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buckybuck
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# Posted: 25 Jan 2016 09:07
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I have a lot of electronic items that I run at home that use either a 9 volt wall wart or a 5 volt (USB) wall wart.
In general, which would be the more efficient way to power these sorts of voltages off-grid—by using the same wall warts with an inverter, or by powering the 9 volt or 5 volt items with cigarette lighter-type voltage regulators plugged directly to a 12-volt battery?
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copperhead1971
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# Posted: 25 Jan 2016 09:33
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you can get small inverters that use little power and would have a usb port and a plug in ...if you have the wall plug in for your 9volt you would be set
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buckybuck
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# Posted: 25 Jan 2016 10:06
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I actually have a little 80-watt inverter just like that. I'm just doing some wintertime pondering about which is better in terms of efficiency—using the inverter or going straight from the battery.
You know, the more I ponder this, the more I realize that nowadays in most cases I have to reduce voltage REGARDLESS of whether I power directly from a 12-volt battery or through a battery-inverter combination.
Just about everything I use these days runs off 5 volts—at my cabin, I watch all my movies and listen to music through a smartphone or tablet paired to a Bluetooth speaker, listen to a NiZHi tt-028 radio, and use USB-powered table fans and lights. I'm guessing that for many of us part-timers, 5 volts is the new 12 volts.
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MtnDon
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# Posted: 25 Jan 2016 11:56 - Edited by: MtnDon
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If you have no other 120 VAC power needs at the same time as needing 12, 9 or 5 VDC it would reduce battery consumption to use direct off the battery. That is assuming the cost of the extra DC wiring and hardware does not have to be factored in.
We have a couple of 12 VDC circuits I use to power a few DC devices. I also use a couple of step down converters to obtain voltage lower than 12. Like this. You can find them in many different voltages.
If you find 5 VDC USB used a lot one or two of the lithium USB power packs can be very useful and are portable.
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buckybuck
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# Posted: 27 Jan 2016 10:32 - Edited by: buckybuck
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Thanks for the link, MtnDon. If I'm reading the description correctly, that particular step down converter has an efficiency rating of 96 percent. That's impressive.
My initial question was prompted in part by something I read somewhere about how car smartphone chargers can be a hidden drag on a car's fuel efficiency, because many of these cigarette lighter chargers are only around 40 percent efficient. That made me wonder if it might actually be more efficient to use CEC certified (0.5W no-load dissipation) wall warts hooked to an inverter rather than using less efficient cigarette lighter adapters straight from a battery.
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Nate R
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# Posted: 27 Jan 2016 10:53
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Quoting: buckybuck something I read somewhere about how car smartphone chargers can be a hidden drag on a car's fuel efficiency, because many of these cigarette lighter chargers are only around 40 percent efficient.
So, the highest/fastest chargers are 5 Volts, 2 Amps. (10 watts). 40% efficent would be 25 watts in. Alternator is probably around 70% efficient, so let's say 36 watts required from the engine. That's .05 HP. Can't see it being a huge drag on fuel economy in most vehicles.
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buckybuck
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# Posted: 27 Jan 2016 11:53 - Edited by: buckybuck
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Found it:
URL
I acknowledge that's not going to make me stop using a phone charger in my Ford F150. But for a small, off-grid system, I wonder if car charger inefficiency is large enough to make a difference. That's really the point of my wintertime ennui-fueled question.
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SE Ohio
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# Posted: 27 Jan 2016 13:08
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I plug my "leftover" Harbor Freight solar controller (my solar setup uses different controller) into 12 volts, using its 5 and 9 volt outputs. If one can solder, one might consider using a switched LM337 voltage regulator circuit to provide 5 or 9 volts. Might add an idiot light to circuit to remind to switch off when not in use.
http://www.learningaboutelectronics.com/Articles/LM337-resistor-and-voltage-calculato r.php
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Nate R
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# Posted: 27 Jan 2016 13:20
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Quoting: buckybuck Found it: URL I acknowledge that's not going to make me stop using a phone charger in my Ford F150. But for a small, off-grid system, I wonder if car charger inefficiency is large enough to make a difference. That's really the point of my wintertime ennui-fueled question.
Yeah, they're talking 1/10th of 1% difference in fuel usage. I just didn't want people thinking it was a big deal in a car. Keeping your tire pressure correct and/or running low-rolling resistance tires would make a much larger difference.
But, I agree that in the off-grid cabin side of things, a few watts can really add up there.
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Al Burton
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# Posted: 27 Jan 2016 14:57
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Here is what I used to get rid of all my "wall warts". I run 24vdc from my battery bank in then run small dc-dc converters for each voltage I need. You do need to watch maximum power ratings. These are cheap and so far have been working perfectly for about 2 years.
http://www.ebay.com/itm/DC-LM2596-4-0-40-to-1-3-37V-LED-Voltmeter-Buck-Step-down-Powe r-Converter-Module-/261713002463?hash=item3cef4f7fdf:g:GnsAAOSwiCRUj5Cc
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Al Burton
Member
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# Posted: 27 Jan 2016 14:59
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Here is a picture of my set-up.
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Al Burton
Member
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# Posted: 27 Jan 2016 15:00
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Why do my pics always post upside down? lol
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SE Ohio
Member
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# Posted: 27 Jan 2016 15:27
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Al,
Those DC-DC step-down converters are cheaper than the cost of the LM-337-based circuit parts, plus have extra features (e.g. idiot diode!). Very nice. I'm guessing you spent more on the project box than the parts in it!
SE Ohio
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buckybuck
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# Posted: 27 Jan 2016 16:23
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Ooooo. LEDs and nixie tube. I likee. I just ordered two.
How do you handle devices powered by USB? Do you just sacrifice an old female USB plug and wire it to the converter?
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Nate R
Member
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# Posted: 28 Jan 2016 23:11
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I like those with the voltage display! Makes it easy!
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slgerber
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# Posted: 31 Jan 2016 09:40
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Another option that some people might want to consider when setting up a small basic off-grid system would be to choose a battery charge controller with builtin USB charging ports. I have the VicTec Intelligent LCD 30A 12V/24V 360W/720W PWM Solar Panel Regulator which has two builtin USB ports. It's a rather lowend inexpensive device but it works ok for my simple system made up of a 100 watt panel and one deep cycle battery. I don't really like the wire connectors though. I can barely fit 10ga wire into the connectors and it's difficult to really tighten them well.
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