Validation of 12v Battery requirements

Ruburnel · Aug 15, 2022

I'm planning to try and power a domestic washing machine from a 12v LiFePO4 battery with a 3Kwh inverter (UK - 230v) and have done some maths but wanted to make sure I'm heading in the right direction.
I've been monitoring the washing machine (running from a normal 230v outlet) over a period of time and have seen it use a maximum of 2200 watts and 1.3Kwh for a complete cycle.
By my calculations (which may well be wrong) I'd need a 200ah battery, due to the fact that the 1300wh / 12v = 108ah, and will also need to be able to pull (2200watts / 12v) = 183amps ?
Please let me know if this is correct....or not.......

Cheers for now

Russell

sunshine_eggo · Aug 15, 2022

Does your washing machine have a surge associated with the electric motor startup?

Inverter inefficiency factored in to your calculations:

1300Wh/12V/.85 = 127Ah

2200W/12V/.85 = 216A

216A exceed the discharge rating of typical 200Ah cells.

Ruburnel · Aug 15, 2022

sunshine_eggo said:
Does your washing machine have a surge associated with the electric motor startup?

Inverter inefficiency factored in to your calculations:

1300Wh/12V/.85 = 127Ah

2200W/12V/.85 = 216A

216A exceed the discharge rating of typical 200Ah cells.

Thanks for the response sunshine

I assume that the maximum wattage of 2200 was the "surge" but can't be 100% sure tbh as I was just using one of those plug-in digital devices that shows the maximum and minimum wattage and total Kwh since the last reset, etc. From what you've pointed out I might have to have a re-think about using 12v and maybe look at 24v instead.

sunshine_eggo · Aug 15, 2022

Surge or "inrush" are typically not captured without a specialty tool designed for that feature. Many monitoring devices can capture "max", but that usually isn't the surge.

Can you link a manual for the model of washer? Sometimes the electrical specs give you an idea.

2200W is within the realm of reason for 12V. The ~280Ah cells seem to be the most favorable $/kWh at this point. 24V would required you to purchase 2X, but you could get away with smaller cells and likely keep the cost similar.

Another thing to consider is the BMS. BMS with 100A ratings are prolific. 200A+ are less common.

Ruburnel · Aug 15, 2022

sunshine_eggo said:
Surge or "inrush" are typically not captured without a specialty tool designed for that feature. Many monitoring devices can capture "max", but that usually isn't the surge.

Can you link a manual for the model of washer? Sometimes the electrical specs give you an idea.

2200W is within the realm of reason for 12V. The ~280Ah cells seem to be the most favorable $/kWh at this point. 24V would required you to purchase 2X, but you could get away with smaller cells and likely keep the cost similar.

Another thing to consider is the BMS. BMS with 100A ratings are prolific. 200A+ are less common.

I've found a UK manufacturer/supplier of 12v batteries that have a 200A discharge rating:

Roamer 160SMART3 - 12V 160Ah LiFePO4 Lithium Leisure Battery

The Roamer 160SMART3 is a compact drop in 12V 160Ah LiFePO4 battery for install in a campervan, motorhome, boat, tiny house or even wild camping. Includes 200A continuous discharge, active balancing, Roamer BMS bluetooth app and handles for additional portability. Free delivery, Roamercare, 10...

roamerbatteries.com

The washing machine is a Hotpoint and I found the attached specification sheet but it doesn't give any idea of the "surge" rating.

Cheers for now

StuartV · Aug 15, 2022

How long is the wash running for? I have a Hoover washing machine. I have been running it off solar through my AiO. The most I've seen it use was 1.7kwh (heating up the water), thats on a 30C wash for a 59min cycle. My washing machine doesnt use 2kw to do the whole load.

My set up has an electricity monitor in the fuse box, and after 1 wash at 30C on the 59min cycle, it has used about 300watts maybe.

