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Old 02-21-2017, 01:26 PM   #1
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Default Car/battery inverters with computers and related parts.

Any of you have experience with this?

I'm using a 300W modified sine wave inverter thru the cig. lighter to power my laptop (batter disconnected) and it works just fine. I did that in ~4 hour sessions so far with the engine running, the A/C and the sound system.

I'm planning to get a pure/true sine wave inverter (my search say it's needed for TV's and lights) for small camps/picnics to to power, in addition to the laptop, 2.1 speakers, a 27" LED monitor and a couple of power saving lights, to game for 4-5 hours.

Any idea what requirements needed here? According to my calculations, the above devices use a pessimistic max of 220W.

My car has a 115A alternator and, if it's important, a 88A battery. Dunno what current that alternator can give at idle, but some people say about 65A.
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Old 02-22-2017, 06:28 AM   #2
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Default Re: Car/battery inverters with computers and related parts.

If you want to use more than 140W or so then you need to wire directly to the battery with heavy gauge wire and avoid the cig. lighter socket which lacks the current carrying capability to handle more wattage.

It is recommended to mount the inverter as close to the battery as possible and keep the length of the DC cables as short as possible. If the power need is not close to the battery, use an extension cord on the AC side.
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Old 02-22-2017, 07:06 AM   #3
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Default Re: Car/battery inverters with computers and related parts.

Agree with Strollin. I had a 3KW one on my boat fed by a bank of four 120amp/hour leisure batteries. That worked okay but my laptop wasn't overly keen on it because It wasn't a true sine wave inverter. Be careful with "pure sine wave" inverters. If you think about the way they convert DC to AC they can in no way be "pure." Ac is normally generated in a power staion or from some form of hydro electric plant. This meands that the generators are rotary machines and generating a "pure" sine wave voltage is easy. An inverter converts DC voltage to AC voltage by chopping the voltage electronically. The more a DC voltage is sampled digitally then the closer it will come to being a pure sine wave but it will never be truly pure.

You are right that a pure sine wave inverter is needed for televisions and LED lights and some laptop power supplies.

The location of the inverter and the size of the 12 volt supply wires is critical as Strollin has quite rightly pointed out. Have a look at Land Rover restoration web sites or any Camper/caravan/boating site. Loads of info on those.
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Old 02-22-2017, 10:42 AM   #4
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Default Re: Car/battery inverters with computers and related parts.

I have a second house in the mountains that is off grid and power it with solar recharged batteries and a 1500 watt inverter. I run everything I use there.
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Old 02-22-2017, 10:45 AM   #5
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Default Re: Car/battery inverters with computers and related parts.

Cool!

Yeah, I forgot to mention that I'm gonna use it directly from the battery as the thread name suggested. The cig. lighter in this car uses a 16A fuse but that's probably to run for couple of seconds to light the lighter only, not to run continuously. The laptop is 120W.

I'm planning on putting a volt reader to monitor the battery too. I don't want it to drain. I believe 13.5-14V reading means the battery is being charged and things are just fine. Is that correct?

I thought true sine wave is the same as pure sine wave! The other two lesser types I know are modified and square since wave. But basically anyway, if the wave is full wave, does that mean any computer device can run of it just like it does at home? With basic preparations taken care of of course.
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Old 02-22-2017, 11:00 AM   #6
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Default Re: Car/battery inverters with computers and related parts.

Quote:
Originally Posted by Technician View Post
I have a second house in the mountains that is off grid and power it with solar recharged batteries and a 1500 watt inverter. I run everything I use there.
Does that include mechanical devices like fans and a washing machine? What sine wave type does it produce?
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Old 02-22-2017, 11:27 AM   #7
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Default Re: Car/battery inverters with computers and related parts.

A true sine wave is what you would get from a continuous rotary type generator. Inverters digitally convert DC to AC and because that entails chopping the DC to do the conversion it cannot ever be as pure as domestic AC. It is damn close to be fair and 99% of devices are quite happy with it but some, and these are mostly devices with some sort of processor, will baulk. A really cheap inverter will actually give a square wave AC. Again a lot of devices don't mind that but processor controlled devices wont like it.
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Old 02-22-2017, 05:03 PM   #8
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Default Re: Car/battery inverters with computers and related parts.

I guess the one I have now is in the middle then. I took pics of it:





And it comes with a cig lighter connection:


and a battery clamps connection:

that can just screwed on.

Yeah, I made a mistake before. It's 400W continues.

Here's the attached guide:


It's weird that it includes small TV's VCR's, lamps and fans. I guess this is expected from a Taiwan made inverter (?). Could the used modified sine wave scale in this model have a good number of steps on it to actually run those devices safely enough? That's the only explanation. Having many steps on the modified wave form could give closer performance to pure sine wave that less steps, I believe.

Is it safe to experiment on it with my subject devices? Non of them use motors. And if yes, should I just forget about testing the lights on it?
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Old 02-23-2017, 03:25 AM   #9
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Default Re: Car/battery inverters with computers and related parts.

Problem is you cannot really tell how good or bad they are without scoping the output. You are right that the less steps there are in the output waveform the closer it will be to a clean sine wave. The problem is that a square wave is made up of lots (we were told "all" in training many moons ago) of different frequencies. All equipments will take an average of the produced waveform and the average frequency of that waveform could be a long way away from what the device needs to work. The less square bits in the modified waveform the better and the closer the average frequency is to what the device needs.
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Old 02-23-2017, 03:30 AM   #10
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Default Re: Car/battery inverters with computers and related parts.

Again the problem with experimenting with your devices is that who knows what will happen. Chances are that they will work, in fact a very good chance. BUT I would hesitate to recomend testing that way. Best way is to scope the output and see how clean the wave form is. There are other items of test equipment that can be used but these are expensive and really you are going down the road of lab testing then. In that case it, probably, is cheaper to risk your dosmestic devices. But don't forget mains voltages are highly dangerous and low voltages can cause fires so make sure that you are going to do any sort of testing SAFELY.
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