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edurbrow

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Posts: 16
Reply with quote  #1 
I am a complete newbe. I got 6 80 watt panels, a 30 watt charge controller and a power inverter from a friend. I have bought just one battery so far.

I just stuck a volt-meter on the charge controller where the solar panels come in. The voltage varies, of course, but I got more or less the same reading from one panel as I did with three, around 16v. Does this make sense? Shouldn't it be three times as much?

Thanks in advance.

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stmbtwle

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Reply with quote  #2 
No. The voltage will be about the same on all "12v" panels, but the CURRENT (Amps) will be more with panels connected in parallel. Connected in series, you'll get three times the voltage but the same current.


You should find a sticker on the back with the specs.
Imp is current at max power.
Isc is max current when shorted
Vmp is voltage at max power
Voc is max voltage open circuit.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
edurbrow

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Posts: 16
Reply with quote  #3 

"The voltage will be about the same on all "12v" panels, but the CURRENT (Amps) will be more with panels connected in parallel. Connected in series, you'll get three times the voltage but the same current."

So which is better on a small system like this, more current or more voltage?

One more question: Theses are 12v panels, so why is the voltage reading 16+v in both instance?

Thank you in advance.

jjackstone

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Posts: 118
Reply with quote  #4 
The 16 volt reading is the open circuit voltage. It should drop down a bit when it is under a load. As Willie said, you need to look at the specs on the back of the panels. 

You will also need to check the specs on the controller as to how you connect the panels together. You need to know the maximum input voltage the controller can handle without self-destructing. My controller has a maximum voltage of 250 volts so I am able to connect four 46 volt panels in series. Obviously 4 times 46 volts is under 200 volts but you have to leave a little headroom for voltage change due to temperature change. Panels are more efficient when they are cold.

The alt e store online has some great easy to understand tutorials.
https://www.altestore.com/howto/


I have no affiliation with them.

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stmbtwle

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Reply with quote  #5 
Solar panel voltage decreases as they get hot, so "12v" panels are designed so they will always have enough voltage (about 14v) to charge a 12v battery. A panel that puts out 16v under "standard" conditions may be only 14v on a hot summer day. However on a bright, cold day you may get over 20v, enough to cook your battery. This explains why you need a controller.

Generally, a higher voltage system will be more efficient, and can use smaller (cheaper) wires. However there are other considerations such as availability and cost of equipment. 12v, though the least efficient, is most compatible with the 12v systems found in most RVs and boats. Off grid household systems may run at 24 or 48v. Grid tied systems may be several hundred volts.

Your power inverter will probably determine your system voltage. If it's 12v, then that's normally what you would use.

Your 30 amp controller can only handle 360w at 12v, yet you have 480w of panels. The same controller can probably handle 720w at 24v. For 12v you'll probably have to buy a second controller (yes you can use two). To go 24v you might need a different inverter, and maybe more batteries. It starts to come down to money. Time for the calculator.

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
edurbrow

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Posts: 16
Reply with quote  #6 
Thank you. That explains the voltage reading. I'm slowly learning.

As it happens, I just acquired a 1000w inverter, two more controllers and 3 more panels from my friend who gave me all the other stuff. These additional panels, I believe he said, are 100w, but one of them is only half capacity as one half is rusted inside the plastic box on it. I haven't opened it and checked it, but that is what he said. I also got a lot of plugs and a few Y cables. I'm pretty sure the inverter is 12v as he said his system is 12v, I'm pretty sure. It is all in parallel. The inverter has a broken switch. That is why he gave it to me. I took it tonight to an engineer friend who will fix it.

The two controllers I got are 10 and 15 amps, I think.
mppt solar charge controller mpt-7210a (brand new)
Morningstar Prostar-15 version ps-15m
both of these seem more sophisticated than the no-name controller I am using. They have displays.
Currently I have two batteries. I can barely run my TV for a short time now, but only a couple of panels are hooked up. When I get everything wired up, I don't think any cable runs will be more than 20 feet. I guess I still need a couple of more batteries. I'll save for them. I'm not sure what I need now. I have heard you should not let lead-acid batteries get below 50% charge. I wonder if I should buy a monitor or can I just use my multi-meter. The charge controller has no display, just three lights and makes a high pitched sound when it is below a certain level of charge (???).
stmbtwle

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Reply with quote  #7 
You will have to check your manuals or the manufacturers as to whether the different model controllers are compatible. From what I've read, each needs it's own solar panels, though I think they can all connect to the same battery. I have connected a controller, an alternator, and a battery charger to the same battery bank with no issues, though as the battery charged they would shut off at different times.

You will likely need more batteries. You are correct about the 50% discharge. As far as lead acid batteries go, deep-cycle batteries are better. For best results all batteries should be the same age and type. Bear in mind that the batteries are the heart of your system... the solar panels just charge them.


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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
stmbtwle

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Reply with quote  #8 
You will have to check your manuals or the manufacturers as to whether the different model controllers are compatible. From what I've read, each needs it's own solar panels, though I think they can all connect to the same battery. I have connected a controller, an alternator, and a battery charger to the same battery bank with no issues, though as the battery charged they would shut off at different times.

You will likely need more batteries. You are correct about the 50% discharge. As far as lead acid batteries go, deep-cycle batteries are better. For best results all batteries should be the same age and type. Bear in mind that the batteries are the heart of your system... the solar panels just charge them.

A battery monitor will help but they are expensive. I'd try a simple volt-amp meter that can measure both charge and discharge up to 100 amps. This should work:
https://www.ebay.com/itm/DC-120V-500A-Volt-Current-Ah-Power-Combo-Meter-Charge-Discharge-Battery-Monitor/152112646540?_trkparms=aid=555018&algo=PL.SIM&ao=1&asc=20131003132420&meid=6de25f249d654c70b628b3a411c7ea0c&pid=100005&rk=4&rkt=12&mehot=ag&sd=181166030904&itm=152112646540&pmt=1&noa=0&pg=2047675&_trksid=p2047675.c100005.m1851&redirect=mobile

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Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Fred

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Posts: 36
Reply with quote  #9 
Also try to match panels as closely as possible per voltage specs.The entire string will default to the rating of the lowest rated one,think of the weakest link in a chain.Using different solar controllers on different groups of panels to your battery bank will work just fine in my experience.[thumb]
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