I've looked at DC-DC converters for 12v to 18v and they usually have low amperage ratings. One for $50 can use 15A with 25A spikes. But cordless tools can pull much more than that, especially the saws (I've read up to 70A). I want to run a cordless reciprocating saw off my car battery (clearing some thick trunk bushes) far from AC outlet, the portable batteries run out of juice fairly quickly (3-5 minutes operating and they are new NiCd).
Yes, can just use the 12v on cables from battery but not the same zip to saw and blades don't seem to get as much bite (not just slower). I'm unfamiliar with how many amps or current I can put through a resistor over time to split voltage to add additional 6 volts though the ones I see rated at 500w are for brakes and such are 10 inches long and cost $22 each. And I don't know if they are appropriate.
Looking to run the saw for ~2 minutes at a time, brief pause, 30 minutes altogether.
Adding a 6v battery (like golf cart or others) and mount them in my vehicle to tie into regular 12v when needed for tool. Guessing I'd need some rectifiers there but will the car over charge the 6v battery? And how do I go about all that?
Update: Ran it directly from car battery and wasn't good till I replaced wires with heavier gauge. Then acceptable. Power continued to diminish and I questioned whether doing this in 105°F weather affected it. Then I noticed some warm spots within the tool. I opened it and there are some fairly thin wires in there. Not much room to stuff wires (especially around the variable speed switch) but thinking up a plan to beef up the internal wiring and see if I can get much more solid performance at 12v.