Introduction: Bidirectional Charge Laptop Powerbank
You ever thought about how you wish your laptop could last longer than usual?
You ever wished you could charge your laptop anywhere?
Look no further as with this laptop powerbank, you can make this a reality.
Note: this only works with laptops with a lightning cable (so macs, :(()
This is a school project so budget is very limited
This project is heavily inspired by this video by GreatScott: https://www.youtube.com/watch?v=_WI9Nwqvplo
Supplies
18650 Li-ion Batteries x8 - I recommend you buy these from your local hardware store, a battery supplier, or worst case a vape shop because all 18650 sold online (not including official stores) are fake.
Electrical tape
Soldering Iron
Solder
Multimeter
Nickel plated strips
wires
IP2368 buck boost type c module
Battery Management System 4s2p
Spot Welder
https://www.lazada.com.ph/products/5000w-high-power-spot-welder-with-detachable-foot-and-soldering-pen-diy-18650-battery-pack-welding-i3696162803-s22618926086.html?c=&channelLpJumpArgs=&clickTrackInfo=query%253Aspot%252Bwelding%252Bfor%252Bbattery%253Bnid%253A3696162803%253Bsrc%253ALazadaMainSrp%253Brn%253Aff7228f7b79ca131a3ed16e36abb3886%253Bregion%253Aph%253Bsku%253A3696162803_PH%253Bprice%253A351%253Bclient%253Adesktop%253Bsupplier_id%253A500201769719%253Bbiz_source%253Ahttps%253A%252F%252Fwww.lazada.com.ph%252F%253Bslot%253A2%253Butlog_bucket_id%253A470687%253Basc_category_id%253A22695%253Bitem_id%253A3696162803%253Bsku_id%253A22618926086%253Bshop_id%253A3080892&fastshipping=0&freeshipping=1&fs_ab=2&fuse_fs=&lang=en&location=Laguna&price=351&priceCompare=skuId%3A22618926086%3Bsource%3Alazada-search-voucher%3Bsn%3Aff7228f7b79ca131a3ed16e36abb3886%3BunionTrace%3Aa131151917123227880545248e%3BoriginPrice%3A35100%3BvoucherPrice%3A35100%3BdisplayPrice%3A35100%3BsinglePromotionId%3A900000024406447%3BsingleToolCode%3ApromPrice%3BvoucherPricePlugin%3A1%3BbuyerId%3A0%3Btimestamp%3A1712322788400&ratingscore=4.956521739130435&request_id=ff7228f7b79ca131a3ed16e36abb3886&review=115&sale=212&search=1&source=search&spm=a2o4l.searchlist.list.2&stock=1
Step 1: Sketching and Ideation
This step is for you to plan out the theoretical output of your powerbank.
You want to think about your theoretical discharge and charge rates to plan out the correct components to get.
For example, my plan was to create a battery that can supply about 30-40 Watts. Realistically, the best batteries I can get provide a capacity of 1500 mAh with a 3.7 voltage rating. With this in mind, I can arrange the batteries with 2 in parallel, and have those be connected in 4 series to create a 4s2p battery, 4series2parallel. Essentially this will double the battery capacity and quadruple the voltage rating, so we will have 3000 mAh and 14.7 V.
If we follow Power = Voltage*Current (P = 14.7*3Ah), we would get an output power of 44.4 W, a little bit above the target power.
Aside from the theoretical aspect, you also need to draw the schematic of the circuit.
The powerbank I designed is made up of 3 main components: the battery pack, the Battery Management System (BMS), and the buck boost converter with a type C port.
Battery Pack:
- This is where all the power is stored
- Due to the fact I used 18650 Li-ion batteries, I needed to spot weld them all together
- This battery pack is arranged in 4s2p
Battery Management System (BMS)
- Because the battery pack in made up of 4 distinct battery cells, they may have a tendency to have different voltages from each other
- Charging and discharging the cells with different voltages will damage the cells due to over voltage.
- The BMS ensures that all the battery cells charges and discharges with the same voltage throughout the battery pack
IP2368 buck boost type C interface
- This component is a bit unique compared to the typical buck boost converter
- For one it has a USB-C built in already
- It allows for charging and discharging to take place in the same port
- It even has LED displays to show how much power it still has (25%, 50%, 75%, 100%)
You should create a circuit diagram showing how the different components connect to each other in order to keep track of which wire goes where, and how to prevent a short circuit.
You are working with batteries so you should be extra careful.
Step 2: Spot Welding the Battery Pack
If you are a beginner at spot welding, I suggest you get supervision from an expert.
Batteries are explosive.
Applying a lot of heat and pressure on a battery will make it explode.
So the idea of spot welding sounds like a one way ticket to going boom boom right?
