Make Loksound make sense

[Toolbelt]

I'm contemplating installing a 58821 LokSound 5 DCC Direct sound decoder. According to their specs, the board has built-in function resistors of 2.2k ohms each, and ESU states the function output voltage is about 1.5V less than the track voltage. PowerCab shows a track voltage of approx 14V. So for purposes of discussion, that would mean the output voltage for each decoder function is about 12.5V before the built-in resistor (which can be bypassed, if needed). ESU is claiming the resistors will result in a current between 8mA and 10mA per function. I will be using 3V/20ma SMD led's.

When I plug their numbers into any simple resistor calculator, I get a function current output of only 4.32 ma, not 8-10 ma. Am I missing something? When bench-testing the leds for desired brightness, 9.09 ma seemed to be a nice brightness for my tastes, realizing that I can also dim them more using CV's once installed. Why does their current output differ from Ohm's law?

note: I bench-tested my led's using a 3v watch battery with a 330 ohm resistor, which my quasi-math skills worked out as 9.09 ma, but don't quote me on that.

 

[Toolbelt]

Loksound is located in Europe where track voltage might sometimes possibly be higher than North America? I've heard the Lenz brand can put out up to 22 volts at the track. In any case, the Loksound decoder indicates that it was made for North American only, so that might disprove my theory, or not. Sometimes the language barrier throws in some odd words or phrases in their manuals. Perhaps they're mixing up track voltages between continents?

 

[Toolbelt]

According to a response on ESU's support forum, they used a track voltage figure of 16V, not 14V. In poking around, it seems 14V is the standard here in most cases. If that is the case, it would seem odd that this decoder is made specifically for the North American market, per their webpage.

 

[RhB Michael]

The only reason it is for the N. American market is that it doesn't include Euro-centric DCC protocols commonly used in Europe. The N. American model is strictly DCC only without the additional protocols.

 

[Toolbelt]

The only reason it is for the N. American market is that it doesn't include Euro-centric DCC protocols commonly used in Europe. The N. American model is strictly DCC only without the additional protocols.

So the "North American" claim is more about informing Europeans not to buy that decoder than it is to inform North Americans to buy it? Typically on-board resistors are a great feature, except in the case of North Americans, who must now not only add resistors for their LED's, but also solder the bridge pads to by-pass the built-in resistors. How hard would have been to simply use 1k-1.5k resistors instead of 2.2k at the factory? Surely the North American market is large enough to warrant that small change?

 

[RhB Michael]

Essentially yes. It is to inform Europeans that the decoder may not work on their DCC system. I'm not certain (because I've never checked) that the N. American models are even sold in Europe.

Multi-protocol decoders work just fine on N. American DCC systems. The other protocols are ignored by the command station and DCC is selected automatically.

 

[Iron Horseman]

I'm contemplating installing a 58821 LokSound 5 DCC Direct sound decoder. According to their specs, the board has built-in function resistors of 2.2k ohms each, and ESU states the function output voltage is about 1.5V less than the track voltage. PowerCab shows a track voltage of approx 14V. So for purposes of discussion, that would mean the output voltage for each decoder function is about 12.5V before the built-in resistor (which can be bypassed, if needed). ESU is claiming the resistors will result in a current between 8mA and 10mA per function. I will be using 3V/20ma SMD led's.

When I plug their numbers into any simple resistor calculator, I get a function current output of only 4.32 ma, not 8-10 ma. Am I missing something? When bench-testing the leds for desired brightness, 9.09 ma seemed to be a nice brightness for my tastes, realizing that I can also dim them more using CV's once installed. Why does their current output differ from Ohm's law?

Does seem funny and, no I did not get it to match the Ohm's Law either, but there might be other circuitry in there too.

So have you hooked up the LEDs you want to use to the output of the decoder to see what the results are? Seems like that is the solution. Do they say if the accessory output is DCC or DC? From the 1.5V drop I would guess DC. That is a normal full wave rectifier type drop. But one can do all the math in the world and that is not going to tell you how it looks to your eye.

Since your LED is specified as 3V it sounds like it already has a resistor or voltage regulator built in, have you considered that value in your calculations?

I would suggest connecting the LED and decide if you want it brighter or dimmer and adjust by adding resistance, or cutting the trace and putting in less resistance (less than 2.2k).

 

[Toolbelt]

Since your LED is specified as 3V it sounds like it already has a resistor

My LEDs are 3V/20ma 0605 smd's. As I mentioned, when bench testing them with various resistors, I found 9.09ma produced just the right amount of light for my needs. Apparently ESU used a higher track voltage than 14v when doing their calculations, which based on Ohms law, would be around 19.8+v track voltage, less the stated 1.5v voltage drop before the on-board resistor to come up with 8.3ma. I guess Europe runs on higher track voltages. If I run with their on-board 2200k resistors, I will only be giving my leds 4 ma, which will likely be at the very low end of being acceptable, especially running in the daytime. I will likely have to not only add my own resistors, but also bridge solder their decoder to bypass the on-boards. I'm just surprised they wouldn't tailor their US marketed products to better accommodate our norms. It's not like North America is some obscure island of a few thousand consumers.