Wikipedia:Reference desk/Archives/Science/2021 December 17

= December 17 =

Mobility scooter wiring
I've just replaced the batteries in my scooter's battery box and am somewhat puzzled by the wiring. There are two batteries in series to give 24V. Externally there is a three pin charging socket and underneath three main contacts for power delivery. Obviously Charging+ -> Battery+ -> main contact+ and likewise for the negative half of the circuit. The question though is what use is the third pin? It is connected directly from the charging socket to the third main contact, but to nothing else. It is not attached to the inter-battery connector as I might have guessed. Is this some sort of earthing connector? Martin of Sheffield (talk) 09:47, 17 December 2021 (UTC)
 * Standard interchangeable parts, where the inclusion of an unused earth wire is cheaper than producing two versions of the part, are a possible explanation for a wiring bridge to nowhere. I'm aware of the risk of getting you electrocuted if I'm wrong, so please regard this as only a tentative explanation. Card Zero  (talk) 15:14, 17 December 2021 (UTC)
 * 24Vdc is pretty safe! Martin of Sheffield (talk) 15:36, 17 December 2021 (UTC)
 * Oh good point, I was thinking of great big electric car batteries for some reason. I guess another reason why it might need earthing is in case the electronics on your console get fried. (That's enough guessing now.) Card Zero  (talk) 15:57, 17 December 2021 (UTC)
 * Odder yet: the cable from the manufacturer supplied charger is only two wire, pos and neg. There's no connection to the "bridge to nowhere"! Martin of Sheffield (talk) 16:08, 17 December 2021 (UTC)


 * I'm not familiar with the batteries or charger you're using, but one possibility is that it's for a thermistor. Some batteries have them built-in to monitor their temperature when they're connected to a high-load or a fast-charger. ApLundell (talk) 04:16, 18 December 2021 (UTC)
 * Yes, my presumption is it's some kind of status or data wire for monitoring charge level and/or other information. Hard to say for sure without knowing the scooter design. It probably uses lithium-ion batteries. Every li-ion battery has integrated electronics to manage the cells, because li-ion cells have finicky behavior, and are dangerous if overcharged, so they need a controller for safety. When used in electronic devices, the batteries often have a communications channel made available to allow the device to get information from the controller. --47.155.96.47 (talk) 02:13, 23 December 2021 (UTC)
 * It's not connected to the batteries though (which are lead-acid types). Nor yet is it connected to the charger.  It just connects the charger socket to a substantial main contact, nothing else.  That's why I was puzzled! Martin of Sheffield (talk) 09:16, 23 December 2021 (UTC)
 * Oh, whoops. I read "scooter" and thought of one of the "electric scooter" things that have become popular. "Two batteries in series to give 24V" tells you they're lead-acid if you know electrical stuff, but I just glided right over that. --47.155.96.47 (talk) 01:55, 24 December 2021 (UTC)