# Who has a 48 volt battery bank?



## canfossi (Sep 18, 2005)

What number is your invertor reading for the battery voltage in the morning, for a 48 volt system on average? Mine is usually between 46v to 47v and was wondering if this was too low? This is during winter when there is less sun. Hope you can help, thanks Chris


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## NW Rancher (Mar 8, 2008)

Well, the lowest of those readings would indicate a minimum voltage of 11.5v in each 12v cell of your bank. That's not terrible, but if you are drawing them that low every night they might not last as long as you would like. I'm no expert in these systems, but if I were you I would talk to the battery manufacturer and see what they recommend as maximum repeated discharge levels. If 11.5 is too low, you might need to increase your Ah capacity.


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## canfossi (Sep 18, 2005)

Thanks, well right now I am looking into more solar panels, unfortunately there isn't enough wind here for a wind turbine, so they tell me. Thanks Chris


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## NW Rancher (Mar 8, 2008)

Before you spend $ on more charging capacity, you should look at your storage and usage figures. If you are reaching dusk with your batteries at full charge, more panels won't help you get through the night. You would need more storage (batteries) in that case. If the system can't keep up with your usage during the day, then perhaps more panels will help. Also, it's often cheaper and better system design to look at all your uses and cut power draw at the end of the chain then it is to increase the size of your system.


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## trkarl (Dec 15, 2009)

Hi Chris,

I have a 48v bank I cycle daily. My voltage in the morning is usually around 50v.
My bank consists of 8 Surrette 6cs17ps batteries with an amp/hr rating of 546 at the 20 hour rate.

Usually I pull on average 90 amp/hrs per night so this is not even a 20% discharge. A little info about your batteries may help with your problem such as:

How old are the batteries?
What is the amp/hr capacity of the bank?
How often does it get fully recharged?
Are you able to measure the specific gravity or are they sealed batteries?
How many amps are you pulling from the bank when the voltage is read?

Here is a little article from Home Power Mag in 1993 but pay attention to the graphs especially the second one that shows battery voltage and state of charge during discharge. Though it may not be exactly the same for your batteries they will be real similar.

http://www.arttec.net/Solar_Mower/4_Electrical/Battery Charging.pdf

IMHO your voltage is extremely low in the morning unless you are pulling an unusually large load off them when you take the reading.

Do you have a meter like the Trimetric 2020? I like mine because it will tell you exactly what you pull off the batteries every night.

According to the graphs from the article if you are pulling from the batteries at the 10 hour rate which is C/10 a 12v reading, 48v in your case would indicate about a 50% discharge which is basically as low as you want to go and have long life from your batteries.

If you are discharging at C/20 then you would be at about an 80% discharge at 12v (48v). Not good.

Hopefully they are FLA batteries that you can read the specific gravity of. That will tell you exactly how charged your batteries are.

If you are getting down to 46 - 47 volts in the a.m. then that would indicate usually that the batteries are almost depleted or severely sulphated or maybe even a shorted cell.


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