[Home Stay - Stay Alive Movie In Hindi Free Download 3gp
Everardo Laboy
I do not think there's any secret regarding making a decent DIY stay-alive. But there is always a way to improve.
I was wondering if it was possible to make small supercapacitor based stay-alives. I recently found a relatively cheap and small supercapacitors 2.7V 0.35F of dimensions 12mm x 5mm x 5mm.
Since I am using a 12V DCC system and five capacitors can bare up to 13.5V, I did not use a Zener diode for protection, just a current limiting resistor and a drain diode. The finished product measures 30mm x 12mm x 6mm and could be made even smaller by removing the protective layer from the capacitors and using finer heat shrink tubing and an SMD diode and resistor. However, these dimensions are sufficient for most of my locomotives.
Several points: In practice, designers leave plenty of safety margin here. A common practice is to use capacitors that are rated to withstand twice the maximum voltage that you expect your design to produce. Plus, although your supplier says that the capacitors have a working voltage of 2.7v, what happens if a marginal batch gets shipped to you that is 5% below spec, with a working voltage of 2.565? A stack made of those has an actual working voltage of 12.825v-- getting pretty close. Your supplier doesn't state the tolerance for its working voltage spec, but if I were betting, it would say it is no better than 5%, and might be 10%. And don't forget, some low cost suppliers ship product that doesn't fully meet their specs.
In addition, your 12v DCC system is producing a signal with a peak amplitude that is "nominally" 12v or less. However, depending on the design of your DCC system, it could go higher than 12v during a surge in the AC supply voltage or as a result of other conditions. In addition, depending on your DCC wiring, there could be ringing on your DCC signal lines that could produce spikes that exceed 12v at the rising or falling edge of the signal.
I would also note that adding a suitably-spec'd Zener Diode accross Pyg's "series capacitor chain" would act as effective Over-volt protection, with almost no appreciable increase in physical size of the overall package...
Thank you very much for the comments. Let me start with a disclaimer:
I am not recommending not using a Zener diode, I am just describing my setup. If you use a Zener diode, it will add another 2mm to the stay-alive.
Now let me continue with my reasoning: 2mm does not seem like much, but for some reason the width of virtually every Mehanotehnika train cabin is 30mm. Perfect empty space for stay-alives like the one above.
Also, I'd like to say something about low cost suppliers on AliExpress. I have been buying electronics there for six years - admittedly nothing fancy like chips for $100, but elements for up to $5 each. I have only had a problem once. The chip just would not work right. Long story short: After buying chips at Mouser and troubleshooting for two months, I found that the US chip manufacturer's manual was flawed (doh!) and the low cost supplier's chip worked just fine...
Of course, there's a chance you are getting an overvoltage from the power supply - a more unlikely cause is a faulty power supply and much more likely is a lightning strike. However, if I ever decide to play with my locomotives during a thunderstorm and a lightning induced voltage surge occurs in my home, I am pretty sure broken $4 stay-alives will be the least of my worries.
Finally, most stay-alive circuits on the internet contain Zener diodes. If the stay-alives are created with five 2.7 V supercapacitors, the Zener diode is usually 13 V. My impression is that five supercapacitors in series can handle up to 13V, and that the Zener diodes are more of a protection in case someone accidentally runs their locos on a 16V DCC system. In that case, no Zener diode stay-alive definitely means ex-stay-alive.
It seems that the biggest problem with these supercapacitor configurations is the uneven distribution of voltage between all the capacitors. I think that in my situation, putting a large resistor in parallel with each capacitor for voltage balancing would be much more beneficial than using a Zener diode. But maybe I am wrong.
No sound in mine Brian. I would see James Regier's (hope I spelled it correct) as to how he did his. There are some components that are all SMT that can be used. But I will tell you that it will run for quite a long ways with out track power.
Of course as someone has pointed out I must consider how closely together these potential insulated frogs might be in reference to how long it takes the KA's to recharge to make it across multiple ones?
I have to agree to the over voltage protection. Similar situation .... my DCC track voltage is set to 13.8 volts. I used a single 16V capacitor in a passenger car, assuming I had enough headroom. After about ten minutes of running the capacitor exploded.
