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Old 26-09-2015, 10:18   #16
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Re: USB outlets

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Originally Posted by colemj View Post
In that test, he was using a cheap Walmart MSW inverter, which accounts for 25% of that 29% inefficiency. Transformer loads like a wall charger just HATE MSW inverters. Some to the point of burning up.

I could chose an inverter/charger setup that is even more inefficient if you want to see even greater differences. Or I could show you a similar setup with <5% loss of efficiency that wouldn't be noticeable in practice.

The AC/USB combo outlets I posted would have essentially no efficiency losses - particularly when you consider that charging is going on when you are using the AC outlet for something else anyway.

Mark
Why charge with a 12v USB hard wired? And not use the inverter???
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Old 26-09-2015, 10:35   #17
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Re: USB outlets

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Why charge with a 12v USB hard wired? And not use the inverter???
I am no expert but using dc seems simple. You are not going dc to ac to dc. You still have power if your inverter goes out.
I am just trying to be efficient.
rdw
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Old 26-09-2015, 10:44   #18
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Re: USB outlets

The one I put in my boat:
https://www.bluesea.com/products/104...-_Socket_Mount

4.8A of output current, and it fits a cig lighter hole, so it's easy to change out. I had mounted 2 cig lighter sockets, replaced one with this.

Works great, tiny parasitic current draw.
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Old 26-09-2015, 11:28   #19
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Re: USB outlets

Quote:
Originally Posted by jeepbluetj View Post
The one I put in my boat:
https://www.bluesea.com/products/104...-_Socket_Mount

4.8A of output current, and it fits a cig lighter hole, so it's easy to change out. I had mounted 2 cig lighter sockets, replaced one with this.

Works great, tiny parasitic current draw.
I had been looking for a "high" output Blue Sea USB plug and could not find one. So I tried your link. On the page it says "Available Jan 2016". Did you get a preview model or did they have another one? Thanks.
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Old 26-09-2015, 12:22   #20
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Re: USB outlets

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Originally Posted by RDW View Post
I am no expert but using dc seems simple. You are not going dc to ac to dc. You still have power if your inverter goes out.
I am just trying to be efficient.
rdw

I mis typed... that was exactly my thoughts... Why NOT use 12v and NOT bother with an inverter?

mea cupla
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Old 26-09-2015, 12:45   #21
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Re: USB outlets

Quote:
Originally Posted by colemj View Post
In that test, he was using a cheap Walmart MSW inverter, which accounts for 25% of that 29% inefficiency. Transformer loads like a wall charger just HATE MSW inverters. Some to the point of burning up.

I could chose an inverter/charger setup that is even more inefficient if you want to see even greater differences. Or I could show you a similar setup with <5% loss of efficiency that wouldn't be noticeable in practice.

The AC/USB combo outlets I posted would have essentially no efficiency losses - particularly when you consider that charging is going on when you are using the AC outlet for something else anyway.

Mark
Mark,

That test was to simulate what I see on the boats I work on daily. I am on-board hundreds per year and I would estimate 85% +/- are using a large or small inverter to do nothing but charge phones, pads and computers. This is not because they want to, but rather most don't realize the USB 12V inserts exist nor do they realize 12V adapters are available for computers as well.

Sure if you are already running an inverter for other uses by all means the 120V USB chargers work great. If not the USB 12V inserts will be more efficient, charge just as fast, and cost less than a six pack of beer...
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Old 26-09-2015, 13:48   #22
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Re: USB outlets

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Originally Posted by Sandero View Post
Why NOT use 12v and NOT bother with an inverter?
Quote:
Originally Posted by Maine Sail View Post
Mark,

That test was to simulate what I see on the boats I work on daily. I am on-board hundreds per year and I would estimate 85% +/- are using a large or small inverter to do nothing but charge phones, pads and computers. This is not because they want to, but rather most don't realize the USB 12V inserts exist nor do they realize 12V adapters are available for computers as well.

