Gaugemaster GM500D Relays not Designed to Work with CDUs

[rjpwilliams]

I recently bought some of these relays and was surprised that the instruction sheet warns "never connect high pulse items such as CDU's".  My locomotives run on DCC but I have decided not to turn the point switching to DCC yet - apart from the expense, I like the physical feel of running a pointer along a set of studs setting the route and watching the leds light up.  The points are switched from a standard Guagemaster CDU and presumably it is just a matter of limiting the amps going into the relay but there are no clues about what strength of resistor is required.  Any ideas?

[RFS]

Isn't the GM500d designed specifically for connection to a DCC accessory decoder, whereas the GM500 is for analogue/CDU connection? But there again, some accessory decoders have CDUs built-on so I don't see how you can follow Gaugemaster's advice in that situation.

 

Perhaps worth giving Gaugemaster a call. 

[eastglosmog]

Beware that the GM500 is wired up with reverse polarity to the GM500D as I found to my cost some years ago.

[kevinlms]

23 hours ago, rjpwilliams said:

I recently bought some of these relays and was surprised that the instruction sheet warns "never connect high pulse items such as CDU's".  My locomotives run on DCC but I have decided not to turn the point switching to DCC yet - apart from the expense, I like the physical feel of running a pointer along a set of studs setting the route and watching the leds light up.  The points are switched from a standard Guagemaster CDU and presumably it is just a matter of limiting the amps going into the relay but there are no clues about what strength of resistor is required.  Any ideas?

The GM500D is specifically a low current device for DCC operation of points, so it makes sense to not allow a CDU anywhere near it.

 

Perhaps your supplier will swap it for a GM500 version?

[meil]

On 24/07/2019 at 19:18, eastglosmog said:

Beware that the GM500 is wired up with reverse polarity to the GM500D as I found to my cost some years ago.

That's because Accessory Decoders use a +ve common and CDUs use a -ve common. Although there is no reason why you could not adopt a +ve common with a CDU.

[Dublo Jim]

I think the warning about not connecting high pulse output devices only applies to the relay switching circuit, contacts labeled 1-6. The controlling input/output, labeled A B and C, are fine to be powered by a CDU......at least, that’s my interpretation of the instructions. I’ve had no problems using a CDU to power both a GM 500 and PM1 point motor in tandem, apart from having to bypass the input current limiting resistors on the 500. If you don’t bypass these, the PM1 takes the ‘lion’s share’ of the CDU output and there’s not enough current to switch the relay. Gaugemaster have told me that the 500D doesn’t have these resistors so it shouldn’t be an issue. Certainly, the 500 and 500 D use exactly the same subminiature DPDT relay. As far as I can see, the limitation only applies to the switch within the relay, which is rated at 2 amps/30 volts.

Edited April 1, 2020 by Dublo Jim
Grammar