On Tue, Dec 14, 2004 at 12:52:47PM -0600, djgoku wrote:

Reading on some solar panels that are out there I found these since my computer is using around 300 watts with monitor. I'm kinda confused on what Approx. Watt-Hrs / Day = 1200 - 1500. I know you just can't run your computer off these panels but you would need a battery of some sort for the panels to charge. But does that mean that it charges 1200 -1500 watts/ a day so you would need a couple 700 watt batties or? Most car batteries are like 300-700 watts no? not crank just the storage part if that is what it is called.

http://www.icpsolar.com/ssfamille.php3?id_rubrique=56

From my read of the "my laptop ate my TV" thread, I know there

are people on this list who have more experience doing these kinds of calculations and can probably explain it better, but here goes:

A watt is a unit of power. Power is a measure of energy transferred per unit time (electricity being just one way of delivering power) watt-hours are a (common, but non-SI) measure of energy. Energy is something that gets stored, power isn't.

The SI unit of energy is the Joule (J). A watt is a rate of energy transfer equal to one Joule per second. So, a watt-hour is 3600 joules (1 joule/second * 60 seconds/minute * 60 minutes/hour * 1 hour).

When speaking of batteries, watts would be relevant in the sense of how fast you could charge or discharge the battery, but not so much in terms of what its storage capacity would be. A common (but again, non-SI) unit of battery capacity is amp-hours. Amps are similar to watts in that they are a unit used to express the rate of transfer of something. In this case, though, instead of it being the transfer of energy, it's the transfer of charge. The SI unit of charge is the Coulomb, which is the charge carried by one mole (~6.02E23, in other words, a whole lot) of electrons. The flow of one coulomb (C) per second is an amp. So, one amp-hour would be a charge of 3600 coulombs.

Now, the one missing piece here is how to tie the amount of charge to the amount of energy. This is where potential, expressed in terms of volts, comes in. One volt is one joule per coulomb. So, every amp from a 12 volt lead-acid (ie, car) battery translates into:

1 amp = 1 C/s * 12 J/C = 12 J/s = 12 watts

A typical home circuit, let's say a 15 amp circuit at 120 volts, provides:

15 amp = 15 C/s * 120 J/C = 1800 watts

and so on and so forth.

Aside from blue-skying about solar power possibilities and trying to figure out battery capacities, getting a handle on the arithmetic and factor-analysis involved is useful for sizing power supplies, among other things.

I was just shopping at Radio Shack for some DC power supplies for some hand-held consumer electronics devices we have (a TV and a digital camera--there seems to be no substitute for actually trying out all those little tips) and we ran through some rough calculations to make sure that the 800mA power supply I was looking at had a transformer big enough to supply the TV (which, I figured, needed a bit over 500mA). The specs given for the two devices, the power supply and the TV, were not expressed in the same terms, exactly, so we had to do this kind of conversion.

Beyond this, there are other fun things you can do, like digging up the factor for converting between British thermal units and joules, and, with a couple of utility bills, figuring out just how much more expensive it would be to heat your place with electricity instead of gas. (Or, to turn that on its head, you can figure out how much your computer hardware habit is contributing towards your heating needs in the winter, and what kind of cooling burden they place on your AC in the summer, since all the electricty consumed gets dissipated pretty much as heat, all but for that bit of monitor and LED glow that escapes the house through the windows).

One can also use this sort of thing to help understand the appeal/practicality of heat+electricity co-generation, fuel cells, hybrid vehicle powertrains, etc etc.

Good times for geek minds.

I have spent $70 on a 400VA 700W apc UPS, I would like to seek out another alternative that maybe better. I wouldn't mine making something that would that would cost a little more then what I paid already that would say better quality and will last longer. How long do UPS batteries last do they need to be changed every couple of years? I would like for all my computers to last 2-3 days if needed... How much are marine batteries and how do you charge them? How you know how much juice it currently has? Do you charge them periodically? And is all this in an enclosure that could pass safety regulations?

Thanks,

jonathan

On Wed, 15 Dec 2004 10:29:03 -0600 (CST), Duane Attaway dattawaykclug@dattaway.org wrote:

On Tue, 14 Dec 2004, djgoku wrote:

...

Reading on some solar panels that are out there I found these since my computer is using around 300 watts with monitor. I'm kinda confused on what Approx. Watt-Hrs / Day = 1200 - 1500. I know you just can't run your computer off these panels but you would need a battery of some sort for the panels to charge. But does that mean that it charges 1200 -1500 watts/ a day so you would need a couple 700 watt batties or? Most car batteries are like 300-700 watts no? not crank just the storage part if that is what it is called.

http://www.icpsolar.com/ssfamille.php3?id_rubrique=56

Since this stuff isn't at Walmart yet, the possibilities are only limited by imagination...

