Dave:
I checked with Canadian Tire's help line for this product, and found this question and answer:
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Problem: The alarm is always coming on. asked 7 months ago by Tula on MotoMaster 300W Mobile Power Outlet and Inverter
Answer:
If the alarm keeps on, that means the battery voltage is below 11V.
At first, we suggest you use this inverter on other vehicle or a fully charged healthy battery. If the alarms still on, please contact with the following support line at 18774668191 for further assistance.
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We had a 200 watt MotoMaster inverter which plugged into a 12 volt outlet in the trailer, but the alarm also came on when I thought the battery had enough power.
I have since replaced it with a GoPower 300 watt true sine wave inverter and have not had any problems.
http://www.flickr.com/photos/27335095@N08/8530157914
The purpose of the low voltage alarm is to prevent running down the battery. It would be a good idea to check the line voltage at the 12 volt outlet when you are running the inverter to see if the voltage really is low.
It is possible the culprit is the voltage drop in the supply to your 12 volt outlet. Do you have the same problems if you connect directly to the battery?