Best Of LokSound 5 Nano - Capacitor Connection?

[cbroughton67]

Has anyone connected a capacitor(s) to the LokSound 5 Nano? Blue goes to anode (+), and the cathode (-) goes to the pad marked GND, correct? Just wanting to confirm, because let's just say my experience has been less than stellar in my attempts to do so... I'm using the same caps I've used in all my other LokSound installs, but this is my first experience with the Nano. What am I missing?

Can someone confirm for me with a photo where these connections are made on the Nano board?

Thanks,
Chris

[Steveruger45]

Here you go. 
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[cbroughton67]

Here you go. 
(Attachment Link)

I'm using tantalum caps, not an ESU Power Pack. So, I'm only using the GND and Blue/U+ connections. So far, it makes for quite a fireworks display...

[Steveruger45]

I'm using tantalum caps, not an ESU Power Pack. So, I'm only using the GND and Blue/U+ connections. So far, it makes for quite a fireworks display...

The connection points, GRD for the cap negative and U+ for the cap positive, is correct..
Maybe your capacitors are bad or underrated or shorted?
Presume you are using 25v tantalum caps.
Try proof testing the capacitors first.  You can do this by hooking upto a 18v or 20v power drill battery.   Use long wires so when you make the last connection to the battery you are far enough away from it in case it blows.   I did this to a bunch of eBay Chinese 25v rated tantalum caps and had a failure rate of about 20%.
If they don’t blow straight away leave them on the battery for a couple of hours.
This was quite a while ago and Since then I changed out all my installed cheap tantalum caps for quality poly tantalum’s and those I had spare I threw in the trash.
I only use about 400 to 450 uF of poly tantalum caps, so I don’t use the added resistor and diode as shown on this picture.

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[cbroughton67]

I only use about 400 to 450 uF of poly tantalum caps, so I don’t use the added resistor and diode as shown on this picture.

(Attachment Link)

After pondering this more, in the absence of the resistor, how is the cap not seen as a dead short to a non-DC signal? DC would see it as an open. @peteski ? Without a current-limiting resistor, wouldn't the inrush current blow the cap all by itself?


Chris

[peteski]

After pondering this more, in the absence of the resistor, how is the cap not seen as a dead short to a non-DC signal? DC would see it as an open. @peteski ? Without a current-limiting resistor, wouldn't the inrush current blow the cap all by itself?


Chris

Chris, decoders are micro computers -- they require DC power to function. Same with the motor and function-powered devices.

Every decoder has a bridge rectifier which takes the DCC pulses and rectifies them into a DC voltage.   The decoder also has some fairly small value filter caps connected at the DC side of the bridge rectifiers to smooth out the voltage.  That is also the location where you connect additional Keep-alive circuit. Those are either some larger value capacitors which will store enough energy to keep the decoder's electronics from resetting during very brief power pickup interruptions (dirty track), or a SuperCap-based keep-alive circuit which stores enough energy to keep the entire model functional (the decoder's electronic, motor and function outputs) for few seconds.

That is why you don't have to worry about the capacitor blowing up*.  Inrush current is also not the correct term used when AC voltage is applied to a cap.  Inrush current occurs when a DC-voltage is applied to a discharged capacitor.  At that point the "empty" capacitor will "suck up" as much current as it can. That current limited by the capacitor's internal resistance, and by the external resistance between the cap and the source of power.   But that current spike is very short (it depends on how large the capacitance is).  As the capacitor charges (fills up with electric charge) the current decreases until it is zero when the cap is fully charged.

With the keep-alive caps we use in N scale trains (usually less than 1000 micro Farads) we don't really have to worry much about the inrush current.  For larger value caps, the circuit Steve posted is used. That resistor/diode circuit is also used in the SuperCap-based keep-alives.

I like to add a coil in series with he cap.  Coils pass DC voltage, but exhibits higher resistance (impedance) to any change in the current passing through them, like the current pulses which occur during programming on programming track.  Adding a coil usually makes programming possible without disconnecting the keep-alive capacitors.

* No guarantees that a tantalum cap will not flame up inside the model. That is usually caused by defective cap, and applying voltage that is too close to the cap's max. operating voltage.

[Silverexpress]

Fyi,

[peteski]

That lengthy video only covers adding factory made SuperCap-based  2-wire stay-alive circuits.  The question in this thread was about adding just standard discrete capacitors, and what (if any) ancillary components are needed.

[cbroughton67]

@peteski Thanks for the explanation / clarification. It's been a three decades since I last studied electronics, so "rusty" would be putting it mildly.

I originally tried 16v 330uF and 470uF tantalum caps (from the same batches I've successfully used with v4 decoders) with this Nano, and they've all blown. So, @Steveruger45 's recommendation, I ordered some 25v 220uF caps and tried those - same result. Anode (+) (end with the stripe) goes to blue, cathode (-) goes to the GND pad. This isn't rocket science, and I've installed these many times before without issue. So, at this point I'm thinking something else is afoot. I'm at the point of trying a 12v zener diode and 100ohm resistor across the cap and see if that helps. Otherwise, I'm at a loss.

Thanks again,Chris

Chris, decoders are micro computers -- they require DC power to function. Same with the motor and function-powered devices.

