Hi.  I'm new to this forum and to Solar power.  I have ordered the parts for putting in a solar system on my 5W.  I have done quite a bit of research, but as I'm quite anal about things I still have questions I haven't been able to find the answer to.  For right now, all I want to know is:  Do I have to change any of the current wiring on my set of two 12V deep cycle batteries that are wired in parallel or do I simply run the new wires over from the MPPT charge controller and add to the stack?  I guess what I'm wondering about is what happens to all the charging that happens from when I'm connected to the truck or have the genny running for the microwave, etc?  Does it cause any conflict?

Bill,

Thanks so much for your quick and helpful reply. It confirmed what I expected, but wanted to be sure. Also thanks for keeping it simple; as you can tell I would not have understood anything too deep. Thanks for the link too and I will review that in depth soon. The link may answer this next question, but I'll ask it anyway. You suggest using #2 or #4 between the controller and the battery, but since the wire coming off the panel to the MPPT controller is 10 guage (single 250 watt panel), is that not your weakest link and putting 2 guage or 4 guage from the MPPT controller to the battery is a little late in the game??? Incidentally, the distance from the panel to the controller will be about 8 feet and from the controller to the Battery should only be a couple feet.

Bull Rhino wrote:

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Hi.  I'm new to this forum and to Solar power.  I have ordered the parts for putting in a solar system on my 5W.  I have done quite a bit of research, but as I'm quite anal about things I still have questions I haven't been able to find the answer to.  For right now, all I want to know is:  Do I have to change any of the current wiring on my set of two 12V deep cycle batteries that are wired in parallel or do I simply run the new wires over from the MPPT charge controller and add to the stack?  I guess what I'm wondering about is what happens to all the charging that happens from when I'm connected to the truck or have the genny running for the microwave, etc?  Does it cause any conflict?

-- Edited by Bull Rhino on Thursday 18th of July 2013 09:51:56 PM

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Welcome to the Forum:

You can add to the stack as you say.  +12 to positive out of the MPPT controller to the 12 volt stack and ground to the ground (minus) of the stack.  Be sure to use the recommended wire size to minimize losses from the controller.  I used #2 but #4 may be enough depending on the size (amps) of the MPPT controller and the distance to the batteries from the controller.  Always follow the manufacturer’s recommendations.

The MPPT controller should work fine when your 12 volt converter (charger) or genny is running.  I.e. there is no need to turn most MPPT controllers on or off as such.  The MPPT controller should be looking at the state of the batteries and responding with appropriate charge accordingly.  (A very large simplification to answer the question)  Again, follow the manufacturer’s recommendations.

Highly recommended resource:

http://www.jackdanmayer.com/rv_electrical_and_solar.htm

Bill

I had assumed (always a bad thing with a simple answer) the MPPT controller and your system was a bit larger.  Short version: I would still use #6 if possible.

The function of the MPPT controller, if the solar panel is a higher voltage capable panel, (i.e. greater than ~12.6 volts, etc.,) is to maximize the power transfer (so to speak.)  With higher current you need larger wire for less loss (usually.)  No the #10, believe it or not, is not the limiting factor. Due to how an MPPT controller works, assuming the solar panel is a higher voltage panel, the MPPT controller can take advantage of the higher voltage panel output and increase the current charge to the battery..  (You still charge the 12 volt batteries at the correct voltage out of the MPPT controller / charger.)  This is sometimes marketed under the phrase "boost."

All this wire size has to do with what is called IR² losses in the wire which is a lot more than you want to know.  If #6 is a physical problem to use don’t lose a lot of sleep because with one panel your charging current isn’t going to be that high and the #10 will work if that is what you have. It just may have a bit more loss.  I was just suggesting a more “optimized” condition without knowing all about your system.

‘Hope that helps and doesn’t confuse more

Bill

Bull Rhino wrote:

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Bill,

Thanks again, you're awesome! I'm going to trust you and use at least a #6. I know it can't hurt to go a heavier gauge and their is really no reason I can't, at least between the controller and the battery. From the panel to the controller I guess I'm stuck with #10. My solar panel is 8.15 Amp, 30.7 Volts and, obviously, 250 Watts.

Any other hints or tips are always welcome and I will review that link you sent.

Again, Thanks!

Scott

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Scott:

Don’t fret about the #10 from the panel to the controller.  Actually, that is the nominal size for higher voltage panels like you have.  Nice panel actually and #10 is appropriate at that point in the circuit. 

Since you sort of asked and please, just skip this if is confusing:  In general, when you have higher voltage (like at the panel)  you can use smaller wire, #10, to transfer the same POWER.  That’s why those power lines on the poles can be so small and yet provide power to so many homes. They carry very very high voltage and then that voltage is stepped down to 120/240 to go into the home.  But the current (amps) goes up when you do that to make the same “power.”  Power (watts) = volts x amps.  It's just math.

So, you can have a 100 watt (power) light bulb operating at 100 volts @ 1 amp OR 10 volts @ 10 amps.  Either way the math says 100 watts.  This is an example only. The bulb has to be designed for he voltage used just like anything else.

