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.Īlmost 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. As per the video's above, these Flex Volt batteries do indeed have some sophisticated circuitry built in. I used the two terms incorrectly in my previous posts. My question to DeWalt was whether or not the battery contained a low voltage cutoff circuit, not specifically a BMS. Wire a double pole double throw switch as shown: View attachment 89402Ĭlick to expand.Very interesting video. Here are a few crude over simplified drawings that might help:įirst, you need to access the wiring between the battery and controller: View attachment 89401Ĭut the positive & negative leads (usually red & black) View attachment 89403 Unfortunately, a schematic for wiring up a rig like this will vary depending on the e-bike you have. 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. Battery management is handled by the power tool in which they are designed to be used. I imagine a circuit to power a 48V e-bike with power tool batteries is possible but I'm not familiar with specifics.Īnother 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. 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. If your bike uses a 36 or 48 volt battery, be aware that this scheme may cause damage to the bike components. In this case, the overage isn't significant enough to cause damage. 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. 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 switch lets you choose which battery is to be used. Wire a double pole double throw switch as shown: Here are a few crude over simplified drawings that might help:įirst, you need to access the wiring between the battery and controller:Ĭut the positive & negative leads (usually red & black) I'm curious how others who use them handle battery management.Ĭlick to expand.Unfortunately, a schematic for wiring up a rig like this will vary depending on the e-bike you have. Using power tool batteries on an e-bike is nothing new and the idea has been discussed here before. I also don't know whether the low voltage cutoff circuit is located in the tool or the battery itself.Īt $250 each, I don't want to damage the battery by over discharging but I also want to get the maximum range possible. I don't know how the voltage relates to the actual % of charge and, more importantly, what the safe max discharge voltage is. I don't know what type of cells are used however and the voltage does not match that of "standard" lithium cells. 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. Consequently, I'm using a voltmeter to determine the battery state of charge. It does not cause any issues with the controller other than an inaccurate battery gauge reading on the display. The fully charged voltage of the DeWalt battery is 61.2V which is higher than the 58.8V for the OEM.
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