still confused what to do as I am reluctant to purchase multiple transformers when there may be a way of doing it with one transformer.

 

Ah I am using old Printer power supplies as I acquired a number of printers which although the power supplies worked the printers did not so I do not have to worry about overload as I have separate supplies for each corner of the layout

it is 20 foot long by 12 foot wide so it is simpler to separate everything makes the wiring looms a little simpler

[jazz]

Hey up Gray, that takes me back about 40 years when I used the motors out of old police and work vehicle roof mounted dome flashing lights. These were great on my early scratch built 0 gauge models. Very powerful they were too, coupled the CCW gears.

[APOLLO]

I wire up all mine in parallel, feed is a cheapie ex train set Bachmann controller. 12V DC 1.5 amp. 20 odd bulbs. I just turn it on and adjust the voltage to the required brightness level, turn it down before you turn it off, bulbs should last for-ever (not change any in last 10 years). No switches needed.

 

Brit15

[jazz]

Hi Brit. I cannot understand what is wrong here. I have 21 bulbs wired in parallel running on a H & M 1 amp power controller as a test. I set the lights at a fairly dim brightnes and the  H & M cutout trips after 5 minutes. So next is to find time to rewir into series and see how that performes I guess.

[HLT 0109]

Ken.

 

I have used these bulbs extensively and confirm that 60 will draw about 4.8 amps.  Aurora do a range of 12v transformers but they all require a minimum load which is greater on the larger capacity units.  A couple of months ago on RMWeb there was an exchange on this topic and someone found a transformer that would run from one to about 200 (I think) such bulbs but I have been unable to find the thread.  I recall that the cost was about £24.  I will have a more thorough search and post again if I find it.  I have about 160 bulbs on my layout and run them through two separate circuits/transformers in order that I can operate just a few lights at a time if I require.  I also have a standard dimmer between the houehold supply and the transformers.  One of the smaller Aurora units is rated to run from 20 to 60 bulbs but there is a margin at both ends.

 

I do not think wiring the bulbs in series will reduce the current drawn; they will share the voltage but I think the current draw will remain the same.

 

Harold.

 

Edited to add link to supplier of transforners

http://www.tlc-direct.co.uk/Main_Index/Transformer_Index/Lighting_Transformers/index.html

[raymw]

All filament lamps have a non-linear resistance - they have a lower resistance when cold. (that's why they generally 'blow' when you turn on the power). Usually, connecting them in series reduces the light output more than you might expect. (This effect is/was used in some controllers - the series bulb glows when the controller op is shorted, but in normal use the current through the lamp does not give much voltage drop).

 

You can do some sums  V=I*R and W =V*I (for dc, where V=Volts, I= Current in Amps, R = resistance in ohms, W= power in Watts. For resistances in series, total resistance = R1+R2 +R3 + etc. For resistances in parallel total resistance = (R1*R2*R3)/(R1+R2+R3) . It would pay you to get a cheap(or expensive) digital multimeter - one costing about a fiver will be quite adequate for model railway voltages.

 

To get the same illumination, it will require the same power - it makes no difference if the lamps are wired in series or parallel. Of course, series will need more volts, and parallel more amps

 

Best Wishes,

 

Ray

[jazz]

Thanks very much, Harold and Ray. Very informative.

 

Harold, I've looked the the Aurora links and would appreciate some advice which model is suitable and any extra items I would need to power 60 t0 70 bulbs, I will be splitting some of the lights via on/off switches.

 

Regards Ken

[Madcaravanner]

Hi Brit. I cannot understand what is wrong here. I have 21 bulbs wired in parallel running on a H & M 1 amp power controller as a test. I set the lights at a fairly dim brightnes and the  H & M cutout trips after 5 minutes. So next is to find time to rewir into series and see how that performes I guess.

 

I have a one amp controller for one of my track circuits and after a while it overheats and cuts out  when I can afford it it getting relegated to a smaller track circuit could be a fault on th controller if you have one try a 1.5 amp or bigger controller 

[HLT 0109]

Hi Ken.

