Minimum track voltage to run a decoder...?

Zerogee

Zerogee

Clencher's Bogleman
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Quick question: what is the minimum input voltage (track voltage) necessary to make a large-scale sound decoder - say a Massoth XLS - function properly?
I know that when you run one in analogue mode the sounds (and loco movement) seem to start up at around 5-6 volts or so, but what's the minimum on which the decoder will actually function in DCC mode?

Jon.
 
NMRA DCC standard S-9.1 says that the minimum voltage a decoder should work at is 7 volts.

I don't know if Massoth decoders comply with this or not. I'd just try by trial and error to find the minimum voltage starting at 7 volts.
 
5volts i think...
 
I would go with the NMRA standard..
'Someone' could test this, but it would take a heck of a lot of back-to-back diodes, or some seriously high wattage resistors, to do so!
:o ::) ::) ;)
 
From my observations when bench testing decoders after fitting, I'd agree with around 7 volts on average but it depends on the brand of decoder.
 
OK chaps, thanks for all the answers! :)

As you've probably surmised, this ties in to my search for the ideal onboard battery pack to run the DRS/DCC setup with - enough voltage to run the decoder without needing a voltage step-up circuit board. The Tam DRS Rx requires a 7.4 volt to 24 volt input, but although everyone's replies here suggest that 7.4 volts should be JUST enough to make the decoder function correctly, I'd rather have a bigger margin....

I thinking that my original ideas of going as high as 19.2 volts (2 x 9.6 packs in series) might be considerably more than I'd need in practice - I'm NOT wanting to do any high-speed main-line running, just a gentle meandering pace suitable for European narrow gauge - and it might be better to go for fewer but larger cells, sacrificing voltage in return for extra amp-hours....?

What do folks here think? 8.4 volts still too low, I feel.... how about 12 volts (10 cells of NiMh)...?

Jon.
 
I discovered a bit of no-mans land between 5 & 7 volts dc where a chip would keep its settings but the engine wouldn't move. I used it as sort of crude 'brake on DC' to hold a train at a signal. The train switched a section it was in from DCC to 9v and then 6v dc, which halted the loco with the lights on.When the signal was released, the section reverted to full on DCC and the train pulled away using its last known settings. Wierd.
 
Clever idea, David, never heard of anyone doing that before! :)

Still looking for opinions on battery pack voltage, if anyone out there has them?

Come on chaps, this is the Interweb - EVERYONE has an opinion about EVERYTHING....! ;)

Jon.
 
I would stick with 'standard' battery packs / holder sizes and what you can comfortably fit (with everything else) in the vehicle..
Presumably, a higher voltage pack will be less stressed, so give you a longer run-time??
Two 7.2V packs in series, or make up to your choice with standard cells and holders.

A simplistic answer, but I doubt you need to run anywhere near the top end voltages to get the speeds you need.
 
Phils answer makes a lot of sense to me. 6 cell packs are very common, so two of these. 14.4 V should be ample.
 
Zerogee said:
I thinking that my original ideas of going as high as 19.2 volts (2 x 9.6 packs in series) might be considerably more than I'd need in practice - I'm NOT wanting to do any high-speed main-line running, just a gentle meandering pace suitable for European narrow gauge - and it might be better to go for fewer but larger cells, sacrificing voltage in return for extra amp-hours....?
Click to expand...

That depends on how your DCC decoders are already set up. I run my DCC on about 18V DCC and the max speeds of all my decoders have been adjusted (via CVs) to run at what I consider to be a reasonable max speed already. This spreads the speed steps over the range I want to run it at and does not waste lots of them at unrealistic ultra high speeds. If I fed in less than about 18V my locos would run at less that the top speed I would like.

Now none of this matters if you only want to run on battery or you have not adjusted the unrealistic max speed most decoders will run an engine at out of the box.

As I want to run my engines on either DCC or battery I decided to keep the DCC input voltage approximately the same in both cases.
 
Very good point, Cliff!
I suppose it would also affect things like lamp brightness, where it may be set in the decoder as a % of the available voltage... would the same apply to sound volume settings?

Jon.
 
Most DCC decoders run the "brains" on a regulated 5 volts, so normally the lowest track voltage is 7 volts, because there must be the "voltage headroom" for a 5 volt regulator to run, it normally needs 2 PN junction voltage drops (about .7 volts each)...

