Using A Power Tool Battery As A Range Extender

6zfshdb

Well-Known Member
Region
USA
City
Northeast Pennsylvania
I'm presently using this DeWalt 60V 12AH battery with this adapter as an emergency range extender. At 60V, the battery capacity is 4AH which gives me around 12 extra miles using PAS 2.


61aThHjfHgL._AC_SL1500_.jpg

61YOD+8wWBL._AC_SL1402_.jpg
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The bike uses a 52V battery with a controller rated at 61V. The fully charged voltage of the DeWalt battery is 61.2V which is higher than the 58.8V for the OEM. It does not cause any issues with the controller other than an inaccurate battery gauge reading on the display. Consequently, I'm using a voltmeter to determine the battery state of charge.

Very little information is available for these DeWalt Flex Volt batteries except that they use 3 strings of 5 cells wired in series for 60V or parallel for 20V. I don't know what type of cells are used however and the voltage does not match that of "standard" lithium cells. I don't know how the voltage relates to the actual % of charge and, more importantly, what the safe max discharge voltage is. I also don't know whether the low voltage cutoff circuit is located in the tool or the battery itself.

At $250 each, I don't want to damage the battery by over discharging but I also want to get the maximum range possible. Using power tool batteries on an e-bike is nothing new and the idea has been discussed here before. I'm curious how others who use them handle battery management.
 
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harryS

Well-Known Member
How do you connect them to the bike?
These work best for DIY bikes, where we often have exposed cables coming from the battery cradles, if those are used. Many DIY bikes carry batteries in rack bags, so that cabling is quite accessible,

Some owners with Lectric XP's, where the battery is inside the frame, have been tapping into the battery wires and running cables out for an aux battery. You probably aren't going to do this with a $6000 ebike. You'll spend $900 for the spare pack, but when a Lectric XP was only $899, one can do a little mod work as long as one is careful.
 

2ster

New Member
Region
USA
I'm presently using this DeWalt 60V 12AH battery with this adapter as an emergency range extender. At 60V, the battery capacity is 4AH which gives me around 12 extra miles using PAS 2.

View attachment 88968

View attachment 88969

The bike uses a 52V battery with a controller rated at 61V. The fully charged voltage of the DeWalt battery is 61.2V which is higher than the 58.8V for the OEM. It does not cause any issues with the controller other than an inaccurate battery gauge reading on the display. Consequently, I'm using a voltmeter to determine the battery state of charge.

Very little information is available for these DeWalt Flex Volt batteries except that they use 3 strings of 5 cells wired in series for 60V or parallel for 20V. I don't know what type of cells are used however and the voltage does not match that of "standard" lithium cells. I don't know how the voltage relates to the actual % of charge and, more importantly, what the safe max discharge voltage is. I also don't know whether the low voltage cutoff circuit is located in the tool or the battery itself.

At $250 each, I don't want to damage the battery by over discharging but I also want to get the maximum range possible. Using power tool batteries on an e-bike is nothing new and the idea has been discussed here before. I'm curious how others who use them handle battery management.
 

2ster

New Member
Region
USA
As a total newbie, could you lay out the schematic for the battery setup. I am extremely curious. Thank you.
 

Bitmugger

Active Member
Region
Canada
61v is probably 15 cells which aligns with the statement "3 strings of 5 cells"

I have Makita products myself and looked into this and couldn't see any reason it wouldn't work perfect. The BMS in these power tools are normally really durable and given the tools they run (table saws, grinders, routers) they can really pour out the juice so discharge rate should be fine. I don't for sure know the DeWalt batteries have a BMS but I am 100% certain Makita has the BMS in the batteries and I suspect all the big players like DeWalt do similar. Great solution to adding a little extra range! Be careful with the 61v being a bit over the rated limit of your controller but sounds like it's working great.
 

6zfshdb

Well-Known Member
Region
USA
City
Northeast Pennsylvania
As a total newbie, could you lay out the schematic for the battery setup. I am extremely curious. Thank you.
Unfortunately, a schematic for wiring up a rig like this will vary depending on the e-bike you have. Here are a few crude over simplified drawings that might help:

First, you need to access the wiring between the battery and controller:
P1080882b.jpg

Cut the positive & negative leads (usually red & black)
P1080882e.jpg

Wire a double pole double throw switch as shown:
P1080882d.jpg

The switch lets you choose which battery is to be used. It must be rated for >40 amps.

Please note this scheme is for an e-bike that uses a 52V battery and is equipped with a controller rated for at least 60V. The actual output of the DeWalt Flex Volt battery is 61.2V which is a bit higher than the 58.8V of the OEM bike battery. In this case, the overage isn't significant enough to cause damage. If your bike uses a 36 or 48 volt battery, be aware that this scheme may cause damage to the bike components.

I have seen two 18V power tool batteries used in series in a scheme similar to this to power an e-bike with a 36V system. I imagine a circuit to power a 48V e-bike with power tool batteries is possible but I'm not familiar with specifics.

Another thing to keep in mind is this: I was told by DeWalt that these lithium power tool batteries do NOT have a BMS or low voltage cutoff circuit built in. Battery management is handled by the power tool in which they are designed to be used. It is possible to ruin these expensive batteries by over discharging so monitoring with a voltmeter is essential! Other manufacturers may have BMS circuitry in their batteries but it would be prudent to verify.
 

2ster

New Member
Region
USA
Unfortunately, a schematic for wiring up a rig like this will vary depending on the e-bike you have. Here are a few crude over simplified drawings that might help:

First, you need to access the wiring between the battery and controller:
View attachment 89401

Cut the positive & negative leads (usually red & black)
View attachment 89403

Wire a double pole double throw switch as shown:
View attachment 89402

The switch lets you choose which battery is to be used. It must be rated for >40 amps.

