RMS only works on sine waves (in the general sense). From: George Skorup Sent: Thursday, January 25, 2018 9:20 AM To: [email protected] Subject: Re: [AFMUG] Watts and VA on DC vs AC
IIRC, VA = RMS current x RMS voltage. VA=Watts when you have a constant load like a lightbulb. Introduce things like switching power supplies and it's not so constant. I would just ignore the VA since you're interested in the current across the battery. A watt's a watt, but you do also have inverter inefficiency. Maybe 90% at best? Which I'm sure gets worse as the battery voltage drops. On 1/25/2018 9:49 AM, Adam Moffett wrote: I wanted to rig up a load test for some batteries. I don't have a substantial 12V DC load, so I set up a 1000W inverter, a short extension cord, a Kill-a-Watt meter, and a heat gun. With the heat gun on low, The kill-a-watt reads 110v, 606 VA, and 355W. The question is how much load is this putting on the battery? Somewhere between 30 and 60amp I guess, and either way my multimeter can't measure more than 10A DC current, so I can't measure it directly. My Googling on the topic has failed to enlighten me. My instinct is to think that Watts is Watts, so I should probably use 355W in my calculation of battery capacity, but I'm not sure.
