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MyPrepperLife
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Discussion Starter · #1 ·
I am preparing to create a small PV system this summer. I think I want to do it in a way that is kind of unusual, mainly because I already own and understand how to use some of components that can be utilized for part of the system.

I am a novice when it comes to electricity. I have been educating myself, but I have a lot to learn.

I have come up with the following (tentative) design.

PANELS: four Grape Solar 160W Monocrystalline panels (amperage 8.65, voltage 18.5)

BATTERIES, CHARGE CONTROLLERS, INVERTERS: I own two Goal Zero Yeti 400 power packs. Each of these consists of a case containing: a PWM charge controller, a 12V 36 Ah battery, a 12V output port, two USB output ports, two AC output ports powered by a 300W inverter, an input port that allows you to charge the batteries from any of three sources (AC power from the wall, a 12V source such as a vehicle's cigarette-lighter port, or solar panels). The Yeti 400 also contains various other circuitry and so forth: fuses, status display, etc.

Each Yeti 400 has a plug-and-play way to add more storage by creating a parallel connection to another battery. Ideally that battery would be the same kind of battery that's inside the Yeti 400. One Yeti 400 chained to one of these batteries would allow me to store about 800 watt hours (but not really, because I don't want to draw the batteries down that far - so let's round that down to 500 watt hours). I'm planning to have four Yeti 400s each of which will be chained to one battery, so I'd have maybe 2000 watt hours of storage. This isn't a lot, but given the fact that I've become really adept at conserving electricity, this will probably serve me pretty well for a year or so until I can afford to build a much bigger PV system next year.

I want to put the four solar panels on the roof of a shed that is about 110 feet from my house. The Yeti 400s and their attached extra batteries would be in the basement of the house. The question is how to feed the four Yeti 400 charge controllers from the panels.

Conceptually, the simplest way would be to run four cables from the shed to the house; each of the four cables would connect one panel to one Yeti 400. The problem with this, though, is the voltage drop. I would need four pretty expensive cables, and they would either need to be direct-bury cables, or I'd need to stuff all four into one conduit, or I'd need four separate conduits. None of these scanarios appeals to me (too much work and too much money).

Putting the panel array closer to the house isn't an option because of shadows from trees I don't want to cut down.

So I am wondering if I could do this: connect the four panels in series (so I'd have one 48-volt push instead of four 12-volt pushes) - but then once the cable enters the basement of the house, I'd want to split the 48-volt feed into four 12-volt feeds, one for each of the four Yeti 400s. That last bit is the part I'm not sure about. Is it possible? If so, how would I do this?

Note the following: creating a bank of eight batteries by connecting the four Yeti 400s plus the four extra batteries in parallel probably would not work out well, because I think the charge controller on the first Yeti 400 in the chain would be a bottleneck. In other words: I don't think it would make sense to feed the 48-volt push to the 8-battery bank.

Any and all advice and comments will be appreciate.
 

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Militant Normal
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10,410 Posts
Inverters, transformers, and rectifiers. Which will waste more electricity than the resistance in your four 12v. cables. Use stranded wire, not solid, and use a heavy enough gage. Your resistance losses will be small.
 

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Why are you spending the money on Yetis?* Better is to get a good quality MPPT charger and simply buy panels, batteries and a inverter for converting DC to AC for longer distance transmission. DC voltages are not easily transformed.

*On re-read I notice you already own two of the Yetis. I would leave them out of your normal solar system and use them as temporary power packs which is all they are designed to be.
 

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Premium Member
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So I am wondering if I could do this: connect the four panels in series (so I'd have one 48-volt push instead of four 12-volt pushes) - but then once the cable enters the basement of the house, I'd want to split the 48-volt feed into four 12-volt feeds, one for each of the four Yeti 400s. That last bit is the part I'm not sure about. Is it possible?
Yes and no, and maybe... I'll explain.

Yes: If you had a 48V battery bank in the shed (mine is in the barn), one could run a single pair of wires. In the house, use a transformer to change the 48V into 12V for your devices. The original power (watts) you had back in the shed would flow into the various 12V devices (minus the wire losses and the extra 48->12V transformer).

No: If your Yeti has circuitry to maximum the energy it harvests from the panel (called MPPT), then no. Each of your Yeti's is meant to have it's own panel connected to it. You can not connect two MPPT controllers to the same panel. The price of the Yeti makes me think it does not have a MPPT in it.

Maybe #1: If you wired your panels in a parallel so they stay at the voltage your Yeti expects (that is why the Goal Zero chart shows which panels go with each model). So you would be burying a 12V cable carrying a lot of Amps. It's going to be a very heavy duty cable ($/ft). Also, you'd some kind of box to combine those panels in a way not planned by Goal Zero... Your wording makes me think you're realized the problem with 12V high current.

