Straight Answer on Using Lithium Power Tool Batteries

Ok. I've been doing lots of reading...and I'm not 100% sure and wanted to double check one last time before going into using lithium power tool batteries for non-power tool applications.

Can I simply connect to the positive and negative connections to power my device and call it a day?

There always seem to be 4 plugs on a power tool battery. On far left and right are Positive and Negative. In the middle are two connections that one usually has an OHM symbol and the other one I think has C.

My assumption is the two middle ones are using for the charger to balance the cells when charging only...and do not affect use when discharging with a device.

So am I safe to plug in to both + and - and call it a day?

It depends. Some cordless tools require an electronic "handshake" between the battery and the device before the battery will send power. Most don't, in my experience.

Does the drill (or whatever) that goes with the battery have only two contacts, or does it have more? If it does, you can bet they are there to do something.

Most of the time at least one of the extra contacts is a temperature signal from the internal BMS in the battery. Normally this is only used by the charger to let the battery cool off before charging.

unclejemima said:

Ok. I've been doing lots of reading...and I'm not 100% sure and wanted to double check one last time before going into using lithium power tool batteries for non-power tool applications.

Can I simply connect to the positive and negative connections to power my device and call it a day?

...

So am I safe to plug in to both + and - and call it a day?

Click to expand...

It depends on the battery. Virtually all of them embed a BMS to monitor the voltage, and do balancing.
All of them use a MOSFET as a power switch. So the behavior all depends on the BMS.

There are several threads here discussing the nuisance action of the Ryobi 18V lithium going into "sleep mode" when tied in serial/parallel configurations for example. It's a protection mechanism of the embedded BMS.

Currently I'm working with Kobalt 24V Max batteries and Ryobi 40V. With both I'm finding that I need to parallel them. The original format for either really isn't conducive to parallel them. So I'm in the process of opening them up, essentially bypassing the embedded BMS, and paralleling the cells directly. I'm still trying to figure out a way to add a parallel/balance connector along with a BMS power bypass while maintaining the original form so that it can still be used with tools.

So which types of batteries are you thinking about using?

ga2500ev

I'm sure you quickly figured out Kobalt packs are 21.6 nominal, they use three tabs, (+) and (-) on the outsides and one middle tab goes to the charger, one is unused. They call them 24v just like a lot of 18v packs are labeled as 20v by other manufacturers. I took the flashlight apart to look at the wiring, want to crack the charger open at some point and see what's going on in there.

Hey guys.
First post here on ES.
What a wealth of information.
Thank you all for your passion!

I'll be posting my first ebike build....called a "pulse bike" soon..standby.

Till then, I wanted to let the OP know that there are some videos on YouTube with guys that have used li ion power tool packs AS IS.
They've made battery slots? of their own, or used the power tool slots.

https://youtu.be/ISR8pKoIa5k

https://youtu.be/izBDbKbOj9w

Hope this points you in the right direction.
Good luck and keep us posted on your progress.

Peace

We have a couple of threads exploring the EGO series of 56V yard tool packs for Ebike and other uses here on ES. There are some builds using these packs. We have a design for a 3D printed connector that is in the prototype test phase. These are 14S packs which are a good fit for 48V systems. Maximum full charge voltage is generally a little under 58.8V using the EGO chargers. Makers of 14S Ebike batteries call them 52V or 50V whereas EGO calls them 56V, which is about their resting voltage after sitting fully charged. They reportedly have timers in the packs to drain them down to storage level after 30 days, but some people have reported that their packs don't seem to do this. There is a clock chip in the BMS, perhaps for this function.

In many tool packs (including the EGO 56V) there is no BMS hardware protection for overdischarge. The tool is generally responsible for providing this feature, so it is not integrated into the pack BMS hardware (no FET power switch). At least on the EGO pack the four pins are for negative, positive, temperature (thermistor) and data communications with the BMS. The data communications format has not been looked at, but that would be a good small project for someone. Without that the low voltage cutoff in the controller must be used to protect the pack against overdischarge.

The BMS is engaged by the charger and apparently provides cell level balancing.

Many tool packs are not designed for high current and will get hot or even overheat at Ebike current levels. EGO packs have better cooling design than most others I have looked at. The EGO battery powered yard tools are also fairly good so the batteries can be a true multi-use item. We are starting to see discounts from some sources on the battery packs. The battery packs carry a 3 year warranty that can be accessed via local hardware stores so that can be of some value.

More information here:
https://endless-sphere.com/forums/viewtopic.php?f=14&t=93563