Go-kart Battery Upgrade
New battery from old laptops
28 Oct 2015
I'm building a new battery pack for the go-kart using old laptop batteries.
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
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
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.
7 Nov 2015
Testing with a Wattmeter:
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:
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.
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.
12 Dec 2015
Ran the go-kart at the Moera Christmas Party for 2 hours of free rides.
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 got a 2 meter roll.
I made the usual beginners mistake of overheating the think heat-shrink with my heat gun.
This heat shrink is only 0.15 mm thick so it's very easy to over heat.
I added a seond later over half the pack to cover the hole.
All packed away and looking a bit less messy.
I'm think about using this stuff for my 2 kWh Laptop Powerwall project.