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nayubis
01-27-2011, 06:50 PM
Question on charge controller, battery & inverter connections.

From the off-grid basic setup scheme :
Array >> Charge Controller >> Battery / Inverter >> AC load

1 - Where is the inverter drawing power from?
2 - Are the battery & inverter connected in parallel to the charge controller or are they
connected in series?

If the battery & inverter are connected in parallel (that is, battery & inverter positive terminals connected together & their negative terminals similarly connected together) and then connected to the charge controller, is the inverter drawing power from the battery or from the charge controller ?

Is it possible for the inverter to draw power directly from the array instead of getting power from the battery during DAYTIME to lessen the charge/discharge cycles of the battery? And then at the same time charge the battery to be used during NIGHTTIME.

Is this possible at all? Can anyone help, please?

Thanks.

Mike90250
01-27-2011, 07:38 PM
First, connect the inverter cables to the battery posts. This places the high current wire next to the battery terminal, less loss.

Then, either on top of inverter cable, or on the other side of the battery post, your charge controller connections, and the Battery Temperature Sensor goes on top of that.

If you have more than one battery, read up on connecting on the "diagonal"

Inverter and Charger connect to the same terminals.

Here's a great article about connecting batteries in parallel (on the diagonal)
http://www.smartgauge.co.uk/batt_con.html (connect batteries on diagonal )

and some other battery stuff:

http://www.windsun.com/Batteries/Battery_FAQ.htm (short & sweet)
http://www.batteryfaq.org/ (very large)

Generally, much easier to manage 2, 6V in series, than 2, 12V in parallel. Same wattage.



Don't forget a fuse on your battery, I love the simple and compact MRBF terminal fuse by blue sea (MRBF - Marine Rated Battery Fuse) (http://bluesea.com/productline/overview/378)
http://bluesea.com/files/images/products/thumbs182/5191_182x182.jpg
Get the fuse & holder.

Sunking
01-27-2011, 07:39 PM
1 - Where is the inverter drawing power from?
2 - Are the battery & inverter connected in parallel to the charge controller or are they
connected in series?

1., From the batteries mainly, sometimes from both batteries and solar panels, and at rare times just the panels. Depends. Battery acts as a buffer..
2. Neither really. The batteries are connected to the output of the CC



If the battery & inverter are connected in parallel (that is, battery & inverter positive terminals connected together & their negative terminals similarly connected together) and then connected to the charge controller, is the inverter drawing power from the battery or from the charge controller ? It depends on the state of charge of the batteries, how much load you are demanding, and how much power the panels are producing. It is all a balancing act that has to equal.

For example lets say it is solar noon, batteries are fully charge, and power demand is less than the maximum input power to the CC from the panels. In that case provide the power.

However if demand exceeds the input power from the panels it comes from both panels and batteries making up for the short fall If it is dark, all batteries.





Is it possible for the inverter to draw power directly from the array instead of getting power from the battery during DAYTIME to lessen the charge/discharge cycles of the battery? And then at the same time charge the battery to be used during NIGHTTIME.Think I just covered that. However if you asking can you connect panels directly to a battery inverter the answer is NO.

Battery inverters have vary narrow input voltage requirements that have to be met, and solar panels are not voltage sources they are current sources with willy large voltage variations the inverter cannot tolerate. Therefor you must have a battery acting as a buffer, or some kind of voltage regulation.

nayubis
01-29-2011, 08:24 PM
Thank you for the quick response.

xyxoxy
05-19-2011, 01:26 AM
My question is very similar to the one posted here but I just want to be sure I understand.

Mine is a very small system designed to add minimal LED lighting to an out-building. One 50W x 12v panel with a single 12v x 50 Amp Hour AGM battery and an 1100 Watt inverter.

My charge controller has a set of terminals each for the panel(s), the battery, and the "load". The connections to the solar panel and the battery are obvious and if I understand correctly I can use regular 12-14 gauge household wire for those connections as they are only carrying a small charge from the panel and no run is more than 20 feet.

However I'm not sure if I should connect the inverter to the "load" terminals on the charge controller or directly to the battery. It seems the charge controller should be able to kill the load on the battery if the charge drops below a set level... assuming the inverter is connected to it. Or should that be the inverter's job? Are the "load" terminals only for DC powered devices?

