AC power question

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AC power question

Postby Ben13 » Mon Dec 12, 2022 12:53 pm

Hi folks,

For the teardrop I'm making I plan to have interior lights, diesel heater and a fan running on DC from my Bluetti 600W battery. Pretty standard stuff. But I'm also thinking about running a 120V 3-pin extension cord from the battery's AC output through the wall to an outlet in the cabin, primarily for a laptop. The idea is to hard wire the output of this cord to a standard 3-pin receptacle (socket), the type you have in your house. I then though about getting a receptacle with a USB port too, to charge my phone and such. Has anyone done this? Would anyone recommend this?

Cheers,
Ben
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Re: AC power question

Postby TCJ » Mon Dec 12, 2022 2:31 pm

I run a standard 120V outlet hardwired to a small inverter, which is pretty much the same thing. Don't see why you couldn't use an outlet with USB outlets too. Do you also have 120V outlets in your cabin that are connected to a shore-power circuit (when you're connected directly to 120V by a cable)? If so, you might want to distinguish the two types of outlets so you don't confuse them, as I suspect the Bluetti can't put out the same amperage as a typical 15A shorepower circuit.
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Re: AC power question

Postby philpom » Mon Dec 12, 2022 2:41 pm

I wouldn't use an outlet like that and would opt for something like the photo below. Converting from DC to AC creates a loss of energy and then you are converting again from AC to DC for the USB port. More loss. The panel below runs straight DC. This along with a 12 volt adapter for the laptop will help extend your battery power life between charges.

The 1 AC port I have can operate using shore power, generator power or battery inverter power making it very flexible while leaving everything else 12v DC to easily support battery only operation.

Image
Last edited by philpom on Tue Dec 13, 2022 9:10 am, edited 1 time in total.
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Re: AC power question

Postby tony.latham » Mon Dec 12, 2022 11:34 pm

You might look for a 12 volt adapter cord for your computer. I've got a Macbook that uses a USB-C and I just run it from a USB outlet. Works great.

The black box in your computer cord is an inverter (since computers run on DC current). Obviously there's an inverter in your Bluetti. You'll lose about 20% of the power when running it through an inverter... so 2 x 20% = 40% power loss. Your plan is to convert DC to AC in the Bluetti and then AC to DC in your power cord. Awful inefficient.

Just a thought. :thinking:

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Re: AC power question

Postby pchast » Tue Dec 13, 2022 10:42 pm

My first thought too. Check your system for the input requirements.
Its likely 12 volt solutions are available for it. :thumbsup:
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Re: AC power question

Postby Ben13 » Tue Dec 13, 2022 11:15 pm

Thanks for the feedback, all!

My MacBook uses the MagSafe charger, and so far I cannot find a 12V adaptor for that. I haven't really considered shore power yet. I will probably just hook up a system that enables me to charge the Bluetti, as I don't intend on having a 120V circuit for anything else.

I've previously been told that the converter (or inverter) on the Bluetti is pretty good, so I think I'll install a 120V 3-pin outlet and a cigarette charger outlet, and USB. I'm not ready to buy a new Mac just yet!

My next question: would it be better to have the USB on the 120V outlet or the 12V cigarette outlet? Or is there no difference?

Many thanks,
Ben
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Re: AC power question

Postby GTS225 » Wed Dec 14, 2022 7:41 am

tony.latham wrote:The black box in your computer cord is an inverter (since computers run on DC current).
Tony


I beg to differ. A device that turns 120AC into 12vdc is a CONvertor, where a device that turns 12vdc into 120ac is an INverter.

Ben13 wrote:My next question: would it be better to have the USB on the 120V outlet or the 12V cigarette outlet? Or is there no difference?


Won't really make a whole lot of difference. Either is a 5vdc output for USB. Your only worry is how much battery reserve you might have if you pull it off of the battery.

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Re: AC power question

Postby H.A. » Fri Dec 16, 2022 5:55 pm

Be aware those receptacles with built in USB constantly draw power which may cause problem if the Bluetti has an automatic load sensing function.
Even without load sensing, If you are not charging your computer. Bluetti's inverter will still have to be switched on so you can USB charge. Using bluetti's 120V inverter to power USB's will take about 15-20% more energy from your Bluetti over charging directly from Bluetti's built in USB's.

Ben13 wrote:Hi folks,

For the teardrop I'm making I plan to have interior lights, diesel heater and a fan running on DC from my Bluetti 600W battery. Pretty standard stuff. But I'm also thinking about running a 120V 3-pin extension cord from the battery's AC output through the wall to an outlet in the cabin, primarily for a laptop. The idea is to hard wire the output of this cord to a standard 3-pin receptacle (socket), the type you have in your house. I then though about getting a receptacle with a USB port too, to charge my phone and such. Has anyone done this? Would anyone recommend this?

Cheers,
Ben
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Re: AC power question

Postby tony.latham » Fri Dec 16, 2022 7:34 pm

I beg to differ.


You got me there. But I still think you lose about 20% on both. Or am I wrong?

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Re: AC power question

Postby tony.latham » Fri Dec 16, 2022 7:36 pm

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Re: AC power question

Postby bdosborn » Sat Dec 17, 2022 5:47 pm

tony.latham wrote: I still think you lose about 20% on both. Or am I wrong?


Nope, you're spot on. A good inverter like my Victron Compact 2000 uses 12W just turned on and doing nothing. That's on top of the efficiency losses of inverting 12v DC to 120V AC. Its about 88-90% efficient when it's running partially loaded (like a laptop load would represent). Here's an efficiency table from Victron, one of the few companies that publishes detailed inverter efficiency.

Image
Victron White Paper on inverter efficiency

The black box converters for laptops are notoriously inefficient. So I'd say 20% loss to go from 12V to 120V to 12V is generous, it's probably lower than that. The USB plugs integral with the 120V plugs add yet another efficiency loss on top everything else. Inverter efficiency is directly proportional to price so caveat emptor. I don't use any 120V in the trailer, everything (including my wife's CPAP) runs off 12V DC. I splurged in the van and added a largish inverter. Watching how much real life power it uses has been eye opening.
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