Question about contolling polarity

Madman

Madman

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OK, I have a Mr Railway sound unit that I have installed in one of my Davenports. It runs on the 12 volt Li-on battery that powers the loco. Since these sound units are polarity sensitive, I have a diode wired into the circuit. The only problem is that I can only get sound when the loco runs forward. That's OK for continuous running. But if I want to do some shunting with this loco, I have no sound in reverse, which I knew when doing the hook-up.

Isn't there some type of electronic piece that keeps the polarity the same to a device hooked up to it ? I know that sounds overly simplified, but my brain is overly simplified when electronics are involved. :confused:
 
Yep!! It is called a bridge rectifier.
Made up of four individual diodes or can be obtained as a single four legged device.
A one amp one should be readily available from most electronic parts stores for just a few cents.
 
OK, I just Googled a Bridge Rectifier. All of the images and descriptions indicate that AC power is the input. I have DC power. So what gives?
 
Madman said:
OK, I just Googled a Bridge Rectifier. All of the images and descriptions indicate that AC power is the input. I have DC power. So what gives?
Click to expand...
DC the way round you want it :) less a small voltage drop.
 
Madman said:
OK, I just Googled a Bridge Rectifier. All of the images and descriptions indicate that AC power is the input. I have DC power. So what gives?
Click to expand...
If you feed DC into the AC input, it will still give you DC out....
 
Dan
All above are correct..
Feed the DC into the two connections marked with the AC 'squigles' (does not matter which way round).. You will get positive out from the terminal marked + and negative from the terminal marked -.
There will be a small voltage drop compared to that going in, but nothing to worry about.
As Tony says, a one amp device should be more than adequate.
PhilP.
 
..........if in fact a Bridge rectifier is really needed.
Depends on how the unit is meant to be wired up.
A link to the instructions would be helpful.
 
Tony,
Need OP to come back to us, but it might well be a unit from mrrails.com ??
Nearest thing to Mr Railway I have been able to find..
PhilP.
 
I've got an MRRails sound card in one of my diesels. Bought a few years ago (2007?), it's an adsmk1 and was sold as a complete dcc compatible unit with a separate rectifier and voltage regulator board, speaker and on-off switch. It has inputs connected across the motor to sense the speed.

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It's a very basic sound, I prefer the MyLocoSound card. MR-Rails now sells the adsmk2 - it looks totally different. No idea how the sound compares.

The one posted in Dan's link above is the manual stationary (under baseboard) version - it doesn't have the speed sense input? If it's being powered from the same reversible DC source as the loco motor then it just needs a bridge rectifier as has been said.
 
Maybe I've not understood the problem, but it seems to me that if the sound unit was wired up directly to the battery, rather than after the reversing switch or ESC, wouldn't that solve the problem?

Rik
 
ge_rik said:
Maybe I've not understood the problem, but it seems to me that if the sound unit was wired up directly to the battery, rather than after the reversing switch or ESC, wouldn't that solve the problem?

Rik
Click to expand...

Wouldn't it then simply assume the loco is at full speed all the time (i.e. 12 volts continuous) and make an unchanging noise?
 
Depends.
Original post infers it follows polarity/motor voltage. - Hence diode to prevent reverse polarity to sound unit..
In a later post, it is suggested it is an 'under-board' unit which may not change noise depending on speed.

If the former, the a bridge rectifier will allow the motor polarity to change, but maintain polarity to the sound unit. With a variable supply to the sound unit to change the 'engine noise.
If it is an under-board unit with no variable sound, then yes it could be wired directly to battery, but sound will be constantly 'on' whilst the power is on.. Not dependent on whether the loco is moving.

At least that is how I read it.
 
Tony Walsham said:
I am still waiting for a link to the instructions for this unit. Nothing showing as available at the Mr Rails website.
Click to expand...

Don't hold your breath Tony! I've looked through mrrails.com and the old site mrrails.co.uk, no sign of any links to product manuals.

When I bought my sound card it came with a few pages of printed instructions.

If Dan's card really is the stationary under-board version (that's the model he linked to) then it doesn't look like there's any sort of speed sensing input, just volume and speed knobs.
 
Madman said:
And here is the link to the product in question http://www.mrrails.com/html/mdsmk1.html
Nothing too high tech, but for the money they are not bad.
Click to expand...
ntpntpntp said:
If Dan's card really is the stationary under-board version (that's the model he linked to) then it doesn't look like there's any sort of speed sensing input, just volume and speed knobs.
Click to expand...
According to Dan's link to the product (see above) it's a basic board without motor speed sensing with, as Nick suggests, just a volume pot and a speed pot. As I see it, all it needs is power from a battery (maybe via a switch if the volume knob doesn't include one)

Rik
 
ge_rik said:
Madman said:
And here is the link to the product in question http://www.mrrails.com/html/mdsmk1.html
Nothing too high tech, but for the money they are not bad.
Click to expand...
ntpntpntp said:
If Dan's card really is the stationary under-board version (that's the model he linked to) then it doesn't look like there's any sort of speed sensing input, just volume and speed knobs.
Click to expand...
According to Dan's link to the product (see above) it's a basic board without motor speed sensing with, as Nick suggests, just a volume pot and a speed pot. As I see it, all it needs is power from a battery (maybe via a switch if the volume knob doesn't include one)

Rik
Click to expand...


It is the basic board, meant for mounting under the baseboard or layout table. It is supposed to run on 8 AA batteries. I checked with the manufacturer before installing it in the loco to be sure I could use a 12 volt Li-on battery as power. The same battery powers the loco. The manufacturer did tell me to be sure that the polarity on the input stays the same. So I wired in a diode which works. My question was how to keep the polarity to the sound board constant when the loco reverses. Simply put, when I power up the loco, power also goes to the sound board. When the loco stops, the sound stops.
 
Dan we know what the question is, but, given your stated lack of understanding of things electrical, having a wiring diagram to which we could refer would be of great value in our helping you.
With no diagram, we would just be guessing.
 
Tony, there really is no wiring diagram. The link I have supplied shows a photo of the board and some instructions. The only way I can give you a wiring diagram of my work is to say the power that supplies current to the motor also supplies current to the sound module. The same two wires that run to the motor are spliced into and these extra two wires* run to this sound board.
Someone mentioned that the Bridge Rectifier can be fed with DC current. If that's the case, then maybe it's that simple. Take those two extra wires* I mentioned and connect them to the input side of the B.R.. Then connect the output side to the sound board.
 
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