The paralleled “16650” cells from the last post – were did they come from in the first place?
Our old laptop computer, an MSI MS-1013 Blue Media, had worn out it’s pack, so I built the supply with linear voltage regulators. But only after ordering a used pack from eBay. And that didn’t work, so the vendor sent another one. And that didn’t work either.
It seems that the at least one of the ICs inside gets unusable as soon as the supply voltage falls below a certain threshold.
Safety blah blah: the energy stored in the laptop battery pack is about the same amount as in a common hand grenade. The protective circuit below is not an option. The pack I built for the RC car further down uses a polymeric positive temperature coefficient device (polyfuse, PPTC – the yellow disc) to limit current through the pack, should somebody be stupid enough to short the poles with tools (you can’t do this by accident as the terminals of the connector are shrouded). The alligator clips below are only used while the cells lie in a flower pot.
The cells would not all be dead, so I soldered the suitable „cell voltage“ and „voltage limit“ resistors to alligator clips to get a suitable charging cable for my CCS 9620 EV3 charger and juiced them up pair by pair.
I used an ELV HET-20 „Hochstrom Entlade-Testgerät“ / „Akku-Einzelzellen-Tester“ (more pictures, some additional german info and the manual -Bau und Bedienungsanleitung- here) to count ampere hours while discharging the cells. Some of them were indeed unusable. But a lot of them were fine.
…useful if your son has just discovered his uncle’s old RC monster truck. 😉
The kid was too young to handle it properly, the toy itself nothing proper (can’t even steer as long as the drive motor is idle) and investing any money would have been a waste – but I had the parts, so I could make an alternate power pack. Just like the iFixit Self-Repair Manifesto wants things to be.
As the batteries don’t like heat the contact strips are normally spot welded. I have no spot welder. A powerful soldering iron and maximum temperature to minimize soldering time (along with plenty of flux) did the job for me. Without any explosions.
Excellent: My son could practice with a toy we would not have bought, repaired with parts we did not throw away instead of throwing everything away alltogether!
And I also could potentially use every cell with a boost converter to charge my phone (that was before powerbanks became common – and it still works, naturally).
Nevertheless: having survived for decades did not mean that this Nikko Silencer was robust. Soon a broken gear lever meant the two speed gearbox was not meshing the tooth anymore – I had to lock then in „low“ gear.
And to avoid gramps (or anybody else) putting the thing into the cellar without switching off the receiver I even made a quick & dirty upgrade…
(Summarized from http://www.metalforum-owl.de/viewtopic.php?f=21&t=138&start=100#p39862, July 17th 2011 and http://www.metalforum-owl.de/viewtopic.php?f=21&t=138&start=180#p49566), September 25th 2012)