New Solar System, Battery Question

Joe M

I hooked up my new solar system yesterday (purchased from nothern arizona w & s) without any issues. I just have a question about the behavior of my batteries. I have eight 6 volt batteries wired in series for 12 volts. The batteries were at 12.7 volts after 1.5 hours of charging. The voltage kept rising to a peak of 13.5 volts. In the afternoon as the sun faded the battery voltage started to drop to 13.3, 13.2, 12.9, and so on. The midnite classic stayed on bulk charge the entire time. It was then that I noticed the batteries were fizzing and bubbling like crazy. I didn't want to damage the batteries so I turned off the solar panel breaker. The battery voltage continued to drop until it was at 12.7 and then stabilized. The inverter was turned off the entire time.

I have the midnite classic set on it's default settings for 12 volts.

Bulk 14.3
Float 13.6


Is this normal battery behavior?

Was the charge controller over charging the batteries?

Should the battery voltage drop as the charge controller output drops?

Thanks

I appreciate any help.

Rybren

Re: New Solar System, Battery Question

The experts will chime in soon, but...

2 x 6V in series = 12V. If you have 8 x 6V batteries and a 12V system, then you must have 4 parallel strings. Most folks will advise you that this is a bad idea. Your wiring will have to be perfect and you'll have to be religious in your monitoring of the batteries.

Do you have a hydrometer and did you check the SG of the batteries? This will be very important to monitoring the health of your batteries.

The batteries never reached the Bulk/Absorb voltage of 14.3 (which is likely too low) so you weren't overcharging. The bubbling and fizzing is normal.

Make sure you get a hydrometer, and soon!

Edit: Provide us with all of the specs for your setup: Panel details and numbers, battery brand and model, inverter specs, etc.

Joe M

Re: New Solar System, Battery Question

Thanks for your response.

You're right. The batteries are 4 parallel strings.

I don't have a hydrometer. I'll get one.

What do you mean "your wiring will have to be perfect?"

I have 2/0 wires for the battery interconnects. The batteries are 186 amp hours each for a total of 744 amp hours. My panels are three 315 watts for a total of 945 watts.

Are you suggesting that I remove two of the batteries?

Thanks again.

Joe M

Re: New Solar System, Battery Question

Rybren wrote: »

Edit: Provide us with all of the specs for your setup: Panel details and numbers, battery brand and model, inverter specs, etc.

Panels: Kyocera 315 watt x 3
Charge Controller: Midnite classic 150
Batteries: Nappa 8144 6 volt 186 amp hour x 8
Inverter: Xantrex sw 1000

The inverter I just turned on a couple seconds to make sure it worked. I let the batteries charge the rest of the day.

Thanks again.

vtmaps

Re: New Solar System, Battery Question

Joe M wrote: »

What do you mean "your wiring will have to be perfect?"

Welcome to the forum.

Batteries are very low internal resistance. That means that subtle differences in the resistance of the wiring will cause the current to flow through the batteries unevenly.

Actually, even if your wiring is perfect your battery bank is problematic. To learn why, read:
http://forum.solar-electric.com/showthread.php?14674

The fundamental problem with parallel batteries is that while they are being charged the current does not divide equally among the batteries... some will be doing more of the work. This is because (assuming your wiring is perfect) no two batteries have the exact same internal resistance. As they age unevenly the problems accelerate.

I'm not saying that four parallel strings of batteries can't work, but it is a lot more effort on your part to monitor them for the inevitable issues. You need to buy a DC current clamp ammeter and use it regularly. And when issues do crop up what do you do?

One solution is to take the same batteries and put them all in series (48 volt system). They will have the same energy storage that you have now. Unfortunately, you will need a different inverter. Your Classic will also be happier with a 48 volt system (less current to handle).

Joe M wrote: »

Should the battery voltage drop as the charge controller output drops?

During absorb the voltage is constant, but the current tapers off. When the batteries are fully charged, the voltage drops down to the float voltage.

--vtMaps

Joe M

Re: New Solar System, Battery Question

vtmaps wrote: »

One solution is to take the same batteries and put them all in series (48 volt system). They will have the same energy storage that you have now. Unfortunately, you will need a different inverter. Your Classic will also be happier with a 48 volt system (less current to handle).

--vtMaps

I didn't know that it was possible to wire 6 volt batteries into 48 volts. I'll look into that.

Thanks so much!

Here is a video I made yesterday of my 'work in progress' system.

http://youtu.be/J2qINQxdi2U

BB.

Re: New Solar System, Battery Question

I would suggest that you also get a DC current clamp type DMM... It will make checking current flow in different parts of your system much easier.

Also, just for the heck of it... Start your car up and check the battery voltage with your DMM and see what it reads... You should see something around 14.2-14.4 volts when charging (some cars may read as low as 13.8 volts). Just to make sure you meter is accurate.

Congradulations on not having a 3kW inverter on your system. For practical off grid power (lightning, computer, cell phone charging, etc.) a smaller inverter is usually the better solution. Large inverters can waste power and most smaller system battery banks are not large enough to run a large inverter at full load for very long.