Looks like you good to go. Enjoy.

Bill

OK  Assuming, I hate to do that, this is for the main 12 volt fusing:

This link should help as to a holder and a 200 amp fuse.

http://www.amazon.com/Go-Power-FBL-200-Class-Block/dp/B001539B60/ref=sr_1_1/187-0558767-2307900?ie=UTF8&qid=1374709559&sr=8-1&keywords=class+t+fuse

This “T Class” fuse is a nominal type for RV installations.  There are other sources, Amazon’s link just came up first.

Here is the deal.  This fuse’s purpose is for catastrophic failure or a full short of the 12 volts coming from the battery to the inverter or any part of the main feeds to the 12 volt system.  It is there to protect the "big wires" and the batteries.  Not a light circuit in the bedroom.

I know this sounds strange, but mechanically, that is physically, you can put this fuse in the positive or negative lead coming from the battery as long as the fuse is the first thing in line from the battery.  The closer the better but if you went 162mm it doesn’t matter.  The deal is you want to protect as much wire as possible.  So the closer to the battery the better.

I mentioned the negative side.  Seems strange, but either side of the battery can be fused and sometimes the negative side is mechanically easier as long as there is nothing between the fuse and the battery terminal post.

Remember to use the same size wire to connect to the fuse as is connected to the battery in the first place. 

Now, in reality 200 amps might be a little high for your setup but I don’t know the maximum current draw from you inverter.

You can look on this page to purchase a spare fuse, which I would.

http://www.amazon.com/s/?ie=UTF8&keywords=class+t+fuse&tag=mh0b-20&index=aps&hvadid=1471170784&ref=pd_sl_6ip6z0bsit_b

The odds of this fuse failing when there isn’t a problem is remote.  However, if it does fail you have zero volts coming from the battery and you won’t find this fuse, as you say, at the local hardware store.

There are other solutions.  This one is one of them assuming I understand the question properly.b

Bill

Edited to make links work.

I got my MPPT controller today and it says I should put an in-line fuse holder no more than 150 mm from the positive terminal on the battery.  The problem is it doesn't say what fuse I should put in there.  I am installing a 250 watt, 8.7 amp solar panel and the MPPT controller is good to 20 amps.  Two questions:  first, what size fuse should I put in and second, where is a good place to get the fuse holder and the fuse.  Is this something I would get an an electric supply store or an automotive store or an RV store?  I know my Home Depot doesn't have it.

You would think that at the price of those controllers they would have a built in circuit breaker or fuse. Those circuit breakers in the link seem to only go down to 50 amp. The ones they have in the 15 and 20 amp level are not as good for using as a manual disconnect, and are harder to find in stock at the local stores than you would think. Anyway, I'll get it sorted out and thanks for your help again.

Incidentally, since I was having kind of a hard time finding a circuit breaker in stock I decided to look for a fuse, like the instructions said, and all the ones for even up to 32 v and 30 amp had 12 AWG lead wires.  Wouldn't it be a wast to run 4 or 6 gauge wire from the charge controller with 12 guage on the inline fuse holder.  There has got to be a better way.

Bull bRhino wrote:

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Again thanks to both of you for your responses. There is one thing I want to clarify. As I went back and reread my post I see that I did not specifically say that the instructions are telling me to put the in-line fuse between the Charge Controller and the battery. Since Bills reply says "This fuse’s purpose is for catastrophic failure or a full short of the 12 volts coming from the battery to the inverter or any part of the main feeds to the 12 volt system." I wanted to make sure I was understanding him. So I'm thinking it is talking about power going to the battery, not coming out of the battery, but as you've figured out by now I don't know what I'm talking about. So with this clarification in mind, are we still thinking up to 200 amps when the charge controller is only 20 amps?

Thanks soooooo much for your patience with me.

Scott

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Scott: 

Yea, I was thinking that could be the case this morning.  OK go to an Auto Zone or Pep Boys and ask them for an inline circuit breaker.

They physically look like the ones on this page:

http://www.wiringproducts.com/electrical-supplies/circuit-breakers/high-amp-circuit-breakers

But you need one for about 15 amps or perhaps a 20 amps depending on what they have with an 8 amp or so output from the MPPT.. Put it between the charge controller and the wire to battery. Make sure it goes right after the MPPT charge controller as that is what this is protecting.  This type of device will also give you a way to manually disconnect the MPPT as this can be used as an on-off switch as well as a circuit breaker.  I like these a lot.

The other fuse I recommended is still a good idea to protect from a big problem should it occur.  The reason I suggest the negative side is due to sometimes having too many wires to connect to the positive of the battery and the negative side usually has but one wire.  It's just an option.

BTW, feel free to continue asking questions.  That's how we learn.

