batteriesnimhsafetysoldering
I'd like to know if soldering two wires directly on a NiMh battery is considered as safe or not.
My fear is that battery would explode (right in my face) because of excessive heat caused by the soldering iron. Other possibility would be the battery slowly inflating and then spreading toxic fumes (or corrosive materials) trough a hole (like a capacitor under excessive voltage).
The battery I want to use is made of 10 units of 1.2V (thus generating 12V)
A 15-cell NiMH pack will give 18 volts fully charged, instead of 24 volts. The bike's electronics is likely to see the lower voltage as a heavily discharged battery pack and refuse to operate to protect the pack from damage. Even if not and the motor will run at the lower voltage, it will be drawing more current and it or the wiring may overheat. Without knowing details of the bike's electronics, I really cannot be sure. You can try it but you are risking damaging the bike.
I found this charger circuit :
And modified it so that it should be able to both charge the batteries in parallel and discharge them (minus diode voltage drop) back to the computer when power is disconnected. I would reccomend low-drop (Schotty) diodes to minimize loss. I hope this helps!
Best Answer
It's probably safe enough from your point of view, but not from the battery's. You really shouldn't solder to batteries unless they explicitly have solder tabs for that purpose. Most batteries, and NiMH are no exception, are damaged by soldering temperatures.
The way to make a permanent connection to a battery that doesn't have solder tabs is to use spot welding. This presses the battery terminal and the contact together, then zaps them by discharging a capacitor thru this connection. That heats the two parts enough for a little metal to melt and bond. However, the zap is very short and localized, so the total energy is low and high temperatures diffuse well before they get to sensitive parts of the battery.
Note that no solder is evident in the picture you show. That is because the tabs were spot welded, not soldered.