Having some fun

[stoic]

So going solar really sparked my interest in electricity... i think i may have missed my trade.

I had a router out in the field that was still connected to utility, so I converted it to have its own little battery backup. 

what i had to play with:

1. 12v 7ah lead acid battery (sealed - the gate motor type), its an old battery that was replaced
2. 12v battery chareger (it does not have built in over charge protection)
3. tiny little 12/24v solar charge controller.

What i ended up dong is connect the battery charger to the panels input of the charge controller, connected the battery to the battery terminals and i connected the router to the load side of things. To my surprise (even though i hoped for the result) the SCC actually charged the battery till it was full and stopped. So i was a happy chappy... my first little low voltage concoction worked.

I nearly died when we were load shedded 16 hours yesterday... my battery out in the field did not get enough time to charge and the internet connection out there was gone.

Plan B .. i need a new battery.

I have a laptop that had seen better days... the mobo crashed. I took the battery pack apart and found 9x18650 batteries in it. The battery pack should still be good, so i tested the individuial cells, all read approx. 3.6/3.7v.. all except three of them. I do not have the equipment to do propper tests but 3.6/7v is at lest an indication that the cell could still be good.

My next thought was to take 4 of the 6 good cells, set them up in serie and i should have around 14.4v @ 2800mah. This will be waaay more than what my router pulls. and if the cells are good it should even outlast the spent lead acid battery.

Finally... the question:

My Charge controller is rated 12/24v but for Lead acid and Gel batteries, will this poor bugger be able to charge the 18650 batteries in the above configuration? my initial though is NO as it delivers up to 16V if the batteries are below 24v and as far as i can tell you are not supposed to charge the 18650's at more than 5V, but then again, the configuration is set to be around 14V so does this really matter?

 

[Richard Mackay]

13 hours ago, stoic said:

12/24v but for Lead acid and Gel batteries, will this poor bugger be able to charge the 18650 batteries in the above configuration? my initial though is NO as it delivers up to 16V if the batteries are below 24v and as far as i can tell you are not supposed to charge the 18650's at more than 5V, but then again, the configuration is set to be around 14V so does this really matter?

 

Unfortunately it does!

Li-Ion cells typically have a maximum charge voltage of 4.2V per cell and discharge of 3V per cell Also these cells will be in series and each cell/bank has to be monitored for this. So what is is installed to protect the batts is a a BMS 'system'. 

If however you take the time to match the cells for same charge/discharge characteristics you can do away with a BMS but you need to take an interest (and be able to use a multi meter!)

Edited December 11, 2019 by Richard Mackay