I agree with you that transient over voltage due to possible ringing on the DCC bus will not be a problem due to the long time constant resulting from your series resistor-- I was incorrect in my original comment when I said that DCC bus ringing could be an issue.
Capacitors also have tolerances on the value of their capacitance. The specific 0.35F 2.7v ultra caps that you referenced in your original post do not provide a reference to any data sheet. The product listing makes no mention of what the tolerance is on the capacitance value. If you look for 0.35F 2.7v ultra caps on various distributor's web sites (Arrow, Digikey, Mouser, etc.) you see that there is a wide range of tolerances for sale, including capacitors whose C value can be as much as 30% below the nominal value. Yes, you can also buy capacitors whose tolerance for the value of C is -0% to +50%. The problem that I see is that without a datasheet, there is no way to know what the tolerances are for your capacitors.
transient over voltage due to possible ringing on the DCC bus will not be a problem due to the long time constant resulting from your series resistor-- I was incorrect in my original comment when I said that DCC bus ringing could be an issue
Actually... high voltage transients are an issue, and are an issue that many modelers, even vendors regularly ignore.Supercaps, similar to electrolytic caps, do not behave the same way across the frequency spectrum. They generally loose there effective capacitance as frequency increases. The figure below:
demonstrates effective capacitance falloff as frequencies rise above 1000 Hz in large supercaps. The smaller supercaps we use in modeling exhibit similar characteristics. The RC calculation cited previously would need to account for this, yielding much smaller time constant calculations, rendering the keep-alive ineffective as a high frequency filter.
The typical failure mode of supercaps exposed to over voltage conditions does not usually yield a catastrophic failure, but is based on the high voltage exposed, the duration of exposure, and the frequency of exposure. The actual observed failure is an incremental degradation of the effective capacitance, rendering our keep-alives less "supportive" over time.
Last, I have measured actual DCC overshoot of 207% (29 Volts+) over 60% of a DCC bit time. I have also run simulations where, dependent on DCC bus electrical properties (resistance, capacitance, and inductance, and DCC transition rise and fall times), it it is even possible to generate worse overshoot, under precisely poorer conditions.
Surely the bridge significantly mitigates "pulsing due to polarity swing",
and the Volt Reg stage minimises the severity (amplitude over time) of "overshoot" conditions?
NB I'm not saying these conditions don't happen, far from it,
and I'm not suggesting eiter Bridge or Volt-Reg are somehow immune from Hysteresis or switching-lag,
but at the Post Bridge, Post Reg point in the circuit,
where the KA is commonly connected,
are these conditions really as-extreme as "measuring straight accross the rails" suggests?
Dear Prof. Klyzlr
yes, indeed, stay alive is behind the rectifier bridge. Of course, the rectifier bridge still transmits the ringing of the voltage, which as I understand occurs after any voltage reversal. So if I understand Geoff's argument correctly, the stay alive "feels" voltage of 12 V with voltage spikes of 29 V every 0.05 ms (that's half the period of the DCC signal). Yes, that's a huge spike, but it's also a very short spike, cushioned by the fact that the impedance of the 100 ohm resistor is much larger than the impedance of the battery pack, even with reduced high frequency capacitance.
Again, I am arguing only from a theoretical standpoint. In the real world, capacitors degrade even when not subjected to overvoltage. So maybe those voltage spikes can harm supercapacitors, even if simple theory can not predict it.
While I have no argument, Marko, with your theoretical calculations, I am very much in Geoff's camp with regard to capacitor degradation particularly when subjected (however briefly) to high voltages.
Any voltage applied across an electrolytic or super capacitor causes both physical and chemical changes in the materials of which it is made throughout the capacitor's life, and the voltage rating of capacitors is determined in part by their predicted life expectancy and their operational reliability based on such changes.
In the military and aerospace areas, where I spent the majority of my professional engineering career, we are only allowed to use such capacitors at a maximum of 40% of their rated voltage, ie. to operate at 12V, the capacitor must have a voltage rating of at least 30V.
While model railroad applications are obviously not subject to such rigorous rules, in my view operating your supercapacitors rated at 13.5V with a 12V supply is pushing them to the limit, and I would not expect them to have a very long life, even without the presence of high-voltage transients.
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