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Thread: general inverter question

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    general inverter question

    As I know there are a fair amount of electrical guys on here:

    Just went through 4 hours of load shedding. Now I want to connect an inverter to my car battery - just to run my 32inch LED TV and DSTV player.

    Could you maybe tell me VERY ROUGHLY

    1) What sort of inverter I would need - thinking a 500W modified sine should be ok?
    2) How many hours can be safely taken out of the battery (standard 12v car battery) - I do not want to kill the battery!

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    Platinum Member SilverNodashi's Avatar
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    Quote Originally Posted by Pap_sak View Post
    As I know there are a fair amount of electrical guys on here:

    Just went through 4 hours of load shedding. Now I want to connect an inverter to my car battery - just to run my 32inch LED TV and DSTV player.

    Could you maybe tell me VERY ROUGHLY

    1) What sort of inverter I would need - thinking a 500W modified sine should be ok?
    2) How many hours can be safely taken out of the battery (standard 12v car battery) - I do not want to kill the battery!
    1) I have done this many times with a cheap 300W modified sinewave.
    2) how many Ah is your battery? Work out how many Watt your TV uses (quite often about 70% of the rated wattage on the sticker), then time 12V x (let's say your car battery is, ) 45A, which gives you 540Wh (Watt/Hour). Divide that by half, now you sit with 270W/h. If your TV uses 100W, you have about 3 hours's TV time. Then you need to calculate your losses, on the cable, the inverter's power factor (0.8?), etc.
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    Diamond Member Justloadit's Avatar
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    Reliant on the inverter shutting down when the battery voltage is low, is an "already" to late stage, as the battery is discharged to very low point. A number of these discharges around 30 or so, will damage the battery. When the load is switched off, the battery voltage will increase again, because of the electrolyte sort of recovers from the load, and the inverter switches on again, and then switches off again, not good for the battery or load. You should have a latch circuit which monitors the battery voltage, and as soon as it reaches 11V, switches off and remains latched until the battery is charged again.
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    Good point. Will monitor the voltage every 30 minutes or so the first few times -certainly do not what to mess up the car battery.

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    Full Member ghostwriter's Avatar
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    it does work but the battery will not last very long I used a spare battery for 3 months on and off running a 500Watt inverter for my small TV and DSTV i killed the battery. charging it doesn't help because the plates eventually bend. Get yourself a deep cycle battery and a proper charger for it. it is worth it because you can watch for longer and a proper charger will keep it going for much longer. mine is a year old now use it for camping had no troubles.
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    Diamond Member AndyD's Avatar
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    I'd also suggest you don't use a car battery, I doubt it will last long and will be an expensive option in the longer run.
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    cheers guys - might just do that - will see how much they go for when my inverter arrives.

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    Went through my first bit of load shedding with my new inverter - brilliant. Check the volts a few times - in the two hours went from 13 - 12v. Bought 4 inverters, will keep one and sell the rest (R650 plus postage if anyone is interested - rated 1000W - std cheap chinese one that will take a 2 prong not SA 3 prong) - with a bit of luck will hopefully get 1/2 a deep cycle battery with the profit.

    Just a question. I've got a two prong - which then goes into ext lead. So basically live and neutral can get switched around. Obviously not a problem with all appliance with 2 prongs - but the questions is:

    What kind of appliances need the N and L to be correctly connected?
    What happens when they not? Guess a bit of a snap, crackle and pop accompanied by smoke and melting
    I thought of this after plugging in my lap top charger - was fine, but you do of course have a 50% chance of getting it right.

    Lastly, the unit has a usb port - while I understand that is fine for charging phones and small devices, could that charge a laptop? As in USB - USB? Or am I just being stupid.

    My knowledge on electricity is obviously a lacking!

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    Diamond Member AndyD's Avatar
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    The thing that makes a neutral a neutral and a live a live is their voltage with respect to earth, a neutral is always at 0V WRT earth. I think you'll find the output live and neutral of the inverter are just floating with respect to earth so there is no live and neutral as such, just two wires that have 230v between them.

    It can supply any 230v appliance without damaging it, regardless of which way around it's plugged in but there's a safety issue especially if it's supplying more than one appliance in close proximity. It shouldn't really be used to supply any appliance that requires an earth ie any appliance that isn't classII because it won't be earthed when it's plugged into the inverter so if there are faults there's a chance of getting a shock.

    This type of inverter is basically a camping inverter and shouldn't be wired into a DB, it should only be used with an extension lead.
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    Thanks for that Andy - even I could follow you.

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