controlling back EMF on a model railway DCC accesory decoder .

[garyd]

also most other decoders (2 wire ) output 12 volts DC .

 

[garyd]

I've spent a good few hours playing around with things and googling various stuff and what i've discovered is this - No 1 the supposed 16 volt AC psu that supplies the LS150's power actually reads 18.2 volts on a multimeter No 2 the LS150 when fitted with 2 diodes as for a motorised point motor delivers 8.4 volts DC No 3 is this item which only came on the market recently http://www.train-tech.com/index.php/accessories-extra/relay-controller ,in the video the guy say's "you could power it with a battery" so i'm guessing he means 9 volts so maybe the 8.4 volts from the LS150 would be enough ? and i'd supply it with the 20 volt DC laptop psu that I already know lifts a coupler very nicely , it's not cheap but as I said before cost is not a major consideration , what do you think ? i'm attracted to it as it seems an elegant solution .

 

[rjenkinsgb]

The 8.4V is the average from a single diode (for each output), half-wave rectifying the output; 16.8V / 2, in effect.

The bridge rectifier output should read around 16V DC from the same supply...

 

[garyd]

I'm just getting a very low reading ie something around 143 , I have taken 3 pics of how I wired the BR with the short stubby black and red wires being the conne

ction to the LS150 and the plain black and red wires being the DC output to an uncoupler, does it look right to you ?

 

[garyd]

i've just remembered something that may or may not be relevant in that the 16V AC psu is only rated at 0.500 milliamps .

 

[eTech]

Hello

The root of the problem is that you haven't provided specifics for powering the uncoupler. Do you have a part number so we can look it up?
If it is a DC powered uncoupler, you can try this (see below). The circuit is derived by info from rjenkinsgb.

D1 will convert AC to DC, C1 will smooth and boost the output voltage a little to about 12vdc. The relay is an ordinary automotive 12v cube relay.
I've shown a 18VDC power supply for the uncoupler but it can be any voltage the uncoupler needs to work.
The relay should energize when the controller output voltage is present, and in turn, energize the uncoupler. However, the DCC output is a pulse of 0.1 to 10 seconds, so you'll have that duration of time to check the uncoupler operation. It doesn't have an option to make the output continuous. That may be a problem because you'll have to time the output with the movement of the rolling stock. But at least you'll have the ability to prevent unwanted uncoupling as cars pass over the uncoupler.

You can also replace D1 with a bridge rectifier if you like.

 

[garyd]

Now you see you are using a relay which was my first instinct but I had no idea how I could use the LS150's AC output to use as the signal to a 12 V relay or pair of relays , the manufacturer(Seep) provides very little info but there is this from a company that retails Seep products , https://www.gaugemasterretail.com/magento/seep-gmc-em1.html , it states 18 -25 V AC or DC , I have read from articles online that in practice they work best with DC at 18-20 volts and I have used a 20 volt DC supply to power one manually with great success , people have written that on AC they can hum annoyingly and the lifting action on the coupler is not as smooth as DC , your drawing shows 15VAC but if you only use the common terminal and + terminal on the LS150 you get a very low voltage whereas if you use 2 diodes you get around 8 volts half wave DC .

 

[eTech]

Now you see you are using a relay which was my first instinct but I had no idea how I could use the LS150's AC output to use as the signal to a 12 V relay or pair of relays , the manufacturer(Seep) provides very little info but there is this from a company that retails Seep products , https://www.gaugemasterretail.com/magento/seep-gmc-em1.html , it states 18 -25 V AC or DC , I have read from articles online that in practice they work best with DC at 18-20 volts and I have used a 20 volt DC supply to power one manually with great success , people have written that on AC they can hum annoyingly and the lifting action on the coupler is not as smooth as DC , your drawing shows 15VAC but if you only use the common terminal and + terminal on the LS150 you get a very low voltage whereas if you use 2 diodes you get around 8 volts half wave DC .

Hmmm.

The DCC document states 16v out, but somewhere else in the doc it states 1v less that the AC supply input. So that means 15vac out.
If you do the math for a half-wave rectifier, AC/sqrt(2), that equals 15vac/sqrt(2)=10.6 volts dc. If you use the bridge rectifier and you'll get a little more dc voltage output and may not need the relay.

If you don't know the voltage/current requirement for the uncoupler, grab a DC power supply that can output 15vdc.

To measure the current:
Set your meter for current measurement and connect it in series between the power supply and the uncoupler coil.
Make sure your meter can read 2 amps without damage. The meter should have the MAX current capability written somewhere on the meter.
Connect like shown below:

+PS|----------|+coil-|-------|+Meter-|-----|-PS

Set power supply to 0v. <----Note!!
Set your meter to read 2Amps.
Turn the supply on.
Slowly raise the power supply voltage to 15vdc while monitoring the meter.
Hold at 15vdc, then note the current reading on the meter.
Report back.

 

[eTech]

Also,

Measure the AC output voltage of the DCC with nothing connected to the output terminals.

Measure the AC output voltage from DCC_+ to DCC_C while the output is on.
Measure the AC output voltage from DCC_- to DCC_C while the output is on.

Its my understanding only + or - can be ON at time, not both. Please confirm.

Report back.

 

[rjenkinsgb]

I'm just getting a very low reading ie something around 143 , I have taken 3 pics of how I wired the BR with the short stubby black and red wires being the conne

ction to the LS150 and the plain black and red wires being the DC output to an uncoupler, does it look right to you ?

You have the bridge rec connected wrongly.
Read my original wiring description!

Positive is the chamfered corner. Negative is opposite that.

The other two are the AC input.

 

[garyd]

Ah thanks , I did wonder , I knew the chamfer was the positive but the case markings made it appear that the AC input was opposite the positive because the case has AC marked there , i'll get to it tomorrow as I have a few hours work to do outside of the flat tonight .

 

[garyd]

Hi , i'm getting about 8.4 volts but it's not lifting the coupler so I think i'm going to investigate further the DCC relay option I linked to earlier and i'll use the 20 volt DC supply to power it which means the LS150 is going to be finding itself on Ebay , I thank you for all your help and patience but I really do think that i've now reached the end of this particular line .

 

[eTech]

Hi , i'm getting about 8.4 volts but it's not lifting the coupler so I think i'm going to investigate further the DCC relay option I linked to earlier and i'll use the 20 volt DC supply to power it which means the LS150 is going to be finding itself on Ebay , I thank you for all your help and patience but I really do think that i've now reached the end of this particular line .

If you want to give another try, you can try this option using a 6vdc automotive relay.

EDIT:Fixed the annotations

 

[garyd]

Hi , I appreciate you spending the time to give further help and thank you for it but I have today telephoned the makers of the twin DCC relay I linked to earlier as I was unsure as to whether it needed a DCC accesory decoder to go with it so it had a DCC accessory address but apparently it has a decoder built in , it was not on the market whilst my father was still with us or I think had he been aware of it he'd have gone that way .The twin relay is £40.00 and a good barely used LS 150 will fetch that on Ebay so the extra cost will be minimal and will give a more elegant solution I think .

 

[rjenkinsgb]

Hi , i'm getting about 8.4 volts but it's not lifting the coupler

OK; it's possible the bridge rec has failed, as the original connection put one diode directly across the AC supply..

 

[garyd]

Yes that had occured to me but as I said to eTech i've found a solution that will just work out of the box and it all comes in just one neat package , i'm really grateful to you for all the time and advice you've given to me ,This whole thing as far as i'm concerened has been a big learning exercise for me and i'm also grateful to you for that .