What lithium batteries have built in BMS?

[JackOfDiamonds]

I found out my M12 batteries don't have any battery management or protection circuitry in them. That means if you use them with those 12v adapters, etc, you can discharge them too far and ruin them. I assume Milwaukee tools all have the proper circuitry in the tools.

Do all 18V batteries that have charge gauges on the battery have internal protection? Is it possible to damage those by over discharge?

I am building a 12V accessory circuit for my bike, and looking for a 12V battery. It needs to be 12V because I have some automotive accessories like grip heaters that will run off of it.

I planned to use M12 batteries but found out those don't have any protection circuitry on them. So I will probably kill the batteries the first time I run them down. I also looked into LiPo batteries for RC cars, but those also are "naked" and die or explode if they are fully discharged. I need a battery that has a built-in low-voltage cutoff.

I heard most 18V tool batteries that have the state-of-charge indicators on them have built-in battery management circuits that prevent them from over-discharging, but 18V is too much voltage (probably).

 

[whateg01]

I thought most tools had the bms built into them, even if the battery has an indicator. DeWalt batteries have the indicator on them. Maybe there's a YouTube video of somebody dissecting one.

 

[bluedog225]

Lots of the LiFePO4 stuff has bms. Eg SOK and Battle Born. And many competitors. You will want Bluetooth access and the ability to set a cutoff point. To prevent over discharge.

 

[bluedog225]

I think bms and prevention of over discharge are two different things.

 

[manac]

You could use individual protected cells or a low voltage cutoff like this Link
I use Makita packs and I think they work with the tool for the low voltage cutoff.
I have a couple of the boards in the link but just started playing with them.

 

[whateg01]

You could use individual protected cells or a low voltage cutoff like this Link
I use Makita packs and I think they work with the tool for the low voltage cutoff.
I have a couple of the boards in the link but just started playing with them.

curious to see how they work for you. I want to drive a worklight off of my dewalt batteries, so I ordered a similar board, but haven't gotten around to setting it up.

 

[Drunkonunleaded]

Kobalt 24v but that’s way over your voltage limit unless you run a step-down converter or something.

 

[mike93lx]

Dewalt puts the over discharge circuitry in the tools, not the batteries

 

[Citation]

All competently designed battery packs will have a circuit to protect from over charge/discharge etc. The only common examples I'm aware of that don't have such circuits in the batteries are RC cars/planes. They often use cells without protection but they also typically have voltage warning devices on the vehicle. Those can be purchased off Amazon etc for not much money. Something like this:

1-8S Low Voltage Buzzer Alarm Lipo Battery Voltage Indicator Tester for RC Car Boat & Drone - 1Pc

Features:100% Brand new and high Quality.Check your lipo battery voltage.Voltage display function and low voltage alarm funtion.Suitable for 1-8s Lipo/ Li-ion/ LiMn/ Li-Fe.Protect the battery from overcharging or overdischarging.Test the working state of lithium battery.Automatic protects...

www.jteamhobbies.com

(not an endorsement of the product or seller)

The cordless drill batteries almost certainly will have such a circuit. However, you should keep in mind that "12V" Li-ion batteries are not really "12V". When discussing battery voltage the typical way to do it is use the "average" cell voltage (1.2V for NiCAD, 3.6V for Li-ion) * the number of cells in series. Thus your old 12V NiCAD drill was 10 cells in series. Note that 3.6V*3=10.8V and 3.6V*4 = 14.4. So, using typical descriptions, there isn't a "12V" Li-ion drill battery. However, the mfrs figured it would be hard to sell a 10.8V drill as an upgrade over the old 12V NiCAD drill so they fibbed just a bit. The peak charge voltage of a freshly charged Li-ion battery is a bit over 4V so off the charger it is a 12V battery. To avoid the lawsuits this is written in fine print somewhere in the sales material.

Now consider that in your car the system voltage is typically over 12V when the car is off and more like 13.something when the engine is running. So you have something that is meant to run on more like 13V and you are suggesting giving it more like 10.8V. You might be better off using an 18V battery and a high current buck converter. That would allow you to provide a true 12V (or 13V) with a battery more than 12V.
https://www.amazon.com/EPBOWPT-Conv...ransformer/dp/B07V6X6L89?tag=atomicindus08-20
Again not an endorsement of a specific model, just an example. I will note that example says it takes a range of inputs, not just 24V.

 

[mike93lx]

The cordless drill batteries almost certainly will have such a circuit.

Some put it in the tool, some are in the battery.

