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Maybe. For a PMOS, you ground the gate to turn it on. There should be a resistor connected to battery positive and the MOSFET source pin. The detector acts like a switch that either allows the connection to ground when voltage is above the threshold or opens the connection to disallow the connection to ground when battery voltage is below the threshold. Here's a schematic, might have already posted it in this thread but here it is again anyway;
I get the feeling people don't believe me when I say how delicate MOSFETs are. It's the gate pin that's the culprit. The insulation between the gate junction and the source-drain channel is literally only molecules thick. It's very easy to damage with any voltage above the absolute maximum even for a nanosecond. Just walking around, a person typically carries around 20V or 30V of static charge on them. Not enough to make a static spark, but enough to fry a MOSFET. A ground strap is required when working with them. Optionally, protected ones are available that have built-in TVS diodes and are safe to handle without any ESD grounding. However, the unprotected ones are much more common.In terms of heat tolerance, they're pretty robust. For test circuits, I've resoldered them several times without failure. Of course, if you're using a soldering pencil that does not have a regulated temperature, all bets are off. You can overheat one on the first solder job with one of those.
That ~is~ weird. Normally flux is not conductive at all, a little capacitive maybe. If it is conductive, that's not the right stuff.The main reason you need to clean the flux off is the standard activated stuff is somewhat corrosive. Though you can get "no clean" fluxes that are non-corrosive and don't have to be cleaned off, but they don't work as well. You can get water soluble flux that can be cleaned off with water, but nothing works as good as regular activated or mildly activiated rosin flux.