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DavidS
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Low Power.

Sun Mar 05, 2017 4:58 pm

Having made a quick mention in another thread, I do not want to hijack the other thread.

As I am sure that many RPi users are among those attempting to use as little power as possible I feel this has a place here in off topic land. The Raspberry Pi is after all a completely usable computer that uses less power than most peoples cell phone (if you have a cell phone).

For us the thing that makes some things obsolete is there power consumption. As such we look always for ways to reduce our power usage. For some this is because we wish to reduce the size of our active solar system and have more backup panels. For others this is to bring down the power bill, as $20 per month is a lot.

For me I am keeping my solar system as small as possible. To this end I begin with using a 450 farad super capacitor bank to store power, as it wastes a lot less than lead acid batteries.

For lighting I use single white LED's, at most 4 per room. As my power source is 12v DC this has no loss of conversion.

For fridge I use a low power electric cooler box, that keeps its internal temp up to 40 degrees F below ambient, and thus must be in a room of 78 degrees F or lower. This draws between 20 and 45 watts when cooling, nothing otherwise, and is thermostatically controlled.

For cooling I use a custom 12 volt evaporative cooler that draws up to 20 watts.

For heating I use a small custom wood gas stove, that also burns the solid charcoal it produces as a waste product.

For laundry I use a human powered washer, with a clothes line to dry.

For computers I use Raspberry Pi with 0.3 watt composite monitors.

For cooking of any kind I use a solar stove and solar oven.

I do have a 3D printer that takes more power than I would like, though I am building a lower power replacement for it.

The modem provided by my ISP takes way more power than I like (12 watts) though there is nothing I can do about that.

I know there is more I could do to further reduce my power usage, though I have to take my time do to limited resources in other areas (like money).
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emgi
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Re: Low Power.

Sun Mar 05, 2017 5:42 pm

So just about the only thing we don't know yet is where you go to take a crap.

Conventional toilets waste a lot of water.... :mrgreen:

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Re: Low Power.

Sun Mar 05, 2017 5:45 pm

emgi wrote:So just about the only thing we don't know yet is where you go to defecate.

Conventional toilets waste a lot of water.... :mrgreen:
Interestingly the folks who want to live "off-grid" are going to use a digester to turn human waste into a valuable source of methane.
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DavidS
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Re: Low Power.

Sun Mar 05, 2017 5:46 pm

emgi wrote:So just about the only thing we don't know yet is where you go to take a crap.

Conventional toilets waste a lot of water.... :mrgreen:
LOL.

I have not used much water in an out house yet.

Though that is not the only thing, my hot water is from solar, my water well pump is wind powered.

Now I think you know about everything about my waste of resources :) .
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Re: Low Power.

Sun Mar 05, 2017 5:51 pm

Ok I left two out:

My quad runner (my only vehicle) takes about 1 galon of fuel for 120 miles (about 1 liter per month).

And my electric wheelchair takes about 500 watt/hours to charge from near dead (hence why I prefer to use my manual wheelchair).

Now that should cover pretty close to everything there is to know about my waste of resources.
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Re: Low Power.

Sun Mar 05, 2017 7:30 pm

8-)

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DavidS
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Re: Low Power.

Mon Mar 06, 2017 6:34 pm

I realize that while everything releated to day to day life take very little power now, I do not have any way to complain about the 5 watts that an HDMI monitor draws. Not when the other things I use are taken to factor.

I have my metal working lathe, mill, drill-press, hot air soldering station, normal soldering station, soldering oven, etc, etc. A bunch of tools that pull more power than I even want to think about, and they are tools I use way more than I use my Raspberry Pi systems (my only computers that are in use at all).
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Re: Low Power.

Fri Mar 10, 2017 2:07 am

In irony I had to dig out some AGM SLA batteries to add in to the system.

This conversation (as well as the portion in the other thread) made me realize that I could afford to hook up an HDMI monitor, as well as an x86 PC. Well that put it over the limit for the super capacitor bank, so until I can expand the capacitor bank it is temporarily back to SLA (or not using the x86 PC after dark, unless it is windy enough to keep up :) ).

Now I have feelers out for a working but free digital camera locally. Then it will be time for photos, as requested by Heater.

Though I am attempting to find a taker to trade a Raspberry Pi 3B with case and US 110v power supply for 2 Parallax P8x32A Propellers in 40 pin DIP, 2 32KB (256Kb) I2C EEPROMs in DIP, and one Prop Plug. That is to save power to reduce the temptation to use the RPi 3B (the 2B is bad enough, and adding an x86 PC is terrible).
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Re: Low Power.

Fri Mar 10, 2017 2:29 am

I really want to see a picture of this super capacitor bank.

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Re: Low Power.