Also I believe the inverter needs to connect to the battery with heavier gauge wire than what comes from the panels since the current depends on what you are trying to power. I think something I read said to use 6 Gauge battery cables. But I'm not sure what gauge wire is safe to use with my small 10 Amp charge controller if it is between the battery and the inverter.

I'm just figuring this all out and still waiting on some parts so any advice is appreciated.

- Mickey

Mike90250
05-19-2011, 03:52 PM
Charge controller load terminals are only for small, low amp loads. Connecting an inverter will blow the controllers fuse, or the controller. It should state the limits in your paperwork.

inverters generally have their own Low Voltage Disconnect.

14 ga wire is generally safe for 15Amps Be sure you use a fuse near the battery, in case the + wire develops a short, the fuse blows, life is fine. No fuse, and something happens, you get a fire.

Use what the inverter suggests for wire.

Longer wires need to be larger gauge (smaller number, 12ga is larger than 14 ga, just like shotguns ! )

xyxoxy
05-19-2011, 04:25 PM
Thank you for clearing that up!
I expect most of my load will be from AC devices through the inverter. So unless I'm going to string some 12v DC xmas lights or something along those lines I probably won't even use the "Load" terminals on the controller... is that right?

I was also planning to ask about fuses next. You say "... Near the battery...". Can you be more specific? Are we talking a 10Amp fuse between the battery and inverter? Between the controller and the battery? Both? And do I only need to fuse the positive wire(s) or negative as well? If I don't fuse the negative do I need a ground wire?

I'm pretty comfortable with AC household wiring projects but this off-grid DC stuff is new to me.

Thanks again!
- Mickey

Mike90250
05-19-2011, 04:55 PM
I love the simple and compact MRBF terminal fuse by blue sea (MRBF - Marine Rated Battery Fuse) (http://bluesea.com/productline/overview/378)
http://bluesea.com/files/images/products/thumbs182/5191_182x182.jpg
Get the fuse & holder. Bolts to the battery terminal, and is a very clean install.

Sunking
05-19-2011, 05:03 PM
I love the simple and compact MRBF terminal fuse by blue sea (MRBF - Marine Rated Battery Fuse) (http://bluesea.com/productline/overview/378)
http://bluesea.com/files/images/products/thumbs182/5191_182x182.jpg
Get the fuse & holder. Bolts to the battery terminal, and is a very clean install.Only problem I have found with that Mike is the terminal bolt size. Works great if you select the right battery terminal post when you buy the batteries, suks otherwise because you have to rig something to make it work. Not too mention a bit pricey of around $16 to $30 for the connector, plus another $12 to $25 for the fuse. But i have used then and they are slick.

xyxoxy
05-19-2011, 07:15 PM
The battery fuse looks very cool! Never knew such a thing existed.
My battery has an L2 post so I'll have to see how that works out.

So it looks like that one fuse will cover everything... and I guess there is no real need for a ground wire on my little system?

Thanks again guys. It's great to ask a question and actually get an informed answer.

Mike90250
05-19-2011, 07:59 PM
Well, any panels outdoors, you need a wire to ground the FRAME to "earth".

Follow the INVERTER instructions about grounding it, some are allowed, some will smoke.

The battery - terminal will be called the Common or Return, and should not have a fuse. The more extensive your system is, the more importance is attached to grounding the battery - ( but not to the same point as the solar panel frames)

Grounding a mixed DC and AC system is a "fuzzy" science.

Sunking
05-19-2011, 09:23 PM
So it looks like that one fuse will cover everything... and I guess there is no real need for a ground wire on my little system?Completely false statement. Depending on the voltage of the system whether or not the system has to be grounded or not. If the system is below 50 volts there is no requirement to ground anything except framework. If the system is ungrounded only having one fuse will do nothing to protect anything.

Sunking
05-19-2011, 09:27 PM
Grounding a mixed DC and AC system is a "fuzzy" science.Not really it is quite precise, you just have to know the rules and how to apply them. You know the link to the document that covers it Mike. But I will not answer questions about specific topologies. Not because I am mean, but because DIY do not even know the thousand of other questions they need to ask and know about. Heck I know 10 year veteran electricians who still have to ask questions about it.

