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Old 05-26-2014, 09:02 PM   #1
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Time for an inverter - how to size?

Am going to be heading up to the NW Overland Rally and need to find a way to change my camera batteries and run my computer. Canon does no make a 12v charger for their batteries and neither does Apple so I need to use an inverter. How do I go about sizing the inverter. Here is what the power bricks have printed on them.

Video camera battery: input 120V 0.18A, output 8.4V 0.7A
Still camera battery: input 120V 0.2A, output 8.4V 1.2A
MacBook Air: input 120V 1.0A, output 14.85V 3.05A

Is it as simple as adding up the total simultaneous amp draw at 12V, 4.95A, and look for a pure sign wave inverter that has at least that much output capacity? Am not sure that I will have the computer plugged in at the same time as the other devices but may have.

My electrical system consists of 270W of solar and a single group 27 battery. Have multiple batteries so plan on charging only during the day.

Thanks for the help.
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Old 05-26-2014, 09:19 PM   #2
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Re: Time for an inverter - how to size?

One of these for your laptop (has a 19V output port), and a second battery for your Canon? A lot cheaper than an inverter, but if you need an inverter for other electronics, that's probably a better way to go.

http://www.amazon.com/Antigravity-Batte ... 019&sr=1-1


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Old 05-26-2014, 11:32 PM   #3
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Re: Time for an inverter - how to size?

Quote:
Originally Posted by larrie
Video camera battery: input 120V 0.18A, output 8.4V 0.7A
Still camera battery: input 120V 0.2A, output 8.4V 1.2A
MacBook Air: input 120V 1.0A, output 14.85V 3.05A
I use a Harbor Freight one. the 750 watt I use is on sale for $35

http://www.harborfreight.com/750-watt-c ... NyJ9%0D%0A

The picture doesn't show it, but it has a cig lighter connector. I use the computers on battery and only plug them in for charge. I doubt the claim of what it does, but it does run a little blender I have.
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Old 05-27-2014, 01:05 AM   #4
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Re: Time for an inverter - how to size?

You need to watch out trying to supply a large watt inverter through a 12vDC outlet that's only rated for light Amps. I wouldn't run much more than 200-300 watts through a 20A 12 volt port. Most of the larger inverters have cables rated for max load. It don't mean you can't use the 12v adaptor on an 700w inverter and load it up to only 100 watts. Some 12v outlets are rated higher but you just need to check. A 300 watt inverter should be able to supply about 2 AC amps in load. Whistler make a fairly nice 200 watt that's more than enough for your load. Maybe grab a couple. I carry a couple little cheapos plugins on my van. Duracell even make a few. Not the cleanest power by far but as long as you use the dongle you should be OK.
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Old 05-27-2014, 01:14 AM   #5
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Re: Time for an inverter - how to size?

This is where I go for inverters:
http://www.donrowe.com/
The FAQ page has some sizing info.

BTW he's local-ish (Monroe).
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Old 05-27-2014, 06:06 AM   #6
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Re: Time for an inverter - how to size?

Quote:
Originally Posted by larrie
.....cut......

Video camera battery: input 120V 0.18A, output 8.4V 0.7A
Still camera battery: input 120V 0.2A, output 8.4V 1.2A
MacBook Air: input 120V 1.0A, output 14.85V 3.05A

Is it as simple as adding up the total simultaneous amp draw at 12V, 4.95A, and look for a pure sign wave inverter that has at least that much output capacity? .......cut........
Larrie, I think you need to estimate power based on how much each battery charger uses and not how much it puts out. If you roughly estimate watts as Volts X Amps (doesn't include power factor), you can see that your chargers are less than 50 percent efficient. As expected they must use more power than they produce.

To me it seems you need an inverter that can produce at least 1.4 Amps at 120 Volts. That's at least a 200 Watt nominal size. And for what it's worth, I've been using a 400 Watt inverter to charge tablets, cameras, phones, and an old huge laptop that uses lots of power. And I've never had a problem powering it from cigarette lighter or other 12 Volt factory plug.
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Old 05-27-2014, 07:01 AM   #7
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Re: Time for an inverter - how to size?

Quote:
Originally Posted by carringb
This is where I go for inverters:
http://www.donrowe.com/
The FAQ page has some sizing info.

BTW he's local-ish (Monroe).
Agreed, DonRowe is a great place to read up. I think their prices can be beat, but they are a small specialty business which is the type I like to support. That Xantrex pure sine wave 600 watt for $169 on their front page looks like a great deal though.

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Old 05-27-2014, 08:14 AM   #8
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Time for an inverter - how to size?

We used those little plug in 200W inverters for years, they work fine for charging camera batteries or other small loads. We just wired in one of the Xantrex prowatt 1000's under the bench seat with the remote on/off mounted up by the van radio/extra battery and water pump switches. It powers a single dedicated outlet for simplicity, again mounted under the sink area in our RB-50. There is also a 600W version. Someone posted up an install of one of these, they integrated it into the fuse block so that all of the outlets ran off of either shore power or from the inverter, but I recall them having to flip things off to make sure they don't fry the system by plugging in to shore power? Anyway, works great for our larger loads like running a small nutri-bullet blender for road smoothies and margs, the important stuff....
PROwatt SW 1000 DC-to-AC Power Inverter by Xantrex http://www.amazon.com/dp/B002I04A74/ref ... Htb04CA4DM
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Old 05-27-2014, 08:16 AM   #9
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Re: Time for an inverter - how to size?

Here's the link to the integration, no manual switching, just a transfer relay...
viewtopic.php?t=8219
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Old 05-27-2014, 11:53 AM   #10
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Re: Time for an inverter - how to size?

Don Rowe has a nice 300 watt http://www.donrowe.com/Samlex-PST-30...pst-300-12.htm. This is a Pure Sine Wave unit so there should not be any issues with chargers or anything else. Chance was correct you would add up you AC- input usage 1.2 amps X 120. If this is going to be your major usage it should work fine. You do not really want to get to much power as you will get less efficient with smaller loads.

You could also look at DC to DC converters http://www.powerstream.com/dc-dcz8403.htm these should cover battery charger, and I would be surprised that Apple does not offer a Apple version of a auto lap top supply. Power stream also has units for that also.

DC to DC would be the most efficient way to make the conversion.

-greg
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