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von
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# Posted: 4 Aug 2015 08:32pm
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Hi, 1st post, (but off (electric) grid for 10 years).
So I have a basic 12v solar system & upgrading my computer/net access.
Problem my new/used Led monitor is 14v & the new modem 12v.
Its seems easy to boost/buck voltage above or below the batteries voltage range of >11v to~15v.
But how do I achieve exactly 12volts or 14 volts?
A Buck converter can get below battery v. A boost converter above battery v, but what kind of regulatory will hold an output of 12v or 14v as the batteries voltage fluctuates?
Thanks for any help?
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von
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# Posted: 4 Aug 2015 09:43pm - Edited by: von
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I may have answered my own question after a week of reading & searching. I find this the best explanation yet
http://www.analog.com/library/analogDialogue/archives/45-12/buck_boost.html
"the buck/boost converter is used to generate an output voltage less than, greater than, or equal to the input voltage."
Always open to other suggestions. thanks
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groingo
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# Posted: 5 Aug 2015 12:37am
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I did a quick search regarding LED monitor voltage and found a common thread which was operating voltage tollerances of between 12 to 14 volts so it sounds like it should run fine somewhere between the two however without specs its just guesswork.
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Al Burton
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# Posted: 5 Aug 2015 11:01am
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Here is what I did. I bought some dc-dc converters off of ebay to run everything that had a wall transformer. I have 24vdc in. the outputs stay constant throughout the charging voltage range.
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Al Burton
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# Posted: 5 Aug 2015 11:04am
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sorry first upload! what is the trick to getting the picture right side up?
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creeky
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# Posted: 5 Aug 2015 05:04pm
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Al. How did you set the voltage out on those? I hear some devices can be quite particular. 13.8 for ham radios I think? nice set up. btw.
von.
groingo is right. some devices (check the specs) can handle a wide range of voltages. fans. pumps. yet others seem to be pretty finicky. you may want a set up more similar to Al B.
Note. there is some newer tech out there. since 2005? the newer dc-dc converters can be as much as 98% efficient. so watch the "era."
And. finally. my take:
a small pure sine inverter can also be very efficient (93%) and you can use it for a variety of device needs.
(ie. plug in various dc voltage converters for devices; tv, radio, modem, laptop etc). plus use it for a/c appliances.
seems redundant. but when you consider that so many electrical devices come with an ac/dc converter in the box (or built in like a tv). it can really simplify things. you know. buy one inverter and a power bar vs many dc-dc converters. (Al has 5 in his picture).
you mention a monitor and a modem. both would come with ac/dc adapter. so. then it's no worries. just plug 'em into the power bar. and they receive stable, appropriate power.
this is the way I would go. sure you pay some overhead. but you gain flexibility.
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Al Burton
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# Posted: 5 Aug 2015 07:38pm
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these have a voltage output pot to adjust output. I think this is the one.
http://www.ebay.com/itm/DC-DC-Step-Down-Power-Module-4V-38V-to-1-25V-36V-LED-Voltmete r-Adjustable-5A-new-/331471874924?hash=item4d2d436b6c
For me this is a much better way to conserve power. dc to ac and back to dc didn't make much sense. I wouldn't use one of these for something with a large current draw but I also have a much larger 24 to 12 volt converter for those type of items. I run a direct vent 12v propane boiler off of that for my hydronic heat.
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Al Burton
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# Posted: 5 Aug 2015 07:42pm
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this one.
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Al Burton
Member
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# Posted: 5 Aug 2015 07:43pm
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still upside down!
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creeky
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# Posted: 5 Aug 2015 08:46pm
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Not to hijack this thread, bet i'd like to hear about your 12v propane boiler.
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Al Burton
Member
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# Posted: 5 Aug 2015 08:54pm
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Found this bad boy on Ebay not working. Quick fix and it works great. I just need to upgrade my solar a bit for those short winter days.I elected to do in floor hydronic as opposed to the convectors because the building it is in is quite small. It is a mechanical room/bathroom/water storage I will keep heated all winter.
http://www.alde.se/usa/heat-technology/how-it-works/
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von
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# Posted: 5 Aug 2015 11:23pm
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Thanks everyone.
The led monitor was really cheap (Samsung S22A100N 22) & could be sacrificed. Through my research I found also that people do use them straight, but the overall opinion was it would shorten its life. I try to aim to do the best job 1st, it saves having to redo stuff in the future.
