I am in the process of building a hi rail vehicle and am concerned that it will operate poorly due to its short wheel base and small wheels causing poor electrical pickup. I was thinking that installing a capacitor between the pickups and the decoder would help it to operate better. Is this a good assumption? If so how do I go about finding the proper capacitor for the job. Any help here would be appreciated.
Thanks, Greg
A Lenz decoder with a USP would work (if you have the space) www.lenz.com then look for products- power1 USP.
Ken.
NZRMac wrote: A Lenz decoder with a USP would work (if you have the space) www.lenz.com then look for products- power1 USP.Ken.
That's a better solution. I believe that a capacitor between the pickups and the decoder would serve to degrade the DCC signal if it help voltage long enough to help. The DCC signal changes polarity in order to transmit data, the capacitor would fight that. The place it might do some good is betweent he decoder and the motor, which is part of what the USP does. It also uses a somewhat different method of detecting the signal, which help it see the signal despite bad contact with the track.
Jeff But it's a dry heat!
Poor wheel-to-rail contact is one of the biggest problems in DCC. Any dirt or grime on the rails can cause hesitation, stalling (especally at slow speeds) and flickering lights. This flickering light problem bugged me to no end, UNTIL I installed a miniatronics light bar for my passenger car interiors. The LED's of the light bar are powered from the rails and use a super capacitor for FLICKER-FREE lighting. Once I saw that first dinner at night, beamming with light, streaming out the windows with no flicker, I went to the LHS and purchased 10 more and put them in evey passenger.... and will do the same for my cabo's. Unless, of course, you want that strobe effect for a party train LoL
After I saw how much a SIMPLE cap totally soloved that problem, I was ready to look into the Lenz USP as I too have some areas of track and especally turnouts larger that #6's where locos would buck, or stall. IT WORKS! My next Big Boy conversion will have one of these and I will put them in evey conversion hence forth and I will need to put them on a few of my road switchers that are already DCC.
By the end of next year... or such, these will become a standard! Mark my words! I saw a demo. I put elect tape on BOTH rails for 12 inches.... and a GP7 rolled right over it like nothing happened.
zero wrote:I am in the process of building a hi rail vehicle and am concerned that it will operate poorly due to its short wheel base and small wheels causing poor electrical pickup. I was thinking that installing a capacitor between the pickups and the decoder would help it to operate better. Is this a good assumption? If so how do I go about finding the proper capacitor for the job. Any help here would be appreciated.Thanks, Greg
DCC switches from plus to minus thousands of times a second. This kind of signal looks like AC to a capacitor. AC passes right thru a capacitor, it does not get stored. Capacitors only store DC, they pass AC thru them. So a capacitor across the wheel pickups of a DCC locomotive will bypass the DCC signal around the decoder, weakening the signal seen by the decoder and drawing more current from the DCC booster. Not a way to improve performance. Nor will placing a capacitor in series with the decoder help, the cap just impedes the flow of DCC signal to the encoder, it doesn't store it.
The decoder turns the AC track signal into DC (probably pulsed DC, but no matter) and feeds it to the DC motor. To reverse the engine, the decoder reverses the polarity of the DC going to the motor. In principle, a large enough bipolar capacitor, placed across the motor, downstream of the decoder, would store juice and keep the motor turning thru power interruptions. Bipolar means the capacitor works right when biased plus-to-minus AND minus-to-plus. Unpleasant fact of life. All big capacitors are uni-polar , when biased plus-to-minus they work like capacitors. Bias them in reverse, minus-to-plus and they go bang. A big uni-polar cap across the motor brushes would help going one way and self destruct when the locomotive was reversed.
There is a line of humoungus caps with capacity measured in Farads, instead of the usual microFarads. But, they are unipolar. And they are electrically tender, they can only withstand 5 volts DC, whereas HO motors get driven by 12 volts DC. The supercaps are coin shaped, a bit larger than a pair of quarters stacked on top of each other.
I once used a supercap to power marker lights in a caboose. It needed a full wave bridge rectifier, a 5 volt regulator , a couple of diodes and an NPN transistor plus the LED. My homebrew perfboard circuit pretty much filled up the interior of that caboose. The cap would store enough juice to keep the lights burning for 20 seconds after track power was turned off.
