I'm not entirely sure if this is the best place to put this, but I'm having an issue with a mega-battery I'm working on.
The battery is two AGM 12v batteries in parallel, with an inverter stepping up the voltage to 120VAC. However, I only measure 90V on the output.
When I connect the battery to a fan, the fan buzzes loudly, and does not spin quite as fast as usual. I measured the voltage as 90V, while the mains in my house is 240V, with split-phase power so 120V at each outlet.
Sound difference: From outlet: https://drive.google.com/file/d/1Nxzmv7j3tZUn3u-P-dO2HALBsROkLexd/view?usp=sharing The sound is the normal slight hum on startup and low wooshing noise from the fan.
From battery: https://drive.google.com/file/d/14qAOo2tkDCe9d_dRLISRUL3OLf2PiKGT/view?usp=sharing The sound is a loud buzzing sound with the fan turning on much slower.
The fan is just a normal fan, no heating done.
The batteries are good. 13.2V no load, drops to 12.9V under load. They are just a few months old.
The inverter is one I found in the garage, Vector VEC024. The wiring is 12 ga, capable of handling up to 20A through it. Inverter is rated for 400W. The fan is a Lasko U15617.
What's going on here? Why is the inverter putting out less power than it should? How can I fix it?