New battery from old laptops
28 Oct 2015
I'm building a new battery pack for the go-kart using old laptop batteries.
Attach:go-kart-pack01.jpg Δ I've got 168 18650 Li-Ion cells (84 pairs) averaging 1789 mAh capacity each, ready to solder together. It'll be wired into groups of 24 cells in parallel, then 7 groups in series for a nominal voltage of 25.2 v and over 1 kWh total capacity. (Here's my Thingiverse page for the 3D printed battery holders.)
29 Oct 2015 BMS
I'm testing:
- http://www.aliexpress.com/item/7-cells-20A-balancing-Li-ion-Lithium-18650-Battery-In-Out-BMS-Protection-Board/32389617021.html
- http://www.aliexpress.com/item/24V-30A-60A-7S-BMS-PCM-PCB-24V-Lithium-battery-BMS-for-7S-3-7V-lithium/32472276216.html
- http://www.aliexpress.com/item/24V-30A-7S-BMS-PCM-PCB-24V-Lithium-battery-BMS-for-7S-3-7V-lithium-cell/32469245428.html
Also looking at:
- http://www.aliexpress.com/item/7s-BMS-12v-lithium-battery-BMS-12v-7s-PCM-for-electric-bike-lithium-battery12v-50a-battery/32317936268.html
- http://www.aliexpress.com/item/7S-29-4V-or-24V-truck-jump-starter-lithium-battery-BMS-and-PCB-with-800A-Max/32293712042.html?spm=2114.10010108.1000014.14.uvZhZv
- http://www.aliexpress.com/item/7Strings-of-29-4V-or-24V-lithium-battery-BMS-and-PCB-with-100A-Constant-discharge-current/32467901606.html
29 Oct 2015
Attach:go-kart-pack02.jpg Δ Here it is all soldered up with power and balance leads. I've got it plugged in to my iCharger to balance charge the whole pack at 2 Amps - which is nice and slow for it's first time charge. It might take a couple of days to finish. I (or more likely my son) should be able to take it for a good test drive in the go-kart this weekend.
I've got a 30 Amp BMS (Battery Management System) board on order.
31 Oct 2015
Attach:go-kart-pack03.jpg Δ Here's the battery pack bungeed on to the back of the go-kart. Adam is ready for the first test run. Initial testing seems promising. More testing once I've added the BMS.
Battery:
- 168 x 18650 cells (as 84 pairs)
- weighs 7.6 kg
7 Nov 2015
Testing with a Wattmeter:
- 35 Amps peak
- 914 Watts peak
- after 3 test sessions with kids the voltage is still over 27 v and has not sagged below 27.03 v.
Looking good for a full day of use at the upcoming school fair.
5 Dec 2015
I took the go-kart to the Randwick School Fair this morning and sold "$1 for 2 minute" rides. It was going constantly from 9am to a little after 12 noon. I raised about $60. The kids love the surge of acceleration and the adults appreciate the low running speed.
It ran well all morning.
Battery power data:
- Started at 28.65 V (fully charged)
- Ended at 25.87 V
- 26.922 Ah
- Roughly 726 Wh (calculated from 26.922 Ah * 27 V)
- 38.34 A peak (which is about 1.5 C, assuming 1 Amp per cell)
- 25.85 V minimum
- 962.2 W peak
Attach:60vdc-power-analyser.jpg Δ I use one of these to gather this data: Digital 60V 100A Battery Balance LCD Voltage Power Analyzer Watt Meter
The individual cells ended at; 3.66 V, 3.66 V, 3.66 V, 3.73 V, 3.76 V, 3.68 V, 2.71 V, total 25.9 V according to my cheap cell monitor. I'm now recharging it and we'll see how many Ahr go into it.
Attach:1S-8S-Lithium-Battery-Buzzer-Alarm.jpg Δ And I use one of these to monitor the battery whilst it doesn't have a real BMS: 1-8S Lipo Battery Tester Low Voltage Meter
6 Dec 2015
Recharged with iCharger at 3A in balance mode.
- 29.178 Ah
- 13 hours 49 minutes to fully charge
- Roughly 800 Wh (calculated from 29.178 Ah * 28 V)
12 Dec 2015
Ran the go-kart at the Moera Christmas Party for 2 hours of free rides.
- 10.573 Ah
- 267.3 Wh
- 37.75 A peak
- 25.62 V minimum
- 984.8 W peak.
- 27.18 V at finish.
27 Dec 2015 Dell PC enclosure
I've packaged the battery inside a small Dell Optiplex GX520 desktop box. It's just the right size for the batteries plus BMS. I stucking on a 40Amp breaker switch too.
Attach:1kW-18650-battery-inside-computer-box.jpg Δ
This makes it a much more robust battery. It also means if I build several of these batteries I can stack them reasonably neatly.
Attach:1kW-18650-battery-computer-box.jpg Δ
I'm not sure yet how best to attach the breaker switch.
The small screen on the top is a 4 way temperature sensor. I'm keeping an eye on the battery temp to look for variations. It all seems fine so far.
The battery and case weigh 9.4 kg
2 Feb 2016 Nice blue heat-shrink
I bought some giant 360mm wide heat-shrink to encapsulate the batteries in. http://www.aliexpress.com/item/1m-long-355mm-width-0-15mm-thick-blue-PVC-heat-shrinkable-tube-packaging-film-HM-battery/1971473370.html
This is useful to keep thinks from shorting the cells. I've left the ends open to retain some airflow.
Attach:P1080092-small.jpg Δ I got a 2 meter roll.
Attach:P1080095-small.jpg Δ I made the usual beginners mistake of overheating the think heat-shrink with my heat gun.
Attach:P1080096-small.jpg Δ This heat shrink is only 0.15 mm thick so it's very easy to over heat.
Attach:P1080098-small.jpg Δ I added a seond later over half the pack to cover the hole.
Attach:P1080099-small.jpg Δ All packed away and looking a bit less messy.
I'm think about using this stuff for my 2 kWh Laptop Powerwall project.