The amps on Titans and many other modern units are Class D amps, i.e. switchers, not analog, and should have higher output at higher voltages, but I have not confirmed this theory.

Greg
 
Thanks Greg - so what kind of battery voltage would you recommend for the setup I outlined above? I'm leaning towards two 7.2 volt NiMh packs (because they are easy to get, and available in fairly large Ah capacities) in series, for a 14.4 volt total. All my loco stable is Euro style, mainly LGB with some Piko, a couple of TL45 and a few "oddities" (two Dingler Ts3's, a Dietz railbus etc) but nothing American built - all decoders, so far anyhow, are also from European manufacturers - mostly Massoth, plus the odd Zimo and Dietz.

Jon.
 
Cliff George said:
It is good to see Greg contributing here now.

I noticed recently that CPC have started selling protected 14.8V Li-ion battery packs and chargers:

http://cpc.farnell.com/ansmann/2447-3036/battery-pk-li-ion-4s1p-14-8v-2/dp/BT06048

http://cpc.farnell.com/ansmann/2447-3035/battery-pack-li-ion-4s2p-14-8v/dp/BT06049

http://cpc.farnell.com/ansmann/9c94131-01/charger-li-ion-14-8v-1-2a/dp/BT06054?in_merch=New Products

Maybe these would be of use to you?
Click to expand...

Thanks Cliff, very useful links.....
Despite all the useful info that folks like Ross have pointed me to, I still can't QUITE get my head around the "dangers" (real or apparent) of Li-Ion and Li-Po batteries. There are a lot of scare stories, but do these result from mishandling (charging too fast, or using the wrong type of charger) or is it an innate risk with these battery technologies....?

I suppose what I REALLY need a simple, firm answer to is this: IF a battery of this type is treated properly, not over-charged or over-discharged, and you use the correct charger in the correct manner - ARE they "safe", or is there still a risk of them bursting into flames and taking £500 of loco with them....?

In these battery conversions I need a battery type that can be permanently installed in the loco body, with just a charging plug accessible from the outside. I DON'T need to "fast charge", a slow overnight charge rate is fine, and I don't need to be able to swap battery packs during a running session. Should I stick to good old proven NiMh technology, or not?

Thanks,

Jon.
 
Zerogee said:
I suppose what I REALLY need a simple, firm answer to is this: IF a battery of this type is treated properly, not over-charged or over-discharged, and you use the correct charger in the correct manner - ARE they "safe", or is there still a risk of them bursting into flames and taking £500 of loco with them....?
Click to expand...

Almost everything carries some degree of risk (including, for example, NiMh batteries) and, IMHO, it's up to you to decide if the level of risk is acceptable in view of the advantages. I'm pretty sure that most laptops, mobile phones and similar devices use Li-Ion or Li-Po type batteries with only a very small percentage giving any trouble. There must be info. about the failure rate of these devices out there somewhere to help you decide.
 
Thanks Neil - that certainly makes sense.

Can anyone give a simple answer to whether there is a significant difference in terms of safety between Li-Ion and Li-Po battery chemistries - is one a better choice than the other, or do they share the same potential problems...?

I notice that the packs that Cliff linked to, such as this one:
http://cpc.farnell.com/ansmann/2447-3035/battery-pack-li-ion-4s2p-14-8v/dp/BT06049
appear to have just two simple wire leads, and no fancy extras like the multi-pin balance plugs - is this because they are Li-Ion and not Li-Po...?

As an aside, I'm happy to pay a little extra to buy the battery from a reputable UK-based supplier, rather than scavenging around for the cheapest Chinese seller on evilBay to save a few quid.... ;)

Jon.
 
MMmm

of the zillions of laptops in circulation that have Li- batteries, a handful have had problems.

A couple of Boeing Dreamliners have also had issues, but for the most part, there are equally a fair few thousand Li- battery packs being used in the model world with no difficulties.

Most people who have had issues with Li- battery packs were trying to take them apart - that is one thing that is a big NO-NO >:( >:(

The other pre-requisite for any battery installation is a fuse or auto reset circuit breaker (probably already mentioned in this thread but you cannot mention it often enough) ;) ;) ;)
 
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