manufacturers claim for appliance run time - Calculations?

[shine]

First, Your website and videos are fantastic, very good information…thanks.

I am having trouble understanding how the manufacturers are calculating the hours that certain appliances can run on their solar battery “generators”.

Bluetti AC200 – 1700Whr battery – max inverter output = 2000watts

They claim:

Refrigerator(300 watt) – run for 17 – 19 hours

Toaster (900 watts) -run for 1.6 – 3.2 hours

Fan (25 watts) – run for 36 hours

I thought:

• amps X voltage = watts
• battery capacity given in watt/hrs – meaning that a 1700 watt/hr battery could produce 1700 watts for one hour and then it was empty. Or 17 watt for 100 hours.
• Amp rating for appliance x voltage of appliance = watts (continuous need to run appliance)
• So for example the refrigerator referenced by Bluetti (AC200) uses 300 watts continuously.
• 1700watt hrs divided by 300 watts = 5.6 hours. What are they talking about 17 -19hours????

 

[Hedges]

Typical full-size fridge is only running 25% of the time. Consumer label for energy consumption shows 500 kWh/year, more or less. That's 1500 Wh/day, about 60W or so average. So you get more hours.

 

[Dzl]

First, Your website and videos are fantastic, very good information…thanks.

I am having trouble understanding how the manufacturers are calculating the hours that certain appliances can run on their solar battery “generators”.

Bluetti AC200 – 1700Whr battery – max inverter output = 2000watts

They claim:

Refrigerator(300 watt) – run for 17 – 19 hours

Toaster (900 watts) -run for 1.6 – 3.2 hours

Fan (25 watts) – run for 36 hours

I thought:

• amps X voltage = watts
• battery capacity given in watt/hrs – meaning that a 1700 watt/hr battery could produce 1700 watts for one hour and then it was empty. Or 17 watt for 100 hours.
• Amp rating for appliance x voltage of appliance = watts (continuous need to run appliance)
• So for example the refrigerator referenced by Bluetti (AC200) uses 300 watts continuously.
• 1700watt hrs divided by 300 watts = 5.6 hours. What are they talking about 17 -19hours????

Sounds like you have a pretty good understandings of the basics and the basic math. The final variable you are missing is duty cycle (and/or actual power draw if it is variable).

Duty cycle is the ratio of time spent running vs not running. A fridge cycles on and off to maintain whatever temperature it is set at (or if its a DC fridge or inverter fridge it varies the speed of the compressor and draws more or less power to maintain the temperature. This is why the Volts x Amps method won't work for calculating the consumption over time of this sort of load.

If there is an energy star sticker, you can take the kWh per year and divide by 365 to get the daily consumption, if your temperatures will be above 70-80*F add a bit on top

 

[shine]

Ok wow!! did not think about it turning on and off...dah That makes sense...Thank you to both of you

 

[shine]

Ok now I looked at an appliance that runs continuously - the fan using 25 watts. then 1700watt/Hr battery divided by 25 watts = 68 W/hr ????
Manufacturers states 36 hours. What are the assumptions there?

 

[shine]

68 hrs ---correction

 

[Hedges]

Probably doesn't cycle its battery from 100% to 0%, longer life with partial cycle.
Maybe they only allow 900 Wh from the 1700 Wh battery? That would explain 36 hours for 25w load.

The toaster may also cycle on and off rather than drawing 900w continuously - depends on model?

 

[gnubie]

Can't say I've ever come across a toaster, not cheap nor fancy, that cycled the element. It's just full bore until the bread is toasted and potentially beyond.

 

[shine]

Hedges, Thanks - got it. manufacturers may have all sorts of variables and assumptions in the calculations.

 

[Forbisher]

Probably doesn't cycle its battery from 100% to 0%, longer life with partial cycle.
Maybe they only allow 900 Wh from the 1700 Wh battery? That would explain 36 hours for 25w load.

The toaster may also cycle on and off rather than drawing 900w continuously - depends on model?

Bluetti makes all kinds of mistakes which explains the fan hours.

Toaster (900 watts) -run for 1.6 – 3.2 hours
1700w x 0.85 inverter efficiency is 1445w divided by 900w is 1.6 hours so they got it right.
Dunno about the 3.2 hours but as I said Bluetti is all over the map on their specs.

 

[Dzl]

Both toasters and fans tend to have power levels and/or speeds settings so that may explain the ranges

 

[Forbisher]

Both toasters and fans tend to have power levels and/or speeds settings so that may explain the ranges

1700w x 0.85 inverter efficiency is 1445w divided by 25w fan is 57 hours