Tesla Module Load

How much load can a Tesla Module handle

Using a Tesla Module for energy storage is a great option for upgrading an RV. When designing a system must the possible Inverters be considered. A Magnum MS4024 has a low Volt cut-Off for 20 Volt with up to a minute delay or a 19 Volt instant Cut-Off. This is to protect theĀ Inverter for excessive Current and Heat.

Working with a Tesla Module is the operating range from 100% State of Charge (SoC) with 25.2 Volt and 0% SoC with 19.8 Volt. A Tesla Module has an almost linear SoC to Volt curve and in the calculations is it assumed to be linear. Lithium batteries charged to 100% SoC is experiencing higher degradation and run a higher risk for in-balance to charge to critical Volt per Cell. A good use is to leave some room and not charge to 100% SoC, 90% to 80% SoC is a common range also used in the Tesla Car.

With 80% SoC (0.80 * (25.2-19.8) + 19.8 = 24.12 Volt) to low Volt Cut-Off 20 Volt ((20 – 19.8) / (25.2 – 19.8) = 3.7%) is 76% of the capacity of a module available but allow good range for in-balance security and take into account the low Volt Cut-Off of the Inverter. 76% of the capacity in a Tesla Module is around 4.0 kWh of useful energy.

The other thing to consider is the drop in Volt during load. Doing measurements on our House Battery allows estimating what load a single module can support.

With Testing reaching a level of 0.1C (10% of fully discharging in 1 Hour) is the drop in Volt looking linear to the loads. That can now be used to calculate “Early Cut-Off” for an inverter based on load, this calculation does not take into account other losses like the drop in Volt in the wiring that is going to make this even worse.

Looking at this can a Single MS4024 Inverter that allows up to 5000 Watt in 1 Minute Bursts or 4000 Watt 24/7 require a single Tesla Module to be over 50% SoC to handle the load without risking an Inverter disconnect. With our 80% to 4% is the 22.7 Volt 66% SoC ((22.7 – 20) / (24.1 – 20)). This is the main thing to think about when designing the Battery Pack. If loads of 5000 Watt occur just for a minute that reaches the Inverters limit is a single Tesla Module, not a viable option since the Volt of the single Module drops below Cut-Off for the inverter when only 30% of the stored energy is used.

We have 5 Tesla Modules in parallel and that means each Module is only loaded with 1000 Watt, that allows using the Inverter to full capacity all the way to 14% SoC. Looking at this should a Single Tesla Module never be used for anything like a Hair Dryer, Air Condition or Microwave Oven. Dual Tesla Modules can run one of these devices, but 3 or more Tesla Modules is when this can handle multiple high loads.

 

 

2 thoughts on “Tesla Module Load”

  1. Very Cool! I have wondered about this. Because of the voltage drop our inverter cut out is set at 19V which helps under temp heavy load at lower SOC. Were only running one module.

    1. Thanks. The Magnum Inverters have hardcoded values for the Low Voltage cut-out to protect the electronics. It can also allow a short time down to 19 Volt, but more than a minute is 20 Volt. This is not adjustable down only up.

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