Under load voltage drop

[carmelo]

Hi. I have a question.

I have a 48v Deka solar 370ah bank that consist of 8 6v batteries in series. The bank is farely new (5 months old).

Iam worried regarding a voltage drop that is showing in the Classic when under load. As an example:

Came home and voltage was showing 50.4 with a load of 10.8 amps. I shutdown the inverter (that powers all the house loads) and after 5 minutes, the voltage was at 51.3.

Is it considered "normal" a drop of 0.9v with such a small load? Or am I having a battery or wiring problem?

Specific gravity is good on all batteries. 1.27 to 1.28 when full.

[ClassicCrazy]

Depends on how your system is wired up.
There is always some voltage drop if you have a load.
But you could also get some voltage drop if your wiring is undersized between the batteries and inverter/Classic .
Also did you break in new your batteries with some deep cycles ?

Larry

[carmelo]

Also did you break in new your batteries with some deep cycles ?

Larry

Yes. They have gotten discharged to 60% a few times by now.

[kitestrings]

That sounds pretty normal to me.  You might check your battery manufacture's specs, but a fully charged battery, no load will be about 50.5-50.9V.  As soon as there is any load, it will drop some, and at a C/20 or C/30 rate you won't be much over nominal at 45-50% discharge.  There are some pretty handy charts - we have a set on the wall - that plot voltage vs. state of charge under charging, and under discharging.  Home Power archives would fetch them, or perhaps the battery university.

Sizing the wire is important to limit voltage drop as Larry says.  We aim for 2%; 5% is probably tolerable.  Best ~ks