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
Also looking at:
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
- 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.
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.
This makes it a much more robust battery. It also means if I build several of these batteries I can stack them reasonably neatly.
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.
I'm think about using this stuff for my 2 kWh Laptop Powerwall project.