April project questions and comments here please.

A Railway Modeller without a Multimeter quest:quest:

Yes, in series for some , in fact 2 in series instead of parallel could reduce total current by 75%

for example: assume volts = 12 & lamp resistance =24 ohms means each lamp requires 1/2 Amp - two in parrallel = 1 Amp  but in series 12 volts with 48 ohms = 1/4Amp but the brightness is reduced

so if you had before 8 lights in parallel = 4 amps but put those 8 lamps into 4 groups of 2 = 1 amp so the power souce is not overloaded.

Hi Rick, I have done a bit of research. Have found the lamps you are using, but cannot find any power consumption info on them. However 12V grain of wheat bulbs in the Squires catalogue are rated at 65mA, and I have also just tested a Hornby colour light signal and that also draws 65mA for each bulb when attached to the Hornby controller fixed output (R965). I have a few of these controllers which I have taken apart to use on my grandsons layout(s).

They are protected by a thermal cutout on the input side. The standard Hornby transformer which provides the input (C912) is rated at 13VA, which means that it will deliver no more than 1 Amp at full load.

I have just tested the trip current on the controller and it seems to go at about 350mA - seems low to me, but may explain why the controllers trip out if a loco on the grandson's layout stalls due to valvegear locking up !!!

Anyway, back to the calculations. If your lamps are taking 65mA each, and the controller trips at 350mA, then you should be able to have 5 lamps connected in parallel, but no more. How many do you have? By the way, the lamps will get warm. 65mA at 12V is just over three quarters of a watt. If you try to hold a half watt resistor running at full rating, you will find that you have to let go eventually.

A Railway Modeller without a Multimeter

I dare say I'm not the only one  I do have a basic current flow device (of the "glowing screwdriver" type) which is handy to prove shorts and current deficiencies but does not indicate actual current passing beyond the inexact science which is the relative brightness of the element.

In response to both the above posts I now have some rewiring to try over the next few days with thanks for explanations about as simple as electrickery can be.

Each platform has 8 lamps from memory (and I'm not off outside at midnight to check!) so if they were wired in parallel in groups of four would I then be able to connect those groups in series or will that still trip the supply?  If I need to have four separate supplies (one for each group) I might need to look at alternatives as there are four street lights (of another brand) yet to be wired in as well.

[user=316]Gwiwer[/user] wrote:

Each platform has 8 lamps from memory (and I'm not off outside at midnight to check!) so if they were wired in parallel in groups of four would I then be able to connect those groups in series or will that still trip the supply? If I need to have four separate supplies (one for each group) I might need to look at alternatives as there are four street lights (of another brand) yet to be wired in as well.

Your suggested parallel/series/parallel grouping should cut the current drawn but to what level we cannot be sure. Sol's calculations are okay except that the resistance of lamp is not very constant and often varies according to its brightness and that is further complicated by the power supply you are using which is NOT true DC but just a "chopped up" AC supply.

Have a look at my latest recommendation in the main thread. There are a number of those switched mode supplies available, many cheaper than the one I suggested if you are not trying to power as many as 100 lamps. Taking 8 plus 4 and then doubling to allow for possible future expansion, you might look for a 2Amp supply - such as one of these:-

http://www.rapidonline.com/sku/Electrical-Power/Power-Supplies/Desktop-PSUs/12W-25W-DC-Miniature-desktop-switch-mode-PSU/71064/85-2944

an old computer power pack converted will supply all the power needed,can be got cheap from most repair shops,
then follow Daves hoe to on here (87101 ) im the index too.
lol::cool:

then follow Daves hoe

Are you sure, Owen??? :shock::thud