SIMPLE QUESTION: seeking simple and correct answer

[CLOUD WOMAN]

Dear Friends,

I had a 300w Renogy   Solar system installed at the Van build but I only had one battery hooked up. I have now bought a second battery to install into that system. I do not know how to do this. Do you have a simple answer that I can understand and follow as to how to install the second battery. Jamie mentioned at the build that there is a certain way, a chronological order that has to be followed, or the system may get fried. 

Please...NO GUESSING...this was a very expensive system to install. I appreciate all of our community and the vastness of knowledge here. I really have to get this right the first time. 
THANKS A BUNCH!
Cloud Woman

 

[Trebor English]

When you add the second battery the first battery will at some point be disconnected.  Solar charge controllers have warnings in the instructions to connect the battery first and the solar panel last.  When disconnecting the order is reversed.  Disconnect the solar panel first and disconnect the battery last.  

Some solar charge controllers fry themselves if they have solar panel connected with no battery.  Some will fry themselves under some circumsyances but not others.  Just because you did it backwards and it didn't fry once doesn't mean it won't fry next time.  

Rather than disconnect the solar panels you could do the work at night or cover the solar panel with cardboard.  With my luck a gust of wind would blow off the cardboard.  Inside a garage would work.

 

[skyl4rk]

Connect positive to positive and negative to negative.

 

[B and C]

^^^ But disconnect the solar panels before you do.

 

[mpruet]

Dear Friends,

I had a 300w Renogy   Solar system installed at the Van build but I only had one battery hooked up. I have now bought a second battery to install into that system. I do not know how to do this. Do you have a simple answer that I can understand and follow as to how to install the second battery. Jamie mentioned at the build that there is a certain way, a chronological order that has to be followed, or the system may get fried. 

Please...NO GUESSING...this was a very expensive system to install. I appreciate all of our community and the vastness of knowledge here. I really have to get this right the first time. 
THANKS A BUNCH!
Cloud Woman

I'm assuming that both of the batteries are 12-volt and have similar capacity.  You would first need to wire the two batteries IN PARALLEL.  To do this you would wire the two positive ends of the battery together and the two negative together.  Lets name the two batteries as B1 and B2.  Let's assume that B1 is your existing battery and currently have all connections to it.  You would now move all of the connections on the negative pole of B1 to B2.  That's the basics of what would need to happen. 

DO NOT connect the negative of one battery to the positive of the other.  That would double your voltage which would burn out all of your existing stuff!!!

OK - for some specifics.  Before you even start you need to cover the solar panels so they don't have a charge. Then disconnect the panels from your solar controler.  Then you would disconnect all of the cables going to the positive terminal of your battery.  You should also put a tape on those cables and mark them as B1+ because they will eventually be on the positive post of B1.  Then disconnect the existing cables on the negative pole and mark them as well but with B2- because they will be on the negative pole of B2. 

Once that is done, then you would wire the two batteries IN PARALLEL as I described above.  Plus to Plus and Negative to Negative.  (You will be able to get the cables to connect the batteries from your friendly NAPA store.)  Only after that is done do you connect the previously mentioned cables to B1+ and B2-.   Finally after all of that is done, reconnect the panels to the solar controler and remove the covers that you put on top of the solar panels. 

Technically you could just disconnect the solar panels, but it is better to cover them as well.  Use masking tape to prevent the wind from blowing them off.  The panels will still be producing a charge and the panel cables could accidentally make connection with something.

Maybe someone else would check or any any other suggestions...

 

[highdesertranger]

batteries in banks should be the same age, the same type, and the same amp hour rating. highdesertranger

 

[mpruet]

batteries in banks should be the same age,  the same type,  and the same amp hour rating.  highdesertranger

Good point.

 

[JD GUMBEE]

As long as it is the same kind of battery and of equal size, go ahead and add it.

You may lose a tiny bit of charge capacity as they equalize to each other, but the gains by doubling your bank size are irrefutable.

In solar systems, people pay attention to the right side of the decimal point too much.
You will not harm a thing.

Your controller sees all your batteries as one big cell.
Batteries vary from unit to unit brand new, right off the shelf.
When you buy them, you often get one from 2017, one from 2018.
People lost in equations read this and spread what they were taught.
In a brand new setup, make it all match.
In real life, they replace a bad unit 18 months later all the time.

...PS Cover the panels??? Say what???
You mean that Renogy does not have a kill switch to change batteries? Are you kidding?
There should be a disconnect right there if it installed properly. CLICK

 

[John61CT]

If not many controllers easy to just disconnect at the input.

Adding a new battery to an old bank just means more likely the new batt will only last as long as the old ones, weakest link wins.

If that's OK with you, go for it.

But generally best is for all members of the bank to be identical.

 

[highdesertranger]

I have tried to mix batteries of different ages more then a few times and never had good results. now if the age of the batteries are fairly close then yes go for it. now a days if I am buying batteries for a battery bank I make sure the are the same age. highdesertranger

 

[JD GUMBEE]

So If I test my three batteries and they test fine...
Then I buy a new one (same type and size) and add it to my bank.
The three original batteries will make the fourth all die at the same time?

