Electrical – Battery bank system for a load of 1600 Watts

batteriesbattery-charginginvertersolar energy

How many batteries of 12 V x 125 Ah needed to continuously run a load of 1600 Watts using an inverter of 24 VDC x 120 VAC that uses a battery bank as primary source?

  1. For a load of 1600 W , at least an inverter size of 2400 W is needed. The existing inverter output is 3000 W, it will be able to run the load at near 55%. The question is to arrange a battery bank system so that the load can be run without depleting the batteries with a runtime of at least 10 hr.

  2. The batteries of 12 V x 125 Ah need to be in parallel and in series in order to provide the 24 DC source to the inverter. There are currently some 12 V x 125 Ah and more may be needed. We need a way to compute how many more batteries of 12 V x 125 Ah to arrange in order to satisfy the inverter input of 24 DC and the minimal runtime of 10 hr for the loads.

After some computations, I found that the minimal needed for the load for 10 hr will be around 1300 Ah that will give about 10 batteries of 12 V x 125 Ah

  1. What needs to be taking care is the remaining 14 hr runtime, an extra load of 1600 W that may be needed later on and how the batteries will be charged.
    Based on the specs , it’s an inverter/charger that can be auto switch. To avoid discharge of the batteries the inverter can be set to autocharge the batteries from a generator or solar panels for the remaining 14 hrs

If in need to add another load of 1600 W, since the first one works at 55% adding extra batteries in the bank may help in order to avoid overload of the inverter. This part of the problem is to find out how many batteries can be added to the system without risk.

The inverter Specs
Output Specifications:

•   Continuous Output Power: 3000 Watts
•   Surge Rating: 9000 Watts (20 Seconds)
•   Output Waveform: Pure Sine/Same as input (Bypass Mode)
•   Nominal Efficiency: >88% (Peak)

Input Specifications

•   Nominal Input Voltage: 24.0 VDC
•   Minimum Start Voltage: 20.0 VDC
•   Low Battery Alarm: 21.0 Vdc-22.0 VDC

Batteries Specs

•   Nominal Voltage : 12 V
•   20 Hr Capacity : 125 Ah
•   Charging Current : 8A-35 A
•   Charging Voltage : 14.4-14.9 V
•   Float Voltage : 13.5V-13.8 V

Bitcoin miner load specifications

•   Hash Rate: 11.5 TH/s. ...
•   Power Consumption: 1450 W +7% at the wall, with Bitmain's APW3 PSU, 93% efficiency)
•   Power Efficiency: 0.126 J/GH + 7% at the wall, with Bitmain's APW3 PSU, 93% efficiency)
•   Rated Voltage: 11.60 ~ 13.00 V.

Best Answer

Minimum of 4 Batteries. 2 in Series to give you 24V connected in parallel to another 2 in series. 12 x 125 A = 1500 W per battery for 1 hour of operation at inverter efficiency of 88% would give you 1320 Watts per hour final. So two connected in series would give you 24 V Nominal and 1320 Watts for 1 hour. Another set of two in parallel would give you a total of 24V nominal and 2640 Watts for 1 hour.

Your load is a continuous 1600 Watts. So in 1.65 hrs your batteries will be depleted. Most of us know batteries do not last till 0 %. If you want to maintain the batteries in good working condition 50% of battery depletion is recommended. Given the above scenario your 4 battery capacity to support the load is 1.65/2 = 0.8 hrs.

Please note the surge of your load is not mentioned. So you also need to account for it in addition.

My recommendation would be using 6 V batteries with higher AH rating. ( 235 HA or 435 AH ) ( 6V x 4 ) + (6V x4)

Later if you double the load with same inverter you need to resize the battery bank to support the load and making sure your inverter can handle the continuous/ surge load requirements of your load.

Ask further if you need clarification.

Sample system 48V. 6x 435 AH deep cycle lead acid batteries (20.88 kWh Total battery capacity) 48V Inverter charger 24 V 235 W solar panels ( 15 total, 3 in series x 5 sets)

The above system was used on a household with a typical draw of 10kWh per day and with typical charging of battery bank from Solar panels only. 4-6 hours of Sunlight is enough to charge the batteries from total depletion to full.

Most starters including myself have made the mistake of powering heavy load with 12V deep cycle batteries. If someone intend to operate heavy loads best deep cycle batteries would be 2V or 6 V. Reason is simple, these batteries has the volume and thick plates to sustain the load for longer time duration with less heat and chemical reaction.

Always remember anytime an inverter is used power is reduced by at least 10%. (published manufacturer data is always higher than actual data) Please pay attention to proper battery ventilation, if Lead Acid batteries.

Safety is paramount when building a system. Proper circuit protection both incoming and outgoing power is a must. So please have your system inspected by a qualified professional before operation.

Finally, do not be discouraged by technical information. We are all humans, and we learn well by making mistakes and learning form our mistakes.