EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: MJK on May 27, 2020, 02:43:14 pm
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Newbie (electronically!) here – though I've been watching some of Dave's videos for years – but had never thought of looking up EevBlog! And, superb discussions here, and great help, and great atmosphere – thanks to you all!
I've searched here, and on many other sites, and I've looked at hundreds of LM317 schematics, op-amps, etc, etc, without getting anything that, I think, matches my needs – so maybe what I'm seeking is impossible, or so simple that nobody has bothered to address it! (Personally, I studied VALVEs a little, over 50 years ago, but have done very little electronics since then).
Standard home alarm, maybe 30-35 years old, with an external “bell box” – containing a 12V siren and 12V strobe light. That circuit (quite thin cable) is about 50 feet long, and has a loud internal buzzer, and the 12V supply, at the other end. The old strobe light had a small PCB, with about 15 components (resistors, diodes, small trafo, caps – and one large item, maybe a cap, marked “630V, 7-Stars”! There's a glass/neon-type light on it – I've no idea what it's called; schematic and/or photos available, if useful. That light no longer works – perhaps the “light” itself is shot.
So, I got a standard LED-based strobe, with about 25 LEDs. The light flashes at about two-per-second. I've watched the current usage of the strobe light – it's interesting – it goes to about 120mA for about 2 seconds, then drops to about 5mA for another 5 seconds, and repeats that cycle.
However, when wired up, the new strobe does not work well! When the 12V is applied, at most, it might emit a few weak flashes, and no more.
My guess is that the the 12V supply is inadequate to drive the local buzzer, the long, thin cable, the old siren, and the new strobe. I'm guessing that the supply might drive 600-700mA, and that the buzzer takes about 150mA, the siren about 350-450mA, and the strobe 120mA.
So, I wonder if there's any component/circuit available that I could install (and adjust) at the feeds to the three loads, to throttle (restrict, balance, limit?) the currents going into them? Obviously, the new circuit(s) would need to use very little current – maybe a few mA each – and drop the voltages only minimally also – maybe 1-1.5V max?
If nothing is available, I guess I should search for a strobe that needs less current, or a new box, with integrated siren and strobe, and, hopefully, a max load of about 300-400mA.
Many thanks for any advice, or links, that you might have. Michael.