High resistance?

9 posts / 0 new
Last post
Blazer1
Offline
Last seen: 7 months 3 weeks ago
Joined: 01/23/2014 - 17:04
Posts: 59
High resistance?

I received my new Vapecell S4 plus charger today and have been testing some of my 18650 battery collection.

I have noticed most of my batteries range from 20milliohm-40milliohms but a few have much higher resistance such as 245milliohms.

What does high resistance tell me about a battery?

xxo
Offline
Last seen: 3 hours 14 min ago
Joined: 03/22/2019 - 14:35
Posts: 306

It tells me that your cells are very worn out or more likely that you have high contact resistance caused by the poorly designed slider mechanism used on most chargers, that give wildly inaccurate IR readings.

Take 10 readings, resetting the slider each time and take the lowest number as your approximate IR number.

Blazer1
Offline
Last seen: 7 months 3 weeks ago
Joined: 01/23/2014 - 17:04
Posts: 59

xxo wrote:
It tells me that your cells are very worn out or more likely that you have high contact resistance caused by the poorly designed slider mechanism used on most chargers, that give wildly inaccurate IR readings.

Take 10 readings, resetting the slider each time and take the lowest number as your approximate IR number.

I would typically agree with that statement except that the readings are consistent from battery to battery.

My “red” batteries from a laptop pack all read high milliohms where as my new Molicel P26A’s all read low resistance, same with my Samsung 25r’s.

thefreeman
thefreeman's picture
Online
Last seen: 13 min 32 sec ago
Joined: 01/06/2020 - 09:56
Posts: 874
Location: France

250mΩ from used laptop cells is normal, it’s pretty rare to get anything under 50mΩ.

Look here for common values for new cells, using a standardised method : https://budgetlightforum.com/comment/1558703#comment-1558703

The method used will change a lot the results, and as xxo mentionned, those round cell charger are not very precise.

Blazer1
Offline
Last seen: 7 months 3 weeks ago
Joined: 01/23/2014 - 17:04
Posts: 59

I may not be asking my question correctly. How does a high resistance cell behave compared to a low resistance cell? Smile

thefreeman
thefreeman's picture
Online
Last seen: 13 min 32 sec ago
Joined: 01/06/2020 - 09:56
Posts: 874
Location: France

It’s like you have resitance in series with the cell, so if you draw 1A on a 250mΩ cell you will get a 250mV drop (roughly as the internal resistance varies with the state of charge, temperature and current).

You’ll waste more power in the cell, and with the voltage drop you wont be able to draw much current.

High power cells have a very low internal resistance.

xxo
Offline
Last seen: 3 hours 14 min ago
Joined: 03/22/2019 - 14:35
Posts: 306
Blazer1 wrote:
I may not be asking my question correctly. How does a high resistance cell behave compared to a low resistance cell? Smile

Reduces Voltage under load, limits the current the cell can deliver, causes the cell to heat up more during charging and discharging. Generally makes the cell unsuitable for high current applications. Could also be a sign of an internal short in extreme cases that may cause self discharge.

flydiver
Offline
Last seen: 22 hours 2 min ago
Joined: 06/19/2013 - 19:16
Posts: 1296
Location: Seattle, WA

Think of current as water through a pipe. As the diameter of the pipe gets smaller. the resistance goes up, thus, less current flow with high(er) demand.

To Air is Human, to Respire….Divine.

chops728
Offline
Last seen: 17 min 9 sec ago
Joined: 08/30/2014 - 16:00
Posts: 1455
Location: Swampland,La

Most of the higher amp cells will test lower in resistance (Sony VTC 5A test very low)— you can get a baseline avg for cell types/brands—as they get worn out that number will rise—— the sanyo red (laptop pulls ) usually test real high over a 100
Those cells testing really high —check them on the tail end of charging —if they take forever to finish charging or get very hot when charging above 4.10 v
Toss them —they aren’t worth keeping —- their capacity is probably low also