Marshall III controller bulb

[Free_at_last]

I was recently given this controller but it is missing its overload(?) bulb, any idea what size/rating it would have been?

[Ironduke]

Can you see the socket?

[Free_at_last]

Can you see the socket?

Yes, it looks torch bulb size, M.E.S.
Someone suggested a car bulb, 12v 21w but the largest I have seen in M.E.S. is 5watt.

[Ironduke]

But is it an overload lamp or a simple power indicator?

[luckymucklebackit]

I used to have one of these many years ago and I am sure this is the overload indicator.

Jim

[Ironduke]

I don't see how such a small bulb could be the actual overload protection device such as you would use a car light bulb for. I wonder if it's just an indicator? Sorry, I've Googled and even Binged the crap out of this and I can't find any info other than old ebay-like pictures.

[Free_at_last]

After finding a torch bulb of unknown value I tried the controller and noticed the light was flickering when running an old Triang Hornby Jinty that hasn't been run for years, and was spluttering along as it was in need of a good service. I spent a bit of time cleaning up the Jinty and it ran a lot better, I also noticed the bulb only lit when the loco was on the track and went from dim to bright with slow and fast. Then I noticed the light had stopped working, I caused a short on the track to test the light but nothing happened, so I took it out and found it had blown. The controller still worked without the bulb. So I'm non the wiser of its purpose.

[Flashbang]

Hi

From what you're saying, it reads as though the lamp illuminates upon a short circuit or overload. Its most likely connected across the overload trip or via the trip making contact to it when the trip is open from the main output due to an overload/short. Usually the overload trip is a thermal bi-metal strip in these old controllers.

I would try and locate a 12volt 2.2watt MES (E10) lamp and test with that in place. Maplin sell singles https://www.maplin.co.uk/p/12v-22w-roun ... -e10-wl81c

[RAF96]

Using a multimeter can you read a voltage from the centre contact to outer threaded bit:
a) as an ever present or selected voltage
and/or
b) only in overload conditions - e.g. stall a hungry motor at max chat.

[Free_at_last]

Using a multimeter can you read a voltage from the centre contact to outer threaded bit:
a) as an ever present or selected voltage
and/or
b) only in overload conditions - e.g. stall a hungry motor at max chat.

Ok, just been out for a bulb, could only get 12v 1.2w.
Before installing I checked for voltage at the bulb holder, no voltage at all with no loco on the track. With a loco on running on the track the voltage varied with the controller but I forgot to take note or compare with track voltage.
Loco still runs with no bulb.
With bulb installed there is a no light with full volts with no loco on the track, with old Jinty there is slight to mild glow from the bulb whilst running and a bigger glow when stalled.
Full brightness with a short on the track. Did not apply short long enough to see whether the unit tripped, I'll try that next time I'm in the shed.

[Bufferstop]

If the loco runs with no bulb it's only a trip indicator, 1.2Watt may be OK, if it appears to glow too much when the loco is running or the loco seems to lack power try to get the next bulb up, probably around 2.3watt.

[RAF96]

Quote from the free downlod book on the MERG web site. This is from page 85. There is an associated picture showing the bulb in series with the controller and track but I cant get it to load here.

Car bulb
Perhaps one of the oldest, and most controversial, protection methods is the use of a 12V 25W car tail light bulb.
A car bulb is wired in series with the supply to a track section and provides almost no resistance when unlit. The locos run happily with their full voltage. When a short occurs, the current increases rapidly, causing the bulb to light. A lit bulb has a much greater resistance than when unlit. This increased resistance then limits the amount of current flowing in the circuit, This increase occurs very rapidly, around 4mS. When the short is removed, the bulb cools down and its resistance lowers again.
Car bulbs are cheap and you may like the idea of an immediate visual indication when a short occurs.
However, it is important to remember that they are not cutouts, only current limiters. If a short occurs the current round the wire and the track is limited to a maximum of 2A, which still has potential for causing overheating damage.
If using car bulbs, choose their position carefully, as they are very hot when lit.


Rob

[Bufferstop]

My first thought was that it was the current limiting arrangement, but on re-reading the fact that the train ran with the bulb removed shows that it's a trip indicator. In normal running, it will be in parallel with the winding on the cut out, both being in series with the motor. If the bulb wattage is too great it will delay the point at which the trip operates. It won't hurt to try it out with a 1.2 or 2.2 watt as suggested by flashbang. I don't know how high wattage 12volt MES bulbs go, as it's functioning as an indicator I can't see a higher wattage being useful.

[Flashbang]

Hi
All the talk of 12v 21watt lamps and current limiters is confusing the matter I feel.
The simple fact is the lamp in the controller illuminates when an over load or short circuit occurs warning the user of a fault.
A 12v 2.2 watt MES E10 lamp is all that is needed, similar to that which I linked to in my previous post.

[Ironduke]

I suspect Pete was hoping someone who already owned one might take the bulb out, inspect it, and reply.
Sorry, Pete.