Dewalt is the former

 

[GeoBruin]

All competently designed battery packs will have a circuit to protect from over charge/discharge etc. The only common examples I'm aware of that don't have such circuits in the batteries are RC cars/planes. They often use cells without protection but they also typically have voltage warning devices on the vehicle. Those can be purchased off Amazon etc for not much money. Something like this:

1-8S Low Voltage Buzzer Alarm Lipo Battery Voltage Indicator Tester for RC Car Boat & Drone - 1Pc

Features:100% Brand new and high Quality.Check your lipo battery voltage.Voltage display function and low voltage alarm funtion.Suitable for 1-8s Lipo/ Li-ion/ LiMn/ Li-Fe.Protect the battery from overcharging or overdischarging.Test the working state of lithium battery.Automatic protects...

www.jteamhobbies.com

(not an endorsement of the product or seller)

The cordless drill batteries almost certainly will have such a circuit. However, you should keep in mind that "12V" Li-ion batteries are not really "12V". When discussing battery voltage the typical way to do it is use the "average" cell voltage (1.2V for NiCAD, 3.6V for Li-ion) * the number of cells in series. Thus your old 12V NiCAD drill was 10 cells in series. Note that 3.6V*3=10.8V and 3.6V*4 = 14.4. So, using typical descriptions, there isn't a "12V" Li-ion drill battery. However, the mfrs figured it would be hard to sell a 10.8V drill as an upgrade over the old 12V NiCAD drill so they fibbed just a bit. The peak charge voltage of a freshly charged Li-ion battery is a bit over 4V so off the charger it is a 12V battery. To avoid the lawsuits this is written in fine print somewhere in the sales material.

Now consider that in your car the system voltage is typically over 12V when the car is off and more like 13.something when the engine is running. So you have something that is meant to run on more like 13V and you are suggesting giving it more like 10.8V. You might be better off using an 18V battery and a high current buck converter. That would allow you to provide a true 12V (or 13V) with a battery more than 12V.
https://www.amazon.com/EPBOWPT-Conv...ransformer/dp/B07V6X6L89?tag=atomicindus08-20
Again not an endorsement of a specific model, just an example. I will note that example says it takes a range of inputs, not just 24V.

Lithium ion batteries in the common chemistries were talking about here (LiCoO2, etc) come off the charger at 4.2 volts and are considered dead somewhere around 3 volts (depends on where the manufacturer sets the low voltage cutoff). I find that slightly higher is common to account for voltage sag under load with high current draw applications like power tools, like 3.4 volts.

So in a 3S configuration, the actual operating voltage range is 12.6 volts to 10.2 volts. It of course depends how voltage sensitive your accessories are, but that is not a bad approximation for a car battery voltage, especially for accessories that run when the alternator is not on.

 

[WhataTool]

Plenty of 18V batteries will discharge to death including DeWALT. Ridgid is an example of one that wont, as well as Makita

 

[Citation]

Some put it in the tool, some are in the battery.

Dewalt is the former

I haven't torn these down but the few videos I've seen always show some basic circuit in the battery. I can believe the tool would also have something but the basic under voltage projection is cheap and typically integrated into the same circuit that handles over voltage.

 

[mike93lx]

I haven't torn these down but the few videos I've seen always show some basic circuit in the battery. I can believe the tool would also have something but the basic under voltage projection is cheap and typically integrated into the same circuit that handles over voltage.

It is what it is.

They have circuitry for the level indicator and likely a temp sensor.

Its an issue that arises when using these batteries in other applications, like power wheels or with adapters into other tools.

 

[Citation]

Lithium ion batteries in the common chemistries were talking about here (LiCoO2, etc) come off the charger at 4.2 volts and are considered dead somewhere around 3 volts (depends on where the manufacturer sets the low voltage cutoff). I find that slightly higher is common to account for voltage sag under load with high current draw applications like power tools, like 3.4 volts.

So in a 3S configuration, the actual operating voltage range is 12.6 volts to 10.2 volts. It of course depends how voltage sensitive your accessories are, but that is not a bad approximation for a car battery voltage, especially for accessories that run when the alternator is not on.

When I worked in this industry (well before power tools used Li-ion cells) 4.2 was the peak village per cell during charge. Fresh off the charger you would see 4.1. with about 10-15% capacity consumed (ie mostly charged) the voltage would drop to under 4V per cell. We considered 3.6 to be the average voltage over the discharge of the battery. That is why we rated a 3S laptop battery at 10.8V vs 12V. We used 3.0 as the end of discharge voltage but that was under a less than 1C load.
Ultimately the "12V" label is a marketting claim and isn't labeled the same way as the old 12V NiCAD batteries where 12V was the average voltage vs the just a bit off the charger voltage. It's not quite as egregious as the "peak" HP Air compressors but it's in the same direction.

 

[Citation]

It is what it is.

They have circuitry for the level indicator and likely a temp sensor.

Its an issue that arises when using these batteries in other applications, like power wheels or with adapters into other tools.

Amazon.com

Looking at that circuit (aftermarket replacement for M12) I would say you are right. I'm surprised they would do that. Perhaps they feel the risk of aftermarket chargers isn't that big?

 

[whateg01]

...ge. It's not quite as egregious as the "peak" HP Air compressors but it's in the same direction.