While the idea of spot welding batteries sounds dangerous (it is if done incorrectly), with the proper precautions, spot welding is a simple and safer way of connecting batteries to each other as opposed to soldering them. It produces a quick burst of heat welding your nickel strips onto the batteries. And while there are sparks, they are mostly harmless and they barely heat up the battery at all. For any questions about the necessary output of the spot welder, I suggest you consult an expert or the instructional manual of your welder.
The plan is to connect the batteries according to the schematic: 4s2p.
You need to connect the batteries with two in parallel and four in series. You can start connecting them in either way, but I recommend you start with connecting them in series, since connecting them in parallel increases its capacity(current), and if any accident like short circuits were to occur, would be more severe (boom boom).
To connect the batteries in series,
- you want to connect them by positive to negative; connecting them by the same magnetic pole will create a parallel connection.
- Make sure to NEVER loop these batteries to themselves. You will short the circuit and damage the batteries.
- Create two of these 4 battery series connections, you will be connecting them next in parallel.
- For the parallel connection, make sure you line up the 2 series connections side by side; they should be facing the same side.
- Connect the cells in a 2x4 position, connect the cells positive to positive, negative to negative.
Once you connect the batteries all together, you should have a functioning battery pack.
To measure if the battery is assembled correctly, check the values of each cell.
To do this:
- Attach the negative probe of the multimeter to the negative side of the entire battery pack
- Using the positive probe, measure the voltage reading of each cell in series; starting from the battery closest to the negative probe, all the way until the last battery
- The readings should be close to: 4.2V, 8.4V, 12.6V, and 16.8V respectively.
- If any of the values are relatively the same as the ones above, you should be able to go to the next step
Step 3: Connecting the BMS
For this step, you will be attaching the BMS onto the battery pack.
This will require a soldering iron and solder to connect your wires to the battery pack.
General conventions ask that you use brighter color wires that carry positive voltage, while darker color ones go to ground.
Before starting it should noted that to prevent the soldering iron from heating up the batteries, you can spot weld a thin sheet of nickel strip going outwards from the battery pack. That way, you can solder your wires there without fear of your battery heating up.
To start connecting the BMS:
- Prepare the negative and positive part of your battery pack
- Apply solder onto the nickel strip for each respective part
- Apply solder to respective wires
- Solder the live wire to the positive end of BMS
- Solder ground wire to negative end of BMS
Now your BMS should be a part of the battery; this means it is live and can short circuit if not careful.
To test if it is live, check it with the multimeter; you should get around 16.8V or close.
Once you are sure it is connected, we can move on to connecting the BMS to each individual cell. To do this, you need to solder your wires onto the links between each series. So in total, you need to solder 3 links for the 4 series connection.
Just repeat the same process as before but you need to connect them to their corresponding voltage reading: 4.2V, 8.4V, and 12.6V. You can double check by using the multimeter.
Step 4: Connect to the Port Module
Now that the BMS is hooked up to the battery pack, we can now connect them to the Buck Boost USB-C port module.
The exact port I got was one that had an IP2368 built in within it. What this exactly does is it allows you to charge and discharge from the same USB-C port. It was also designed for 100W, but due to availability of batteries, I had to settle for less.
To attach this to the BMS, you must simply solder wires from the BMS output to the module; Positive-Positive, Negative-Negative.
Due to the amount of power being transferred, you may require thicker wires compared to the ones used for the BMS. You can achieve that by soldering 3 wires together.
Once you finish soldering, test if it is working by using the multimeter.
You should get an output of around 16.8V.
Step 5: Insulation and Protection
In this step we protect the battery from outside harm.
Normally you should first use some kapton tape to protect the electronics, but due to budget reasons I didn't use any.
What I did first though was attach the BMS to the battery pack. This was due to the BMS having many connections to the battery, as such is very susceptible to short circuiting. What I did was use a layer of foam to separate the battery pack from the BMS before gluing them all together.
Once they were attached, I then used electrical tape and wrapped it allover the battery pack. I made sure to not let any gaps show and wrapped the entire thing about 2 layers. By the end of it, all thats exposed is the type-c module and the wires that connects to the BMS.
Ideally, you would want to get rubber insulation and vacuum seal the battery pack, but that was outside of budget.
Step 6: Discussion
The battery pack is capable of charging phones and laptops with a USB-C port.
The design that was made has many rooms for improvement:
- The batteries used had a capacity of 1500 mAh, initially I wanted to use 3000 mAh for a higher capacity but finding legitimate batteries are really hard. I recommend you find a good and trusted supplier before anything else
- The battery could use more protection like the kapton tape or the rubber insulation.
- A case with a hole for the port could add a hard layer of protection against outside forces and increase durability.
- The case can be either 3D printed or can be made up of acrylic to see the remaining power in the battery
- Other battery types can be experimented with to hold more capacity, produce a higher output, make the design more compact, other safety reasons.
For what its worth, the design fulfills what it needs to do, albeit with the need of improvement.
