Introduction: Fast Electric Skateboard LiPo Charging System (BMS + CC/VC PSU)

The charging of lithium-ion battery backs, typically found in DIY electric skateboards and bikes, is typically done with a balance charger, like an IMAX B6. These chargers can be set-up for a variety of battery packs, but they typically require an external power supply, and are bulky and cannot charge very quickly.

This instructable is going to go over a new battery charging system for electric skateboards. I'm going to cover how to connect an inexpensive BMS (Battery Management System) to an electric skateboard's battery pack, and how to convert an inexpensive, yet powerful power supply, into a battery charger, by putting a current limit on it.

This battery charging system can be adapted for electric bikes as well, and can even be used with pre-made laptop-brick style charging units, which are a very portable and convenient solution.

Step 1: Watch the Video!

This video will go over the basics of this Instructable. It's not a step-by-step guide, but it will gloss over the basics of this system.

Step 2: Choose a BMS and Power Supply

Choosing a BMS

The best place to find a BMS for your LiPo pack is on eBay. They are typically around $16, and come in a variety of different cell configurations. You will need one that has a rating of however many LiPo cells you have in series. (I have 6 in series, so I will use a 6s BMS). It is very important that you choose a BMS with a "balance cell" feature. Some BMS units are incorrectly labeled, and are actually just a protection circuit.

These BMS boards typically have a current-cutoff as well. It does not matter what the current cut-off is. These current cutoffs go up until about 30 amps, which is still too low for electric skateboards, which can pull up to 100 amps. Go with the cheapest BMS that satisfies your LiPo cell count, and has a balance feature. Here's the link which I use to search with.

Choosing a Power Supply

These inexpensive power supplies on eBay are fitted with potentiometers, which can adjust the voltage range, give or take ~20%. You will need a power supply that can be set to a higher voltage than the fully charged voltage of your battery pack. For example, my 6s system is fully charged at 25.2 volts. A 24v power supply would be able to provide that 25.2 volts. Here's a list of typical power supplies, their voltage range, and the number of cells they can charge:

  • 5 volt PSU (4.5v - 5.5v, 1S)
  • 12 volt PSU (10.6v - 13.2v, 3S)
  • 24 volt PSU (19.5v - 29.8v, 5S 6S)
  • 48 volt PSU (43v - 53v, 10S 11S 12S)

You will need to choose the power supply that fits your cell count. Additionally, the voltage adjust potentiometer can be replaced to give you a bigger voltage range, however, it is not recommended to go above the max voltage because it can damage some of the capacitors. Going below the preset voltage can result in unintended operation. The wattage of the power supply affect the speed at which you can charge your batteries (more on that later).

Using a Preset Power Supply

It is also possible to use a preset power supply to charge your skateboard, which comes in the form of a laptop-style power brick. You will simply need to choose one that is for your particular cell count. These power supplies are typically cheaper on Amazon, but they do tend to have lower current-ratings.

Step 3: Connect the BMS to Your LiPo Cells

Connect your BMS to your battery pack by soldering the connections above. Typically, the eBay seller pages have a diagram which you can follow. However, since we are going to be overriding the current limit of the BMS, you can just solder your ESC wires directly to the batteries. If you want your system to be modular, you can also use gold-plated bullet connectors to connect everything together.

You are also going to need to solder some sort of connector to the input of the BMS. The cheapest option is here, for about $0.70. This kind of jack is used on the E-GO boards. However, I decided to go for something a bit more durable. It's advisable to use a female jack on the skateboard side in order to prevent accidental shorts.

Step 4: Change the Current Limit on the Power Supply

The first step to converting your power supply, is to set the voltage to the max voltage of your battery pack. I'm using a 6S battery pack, so I will set it to 4.2v * 6 = 25.2v.

Unfortunately, these Chinese power supplies are meant for audio applications, and are typically set to ~130% their rated constant output (in order to be able to handle bass-drums). Thus, if we were to plug the power supply into the BMS, the battery would draw current proportional the the total resistance * difference in voltage (AKA that would melt the power supply in a short time).

