Differing readings from charge controller and inverter.

Seanadirondacks

Hello helpful solar people. I have 14x 80watt 12volt panels and 7x 12volt optima yellow top deep cycle batteries. A 60 amp charge controller and a 1500watt inverter. The charge controller in full sun is reading 14volts give or take and telling my my batterys are at 100 percent. I have a volt meter hooked to my inverter and is reading 12.40volts under the same conditions. I have the batteries in series and the invertor and charge controller connected at opposite ends of the bank. Any ideas? Thank you!

Brigon

If I interpret your wiring correctly, my guess is that when charging, most of the charge is going into battery one due to resistance in the cables. You are then trying to pull power from the other end of the chain that is not getting fully charged. Correct wiring would be to connect + ve to battery 1 and -ve to battery 7, for both CC and INV. Usually just one set of wires to the battery, and split up to Cc and INV after a shunt. One way to check this is to check individual battery voltages. I would expect bat 1 to be highest, working down to bat 7 being lowest.

Brigon

Also, I suspect your batteries are wired in parallel ( for a 12 v supply). Rather than series for a 84v supply

Estragon

Sounds like the batteries are in parallel, not series. In series, they would be 7x12v=84v nominal.

A couple of possibilities:

Having 7 batteries in parallel will be very difficult to impossible to keep in a balanced state of charge, requiring very careful wiring, monitoring, and early intervention to remediate problems as they develop. Very hard to do, especially with sealed batteries which you can't check for specific gravity. Some batteries will be getting fully or overcharged, while others are undercharged. To remediate, undercharged batteries should be fully charged individually, so state of charged isn't masked by fully charged ones. After resting for several hours with no loads or charging sources, each individual battery's voltage should read (using a multimeter) ~12.8v. Any with individual readings below this will need remedial individual charging.

Another possibility is too-small and/or too-long wiring to the inverter causing voltage drop on that circuit.

Depending on loads, location, etc, power from the panels may be a bit low for proper charging as well.

Seanadirondacks

First thank you all for your knowledge and help. I did surely mean parallel! Second, BRIGON I think you really helped. I do have the positive cable for the invertor at one end of the bank and the negitive at the other and same for cc but the other sides of the batterys. So as you said one side is getting charged and the other drawn. So you suggest one set of wires positive from battery one and negitive from battery 7 and split once off the bank and send to both inverter and cc from the same positive and negitive terminals. Thanks again

Brigon

Thanks, I think that is the best with what you have, but as Estragon points out, 7 batteries in parallel is far from ideal. Have all battery cables the same length and somehow monitor for charging differences between  batteries.

Seanadirondacks

I understand the need to indepently check each battery for correct charge but why is 7 batterys in parallel not ideal. What would be my other option with my system? Thanks 

Thom

wow 7 strings of batteries 

mcgivor

Seanadirondacks said:

I understand the need to indepently check each battery for correct charge but why is 7 batterys in parallel not ideal. What would be my other option with my system? Thanks 

Read this, it will explain in detail why http://www.smartgauge.co.uk/batt_con.html

Photowhit

Seanadirondacks said:

I understand the need to indepently check each battery for correct charge but why is 7 batterys in parallel not ideal. What would be my other option with my system? Thanks 

It's not ideal as it is pretty much impossible to keep the resistance the same for each battery. Without the same resistance, the batteries will not share the load evenly. Something you might be seeing currently. 

Other options would be to go to larger battery cells, Them make very large 2 volt cells, or larger capacity and less batteries. perhaps a 12 volt forklift battery.  Another option is to move to a higher voltage. 8 12 volt batteries make just 2 string in a 48 volt configuration.

Seanadirondacks

So if i wired my bank like this with my 7 batteries and connected both the invertor and cc to the + - posts would you say that would give a pretty equal charge/draw? Or should i take a battery or two out of the bank to reduce the number. Thanks again

mcgivor

With method 2 notice how the outer pair do most of the work, this imbalance  would probably be greater as the battery count increases. Method 3 would be as close to perfect as one could get, so long as all the interconnects are the same length. Rather than stacking terminals a busbar would be better, additionally some form of overcurrent protection for each battery would be prudent, to protect against all current available entering a failed battery, internal short for example. That's the method I would choose in the same, less than ideal, predicament. If you don't already have one, a digital DC clamp on ammeter is an essential tool, especially with parallel battery banks. 

mike95490

A difference from the charge controller voltage  VS battery voltage would indicate high losses in too small of wire gauge

For 60A, you should have #4 ga wire.  maybe # 6 would be permissible, but no smaller

Seanadirondacks

I am currently using #4 wire.

Estragon

4ga is light for the inverter circuit and battery interconnects IMHO. 1500w ÷12v=125a (or more during voltage sags and load surges). Hopefully the wire is short, and has a properly sized, DC rated breaker or fuse.

Seanadirondacks

I need inline fuses. Embarrassingly i currently do not have fuses as i should.

mcgivor

Good thing you started this discussion, seems as though you'll learn something, which is a good thing, we're here to help and share

Seanadirondacks

mcgivor said:

Good thing you started this discussion, seems as though you'll learn something, which is a good thing, we're here to help and share

I suspect im going to be asking a lot more as i really get going. I bought everything a little at a time starting 2010 and i set everything up at my cabin and that was that. Recently i started noticing the different readings in cc/inv and realized i havent asked any questions or tried to gain further knowledge for many years. Now i realize i need to rewire the batteries using bus bars and up my wire size as well as inline fuses. Lots to learn and im greatful for everyones time and knowledge. I wont have the best most productive set up, but i want to be safe and get the most from what i currently have. Living and learning. Thanks again friends!!

BB.

One of our posters here "2manytoyz" has documented the evolution of his solar power/backup system over the years:

http://www.2manytoyz.com/ (scroll about 1/2 way down on right)

-Bill

westbranch

If you can afford it , I will suggest, strongly , that you consider a 24 volt system.

Check your  CC ,it should handle 24V as well as as 12V, you will need a new Inverter.  At 24 V you can use smaller wire than for 12 V. then you can configure your batteries in pairs of 2, and the 7 th can be put on a maintenance charger, as a spare if it is still good...

hth