Mike90250
05-20-2011, 11:01 AM
You know the link to the document that covers it Mike.

READING THIS DOCUMENT (http://www.nmsu.edu/%7Etdi/pdf-resources/pdf%20version%20divided%20PV:NEC/PV-NEC%201.91/PV-NEC-V-1.91-opt.pdf)

Sunking
05-20-2011, 12:39 PM
READING THIS DOCUMENT (http://www.nmsu.edu/%7Etdi/pdf-resources/pdf%20version%20divided%20PV:NEC/PV-NEC%201.91/PV-NEC-V-1.91-opt.pdf)Yes Sir that is the one.

xyxoxy
05-24-2011, 04:32 PM
...The more extensive your system is, the more importance is attached to grounding the battery - ( but not to the same point as the solar panel frames)...

Just to clarify, can the ground wire from the panel and the ground wire from the battery both terminate at the same grounding rod as long as I keep them totally separated up to that point (i.e. don't run them to a junction box etc)? I suppose ideally a separate rod would be preferable but is it worth the cost and effort to install 2 of them?

Sunking
05-24-2011, 04:36 PM
Do you have a AC service from the utility?

xyxoxy
05-24-2011, 04:40 PM
This is for an outbuilding about 200 ft. from the main house AC service. No connection of any kind to the house and none planned. So I will most likely be driving a new grounding rod at the outbuilding.

Sunking
05-24-2011, 06:17 PM
This is for an outbuilding about 200 ft. from the main house AC service. No connection of any kind to the house and none planned. So I will most likely be driving a new grounding rod at the outbuilding.No it takes a minimum of two to meet code spaced at least 8 feet apart by code, but best to be 2 x the length they are buried. So if code complinat 8 foot rods, spaced 16 feet apart and bonded together below grade by a # 6 AWG.

xyxoxy
05-24-2011, 08:54 PM
Nerts!

Well it makes sense though doesn't it?
The $20-$30 cost of one more grounding rod (and some sweat) is cheap insurance against frying the whole works or setting my shed on fire. :)

Thanks again!

Sunking
05-24-2011, 09:44 PM
The $20-$30 cost of one more grounding rod (and some sweat) is cheap insurance against frying the whole works or setting my shed on fire.Only way that can happen is if you panell is struck directly by lightning. Otherwise the ground rods do nothing or have a real purpose. Even with the rods it will still burn down everything.

xyxoxy
05-25-2011, 02:53 AM
Just when I thought I had a plan...
I'm still uncertain about how to ground the solar panels. I've honestly been looking at various sites for hours and I can't seem to get a definitive answer to this. Most sites have no real information about this topic other than to stress the importance of proper grounding. Others seem to have conflicting solutions.

You said I need 2 ground rods bonded together below grade with #6 AWG. And I do get why that is. But it also sounds like the metal frames of the solar panel(s) may need to go to a separate ground? Page 30 of the "Suggested Practices" doc you linked to earlier mentions using 2 ground rods but it says that the 2 grounds should NOT be bonded together.

Should the aluminum PV frame go to it's own separate ground or can I run it to a junction box where it uses the same 2 bonded ground rods as the battery and inverter etc? Or are we now talking about 3 ground rods?

This is a small system but a larger one may be in my future and I really want to learn to do this correctly.

Mike90250
05-25-2011, 01:30 PM
Aluminun PV frames need to be grounded by a "certified" connector system, to an un-broken wire, to the ground rod for frames only.

That's my take on it. You need stainless hardware, steel will rot out the aluminun frame via electrolosis.

xyxoxy
05-25-2011, 02:05 PM
I swear I'm not trying to be difficult... :)

So if I have a separate ground for the PV frames that is unbonded to the ground used for the rest of the system, doesn't that open the door to potential/voltage difference in the 2 grounds?

Since both grounds should be as close as possible to the equipment, I think the furthest I could space 2 ground rods would be 20-25 feet (one on either end of my outbuilding). But if I use 2 bonded grounds for the battery etc. and a third separate ground for the PV frames I'm not sure I can space them far enough apart.

Mike90250
05-25-2011, 02:37 PM
That's where my brain fuzzes out and rejects the code we must all follow...

it's not always common sense, to have a ground wire, bringing ligntning into your house panel, inside your wall, and then back out to the ground. But it's code....