Thursday, 24 September 2015

07:25 – I have a bone to pick with the US federal government. Why are they wasting the time of SEAL Team Six, Delta Force, and so on by sending them out to track down and kill minor annoyances like Osama bin Laden, when they could instead be sending them out to track down and kill phone and email spammers? I’m completely serious here. I get a dozen or more spam phone calls and thousands of spam emails every day, and I’m sure I’m not alone. (Yes, our phone number is on the DNC list; makes no difference as far as I can tell. What we need is a C/EMAD Call/Email Me And Die list.) We should be relentlessly hunting down and killing telemarketers and email spammers, wherever in the world they may be. And it’s a self-limiting problem. We’d probably have to blow away only 10,000 or 100,000 of them before the rest got the message. What do you call 10,000 dead phone/email spammers? A good start.

Email from Jen. She and her husband are considering improving their alternative electric power situation. They currently have a generator and a limited supply of fuel as well as a 14W portable solar charger. The former is fine until the fuel runs out, and latter is fine if all you need to do is keep a few AA and AAA cells charged. They’re thinking about a low-end off-grid solar installation. They don’t expect to run their AC or even their freezer or furnace, but they would like a bit more solar capacity.

Jen mentioned that they were thinking about buying and installing a Renogy 400W off grid kit and had a lot of questions about whether to go with the MPPT or PWM charge controller, what other items they’d need to buy, how much actual electric power they could expect a small system like this to produce, and so on.

I told her that I’m not an expert on solar power, but I’d be inclined to go with the MPPT charge controller. If they’re concerned about EMP or a solar flare they can stick everything in a Faraday cage and perhaps buy a spare PWM charge controller. Those cost only $35 or so. Under ideal conditions, which conditions never are in the real world, they could expect those four 100W panels to produce maybe 2 kW-hours per day. Real world, I wouldn’t count on much more than 1 to 1.25 KW-hour per day, or about as much as their generator will produce in ten minutes. Still, that’s roughly 25 times as much as their little 14W portable panel produces, and enough to keep all of their rechargeable cells and small devices charged.

They would also need several deep-cycle batteries (like golf-cart batteries), along with the cables to connect their solar charging system to their battery bank and a decent inverter to output 120VAC, ideally a true sine-wave model. A 35 amp-hour 12V deep-cycle battery runs about $75, so they could expect to spend $300+ on those batteries. In a pinch, I told Jen they could recharge standard 12V automobile batteries, although their plates are designed for very high current draws for short periods of time (running a car starter motor) rather than low current draw for long periods, and using car batteries to substitute for deep-cycle batteries would greatly reduce their useful lifetimes. The price of an inverter is determined by its output waveform–square-wave inverters are cheaper than sawtooth or modified sine-wave inverters, which in turn are cheaper than true sine-wave inverters–and its peak/sustained amp rating.

Although I didn’t suggest doing so, I told Jen that they could also get by with buying only the panels themselves and some batteries, doing without both the charge controller and the inverter. These panels output about 18V under ideal conditions, which means they actually output considerably less voltage under real world conditions. They could hook up panels in parallel to provide that same less-than-18V output and run it directly to their battery bank to charge the batteries. They’d have to keep a close eye on things to avoid over-charging or self-discharging but it could be done, although I’d recommend spending the $35 on a basic charge controller. Either way, they could keep a significant amount of energy stored in their battery bank, which they could use with a battery charger intended to operate on normal 12V vehicle power. They’d be able to keep a boatload of 1.2V NiMH cells charged, as well as small portable electronics like emergency lighting, radios, tablets, or notebooks.