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Old 06-28-2012, 05:47 PM   #11
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Most likely that is true to some small extent.
There are inefficiencies whenever power is converted.
The amount of power you are talking about is small compared to the convenience gained.

Like saying we will eat in the dark because we want to save battery power. Fine in an emergency, but I doubt the DW, or I, would make a conscious decision to do that to avoid buying a bigger battery.
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Old 06-28-2012, 07:25 PM   #12
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Originally Posted by herk7769
How cool is this!

Found this item in my email this morning!

7 Port USB 2.0 Hub w/Power Switches and A/C Adapter, White
That's a nice idea. For iPad need at least 15W to stay ahead of the discharge while using it and to fast charge. iPad charger only puts out 9W

On our boat, I installed a Xantrex Inverter, however all devices are 12V and installed higher wattage USB outlets wherever we use them or for convenience with a number of people on board.
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Old 06-28-2012, 07:30 PM   #13
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Originally Posted by tentcamper1
Thanks,
I looked at the belkin but couldn't find the amps for the USB.

I didn't mention that I already have the 15W USB converters from 12V.
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Old 06-28-2012, 07:31 PM   #14
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Originally Posted by miatared
Word of caution, watch the Amps out on the USB port(s), as an Ipad needs more than the typically provided 500mA. I think the iPad needs more than 1A.
Yes, min 750mA. Many of the USB power device are less than that. I purchased them in bulk from China and have had good success with them.
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Old 06-28-2012, 07:39 PM   #15
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Originally Posted by merlin66043
Just want to make sure I understand, you are using the inverter to go from DC to AC correct? What brand of inverter do you have and how big? Just wondering. Sounds like a good idea for our TT. Occasionally we will be without electrical hookup and we have only one 12V outlet and it is not in a very usable place.
I have DC to DC converters that deliver 15W @ 5V - they will power and charge an iPad. We have 3 iPads (yes a little extreme) since everyone does something different and I prefer not having mine installed with a bunch of stuff for the kids. I use them for primary navigation on the boat.

I plan on installing an Inverter/Charger with at least 4 batteries next year. This year we'll have power most places and I'll just add the extra batteries for now.
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Old 07-02-2012, 01:31 AM   #16
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I've run into the double conversion issue with my astronomy gear and have done quite a bit of research into it. The best converters, both up and down, run 85-90% efficiency. If you run two conversions at 0.85; your overall efficiency is just over 72%. This means that for every 3W of output, you'll need 4W of input. Unfortunately, DC to AC converters are usually much less efficient at low power levels than when running at capacity. If you run two USB chargers at 500ma each, the USB standard, you'll need only 5W and you'll be lucky to get 60% efficiency from a large DC to AC converter.

The problem with RVs is that they're not designed to supply power to DC devices. My 2011 Georgetown 327 has two DC outlets; one on the dash connected to the chassis battery and one in the passenger overhead cabinet. The one in the overhead isn't accessible once any electronics have been put in the cabinet and it's dead until the antenna booster is turned on. This is another example of an engineer designing something without any thought given to how it could be used.

My (future) solution will be to install DC power outlets using Anderson PowerPole connectors in the drop down leaf cabinet behind the passenger seat. These will be fed with a separate circuit connected directly to the battery. (Appropriate protection devices will be also be installed.) A multiple cigarette lighter adapter will give me 3-4 additional outlets and I'll also have a good power source for the DC power supplies for the computers. When the motorhome is not being used, I'll be using the connectors for the solar trickle charger to keep the house batteries charged. The trickle charger will also be connected to the chassis battery through the (always active) dashboard cigarette lighter to keep the chassis battery charged.

Phil
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Old 07-02-2012, 01:46 AM   #17
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Originally Posted by pmsherman
I've run into the double conversion issue with my astronomy gear and have done quite a bit of research into it. The best converters, both up and down, run 85-90% efficiency. If you run two conversions at 0.85; your overall efficiency is just over 72%. This means that for every 3W of output, you'll need 4W of input. Unfortunately, DC to AC converters are usually much less efficient at low power levels than when running at capacity. If you run two USB chargers at 500ma each, the USB standard, you'll need only 5W and you'll be lucky to get 60% efficiency from a large DC to AC converter.

The problem with RVs is that they're not designed to supply power to DC devices. My 2011 Georgetown 327 has two DC outlets; one on the dash connected to the chassis battery and one in the passenger overhead cabinet. The one in the overhead isn't accessible once any electronics have been put in the cabinet and it's dead until the antenna booster is turned on. This is another example of an engineer designing something without any thought given to how it could be used.

My (future) solution will be to install DC power outlets using Anderson PowerPole connectors in the drop down leaf cabinet behind the passenger seat. These will be fed with a separate circuit connected directly to the battery. (Appropriate protection devices will be also be installed.) A multiple cigarette lighter adapter will give me 3-4 additional outlets and I'll also have a good power source for the DC power supplies for the computers. When the motorhome is not being used, I'll be using the connectors for the solar trickle charger to keep the house batteries charged. The trickle charger will also be connected to the chassis battery through the (always active) dashboard cigarette lighter to keep the chassis battery charged.

Phil
Thanks Phil.
I prefer the DC to DC converters rather than plugging cords into inverter. Having USB outlets around is cleaner and less loss.

I'm still trying to figure where the best place is to get 12V supply from.
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Old 07-02-2012, 07:38 AM   #18
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They talk about double conversion losses and also the "12 volt DC Television vs 120 AC volt Television on inverter" question in Barre's book "Managing 12 volts".

All other things being equal, using a 12 volt version of an item uses about 9% less power than a 120 VAC version being run on an inverter. He explains why at length.
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Old 07-02-2012, 10:47 AM   #19
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Quote:
Originally Posted by herk7769
They talk about double conversion losses and also the "12 volt DC Television vs 120 AC volt Television on inverter" question in Barre's book "Managing 12 volts".

All other things being equal, using a 12 volt version of an item uses about 9% less power than a 120 VAC version being run on an inverter. He explains why at length.
Lou, you just reminded me about the TV question, what kind to buy?
This year the TT will have 120V service for the summer, but next year we plan on camping where there may not be power and I try to avoid taking a genny.

It seems the engineers (as Phil stated above) don't think about these, yet everything in the TT runs on 12V and not a single 12V outlet, while there are 120V outlets all over the place.
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Old 07-02-2012, 07:15 PM   #20
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I'm still trying to figure where the best place is to get 12V supply from.
I was able to run mine directly from my power supply, under the shower and into the storage area. In the storage area I used a plastic electrical box to house the in-line fuse. (Not sure if it was still needed seeing as I have the outlets on their own circuit.)

From there I was able to run it between the wall of the bathroom and the bedroom; as there is a 1.5" gap between them.

Obviously all trailers are going to be different, but you just have to try and think like a mouse and figure out where the empty spaces are going to be.

Edit- as for 12 volt TVs, look at some of the RCA LED TVs. (Wal-Mart is a good place to look.) Most of them have a 12 volt input; I'm currently using a 19" RCA TV in my trailer.
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