[Makerspace] 18650's, series or parallel?

Greg Hall greghall at brushbox.info
Thu Mar 21 22:04:05 AEDT 2019

A couple of thoughts below.


PS: I'll take some photos of the 7 segment flipper displays.

Greg Hall

On 21/3/19 6:58 pm, Felix Sheldon wrote:
> Thanks Greg,
> Aha, yep, that makes sense!
> Yes, I might well be able to use 7-segment displays!
> It turned out that 4.2 ish Volts was about right for the LEDs and the 
> computer with a 3.3V regulator.
> But I want it to run all day, so I think that's going to take 4 18650s 
> in parallel.
> Do you think it would work to have 1 battery protection module and one 
> 18650 charger module hooked up to each of them, then run 5V into the 
> charger modules for charging?
> https://www.ebay.com.au/itm/5V-Mini-USB-1A-TP4056-Lithium-Battery-Charging-Board-Charger-Module-/351094408792

I suspect that the IN- and BAT- will have a DC path, so all your 5V USB 
would need galvanic isolation. A difficult way to do it.

Consider using your 18650's in series, and a switchmode converter to 
bring it down to your operating voltage. They are only a couple of $$ on 

Alternatively, it's not at all uncommon to open up a Li-Ion laptop or 
drill battery to find cells welded in parallel (with fuses ;)

> https://www.ebay.com.au/itm/153327870301

The LED's really should be run from a constant current supply, something 



Not a big effect, but a switcher has to be better than a resistor, esp 
at 3 watts!


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