Help - dead batteries

AndersE · February 2015

Hi

With good help from this forum, I managed to build and install a small PV system in our family cabin in Norway last winter,

The system i primarily used for Led light, is running 24 volt and consist of:
2x100 W 12V panels in series
Morningstar Sunsaver MPPT
Victron 24-12 DC/DC converter for LED lights
CTEK 24 volt battery charger (To charge the bank from a Honda EU20i if necccesary)
Studer sinus inverter 24/230 volt
Victron battery monitor with shunt

The battery bank has until now been formed by 12 * 9,2 amp 12 volt batteries, that I had from an UPS system. Batteries were not new but in good condition when installed. I wanted to wait with buying a better bank until I had run the system through the first complete season,

The system was installed in march last year, and ran perfectly until this winter.

The cabin/system was left i September fully charged. But when my brother in law arrived last night he found the batteries completely dead. (Almost not voltage)

Before just replacing the batteries i would like some comments and thoughts from you about what went wrong,

Since i was not personally the last person to visit the cabin this fall i cannot guarantee that the DC/AC or DC/DC converters where correctly shutdown before leaving.

My initial thoughts are:

It could be the Sunsaver itself since it has a small self consumption. Also i have read in other threads that problems has been observed with this particular controller in cold weather situations, that prevent it from charging

It could be the DC/DC having not been switched of.
It could be back load from the CTEK battery charger
It could be the Victron batteri monitor self load
Standby/power off load from the Studer inverter.

My initial assumption was that the small current draw from the Sunsaver, CTEK and Victron batteri monitor would be less than what the panels would supply even through the dark and cold winter. This also looked to be the case last winter.

I have a couple more of the UPS batteries that I plan to install in the system next time i visit the cabin, but i need some advise on how to debug the system and find the root caused to the dead batteries.

Also to avoid situation like this in the future I am considering to add a battery guard to the system. In this case should the Sunsaver then be connected the battery guard, og directly to the batteries to allow it to bring the system back to fully charged.

Thank in advance

Anders Esbensen

SandyP · February 2015

AndersE wrote: »

Also to avoid situation like this in the future I am considering to add a battery guard to the system. In this case should the Sunsaver then be connected the battery guard, og directly to the batteries to allow it to bring the system back to fully charged.

I would imagine the Sunsaver should stay connected to the batteries whilst the loads (including the inverter) should operate via the battery guard.

mike95490 · February 2015

The small UPS type batteries, are generally GEL batteries,and only rated for just a few deep cycles. But you have another issue, what drained them down? Below 8V, the charge controller shuts off, not enough power to run it's CPU. Did the inverter get left ON while everyone was away? A couple cloudy days and the battery would be drained. Then you must manually charge from the PV directly to the battery (a jumper of large gauge wire between PV input + and battery + will do this) till the battery comes up to enough voltage to run the controller.
Or any of the other power drains you mentioned, could flatten the batteries in a couple cloudy days. ( DC-DC, monitor, charger....)

SandyP · February 2015

AndersE wrote: »

Before just replacing the batteries i would like some comments and thoughts from you about what went wrong,

Unfortunately I think you will need to get the system up and running again (with one or more batteries) and then use the Victron BMS to show what equipment is using what power and if your solar panels are "replacing" the power that is being used. To determine if you will get enough power during Winter you need to use your latitude and enter this into a webpage that may show the solar insolation for your location and panels. I use the Victron BMS and have also added the comms cable to allow logging to a PC from which you can track amps into / out of the batteries.

Maybe look at : http://www.solarelectricityhandbook.com/solarcalculator.aspx
or http://www.solenergi.no/wp-content/uploads/2010/01/KVT_OB_2013_R046_OREEC_Solressurskartlegging.pdf

Attachment not found.

BB. · February 2015

AndersE wrote: »

The battery bank has until now been formed by 12 * 9,2 amp 12 volt batteries, that I had from an UPS system. Batteries were not new but in good condition when installed. I wanted to wait with buying a better bank until I had run the system through the first complete season,

It really sounds like some load was left on somewhere.

Although, another possibility with 12x 9,2 AH @ 12 volt batteries--It is possible that one battery shorted internally (a cell became shorted) and took down the rest of the bank.

But the fact that your bank went to zero volts really looks like a load left on. Even a shorted cell would take the battery bank down to 10.0 volts or so. Unless, once the battery bank was taken below ~10.5 volts, the solar charge controller shut down (many controllers will stop charging below ~9.0 volts).

Personally, I do not like a large number of paralleled batteries (or battery strings). And, small batteries seem not to be as "rugged" or reliable. I would suggest a single 100 AH or larger battery if you can (this is not a "hike in" cabin?). 2 to 3 parallel strings of batteries would be my recommended maximum.

And make sure they are true "Deep Cycle" Batteries, not an automotive, Marine, alarm, backup UPS type battery. Those batteries tend not to last very long if cycled deeply (below ~85% state of charge) or daily.

-Bill

westbranch · February 2015

BB. wrote: »

And make sure they are true "Deep Cycle" Batteries, not an automotive, Marine, alarm, backup UPS type battery. Those batteries tend not to last very long if cycled deeply (below ~85% state of charge) or daily.

-Bill

My recommendation is to get a set of 6 volt GC ( golf cart) batteries .. Not sure what brands there are available but like these...http://www.trojanbattery.com/markets/golf-utility-vehicle/

AndersE · February 2015

Hi again

Thank you for you comments. We managed to get the battery voltage above 24 volt again, by using the CTEK charger. Batteries are most likely highly damaged, but I will go there myself in a few weeks and see if I can figure out what went wrong.

Do you have any suggestions regarding a batteri guard ?

Br

Anders

BB. · February 2015

Automating an off grid system is a bit difficult... Lead Acid batteries are difficult to make a "simple" device that can be used to turn off the loads before the battery is damaged, turning on/off high DC current (AC inverter input, etc.).

These types of devices can be nice for monitoring your system. Battery monitors can be pretty nice and are almost a necessity to manage AGM/Sealed batteries. However, they can be fooled, be programmed wrong, or drift from actual (estimated) state of charge. So--You still have to keep an eye on battery voltage, how the charging is going, etc.

Battery Monitor (see Trimetric as one of the lower cost/full featured shunt based monitors)

There are a few battery monitors that can be integrated to a computer and even have an alarm contact that an be prgrammed (say alarm at 50% as the battery is being discharged, and turn off the alarm after battery is >80% state of charge).

http://www.victronenergy.com/battery-monitors/

There are a few charge controllers with integrated battery monitors... Midnite MPPT (classic and kid) charge controllers are among the most interesting/subject to ongoing development:

http://www.solar-electric.com/inverters-controllers-accessories/chco/misoclchco.html

Then there are Voltage Only monitors... A couple of interesting ones:

http://www.solar-electric.com/batteries-meters-accessories/metersmonitors/mnbcm.html (a few people here like because it gives you a warning if battery not fully charged in last 7 days, etc.).

And, this company has a very large/public set of documentation that talks about the details of Lead Acid batteries and how they monitor battery state of charge by voltage monitoring only. Don't know anything about their product--But they obviously live and breathe their product:

http://smartgauge.co.uk/smartgauge.html

The above gives you some options to think about...

-Bill

Help - dead batteries

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