#10 wire is cheap...
Just log the voltage drop and battery voltage for an hour or two and you can
extrapolate the Ah.
You can also use a spool of wire in a buck of water as a load. 500 feet of #10
is a half ohm. That will give you 24 amps of load on 12 volts and will also
serve to tell you the current too.
From: Adam Moffett
Sent: Thursday, January 25, 2018 9:49 AM
To: af@afmug.com
Subject: Re: [AFMUG] Watts and VA on DC vs AC
I'll have to get a better meter.
In the mean time I guess I can't say how many Ah I really get out of the
battery, but I can see how far it depletes in a certain amount of time and say
it's between x and y Ah. That should be sufficient for today.
------ Original Message ------
From: "George Skorup" <george.sko...@cbcast.com>
To: af@afmug.com
Sent: 1/25/2018 11:45:24 AM
Subject: Re: [AFMUG] Watts and VA on DC vs AC
Yeah. I guessed about 33 amps based on 13 volts. Could rise quite a bit as
the battery drains, and I'd expect the inverter efficiency to drop as the
battery voltage decreases.
I like having my handy Craftsman AC/DC clamp-on ammeter to verify my poor
attempts at math.
On 1/25/2018 10:12 AM, ch...@wbmfg.com wrote:
Your inverter is probably 90% efficient if you are lucky.
355 watts / .9 = perhaps 433 watts input
433/12 =37 amps input at 12 volts
So, yeah, your guess between 30 and 60 amps is pretty accurate.
You can also insert 1 foot of #10 wire in series with the 12 volt line.
Measure the voltage from one end of the wire to the other.
Millivolts = amps.
You should have about 37 milliamps volt drop across that wire.
From: Adam Moffett
Sent: Thursday, January 25, 2018 8:49 AM
To: af@afmug.com
Subject: [AFMUG] Watts and VA on DC vs AC
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.
