Chinese BT189 battery tester - Page 1
Forum section: electronics / testgear

author: Datman
author_rank: Regular Contributor
timestamp: May 02, 2023, 10:30:38 am
content: Hi allI bought this battery tester:https://it.aliexpress.com/item/1005001381541786.htmlIt reads 1.59V instead of 1,5V and 9,41V instead of 9.00V.Current drawn is 5.35mA @1,5V (280 ohms) and 2.04mA @9V (4K4).The internal voltage converter is a XC6385, giving 3.0V at the output. It should work at 0.9V minimum.The third digit is a bit weird... It shows a number when I attach the power supply, but if I adjust the voltage it doesn't change anymore... 1.51V, 1.41V, 1,31V... But if I retry, it shows 1.52 or 1.53...I'll try to adjust it, also adding two resistors to raise current drawn (22 ohms for 1,5V and 470 ohms for 9V). I could also keep only the converter and make a new meter with a ATmega328P and a 0.96" OLED display...Mechanics appear to be good.Note: on 1.5V contacts it measures also 3.7V (3.2/4.2V) from Li-ion batteries, but they don't fit!

author: TERRA Operative
author_rank: Super Contributor
timestamp: May 02, 2023, 10:46:38 am
content: Quote from: Datman on May 02, 2023, 10:30:38 amGood for you?

author: wasedadoc
author_rank: Super Contributor
timestamp: May 02, 2023, 11:06:58 am
content: Quote from: Datman on May 02, 2023, 10:30:38 amDo you believe that a 1.5 volt cell always gives exactly 1.5 volts and a 9 volt battery always gives exactly 9.00 volts?

author: Datman
author_rank: Regular Contributor
timestamp: May 02, 2023, 11:57:29 am
content: Quote from: wasedadoc on May 02, 2023, 11:06:58 amObviously, no. Otherwise, battery testers would be useless!I wrote:"It reads 1.59V instead of 1,5V and 9,41V instead of 9.00V."but I didn't write I measured a battery.

author: tunk
author_rank: Super Contributor
timestamp: May 02, 2023, 12:00:21 pm
content: A new alkaline AA is ~1.6V, and a new alkaline 9V battery should be around six times that.

author: Datman
author_rank: Regular Contributor
timestamp: May 02, 2023, 12:01:25 pm
content: Quote from: DatmanQuote from: wasedadocQuote from: tunkOk, the nominal 1.5V voltage was 1,4996V. I don't remeber exactly the 9V voltage... About 9.002V?

author: Fungus
author_rank: Super Contributor
timestamp: May 02, 2023, 12:31:08 pm
content: What are you trying to achieve?

author: Datman
author_rank: Regular Contributor
timestamp: May 02, 2023, 12:32:14 pm
content: Sharing with you and...a working instrument?...

author: Hexley
author_rank: Regular Contributor
timestamp: May 02, 2023, 03:09:47 pm
content: That reminds me of something I brought back from Japan in the early '80s -- a Sony battery tester model BC-330D.Was a great device; finally expired a few years ago after the internal coin cells were replaced for the nth time.

author: TheDefpom
author_rank: Frequent Contributor
timestamp: May 02, 2023, 09:44:08 pm
content: It looks like R2/R3 (9V) and R4/R3 (1.5V) are a voltage divider setup, maybe try changing those values very slightly to see if it corrects the reading error.Most likely R3 is too high in value.

author: Datman
author_rank: Regular Contributor
timestamp: May 03, 2023, 08:33:15 am
content: I have done some tests: it seemed I had to add 4k7 in series to the two 100k resistors. I cut the traces and added them. Readings were ok.Then, I had to add the two load resistors: 22 ohms for 1,5V and 470 ohms for 9V but strangely, despite of the resistors soldered on the contacts (with no voltage drops on the wires to the electronics), readings were wrong! ()So, I restored the two 100k without addictional resistors and now it is ok!I don't understand, but it works.The strange behavior of the LCD remains.