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24v Inverter Testing with a Used Tesla Battery module

Because 6 cell Lithium-Ion batteries have an end-of-cycle voltage of 18v, inverters designed for 24v systems may cut off early, reducing the available energy from the battery.

In this experiment, we connected 2 different 24v pure sine inverters to a used Tesla Model S battery module, and checked the power consumption of a variety of constant loads.

The battery for this test is a used 2014 Tesla model S module which delivered 3,632 watt-hours during a full cycle load test.

Graph of actual load test data performed in our shop
Actual load test data performed in our shop. Tesla module ID: 5YJSA1H15EFP61673 4 of 16
construction tools powered by tesla battery

The Inverters used in this test are:

AIMS 1,500 Watt Pure sine model PWRI150024S, $329

WZRELB 2,500 Watt pure sine model WRBP2500W, $319

We chose these 2 models because they both have a well formed sine wave output with minimal distortion, and a reasonable price.

Note that the 2 inverters have different non-adjustable cutoff voltages.

The AIMS documentation specifies “Input under-voltage alarm 19.6 ± 1VDC”, and as tested it alarms at 19.5v, which is at 5% SOC on the test battery.

The WZRELB documentation specifies “Low Voltage Alarm 19.5-21.5v”, and it started beeping at 20.3v, which is at 18% SOC.

The cutoff voltage was tested using a variable DC power supply and a 23w light bulb loading the inverters.

Conclusions

This demonstrates that careful selection of your equipment will help get the most out of your
used tesla battery, without paying a premium price for programmable inverters.

The inverter with a lower cutoff allows you to utilize the full capacity of your battery.

On the other hand, you may prefer the inverter with a higher cutoff, which may extend the cycle life of your battery by not deeply discharging it.

A few surprises stand out in the test data.

First, the microwave oven rated “1150 Watts” could not be started using the 1,500 Watt inverter. When powered by the larger inverter, it pulled 1,888 Watts from the battery, nearly twice the power on the sticker! This is likely due to a large reactive component in the current flow used by the microwave. Because we measured the load using actual DC power flow from the battery, the extra energy must be dissipated by either the inverter or the oven itself. Further testing is needed to determine the most efficient way of powering a microwave oven on inverter power.

The 20″ floor fan only consumed 20% more power at high speed vs low speed, but it moved a lot more air. This fan uses a shaded pole induction motor, which is inefficient at low speed. Running one fan at high speed is much more efficient than running 2 fans at low speed.

Another interesting data point is the hair dryer. It consumed 86 Watts more when running on the AIMS inverter (which is actually 388 watts more than the rated output). This is because the AIMS inverter was supplying 117 Vac, versus 115 Vac from the WZRELB inverter. Since the hair dryer is a nearly 100% resistive load, it’s power consumption is directly proportional to the RMS AC voltage. Most of the other items tested showed little variation between the 2 inverters.

Test Data

Table 1: Average run time using the AIMS 1500w pure sign inverter

As tested, the AIMS 1500w pure sine inverter alarms at 19.5v, which is at 5% SOC of the Tesla battery.
The Tesla Battery will deliver 3450 watt-hours before this inverter’s cutoff voltage.
Wattage is measured from battery draw, including inverter efficiency losses.

DeviceActual WattsRun time until inverter cutoff at 5% SOC
Inverter only, no load. (standby power)16W215.6 h
100w equivalent led lamp37W93.2 h
60w equivalent led lamp25W138.0 h
Small Air compressor (note 1)570W6.1 h
Desktop Computer (note 2)250W13.8 h
Hair Dryer, labeled “1875”1,888W1.8 h
Vacuum Cleaner, (note 5)1,230W2.8 h
20″ floor fan, high speed160W21.6 h
20″ floor fan, low speed136W25.4 h

Table 2: Average run time Using the WZRELB 2500W pure sign inverter

As tested, the WZRELB 2500W pure sine inverter alarms at 20.3v, which is at 18% SOC of the Tesla battery.
The Tesla Battery will deliver 2,987 watt-hours before this inverter’s cutoff voltage.
Wattage is measured from battery draw, including inverter efficiency losses.

DeviceActual WattsRun Time until inverter cutoff at 18% SOC
Inverter only, no load. (standby power)18W165.9 h
Microwave oven rated 1150W (note 4)2,080W1.4 h
5,000 BTU window AC (note 3)430W6.9 h
Laptop charger rated 64w81W36.9 h
55″ TV and sound bar w/sub (note 6)150W19.9 h
Hair Dryer, labeled “1875W”1,802W1.7 h
Vacuum Cleaner, (note 5)1,230W2.4 h
20″ floor fan, high speed167W17.9 h
20″ floor fan, low speed140W21.3 h
Notes:
1. California Air Tools 1P1060S, rated 4.5 amps
2. Small form factor desktop PC, Windows 10, Intel i7, idle, with 3 monitors, plugged into an APC UPS
3. Cool-Living CLW-15C1A-JA09AC window air conditioner. 5000BTU/h, rated 4.0 amps
4. GE Microwave JES1657SM1SS, Rated cooking power 1150 watts
5. Shark NV70 31, Upright household vacuum with brush roll powered, rated 10 amps
6. Element 55″ Roku TV and old Vizio soundbar with bluetooth surround and subwoofer, playing Bob’s Burgers at party volume.

External product links on this page do not contain affiliate trackers- we will not make a profit if you buy either inverter.

1 thought on “24v Inverter Testing with a Used Tesla Battery module

  1. Very interesting test. One thing that stands out for me was the microwave data. This explains my experience powering a rated 900watt microwave with a 2000watt generator. The generator ran the oven but it struggled. I could not understand why a 900watt appliance would make a 2000watt (1800watt continuous) generator moan and groan (but not kick out the generator breaker).

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