Fascinating how dynamic equipment behaves, based on various factors. Thanks for keeping numbers realistic, too. This was a real-world simulation (handled accordingly). Not a white-coat lab experiment stressing out 0.01 precision measurements. Thanks for sharing!
One thing about those kill-a-watts... they are great, but the contacts in the socket on the unit seem to oxidize or corrode or something. I've had kill-a-watts melt a bit around the socket from heat due to that when left for long periods with high loads running through them. In anycase, 85% is very common for inverter efficiency under low loads. Also note that you didn't actually get 90% for your medium load or 87.9% for your high load test because you missed the loss of efficiency at the battery due to the voltage draw-down. The efficiency actually went down, not up, and the reason is due to the voltage drop from the battery and wiring to the inverter (mostly the battery since you had short wires to the inverter). On your high load test, the battery dropped from 13.3V to 12.1V which means the battery itself lost 10% efficiency (relative to its low-load efficiency). Though some of that might have been due to topping the battery off, still at 13.3V it had settled so we will use those numbers. 12.1 / 13.3 = 90.1% In addition to the 87.9% inverter efficiency. So multiply those efficiencies together. 0.901 * 0.879 = 0.792. The high-load test was actually only 79.2% efficient. This is also a good example of why people shouldn't be using 12V topologies any more. At least not for "new" projects. LiFePO4 batteries and all the insundary equipment are available in 24V and 48V and those will reduce voltage-drop related losses to 1/4th or 1/16th the losses you get at 12V with the same wire sizes, and still reduce losses substantially even when thinner wires are used. For example, a voltage drawdown of (1.19V / 2.0) (because also half the amps are being pulled for the same power consumption) on a 24V system takes you from 26.6V to 26.01V, which is 97.8% efficient. Even ignoring the "/ 2.0"... assuming the battery is half the amp-hours at double the voltage, you still get 25.41 / 26.6 = 95.5% efficient. For a 48V system lets say (53.2V - 1.19V) / 53.2V = 97.8% efficient (25Ah 48V battery vs 100Ah 12V battery). The battery voltage drawdown depends on the battery size. But the voltage drop over wiring depends only on the wire size, so the "divide by 2" comes back into play. Ohms law. P = I^2 * R.... power losses over wiring go by the square of the current. So the above efficiencies are actually higher when you put that back into play for the wire drop, particularly if running long wires to the inverter. Either way it is a huge huge huge difference verses a 12V system and that is why, really, nobody should be using 12V for "new" projects. Even when retrofitting old 12V systems with new LiFePO4 batteries, I would still go with a higher voltage and then use a Victron charge controller to down-buffer into the "old" 12V system. Then over time migrate equipment to the higher voltage as you can. -Matt
nice.. makes just want to run a 24v system now instead of 12v due to amp loads are big on 12v since i want to use a small 1000+ heater it will cut that amps in half ...1500 ac heater will drain that 12v battery in like 30 mins
I switched to a 24 volt bank and inverter just for that reason, I thought the Air conditioner's amp load would be half but it actually dropped from 75 amps on 12 volts to around 30 amps on 24 volts. I wasn't expecting that. I now wonder how a 48 volt bank would work.
@@MikeGentry Wire losses are also much lower. Basically losses are a function of the SQUARE of the current, given the same battery amp-hours. So 24V is 1/4 of the losses, and 48V is 1/16th of the losses. If you go by battery capacity, i.e. you are comparing a 100Ah 12V battery to a 50Ah 24V battery to a 25Ah 48V battery, the battery contribution to the losses will be 1/2th and 1/4th respectively at 24V and 48V. But the wire losses will still go by the square of the current (1/4th and 1/16th). Both the battery voltage drawdown due to battery's internal resistance, AND wiring losses are major contributors to efficiency losses in these sorts of systems. At lower battery voltages, the internal resistance is the major component. At high battery voltages, the wiring losses are the major component. Either way, going to 24V or 48V result in massive improvements in efficiency at load. -Matt
Fascinating how dynamic equipment behaves, based on various factors. Thanks for keeping numbers realistic, too. This was a real-world simulation (handled accordingly). Not a white-coat lab experiment stressing out 0.01 precision measurements.
Thanks for sharing!