Please note this scheme is for an e-bike that uses a 52V battery and is equipped with a controller rated for at least 60V. The actual output of the DeWalt Flex Volt battery is 61.2V which is a bit higher than the 58.8V of the OEM bike battery. In this case, the overage isn't significant enough to cause damage. If your bike uses a 36 or 48 volt battery, be aware that this scheme may cause damage to the bike components.

I have seen two 18V power tool batteries used in series in a scheme similar to this to power an e-bike with a 36V system. I imagine a circuit to power a 48V e-bike with power tool batteries is possible but I'm not familiar with specifics.

Another thing to keep in mind is this: I was told by DeWalt that these lithium power tool batteries do NOT have a BMS or low voltage cutoff circuit built in. Battery management is handled by the power tool in which they are designed to be used. It is possible to ruin these expensive batteries by over discharging so monitoring with a voltmeter is essential! Other manufacturers may have BMS circuitry in their batteries but it would be prudent to verify.
The simplest setup I have seen so far. I have a 48V system, so in your opinion would another 48V battery work and would not the BMS manage the backup battery. I will not hold you to anything. I am looking for information. Also, you are kind to take the time to do this. Thank you.
 

Bitmugger

Active Member
Region
Canada
The simplest setup I have seen so far. I have a 48V system, so in your opinion would another 48V battery work and would not the BMS manage the backup battery. I will not hold you to anything. I am looking for information. Also, you are kind to take the time to do this. Thank you.

The BMS won't help you with a second battery, each battery will need their own BMS if it were to have one. I am really surprised the DeWalt doesn't have a BMS in it, a BMS in the tool means limited options for future battery capacities and chemistries vs a BMS in the battery.
 

6zfshdb

Well-Known Member
Region
USA
City
Northeast Pennsylvania
The simplest setup I have seen so far. I have a 48V system, so in your opinion would another 48V battery work and would not the BMS manage the backup battery. I will not hold you to anything. I am looking for information. Also, you are kind to take the time to do this. Thank you.
Yes, this scheme can be used with almost any 48V battery including the LiGo's from Grin Tech mentioned earlier in this thread. The advantage here is most of these batteries have a built in BMS. On most e-bikes, the BMS is located in the battery, not on the bike itself. Batteries without a BMS, such as some of these power tool types, can be used to power an e-bike but the battery voltage must be monitored.

If you are going to buy a battery, you are better off getting one meant for e-bike use with a built in BMS. My purpose in starting this thread was to show how power tool batteries, which many of us already own, can be used as range extenders.
 
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6zfshdb

Well-Known Member
Region
USA
City
Northeast Pennsylvania
The BMS won't help you with a second battery, each battery will need their own BMS if it were to have one. I am really surprised the DeWalt doesn't have a BMS in it, a BMS in the tool means limited options for future battery capacities and chemistries vs a BMS in the battery.
I was surprised as well to find DeWalt does not provide a BMS in their batteries. The email I received from them explained that it is done to keep the battery cost as low as possible. Most quality cordless tools outlast several batteries so it makes sense to put the BMS in the tool.
 

Bitmugger

Active Member
Region
Canada
I was surprised as well to find DeWalt does not provide a BMS in their batteries. The email I received from them explained that it is done to keep the battery cost as low as possible. Most quality cordless tools outlast several batteries so it makes sense to put the BMS in the tool.

Not really no it doesn't make sense to me. A BMS in the battery can be used to prevent counterfeit batteries, it can allow new battery formats, new battery chemistries. If that battery pack is truly unprotected then dropping some steel wool, metal fillings, wires, water, etc around the battery risks the battery having a run away thermal situation which would lead to a fire or destruction of the battery (and that would mean lawsuits).

My jaw is on the floor DeWalt is shipping a large capacity tool battery without a basic BMS and protective circuitry in it. Not doubting what they told you, just very surprised.
 

smorgasbord

Well-Known Member
Region
USA
Interesting teardown of DeWalt 18V-60V Flex Battery (play at 2X speed):

This teardown has a comment that claims the FlexVolt batteries do have sophisticated BMS's inside them:
 

Bitmugger

Active Member
Region
Canada
Wow, so sounds like a bit of a disconnect between what DeWalt told @6zfshdb and what the video says. I wonder if the real situation is the BMS is very minimal and more just basic protections and DeWalt doesn't want to classify it a BMS? Either way the battery is a great idea as a range extender and glad it's working so well.
 

6zfshdb

Well-Known Member
Region
USA
City
Northeast Pennsylvania
Interesting teardown of DeWalt 18V-60V Flex Battery (play at 2X speed):

This teardown has a comment that claims the FlexVolt batteries do have sophisticated BMS's inside them:
Very interesting video. Thanks for posting.

My question to DeWalt was whether or not the battery contained a low voltage cutoff circuit, not specifically a BMS. I used the two terms incorrectly in my previous posts. As per the video's above, these Flex Volt batteries do indeed have some sophisticated circuitry built in. The exact function however isn't clear. I suspect, but can't verify that it is mostly for cell balancing during charging, 20v / 60v output management, over-current regulation and temperature control.

Almost all the information I've found on the net, including the email from DeWalt, leads me to believe that these batteries do NOT contain a low voltage cutoff. Whether or not this function is part of a true "BMS" or not is still a question. An e-bike BMS may be quite different than the circuitry built into a power tool battery.

I appreciate all the input here and I would love to discover these batteries actually do have low voltage protection built in. It would certainly ease my concern as I watch the drop on the voltmeter.