Judging the balance of cells within a battery based upon ending charge profile

My S-10 EV conversion has a battery pack made up of Nissan Leaf modules. I am using a mini-bms system which has a per-cell alarm, but does not report per-cell voltages and also does not do a great job keeping the cells balanced.   To check individual cell voltages, or manually balance cells, I need to pull a few pins and lift up the tilt bed on the back of the truck.   But it is possible to determine when cells in the battery are no longer well balanced based upon the power draw when the ending voltage is reached. You can see this most easily by looking at the charge profile graphs (provided by my JuiceBox EVSE).

When the cells are not balanced, some cells are at a lower SOC than others when the ending voltage is reached, which results in the entire pack drawing more power (in this case, charging ended when the max voltage cutoff was reached, but the pack was still drawing 3,000 watts.

After balancing the cells, the normal charging profile looks like this:

As you can see, the amp/power draw slowly tapers off as the max voltage is approached, and the pack is drawing less than 1,000 watts when the cells are balanced.

I use these end-of-charge graphs to determine when it is time to pop the back of the truck and manually check/balance individual cells. [I still have the mini-bms units to automatically stop the charger if any cells voltage goes too high, or alarm if any cells voltage goes too low.]

First Alert Smoke Alarm with Voice SA511 short service life (Malfunction signal)

In 2017, I purchased six First Alert Smoke Alarms with Voice (Model SA511) for our house. These are battery powered units that run for about a year before the 2 AA’s need to be replaced.

Sometime in the past   (late 2018? 2019?) one of them kept false alarming, and no amount of compressed air, battery changes, resetting, etc would keep it from alarming, so after several calls to First Alert, they replaced it under warranty.

More recently, (in June 2020 and November 2020) the units in my garage and utility room off of the garage both failed with a “Detector Error in <location>. Check Manual” error message (followed by three short “berrps” in rapid succession).

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Lenovo Smart TAB M10 does not work with WPA2 and Android 9

To summarize why I do not recommend buying a Lenovo Android tablet:

  1. Their Android 9 software update borked WPA2 support.
  2. Instead of figuring out the (software) problem and fixing it, they instead instruct their customers to downgrade the security of their wifi.
  3. If that doesn’t work, they RMA the tablet and flash an older (insecure) version of android on it, and disallow software updates.

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October 28th 2020: Orange County Florida COVID-19 Report

It’s October 28th, 2020, how is Orange County Florida doing with COVID-19?

The rate of decline in new cases had grown sluggish at the end of August, plateaued and then had a slight rise in September, and continues to be on a slight upward trend in October. Orange County is averaging 224 confirmed new cases per day over the last two weeks (compared to 147 in the same period in September). Compared to an average of 14 new cases per day in the first two weeks of April, the number of people infected each day is 16 times higher than in April.

We had 105 people die from Covid-19 in Orange County in the last month (slightly worse than the 79 in the prior month) and the total death count is at 549. Continue reading

September 27th 2020: Orange County Florida COVID-19 Report

It’s September 27th, 2020, how is Orange County Florida doing with COVID-19?

The rate of decline in new cases had grown sluggish at the end of August, plateaued and then had a slight rise in September.   Orange County is averaging 147 confirmed new cases per day over the last two weeks, compared to an average of 14 new cases per day in the first two weeks of April, so the number of people infected each day is still about 10 times higher than in April.

(You can ignore that 7 day hump at the beginning of September….a large lab reported a backlog of positive tests all at once.)
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Giving away public Wifi with DD-WRT and VPN

Cliff Notes for setting up a public (unencrypted) wifi hotspot to give free internet to guests with minimal risk to “your” network.

Sometimes it’s nice to give people free wifi, especially if you have more bandwidth than you normally use. However, you don’t want random people being able to access your network (or their random network activity to be traced TO your network….)   This is my set of notes for how to set up a 2nd wifi router (which must support the DD-WRT firmware) to act as a free wifi hotspot to untrusted guests.
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Getting IOT devices / Geeni Smart Plugs working with OpenWRT / dd-wrt

After moving my wifi router to the OpenWRT firmware, my Geeni smart powerstrips were authenticating to the wifi router (I could see their MAC addresses) but not communicating properly (the device name was a question mark, and nothing could communicate with them).

The secret was to turn off WMM mode (Wireless Multi Media) and then they all immediately started working again.

The firewall gets in the way of HP printer device discovery, so you may need to assign the printer a specific IP address and then manually add the IP address to your clients.

HP Device Manger -> Setup -> Network/Ethernet/Wireless network. Then click Advanced Options, choose Manual Discovery, and type the IP address.

August 27th 2020: Orange County Florida COVID-19 Report

It’s August 27th, 2020, how is Orange County Florida doing with COVID-19?

The number of new cases per day has seen steady decreases since late July, possibly due to a mandatory mask ordinance.   The rate of decline has grown sluggish for the last two weeks and the number of daily cases is still ten times that recorded in April. Orange County is averaging 191 confirmed new cases per day over the last two weeks, compared to an average of 14 new cases per day in the first two weeks of April.

