Limiting maximum voltage to motor - which CV?

[Ruston]

I am currently building a working colliery screens building that will load coal into wagons. It uses a 3-volt motors.

 

As I am gradually converting my loco fleet from plain DCC to DCC sound I want to make use of the redundant decoders to operate the motors in the building.

 

I need to know which CV to adjust in order to set the maximum voltage to the motor (3v max.). I have been looking online at instructions for the Gaugemaster DCC25 and 26 decoders but I can't seem to find it...

 

Also, is there are particular value to apply to the CV that will give me a maximum of 3v, or is it a matter of trial and error?

 

Thanks.

[Adrian Wintle]

You probably want CV5 (VHigh - max speed) and it will be trial and error as the actual implementation of it will be dependent on the manufacturer.

 

Adrian

[jamesg]

It might be worth mentioning that most Hornby decoders don't support the Vstart/Vmid/Vhigh CVs.  From page 9 of the Gaugemaster OPTI 25/26 manual (http://www.gaugemaster.com/instructions/DCC25-26%20Instructions.pdf), these decoders use the linear range 1-255 as a value for CV 5.  There are a few 'peculiar' implementations of CV 5; the Bachmann decoders have a range of 0-63, for example.

[dasatcopthorne]

It might be worth mentioning that most Hornby decoders don't support the Vstart/Vmid/Vhigh CVs.  From page 9 of the Gaugemaster OPTI 25/26 manual (http://www.gaugemaster.com/instructions/DCC25-26%20Instructions.pdf), these decoders use the linear range 1-255 as a value for CV 5.  There are a few 'peculiar' implementations of CV 5; the Bachmann decoders have a range of 0-63, for example.

 

With ESU Lok ..... the range depends in whether it's a V3.5 or V4 (1-255)

 

If you do manage to set CV5, don't forget CV6 is a 'middle' setting. ie the voltage at half throttle in relation to full throttle (CV5) Same range values. Most people have CV6 at half of CV5 but that's up to you to suit it to you layout.

 

Dave

[Phil S]

Phil: You may also want to look at the dedicated Busch Decoder they sell for their H0f Mine / Field railways - DCC Control off a standard loco number (I use 9998 and 9999)  and then there are 5 output pairs which vary witht he loco spped control between 0 and +/-3V  - 1 on permanently, and 4 selected ('as per analogue sections') with function keys 1-4.

 

CV5 on a standard decoder simply limits the maximum pulse-width ratio, thus limiting the averaged voltage and therefore maximum  speed - smoothed by capacitance and inductance

 

Look at www.hobb-e-mail (Faversham Hobby Shop) and search on Busch..

 

 

The alternative strategy is to use a standard decoder and drop the output voltage across either a stack of diodes or a resistor of higher rating than the 3V motor ... but dropping upto 9V (3:1 voltage or current,  9:1 power) .... I would opt for the fixed drop of diodes for half the drop, and thn perhaps a resistor matching the motor.  

[Nigelcliffe]

Motors not operated near their limit of load don't usually die from over-voltage. What kills them is high loads and over-current.  So, if the mechanism doesn't have a lot of drag, won't jam, then volts are not likely to kill things.    There is a lot of experience of running 3v, 4.5v and 6v motors in 2mm Finescale on control systems which deliver 12v or more.

 

With DCC chips, what may be an issue is the ability of some decoders to deliver control at/near start, particularly when using low voltage motors.   If the mechanisms need smooth starting from zero, or very good low speed control, then decoders which can do this well may be needed, or means to drop voltages.    

 

Diode dropping strings may be useful - these can be used either before the decoder(s) or afterwards.   Before the decoder they could drop the DCC signal from around 14v to somewhere near 8-9v (need to experiment to find when the chosen decoders cease to work reliably, the theoretical level is around 7v).   Dropping the DCC voltage before the decoder means one set of drops for multiple decoders, and would see a maximum output of the decoder of around 7.5v .    That should be fine for motor control with just CV adjustment.

 

 

-  Nigel
 

[34theletterbetweenB&D]

I am currently building a working colliery screens building that will load coal into wagons. It uses a 3-volt motors...

 An option not mentioned so far; if there are to be motors, then consider wiring them in series.

[Ruston]

 An option not mentioned so far; if there are to be motors, then consider wiring them in series.

Would that not mean that they are all running at the same time? I only want to operate one at a time.

 

Anyway, it doesn't matter as I have decided not to go down the road of using a decoder. The main reason being that the first decoder that I was going to use doesn't want to play. I put the loco (that the decoder is still fitted in) on the main track and went through the procedure to set CV5 but no matter how low or high I set it it made no visible difference to the loco's top speed. So I tried it on the program track and still no difference. When I make the change on the handset it shows "send" and the loco also drives as it should and the decoder address can be changed so if CV5 is actually being changed at the decoder end it's making no difference to the loco's performance.

 

I think I'll just use DC and a speed controller for the motors.