I have an inverter & like most gear now, its all getting dirt cheap. I'm not keen on the fan noise, though I have set up wiring during the build to mount it under the floor ( a messy job in the crawl space). I like efficiency, the mains stepping up then down again doesn't feel right.
Rare new monitors can be had with an external transformer with 19v out put, probably the best way to go, easy to use a car laptop converter on.Its the providers 12v modem that's the real concern.
I have seen new s. panels available as 24v & half the price per watt as 12v solar p. Not sure why? I do need to add a lot more panels, kinda holding out for Eon's Musk new batteries, looks like they will be a huge improvement on the old lead acids.
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von
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# Posted: 6 Aug 2015 05:20am
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funny how it all comes together, a week ago I knew nothing of this stuff.
So what's needed is a
Single-ended primary-inductor converter (SEPIC)
https://en.wikipedia.org/wiki/Single-ended_primary-inductor_converter
"A SEPIC converter is essentially a boost converter followed by a buck-boost converter, therefore it is similar to a traditional buck-boost converter, SEPICs are useful in applications in which a battery voltage can be above and below (or the same) that of the regulator's intended output. For example, a single lithium ion battery typically discharges from 4.2 volts to 3 volts; if other components require 3.3 volts, then the SEPIC would be effective."
this vid 3mins shows a ~$10 unit (review)
https://www.youtube.com/watch?v=vUb5xu72hvQ
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creeky
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# Posted: 6 Aug 2015 09:17am
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Von. Have a look at some of the older solar posts.
It's been recommended here for years that 24 and 48v solar panels of 200 watts or better are the best value.
Also lithium batteries are available now. See balqon. Lifepo4. They are the best value right now.
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von
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# Posted: 10 Aug 2015 07:04am - Edited by: von
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thanks creeky Shame 24 and 48v solar panels of 200 watts or better are the best value.
I guess its economy of scale. Most peeps are probably using inverter systems for standard appliances.
A common reason was conductor resistance, but there's plenty of clean fencing wire at the dump, twist a 3 core #8 slide some irrigation tubing over it (twice if you want dlb insulation). My whole place is wired for 12v. I'd have to drop the voltage on 24 - 48 pv.
History has played out for high voltage due to transport cost, but really as homes become independent of the grid, it seems a back step to cater for high v. But hard to fight the market.
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creeky
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# Posted: 10 Aug 2015 11:47am
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high voltage has some great advantages for sure.
you know an mppt solar controller will convert your 24/48 to 12 with only a tiny loss. I have one of my solar arrays at 96v going to a 12v battery bank. Ya, I lose 4% but i'm way over paneled until I get the next battery pack anyway. then I'll go 24 or more likely 48.
check out amazon. the victron "blue" series of solar controllers is available in n.a. now. the basic one is like 120 bucks.
so you get both more power from your panels and more flexibility.
and in a sense you're future proofing your purchase. higher voltage/lower amps is a good thing for off grid.
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MtnDon
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# Posted: 10 Aug 2015 01:46pm
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Just curious as to the present battery bank; size and type of batteries....
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von
Member
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# Posted: 13 Aug 2015 07:17pm - Edited by: von
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small 2 x 150 Watt hours, lead acid, If I remember correctly, (each battery is about 1' long)
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von
Member
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# Posted: 13 Aug 2015 07:30pm - Edited by: von
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thanks creeky , that's gold, I was thinking last night I might put buck converters on each PV to drop them down to 12v, Found these for $4 each "DC 9A 280W Step Down Buck Converter 7-40V To 1.2-35V Power module LED Driver AL".
But I'll search your recommendation, sounds the way to go, I seem to have a lot of catching up to do, since I installed my system. I really want to have a large system now.
I should add My internal wiring is recycled braided Al, 1/4", 20,000v insulated mains line, (Though dlb insulated 3 strand fencing wire would probably be fine, if not a bit rough & ready) But I'm open to critics 
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creeky
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# Posted: 13 Aug 2015 08:46pm
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Quoting: von (each battery is about 1' long)
my best laugh of the day. and today's been a pretty fun day.
unbelievable what you can buy now for peanuts. Quoting: von $4 each "DC 9A 280W Step Down Buck Converter
thx al for sharing that hydronic unit. I'm looking for something smaller yet. but that's the right idea.
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