Inverters

Submitted: Tuesday, Nov 25, 2003 at 01:21
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Hello all I am wondering if someone could tell me if I am correct in thinking this. If you have a 1300w inverter but are only running a TV or videorecoder of it that is say 250w then the power consumption would only be the 250w plus a small amount for the inverter or will it be using 1300w. Please help as we are trying to decide on what audio visual to use. Car cd/radio and maybe normal TV (maybe LCD)with house type VHS DVD combo unit. Thanks Rod
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Reply By: Deleted User - Tuesday, Nov 25, 2003 at 01:23

Tuesday, Nov 25, 2003 at 01:23
G'Day Rod, You are correct in your thinking i.e. it only consumes what you have connected in a watt value not the max every time you use it. Inverter efficiency and end appliance efficiency comes into it a bit ..... an inverter has about 10% losses so it takes about 100w(12v) input to make 90w(240v). Also some appliances have a power factor (losses) of around .8 ..so consume about 20 % more watts ... this might be more to do with domestic supply rather than an inverter. Collyn might help here ? Power consumption (battery levels) by inverters can be very high because it has to produce watts from a lower voltage thereby using heaps more amps ...about 20 times ...... As an example ...... if you take an appliance that consumes 240 watts ... at 240 Volts that will consume 1 Amp ..... watts divided by Volts = Amps If the same appliance is run from an inverter running off 12Volts lets try the equation again 240 watts divided by 12Volts = 20 Amps. So the appliance is using 20 Amps per hour from your battery capacity. This is why large inverters suck huge amps from the batteries .... if you have say 300amps of capacity in a BT only 150 amp is available ( probably only 120 in a real world) this 20amp load can only run for 6ish hours before you start hurting the batteries. Try this with a 1800 watt inverter .....1800 divided by 12 gives 150 amps (leaving losses aside for now) thats only 1 hour max before you hurt batteries. I think inverters are a necessary evil in a BT . You just need to size them to your needs with some room for expansion. Some basic knowledge of what you are consuming from your batteries is a good strategy and part of good battery management in our BT's. Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker
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Reply By: Turist - Tuesday, Nov 25, 2003 at 01:24

Tuesday, Nov 25, 2003 at 01:24
Or you can apply the K.I.S.S. formula to determine battery drain when using inverter.

Appliance load in watts divided by 10 = battery drain in amps.

Microwave using 1200 watts consumes 120 amp.

Not correct to 2 decimal points but good enough for our purpose.

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Reply By: Noosa Fox - Tuesday, Nov 25, 2003 at 01:25

Tuesday, Nov 25, 2003 at 01:25
We have a 240v Television and a box type fan, and when they are used on the inverter they both draw about 5 to 6 amps, so the batteries will last a long time if you are using either or both of them. An electric toaster surprisingly doesn't use a great deal either, so it can be used for 3 or 4 slices of toast without a problem. The microwave on the other hand uses a hugh amount of power and can really only be safely used for up to about 5 minutes. Things like heaters and electric jugs, just draw too much to be used on inverters. Brian
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Reply By: Deleted User - Tuesday, Nov 25, 2003 at 01:26

Tuesday, Nov 25, 2003 at 01:26
Actually thats not bad Bob ..... a 1200w draw would consume 100 amp but then add in 10 % loss of the inverter ....another 10 amp ....cable resistance .... hot internal temp in the inverter etc ..another 10 % ish gives 120 amp draw !!!!! Because of losses divide by 10 and you wont be far off the mark. I would agree in most appliances except a microwave ....a 800w microwave typically draws 1600-1900 watts to make 800w. I'd hate to see a 1200w jobbie connected to an inverter ....they are very inefficient and gobble heaps of Benjamin Franklin juice. Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker
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Reply By: Turist - Tuesday, Nov 25, 2003 at 01:27

Tuesday, Nov 25, 2003 at 01:27
Now Anthony, I did say a microwave USING 1200 watts.
Typical for the 800 W microwaves commonly found in vans.
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Reply By: Deleted User - Tuesday, Nov 25, 2003 at 01:28

Tuesday, Nov 25, 2003 at 01:28
Brief response to inverter query. A good quality inverter is about 90% effiecient over most of its range, but may fall off to 75% or so on very light loads and also when working very hard. There's also a constant internal loss of a few watts. By and large though you can assume that the current drawn from the battery is about 12.5% more than the wattage of the load for anything that draws more than 10% and less than 90% of the inverter's capability. Regarding the power factor that Anthony mentioned: this is a phenomena that affects certain types of loads running from ac - especially motors, battery chargers and fluro lights. An adverse power factor typically requires about 20% more current to be available from the supply, but whilst it must be available it's not actually consumed! It sort of rushes back and forth 'filling in holes'. This effect is partially why you need a bigger generator than possibly expected to run a battery charger (the other eason is that most battery chargers are only 65-70% efficient). Collyn Rivers
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Reply By: Noosa Fox - Tuesday, Nov 25, 2003 at 01:29

Tuesday, Nov 25, 2003 at 01:29
I was at Sound In Motion today and they were telling me that someone (not on this forum yet) has ordered a van with that much electrical/electronic equipment in it that they doubt that his inverter will be capable of running it all. I think it is important for people who intend on running a lot of 240 volt equipment in the bush, to be prepared to run it via a generator, and not try and run everything on the battery powered inverter. The batteries are only capable of holding so much charge, and you require that charge for essential items such as the fridge, water pumps and lighting. Brian
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Reply By: Tassietracker5 - Tuesday, Nov 25, 2003 at 01:30

Tuesday, Nov 25, 2003 at 01:30
Thanks for all the replies It seams that i was correct but am wondering if i should source 12v Tv screens and 12v Video& DVD recorder so as to lower the amp consumption as I understand how valuable power is out there but I also know that to keep the piece in the family we will have to put a video on for the kids at least at dinner time to get some piece. Thanks Rod
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Reply By: Deleted User - Tuesday, Nov 25, 2003 at 01:31

Tuesday, Nov 25, 2003 at 01:31
Bob, Upon re-reading it so you did ..... accept my apology. Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker
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Reply By: Deleted User - Tuesday, Nov 25, 2003 at 01:32

Tuesday, Nov 25, 2003 at 01:32
Rod, My kids are 5 and 10 and need their fix of channel 2 or watch a video whenever they get bored or confined to barracks with rain. My Sat TV decoder and Orion combo video/tv only draw about 4.5 amps. Not a great deal in the scheme of things especially with 4 x120w panels. I was thinking of upgrading to the Orion video/dvd/tv combo but will keep the setup as it is now and add a laptop to play dvds. That will give us a way to download and edit digital pics when in the BT. Now if I can think of a third use I can get it passed the "equipment approvals director" ....[smile] The only downside is that I have to set up the tv every time as the tv wont travel in the place where it is mounted. The lcd screens and dvd/tv drives eliminate this chore. Someone with a Jaton/dvd/tv system might be able to give amps draw of that system ? Regards Anthony Explore this Great Land ...Do it Easy ...Tow a Bushtracker
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