Series parellel options.

[copperlogic]

HI there, I'm wondering if anybody can help me please? I have 16x12v 150ah batteries. I'm looking to achieve 96v. I have two options as I see it: either parallel two strings of 8 batteries in series or series connect pairs of paralleled batteries in twos. The maths equates either way but I'm not sure which is the better or perhaps only option. Thank you.

[inetdog]

HI there, I'm wondering if anybody can help me please? I have 16x12v 150ah batteries. I'm looking to achieve 96v. I have two options as I see it: either parallel two strings of 8 batteries in series or series connect pairs of paralleled batteries in twos. The maths equates either way but I'm not sure which is the better or perhaps only option. Thank you.

The general rule for lead acid batteries is that you make up the series strings first and then put those in parallel.
Among other things it keeps you from boiling out a battery if its "partner" in a two battery series pair fails with a low capacity or high internal resistance or open circuit.

If you did not do series first you would have to actively monitor the voltage of each parallel pair in the series string.

If you do series first and one battery fails with high resistance, the current to that string will be reduced, effectively protecting that battery.
If you do series first and one battery (or cell) fails by shorting out, then the current through that string will still be limited, protecting the other batteries in the string.

[copperlogic]

That makes perfect sense. Easier to wire up too. Thank you for your reply. I have another question if you could take a stab at it? I have a low frequency 10kW inverter. It is a basic and robust Taiwanese machine 160 pounds in weight . It has AC or DC priority. Mains 220 in, 96 battery in and inverted or mains 220 out. Simple. Something I'm trying to get my head around is how an inverter draws a load from a solar array while the batteries are simultaneously being charged? Is this a case of the draw is less than the array is providing and the batteries are absorbing the difference? The reason I ask this is the charge controller and the batteries are connected in parallel and in turn connected to the inverter. I have chosen to stay away from high frequency do everything inverters. I am happy with a fractionally less efficient set up that I can repair if it comes to it.

[jflorey2]

Something I'm trying to get my head around is how an inverter draws a load from a solar array while the batteries are simultaneously being charged? Is this a case of the draw is less than the array is providing and the batteries are absorbing the difference?

Yes; this is Kirchoff's Current Law in action. If the load is more than the solar array, the additional energy comes from the battery. If it is less than the array, then the additional energy goes into the battery. If the battery is full then the charge controller reduces power.

[inetdog]

The one situation in which this would not work would be where the charger is not powered directly from the panel DC but from the grid/inverter output side in a hybrid inverter.
In that case the AC line interface in the hybrid could either be taking grid current for charging or supplying current to the grid side, not both at the same time. As long as the charging function is independently powered from the panel output there is no reason not to invert and charge at the same time.

[copperlogic]

I have been playing with electrical stuff all my life but I have never heard of Kirchoff's Current Law. It seems elementary in terms of conservation of energy. The energy must go somewhere. Just when I thought I knew something about something I proved myself right. Thanks again