Every decoder has a bridge rectifier which takes the DCC pulses and rectifies them into a DC voltage.   The decoder also has some fairly small value filter caps connected at the DC side of the bridge rectifiers to smooth out the voltage.  That is also the location where you connect additional Keep-alive circuit. Those are either some larger value capacitors which will store enough energy to keep the decoder's electronics from resetting during very brief power pickup interruptions (dirty track), or a SuperCap-based keep-alive circuit which stores enough energy to keep the entire model functional (the decoder's electronic, motor and function outputs) for few seconds.

That is why you don't have to worry about the capacitor blowing up*.  Inrush current is also not the correct term used when AC voltage is applied to a cap.  Inrush current occurs when a DC-voltage is applied to a discharged capacitor.  At that point the "empty" capacitor will "suck up" as much current as it can. That current limited by the capacitor's internal resistance, and by the external resistance between the cap and the source of power.   But that current spike is very short (it depends on how large the capacitance is).  As the capacitor charges (fills up with electric charge) the current decreases until it is zero when the cap is fully charged.

With the keep-alive caps we use in N scale trains (usually less than 1000 micro Farads) we don't really have to worry much about the inrush current.  For larger value caps, the circuit Steve posted is used. That resistor/diode circuit is also used in the SuperCap-based keep-alives.

I like to add a coil in series with he cap.  Coils pass DC voltage, but exhibits higher resistance (impedance) to any change in the current passing through them, like the current pulses which occur during programming on programming track.  Adding a coil usually makes programming possible without disconnecting the keep-alive capacitors.

* No guarantees that a tantalum cap will not flame up inside the model. That is usually caused by defective cap, and applying voltage that is too close to the cap's max. operating voltage.

[Steveruger45]

@Chris, very odd indeed.   To help narrow down the issue, Have you tried putting some caps on the stress test I mentioned using a power tool battery?
If the caps survive that then it is likely not the caps.

[peteski]

I agree that it is very odd.  Especially when using caps rated for 25V.  One thing about tantalum caps is that they are guaranteed to burn up if connected in reverse.  Yes, the marking (stripe) on the caps is on the positive side.  Are you 200% you are connecting them correctly to the decoder?



Do you have a voltmeter?  If not, get one - digital multimeters can be had for $10, and it is a must for anybidy messing around with DCC (or with model trains in general).

Put the loco on DCC powered track. Connect up the voltmeter test leads to the pads where you are connecting the caps.  Black lead to the GND pad and red lead to the U+. Check the voltage and polarity (the meter shoudl show positive voltage).  Then you'll know what voltage and polarity the cap sees.

There is something that just doesn't add up here . . .

[cbroughton67]

@peteski  @Steveruger45 I hooked up my VMM to the the decoder where I'm connecting the caps, and got about 13.7v. Polarity also checked out as expected - + on blue, 1 on GND.

In the absence of a power tool battery, I have an old MRC power pack with a fixed DC-output that measured 15v. So, I connected that to a cap from the batch I've been using, making sure to connect positive to the anode and negative the cathode. After about 10 minutes... nothing. It didn't blow. They've been blowing within a few seconds on the locomotive.

I'm still at a loss... Ideas?

I appreciate your help, gentlemen!

Chris

[peteski]

@peteski  @Steveruger45 I hooked up my VMM to the the decoder where I'm connecting the caps, and got about 13.7v. Polarity also checked out as expected - + on blue, 1 on GND.

In the absence of a power tool battery, I have an old MRC power pack with a fixed DC-output that measured 15v. So, I connected that to a cap from the batch I've been using, making sure to connect positive to the anode and negative the cathode. After about 10 minutes... nothing. It didn't blow. They've been blowing within a few seconds on the locomotive.

I'm still at a loss... Ideas?

I appreciate your help, gentlemen!

Chris

Maybe you just had few bad capacitors?   Next thing to do?    Take one of the 25V rated caps you "conditioned" on the DC power pack, and  connect it to the decoder.  It should not fry.  If that one burns up, I'm really lost for words.

BTW, using 16V rated caps in a 13.7V circuit is cutting it way too close.  Also, I have never used anything larger than 150uF tantalum caps. I think the very large capacitance caps like 330 or 470uF tantalum caps will be very prone to spectacular failures.  Heck, I didn't even think 470 uF tantalum caps rated for 25V or higher were made.

[Steveruger45]

I agree with Pete. BTW I use poly-tantalum caps exclusively as I read somewhere that you can safely apply 80% of the rated voltage on them instead of 50%for the straight tantalum caps.
I can’t think of any reason they keep blowing on you Chris.
Are you sure the decoder to connector board connection is ok?  Just wondering if maybe something amiss there that could be the cause.

[cbroughton67]

@peteski I agree that 13.7v is too close for comfort on a 16v cap. It's easily within the 20% tolerance stated in the specs. The "second" batch is 220uF 25v - the ones I'm working with currently. I'll be out of town for a couple of days, but I'll connect the "conditioned" one (a 220uF 25v cap) when I get back and see how it goes. The 330uF and 470uF caps I have are 16v. 220uF was the highest 25v caps I could find.

@Steveruger45 Do you have a link for the tantalum-polymer caps you use? Also, do you know anything about the 220uF 16v caps sold by SBS4DCC? They're supposed to be MIL-spec, which I believe has a 5% or 10% tolerance. Are those worth a shot, or still too close for comfort re: voltage?

Again, I appreciate the help and suggestions, guys.

Chris