Teensy 4.x RTC battery life

A

avignani

New member
Hello

I have several home-made boards using Teensy 4.0 and 4.1, and on every one I noticed that the external RTC battery has a much shorter life than expected.
On these boards a CR1220 coin cell battery is directly connected to the VBAT and GND pins, nothing else. But after slightly more than one month I find the battery voltage quickly going to zero.
At the beginning of August I put a fresh battery into a board and measured around 3.1V. The board was never powered up or otherwise connected. Last week I measured about 2.6V. Yesterday it was zero.
I'm used to having these type of batteries last for several years, e.g. on an iMX6 with external RTC, and I'm quite surprised of the Teensy behaviour.
Has someone else noticed this? Can it depend on some leak in the diodes used on the VBAT input?

Alberto
 
I've had the same CR2032 hooked up to a Teensy 4.0 for 23 months now. I just popped the top off the case it's in to measure the voltage and it's only down to 2.73V. Not bad for a dollar store battery.
 
There was one other post some many weeks back reporting the same thing. I didn't have one set aside with a battery in to verify.

And of course with those CR Batteries - you never really know what you are getting. Having a $_$tore battery survive 23 months is impressive!

I do have a T_4 in an early TallDog/@loglow breakout where the SD wasn't right so not in active use - and some just ordered 'Energizer ECR1220' cells ... I could put on a time sketch and set aside ... but would take months to offer feedback.
Test begun: TimeTeensy3.ino
Code: 
RTC has set the system time
12:15:14 9 9 2021

Though I didn't test NOOB voltage ...

Voltage good at 3.20V ... but bad gnd needs fixed to the holder - Doh!

Flux and solder the GND wire to fit the socket in use and re-Programmed:
Code: 
RTC has set the system time
12:30:57 9 9 2021
12:30:58 9 9 2021
// UNPLUGGED - idle - POWERED
RTC has set the system time
12:33:50 9 9 2021
 ... // matches minute change on PC
12:35:00 9 9 2021
 
Last edited:
defragster said:
And of course with those CR Batteries - you never really know what you are getting. Having a $_$tore battery survive 23 months is impressive!
Click to expand...
I was impressed. :) I decided that it had done its duty and replaced it with a "Basics" battery from a certain well known Internet retailer. We'll see how it does. 3.5V to start.
 
Silverlock said:
I was impressed. :) I decided that it had done its duty and replaced it with a "Basics" battery from a certain well known Internet retailer. We'll see how it does. 3.5V to start.
Click to expand...

Wow 3.5V! I just ordered those 'name brand' hoping for good life ... as noted started at 3.2V ... and worked 15 mins so far when unplugged.
 
defragster said:
Wow 3.5V!
Click to expand...

Yeah, I wondered about that... then I noticed that the voltage measurement was slowing drifting upwards. I turned on a regulated 5V bench supply and measured that and got 5.7V, drifting upwards. Hmm! Turns out it was long past time for the battery in the multimeter to be replaced! :eek: Changed that and got a nice solid 5.01V out of the bench supply, and 3.14V out of the Basics battery.
 
Silverlock said:
Yeah, I wondered about that... then I noticed that the voltage measurement was slowing drifting upwards. I turned on a regulated 5V bench supply and measured that and got 5.7V, drifting upwards. Hmm! Turns out it was long past time for the battery in the multimeter to be replaced! :eek: Changed that and got a nice solid 5.01V out of the bench supply, and 3.14V out of the Basics battery.
Click to expand...

Arrrgggh! Batteries :)
 
Silverlock said:
I've had the same CR2032 hooked up to a Teensy 4.0 for 23 months now. I just popped the top off the case it's in to measure the voltage and it's only down to 2.73V. Not bad for a dollar store battery.
Click to expand...

