I picked up a battery meter to test some batteries I purchased as well as some that I'm planning to repurpose.
My initial reason for purchasing was to determine if the capacity of the batteries that I'm purchasing and shipping on a slow boat from China (3 months!!!) to know if the capacity of the batteries match the labeled capacity. This is important in order to understand what the battery pack will be rated in terms of amp hours.
Update: Looks like that battery shipment disappeared and I will have to dispute the charges on that purchase. My 2nd shipping problem from AliExpress will more than likely make me avoid using them forever. The issue I have is not the frequency of failures (already high at 25%) but the length of time I need to wait before the shipment failure is confirmed (up to 3 months)
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| My type c battery meter with 3d printed cover |
The other thing my attention deficit addled mind decided would be a great idea is to reclaim old laptop batteries to make flashlight upgrades and maybe portable charger projects.
I want to be able to check which batteries are still good and also mark them so that the batteries with similar ratings can be paired together. I'll probably need to recycle anything with a marginal rating or worse .
Battery pack building
I thought I would throw this chart I found on the net for future reference. I'm going to need this to rate reclaimed batteries for some future rechargeable projects and also because some people choose to use reclaimed batteries for a cheap eBike project. I haven't been able to find enough batteries to consider this option.
Milli-Ohm | Battery Voltage | Ranking |
75-150mOhm | 3.6V | Excellent |
150-250mOhm | 3.6V | Good |
250-350mOhm | 3.6V | Marginal |
350-500mOhm | 3.6V | Poor |
Above 500mOhm | 3.6V | Fail |
Ordering batteries
After a nearly 3 month wait for batteries from AliExpress, the batteries simply disappeared from tracking. I got my refund from them shortly after I ordered batteries from bulkbattery.com and received my order within 3 days. It's so refreshing to not need to wait 3 months only to be disappointed. The other advantage of using this battery wholesaler is I can be assured that the batteries I ordered are going to be close to the rated capacity ( I measured 2 at 2200mah vs the stated 2500mah capacity). I needed 40 but I ordered 42 just in case.
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| 18650 2500mah tested at 2200mah |
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Battery Cell Specifications
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Parallel Connections done with tabs for BMS
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- Voltage: 36v
- Current Storage: 176amps
- Capacity: 9ah (.32 kWh)
- 720Watts at 20amps.
- 19-25 miles of range on light assist (18-23 miles throttle only)
Designing an enclosure
I spent many hours thinking about how I would install my battery pack on the bike with an eye toward compactness (fewer batteries) and lower center of gravity (mounting as low as possible). The current design trend of factory eBikes is to hide the battery inside the frame but since I don't have that ability with an old bike, I tried to make a box that would be semi-permanently mounted since I don't have a way to build a hot swappable battery.
There's lots of makers building enclosures with wood or velcro bags but my goal was to try incorporating my other hobby of 3d printing into this project multiplying the fun factor.
I decided to use a single charge/discharge port so the bike would need to be near an outlet for charging purposes. I'll need to disconnect the power to the bike in order to plug in the charger.
I had plan on using XT60, GX16 connectors and 12AWG wiring to complete the pack but the GX16 connector can realistically only be used for charging and not discharging through the controller so I'm passing an xt60 connector through that hole and see later if I need to add a switch.
I'm using .15x6mm Nickle strips for the parallel connections and .15x8mm strips for the series connections as well as the terminal (positive and negative) connections which was a fortunate mistake since I didn't order enough Nickle strips on my first order (ordered 6mm strips from AliExpress before I did enough research).
I also added a 20amp inline automotive fuse in case anything happened for safety reasons.
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| Controller Mount |
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| Battery and Top Cover |
First charge for this pack was out on the back porch in case it catches fire or something due to a mistake during the build-out.
Fully charged from 35.4v to 42v in about 3 hours.
I should have mocked the designs against the bike because the finished box appears to be unpleasingly tall with respect to the size of the bike. I might have saved my self some work if I had printed a mock up and attached it to the bike to see how it would look. Going back to the drawing board means I'll need to eventually disassemble this battery pack for the new configuration.
After mulling several other designs, I may just purchase a battery case to get the removable functionality along with a switch and perhaps a battery meter. I purchased and cancelled an aluminum case popularly named "silverfish" before I determined that I wouldn't be able to slide that battery on and off my bike due to the way the mounting track requires a long runway to insert the track.
Part of me wants to rebuild the pack as 48v and the other part just wants to leave it alone. I guess I'll see how it goes after I upgrade the controller to allow me to drive the motor at a higher wattage by sending more amps.
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