Problem with new old stock AC converter

[OBBherr]

I just received a bargain basement LGB 51098 AC converter (EUR10 from Modellbahnshop Lippe), which I planned to use with a 51092 power supply to replace a 50110. Object is to power a pair of 51750 switch boxes on my outside layout.

Problem is as follows. When connected to switch box 1:

Point number 1: Works fine in both directions
Point number 2: Works fine in one direction but won't switch back, just buzzes
Point number 3: Initially no movement either way, just a buzz. After being moved across manually, now works fine in both directions as point 1
Point number 4: As point 2

Just to be clear I was using the AC outputs!

On reverting to 50110 straight into switch box, everything works.

My first thought was that there wasn't enough power from the 2 amp transformer but it is specced for the Marklin 2 amp (36W at 18V) version. Unhelpfully, the LGB catalogue persists in using the Marklin part numbers rather than LGB equivalents but I traced it through to the Marklin equivalent of the 51092.

If any of you electrical wizards out there have any insights on why some points work perfectly and others not, I would be very grateful to hear them.

 

[PhilP]

If you are getting a 'buzz' from the point motors, then I would say you have missing (or short-circuited) diodes?

It could just be your point motors are a little sticky, and need servicing?

Clean and (lightly) lubricate the points and motors, and see if that improves things.

PhilP.

 

[OBBherr]

Good idea anyway and will give them a scrub up. Not done this before - what lubricant do you use?

But its not clear to me why the same points with the same switches work fine on direct AC feed from 50110, but not on the rectified feed from the 50198.

I might try a direct feed from a 2 amp LGB transformer I have in stock somewhere. If the issue is, as you suggest, sticky points, they can pull more power from the 50110 so that might unstick them.

 

[PhilP]

If your points / motors are full of dirt and sticking, then you run the risk of burning them out..

Pumping more current into them is masking the problem, not curing it.

PhilP.

 

[OBBherr]

Agreed. So I should be using the 2A version anyway.

 

[OBBherr]

In order to avoid doing so.

 

[dutchelm]

I would suggest you use powdered graphite rather than oil for lubrication. Oil just attracts dirt.

 

[Gizzy]

Although your supply is AC, point motors are DC devices. Diodes are used to half wave rectify the AC to a pulsed DC rather than a smooth constant DC voltage.

So is the voltage the same? A diode needs 0.6 volts to work....

 

[OBBherr]

Will check

 

[Software Tools]

 

[dunnyrail]

Good idea anyway and will give them a scrub up. Not done this before - what lubricant do you use?

But its not clear to me why the same points with the same switches work fine on direct AC feed from 50110, but not on the rectified feed from the 50198.

I might try a direct feed from a 2 amp LGB transformer I have in stock somewhere. If the issue is, as you suggest, sticky points, they can pull more power from the 50110 so that might unstick them.

Make well sure you understand how they look inside before pulling apart. Take lid off and take a close up picture if you have a digi ability. Also remember the turny bit with gear at the end has a small tab that defines the maximum right and left turn. Plus when you put it back together ensure the rack is at one extreme or the other with the tab matching.

 

[OBBherr]

Noted thank you

 

[OBBherr]

An update after further testing.

Hypothesis 1: dirty sticky points masked by used of 5A power supply. Test: replace DC+converter with LGB 5006 with AC output 1.7A. Result: all points work perfectly.
Hypothesis 2: something odd with the AC converter. Test: try out on indoor layout, practically new points and motors: Result. some points work perfectly (2 out of 4) others don't, giving the dreaded buzz. Same result as outside layout.

So as it stands at present there's something about the AC converter approach that is causing the problem. Next step to measure the actual output current and power but no time to do that before holiday.

Thanks to all for the input. Will update when something new occurs.

 

[PhilP]

If you are using AC:

You will need to convert to DC, then DPDT switches.
OR
You can use AC and does on the feed or switches.

Do you have some switches without diodes fitted?

PhilP.

 

[OBBherr]

I’m using LGB 51750 as above.