Maybe #2: As you wrote, you could combine the 4 12's into a single 48V... but before you feed it into the Yeti, you need to drop the voltage. These come in a variety of sizes.
http://www.powerstream.com/dcdc-48V.htm
or
http://www.axiomatic.com/power-supply/48-vdc-to-12-vdc-converter/
or
http://www.everythingcarts.com/p-1150-voltage-converter-36v-48v-to-12v-20-amp.aspx
This last one would give you 12V with 20A (20x12= 240 watts). You would need one of those $70 units for each 240 watt going into your Yeti. I didn't see how many 12V input each wants. I see some larger DC to DC converters, but they get expensive.

You are heading down a complicated path...

I would suggest you spend some time studying this forum:
http://forum.solar-electric.com/categories

In my opinion, you're trying to scale up and apply a 'temporary' support device into a full time device. This likely will shorten its life (# of discharge & charges can use up the battery's life). At some point, you may cross the line about building codes, which impact insurance coverage should you have an accident.

You might do an exercise and add up what your long term solution might cost, and compare to what other kits might cost. For example, http://www.solar-electric.com/solar-panels-mounts-kits-accessories/prsy/rvandsmbasoc/rv-solar-kit-530-watts-mppt.html is a kit for 12V. (This site has many pre-planned kits. I've bought various components for our system from them.)

inMichigan

Edit: How about just keep the units in the shed so they stay topped up by the sun, and bring into the house during a power outage?
 

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MyPrepperLife
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6,333 Posts
Discussion Starter · #10 ·
InMichigan, thanks for the detailed information.

As I told wes79, keeping the batteries in the shed would not work out well because I'm in a cold climate and the shed will not be heated. (If you are actually "in Michigan," I'm surprised you're keeping batteries in your barn. Assuming your barn is unheated, doesn't the cold winter weather cause problems with the batteries?)

RE: MPPT: The Yeti 400 doesn't have an MPPT controller; it's a PWM controller.

Thanks for the links to the DC/DC converters. This is the key to what I'll need to do if I decide to go down this road.

RE <<In my opinion, you're trying to scale up and apply a 'temporary' support device into a full time device.>>

Yes, I'm aware of that, and in the end I might decide not to use the Yetis the way I described in my OP. But there are lots of reasons the Yetis would work out well for me, some of which I explained in my OP and some of which I did not mention - mainly because my post was kind of long and I didn't want to make it longer.

One thing I will mention is that a replacement battery for a Yeti 400 costs only $100, so even if I had to replace all the batteries at some point, it would only cost me $800.
 

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off-grid organic farmer
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When we were designing our system. The design went through a lot of possible modifications. At one point it seemed to make sense to locate our E-panel in the center of the solar array and put the battery-bank there. But the shed would require positive ventilation and a heating system. As we got into more detail, we saw that this shed was going to become a much larger project than we wanted. So we accepted the 2% voltage drop of running DC power from the solar-array and into the house.
 

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statists' be statin'
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3,441 Posts
Regulated voltage splitters can be built that could do this. I mean such electronic circuits exist but I've never heard of one actually made for that application. If you're electronic-nerdy you could design and build one though.
 

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Premium Member
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1,668 Posts
DC Transformer?

Ditch the overpriced Yetis and use batteries.
Them just use a 48V charge controller.
The 48V to 12V DC transformer was for feeding power into typical 12V devices including the Yeti.

Setting up ones' own PV/charger/inverter as an off-grid system would be excellent training for maintaining it. I would think there must be a few places that offer some training/classes


Our system uses 48 VDC. I do have a small 48 to 12 DC transformer in case I want to power small control systems. Currently, it's not hooked up.

inMichigan
 

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Premium Member
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As I told wes79, keeping the batteries in the shed would not work out well because I'm in a cold climate and the shed will not be heated. (If you are actually "in Michigan," I'm surprised you're keeping batteries in your barn. Assuming your barn is unheated, doesn't the cold winter weather cause problems with the batteries?)
The barn is unheated, but it is insulated. The equipment room within the barn stays above freezing this past winter in Southeast MI. Now this past winter wasn't nearly as cold as last years...so time will tell. The solar charge controllers and inverters put out enough waste heat to keep the room warm enough. My batteries are lithium, which do not enjoy being charged when below freezing, so, they are sitting on a small heating pad as a backup. I never needed to warm them.

inMichigan
 

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MyPrepperLife
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6,333 Posts
Discussion Starter · #20 ·
inMichigan

Are you talking something like this http://www.digikey.com/product-detail/en/cui-inc/PYB30-Q48-S12-U/102-3269-ND/4477527

?

If so that is not a transformer, it is a DC to DC converter.
Thanks for that clarification, JDH.

For those following this thread, I just want to mention that the link provided by JDH leads to a DC/DC converter that has one 48V input terminal and one 12V output terminal. (Not sure "terminal" is the correct term??) This wouldn't work for me.

However, some of the links provided in inMichigan's post yesterday lead to DC/DC converters that would meet my requirement, which is one 48V input terminal and four 12V output terminals. (I need to feed 12V to each of four Yeti 400s.)
 
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