Running stuff from power tool batteries

[hotponyshoes]

What's the deal on running stuff from cordless tool batteries?

I've 3d printed some holders for my batteries and it would not take much to add a couple of contacts and use them for projects etc.

I've seen the various things for sale on ebay like soldering irons and flood lights plus plenty of adaptors to use one battery on another make of tool and not seen many reports of problems.

My question (concern) is that all my batteries/tools have more than 2 terminal connections and I'm wondering if I they can get damaged by not using all of them?

What's the deal with over-discharge protection, fire risk and so on..
Is it all built into the battery pack?

A bit of reading up indicates the extra terminals are for charging but I can't see why the tools would also have the extra connections if that's the case?

I have some old batteries that I don't mind loosing for a test but if I actually wanted to make anything usefull then I'd be looking at using 8ah+ packs and I would rather not be risking damage or shortening the lifespan of them due to the cost of replacement

 

[sako243]

Lithium battery packs have protection circuitry built into them (at least reputable ones do) so you should be safe on over discharging etc.

The extra terminals are used by some tools to find out the battery capabilities. For example an 18V 12Ah battery not only lasts longer but can also deliver significantly more current whilst in use due to the capacity being achieved by extra batteries in parallel. A good example of this is my Milwaukee circular saw which is far nicer to use now I've got a 12Ah battery, doesn't bog down so easily as when it was on the 5Ah batteries.

Just need to find out / know which terminals are live. I'm not aware of any batteries that need turning on by the tool, they're almost always live.

 

[m_c]

Big thing to be aware off, is battery low voltage protection is often built into the tool.

You really need to find the details of the connections.
Some use data lines, some are a thermistor connection, some are individual cell connections (so the charger can balance charge cells), some are a basic resistor so the tool/charger knows what size of battery it is.

I've got an idea for building something that'll use Milwaukee M12 batteries, but I need to think about the battery protection. Or I use M18 with a voltage reducer, but that'll still need voltage protection.

 

[Ross365]

I've done it to a very limited degree. I rebuilt a battery pack for an old Bosch which originally used NiCads. I used 3 off 18650 cells (which work wonderfully) and I had enough room on the pack to include two output terminals, and I now use the pack to power my small Minicraft 12 volt drill (like a Dremel, but better). Handy when using it out on the car.

 

[Agroshield]

A bit of reading up indicates the extra terminals are for charging but I can't see why the tools would also have the extra connections if that's the case?

If you have the ability to 3DP, make an adaptor that goes between battery and tool and brings out the three terminals for probing. Start with a fully charged battery and see what voltage is on them at rest and with the tool in use. Then swap to an almost flat battery and see what happens when the tool cuts out.

On Makita, I believe the main ones are always live and the third one is high when battery is usable and goes low when it is flat. Its state is controlled from within the battery and it is a signal line only. That signal is used to control a relay in the tool that allows juice to the power hungry bit or not (on a Makita with a flat battery, the LED will light but the tool will not run, so something has to be coming from the battery).

 

[mtt.tr]

Most batteries only contain circuitry for cell management I think only Makita include over discharge protection.

Most of the protection is in tool thats why the battery thermocouple connects to the tool.

Arguably it's shouldn't be to challenging to build a circuit that keeps and eye on the batteries if one goes low it can cut out a relay.

Over current could be a shunt on the output but I would rather one at every battery.

Again you can utilise the inbuilt thermistor in each battery

 

[hotponyshoes]

I'll do a bit of probing at the weekend...

I'm wondering if it might be simpler to get a cheap/broken tool and take the electronics out of that?
Or even buy the electronics module as a spare part?
Then I could replace the trigger with an on/off switch and just use the 2 motor wires for the load?

 

[Agroshield]

I'll do a bit of probing at the weekend...

I'm wondering if it might be simpler to get a cheap/broken tool and take the electronics out of that?

The broken tool is a good idea. Then whatever MOSFET is in it that is controlled by the battery electronics and switches to allow the main power to pass or not will be the correct size and continuous current rating.

Call your adaptor 'outboard battery diagnostics' and the improved version OBD II. Persuade the manufacturers adopt as 'common auxiliary new tool battery usage system' or CAN'TBUS.

 

[mike os]

The broken tool is a good idea. Then whatever MOSFET is in it that is controlled by the battery electronics and switches to allow the main power to pass or not will be the correct size and continuous current rating.

Call your adaptor 'outboard battery diagnostics' and the improved version OBD II. Persuade the manufacturers adopt as 'common auxiliary new tool battery usage system' or CAN'TBUS.

Not common useable new … ?

Far more accurate anagram

 

[MetalMonkey]

Most batteries only contain circuitry for cell management I think only Makita include over discharge protection.

Most of the protection is in tool thats why the battery thermocouple connects to the tool.

Arguably it's shouldn't be to challenging to build a circuit that keeps and eye on the batteries if one goes low it can cut out a relay.

Over current could be a shunt on the output but I would rather one at every battery.

Again you can utilise the inbuilt thermistor in each battery

The Makita ones have quite a bit of protection built in, and log the cycles, cell health etc.
I know the latest Hikoki ones actually have a complete built in datalogger which keeps a record of which tools you have used it with, the model numbers, if they are brushless as well as all the cell health and history of the overload protection.

Not sure how "smart" the new Dewalt packs are, but I wouldn't be surprised to see more of the brands going that way in the future.
I suspect many of the Chinese clone batteries don't include anything much besides the cells themselves.

 

[Turbo]

Genuine Makita batteries do have protection built in to the battery to prevent over discharge. But my makita site radio will continue to drain the battery after it switches off due to a flat battery and can drain the battery flat if left long enough! Maybe its because the low drain of the radio isn't enough to trigger the cutout in the battery.
So I would be cautious about using a drill battery to power any low drain items.

I suspect many of the Chinese clone batteries don't include anything much besides the cells themselves.

The clone Makita batteries use a very basic BMS based on the one used in old Makita batteries. It doesn't monitor the individual voltages of all the cells so they are not properly balance charged. It's neither very good at protecting the battery from over discharge. I had one in my Makita site radio & it ran all the cells completely flat rendering it scrap!
I had another clone battery that I had upgraded to a newer type bms, similar to the one fitted to genuine batteries, same thing happened with the radio but this time the cells were better protected. It still wouldn't charge in the makita charger but I was able to rescue it by charging the individual cells on my 18650 charger.

 

[hotponyshoes]

I did do a bit of probing with a multimeter yesterday on a couple of brands but can't really figure anything useful out.
I think I'll have to make up some breakout leads so I can measure while they are attached to a tool

 

[m_c]

Genuine Makita batteries do have protection built in to the battery to prevent over discharge. But my makita site radio will continue to drain the battery after it switches off due to a flat battery and can drain the battery flat if left long enough! Maybe its because the low drain of the radio isn't enough to trigger the cutout in the battery.
So I would be cautious about using a drill battery to power any low drain items.

The Makita batteries have protection built in, but they don't disconnect anything and rely on the tool to stop drawing power.
Most tools will still draw some small amount of current even when not 'on', so will continue to flatten the battery past the low voltage cut-off point, which is why you shouldn't store batteries in tools.