Bill

PS, thanks, Jack for the backup.  Yes, I figured I might get flamed on that one.  Nonetheless, sometimes "negative fusing" is just the only physical way to do it with "big wire."  I've had to show people how to do this before when they ran into physical space constraints using 4/0 and the like going to inverters.  In fact I had to put my shunt resister in the negative line as well due space issues with the 4/0 cable in my system.

OK, I know we are dealing with a separate topic considering the controller and batteries, but I have the below on the "big wire" running from the batteries to our inverter.  I'm presuming that this wire and fuse is larger because of a larger "demand" that an inverter might need, instead of a smaller "flow" of power from the solar panels and controller to the batteries for charging purpose.  Is my thinking correct in this regard?

Terry

Terry and Jo wrote:

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OK, I know we are dealing with a separate topic considering the controller and batteries, but I have the below on the "big wire" running from the batteries to our inverter.  I'm presuming that this wire and fuse is larger because of a larger "demand" that an inverter might need, instead of a smaller "flow" of power from the solar panels and controller to the batteries for charging purpose.  Is my thinking correct in this regard

Terry

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Yep. That's correct.  And if that "big" fuse ever fails, just due to whatever - vibration or age, and on the left side that red cable goes direct to the batteries through that hole, which I assume it does, you will have no power in the rig except from the converter - maybe.  (It depends on how they wired it.)

That's the reason for a spare.

Bill

Bull Rhino wrote:

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You would think that at the price of those controllers they would have a built in circuit breaker or fuse. Those circuit breakers in the link seem to only go down to 50 amp. The ones they have in the 15 and 20 amp level are not as good for using as a manual disconnect, and are harder to find in stock at the local stores than you would think. Anyway, I'll get it sorted out and thanks for your help again.

Incidentally, since I was having kind of a hard time finding a circuit breaker in stock I decided to look for a fuse, like the instructions said, and all the ones for even up to 32 v and 30 amp had 12 AWG lead wires.  Wouldn't it be a wast to run 4 or 6 gauge wire from the charge controller with 12 guage on the inline fuse holder.  There has got to be a better way.

-- Edited by Bull Rhino on Thursday 25th of July 2013 02:17:03 PM

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Actually it's better to have the fuse / breaker external for more flexibility.  But that's another conversation.

In general, big wire is always better and this has to do with voltage drop caused by the wire’s resistance.  Bigger wire = less drop.  If the wire run is long then I’d use #6 or bigger if possible. You have a nice, but modest size charger at 8 amps. Not bad at all, just not real big. So #6 short run is likely fine.

In general, unless it is a long run, in your case #2 or #4 is probably a waste from the charge controller to the batteries.  But I have #2 wire from my 45 amp MPPT controller to the battery bank and my run is about 4 feet including the breaker connections.  Then again, I have the resources locally (I know where to find this stuff in town) to do this.  It might be hard for others and I don’t like to make it so hard with the “if you don’t do it this way you’re not doing it right” attitude. “Right” is relative until we get to unsafe.

What you are trying to do is reduce as much as possible the resistance in the wire so that more current (amps) can be transferred into the batteries.

The trouble with all this is not having a fully designed system diagram when making these recommendations.  So we tend to give safe and perhaps more generic answers – at least as best I and others can.  My delimiter is always the same: “It depends.”  That's why I sometimes buy one brand of truck, for example, and other times another brand.  It depends.

Hope that perspective helps and happy to answer other questions as best I can.

Bill

  Thanks to you guys who were sooooo helpful.  I have my system installed and running.  I took video of the entire process and may even put it together in a tutorial type video for Youtube or something.  Of course now that I have it up and running I have new questions, like; how much of the time that it is sitting idle waiting for the next trip should I leave the controller hooked to the battery or the panel hooked to the controller? 

Also, I live in Northern Utah, where we have cold winters, and so in the past when I winterized the trailer I have taken my batteries into my garage and about every month put them on a trickle charger for a few days, because my 5W is stored outside.  I plan to do that again this coming winter unless you tell me different. 

Thanks again!

Scott

Scott:

I leave the solar connected to the batteries all the time and allow it to maintain the batteries with the “smart” charger turned off except when we are using lots of power and are in the rig – like moving the slides. The MPPT controller is “smart,” monitors the batteries including battery temperature and adjusts the charge rate accordingly and won’t cook the batteries, boil them over, as bad as some chargers might.  Plus, it saves a little bit of electrical cost.  Even a "floating" charger draws about 2,800 watts per day.  (120 volts at 1 amp = 120 watts x 24 hours = ~2,800 watts)  My HW-50C surge protector tells me that.  You do have one of these installed don't you?

Based on your location I believe taking the batteries inside during the winter is a very good idea; due not only to temperature but potentially lack of sun in the winter.  In our wintering location – doesn’t get that cold.

BTW, now that you have all this working don’t leave the forum.  Sounds like you might have a lot to contribute.

Bill

  Thanks in large part to the information I got from this forum I've not only installed my solar panel but also made a video of it and posted it on Youtube.  In the information in the description below the video I gave special thanks to Bill and Linda Napier and Jack and Danielle Mayer.  Feel free to share this.