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Discussion Starter #1
Im not sure if this has been asked before. I did some research, but haven't found anything. Is there a way to make a current keeper/keep alive yourself? Or is there too much involved with the electronics to make it worth your while?
 

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It's just a capacitor. Many brands of decoders have solder pads to install a capacitor as a keep-alive device.

Check your decoder operating instructions. There may be useful information for you there
 

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sometimes it's just one, sometimes several, usually they are super caps ...
some decoders have both pads, even labeled, most you have to find the negative pad connections, depends on the decoder ..
it's not hard, just putsy ..
 

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Sure there's not a resistor in the circuit so the cap doesn't unload its entire 500volts all at once?
don't know where 500V comes from. The resistor (and diode) limits the inrush current to prevent the booster/command station from thinking there is a short when power is first applied if there are a large number of keep alives on the layout.

there's a circuit diagram on another site that won't appear here (.gif) showing how a keep alive is connected to the diode bridge of a decoder

super caps have large capacitance values but low voltage ratings. They need to be stacked in series to handle the voltage, but when in series, their capacitance is reduced by 1/N where N is the number of capacitors.
 

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Sure there's not a resistor in the circuit so the cap doesn't unload its entire 500volts all at once?

well, the cap -may- be rated up to 35 volt .. usually no more than that, and a diode takes care of unload duties ...
a resistor [ try 100 ohm for a starter] takes care of loading the cap up when the system powers up, etcetra ..
it's pretty easy to do, especially if the bridge negative is marked on the decoder
 

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Where is 500V coming from?
I noted 500 volts as a point. Some capacitors can store up a heafty jolt.
The real point was, just a cap isn't all there is to it. Some electronic wizzes presume everybody knows electronics well enough to include the additional components in a circuit.
 

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I noted 500 volts as a point. Some capacitors can store up a heafty jolt.
just so that nobody walks away thinking they're going to get jolted by a keep alive ...

no matter what the voltage rating of the cap, it can only charge to the voltages in the system, which in this case is ~14V. A couple 1000 uF caps aren't going to give you much a of jolt.

in college i worked on a pump laser using a couple 1F caps charged to ~600V. we discharged it with a battery cable and there was a very audible crack when we did.
 

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Good Grief! I would think a 2F cap at 600V would melt the battery cable, that's 360,000 Joules!!! When I was a young lad I had an array of one hundred 200uf 1,000V capacitors that I charged up to around 800 volts, that's only 6,400 Joules. I had a very large knife switch to dump the charge into a custom cone with a fine lead wire to start the arc, it would break coke bottles eight to ten feet! The loud crack of the arc was probably why I have poor hearing to this day, it put any gun I've ever fired to shame! Your rig would kill a herd of elephants, and I think audible crack would be a massive understatement of the sound! The shock wave coming from that would have to be been immense, hard to believe that there wasn't damage around the lab from that little experiment.

I won't even get into the wisdom of actually doing what you describe. I was a stupid high school student with no supervision when I was doing my little rig, how a college lab allowed you to do that defies any logic.
 

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Lightning! :D
No no, that's not 500 volts. Lightning gives you 1.21 gigawatts!


...it can only charge to the voltages in the system...
Voltage doesn't kill you, amps kill you. Tesla coils can pump millions of volts through your body without harm, but you can stop a heart with 1/10th of an amp. If you had to use battery cables to discharge those caps, there's no way I'd risk letting that charge go through my body.
 

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if skin resistance is 2k Ohms, what voltage is required to drive 1/10 A through your body?
According to ohms law, that would be 200 volts. However, if your skin is slightly damp, you'll have a skin resistance less than 2K!

You may be asking how I know that. That's simple, tons of people have been killed by 110VAC, so they obviously had considerably less skin resistance, or it took less current to kill them. Either way, they're dead!
 

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so are DCC voltages likely to give you a jolt even if the equipment is capable of delivering more than 1/10 A? (rhetorical)
 

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so if its an open wound, it's not going thru the skin. I don't know what the resistance is of living tissue.

or do you mean the coil, 14 kV? someone told me they got knocked across the room getting shocked by the coil.
 

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Discussion Starter #18
So what im gathering is that there really isn't a way to make a current keeper from scratch. ie schematic, video, forum. I don't know electronics to well so I was looking for a detailed description on how to build one.
 

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Stick your tongue on a 9 volt battery, you'll git a little nip! I recall determining if 1.5v batteries were good by licking a finger and sticking it on one end and then touching my tongue to the other end, good if tasted a little sour. Unlike you two, I didn't mess with high voltage! Maybe because I spent my summers working as an electrician.
 
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