 

On the basis that each grain of wheat bulb draws 80milliamps, each bulb uses 0.95watts on a 12 volt system, so 70 bulbs would draw a total of 66.5watts.  This exceeds the stated capacity of the Aurora 20-60w but, in my experience it would cope. If, however, you want to be sure not to trip the thermal cutout, you would need to go for the next larger unit - the 35-105w.  That would give capacity for additional lights should you decide to expand the layout but it has a stated minimum load of 35 watts which is about 37 bulbs.  I have one of these running about 80 bulbs and it does work with fewer than 37 switched on but it needs probably about 20.  I bought mine from Power discount and I see they still have them at £5.72 plus postage (which I think was about £4).  I gave you a link to TLC website that has a "Premium Electronic Lighting Transformer 0w - 70w" for £7.99 + VAT and postage; that is what I think I would choose in your circumstances - the product code is LT YT70.

 

The reason I say it is possible to exceed the stated capacity of a transformer is that I hadn't understood how much power these small bulbs consume and I was happily increasing the number of bulbs connected to my original transformer that is rated for up to 60w.  All was well when I reached 120 bubs but then I added another 40.  Whilst I had them all lit and was taking photographs, they all went out after about 20 minutes so i switched them off and tried them again after about an hour.  They all worked but I decided to buy an additional transformer and to split the circuit into two - that was when i found that one of my terminal blocks (rated for 3amps) had melted; after all, 160 bulbs drawing 80 milliamps each draw a total of 12.8 amps, So, there is a safety margin but don't overdo it.

 

I hope this helps.

 

Harold.

[jazz]

Harold. Thank you so much for your excellent reply and help. 

 

I will go for the LT Y70. Should I expand beyond the current 60 bulbs, I will simply purchase a second unit.

 

I would never have believed such small bulbs can cause so many problems.  (All my previous latouts have only have the odd building lit. Naturally I had no problems using a 1 amp controller to power them up).

 

Thanks again, Ken

[jazz]

The Transformer & dimmer arrived today. I have 50 bulbs installed (Just the buildings and yard lamps to install now).   All works a treat and thanks to Harold for his recommendation.

 

 

[HLT 0109]

Well done Ken - glad it all worked out well.

 

Harold.

[peter jf]

Hi Ken,

Very interesting discussion between you and Harold.

Seems you have solved a problem I am grappling with.

I understand the use of a LTYT70 and how to wire it in parallel to bulbs.

But I an intrigued about your reference to a dimmer in post #19.

I assume it is to vary the light intensity of the bulbs.

I would be very grateful if you let me know what dimmer you bought and how it was wired into circuit.

Also do you have resisters wired in series with each bulb and if so what value.

Thanks in anticipation.

Peter

[jazz]

Peter, I have just sent you a PM. Ken

[Stringfingerling]

Dropping no more than 9V or 10V across each bulb is likely to provide a more realistic illumination level, as well as greatly increasing the bulbs' lives.

This sounds like a very good idea - but is it possible to give any kind of forecast of a reasonable life expectation?; I'm trying to incorporate lighting in my station building in a way which allows for bulbs to be changed, but even so, it's not going to be easy or quick to get at them.  I'm wondering whether I should change plan and go for some LED's but I would prefer to use GOW's because of the more attractive colour of the light produced.

[brigo]

This sounds like a very good idea - but is it possible to give any kind of forecast of a reasonable life expectation?; I'm trying to incorporate lighting in my station building in a way which allows for bulbs to be changed, but even so, it's not going to be easy or quick to get at them.  I'm wondering whether I should change plan and go for some LED's but I would prefer to use GOW's because of the more attractive colour of the light produced.

 

LEDs are better for long life and the colour can be altered by shrouding them with translucent material such as the orange film of a Jaffa Cake wrapper. Tamiya also make "Clear" orange and red acrylic paint and some craft shops sell translucent paint for colouring glass.

 

Brian