Thus, we need to go inside the BMS, and find a way to lower the current limit just a little bit. I reverse-engineered part of the circuit near the control chip, and I found that adding a 10k ohm potentiometer to the pins of R35 would allow me to adjust the current. The potentiometer is very sensitive, but it seems to be working well. This resistor seems to be the same on other power supplies, and it is commonly known as the "R33 mod" on the genuine MeanWell power supplies.

I soldered the potentiometer with some very long wires, and brought it outside the power supply so it could be adjusted later.

Step 5: Assemble the PSU (add a Case, Switch, and Ammeter)

In order to make this power supply more into a genuine-looking charger, I decided to add an LED toggle switch, and an ammeter (current meter) according to the schematic above. Both of these items are very inexpensive! I did not use any connections this time, and I just soldered everything according to that diagram. You have to take care when connecting the ammeter, current must only flow in one particular way, otherwise it will short-circuit with the power input!

I also added the power plug that I cut from an old computer cord. I suggest you choose a plug with an earth connection, as it will safely ground the power supply in the event of an accident.

Then I cut using a jigsaw, and hot-glued some high-density foam together to make a nice box for my power supply. It seems to get hot even when the batteries are not being charged, so I also drilled some large holes for ventilation above (just a precaution really, I don't think I actually needed them). I glued the current-setting potentiometer to the side of the case, and used heat-shrink tubing to cover all of the contacts up.

Step 6: Calibrate the Voltage and Current

By now, you should have already calibrated the voltage, but just in case, double-check before continuing. Plug the power supply into the skateboard/bike, and flip the on switch. If you have an ammeter, it should be displaying some number. If you don't have one, you will need to connect an ammeter between the skateboard and PSU.

Then use a screw-driver to set the current limit using the potentiometer. Do not set it to the rated current of your power supply. You will need to take the wattage of your power supply (mine was 120 watts), and divide it by the max voltage of your batteries (120 watts / 25.2v = ~4.76 amps). You will then get the current limit that you should set it to.

Don't worry if your power supply goes over it's current limit for a minute or two. It will simply produce more heat than is desired. You can use the potentiometer to bring the current limit down to 0.

Step 7: Enjoy!

And that's it! Enjoy your new speedy charger! In order to roughly calculate how much time it will take to charge, take your battery capacity, and divide it by the current limit you set. Your anwser will be how long it will take to charge in hours. (Keep in mind, this is from when each cell is 3v. Your actual charge time will actually be less if you only discharge to nominal voltage).

Also, a note about using the LED button. The LED light is power by the batteries when you are connected to the PSU without the PSU getting power. That means that the LED will slowly drain your batteries (but don't worry, the BMS will stop them from draining completely!) The LED only light up when you have the batteries connected, or when you have turned the switch on.

Comments

author
ianc119 made it!(author)2017-07-09

Hello! I want to do this with 3 3s batteries for my electric longboard... do you think is it possible? maybe connecting 3 bms, one for each battery. And then connect the power suply in parallel for each bms. Thank you for your help

author
cpercle made it!(author)2016-10-30

How do you know when the battery is charged using the bms? I want to implement this into my project but want to make sure I know when the board is charged.

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author
ianc119 made it!(author)2017-07-09

Wow! your work is amazing

author
pauapau made it!(author)2017-05-07

hey,

i want to charge 2 3s lipo batteries with 5Ah each

can i use this bms(10 A charge/discharge) with that charger(24V with 4Ah)

https://hobbyking.com/en_us/6s-li-ion-10a-pcm.html...

https://www.amazon.de/Netzteil-Ladeger%C3%A4t-Moni...

thank you for your help

cheers pau

author
curtis.newton.104203 made it!(author)2017-04-08

and if it is a well known mod, you did not reverse engineered anything

author
curtis.newton.104203 made it!(author)2017-04-08

"Thus, we need to go inside the BMS, and find a way to lower the current limit just a little bit."