You're welcome and thanks for the comment.
Instructive and relevant as usual.
A T Burke
Thanks for the comment. Much appreciated 👍
That was quite an interesting test. Thank you for the video and the info.
Glad you liked it! Thanks for the comment.
One thing about those kill-a-watts... they are great, but the contacts in the socket on the unit seem to oxidize or corrode or something. I've had kill-a-watts melt a bit around the socket from heat due to that when left for long periods with high loads running through them.
In anycase, 85% is very common for inverter efficiency under low loads.
Also note that you didn't actually get 90% for your medium load or 87.9% for your high load test because you missed the loss of efficiency at the battery due to the voltage draw-down. The efficiency actually went down, not up, and the reason is due to the voltage drop from the battery and wiring to the inverter (mostly the battery since you had short wires to the inverter).
On your high load test, the battery dropped from 13.3V to 12.1V which means the battery itself lost 10% efficiency (relative to its low-load efficiency). Though some of that might have been due to topping the battery off, still at 13.3V it had settled so we will use those numbers. 12.1 / 13.3 = 90.1% In addition to the 87.9% inverter efficiency. So multiply those efficiencies together. 0.901 * 0.879 = 0.792.
The high-load test was actually only 79.2% efficient.
This is also a good example of why people shouldn't be using 12V topologies any more. At least not for "new" projects. LiFePO4 batteries and all the insundary equipment are available in 24V and 48V and those will reduce voltage-drop related losses to 1/4th or 1/16th the losses you get at 12V with the same wire sizes, and still reduce losses substantially even when thinner wires are used.
For example, a voltage drawdown of (1.19V / 2.0) (because also half the amps are being pulled for the same power consumption) on a 24V system takes you from 26.6V to 26.01V, which is 97.8% efficient. Even ignoring the "/ 2.0"... assuming the battery is half the amp-hours at double the voltage, you still get 25.41 / 26.6 = 95.5% efficient. For a 48V system lets say (53.2V - 1.19V) / 53.2V = 97.8% efficient (25Ah 48V battery vs 100Ah 12V battery).
The battery voltage drawdown depends on the battery size. But the voltage drop over wiring depends only on the wire size, so the "divide by 2" comes back into play. Ohms law. P = I^2 * R.... power losses over wiring go by the square of the current. So the above efficiencies are actually higher when you put that back into play for the wire drop, particularly if running long wires to the inverter.
Either way it is a huge huge huge difference verses a 12V system and that is why, really, nobody should be using 12V for "new" projects. Even when retrofitting old 12V systems with new LiFePO4 batteries, I would still go with a higher voltage and then use a Victron charge controller to down-buffer into the "old" 12V system. Then over time migrate equipment to the higher voltage as you can.
-Matt
Thank you for all the great information. I didn't think of the voltage drop under heavy load. Also, thanks for the comment.
nice.. makes just want to run a 24v system now instead of 12v due to amp loads are big on 12v since i want to use a small 1000+ heater it will cut that amps in half ...1500 ac heater will drain that 12v battery in like 30 mins
I switched to a 24 volt bank and inverter just for that reason, I thought the Air conditioner's amp load would be half but it actually dropped from 75 amps on 12 volts to around 30 amps on 24 volts. I wasn't expecting that. I now wonder how a 48 volt bank would work.
Yes it will. You're better off getting an electric blanket. It will last for hours! Thanks for the comment.
@@MikeGentry Wire losses are also much lower. Basically losses are a function of the SQUARE of the current, given the same battery amp-hours. So 24V is 1/4 of the losses, and 48V is 1/16th of the losses.
If you go by battery capacity, i.e. you are comparing a 100Ah 12V battery to a 50Ah 24V battery to a 25Ah 48V battery, the battery contribution to the losses will be 1/2th and 1/4th respectively at 24V and 48V. But the wire losses will still go by the square of the current (1/4th and 1/16th).
Both the battery voltage drawdown due to battery's internal resistance, AND wiring losses are major contributors to efficiency losses in these sorts of systems. At lower battery voltages, the internal resistance is the major component. At high battery voltages, the wiring losses are the major component.
Either way, going to 24V or 48V result in massive improvements in efficiency at load.
-Matt