using Makita 18v tool batteries to power my ebike

[sculpturetim]

I've completed my second ebike now using a combo of kt controller, geared hub motor and Makita tool batteries, each battery has a voltage of 18 volts with 5ah but on full charge can be as much as 21v each, which means if i use 3 packs together to achieve 54 volts i risk blowing the 36-48 volt controller with a potential peak of 63v
I have tried to use buck converters to reduce the voltage but found most of them unreliable on the bike. I have been thinking of the best way to reduce the peak voltage.

Any suggestions for example using some kind of resister to waste a few volts, running a headlight system to make it lower or a reliable 30 amp buck convertor that would reduce from 63v -54v?

I believe they are quite well constructed batteries with bms built in and i own so many that it makes sense for me to try, ideally i would run a 3 battery system perhaps with another 3 in parallel
would give me ideally 54v 10ah

The batteries were purchased at the same time and are charged together

Many thanks for you suggestions

 

[amberwolf]

Anything you use to reduce the voltage by wasting the power (resistors, etc) must be able to handle the full current of the system and dissipate the waste heat generated in the voltage drop created.

If you need 30A, and need to waste 9v, that's 270W. A typical soldering iron only uses 15-20W to melt that solder, so whatever you're going to use needs to dissipate more than ten times that amount of heat.



Converting using a DC-DC needs something that can handle the surges of power and the feedback spikes and noise from the controller/motor system (which usually is done by the battery), so you need something that has enough filtering to deal with this, and enough extra capability to handle surges of current demand.

If necessary, you can add inductive chokes and capacitors between the DC-DC and the controller.

A geared motor has no regen capability, but you may want to ensure the controller has this feature disabled if it exists.

If you have trouble even with all the filtering, you can add a shottky diode between the DC-DC and the controller to prevent any voltage feedback from controller to DC-DC; it will need to be rated for the full worst-case spike current of the system, and heatsinked to dissipate the waste heat generated by the 0.3-0.7v drop x that current.

I'd go with at least a few percent, but more safely 50% more capability (current, power) than you actually need for the DC-DC, to ensure it can handle any surges from the controller. You might not need this; if the DC-DC is designed with a shutdown safety in case of problems, but if it isn't it might just blow the output stage on overcurrent.

 

[marty]

From:

Tool batteries

I am seriously considering using tool batteries to power my beach bike and cart combo. Two 18v batteries in series gets 36v For my needs the range is good. I have a bunch of Ryobi tools, and I’m down to one mostly dead battery. I can multitask my batteries this way! Yes, I’m on a budget...

endless-sphere.com

Connected a boombox to a Makita 18V battery. Worked great till the battery drained too low. Battery was killed dead, never to work again. My guess is that with Matita tools the BMS is in the tool not the battery.

Anyone have any information on which power tool battery's have a BMS or some electronics with a cutoff to prevent the voltage from going too low?

OK...... so I ask a question? Then I answer my own questions. I got the internet

Do Makita Power Tool batteries have built in over discharge?

From personal experience, tearing down tool packs:

Dewalt and Makita have the BMS/LV cut off in the tool.

Ryobi, Ridgid, Milwaukee all have a basic BMS in the battery.

The difference here is that when Dewalt and Makita switched from NIMH/NICD to Li ion they introduced a whole new line of tools tailored for the li ion batteries. The others wanted the new batteries to be reverse compatible with their old tools, so the electronics needed to be in the batteries.

 

[sculpturetim]

Anything you use to reduce the voltage by wasting the power (resistors, etc) must be able to handle the full current of the system and dissipate the waste heat generated in the voltage drop created.

If you need 30A, and need to waste 9v, that's 270W. A typical soldering iron only uses 15-20W to melt that solder, so whatever you're going to use needs to dissipate more than ten times that amount of heat.



Converting using a DC-DC needs something that can handle the surges of power and the feedback spikes and noise from the controller/motor system (which usually is done by the battery), so you need something that has enough filtering to deal with this, and enough extra capability to handle surges of current demand.

If necessary, you can add inductive chokes and capacitors between the DC-DC and the controller.

A geared motor has no regen capability, but you may want to ensure the controller has this feature disabled if it exists.

If you have trouble even with all the filtering, you can add a shottky diode between the DC-DC and the controller to prevent any voltage feedback from controller to DC-DC; it will need to be rated for the full worst-case spike current of the system, and heatsinked to dissipate the waste heat generated by the 0.3-0.7v drop x that current.

I'd go with at least a few percent, but more safely 50% more capability (current, power) than you actually need for the DC-DC, to ensure it can handle any surges from the controller. You might not need this; if the DC-DC is designed with a shutdown safety in case of problems, but if it isn't it might just blow the output stage on overcurrent.

Hi Amberwolf,
thanks for the advice, several elements for me to research , many thanks
Tim

 

[AdR]

Currently running a kt 36/48V 500W controller @58V. No issue so far except no regen braking. Will update any issues..

 

[Firedog]

Anyone have any information on which power tool battery's have a BMS or some electronics with a cutoff to prevent the voltage from going too low?

Makita started selling Lithium ion batteries in 2013. The original batteries had a "charge board" that connected the battery electrically to the tool and provided some charging protection. It also prevented charging (bricked the battery) if it sensed other errors. It had no way to monitor the voltage since no wires are connected to +/- of all the 5 cell groups. The newest Makita BL18xx 2 B batteries and other recent models have true cell BMS monitoring with cutoff on discharge and cell balancing on charge.

All Chinese "for Makita" clones I've tested, still only have the "charge board". No true BMS capabilities. They do however, offer a taller case option of 15 cells (5s3p) and 20cell (5s4p) which allows a capacity of up to 14AH and is more suited for ebike use. I've had custom 15 cell batteries built since 2017 with LG MJ1 cells (3.5ah). I've had no issues with my personal use but I'm careful to never discharge below 75% of capacity. Others, using my builds, have had batteries fail after riding the bike until it stopped due to controller voltage cutoff. If all cell voltage are still matched there is no damage but too often one or more cell's voltage drops ahead of the others and those cells are damaged or shorted.

Solution #1: Use only recent Genuine Makita batteries with true BMS. Makita only sells 3, 4, 5 and 6AH 10cell batteries which is limiting for ebike use.

Solution #2: Replace the simple "charge board" with recently available, true China BMS boards. https://www.aliexpress.us/item/3256...t_main.26.21ef1802vvmc3i&gatewayAdapt=glo2usa
These boards fit in the same space with minor adjustment as the "charge board" so they mount to any Makita tool or bike mount.

Charging is now any 21VDC source.

https://www.aliexpress.us/item/2251832680298864.html?spm=a2g0o.order_list.order_list_main.31.21ef1802vvmc3i&gatewayAdapt=glo2usa

Makita chargers can be fooled to work by mounting an old style "charge board" in the charger and wiring just the 21V output to the new BMS's charge port.
Several batteries (in the same state of charge) can be charged together in parallel.