inverter question

assuming zero loss 1400W / 13.8 V = 101 AMPs. actual load will be more.

just my opinion now but i think you may headed down the wrong path. this is based on my owning an inverter with about the same ratings.

i use 2 parallel deep cycle batteries which in turn bridge the charging system. the 2 batteries alone can run a couple sound systems for a 2 hours before the voltage drops below the shut off threshold. i think that running the chainsaw it would only last a few minutes if the saw would start at all.

assuming you are going to the trouble is rigging this up so you can cut down trees for 8 hours at a time, i suspect you will find that at idle the alternator can not keep up with the demand and you will end up quickly discharging the battery. i also question the ability of the alternator to withstand the close to 100% duty cycle that this load would need.

To further this thought, what you describe is an automotive STARTING battery, the 750A is a Cold Cranking Amp (CCA) rating, meaning it will put out that much current for only 30 seconds, and is NOT designed to be drained all the way down lest it become damaged and unable to fully recharge ever again. What you need to look for is an Amp-Hour (AH) rating, which you most likely will not find on that battery. In the old days, that is how batteries were sold, and from experience I can tell you that battery is probably good for about 60AH max. That also means that at 60AH the voltage will begin to drop rapidly from 11.5V, which in the case of your chain saw, would INCREASE the current draw by the motor, which will INCREASE the voltage drop rate etc. etc. until the saw gets hot AND stops.

So if you look at Tim's calculation of 101Amps from your 60AH battery, you can run that saw for 60/101= .59 hours or roughly 36 minutes, before the battery would fail for you. The alternator would do little to stem that tide, and Tim was correct in expressing concern for continuous use. Most alternators can supply around 25A continuously,

You could spend a bunch of money for deep cycle batteries and a hefty generator like those found on tow trucks, but in the long run it's cheaper to just buy a gas powered saw.

'Wot they said.

But it does depend on how you are using it.

IME, the duty cycle of a 2HP-sized chain saw is pretty light. I use a small one like that more for cutting off branches than chopping down/up trees. So, it /might/ just work.

There are so many things against doing what you propose, though.

Would I run a chainsaw/inverter off the truck battery with the engine off? Only on a steep hill where I could bump start the thing if necessary.

Will the inverter supply the starting power? Quite possibly not.

Will this kill/damage the aged truck battery? Quite possibly.

Will this damage the alternator, if the engine is running? Quite possibly.

It goes on and on, not forgetting the risk that a falling branch will tangle with the power lead and pull the chainsaw in whatever direction it fancies...

And not forgetting that the motors in cheap electric chain saws are total crap - meant for light and very intermittent use. A petrol one will work all day, just needing the tank refilled every hour or so. Whereas you have to give electric ones more time resting and cooling than actual time in use..

I burnt out one and so fitted a capilliary thermometer on the next - 15 mins running (just on small branches) took the motor stator to 80 deg C. So I bought a petrol one and made a portable stand that holds it, so I can use both hands to pull-start it..