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Old 02-25-2019, 07:34 PM   #21
Lemonhawk
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I think there have been several schematics posted for keep alives. Its a bigger problem if the decoder is not set up for a keep alive because the connection needs to go after the decoder signal pickoff and bridge. Using super caps may sound great but they do take some protection circuitry also. I think GRJ had something on this. Something about super caps having internal resistance.
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Old 02-25-2019, 08:04 PM   #22
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I think there have been several schematics posted for keep alives. Its a bigger problem if the decoder is not set up for a keep alive because the connection needs to go after the decoder signal pickoff and bridge. Using super caps may sound great but they do take some protection circuitry also. I think GRJ had something on this. Something about super caps having internal resistance.
It may be worth it to pay the 20-some dollars to just buy it than try to save a few bucks?
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Old 02-25-2019, 08:05 PM   #23
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I routinely work with 24VAC at work, I can grab the two wires, one in each hand, and never give it a second thought. Last fourth of July, hospital took a lighting hit, damage several controllers on their cooling system, I'm working in the boiler room, getting hot and sweaty, grabbed a 24VAC wire to twist the wires together to land it, and got zapped, not bad, but enough to get your attention. So, yeah under the right conditions, even low voltage can shock you.
For a little capacitor fun, check out this video.
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Old 02-26-2019, 04:55 AM   #24
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It may be worth it to pay the 20-some dollars to just buy it than try to save a few bucks?
too bad. were you just interested in saving money or learning something?
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Old 02-26-2019, 06:34 AM   #25
wvgca
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the advantage to 'rolling your own' is that you can make it to fit some pretty

odd shapes and sizes , not available with commercial models ..
but to each thier own , after all it's gotta make YOU happy ..
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Old 02-27-2019, 07:56 AM   #26
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too bad. were you just interested in saving money or learning something?
Both actually, i want to learn more about electronics, and save money.
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Old 02-27-2019, 07:56 AM   #27
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the advantage to 'rolling your own' is that you can make it to fit some pretty

odd shapes and sizes , not available with commercial models ..
but to each thier own , after all it's gotta make YOU happy ..
This is another advantage that I didn't think about!
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Old 02-27-2019, 10:59 AM   #28
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I have read there are some major risks with DIY keep-alives contingent on which capacitors you choose to work with. Some capacitors tout being able to store more energy but are more unreliable and thus prone to failures (literally in firey melt-down), destroying both themselves and your loco in the process. And as such, the best advice is to stick to reputable, commercially-sold products.

But I'm no expert on this topic, so just food for thought...
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Old 02-27-2019, 11:34 AM   #29
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i bought some supercaps but was disappointed when I experimented with them on the bench. They initially lost voltage very quickly before it stabilized. I assumed i just had a bad batch.

i also tried build a keep alive using 16V tantalum capacitors which are smaller than equivalent electrolytics. my engine got about 2 feet before 1 of 4 cap blew and there was a pyrotechnic display. again, i assume the caps from china came from a batch that that didn't meet spec.

just need to test well before using and verify capacitance

i have a couple electrolytic keep alives that have worked fine for years.
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Old 02-27-2019, 11:55 AM   #30
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i also tried build a keep alive using 16V tantalum capacitors which are smaller than equivalent electrolytics. my engine got about 2 feet before 1 of 4 cap blew and there was a pyrotechnic display.
Tantalum! Yes, those are the ones I read about that people said to use caution with. It sounded like they are desirable due to the small form factor, but extremely risky to bet on.
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