Track voltage vs. power supply voltage

[Jbub]

I'm wanting to add some capacitors to my loco's but trying to find 20v or 25v caps with more than 150uF is like impossible right now. Plus they are like 5 bucks a cap for the 150's so you need 3 and bam 15 bucks for some current keeping ability that might not fit in our tiny little loco's. Supposedly Mouser is getting some 220F 25v caps in May 

So I remember John C uses 16v Caps but keeps his track voltage low. Great idea but my problem with that is the only power supply that goes LOWER than 15v is the digitrax 20amp monstrosity. All the other standard power supplies are 15v or higher. That leads me to my question, what kind of voltage drop can one expect from the power supply to the track. I would really hate to put these lower voltage caps in my loco's, turn on the DCC system and start to see melting shells and fire spitting out like a 1:1 GE loco.
I have read other threads about using Zener diodes to clamp voltage but then again you don't have a sharp cut-off with those and you can get into 20% danger area on the polymer tantalum caps.

Any help or suggestion would be greatly appreciated.

Thanks
Jbub

[peteski]

I'm wanting to add some capacitors to my loco's but trying to find 20v or 25v caps with more than 150uF is like impossible right now. Plus they are like 5 bucks a cap for the 150's so you need 3 and bam 15 bucks for some current keeping ability that might not fit in our tiny little loco's. Supposedly Mouser is getting some 220F 25v caps in May 

So I remember John C uses 16v Caps but keeps his track voltage low. Great idea but my problem with that is the only power supply that goes LOWER than 15v is the digitrax 20amp monstrosity. All the other standard power supplies are 15v or higher. That leads me to my question, what kind of voltage drop can one expect from the power supply to the track. I would really hate to put these lower voltage caps in my loco's, turn on the DCC system and start to see melting shells and fire spitting out like a 1:1 GE loco.
I have read other threads about using Zener diodes to clamp voltage but then again you don't have a sharp cut-off with those and you can get into 20% danger area on the polymer tantalum caps.

Any help or suggestion would be greatly appreciated.

Thanks
Jbub

You mentioned polymer tantalum caps. Actually those are pricier, safer, and have less of a selection available than standard solid tantalum caps which we usually used in our hobbies.  Were you specifically looking at the polymer tantalum caps? I do commend you on the 20% safety buffer.

You might be able to find a regulated 13.8V regulated DC high-amperage supply out there. Those are used to run automotive electronics (radios, CBs, etc,) in a stationary location from 120V household current.

[jdcolombo]

So I remember John C uses 16v Caps but keeps his track voltage low. Great idea but my problem with that is the only power supply that goes LOWER than 15v is the digitrax 20amp monstrosity. All the other standard power supplies are 15v or higher. That leads me to my question, what kind of voltage drop can one expect from the power supply to the track. I would really hate to put these lower voltage caps in my loco's, turn on the DCC system and start to see melting shells and fire spitting out like a 1:1 GE loco.
I have read other threads about using Zener diodes to clamp voltage but then again you don't have a sharp cut-off with those and you can get into 20% danger area on the polymer tantalum caps.

Any help or suggestion would be greatly appreciated.

Thanks
Jbub

What kind of DCC system do you have?  Most separate command stations (e.g., the Digitrax Chief, the NCE Power Pro) have a way to set the output voltage via a variable resistor (pot) inside the command station.  This is how I've done it with my Digitrax Chief (which also has an "N" voltage setting on the outside so that I'm starting from about 12.5v instead of 14v for the HO setting).  The first thing you should do is see if your command station has a way to lower the output voltage without changing the input power supply. 

I use 16v, 220uf regular tantalum caps, which are still not exactly cheap (about $1.50 per cap in quantities of 25), but with my track voltage at 11.5v, that's a 4.5v safety margin, or a bit over 25% of the cap's rated value.

John C.

[Jbub]

Currently I have an MRC prodigy express (old style)
My concern is with the new cab control system from esu. The power supply is 15-21v. 15 is too high for n imo.

[DKS]

You might be able to find a regulated 13.8V regulated DC high-amperage supply out there. Those are used to run automotive electronics (radios, CBs, etc,) in a stationary location from 120V household current.

Yes, these can be found on eBay. I've purchased two of them.

[jdcolombo]

Currently I have an MRC prodigy express (old style)
My concern is with the new cab control system from esu. The power supply is 15-21v. 15 is too high for n imo.

Well, maybe.  If the input voltage is 15v, then the question is what the output voltage would be.  A typical bridge rectifier drops 1.4v from a power supply, which would get you to 13.5v, and there may be other voltage losses as well.  I couldn't find an actual manual for the cab control system, so it's hard to tell.

Still, as Peteski notes, you can get a lot of regulated 13.8v supplies or even a regulated 12v supply.  Here's a 10-amp 13.8 one from Amazon:

https://www.amazon.com/TekPower-TP1863-Regulated-Supply-Protection/dp/B00KXGZ2FE

But I'd try to find out what the actual track voltage is from the cab control when fed with a particular supply voltage (e.g., at 15v on the supply side, what is the actual track voltage?).  Then you can better judge what you need on the supply side to get something on the order of 12v out to the track.

John C.

[Jbub]

So esu says to set the voltage on the supply to 16.5v do to the IC in the command station needing that voltage. The track output will be 15 volts and as far as I understand there is no way to adjust that down on the command station. Running 12v motors on 15v doesn't sound good to me.

[woodone]

Don’t think that you motors will see 15 volts . The decoder supplies the voltage to drive the motor and is pulsed voltage too.
I have been using 20 volt caps @ 100Uf. Use two or three depending on the room.
I know 16 volt is too close to the max for me so,I use the 20 volt ones.