Doing my BESS to stay online
Our friends at West Coast Battery Forum are hosting a meet up in Gothenburg on 13th June:
West Coast Battery Forum, a Swedish networking, and knowledge sharing NGO is hosting the 1st Nordic Battery Startup Meet - a one-day conference focusing on the (extended) Nordic region’s most exciting battery startups and SMEs. Expect behind-the-scenes tech stories, startup journeys, and a sprinkle of VC insight. Meet Altris, Rivus Batteries, Cactos, Ionworks, Compular, Sila Nanotechnologies, and more in one room. As special invited plenary speakers: Dr. Ulderico Ulissi, CATL, will share his perspective on technology transfer, and Greger Ledung, Swedish Energy Agency, will give a snapshot of the Nordic soft funding landscape. As always, WCBF will vouch for good food, even better people, and plenty of time to spark conversations. More info and tickets here. Everyone's welcome!
Now onto today’s edition: Kush on power outages and off grid set ups.
My local area had a planned power outage a little while ago. The outage was planned to be 6 hours but ended up being around 8 hours long. Not the end of the world, but less than ideal if, like me, you are coming back from holiday and have a lot of work to catch up on. With the extreme weather we sometimes get here in Houston, unplanned outages are also not the rarest of events. I decided that I want to be able to power my office setup during outages and so would purchase a battery to do the job.
Requirements
The first step in the process was deciding what needs to be powered and quantifying the load.
The main loads for my office setup are my monitor, laptop and phone (my phone’s hotspot can be used when the internet is down). The monitor spec sheet states that it uses a continuous 60W of power with a max potential of 150W. The iPhone and laptop are a bit more complicated as they have internal batteries of their own and so I sized my battery so I can charge the iphone fully once and the laptop fully once. That should get me through the work day. In general, product spec sheets should include a nominal power usage, but if they don’t then a quick google search should provide something accurate enough.
I sized this battery for a nominal 6 hour duration but included an extra 10% contingency in case the outage is slightly longer or I need to power more items. It will also help account for inefficiencies in the chargers.
My laptop battery is 75Wh and my iPhone battery is 17.32Wh. So my load table is below.
I needed a 500Wh battery, but capacity is not the only factor here though so I also considered:
AC Outputs. I wanted the battery to output AC power and have standard US outlet sockets so I can just plug my chargers straight in. This means the battery had to have an inverter built in to convert battery DC voltage to AC.
Max power capability. The monitor has the highest peak load of 150W and so the battery needed to be able to deliver a peak load of 150W.
We could go into more detail about cycle life, round trip efficiency, self discharge rates etc however as this is just a small battery system there is no real need. The key requirements are captured above.
Purchasing a battery
Note: everything below is based on my own opinions and I have no connection with the seller.
I ended up purchasing an ‘ALLWEI LiFePO4 Portable Power Station 500W/512Wh’ from Amazon. This battery most closely matched my requirement for a 500Wh battery and also had a 4.5 star rating from 135 reviews.
The battery is marketed as being useful for RV camping, home use, emergency power and outdoor activities. Below are the specs:
Features
In the box you get the battery, an AC power cord, a DC car cigarette cable and the user manual. Overall it’s pretty well made and has a solid feel to it.
The LCD display is clear and shows a lot of information including the input/output power, SOC%, time remaining on charge/discharge, operating mode and warnings.
There are 3 settable charging modes:
S (silent mode) - charges at 85W (6-8 hour charge)
N (normal mode) - charges at 138W (4-5 hours charge)
Q (quick mode) - charges at 210W (2.5-3.5 hour charge)
The manual states that the run time should be calculated as below, suggesting the unit has a DC to AC efficiency of 90%.
Capacity Test
I wanted to test what capacity I was actually getting out of the battery so I fully charged the battery, my laptop and iPhone and then used the battery to power the office setup during a work day. The load profile is below:
Verdict
Overall the battery powered my office setup for 9 hours and 11 minutes and that will cover me very well for any planned power outages.
The battery actually died when the SOC was showing around 7% which indicates to me that the SOC estimation by the BMS is not calibrated. LFP batteries often have this issue due to the flat voltage curve over the majority of the SOC range, but a few full charges and discharges should calibrate it properly so no big deal.
The area under the graph is the total capacity provided by the battery, which I calculate at 443.3Wh. This is significantly less than the stated spec of 512W, however this can be explained below:
There is a 5% tolerance on the spec, so the spec capacity could be as low as 486.4Wh.
The manual suggests there is a 10% DC to AC conversion loss. That brings us down to 437.76Wh, right around what the battery delivered.
With 443.3Wh, I can charge an Iphone over 25 times, or my laptop almost 6 times.
Overall the battery fits my mission, so I’m pretty happy. But if you’re going to go through the same exercise, bear in mind that the battery capacity will have a tolerance spec and DC to AC loss. Some manufacturers will provide this and some won’t, so if you don’t have it, you can use my numbers as an indicator. In the end, I sized the battery for my mission, not perfection, and so should you. Enjoy!
🌞 Thanks for reading!
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