Does Lithium-ion battery behaves different than DC power supply?

Thread Starter

Andrius Slizys

Joined Jul 20, 2019
8
Hi guys!
I have been thinking of converting my cordless power tools to corded ones. Well, actually not to convert the tools, but one of my dead battery into adapter-like thing so I could plug it into 220V AC mains, but remain capability of using batteries too.

I do understand electronics quite well, but certainly not that deep, so I need your advice on that!

So, Makita batteries runs on Lithium-ion cells, and battery itself has an protection circuit module, that monitors battery and tool while in performance.
And my final question is, if I remove cells from a battery and connect DC supply instead (perfectly matched Voltage and Amperage), do you think it will hurt the tools? Does Lithium-ion battery behaves different than DC power supply?

Still learning English, let me know if I'm not clear.
Cheers!
 

oz93666

Joined Sep 7, 2010
737
The biggest problem you have is delivering the high current power tools often require , lithium are very good at this ...

Makita batteries are described as "18V " often 5Ahr ... they contain 12 18650 cells ... 2p6s fully charged the voltage is actually 25V

To know how much current your power tool requires you need to find out how long the battery will last ... so if you have a drill that will give 1 hr of constant use on a full battery , it consumes about 5Amps .... but stall current will be much higher , perhaps 10A ...

You may need a DC power supply of 20V at 10A , and fairly thick wires , quite expensive to build ...

You maybe better of getting new 18650 cells perhaps about $4 each ...

Or removing the cells , testing them , some will still be OK , you could make a battery with 6 good cells that will work , but with half normal capacity.
 

jpanhalt

Joined Jan 18, 2008
10,097
Welcome to AAC.

Lithium batteries loose voltage as they are used. Your power supply doesn't, but that shouldn't affect operation. Be sure your supply is the correct voltage and can provide enough current.

More important are circuits in the cordless power tool that "protect" it. I am most familiar with Craftsman cordless tools. Early models (circa late 70's) were easily converted and I did it. More recent tools have at least 4 connections to the battery. Two are for power but the other two must be connected to something for the tool to work. In Craftsman, one is a temperature sensor and the other senses voltage.
 

Thread Starter

Andrius Slizys

Joined Jul 20, 2019
8
Thank you oz93666!

I already took account of it, and 10A power supply is way too low. My hammer-drill pulls ~15amps when I'm drilling 18-20mm hole into the concrete, so I believe the peak stall current ~20 amps. I'm going with 30 amp power supply. 10 AWG wires.

I have enough batteries and few chargers, but for certain reasons I would love to have corded.


jpanhalt, thank you. And yes my concern is all about protection board. I'm not sure how it will react to DC power instead of batteries. Of course I could make power to go directly to the tool, but thats not a choice for me, I want that the tool was still protected. Makita has 3 terminals, third one is for communication between battery and tool, for overloading, over-discharging and overheating.
 

digimart

Joined Jun 12, 2020
1
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