Power usages - Fiberglass RV


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Old 10-03-2013, 09:02 PM   #1
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Power usages

Maybe we can start a "power usage" thread. I have a Kill-o-watt power meter which seems to be reasonably accurate. A few measurements I have taken in my TT:

1) ResMed s7 CPap: 12 watts
2) 32" samsung LED tv: 36 watts
3) Toshiba 2 year old AMD quad core laptop (charged state) 9 watts
4) 5 year old Dell Intel dual core laptop (charged state) 22 watts
5) Asus TF300 10" pad (charging) : 3 watts
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Old 10-03-2013, 09:21 PM   #2
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Just to ask: DO the numbers you got from the kill-o-watt match the numbers shown on the devices???
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Old 10-03-2013, 09:34 PM   #3
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Originally Posted by jwcolby54 View Post
Maybe we can start a "power usage" thread. I have a Kill-o-watt power meter which seems to be reasonably accurate. A few measurements I have taken in my TT:

1) ResMed s7 CPap: 12 watts
2) 32" samsung LED tv: 36 watts
3) Toshiba 2 year old AMD quad core laptop (charged state) 9 watts
4) 5 year old Dell Intel dual core laptop (charged state) 22 watts
5) Asus TF300 10" pad (charging) : 3 watts
I believe the Kill-O-Watt meter measures 120 Volt AC power.
Now let's translate the Watts to amps for both 120 AC and 12 DC
1) 0.1 Amp 120 AC -- 1 Amp 12 DC.
2) .3 Amp 120 AC -- 3 Amp 12 DC
3) .075 Amp 120 AC -- .75 Amp 12 DC
4) .18 Amp 120 AC -- 1.8 Amp 12 DC
5) .025 Amp 120 AC -- .25 Amp 12 DC.

If you want to know how approximately much each of those will draw from your battery (12 DC) inverter or direct which ever is required multiply each by the estimated usage time.
Example 1) usage 8 hours x 1 amp = 8 amp hours.
Example 2) usage 4 hours x 3 amp = 12 amp hours.
Example 5) usage 6 hours x .25 amp = 1.5 amp hours.

That should give you some approximation of how long your battery power will last before needing to recharged.

I assumed the reason for the thread is to determine how long the house battery will last.
I did not take into account the efficiency of an inverter which would add 5% to 10%.
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Old 10-03-2013, 09:38 PM   #4
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Just to ask: DO the numbers you got from the kill-o-watt match the numbers shown on the devices???
Nope. The numbers on the device tend to be 'max' numbers, worst case so to speak. Real life are usually less.

My Samsung tv says 59w but then says 33w typical usage. I saw 36w.
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Old 10-03-2013, 10:04 PM   #5
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Yes, the point is to get a feeling for some 'typical' devices we might run on battery. The first thing they say when looking at solar is to figure out your usage, which drives your battery and panel requirements. I use the tv as a monitor for the toshiba laptop.

Right you are, the next part is an inverter to provide the ac used by the devices. The efficiency rating is typically 85-90% so watts + 15%. The total watts gives a picture of the size inverter required as well. I don't try to run any cooking or heating devices.
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Old 10-03-2013, 10:23 PM   #6
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Yes, the point is to get a feeling for some 'typical' devices we might run on battery. The first thing they say when looking at solar is to figure out your usage, which drives your battery and panel requirements. I use the tv as a monitor for the toshiba laptop.

Right you are, the next part is an inverter to provide the ac used by the devices. The efficiency rating is typically 85-90% so watts + 15%. The total watts gives a picture of the size inverter required as well. I don't try to run any cooking or heating devices.
Watts (power) is a good measure when going from one voltage to another. But it's a good idea to change all to current for battery usage since batteries are rated in amp-hours. Also when dealing with solar, the measurement of interest is amps again, because batteries are rated in amp-hours. Most solar panels specifications will give you short circuit out in direct sun in amps. That's a good starting point. In fact in measurements it works out pretty close.
Also charge controllers are rated in amps, with a lot of confusion stuff. Many, if not all, have a "load" connection. That's to be ignored unless you like spending money. I would select a charge controller based on the maximum current from the solar panel.
Example... My case, I have a 65 Watt solar panel. Maximum current is about 4.1 amps. My charge is 6 amps and I power a ham radio with one of my batteries that draws 22.5 amps on voice peaks. If I used the "load" connection I would need at least 25 amp controller at about 3x the cost.

FYI, my solar system is about 5 years old now and we spend about 3 months at a time off the grid.

You're right about not powering heating devices from the batteries, they get very hungry in a hurry.

