Inverter Question

So I purchased an inverter was 400 watt and the lil heater i bought was 400watt and itll start but then the inverter will poop out, I have the inverter connected to DC 120v outlet (cig lighter). What gives? If I have this correctly the cig lighter can only output around 100w-200w cus its connected to the cig lighter as opposed to the actual battery where I can get the full 400w with battery connections to the terminals? Thx for the help. If this inverter experiment doesnt work then I think its better to just buy a generator imo.

 

Short version- yes, you're trying to pull more than the cigarette lighter can supply.
If you add a new connection to your battery (PROTECT WITH A FUSE OR BREAKER) you should be able to pull the rated 400 watts until your battery runs down. This is still somewhat risky because you are pulling the inverter's rated max as a constant load (inverter will get hot and may shut down after a time) and have no battery protection (likely 1-2 hours before your battery is dead), but should work. You'll need 4-8 ga cable depending on your inverter placement. If you need this for more than defrosting your windows, I'd use that generator or get a fuel based heater.

Long version with math.
Let's talk amps. Power is measured in watts, or amps x volts. Volts are how likely something is to short circuit or arc, amps are how likely something is to overheat/melt wires.
Your inverter is pulling ~37 amps at full draw (400W x 1.1 (efficiency loss) /12v = 36.67 A)
The cigarette lighter circuit is only good for 10-20 amps. You're overloading the circuit and it's shutting down before it melts. To fix this, you need a circuit capable of supplying more power.
Blue Sea has a great chart for sizing wiring, take a look at the chart and the article. https://www.bluesea.com/resources/1437
If you undersize the wiring it heats up and pulls more current, if you undersize it too much it melts and the magic smoke escapes.
So you'll want to run 4-8 ga wire for your heater circuit. That'll handle the 37 A draw and, as long as the truck's running, your alternator should put that back.
If the truck's not running, those 37 A have to come from the battery. Not sure what you have installed, but if you're stock it should be in the 45-80 amp hour range. Best case scenario truck gets 2 hours of heater time before the battery is dead.
Without knowing your precise use case, you're likely better with a generator or fuel-based heater.

 

aint sain dont do it

37 amps is a lot o draw........ alot

inverters are not magic

they can overheat..................they can start fires

DC voltage fires are insanely quick

 

It's responses like these that make TW great. Nothing to add to original question I think it's been answered just want to give everybody a shout out for helping this guy. And OP I hope you have it figured out.