brady
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Post by brady on Jun 17, 2016 16:06:56 GMT -8
I know there should be a fuse from panels to the MPPT and from the MPPT to batteries, question is what is the amp for the fuses if on a 40amp mppt -- 40amp fuse, or should I go to 55amp? If the panels are to be wired in series-parallel 24v what size wire should I go with? Overkill to install fuses on each panel before it is coupled and run to the MPPT, or just one fuse from the + wire of the panels?
Im installing in my RV into a 200amp dual 12v battery bank.
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Post by spiderbob on Jun 17, 2016 18:57:50 GMT -8
Can you supply a bit more information, size in AHs your battery, what you are wiring them in as well as your panels. Serires, parallel/series, parallel
Im installing in my RV into a 200amp dual 12v battery bank. I'm not sure what you are saying here, do you mean each battery is 200ah? not amps. |
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brady
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Post by brady on Jun 18, 2016 11:12:04 GMT -8
I thought I had all the info in there. Ya, 200ah, not amps. 4x100(400watt) panels, sorry, wrote it in the title not in the message. Its the kit from renogy.
24v Series-Parallel Configuration as shown in the off-grid manual provided on renogy
Two 12v 100AH batteries in a parallel configuration
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Post by spiderbob on Jun 18, 2016 12:17:48 GMT -8
OK, now you are getting me more confussed. I got the two 12v batteries at 100ah each, and I assume the batteries are not wired in series/parallel as you only have two batteries and if it's your RV, they need to be wired in parallel for a continuous 12v, not 24v.
So, if you are wiring the 4 x 100w panels in 2 x 2 or series/parallel, I like that. So next question how long is your cable length?
If panels wired in parallel, the amps produced by each panel are additive while volts remain constant, that's Ohm's law. So figuring two panels in parallel you have 5.9a x 2 = 11.8amps from your last branch circuit to the controller. There is a cable guide on Renogy, after you get your distance check the guide.
If panels wired in series, the amps produced by each panel stay constant also Ohm's law. So, the cable leading from the connection point of the panels to the charge controller will carry just the amperage produced by a single panel, 5.9 amps at 12 volts.
So parallel = heavier wire.
But, most solar power systems on RVs never reach their full potential current load. That is because during the morning hours, you get most of your charge and by the time the full is high, the controller has alread started cutting back.
Any 24v that you are doing (not sure where this is) before the controller, will be cut back to 12v automatically.
You also don't need to fuse every panel, but no one is going to say no to that either. It doesn't hurt to fuse, it hurts when needed and you don't. For what it is worth I fuse only once before the controller.
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brady
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Post by brady on Jun 18, 2016 17:34:26 GMT -8
Ok lets get on the same page because I think we're close here. RV batteries are wired in parallel (positive to positive, negative to negative) as these are my aux batteries, not the engine battery. That battery is on a whole nother system that will NOT be hooked up to this. Yes, they are 12v 100AH batteries. Im getting 24v from the panels. If you look at the off-grid manual provided here and you look at page 68 it has the description of the system I am trying to configure. I have this kit. It should work because the MPPT would automatically detect the 12v system and convert it there, and the panels would be more efficient in 24v than 12v configuration -- please correct me if that assumption is wrong. The panels would be installed on the roof directly over where the batteries are, I'd say no more than 15ft run from panels on roof to battery (7.5 to MPPT, 7.5 to battery). That is a couple feet generous I'd say, but better safe than sorry. Appreciate the help! |
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brady
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Post by brady on Jun 18, 2016 17:52:20 GMT -8
I guess I should say Im open to swapping to golf cart batteries as those provide more AH, but didnt want to make it more difficult to configure at the beginning.
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Post by spiderbob on Jun 18, 2016 18:29:44 GMT -8
Either way, you are on the right track. I see your 24v and yes, it's a better way to go. When the voltage is doubled like this the current is halved. So the current produced by 24 volt panels is half that of equivalent wattage 12 volt panel (the watts don't change whether the panels are 12 or 24).
Consider 6v golf cart batteries, as they are built with much thicker plates and will last a lot longer as well. They can also take a much harder discharge. Unless you have a space problem, then you have to make that call 
Mine are wired as on page 67, I choose this so if one panel was covered even partially with shade it would not cut all four panels down to nothing.
All my batteries get charged from the solar panels, both chassis and house. There is what is called the BIRD ( Bi-Directional Isolator Relay Delay) which determins the wattage coming from either set and opens or closes depending on the need of the chassis battery. But all my batteries are kept charged this way. The house batteries being the main set. |
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brady
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Post by brady on Jun 18, 2016 21:47:43 GMT -8
Great. so a few questions. What are the advantage of pg68 vs 67 in my configuration? And for the recommendation, what size wires and fuses should i get and where should they be placed? Keep in mind I'll be replacing my 12v's for 2- 6v's now that ive done some more research into the option. I can look up how to do it and wiring for that.
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Post by spiderbob on Jun 19, 2016 17:32:12 GMT -8
Great. so a few questions. What are the advantage of pg68 vs 67 in my configuration? And for the recommendation, what size wires and fuses should i get and where should they be placed? Keep in mind I'll be replacing my 12v's for 2- 6v's now that ive done some more research into the option. I can look up how to do it and wiring for that. Only advantage I see, in mine, if one panel gets shaded even by the size of an 1/8 of the surface, this will knock out that panel leaving three more active, in yours, if the same shadow covers one panel you lose two panels. I will not speculate size of the wire you need, I went with #8 but was told #10 would work fine. The fuse from the panels should be near the controller, if using only one fuse, the fuse to the battery, should be as close to the battery as possible.
Just to throw another option out there, have you thought about a monitor, a good monitor that utilizes a shunt?
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brady
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Posts: 7
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Post by brady on Jun 21, 2016 18:09:14 GMT -8
I actually got the meter with the kit.
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Post by spiderbob on Jun 21, 2016 19:46:06 GMT -8
That will work for you.
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