How Long can I run my 2000 watt inverter? (1 Viewer)

[Fisher23]

Who knows how to calculate this? I'm not sure how to do this math.

How Long can I run my 2000 watt inverter, and how long to recharge it?

Lithium 138 AH battery powers a
2000 Watt inverter with a 90% efficiency rating - running a
500 watt blender then recharged with a
DC 2 DC - 20 amp charger (I heard the 40 amp could damage my OEM alternator)

Is it 138 AH x 12 volts x 90% efficiency = 1490 watts
If I run my blender for 2 hours = 1000 watts then approx. 490 watts remain (or 1/3)

How many hours would the engine need to run to recharge the 1000 watts; I'm not sure on my math?

 

[sdnative]

power (W) x time = energy (Wh)

power = voltage x current

To convert battery capacity (Ah) to battery energy (Wh) multiply by nominal voltage (12.8V for LFP) . As your battery discharges the voltage will drop and the current will rise assuming constant power load.

So your 138Ah battery is ~1766 Wh. Problem is as batteries age and/or are cycled they lose capacity. The battery may have been rated at 1766Wh when new, but probably isn't that now. Also, that is the total energy in the battery, the usable energy will be less, as you can not / do not want to cycle between 100% and 0% SoC. Probably safe to assume 90% of total is usable for LFP. So usable energy is about 1766 x 0.9 =1590Wh when new. Could be much less now, but let's assume it is still 1590Wh for this calculation.

Need to check the max discharge rate of the battery. Some LFP batteries are rated at 1C discharge, others at 2C or even 3C. C-rate refers to the ratio of current to capacity. So a 1C, 138Ah battery could discharge a maximum of 138A. A 2C, 138Ah battery could discharge a maximum of 276A. Since power = voltage x current, max discharge power is a function of voltage and voltage will change as the battery discharges. So to calculate max discharge power, you could use the minimum voltage of say 12V. So a 1C, 1766Wh battery could discharge around 1656W (when at low SoC).

So the max load that you would want to power would be the lesser of the battery max and inverter max, 1656W in this case. You generally want to be inverter limited so a 1500W inverter would be a good fit for that battery. You can use a larger inverter just don't connect loads over the battery max.

For your 2000W inverter: If the 2000W rating of the inverter is at the AC side (probably is), then powering a 500W load through a 90% efficient inverter would equate to a 500W / 0.9 = 555W draw from the battery. So if you are powering a 500W (resistive) load it would draw 555W and you could run it for theoretically 1590Wh / 555W = 2.86 hours. Real world use would be less because the battery capacity is probably not still 138Ah.

This all assumes pure resistive loads (lights, heater, etc) where power factor = 1 and W = VA. The blender has an induction motor and is not pure resistive so run time would be slightly less.

 

[sdnative]

As far as charging, if you used 1000Wh of your battery, and you are charging at 20A x 12.8V = 256W, it would take about 4 hours to recharge the battery. This is a ballpark number as the charge rate will vary depending on battery voltage and the charging phase (bulk, absorption, etc)

 

[e9999]

^ plus another 10% cuz you would actually use 1,100 Wh from the battery, and then whatever the internal efficiency of the charging process is

OP, good thing that you are asking, I'm afraid that you seem to mix power and energy, that is a very important distinction to make.


but the more interesting question is why do you plan on running a blender for 2 hours...? That is a lot of Margaritas...

 

[Fisher23]

As far as charging, if you used 1000Wh of your battery, and you are charging at 20A x 12.8V = 256W, it would take about 4 hours to recharge the battery. This is a ballpark number as the charge rate will vary depending on battery voltage and the charging phase (bulk, absorption, etc)

^ plus another 10% cuz you would actually use 1,100 Wh from the battery, and then whatever the internal efficiency of the charging process is

OP, good thing that you are asking, I'm afraid that you seem to mix power and energy, that is a very important distinction to make.


but the more interesting question is why do you plan on running a blender for 2 hours...? That is a lot of Margaritas...

Thanks !!

Yes Margaritas .. and smoothies.

The battery max continuous load is 150 Amps, but I was unable to find a max "c" rating for discharge, but I did find a c/2 max for charge.
The battery (Valence U27-12XP) I had tested and it's still at 100% and 138 AH.
I did decide to go with the 40 amp dc to dc.

I might have been able to get by with a 1500 watt, but occasionally one of my guests brings her air fryer.

 

[sdnative]

I found this spec sheet. As you said, 150A max discharge with 300A overload for up to 30 seconds.

That would allow just under 2000W AC power when the battery is fully charged, and about 1600W AC power when the battery is low SoC.

On the charge side, 40A is under the C/2 max charge rate so you should be good.

 

[e9999]

I realize that people are often in a hurry, but my take on charging batteries is that I prefer to go with smaller currents in order to lessen the strain on the battery. I have seen data that suggest a big difference in life expectancy depending on how fast you charge them.

 

[sdnative]

Also, forgot to mention above but keep in mind that the usable capacity is affected by the charge/discharge rate. The higher the rate the less usable capacity you will extract. The 138Ah assumes you discharge at 0.2C / 27.6A or below.

I do not believe that battery has a built in BMS. You may want to have something to protect from over-charging and over-discharging. I am using a Victron BatteryProtect for the low voltage protection, and adjust the cutoff voltage of the charger for the high voltage protection.

 

[Fisher23]

Thanks .. I'll take a look at the victron for the under charge. The fridge is auto shut down at approx. 10 volts. I have a 12 volt meter beside the plug that monitors the battery.

the dc 2 dc charger has over-charge protection (plus that special way to charge lithium) and is setup to only start after the engine has been running for 90 seconds.; the solar also has over-charge protection..

Most of the time this is just running the fridge... with 200 watt solar on the roof. Blender when camping is fun.

 

[LandLocked93]

There's always Wits' End air-powered blender. lol