The difference is, on a "12V" battery, you can actually measure the voltage to be =/> 12V when it's fresh off the charger. Nobody is measuring peak horsepower on a 120V air compressor or shop vac to be 7 HP. As far as accessories go, I have found that most LED "bulbs" rated for 12V (all the ones I've tried anyway) work just fine at voltages down into the "this Li-ion battery is dead" range.

 

[JackOfDiamonds]

Amazon.com

Looking at that circuit (aftermarket replacement for M12) I would say you are right. I'm surprised they would do that. Perhaps they feel the risk of aftermarket chargers isn't that big?

Putting in a low-voltage cutoff in the battery would require a big relay in each battery to actually do the disconnection. A solid state switch capable of switching 10+ amps would be even more expensive and more lossy than a relay. So I guess it's cheaper to just have the tool stop drawing current when the battery gets too low. But it's a big problem if you want to use the batteries outside the system like I am, because you have to build your own cutoff somehow.

Milwaukee sells a M12 power source, but it's absurdly priced at $70, only allows 2Amps draw from the 12V port, and automatically turns itself off, which won't work for my application. I like the RC voltage buzzer thing though.

 

[NUTTSGT]

I've merged both threads and then merged the first two posts.

If were to delete the first post, it'll dump the thread.

Feel free to edit out your current original post to what you want. If you need any further help, don't be afraid to ask.

 

[Citation]

The difference is, on a "12V" battery, you can actually measure the voltage to be =/> 12V when it's fresh off the charger. Nobody is measuring peak horsepower on a 120V air compressor or shop vac to be 7 HP. As far as accessories go, I have found that most LED "bulbs" rated for 12V (all the ones I've tried anyway) work just fine at voltages down into the "this Li-ion battery is dead" range.

I think the peak HP numbers were based on using the peak AC voltage (not RMS) and a few other tricks. Basically, the motor did consume 3hp for a microsecond but not on average. In this case the various 12V tools can be compared just as the old compressors could be compared even though we knew the claimed HP was BS. I'm the case it's not so egregious but it's still an inflated claim since most batteries spec average unloaded voltage, not fresh off the charge voltage. The difference isn't going to matter in most cases, especially since the tools are designed around the actual battery voltage range, not just the peak number.

 

[JackOfDiamonds]

Plenty of 18V batteries will discharge to death including DeWALT. Ridgid is an example of one that wont, as well as Makita

It's hard to find good information because "won't discharge to death" usually / sometimes means "won't discharge to death when connected to official tools".

Built-in circuitry varies, but none of the batteries seem to have any mechanism to actually disconnect the cells from the terminals when voltage gets low; they only have mechanisms to "warn" the tool that the batteries are low so that THE TOOL can stop drawing power. I have yet to find any documented example of a tool battery that won't discharge itself to death when connected to a "dumb" external load.

See for example (Reddit thread): https://www.reddit.com/r/Makita/comments/1330jo9/_/ji8ao4x
M12 batteries are particularly dumb, and don't even have built-in charge indicators; even that's on the tool.

 

[Citation]

Putting in a low-voltage cutoff in the battery would require a big relay in each battery to actually do the disconnection. A solid state switch capable of switching 10+ amps would be even more expensive and more lossy than a relay. So I guess it's cheaper to just have the tool stop drawing current when the battery gets too low. But it's a big problem if you want to use the batteries outside the system like I am, because you have to build your own cutoff somehow.

Milwaukee sells a M12 power source, but it's absurdly priced at $70, only allows 2Amps draw from the 12V port, and automatically turns itself off, which won't work for my application. I like the RC voltage buzzer thing though.

It's not that big a relay. We switched 200 amps using a TO-220 package FET*. However, you are correct, it is cheaper to not have the part in the battery. Depending on the setup some batteries use different pins for charging vs discharging. This allows lower current parts to cut off charging current since over charging has the biggest risk of a "vent with flame" event. We typically had 2 independent circuits that could stop an overcharge situation but only 1 for low charge/over current.

We made a custom circuit to use a truck battery to provide current for a resistive heating system. It looked crazy to have welding wires (2 gauge I think) feeding into this little 220 package! But it worked and seemed like a far safer idea than the original proposal which was to build our own custom supply that would use transformers to step up the current available from the wall outlet. It's called a welder and none of us had enough EE knowledge to know what we didn't know! I just knew it seemed more dangerous than I was comfortable with and suggested we use a larger, 12V battery instead. While that did limit our peak current to something near 200 amps, that was plenty and avoided a number of issues. Even then we still had issues with back EMF village etc

 

[manac]

@whateg01 The low voltage board works well. Set a high limit and it won’t start to provide power below that set point (you need a charged battery to start). Set the low limit and the relay opens when the battery voltage drops to it. The board still draws about 12mA with the relay open. The board can also be used as a charge limit, opening the relay when a voltage is reached.