controlling back EMF on a model railway DCC accesory decoder .

Thanks for that as it had me wondering , I want to stick on the present course anyway as like my dad i'm no lover of coding or maths in general , when I have the Capacitors i'll give it a test and then get back to you .,

Hi , i've been doing some experimenting as it occured to me that I should check that the uncouplers do actually work so I just laid a tiny strip of steel( what you have to fit to a wagons or carriages plastic couplers to make them magnetic) on the track immediately above an uncoupler and gave it power from the 18 volt 1.5 amp DC psu and nothing happened the psu is giving power but obviously not enough so I had a rummage around a box of psu's that dad had and found a 20 V 3 amp laptop psu and that definately does the trick so i'll obviously be using that one from now on .I also did more googling on the uncouplers and found that there are 2 different makers but the units are near identical and it turned out that where I thought I had the ones that used 18 volts DC I actually have the ones that use 18 -24 Volts AC or DC , apparently the coil windings are different in the number of turns and thickness of the wire, i'm guessing that the capacitor will not be needed now ? it's no matter that i've ordered 2 as they were cheap and can go in the box of electrical spares in case they are needed for some other purpose in the future even though this job is the last one before it's all software configuration work .

I received the capacitors today and tried one as you recomended with the 18 volt 1.5 amp DC supply but it barely made a difference so it looks like the 20 volt 3 amp one is the way to go because that lifts a coupler nicely so what I think it needs now is a way to use the LS150's 15 volt AC output ( but I can convert it to 12 volts DC ) to trigger the 20 V DC laptop PSU to supply the uncouplers with 20 V DC which I think means a pair of relays with 12 V DC on the coil and 20 V DC from the laptop PSU , or is there a better way ? cost is not a consideration.

Have you tried a bridge rectifier and capacitor on one of the outputs from the DCC module? I'd have expected that to work well...

No I don't have a bridge rectifier , can you give me the spec ? and i'll get one ordered today .

Either four 1N5400 series diodes, eg. a 3A - 5A or higher arranged as a bridge, or an off-the-shelf bridge rectifier.
The specifications are not in any way critical as long as it's rated well above the supply voltage and somewhat highr than the load current.

eg. something like these:

Or like these - massive overkill ratings-wise, but that makes them pretty bombproof, they are easy to connect to with crimp pushon terminals so good for experimentation - and they are cheap!

Ok , i've ordered the second one as it will be easier to mount close to the LS 150 with it's screw hole , I don't have any push type connectors though, would soldering to the terminals be ok ?

garyd said:

Ok , i've ordered the second one as it will be easier to mount close to the LS 150 with it's screw hole , I don't have any push type connectors though, would soldering to the terminals be ok ?

Click to expand...

Perfectly fine.

rjenkinsgb said:

Either four 1N5400 series diodes, eg. a 3A - 5A or higher arranged as a bridge, or an off-the-shelf bridge rectifier.
The specifications are not in any way critical as long as it's rated well above the supply voltage and somewhat highr than the load current.

eg. something like these:

KBU4K-E4/51 | Vishay Bridge Rectifier, 4A, 800V, 4-Pin | RS

uk.rs-online.com

Or like these - massive overkill ratings-wise, but that makes them pretty bombproof, they are easy to connect to with crimp pushon terminals so good for experimentation - and they are cheap!

GBPC1502 T0 | Taiwan Semiconductor Bridge Rectifier, 15A, 200V, 4-Pin | RS

uk.rs-online.com

Click to expand...

Hi , I expect to receive the bridge rectifier tomorrow ( Fri 17th) and have the capacitors already so I now need to know how to connect them to the LS150 , I will as I said be using soldered wires to connect everything up but need to know the following info - which output terminals should I use on the LS150 ? I assume it will be just 2 ? with 2 wires going from the LS's output terminals to the bridge rectifier and 2 wires going from the BR to the uncouplers incorporating a capacitor across the exit wires ( in parallel ) , those 2 wires which will terminate at the uncoupler/s with each wire being duplicated as there are 2 uncouplers , the capacitor has no + marking on it but does have a silver stripe on it's case which seems to have a negative dash printed on it ? , I think i've covered it all as regards questions but if you spot something i've missed then please tell me .

Yep, that sounds OK. Use the same two termionals on the LS150 as before, to the AC connections on the rectifier.
The cap only having negative marked is quite common.

Some bridge recs in that style only have the + output marked; if that one is like that, the opposite corner is negative and the two adjacent to + are the AC in.

just one point i'm not clear on , to which of the rectifiers 2 output terminals should the caps + terminal go ?.

Positive!

Hi, well I have some good but mostly bad news in that I wired up the Cap and bridge rectifier today and it does not work , there is no movement on a wagons coupling and no movement if I place a thin sliver of steel directly over the Electromagnet , i'm thinking that it's just not getting enough power ?.

That makes no sense?? Can you measure the AC voltage at the input to the bridge and the DC output voltage across the cap?

I've measured both and immediately saw the problem in that both read less than 1 volt so I tried differnt combinations of LS 150 output terminals eg leftmost and centre or rightmost and centre leftmost and rightmost but all combos showed very low voltage , I then decided to check that the LS 150 would still throw the twin solenoid points motor and it does and they definately need an absolute minimum of 15 volts , so i'm stumped .

The points motor uses 3 wires , were you aware of that ?

Is the LS150 configurable between pulse and continuous power? I'm guessing that if it's set for a point solenoid, it's only giving a short pulse rather than a continuous output?

yes it is or rather the pulse duration can be adjusted , as default it gives 0.5 second pulse but I have it set for a 3 second pulse the maximum pulse is 10 seconds .

Is the output LED coming on? If not, the load may be too high and triggering the device overload protection. That needs the AC input shutting off to reset it, according to the manual.

Try the bridge rec without the capacitor? The current that takes to charge will increase the likelihood of an overload trip..

The outputs have a joint protection mechanism against overload. If the permissible maximum power is exceeded, the LS150 will switch off the terminal ("+" or "-" of an output) which experienced the short-circuit. You can tell that a blocked status is existent by the fact that the LED does not shine although a command was received for this output.

Click to expand...

Yes the output LED is coming on and remains on for approx 3 seconds .i'm starting to wonder if the LS150 is up to the job and I might be better off using an accessory decoder with just 2 output terminals , the choice is limited to a degree in that it must be on the traincontroller automation softwares compatible DCC systems list or traincontroller won't see it .