Motors take about 20 times the juice of LED's, so a supercap might hold enough juice to keep a motor turning for a second after loss of power. You would need some very tricky electronics to compensate for the unipolar supercap, and the 5 volt limitation. I'm thinking by the time the maker squeezed all that stuff into a locomotive, he could get better energy storage with less complication with a plain old fashioned brass flywheel.
David Starr www.newsnorthwoods.blogspot.com
zero wrote: I was thinking that installing a capacitor between the pickups and the decoder would help it to operate better.
I was thinking that installing a capacitor between the pickups and the decoder would help it to operate better.
Danger Will Robinson. Danger Will Robinson!
Your decoder will not function properly as a bi-polar cap will produce a constant DC charge and the decoder inputs work on AC. And you can't put it across the motor leads either!
You need a Lenz Gold with the Power Module attached. They are sold at Tony's Train exchange pre soldered on for $75. There are other places that sell them as well.
Don - Specializing in layout DC->DCC conversions
Modeling C&O transition era and steel industries There's Nothing Like Big Steam!
Don't ever put a capacitor across the DCC power. You will not like the results.
I put a Keep Alive 1000ufd 25 volt cap with resistor and 1N4007 diode to prevent surge when the capacitor charges in a Roundhouse 4-4-0 DCC/sound decoder and it works very well. I did not have space for a larger capacitor.
Read the below link. He covers this quite well. He is also in the NCE and SoundTraxx Yahoo groups.
http://www.members.optusnet.com.au/mainnorth/alive.htm
This guy has a Lot of DCC info. READ ALL of it.
Yahoo Groups have DCC forums for different DCC systems. You did not mention your system or decoder brands.
I belong to SoundTraxx and NCE groups. These Yahoo groups have Files and Photos sections with loads of good info. There are others. This forum is ok but there is a LOT more information on the rest of the 'Net.
Good luck.
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
Actually IT CAN BE DONE !!! All decoder boards have a bridge rectifier on them, whether it be a series of four small diodes or an actual bridge, it's there. The capacitor needs to be installed on the board AFTER the diode's input. That's the bad news - you need extremely good skills at very fine soldering to access the point of attachment.
I built one using a TCS T1 decoder and it actually works quite well. The only drawback is the size of the required capacitor. Super-caps won't work with this concept unfortunately as they appear to have too much internal resistance.
Check it out for your yourself, there are good and bad points, but if you have the room and the skills, this is a cheap option and it DOES work !!! ....
Mark.
¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ
Rich - Ya beat me to it by 60 seconds !!!
Mark R. wrote:Rich - Ya beat me to it by 60 seconds !!! Mark.
I guess we were trying at the same time. It took at least a minute to post.
Are you the Mark who has the site?
Nope - not me. Pretty slick concept though, isn't it ???
I've spent countless hours searching out stuff like this. As you said, there's tons of stuff just like this out there if you take the time to look for it. Model railroad forums like MR and others will scratch the surface and usually provide you with some good basic answers, but if you really want the "meat and potatoes" you gotta hunt this kind of stuff down. I've saved all kinds of sites containing information like this - it's out there, you just have to find it.
Shnikies! Thanks for your replies guys! This is definitely a lot more complicated then I thought.
You need a Lenz Gold with the Power Module attached. They are sold at Tony's Train exchange pre soldered on for $75.
Are these Lenz decoders something new or will the price on them be coming down soon? Also, tell me if I understand this right. I need to buy a Lenz decoder and a USP unit in addition? If so is it possible to attach these USP units to a different brand of decoder?
Bias them in reverse, minus-to-plus and they go bang.
That is definitely good to know! I hope you did not learn this from personal experience.
Rich and Mark, thanks for the link. Looks like I have a bit of reading to do. Right now this looks like it might be the route I end up taking.
Thanks again,Greg
zero wrote: I need to buy a Lenz decoder and a USP unit in addition? If so is it possible to attach these USP units to a different brand of decoder?
I need to buy a Lenz decoder and a USP unit in addition? If so is it possible to attach these USP units to a different brand of decoder?
Conceptually yes, but practically, probably not. The connection that needs to be made is internal to the decoder. Lenz has broght the connection to where you can get at it, i other decoders you'd have to figure it out on your own. In theory , I think it could be done, in practice, I'm pretty doubtful.