Sure if you are already running an inverter for other uses by all means the 120V USB chargers work great. If not the USB 12V inserts will be more efficient, charge just as fast, and cost less than a six pack of beer...
The only point I was making about inverters is that the efficiency is related directly to the inverter quality itself, not the process of DC-AC-DC conversion. Also, that MSW inverters are horrible things to connect transformers to.

A good inverter will have no practical inefficiencies compared to direct DC. Yes, there will be a theoretical inefficiency, but in practical terms of charging a phone or tablet, this will be likely <1Ahr/day. If one chooses to make their case using a crap inverter from Big Lots in an unadvisable manner, then one will see awful performance.

One will also see awful performance from a cig lighter socket and pink USB plug bought from the Dollar Store and wired with 20AWG. But somehow good DC solutions are being compared to awful AC solutions here under the guise of "it's what I see daily".

However, I think some have overlooked the fact that we have and use BOTH types on board, so I'm not pushing one over the other - just providing options, facts, and experiences.

For $15, one can buy an AC outlet that has built in USB outlets. This means that when one is using AC for anything (regardless of one's inverter), one can charge USB devices without taking up any of the AC outlets for wall warts. The DC conversion on these ports is efficient. In addition, there is usually an AC socket in every compartment on a boat and exchanging the existing outlets for USB combo outlets can be handy when guests are onboard.

Note that I am NOT advocating running wall warts off inverters regardless of the inverter. My goal is to get rid of wall warts completely - they really irritate me.

For another $15, one can buy a DC USB outlet and directly wire that into the DC system. Or place them all around the boat for convenience.

I personally don't like cigarette lighter sockets and plugs as DC solutions. I have seen few that are acceptable to me, and certainly wouldn't be drilling big holes in several places around our boat to install them just to plug stuff into to avoid using an inverter.

So I do advocate against the cig lighter and cheap auto USB plug solution.

Mark
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Old 26-09-2015, 15:23   #23
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Re: USB outlets

Link to Mainesail's article on this subject, test charging an iPad.

www.pbase.com/mainecruising/ipad_charge_&page=2

In his secenario, AC-DC charging used 29% more juice. Small AH's due to small loads, but could add up across multiple devices.
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Old 26-09-2015, 16:54   #24
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Re: USB outlets

Ah, I see now. The sailnet link posted posted by RDW that I responded to is actually the Mainesail experiment link to in in your post. Now I understand MS's reply to me in a different light.

My point still stands - the majority of that 29% inefficiency is due to using a dime store MSW inverter in an inappropriate application. I think even Mainesail will agree with this statement.

It does not represent a general truism regarding using inverters to power USB chargers. Pick a decent SW inverter and a good USB charger and the losses will be far less - and nill in a practical sense.

Mark
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Old 26-09-2015, 18:06   #25
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Re: USB outlets

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Originally Posted by colemj View Post
Ah, I see now. The sailnet link posted posted by RDW that I responded to is actually the Mainesail experiment link to in in your post. Now I understand MS's reply to me in a different light.

My point still stands - the majority of that 29% inefficiency is due to using a dime store MSW inverter in an inappropriate application. I think even Mainesail will agree with this statement.

It does not represent a general truism regarding using inverters to power USB chargers. Pick a decent SW inverter and a good USB charger and the losses will be far less - and nill in a practical sense.

Mark
Although, wall warts are very inefficient too. I tested one once, forget the exact numbers, but it was quite inefficient. So you have cumulative loss of the inverter and the wall wart. Even with a good inverter, going from DC-AC and AC-DC again will net a lot of loss.
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Old 26-09-2015, 18:25   #26
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Re: USB outlets

To me.. It makes absolutely no sense to take DC and "invert" it to AC, then "convert" it back to DC when the desired result is to just drop from 13.5v(ish) to 5V.

Good quality 12V USB charge ports are available, so why not use them. They use switch mode circuits that are 90-95% efficient. It seems like a "no brainer" to me.

As an aside.. You can even use a pencil to create a resistor divider in an emergency situation.
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