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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

I'm testing:

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.

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

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.

  • 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 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.




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Page last modified on 10 March 2016 at 12:47 PM