My marine battery will power my computer and the stuff on my desk for about five hours, perhaps longer. If I were going to rely on solar power, I'd want at least two days of not having to worry. I could be pendantic about math calculations and measurements and push things to their physical limits, but its never exact in the real world. So, let's make that 10 125Ah marine batteries and call it two days.

Now, we could attatch the solar cells directly to the batteries. There's only one problem though. When the batteries reach full charge, the cells will gas the water right out of them. Then the batteries are no good, except for boat anchors. We need a charge regulator that combines the output of the solar cells and maintains the batteries. The charge regulator can have its own inverter and switchgear so it can interface directly with the AC mains. Its all up to you what to get.

What do I use? I use a cheap APC power supply that toasted its batteries in the usual 2 years. When I get solar panels, I'm going to install a DC to DC converter to isolate the panels from the batteries and maintain the charge. That's because UPS supplies usually have the battery tied hot to the AC mains and extending the circuit out to the roof. We don't want corrosion of the panels or a fire hazard, so isolation is a good thing.

How many solar panels? I'd go many as possible and see about getting a peaking inverter that will take excess power and put it directly into your AC mains. That circuit will require monitoring of the utility mains in case there is a blackout and linemen are working in your back yard. We wouldn't want to energize the pole in your backyard when the guy is crimping on new connectors.

Oh, I can push an average of 200 watts of power from my exercise bike. A hamster can put out enough power to light a LED. Must not forget all sources of power that can run our computers!

http://www.otherpower.com/hamster.html http://www.otherpower.com/otherpower_experiments.html

-=Duane http://dattaway.org

Dunae,

I've been under the impression that the more conventional liquid-based automotive or marine batteries were more prone to discharging noxious fumes - vaporized acid and hydrogen being of chief concern. In discussions of using them for solar power they warn to make sure that the batteries are both enclosed and safely ventilated.

The term Gas Recombinant cells certainly implies that they wouldn't pose as much of a problem. What about the "gell cells" that are originally supplied with stock UPSs?

If the stock cells are as bad as conventional "wet" cells, then wet cells wouldn't be any worse and all you'd need to worry about is keeping the "box" upright. ----------------------------------- Further notes on battery types:

Motorcycle batteries are subject to more radical changes in orientation, and usually vent through a tube that can be routed away from things that acid might harm.

Miatas and some other cares now use a battery that has a sponge-like fiberglass fill that gives some of the advantages of a gell cell while not having the problem of the gell shrinking away from the plates.

In aviation, it's more common to see "wet" Nickel-Cadmium batteries as well as conventional lead-acid batteries. NiCads deliver higher current for a longer time than equivalent weight lead-acids. (There has been a lot of advance in conventional battery design, but aviation tends to stick with old tech because it's tried and true.)

There's a lot of information on the web and in the public library on alternative power systems, particularly oriented toward solar and wind, that use batteries for storage and load leveling. I'm sure some research would pay off. --------------------------- Duane, you could take some of the posts you've made over the last few years and make a "UPS Upgrade HOWTO" - as I recall you have somthing like that already on your web site.

Duane Attaway wrote:

On Thu, 16 Dec 2004, Jonathan Hutchins wrote:

...

Miatas and some other cares now use a battery that has a sponge-like fiberglass fill that gives some of the advantages of a gell cell while not having the problem of the gell shrinking away from the plates.

Hopefully, lithium and nickel hydroxide batteries will overtake lead acid. Lead is so cheap to make batteries with, so it might be a while. Lead acid batteries go for about $1/pound.

If you're looking for a "beefy" sealed replacement for the gel cells common to most UPSs, and don't want to risk acid spills all over your floor, take a look at absorbed glass mat lead-acid batteries (which is what I think is being referred to above).

These have been sold for years as military batteries, made by folks such as Hawker Energy (http://www.hepi.com/). These are also big on the combat robot circuit, where you have to have sealed, spill-proof batteries for when your 'bot gets chewed up by the opponent (or the floor saws, etc.). The 'Odyssey' line is pretty cost effective and used by many 'bot-heads, but those with bug bucks will sometimes use parts from the military line (ie: BioHazzard http://www.robotbooks.com/biohazard.htm).

You're beginning to see glass-mat technology in high-end automotive batteries (sometimes called "spiral cell", since the glass-mat electrolyte and the electrodes are frequently rolled together the same way as an electrolytic capacitor). Look for "fully sealed" and "absorbed glass mat" in the battery specs to make sure you're buying more than some fancy marketing hype.

On Thu, 30 Dec 2004, Leo Mauler wrote:

Has anyone looked into the price of one of the smaller fuel-cells? I've heard prices are down around $8,000 for a fuel cell which can provide the electrical needs of a small house.

