Coming to grips with inverters - much to learn, I'm still a bit clueless

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MisterBigglesworth

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Looking at getting an inverter. Did a bit of reading up here...and starting to get an idea of what they are and how they work etc, complete noob here BTW.

So I saw this 800W inverter here.

Input Voltage: DC 10-14V
Input Current: 0.3-25A
Self-Consumption: ≤ 1.5%
Output Voltage: AC 180 – 255V
Output Frequency: 50 – 60Hz
Click to expand...

I would like to run a lamp, old Samsung 40" HD LCD and DSTV Explora on it as a minimum (maybe add an extra light or 2 if it can handle it). From what I read, I need to calculate the watts each item uses and then that should give an idea if this 800W inverter will suffice. Is that right? Read somewhere else about amps per hour (don't know what that means) :eek:

Other question - loadshedding is generally 2.5hrs max...will an 800W inverter running the above be enough to power those items for at least 2.5 hours?

Cheers
 
spiff

spiff

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Oct 17, 2007
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to give you an idea of what you can run

I have the following running off my 1000w PSW inverter powered by a 105Ahr battery

1 x SD Dual view PVR

1 x old 51' CRT tv

1 x 14w LEd light

the above components draw +-300w while running on eskum power

I've had this combo run for 3hrs once when eskum could not switch us back on - but you don't want to go to low with the battery - best to add another battery.
 
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AntennaMan

AntennaMan

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I recently bought myself an inverter for running the TV and a couple of lights while the power is out. The calculations I am going to list is a good starting point and should be valid for solar / pv systems to a certain extent. My reasoning for my specific system is that we are renting, so I can't go the generator of solar route. All of the examples are from my specific case. Plug these equations into an Excel spreadsheet and watch the magic happen. Rounding is allowed...

Step 1:
First decide what you want to run and see how much each power component uses:
1x TV = 117W
3xLights = 33W
1xInternet Router = 20W, Because, priorities :)

Total power=170W This value must be lower than your inverter spec. Remember startup surge power can be 2-3 times normal usage. Inverters usually have a normal power spec and a surge power spec.

Step 2
How long do you want to run your appliances?
6 Hours

Calculate Watt-Hours
W-Hrs = W x Hrs = 1020 W-Hrs

Efficiency of inverter
n=85% This is a general rule of thumb. There are various factors determining inverter efficiency. Usually a higher load on the inverter will have better efficiency. Thus 800W load on 1000W inverter might have 95% efficiency.

Watt-Hours adapted for efficiency
W-Hrs = W-Hrs / n = 1020 / 0.85 = 1200 W-Hrs

Step 3
Determine battery capacity required. This depends on the system voltage (12V, 24V or maybe even 48V). Also keep in mind that deep-cycle batteries should not be discharged completely.

Voltage of system
V-sys = 24V Thus 2x 12V batteries are required

Minimum capacity needed
Amp-Hrs = W-Hrs / V-sys = 1200 / 24 = 50Ah
This is the minimum required. Double de-rate your system to be safe. Thus you need at least 100Ah in total. 2x 50Ah deep cycle batteries should then be good enough.
My personal system has 2x 105Ah deep cycle batteries.

Step 4
Calculate battery usage, just to be safe.

Number of batteries = 2
Battery capacity, each = 105Ah
Total battery capacity available = 2 x 105 = 210Ah

Battery capacity used (in %) = 100 - (Amp-Hrs/Capacity available x 100) = 100 - (50/210x100) = 76%
Thus if the load is correct, and the efficiency is correct and your batteries are still in their prime, after 6 hours of usage 76% of the battery should still be available (thus 24% was used).
 
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heartbroken

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