Graham Farish DC Controller - Too Many Volts?

dannyboy · July 22, 2018, 01:19:42 AM

For testing engines, I have my test track using a GF/Bachmann DC controller, (the grey squarish one), which is relatively new. I was testing a new Dapol Class 56 yesterday and it was running very slowly. With the control knob approximately half way, it was moving but not as I expected. I cleaned out a lot of grease from the gears and things improved slightly. When I turned the knob to increase power, the engine slowed and stuttered. Out of interest, I put the test meter on the output and when the knob was in the halfway position, the controller was pushing out about 12 volts. If I turned the knob fully clockwise, the volts went just over 20! I take it that this is not normal.

. I then used a spare Kato controller and - yes - you guessed it, the engine ran beautifully. Incidentally, the maximum output from the Kato controller was about 15 volts. Any one got any thoughts and/or suggestions please? (Apart from sticking to Kato equipment - but I am biased

).

NinOz · July 22, 2018, 04:17:36 AM

Check voltage with a load on it. Say a loco on the track and check the volts.

dannyboy · July 22, 2018, 04:21:15 AM

Will try and remember to do that when I get up this afternoon - I am at work now.

NinOz · July 22, 2018, 04:29:56 AM

Just checked mine (also use it to test and run locos in).
Input is 12V DC regulated, output max is 11.7V unloaded. The controller is marked as 16V DC input.
Yes, yours doesn't sound normal. Wouldn't risk a loco to it.
What is the input source you are using? 16V AC perhaps or unregulated?

dannyboy · July 22, 2018, 04:47:45 AM

Well, I could say that is a very interesting question..................all I know is that I put the plug in the 240v mains socket, connect the power pack wires to the track and turn it on. I will have to have a look and see what it says on the label.

Paul-H · July 22, 2018, 08:40:21 AM

I have one of the old Graham Farish controllers (The square black one) I use for DC testing mains input and unloaded output is about 19 volts, never use it past halfway which meters at 12 volts. Not tested it under load but would suspect the output to drop quite a bit with a load on it. Most simple power supplies give quite a high output but drop under load to something closer to their rating. More advanced regulated controllers should go better.

Paul

Newportnobby · July 22, 2018, 09:48:24 AM

I used the Farish controller from the Master Cutler train set pack to conduct my experiments on Kato #4 points so tested over 100 items of motive power with no issues. Apart from having no accessory ports I think they are not bad controllers.

mr bachmann · July 22, 2018, 10:42:07 AM

I note no mention of the wall wart out put - test with the meter it could be faulty .

Bealman · July 22, 2018, 10:50:04 AM

Very good point!

ntpntpntp · July 22, 2018, 10:57:57 AM

Quote from: mr bachmann on July 22, 2018, 10:42:07 AM
I note no mention of the wall wart out put - test with the meter it could be faulty .

First thing I'd check to be honest. I know some Bachmann units are known for being rather high output voltage for N gauge but it is down to the input source.

Bob Tidbury · July 22, 2018, 11:55:27 AM

I use one of the very old black Farish power box with a boost button on which is good for testing locos if they are a bit sticky you just push the red button and get a pulse at full power .
I got it for a tenner when GRAHAM FARISH were selling up ,I wish I had bought more and used them on my layout they are very good I've never measured the voltage but I've used it on my test track for years and never had any problems
I really like it ,if I remember it was made by A G M or something similar.
Bob Tidbury

Yet_Another · July 22, 2018, 02:12:51 PM

I asked a similar question, some time ago:

http://www.ngaugeforum.co.uk/SMFN/index.php?topic=27425.msg299008#msg299008

And there's a link in there to a further thread started by Zogbert.

dannyboy · July 22, 2018, 07:58:06 PM

Many thanks for the replies and suggestions and to @Yet_Another for the link.

I did a bit of testing this afternoon and the plug in transformer is shown as 'Output = 16v'. When testing with the meter, it is putting out 18.9v. At the track, with no load and the control dial at just about the halfway mark, the power pack is putting out 12v, when the control dial is at maximum, it is putting out 23.2v. With a 12v motor taken from my electric bits box connected to the track, the halfway voltage drops from 12v to 9.75v. At maximum, it drops from 23.2v to 20.2v. Having read the thread referred to by Yet_Another, those figures do not seem to be too far from what others were finding. It just seems odd that what is, in effect, a 12v power supply, can push out over 20 volts.

cutting42 · July 23, 2018, 12:53:33 PM

These are not precision electrical devices. They are mass produced an the hundreds of thousands if not millions to a price so the tolerances on the components will be pretty wide to allow for a low failure rate.

In addition, they are designed to deliver the target voltage at the max current which you are probably nowhere close to with one small motor running also with no load. For example the current limit on these type of PSU's could be 1 amp and a free running motor will take 50 mA at a guess. You need a proper load to test correctly such as a big wire wound resistor or a motor under load (like a long train) with an ammeter to measure the load then then you can check the voltage.

mr bachmann · July 23, 2018, 08:20:14 PM

the similar controller supplied to the US market has a uncontrolled power output for points / signals etc. Could the innards have been fitted to a UK controller ?