Ultimate Guide: Sizing an Off-Grid Backup Generator

Table of Contents

1. Introduction
2. Understanding the Inverter-Charger
3. The Double Throw Switch
4. Using the Inverter as a Charger
5. Limitations of the Inverter-Charger
6. Sizing the Generator
7. Optimal Route for Generator Input
8. Generator Caution
9. Dedicated Chargers
10. Conclusion

Introduction

Generators play a crucial role in how inverters interface with hybrid, multi-input inverters. However, there are often misinterpretations and misunderstandings regarding the functionality, limitations, and implications of using generators with inverter-chargers. In this article, we aim to provide a comprehensive understanding of the relationship between generators and inverter-chargers, shedding light on the math and constraints involved. By delving into topics such as the double throw switch, generator sizing, and optimal routes for generator input, we aim to equip readers with the knowledge necessary for making informed decisions when it comes to utilizing inverters and generators together.

Understanding the Inverter-Charger

An inverter that also serves as a charger functions with separate AC inputs and outputs. Internally, it consists of an inverter power head and a double throw switch. The AC out is always connected, whereas the AC in is connected to a relay. This relay determines whether the inverter powers the AC out or the AC in.

The Double Throw Switch

The double throw switch within the inverter-charger enables the flow of power. It redirects the AC input from the AC in terminal, allowing the inverter to function as a charger. When the inverter operates in charger mode, it draws power from the power grid. However, it is important to note that the inverter cannot simultaneously function as an inverter and a charger.

Using the Inverter as a Charger

When using the inverter as a charger, it is essential to consider the power limitations. Each inverter can potentially supply up to 4,000 watts of power to the batteries. Therefore, if multiple inverters are employed, the total power input to the batteries can increase significantly. However, this poses a challenge as generators need to be kept under 60 percent of their nameplate rating to ensure stable power quality. If the load exceeds this threshold, the generator's power quality may deteriorate, leading to damage to the inverter and its connected electronics.

Limitations of the Inverter-Charger

To determine the appropriate size of the generator for utilizing the inverter as a charger, a thorough calculation is necessary. By considering the power inputs from the inverters and dividing it by 0.6 (representing the 60 percent threshold), the required generator size can be determined. However, this approach often necessitates a large generator, which may not be the most cost-effective or practical solution.

Sizing the Generator

Considering the limitations outlined above, it becomes apparent that using a dedicated charger offers a more efficient alternative. A dedicated charger, whether with a 25 amp/1.5 kW or an 80 amp capacity, can be directly plugged into the generator. This setup allows for a steady feed of DC current to charge the batteries. As a result, the inverters can continue to power the loads in the house, while the generator acts solely as a source of DC current for charging.

Optimal Route for Generator Input

Opting for dedicated chargers instead of relying on inverters as chargers offers various benefits. This approach minimizes wear and tear on the inverters, prolonging their longevity. Additionally, it reduces strain on home electronics, such as TVs, refrigerators, and computers, which are not designed to be run directly by a generator. By converting gasoline or propane to DC current as a backup, the inverters can remain in one mode, ensuring optimal performance.

Generator Caution

It is crucial to exercise caution when utilizing generators with inverters. While it is theoretically possible to use a large enough generator to power all inverters at once, it is not always the most practical or cost-efficient option. Oversizing a generator may result in tripping and power shortages, jeopardizing the functionality of the system. Therefore, it is prudent to consider alternate solutions, such as dedicated chargers, which can offer a more reliable and efficient setup.

Dedicated Chargers

Utilizing dedicated chargers, such as 1500-watt chargers, in conjunction with tractor supply generators provides a viable alternative to back-feeding inverters. This approach helps prevent power shortages and ensures a stable source of power for both the inverters and connected loads. By carefully selecting chargers compatible with the generator's specifications, users can create a robust and optimized system.

Conclusion

Understanding the intricacies of how generators interface with hybrid, multi-input inverters is essential for making informed decisions. By comprehending the limitations, calculating the appropriate generator size, and considering alternate solutions, users can create a reliable and efficient setup. By opting for dedicated chargers, the strain on the inverters and home electronics can be minimized, leading to optimal performance and enhanced longevity.