lithium thionyl chloride cell in a tek 2430 scope replacement - Page 1
Forum section: electronics / repair

author: m3vuv
author_rank: Super Contributor
timestamp: December 30, 2021, 01:05:25 pm
content: Hi all i have this scope with a dead battery for the cal values etc,its 3.6v normaly,could it be replaced with either a 18650 cell or a cr2032 cell,ie 3.7/4.2v or 3v for the cr2032?

author: tooki
author_rank: Super Contributor
timestamp: December 30, 2021, 03:05:09 pm
content: Whether a 2032 cell works depends on the circuit, but most likely yes. It just won't last as long as the 3.6V lithium cell.I wouldn't use an 18650 Li-Ion, since the maximum voltage is too high, and you'd have to take it out frequently to recharge. (And you absolutely must use a cell with built-in protection IC that'll stop it from getting deep discharged.)What's wrong with getting another 3.6V lithium cell? They're not particularly hard to get (by mail) and last forever with a very stable voltage until the very end, which is why they're used for these applications.

author: David Hess
author_rank: Super Contributor
timestamp: December 30, 2021, 05:41:56 pm
content: The CR2032 will work but the lower voltage will likely trigger the CMOS battery low warning.The voltage of the 18650 lithium-ion cell is higher, but will not damage anything.Lithium thionyl chloride cells are not expensive compared to an 18650 and will perform better. I bought one not long ago which would be suitable and would last at least a decade:https://www.mouser.com/ProductDetail/667-TL5155P

author: m3vuv
author_rank: Super Contributor
timestamp: January 01, 2022, 12:59:01 pm
content: in the end i used a 18650 charged to 4v in a holder,that way easy to remove to charge,its a 1.5ah so should last ages before it needs charging,now all self tests pass fine.,i may get the correct battery when funds permit.

author: David Hess
author_rank: Super Contributor
timestamp: January 01, 2022, 08:55:54 pm
content: Quote from: m3vuv on January 01, 2022, 12:59:01 pmThe self discharge rate of a lithium-ion cell is high compared to a lithium thionyl chloride or lithium manganese oxide cell, so operating life will be much lower than predicted by the capacity.A simple charging circuit could be added with an operational amplifier and transistor.

author: tooki
author_rank: Super Contributor
timestamp: January 04, 2022, 11:24:38 am
content: Quote from: David Hess on January 01, 2022, 08:55:54 pmThat is really bad advice. Lithium ion cells need more complex charging methods than that, and they hate being kept at full charge for extended periods of time.Of course, I wouldn’t recommend a lithium ion as a backup cell anyway, it makes no sense for the application.

author: David Hess
author_rank: Super Contributor
timestamp: January 04, 2022, 07:06:09 pm
content: Quote from: tooki on January 04, 2022, 11:24:38 amThey need a current limited constant voltage charging circuit, and there is nothing which requires charging them to their maximum capacity so the charging voltage can be set lower, for like a 60% capacity for maximum life.

author: scopeman
author_rank: Frequent Contributor
timestamp: February 07, 2022, 09:05:25 pm
content: You could use a standard lithium primary cell (not a rechargeable) in that instance. The only difference would be the operating life would be different if the cell capacity is not the same as the one that you are replacing. You might look at the Bromine series from Panasonic.You should be able to find the same chemistry cell from DigiKey as I have purchased them before. The only issue is that they will not ship these cells by Air only by surface shipment.SamW3OHM