Where did you come by this information?

Are we talking wet cells here?

One of the new MPPT controllers?

 

[tx2sturgis]

Well, the 'simple and correct' request just went out the window...

:dodgy:

Truth is, if both batteries are the same type, about the same ah capacity, fairly new, charged, in good shape, and at approximately the same voltage, around 12.5 to about 13 or so, then you can actually make the parallel connections without disconnecting or frying anything.

It's the same idea as a battery switch that disconnects (or reconnects) one battery from (or to) another battery. 

This is not a guess. It IS correct.

Now if one battery is depleted when hooked up to a fully charged battery, or the batteries are completely mismatched (as in different battery chemistry) then there could be issues...so please don't do that.

 

[wayne49]

I only checked this thread to see the usual posts to a CRVL Electric question.

"Simple and Correct" is an incompatible state whenever Electricity is involved.

Pictures of the connections from the solar panels to the solar controller and then to the battery would help to clarify the necessary instructions. Helps to learn the names of the parts involved.

In a "good" solar installation:

There should be a fuse or a circuit breaker (already not simple!) on the solar side that should be pulled out to disconnect the panels.

There should be another fuse between the battery and the controller that should be disconnected whenever working with the wiring.

Then you need two short thick cables to connect the batteries + to + and - to - (in parallel) to create a "battery bank". It has been suggested to connect the battery bank to the system through the + of one battery and the - of the other battery. It makes sense to do this to ensure both batteries are involved.

Replace the fuses in reverse order. Battery to solar controller. Observe that the controller sees the battery bank with no issues. Next the panels to the controller. Observe that the controller sees the panels.

This being your first solar install your batteries will die prematurely anyway. It happens. There is a learning curve to living with off grid power. You are now responsible for power generation, no utility company to rely upon. At that time select two new batteries of equal voltages (you will need a handheld meter to do this, which you should have anyway) and manufacturing date (little stickers on the top of the battery, e.g "6/18") as replacements for the two batteries in the bank.

Anything you don't know or understand just ask. And keep at it until you do, don't be put off by the experts.

 

[Canine]

Like wayne49 said, it isn't simple in the sense that connecting your batteries is only a 2 or 3 step process. There are a few things to know if you want to make the extra effort to do a good job like having good crimps, using deoxit, using good quality wire (not that cheap crap from Home Depot), etc. With the especially small systems we have, making the most out of every watt is important.

It is simple in the context that there are only two wires one of which is negative and the other positive. What is a bummer is both wires that come off of the solar panels are solid black, so when you cut them, you really need to pay attention and mark the wires (+) and (-). I cut the positive wire at a severe angle and the negative one perpendicular so I can see which one is which without having to tape them or otherwise mark them.

Higher quality charge controllers will be reverse polarity protected so if you connect your solar panels backwards, no harm is done.

One thing I did that I'm so happy about is I put switches on both of my panels and both of my controllers. That makes it so easy to test or add/remove items to/from my batteries. I hit four switches and I'm off to the races. No fussing with removing fuses. (I still have fuses of course, I just don't need to remove them to disconnect the power.)

 

[John61CT]

> So If I test my three batteries and they test fine... Then I buy a new one (same type and size) and add it to my bank. The three original batteries will make the fourth all die at the same time?

Yes that is the case.

A bank becomes a single battery.

Healthier cells it gets "leaned on" and work harder. One failing completely can kill the others.

> Where did you come by this information?

Where are you getting this information that gravity causes everything to stick to the Earth?

Something everyone with a clue about the topic just knows because that's what everyone with more knowledge says very early on in their learning curve.

Feel free to spend your money verifying it independently.

If you have a cheap bank to start - as those just starting out should - it won't cost you too much.

> Are we talking wet cells here?

Any chemistry, but those that last decades would have more leeway


> One of the new MPPT controllers?

Nothing to do with solar, just batteries, whatever the charge source.

 

[highdesertranger]

"Where did you come by this information?"

from experience. since I have been using multiple batteries in banks for about 50 years. highdesertranger

 

[sushidog]

Make sure the battery chemistries are the same. For instance, don't mix a flooded lead acid battery (one with caps that you must add water to) with a sealed battery and definitely not a lithium battery as they all perform differently, run at different voltages, charge at different rates, etc.. Ideally the batteries should be the same size and by the same manufacturer (as well as being as close to the same age and condition as possible). Don't mix a starting battery with a deep cycle either.

Chip

 

[SoulRaven]

Truth is, if both batteries are the same type, about the same ah capacity, fairly new, charged, in good shape, and at approximately the same voltage, around 12.5 to about 13 or so, then you can actually make the parallel connections without disconnecting or frying anything.

They gotta have same birthday to play well together, or one picks on another, or so they said 

 

[John61CT]

Google for

"It is industry practice not to enlarge an old battery bank by adding new battery strings. As the battery ages, the aging is not uniform for all cells."

to find a technical explanation.

Easy to find dozens, even hundreds.

Again, not the end of the world, just not optimal if you're talking about more than a minimal difference or an expensive bank.

 

[RVTravel]

Read the instructions that came with your gear.