Yes, but a CR2032 is 6x more powerful than a CR1220 (235mA vs 37).
I suspect that the CR1220 is not powerful enough to keep up a Teensy 4 for more than a couple of months; if you look at the specs at https://data.energizer.com/pdfs/cr1220.pdf this battery lasts only about one month with a 46uA drain.
Now, the RTC in the iMXRT106x should consume no more than 6.5uA, but they become 20 if the ring oscillator is active; factor in some other leak and the battery will need replacement quite often.
I will now try to use a CR2032 and see what happens.
Alberto
 
Still good on 1220 after 5 whole days - will check for voltage change when I get back:
Code: 
RTC has set the system time
15:12:53 14 9 2021

Yes, 1220 is tiny

Battery 'in circuit' when not powered and showing 2.91V today - still good but not 3.2V of 9/9:
Code: 
RTC has set the system time
2:09:06 16 9 2021
 
Last edited:
Plugged this in again - still good with the 1220 cell: seeing 2.81 volts
Code: 
RTC has set the system time
21:28:34 26 10 2021

Down from 3.20 V on Sept 9th - may not make it much longer ... 47 days
 
bicycleguy said:
see below
https://forum.pjrc.com/threads/64216-Beware!-T4x-RTC-power-consumption?p=257979&viewfull=1#post257979
Click to expand...

Thanks ... Saw that then ... though didn't look it up ...

bicycleguy said:
Thought I was getting defective CR1220 button cell battery's. However, measuring RTC currents:
T3.2 1.24uA
T4.0 30uA

Doesn't seem like much but with a 35mAH, 20mm dia. coin cell battery that's only 48 days vs 3 years.
Still great for power failures but not so good for keeping time on intermittent use projects.
...
Click to expand...

Seems about right - depends on the cell - but doesn't seem much more should be expected from 1220 than 47 days ...

Though the CR2032 of @Silverlock may not make it 3 years given the voltage drop already ....
 
Plugged in again - time lost and doesn't even hold a second across repowering ... not measuring a half volt ...
 
That earlier 2.95V reading may have been a poor connection on my part. Checked a couple of times over the past week and still reading a steady 3.00V here on the CR2032. Double checked the DVM against a known steady regulated supply (and swapped the DVM battery out just in case). After having a dollar store CR2032 still keep time after 23 months, I wouldn't bet against ~3 years.

Looking at a typical discharge curve of a coin cell, there's a short initial steep decline from above 3V before stabilising at 3V; maybe I just got nice fresh CR2032s out of Am$$on.
 
DVM here first suggested 20 mV ... and was moving around ... Pushed the probes harder and it showed just over half a volt - but not enough even to keep it alive on a quick switch off to on ... couting form zero again ...
 
I need to replace the CR2032 with a DC voltage regulator for T4 RTC.
My idea is to use the 12v battery of the car as Vin.
I have seen this: ST715.

what do you think?
 
I was thinking about measuring battery voltage with ADC and give notifications to the user. Is it a good or bad idea? I am afraid, that connecting Vbat to some of the Teensy4.1's pins will cause extra current leakage and the battery will drain faster. Am i right or wrong?

The device will usually be disconnected and i will use it once or twice a week for, let's say, 15-30minutes.

Thanks!
 
Get one of these, the battery will last for years and will unlikely need adjusting!
If I remember correctly accuracy is quoted as being better than 1.5ppm which is about 1 second in 7 days.
 
Thanks. For the price i can change the battery for about 15 times :)
Just trying to keep the price low and i am pretty happy with built in RTC. I will put the bookmark in case i need more accuracy next time. Thank you!
 
You could try going to the manufacturer here. I did and got 5 free samples and MORE IMPORTANTLY a free demo board.
I obviously asked for the samples and demo board. I am not sure that they will send you the demo board if you don't ask for the samples.
Must look like a potential user of the ICs.
 
Just to add another data point. I have a couple of Teensy 4.1 based products out in the wild and the RTC backup with a CR1220 battery seem to last 72 days +- 3 days based on the last 12 months usage. I'm almost tempted to dive into the PDF manual to see if its possible to disable anything except keeping the clock crystal ticking.
 
BriComp adviced unit might be good solution for you. Especially if the Teensy is installed in the wild and there are many units.
I am using 2032 battery, which correcponds to about 1.2 year battery life (1220 is ~ 35mah and 2032 is ~340mah).
 
It's been a year now since I replaced the CR2032 in my Teensy4.0 setup with one from a well known Internet retailer of everything under the sun. After checking that the battery in the meter was still good by measuring the output from a regulated 5V bench supply, I checked the CR2032 and got 2.77V. Since the battery backup supply is good down to 2.40V, I think the odds are pretty good that this one might last for another year and beat the dollar store CR2032 that I pulled at 23 months.
 
You must log in or register to reply here.
Back
Top