Maybe it is because we have more than one wireless network here at the ranch (3 actually) and maybe it is because we like our off-site streaming video options, and maybe it is because I like to have a belt, pair of suspenders, a tight pair of pants, and walk around upside down to make sure nothing falls off….in any regard, this note from Radio Ranch Bill was just really damn good and worth sharing:
I discovered a couple of years back that my TelCo DSL modem, which on its rear panel wants something odd like 16 volts AC, will actually work perfectly with 12 VDC applied to the power jack. I also discovered my slightly antiquated LinkSys 54G router would also work just fine on 12 VDC.
So, I whipped up a wall-wart motorcycle battery (20 AmpHour) charger, and run the devices off the battery. (The linear charger makes a bit more juice than the boxes need, so it’s perpetual motion.)
Around here, the power wires are strung in the trees and on power poles, so interruptions are frequent. Oddly, the DSL never goes out. Lower down on the poles, and heavier wire, I theorize.
I interviewed a lineman working on one of those refrigerator sized local network boxes, and I asked how long it was good for in a power outage.
See, power for the phone used to come all the way from the Central Office huge battery room, and would last a LONG time. No more. Emergency power now comes from the small-ish battery bank in the network box. “Eight to twenty hours,” he told me. That gives us the time to bring in generators for the network boxes for a longer outage.
Anyway, you ain’t the first by a good ten years. Now, it’s all on my 400 amp-hour main 12 VDC battery bus, juiced by four 100+ A.H. flooded batteries, from four old UniSolar 100watt panels, with four Morningstar charge controllers, AND together with some big-ass diodes, and the whole affair tied together with Anderson Powerpoles for flexibility.
This opens the door a crack into one of my favorite all-time topics, robust home power. For Peoplenomics.com subscribers, there is a dandy article of three in the Peoplenomics archives, not the least of which is in the eBook series “13-Acres and Independence: Robust Home Power.”
This article (from 2008) goes through the basics of how to do a load sheet. You see, the way we actually design DC power systems is to look at loads, then (and only then) do you size the battery bank. And once you have that figured out, then you figure out how much source (for charging) you need.
So if, over the course of spring into summer, you need to do something with batteries, the steps are what?
1. Write up a load sheet. Figure out how much load you will be actually pulling and for how long.
Let’s say I need a 100-watt light bulb worth of power.
P = E * I
Which is electrical engineering talk for “Power in Watts is Equal to Electromotive Force (measured in Volts) time Current in Amperes.
Since we know we need P to equal 100 watts, and we know this will be a 12-volt system current requirement is actually P/E=I. Or 100 WATTS /12 VOLTs = 8.333 AMPS.
But now let’s suppose that the light you have is not a 12 Volt light. Suppose it is a 120 Volt light such as you have around the house.
“Shoot, Bubba, I’ll just hook me up one of them 150 watt cheap inverters to run the light…”
Well, just fine and peachy. Something like a Tripp Lite PV150 Portable Auto Inverter 150W 12V DC to AC 120V 5-15R 1 Outlet will set you back less than $30 at Amazon.
BUT remember that inverters are not 100% efficient. When I was doing DC system work, I always figured the inverter was ab out 85% efficient. So we take our 8.33 AMPs and divided it by .85 to give us power at the inverter power in. Came out to 9.8 AMPS but I just call that 10 AMPs for two reasons.
1. I am too lazy at this out to worry about decimal points.
2. Battery voltage sags over time. A freshly charged battery will maybe show 12.8 VOLTs on my Fluke 115 Compact True-RMS Digital Multimeter. BUT the way battery manufacturers work out AMP-HOUR capacity of batteries, they keep counting power as useable until the battery has come down to 10.5 VOLTS (terminal voltage under load is how you think about this).
So to keep our 100 WATT light going with a 12 VOLT Battery (a battery is a collection of cells) we need at least 10 AMP-HOURS to keep the light on for one hour.
One Amp of current for one Hour is an amp-hour. (See? This ain’t so hard, is it?)
Since we have a 10 Amp load we want to keep going for one hour, we buy at least 10 AMP-HOURS.
But realistically? Buy at least twice that. Wondering why? (Since you may be as cheap as me…)
CYCLE DEPTH is Proportionate to Cycle Life
I hand you a 12 Volt battery. You discharge it to the 100% empty level. Usually this is done over a six-hour or 20-hour load.
By definition, a 100 AMP-Hour Battery (Group 27 size, 63 pounds) will generally deliver 5 Amps from 12.8 volts down to 10.5 volts in 20-hours.