Fri Mar 10, 2017 3:10 am

Heater wrote:I really want to see a picture of this super capacitor bank.
Camera does not come overnight, you will get the chance to see it once camera is available. Not that it is really a big deal, just a larger version of the capacitor banks a lot of people use to replace the batteries in there cars.
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Re: Low Power.

Fri Mar 10, 2017 3:44 am

DavidS,
...just a larger version of the capacitor banks a lot of people use to replace the batteries in there cars.
That is the thing.

I have never heard of anyone replacing the batteries in their cars with capacitors.

As far as I know it's not possible to put so much energy into any normally available capacitors.

To be frank. I don't believe a word of it.

I want to know, how many Farads you have there. Charged up to what voltage.

Then I can judge how much energy you have stored.

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DavidS
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Re: Low Power.

Fri Mar 10, 2017 3:55 am

Heater wrote:DavidS,
...just a larger version of the capacitor banks a lot of people use to replace the batteries in there cars.
That is the thing.

I have never heard of anyone replacing the batteries in their cars with capacitors.

As far as I know it's not possible to put so much energy into any normally available capacitors.

To be frank. I don't believe a word of it.

I want to know, how many Farads you have there. Charged up to what voltage.

Then I can judge how much energy you have stored.
Step one, do a search for car battery replaced with capacitors, you will find it to be fairly common practice (though relatively low power banks of only about 4 to 15 farad at 13 volts). Then we can talk about the rest. First step is for you to believe something that is both true and common place, then the expansion on that idea can be discussed.

In other words look it up, as not believing that it is used in cars is like not believing that some people wear tennis shoes (aka tinni shoes, tinni runners, running shoes, etc). We first need to establish the more common, and then we can talk about what you do or do not believe about my setup.
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DavidS
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Re: Low Power.

Fri Mar 10, 2017 4:24 am

Heater wrote:DavidS,
...just a larger version of the capacitor banks a lot of people use to replace the batteries in there cars.
That is the thing.

I have never heard of anyone replacing the batteries in their cars with capacitors.

As far as I know it's not possible to put so much energy into any normally available capacitors.

To be frank. I don't believe a word of it.

I want to know, how many Farads you have there. Charged up to what voltage.

Then I can judge how much energy you have stored.
As my first responce to the same, do a search for replacing car battery with capacitors.

It is the common place use of capacitors in place of car batteries that prompted me to do the same for my house solar. Yes it has limited me a bit, as there is a limited amount of usable power stored (charges to 13.4 volts, and most things that require 12 volts stop working somewhere around 10 volts). Though without a common ground of understanding, I could show you photos all day once I have a camera in hand, and type about the setup until I am blue in the face, it would mean nothing and still not be of reason until you see what is common.

At night I can not use to much power when just using the capacitor banks. I can not use my 3D printer, filament extruder, any heavy power tools, soldering iron, or swamp cooler after sun set. I also have to refrain from getting into the cooler box after about 2 hours before sunset till sun rise in order to minimize the power it takes at night.

Do to the same limits I can pretty much only use 2 Raspberry Pi computers (assuming power draw of RPi 3B), my lights (White LED's running off of the 12 volt directly), and one display (up to 3 if I go composite lower power). That is why using an x86 PC has forced me to use SLA batteries.

The Solar system produces more than enough power to keep up through the day, even on cloudy and rainy days, it is just after sunset that I am running on the capacitor bank.

The x86 computer that pushed me over the limit is not a power hog either. It is a fourth hand computer that came with a 12 volt 4 amp power supply (not being used, directly off of the 12 volt system now).
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Re: Low Power.

Fri Mar 10, 2017 4:28 am

DavidS,

You are winding me up right?

OK I will bite...

Before I going searching high and low, how about this:

The energy you can store in a capacitor is:

E = (C * V^2) / 2

I think you can guess the units there.

So for a 15 Farad capacitor at 13 volts we have 1267 Joules of energy stored.

Where as, a kilo of gasoline provides nearly 50 million joules !

So no, I don't believe a word of it. Perhaps a capacitor bank can start the motor. It won't get the car out of the garage!

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Re: Low Power.

Fri Mar 10, 2017 4:36 am

Heater wrote:DavidS,

You are winding me up right?

OK I will bite...

Before I going searching high and low, how about this:

The energy you can store in a capacitor is:

E = (C * V^2) / 2

I think you can guess the units there.

So for a 15 Farad capacitor at 13 volts we have 1267 Joules of energy stored.

Where as, a kilo of gasoline provides nearly 50 million joules !

So no, I don't believe a word of it. Perhaps a capacitor bank can start the motor. It won't get the car out of the garage!
True enough. Though I am not speaking of electric cars, I am speaking of good old petrol burning cars, and the battery/capacitor bank only needs store enough to start the engine, and keep what ever low power electronics that stay active in power down going between uses of the car.
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Re: Low Power.