-Bill

Rybren

Re: New Solar System, Battery Question

I've stolen this from BB's work. You generally want 5% to 13% charge rate for your batteries.

The calculations would look like this:

•744 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 700 watt array minimum
•744 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 1400 watt array nominal
•744 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 1821 watt array "cost effective maximum"

So, at 945W of panel, you have roughly:

744 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.067 rate of charge = 945 watt array ( or 6.7% rate of charge)

It's not terrible, but adding a fourth panel wouldn't hurt.

Joe M

Re: New Solar System, Battery Question

vtmaps wrote: »

One solution is to take the same batteries and put them all in series (48 volt system). They will have the same energy storage that you have now. Unfortunately, you will need a different inverter. Your Classic will also be happier with a 48 volt system (less current to handle).

--vtMaps

I've been searching the internet unsuccessfully for a diagram of how to wire my eight 6 volt batteries in series for 48 volts. I know to connect one battery's postive to the next battery's negative for every battery. The two battery post remaining with nothing connected go to the inverter. But which posts do the postive and negative from the charge controller connect to? I know it's simple but I've just spent 2 hours trying to figure it out.

vtmaps

Re: New Solar System, Battery Question

Joe M wrote: »

I've been searching the internet unsuccessfully for a diagram of how to wire my eight 6 volt batteries in series for 48 volts. I know to connect one battery's postive to the next battery's negative for every battery. The two battery post remaining with nothing connected go to the inverter. But which posts do the postive and negative from the charge controller connect to? I know it's simple but I've just spent 2 hours trying to figure it out.

The same two posts that the inverter goes to. Don't forget that you need fuses or circuit breakers between the battery and the inverter, and between the battery and the controller. Actually you need fuses between the battery and ANYTHING connected to the battery.

I believe that all of your equipment (inverter and controller) has wiring diagrams in the manual. If you buy a 48 volt inverter that will also have wiring diagrams.

Before you do anything precipitous (like spend money) ask here first. There are a few things to discuss, for example what inverter are you thinking of buying? What are the specs on your panels, and how should they be configured in a 48 volt system.

Also, consider that your batteries could be hooked up as two strings of 4 batteries to make a 24 volt system. Two strings is not as optimal as one string, but it not the disaster that four strings is.

--vtMaps

BB.

Re: New Solar System, Battery Question

Same place as the inverter leads go to... You can either stack connections on the posts/bolt up flags--Or run a pair of heavy cables (plus fuse/breaker) to a set of + and - bus bars... And make all of your electrical connections there.

The battery charger and inverter/other DC loads all want to connect as close as practical to the battery bank. You don't want too long of cables/too small of diameter of wire between the battery and the charging sources/loads (keep voltage drops low).

Always remember to fuse/breaker your battery connections... A good sized lead acid battery bank can put 100's to 1,000's of amps into a dead short.

Poster "2manytoyz" has a nice set of posts on his website regarding his DIY solar installation (from the beginnings through a move/complete redesign):

http://2manytoyz.com/battbank.html

Perhaps this will clarify things for you.

-Bill

Joe M

Re: New Solar System, Battery Question

vtmaps wrote: »

Before you do anything precipitous (like spend money) ask here first. There are a few things to discuss, for example what inverter are you thinking of buying? What are the specs on your panels, and how should they be configured in a 48 volt system.

--vtMaps

Here are the specs on the panels.
Pmp = 315 Watts
Vmp = 39.8 Volts DC
Imp = 7.92 Amps DC
Voc = 49.2 Volts DC
Isc = 8.5 Amps DC

They are wired into a combiner box. So they are parallel.

I didn't realize that I would have to change the panel wiring to go to a 48 volt battery bank. I assume that the panels would have to wired in series?

PNjunction

Re: New Solar System, Battery Question

No matter what series / parallel setup you end with, I'd be very tempted to try and balance the new batteries by charging each individually with a nominal 6v battery charger, or perhaps in 12v pairs closely matched in voltage with a charger like an Iota prior to putting them into service as a big string.

vtmaps

Re: New Solar System, Battery Question

Joe M wrote: »

I didn't realize that I would have to change the panel wiring to go to a 48 volt battery bank. I assume that the panels would have to wired in series?

Three panels won't work with your charge controller at 48 volts. If you put all three in series, the Voc will be too high for a Classic 150.

24 volts is looking better... you could leave your panels in parallel.

If you purchased another panel you could put the panels in series/parallel (two strings of two panels) and make a 48 volt system work.

Its hard to know what advice to give you... we usually design a system to meet a need, and we don't know what your needs are. Your needs, of course, are your loads. If your heavy loads are during the day, we can upsize your panels and downsize your battery. If the loads are at night, you need more battery storage.

It would help to know where you are located... if its very cold we need to consider that because it raises the Voc of your panels. If its very hot we need to know that because it lowers the Vmp of your panels and there might not be enough voltage to charge your panels. If we don't know how much sun you get, we don't know if you will get enough sun to charge your batteries.