You're on the right track.
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Old 10-04-2013, 01:42 AM   #7
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... I would select a charge controller based on the maximum current from the solar panel.
E....
Byron, most people don't have an issue with incorrectly sizing the controller but I think the bigger issue is that many controllers don't charge efficiently (correctly) and put out far less voltage than required and some aren't very well staged in cycling design; watts (lots) of panel charging capacity going to waste.
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Old 10-04-2013, 02:07 AM   #8
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Byron, most people don't have an issue with incorrectly sizing the controller but I think the bigger issue is that many controllers don't charge efficiently (correctly) and put out far less voltage than required and some aren't very well staged in cycling design; watts (lots) of panel charging capacity going to waste.
Oh? So you think it would be ok if used a 1 amp charge controller attached to my 4 amp solar panel?
I won't go into detail about your voltage concerns, most of the voltage requirements issues are myths and sales talk.
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Old 10-04-2013, 02:12 AM   #9
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John,
If you have the same furnace that I have it's about 3.5 amps when running
The incandescent lights are about 1.5 amps each.
I don't know what the water pump if have an electric water you'll need to find out how much current that draws.

I switched LED lamps and they're about .1 amp each and installed a couple LED fixtures that I modified to have two levels of like, the low level is quite enough and that's about .05 Amps. each. The LED lights along save a whole lot of power.
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Old 10-04-2013, 06:31 AM   #10
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All my lights were switched to led by the po. Thanks for the furnace info. I also have a fantastic fan, three different speeds.

There really are two different issues, overall dc power draw affecting solar panel and charger selection and then ac draw affecting inverter selection.
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Old 10-04-2013, 08:33 AM   #11
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Angry

In 1969 I was in 9th grade. I was given a bunch of ARC5 and other tube based WW2 receivers and transmitters. These came out of airplanes. A 1955 radio amateur manual was included. By the end of the year i had read the book cover to cover several times and knew ac/dc theory, tuned circuits and filters, amplifiers, oscillators, etc. All tube based of course. With the help of a ham operator we got my stuff working and I listened to the lower ham bands for hours. I practiced morse but never quite got fast enough to get my license. I did get a late 60s arrl manual and learned transistor and fet stuff, phased lock loops and so forth.

In 1972 I joined the navy and went to 90 weeks of school to repair computer mainframe and peripherals, then spent several years on a carrier fixing their systems. So by then I was into digital which i continued to fix and build my own ucomputers until 1986 when i finally moved full time to programming. However ucontrollers continues to be a hobby. In the early 80 I studied op amps extensively. All during that time i built by own computers as well as audio gear.

I never did get back to amateur radio. But i do have the background to understand and analyze every aspect of solar systems, chargers, charging algorithms, inverters etc. I know down the circuit level the various functional blocks inside these components.

It is my educated opinion that most of the low end stuff is junk. The people specing the stuff in my scamp don't understand what they are buying and assembling. They don't have a clue about battery voltage levels, amps required, wire size and resistance per foot, voltage drops on those wires, etc. All i hear is 'use 10 ga' when that is just waaaaay small for battery to anything. My pd 'all in one' is located at the rear of my scamp with my batteries about 15 feet away as the cable runs. Yea the wires to the lights are fine, but to charge the battery? No remote sense that i can see. The pd power widget should have been placed under the front seat 3 feet from the battery. Moving it is a nonstarter, everything is wired to the back seat.

As someone trained to understand the ramifications, i am seriously annoyed with my electrical system!
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Old 10-04-2013, 08:51 AM   #12
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Here is a cool calculator for voltage drop. Somebody mentioned charging a battery from the alternator. Feed this to the calculator

Dc
10g
15v
20 ft.
50 amps

You end up with 13v at the battery. Hmmmmmm

Voltage Drop Calculator
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Old 10-04-2013, 10:09 AM   #13
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CAUTION... Verbal Prozac follows:

While not a highly trained computer technician, I can claim about 12 months Navy schooling on aircraft electrical systems, that is if any one really gives a rats patootie....
------------------------------------------------------------
That said.....

Fortunately some things work well in practice, if not on paper. I have used #10 & #8 wire for battery charging lines from vehicle alternators to coach battery's for about 40 years now without every finding that my coach battery wasn't being charged adequately.

Hopefully no one is going to move more than about 15 amps through that wire when charging, otherwise a boiled over battery or warped plates are almost a guarantee. Interstate Battery, for one, indicates that prolonged charging rates over 15 amps on a group 27 battery can damage the battery.

And, anyway, most automotive alternators sense voltage at the vehicle battery and start shutting down as it's fully charged state is reached, leaving the coach battery what technically might be called "Sucking Hind T!t" based on the averaging voltages between the two or more batteries in the circuit.

In the PD-4045, Progressive Dynamics has indicated that their smart charger circuit senses battery voltage during a null period in the charging cycle (when there is no voltage drop) and adjusts the charging mode/rate accordingly. Also note that the desulfating cycle is short in duration, again to prevent damage to the plates.

Just my somewhat sophomoric take on the issues.....

As the Other Bob said:
"Don't Worry, Be Happy"
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Old 10-04-2013, 10:16 AM   #14
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I'd be surprised if 10 gauge is even rated for 50 amps....
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