But you can’t do that very often, even if it is a deep cycle battery. You need to limit your DoD (Depth of Discharge) to 60% of capacity or your cycle life will quickly go to hell. You can full to empty a battery maybe 20-80 times and it’s a throwaway.
I happen to think the world of Trojan Battery Company. I like their T-105 Deep Cycle Six-volt batteries a lot.
This is from their spec sheet and you can see the point I am making. They claim that at a 100% depth of discharge they can be cycled about 700 times, but I would be curious about ultimate capacity along in there. I expect it would not be 100 AMP-HOURS (or 200 AMP-HOURs in the Six Volt size.
I am not as fond of other makes of batteries. I am about to swap out my original eight golf cart batteries for our 3.5 kW grid-interactive power system here at the ranch. They have been in service since 2008 and they are down to about 25% of rated capacity. These were Interstate golf cart batteries, but in fairness batteries like people enjoy that 60-80F temp range.
As temperatures go, do visit the West Marine discussion of battery types and charging. They have a dandy discussion and the West Marine staff knows a tremendous amount about batteries – at least where there are plenty of rag-boats, since as an old (reformed) sailor, there is nothing more useful than having lights to run things like the navigation system all night when you’re working coastwise in the middle of the night. Out there, you’ll want to have your radar on, too…and they can fix you up with that, too.
Main reason to think about West Marine is that they have a great battery discussion online over here.
The one thing I wanted to mention (with regard to Radio Bill’s home-made router backup power system, is what happens if you are running a small battery and you run it above the acceptance charging level for more than 1 1/2 to 3 1/2-hours.
The battery will begin to gas. When it does, it’s not really “boiling.” It’s just that the battery can’t absorb any more charge and since it is full, it will break some of the electrolyte (water) down into Brown”s Gas – which everyone knows is hydrogen and oxygen.
Battery temperatures going up (say 110-degrees) lowers the gassing voltage to about 12.6 (6.3).
There is a longer discussion available about AGM (absorbed glass matt) batteries (like the Concord we have in the plane. And the West Marine SeaGel sealed gel cells which are ideal for boats – particularly salt water fishing in a low boat that might ship a little water now and then – like a Whaler. Then sealed batteries make a lot of sense.
And that’s our safety addendum to Bill’s note.
Except to say that on our main network we use a simple prepackaged solution ($58-bucks) APC BE550G Back-UPS 550VA 8-outlet Uninterruptible Power Supply (UPS) which gives us enough power to keep not only the router up for more than an hour but also the WD 4TB My Cloud Personal Network Attached Storage.
I suppose I could have done it with a motorcycle batteries and a wall-wart…at least for a while. But when your whole life is organized as mine still is about 100% reliable connectivity, having your own streaming backup AND the backup power for the router, too, is worth the extra expense of a packaged solution.
On the other hand, the DC power discussion means you can scale and back up the freezer…
Speaking of Solar Power
I don’t usually do free ads for people, but then again, I’m an idiot.
Still, been watching solar panel cost-per-watt and the Suniva 325 and 330 watt panels are going for $0.45 a watt at Sun Electronics www.unelec.com. John Kimball and crew –probably move more panels than most other places in the country.
I also know they occasionally get B and C grade panels in (which can’t be sold in the US) but if you’re building a hideaway offshore somewhere (somewhere on Providenciales north Grand Turk would be nice…) that’s a source for you,
User Follow-Up: Chop Saw
I mentioned a week or two back about the Family Handyman ad for Harbor Freight and how I was getting one of the 12” sliding compound saws. Think of it as a chop saw that slides so you can cut a 4X8 on one pass.
OK, the first thing I discovered was that the saw came without the blade. I didn’t read the fine print.
So Elaine volunteered to hit Lowes and came back with a nice Kobalt 80-tooth blade, but it was $51 bucks by the time the governor got his cut.
As a backup, I ordered a two-pack of spares: DEWALT DW3128P5 80 Tooth and 32T ATB Thin Kerf 12-inch Crosscutting Miter Saw Blade, 2 Pack for $45 before tax.
I should have figured all this out in advance, but that would involve advance planning and we certainly don’t want to do too much of that, lest we actually get something right the first time.
Oh…one more point: See that circled area in the picture of the saw as set up in my shop? Damn interesting tale there: The back of the saw – the slidy-part – sticks out a fair distance so don’t plan on this kind of saw unless you have it in some easy-to-move configuration. A good chop saw stand is a fine thing. But without it, this is something of a space-eater.
OK, on to projects…
Write when you beak-even,