Mike Nickerson via EV wrote:
If the long term current draw will be less than 10A or so, you could use an in rush limiting resistor. That is a resistor with a negative temperature coefficient. When cool, they have a very high resistance. As they heat up, their resistance drops.
This is probably the opposite of the function Gary wants. Inrush limiters have a very LOW resistance initially, so the peak current when you first connect the batteries is very high. As the inrush limiter heats up, its resistance rises -- so you wind up with quite a limited amount of current between them.
Gary Krysztopik wrote:
Does anyone have any cheap tricks for regularly connecting two large 12 vdc packs together (one stationary and one mobile) and limiting inrush current when they are at different SOC? They both have huge current capability but I need it for energy vs power so one has small wires and fuses.
The "cheap trick" is to connect a light bulb between them. Pick the bulb so your normal current is well below what the bulb normally draws on 12v. For example, a #57 brake light draws about an amp, and a headlight about 4 amps, and a halogen spotlight around 10 amps.
The bulb won't allow more than its normal rated current to flow between the batteries. If you try, it just lights up. But when the current is less than this (such as while on standby), the bulb's resistance is LOW. The bulb is out, and the two batteries are essentially connected in parallel for float charging, etc.
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