Maybe change your wash cycle so its at a lower temp and a shorter wash ?? Be cheaper on batteries then.

sunshine_eggo · Aug 15, 2022

Ruburnel said:
I've found a UK manufacturer/supplier of 12v batteries that have a 200A discharge rating:

Roamer 160SMART3 - 12V 160Ah LiFePO4 Lithium Leisure Battery

The Roamer 160SMART3 is a compact drop in 12V 160Ah LiFePO4 battery for install in a campervan, motorhome, boat, tiny house or even wild camping. Includes 200A continuous discharge, active balancing, Roamer BMS bluetooth app and handles for additional portability. Free delivery, Roamercare, 10...

roamerbatteries.com

The washing machine is a Hotpoint and I found the attached specification sheet but it doesn't give any idea of the "surge" rating.

Cheers for now

Based on the datasheet, 13A * 240V = 3,120W

StuartV said:
How long is the wash running for? I have a Hoover washing machine. I have been running it off solar through my AiO. The most I've seen it use was 1.7kwh (heating up the water), thats on a 30C wash for a 59min cycle. My washing machine doesnt use 2kw to do the whole load.

My set up has an electricity monitor in the fuse box, and after 1 wash at 30C on the 59min cycle, it has used about 300watts maybe.

Maybe change your wash cycle so its at a lower temp and a shorter wash ?? Be cheaper on batteries then.

Please review your use of kW and kWh.

Ruburnel · Aug 15, 2022

StuartV said:
How long is the wash running for? I have a Hoover washing machine. I have been running it off solar through my AiO. The most I've seen it use was 1.7kwh (heating up the water), thats on a 30C wash for a 59min cycle. My washing machine doesnt use 2kw to do the whole load.

My set up has an electricity monitor in the fuse box, and after 1 wash at 30C on the 59min cycle, it has used about 300watts maybe.

Maybe change your wash cycle so its at a lower temp and a shorter wash ?? Be cheaper on batteries then.

Apparently, it's one of those "smart" machines that varies the run time based on the weight of the load and I'm reliably informed by the lady wife that using a 30deg wash is worse than useless in most cases, so I just go along with what she tells me

It's just a little project for me to play around with while I wait for some 48v LiFePO4 batteries to arrive in stock for the "real" off-grid utility room plan.
If I can't run the washing machine, I can look at the dishwasher instead as we tend to run that on the "economy" setting which will hopefully be less power hungry than the WM

Ruburnel · Aug 15, 2022

sunshine_eggo said:
Based on the datasheet, 13A * 240V = 3,120W

Please review your use of kW and kWh.

Most UK appliances have a 13A fuse/rating but I've just noticed the line above the Current says "Electrical connection rating (W) = 1850, so maybe the 2200W I've seen includes the "surge"?

Ruburnel · Aug 16, 2022

I think we can say that my original calculations were pretty accurate, apart from missing the 85% efficiency of the inverter

Having said that, I could use a voltage of 12.8 as that seems to be the nominal voltage of the 12v battery that I've been looking at:

1300Wh/12.8V/.85 = 119Ah

2200W/12.8V/.85 = 202A

afro-solar · Mar 19, 2023

Ruburnel said:
I'm planning to try and power a domestic washing machine from a 12v LiFePO4 battery with a 3Kwh inverter (UK - 230v) and have done some maths but wanted to make sure I'm heading in the right direction.
I've been monitoring the washing machine (running from a normal 230v outlet) over a period of time and have seen it use a maximum of 2200 watts and 1.3Kwh for a complete cycle.
By my calculations (which may well be wrong) I'd need a 200ah battery, due to the fact that the 1300wh / 12v = 108ah, and will also need to be able to pull (2200watts / 12v) = 183amps ?
Please let me know if this is correct....or not.......

Cheers for now

Russell

First question - what is your inverter's Pf (power factor)?

Second question - is your inverter a 12V or 24V unit?

Ruburnel · Mar 21, 2023

I should have updated this thread a while ago, as I purchased a Roamer 160ah 12v battery and it has been happily running our Washing Machine via a 3000W 12 v Inverter from FCHAO

afro-solar · Mar 21, 2023

Ruburnel said:
I should have updated this thread a while ago, as I purchased a Roamer 160ah 12v battery and it has been happily running our Washing Machine via a 3000W 12 v Inverter from FCHAO

Happy days.

Validation of 12v Battery requirements

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Roamer 160SMART3 - 12V 160Ah LiFePO4 Lithium Leisure Battery

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