Fri Mar 10, 2017 4:43 am

Actually David, I would delete my previous post on the grounds of misunderstanding what you meant. But won't.

I guess it is possible to replace a normal gasoline powered car battery with a capacitor bank.

For starting the motor and such.

Sounds like an expensive and unreliable thing to do. But whatever works for you.

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Re: Low Power.

Fri Mar 10, 2017 4:46 am

We are posting over each other.

Given the gigantic energy consumption of a regular gasoline powered car, what is the point of trying to replace it's lead acid battery with a capacitor bank?

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Re: Low Power.

Fri Mar 10, 2017 4:55 am

Heater wrote:We are posting over each other.

Given the gigantic energy consumption of a regular gasoline powered car, what is the point of trying to replace it's lead acid battery with a capacitor bank?
Well it is more reliable long term than a lead acid battery. It has the down fall that it needs to be kept up to charge, though it has the advantage of not going bad nearly as quickly as a lead acid battery (in some cases longer than others, depending on the choice of capacitors). This is especially true here in the desert where we are lucky if a regular lead acid battery will last a full year of normal use, lead acid batteries tend to die in a hurry in this climate.

For my system, all be it a minimal setup for solar usage, I am using oil bath capacitors of 5 farad each, with a bank having a total capacitance of 450 farad. There are two isolated and separate circuits, with separate sets of solar panels, separate wind generators, and all else, each has a capacitor bank identical. This is a system that does have its issues, though it takes a lot less power to charge capacitors than to charge lead acid batteries (do to conversion loss).

My primary goal is to run on as few solar panels and wind generators as possible, so that I can put as many as possible back into storage as backups. This is the reason for some of my extremes.

This has been a good discussion overall, it has got me looking at a lot of what I do use that I had not given to much thought to before.
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Re: Low Power.

Fri Mar 10, 2017 5:29 am

Interesting.

In the cooler climate of good old England a lead acid car battery works for so long that you almost forget about it.

I think my last car ran for about 200,000 miles with the same battery.

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Re: Low Power.

Fri Mar 10, 2017 6:13 am

I think one motivation for capacitors in cars (I have heard of that) is weight saving. Lead is heavy. I'm not convinced there's a practical benefit. I can see a point in solar of higher efficiency, although I would think the low capacity risks wasted energy if they fill up.

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Re: Low Power.

Fri Mar 10, 2017 11:36 am

I've just done a hand-waving calculation.
Halfords tells me my car (AJ 09 PZG) has a 75AH battery.

At 12v, that's 900WH, or 3MJ
To get that energy in a 12v capacitor I'd need 40,000 F.
Seems rather a lot.

At 115 v, it comes down to 450F
Still seems a lot to squeeze into a Volvo.

Or am I missing something?

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Re: Low Power.

Fri Mar 10, 2017 1:58 pm

Burngate wrote:I've just done a hand-waving calculation.
Halfords tells me my car (AJ 09 PZG) has a 75AH battery.

At 12v, that's 900WH, or 3MJ
To get that energy in a 12v capacitor I'd need 40,000 F.
Seems rather a lot.

At 115 v, it comes down to 450F
Still seems a lot to squeeze into a Volvo.

Or am I missing something?
You are missing that you do not need nearly what your battery holds. If you think about it you can crank your car for 20 minutes or more, though it only takes about 2 seconds to start the engine.
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Re: Low Power.

Fri Mar 10, 2017 2:00 pm

PiGraham wrote:I think one motivation for capacitors in cars (I have heard of that) is weight saving. Lead is heavy. I'm not convinced there's a practical benefit. I can see a point in solar of higher efficiency, although I would think the low capacity risks wasted energy if they fill up.
There is lost energy if it is not used fast enough during the daylight/windy times. There is no such thing as a perfect system (at least not that I know of).

Though if I keep close enough to using the power that is produced by the system through the day it is very little loss.
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Re: Low Power.

Fri Mar 10, 2017 2:04 pm

Heater wrote:Interesting.

In the cooler climate of good old England a lead acid car battery works for so long that you almost forget about it.

I think my last car ran for about 200,000 miles with the same battery.
That is a better climate for lead acid batteries, by a long ways.

Here we get many many days above 43* C (110* F), and enough above 48* C that it is hard on a battery. Sorry for using the asterisk for degrees.
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Re: Low Power.

Fri Mar 10, 2017 4:50 pm

I can't help thinking that if capacitors were a sensible and economic way to store electricity then we would not be using batteries all over the place. From torches and phones to Teslas.

We don't. So I guess they are not.

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