New problem involving boiling batteries

[TXtrucker]

I have 6 145w DM Solar panels, a 60 amp Outback CC, a 12v 1800watt Xantrex inverter and 6 6 volt batteries. Prior to the 6 batteries I had 4 and everything was running fine. I added 2 more to increase my amp hours to 660. Prior to doing this the system was consistently charging to 13.8v. I went into the building where the batteries are and noticed a strong odor that was not there before. I learned this was the gasses coming from the batteries. When I checked the voltage on the inverter readout it was showing 14.4.

Turns out that one of the batteries was bad, but after replacing it I am still getting the higher voltage readings. I will know more tomorrow when the sun comes up and the charge controller wakes up. Anyone have any ideas on what is going on? Thanks

[Cariboocoot]

Well for one thing 14.4 Volts is the proper (but lower) Absorb level for flooded cell batteries on a 12 Volt system. Gassing is also normal, but it could be going on for too long.
So first let's check the numbers.
Six 145 Watt panels is 870 Watts. That should be enough for 55 Amps max out of the MX/FM60. That's an 8% charge rate so it ought to work.
Now, time to check some more numbers; specific gravity on each and every battery cell. Look out for differences over 0.010.
If you had a shorted cell it would put too much Voltage into the rest in that string, causing it to gas those cells more vigorously (like running an EQ cycle).
You should also check the Absorb time limit and compare it to the Bulk time and the Amp reading at the end of Absorb. If the Absorb time runs out when the Amps are down around 2% (13) it should be good.
Float Voltage setting should be 13.8.

[TXtrucker]

I will check the numbers tomorrow as the system runs. Thanks for you comments.

[TXtrucker]

I will get a good hydrometer to measure the gravity. All I have now is a cheap float type hydrometer. Thanks

[BB.]

If you can get a DC Current Clamp meter (like one of these or better), you can measure the current to each battery.

A shorted cell would certainly cause a string to have too much current. And if one of the other strings has poor connections or an open cell, those would not have enough charging current. A DC clamp meter will show any current sharing problems right away.

Measuring the voltage across each battery can also show problems too--All batteries should be fairly close in voltage to each other (check when charging, discharging, and no load/floating). Anything that stands out needs investigating.

-Bill

[TXtrucker]

I have a voltmeter. Can I use it to get a good reading? Do I need to isolate each battery or can I leave them all hooked up? Thanks

[BB.]

You can do a lot with a good volt meter.

First, measure the voltage across each series connected battery... I.e., 7.2 volt each when charging (or on batteries with exposed bus bars between cells, 2.4 volts per cell). Do the same thing when discharging and resting. You are looking for differences, both in a string, and across strings.

Also, you can set your meter to 2 volts or even 0.2V /200 mV full scale. And measure the voltage drop across each connection. And large voltage drop, take apart and clean (note, you check voltage drop under heavy charging or heavy load; but clean when very low current so you avoid sparks and arcs--always wear appropriate eye protection, no jewelry, and protective clothes).

And--When I don't have a DC Current Clamp Meter (aka--the first 55 years of my life ), pick a similar length of cable (should be the longest) in each battery string. Use the DMM set to 2.000v or 200mV full scale and measure the voltage drop. This will allow you to compare current flow (roughly) between battery strings by using the length of wire as resistor/current shunt.

-Bill

[Ralph Day]

Don't fret about a cheap or expensive hydrometer. I've checked my $50 float type against the results of a $5 type and the results are the same. Just make sure when you're taking the reading that the float is not sticking to the tube's sides.

Ralph

[TXtrucker]

Update: My system is working perfectly. The problem was the bad battery. Thanks for all the comments.