Deaths are lagging new cases by about 3 weeks and as the number of new cases have declined, the rate of deaths has also declined, averaging only 3 per day in the last two weeks.   Unfortunately, the total number of deaths in Orange County has gone from 179 on July 27th to 369 today (adding 190 deaths), a doubling of total deaths in the last month.

If the new deaths curve is actually lagging the new cases curve by 3 weeks, and also plateaus at the current levels, we will have a sustained period of 5-8 deaths per day for the next month, doubling the total number of deaths to date in the next month. [My unfortunately correct prediction from last month.]

A Positive Sign
A positive sign is that the percent positivity rate on tests has hovered just above the 5% goal (and has actually been below 5% for 4 of the last 14 days), indicating that community spread is almost at a manageable level.

How many people have been infected

The US Census bureau estimated that Orange County Florida has a population of 1,393,452 people (July 1st, 2019).     The Florida Department of health reports today that 35,245 cases of COVID-19 (confirmed by either a positive PCR or Antigen test result) have occurred in Orange County so far.     That means at least 2.5 percent (35245/1393452   =.02529330) of the population has been infected.

The actual number is likely to be higher, as many infections are asymptomatic, or not confirmed with a lab test.   Robert Redfield, the director of the CDC estimates that the number of people actually infected may be up to 10 times higher than confirmed with lab tests, putting an upper bound of 25% of the population of Orange County as already having been infected.

How many people have been hospitalized or died

Of those confirmed infected, 1,089 or 3 percent ( 1089 / 35245 = .0309) have been hospitalized, and 369 have died.   The death toll is currently 1 percent of all detected cases (369 / 35245 = 0.0104695701 ).

In the last month (July 27th to August 28th) the number of dead has doubled (from 179 to 369).

Florida average percentages for hospitalizations and deaths are 6.2% and 1.8% so Orange County has fared better than the rest of the state of Florida for hospitalizations and mortality so far.

Median Age is holding steady

Last month the median age of those infected was 42 , and this has held relatively steady, as 37 was the median age over the last 7 days.   [The median age of Florida residents is 42.2 ]

However, Orange County schools have re-opened on Friday Aug 21st, with at least 30% of the students opting for in-person schooling. I would not be surprised to see a dip in the median age as school age children begin to be infected at school. Fortunately, young children vary rarely face serious consequences from infection, but they may drive an uptick in community spread leading to deaths in older adults.

[Charts/Numbers used can be found in this open document spreadsheet: orange_county_florida ]

July 28th 2020: Orange County Florida COVID-19 Report

It’s July 28th, 2020, how is Orange County Florida doing with COVID-19?

The number of new cases per day has surged up, but appears to have plateaued at an average of 606 new cases a day for the last month. Deaths appear to lag new cases by about 3 weeks and have reached a rate of 7-8 per day.

upward surge of new cases, laged by new deaths 3-4 weeks later

If the new deaths curve is actually lagging the new cases curve by 3 weeks, and also plateaus at the current levels, we will have a sustained period of 5-8 deaths per day for the next month, doubling the total number of deaths to date in the next month.

How many people have been infected

The US Census bureau estimated that Orange County Florida has a population of 1,393,452 people (July 1st, 2019).     The Florida Department of health reports today that 27,820 cases of COVID-19 (confirmed by either a positive PCR or Antigen test result) have occurred in Orange County so far.     That means at least 2 percent (27820/1393452   = 0.019964) of the population has been infected.

The actual number is likely to be higher, as many infections are asymptomatic, or not confirmed with a lab test.   Robert Redfield, the director of the CDC estimates that the number of people actually infected may be up to 10 times higher than confirmed with lab tests, putting an upper bound of 20% of the population of Orange County as already having been infected.

How many people have been hospitalized or died

Of those confirmed infected, 756 or 2.7 percent ( 756 / 27820 = 0.02717469 ) have been hospitalized, and 179 have died.   The death toll is currently 0.64 percent of all detected cases (179 / 27820= 0.00643421).

Graph of deaths in OC Florida to date 179 total

In the last month (June 27th to July 27th) the number of dead has tripled (from 56 to 179).

Median Age is Increasing

Florida average percentages for hospitalizations and deaths are 5.6% and 1.38% so Orange County has fared better than the rest of the state of Florida for hospitalizations and mortality so far.   This may be due to the fact that South Florida was hit hard first, giving Central Florida a stark warning and time to prepare.

Unfortunately, the median age of the infected is rising. The first big surge of cases detected in mid-June (after bars reopened) were primarily very young individuals, with a median age of 22 for new cases. The current median age is 42, a generation older. As more older individuals are infected the percentages for hospitalizations and deaths may increase in Orange County to match the averages seen in the rest of Florida.

 

[Charts/Numbers used can be found in this open document spreadsheet: orange_county_florida.ods ]