you mean the batttery, not the bms ?

author
curtis.newton.104203 made it!(author)2017-04-08

since the bms deals with the charging and sensing the cells, why would you need apower supply that "fits your cell count"

does not make any sens

author
ahaho made it!(author)2017-02-21

am i right when i say that i can connect + and - from the battery pack to the + and - on the ESC and than just plug balance connector from the battery pack to the bms and solder connector for charging via the bms ?

author
ahaho made it!(author)2017-02-19

my motor can drain 70A so do i need bms for 70A or can i buy this bms : http://www.ebay.com/itm/17V-Protection-Balance-Module-BMS-PCM-5A-For-6S-22-2V-Li-ion-Li-Po-Battery-/322365863089?hash=item4b0e80b4b1:g:NgUAAOSwcUBYHYVP

author
AndreasG29 made it!(author)2017-02-19

if you wire it like vlad and his picture you are gonna bypass the bms drain. which means the bms only will be used to control the charging not the output from the batteries to the esc. so basically you could buy one rated 0.1A and it would still work (it would just charge the batteries slower)

author
ahaho made it!(author)2017-02-20

am i right when i say that i can connect + and - from the battery pack to the + and - on the ESC and than just plug balance connector to the bms and solder connector for charging to the bms ?

author
ThomasN62 made it!(author)2017-02-14

Vlad I was curious as to how safe this is. Surely if one of the cells gets damaged and wouldn't charge then the other cells would over charge and could cause a serious hazard. Am i right in thinking this or did i miss something?

author
Frenkii made it!(author)2017-01-26

Hello

I bought all the components and got it all figured out except my power supply internals are different.CAN SOMEONE PLEASE TAKE YOUR TIME TO LOOK,I WOULD BE VERY GRATEFUL.I dont know where to solder the resistor.

Thanks

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oscarW14 made it!(author)2017-01-10

hi vlad! Do you think you could explain the wiring process of the battery to the bms again because I'm a bit confused but still ended up buying everything. Hope to hear back thanks oscar.

author
AliK209 made it!(author)2016-12-28

Hey Vlad! I bought a BMS from signalab (http://www.ebay.ca/itm/BMS-PCB-PCM-for-24V-25-2V-7S-Li-Ion-Li-Polymer-Battery-Pack-30A-60A-With-Balance-/152322936768?hash=item2377278fc0:g:2KAAAMXQ855RvpyC) and I wired everything correctly and it charged the batteries up to about 60%. Then it stopped working. Tried again multiple times (even started smoking) and rewired everything to the diagram (everything correct) and kept trying eventually the connector from the battery to bms (main) literally blew up in my face. Any ideas as to why?

author
JustinP89 made it!(author)2016-10-27

How did you connect the two 3s Balance plugs into the BMS?

author
JdogAwesome made it!(author)2016-09-24

Hey Vlad im using pretty much exactly the same setup for my board based on this design but I had a couple questions. First off my 24V PSU doesn't have an IC controlling the current limitation, its a lot simpler and only has voltage regulation, so I was wondering how you control the amount of amperage the BMS draws? I had a 3S BMS that drew different amounts of current based on slightly changing the voltage higher or lower and I was wondering if it was the same principal here. If not would I be better off using a 5A constant current module for it?

author
markyoe made it!(author)2016-08-28

Hey comsa42! I built your Electric Longboard V2.0, and it runs great! I'm thinking about building a battery using this instructable: https://www.instructables.com/id/How-to-Make-a-Lith...

Would it be possible to add a BMS to make it so I don't have to remove the battery and just hook it up to a laptop power supply? What type of BMS would I get?

Thanks man!

author
sjors_02 made it!(author)2016-08-21

Your projects are great! But what is the range of this board?

author
comsa42 made it!(author)2016-08-21

10-18km, depending on how you ride it.

About This Instructable

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Bio: I'm a highschooler who is interested in technology, science, and engineering. In my spare time I work on projects that allow me to learn ... More »
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