--vtMaps

sunbunny

Re: New Solar System, Battery Question

First thing to do while you do some more research is check out this link http://www.smartgauge.co.uk/batt_con.html and wire your batteries better. Having the inverter/CC coming off of one battery pair is less than optimal. A better set up would end up with the negative off one end and the positive off the other end.
When the batteries were bubbling, was it all of them or just a pair ?

Joe M

Re: New Solar System, Battery Question

sunbunny wrote: »

When the batteries were bubbling, was it all of them or just a pair ?

All of the batteries were bubbling. It was quite loud. I guess I couldn't hear it during most of the day because the charge controllers fan was on. When the temperature went down the fans turned off. That's when I heard it. I then turned off the solar panel breaker. I didn't know what was going on.

I think I will re-wire my battery bank to a 24 volt battery bank.

In the future I may add another panel and go to a 48 volt battery bank as vtmaps suggested.

Thanks everyone for your help.

One thing I still don't understand is why the voltage on the batteries kept dropping as the sun went down and after I turned off the breaker. It dropped around .8 volts from it peak. I didn't have the inverter turned on. I monitored each pair of batteries through out the day. They just slowly dropped voltage until 12.6.

vtmaps

Re: New Solar System, Battery Question

Joe M wrote: »

One thing I still don't understand is why the voltage on the batteries kept dropping as the sun went down and after I turned off the breaker. It dropped around .8 volts from it peak. I didn't have the inverter turned on. I monitored each pair of batteries through out the day. They just slowly dropped voltage until 12.6.

When a battery is fully charged its voltage (after resting for a few hours) is about 12.7 - 12.8. While it is being charged, its voltage is higher. When you stop charging a battery, its voltage settles down to a value that reflects its true state of charge.

Likewise, when you have a heavy draw off of a battery, its voltage sags. When you stop drawing current and let it rest, its voltage rebounds to a value that reflects its true state of charge.

Since your peak voltage today was 13.4, you never got your batteries fully charged. You need to get the voltage up to 14.4 for at least a couple of hours.

Because you have four parallel battery strings, you really don't know what's going on. Some of those strings may have been fully charged, and other strings may have been under charged. When you stop charging, some strings may be discharging into the other strings.

--vtMaps

Joe M

Re: New Solar System, Battery Question

vtmaps wrote: »

When a battery is fully charged its voltage (after resting for a few hours) is about 12.7 - 12.8. While it is being charged, its voltage is higher. When you stop charging a battery, its voltage settles down to a value that reflects its true state of charge.

Likewise, when you have a heavy draw off of a battery, its voltage sags. When you stop drawing current and let it rest, its voltage rebounds to a value that reflects its true state of charge.

Since your peak voltage today was 13.4, you never got your batteries fully charged. You need to get the voltage up to 14.4 for at least a couple of hours.

Because you have four parallel battery strings, you really don't know what's going on. Some of those strings may have been fully charged, and other strings may have been under charged. When you stop charging, some strings may be discharging into the other strings.

--vtMaps

That makes perfect sense. I'm going to start building my ground mounts on thursday. When I finish I'll turn the breaker back on and let them fully charge. I'll re-wire the battery bank to 24 volts in a week or two.

Thanks so much everyone. I should have spoken to you folks before I built it.

It seems the only mistake I made is the battery bank voltage.

You folks are the best!

NorthGuy

Re: New Solar System, Battery Question

Joe M wrote: »

I'll re-wire the battery bank to 24 volts in a week or two.

The most important thing when re-wiring the bank not to forget that you need a new inverter. The old one may not like 24V.

vtmaps

Re: New Solar System, Battery Question

Joe M wrote: »

I think I will re-wire my battery bank to a 24 volt battery bank.

Do you know how to do that? You must make sure that each of the two strings has the same length of wire. In this diagram, the wires labeled "A" must both be the same length. Note that when current is flowing through the upper string, it passes through "A" on the left and three "B"s. When current is flowing through the lower string, it passes through three "B"s and "A" on the right.
Attachment not found.
--vtMaps

Joe M

Re: New Solar System, Battery Question

vtmaps wrote: »

Do you know how to do that? You must make sure that each of the two strings has the same length of wire. In this diagram, the wires labeled "A" must both be the same length. Note that when current is flowing through the upper string, it passes through "A" on the left and three "B"s. When current is flowing through the lower string, it passes through three "B"s and "A" on the right.
Attachment not found.
--vtMaps

Assuming that the long wires shown are the input, would the output positive be attached to the top left battery, and the output negative attached to the lower right battery?

Cariboocoot

Re: New Solar System, Battery Question

Joe M wrote: »

Assuming that the long wires shown are the input, would the output positive be attached to the top left battery, and the output negative attached to the lower right battery?

Charging and loads both go to the same place.

Joe M

Re: New Solar System, Battery Question

Cariboocoot wrote: »

Charging and loads both go to the same place.

Okay. That's different than the other 24 volt diagrams I've seen. It makes it simpler though.

Thanks so much!

Cariboocoot

Re: New Solar System, Battery Question

Joe M wrote: »

Okay. That's different than the other 24 volt diagrams I've seen. It makes it simpler though.

Thanks so much!

You just "expand horizontally" to adjust the battery/system Voltage.