Keep a small solar array to produce the hydrogen for the fuel cells, and you've got your own electricity generator which is essentially powered off the sun and water, without having to worry too much about long cloudy periods, especially in the winter months. Hook that bicycle generator up to the hydrogen-producing unit to make exercise do more than burn off the calories.

With solar arrays to charge batteries coming in at around half the cost of a fuel cell, but only producing one tenth the energy produced by the fuel cell, it seems worth it to look into the fuel cell technology if the end goal is to have a reliable source of energy if the main AC power lines go down. If the end result is a much lower power bill as well, this is a major bonus.

The stuff to play with is getting cheaper and more available every year.

I can produce about 200 watts on the exercise bike, compared to running. The sun puts out 1,000 watts per square meter on a good day. Our solar cells can make 130 watts out of that square meter. Storing hydrogen gas in bottles is fun.

Its going to be a while before it becomes popular (20 years and then some.) Once the prices of well designed inverters and switchgear saturate the market (competition and lack of patents) it will become viable. Placing anything on the market these days for the small guy seems to be legal suicide. There's always someone who pops up and claims rights for every idea possible.

-=Duane http://dattaway.org

Jonathan Hutchins wrote:

On Thursday 30 December 2004 02:07 pm, Leo Mauler wrote:

...

Keep a small solar array to produce the hydrogen for the fuel cells, and you've got your own electricity generator which is essentially powered off the sun and water, without having to worry too much about long cloudy periods, especially in the winter months.

The only application where I've seen fuel cells used for solar electric storage is in space, where I presume the weight penalty of conventional batteries makes the difference.

In any case, adequate, even practical systems already exist using conventional batteries instead of fuel cells, so if you're interested in this there's no reason not to go ahead and do it.

RE: weight penalty . IF weight is not a factor look to scrapyards ! Lift truck batteries of obsolete casing styles still possessing years of life often go for the scrap lead price - you haul at your own risks and as is- no warranty of course. Now if you have a good working relationship with a yard they can be bribed into letting you charge a battery over a sat nite thru mon morning to see if it takes a charge- Bring your own charger. Though at times a scrapped lifty may have an onboard charger mated to that pack ! Then by restrapping cells and the routinely overlooked concept of simply disconnecting some dead cells you can make a pack voltage to your needs. DO be painfully aware of the quite potentially lethal nature of screwups . Though lead-acid is humorously most dangerous from it's HYDROGEN outgassing . Google Usenet groups for " battery box " and safety - sadly a large flamewar .

Also the large gage wires needed for serious home power projects can be scrapyarded for the copper market price - usually 15-30 cents on the dollar of virgin wire at WORST .

Due to the dotcom bust truly cringemaking quantities of GOOD inline inverters - 100% duty cycle @ full rated load were literally sold for scrap. In 1000 Lb. average weight - cabinets and often intended to fit thru a 36 inch doorway . Shostak metals in KcKs and several of the smaller scrapyards along the rust belt in this area still get these in at times. Often you can get a 200 amp PER LEG @ 240/120 inline inverter for a few hundred bucks -scrap metal prices . DO be careful to inspect carefully as some have been deliberately "decommissioned" by removal of a brain board or other overt sabotage . And also cruel destructive torch cut up removal renders it mere scrap- or perhaps roll your own parts ? Then again often they were scrapped when a company outsourced their server farm and a 2 year old Libert or APC power and cooling system got curbsided as obsolete to the company . Truly a sin !

Where these big iron cored transformer behemoths shine is in near full load operation . Tutorial on SMPS on request but the efficiency of inverts is greatest at a certain % of design load -almost a 60% variance from min safe load to max safe load in some situations . SO running your whole house on a surplus APC rack is not insane . The bonus comes because some units in this class were designed to interface with external gensets and handshake with the genset in closed loop . A little interface hacking- possibly using a Linux app ? and your battery bank reloading source can be synced to interact peaceably. No breaker trips or regulator wars . Note well that the over/undervoltage sensing on big units is often by remote shunts .

Leo Mauler wrote:

The "low cost dirt cheap" method would be to charge car batteries off a solar or other renewable grid ("bicycle power" is inadequate to the task of charging car batteries, though it might run a laptop) and use them with an inverter to run a laptop's conventional AC adapter.

According to one of the charts at http://www.minoura.jp/index-et.html, I'm putting out about 350W when I ride my trainer in the morning (for short periods, admittedly). My laptop's power supply puts out 72W.

Those with more electronics experience might be able to rewire the laptop to use DC power directly, but stepping down the car battery to the laptop battery power level might require enough complexity that just an inverter with the existing AC adapter might be more workable.

My laptop takes 16 VDC, and automotive adapters are readily available. Couldn't you just use one of those?