Loksound decoders - keep alive caps / chokes - lokprogrammer errors.

[Steveruger45]

I have just made an interesting discovery While I’ve been doing a complete loco fleet firmware update, on about 40 locos, I’ve noticed a trend.

It is known that Having keep alive caps installed can interfere with doing firmware updates, sound file installs and the like causing a lokprogrammer error message.  Putting a 100uH x 340mA choke in series with the caps positive does cure this.  At least it has consistently done so, so far on about six locos I’ve done this too already. it works a dream.

However, Those locos with the 73100 or the 73199, In which I have installed keep alive caps of either 400 or 440 uF, this problem does not occur.  I have eleven of these and all updated without issue.

On the other hand all my locos, twenty-one, with the 73800 decoder and caps and without the choke get the dreaded error on a firmware update.

One common thing stands out.
both the 73100 and 73199 loksound select direct micro, don’t have a dedicated caps negative pad, you have to attach to either the board, by making your own pad, or connect to one of the onboard components as per Peteski’s write up. I’ve done my cap installs on these Both ways.

The 73800 does have a dedicated caps negative pad and I used this on all of this type decoder.

Not sure if this observation makes any electronic sense or not but the fact remains.

Anyhow, at least I know now that my choke install list is now reduced to those locos with the 73800 loksound select micro.

[jdcolombo]

Hi Steve.

Thanks for the update and the data.  I don't currently have to update any of my locos, but when I do (and I'm certain that day will come, particularly with my steam fleet), I'll add the choke.  Will make things a whole lot easier, since up to now I've been disconnecting the keep alive to do updates (I have all 73800's in my engines).

In a couple of weeks I'll be doing LokSound installs for a friend in a couple of HO-scale RS-1's using 73800's and a TCS KA3 as the keep alive.  I'll be interested to see if the problem with keep alives hooked to the 73800 shows up when using a commercial product like the KA3 (far too big for use in any N-scale diesel, though it might possibly fit in a large N-scale steam tender).  I'll report back.

John C.

[Steveruger45]

Hi John,
IIRC and I haven’t used any of these, the large capacitance powerpack type stay alives, as opposed to small capacitance keep alive caps, need to have either the more complex 3 wire resistor, diode hook up or the OTC powerpack already have additional components in their circuit.  As such I suspect a choke will not be needed, at least on the ESU powerpack, And probably on the TCS KA3. I will be interested to hear what you find out on such install.

[Billg]

It is known that Having keep alive caps installed can interfere with doing firmware updates, sound file installs and the like causing a lokprogrammer error message.  Putting a 100uH x 340mA choke in series with the caps positive does cure this.  At least it has consistently done so, so far on about six locos I’ve done this too already. it works a dream.

Hi Steve,
Could you explain to me what a 100uH x340mA is and where does one get these?

thanks!

[Steveruger45]

Hi and sure,
It is a 100 micro Henry x 340 milliAmp fixed inductor, aka choke.
I got mine from digikey as per photo.  The physical size is small about 3mm cubed and they are inexpensive at about 25c each. [ Guests cannot view attachments ]

[Billg]

And where do they get placed, between the + cap (blue wire) and decoder?

[Steveruger45]

[ Guests cannot view attachments ] Yes, that’s correct.  In series between the decoder common positive and caps positive.  The blue wire on those decoders that have a wire like the 73800. I slip a piece of heat shrink tubing over the choke extending about 3mm more each side to cover the soldered wire joints to insulate it and fill in the open ends with some liquid tape.
I’ve had no issues finding space to sneak these babies in either.
I’m still installing and nearly completed, two more to go, and then I’ll be all “choked up”.   
[ Guests cannot view attachments ]

[Steveruger45]

Just a bit of additional info. Just in case anyone was wondering.
It doesn’t matter if the leds positive is wired before or after the choke.
Most of my installs uses the caps positive as the common junction point where all the positives meet.
On others I have used the decoder pad as the junction common point.
And on others a mixture of the above.
But in all cases the choke is between the decoder and the caps.

[peteski]

Correct. The order of the components in a series-connected circuit (in this case the coil and capacitor) is irrelevant.  Same with series connected LED and its current-limiting resistor. The resistor can be wired on either side of the LED.