I tried to run a couple of Taco 005 circulator pumps from a 12 VDC battery and an inverter and couldn't do it - the pumps hummed or buzzed or something but never seemed to run as smoothly as they do when plugged into the house's AC system. The pumps are 1/25th HP with a .5 amp rating and I would have thought that they'd run fine on the inverter. I tried two different invertors, both of which work fine otherwise and also tried running one pump at a time. The invertors are rated at 400 and 700 watts.
What's going wrong and how can I fix it? The objective is to be able to run the pumps from lead-acid batteries.