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Old 08-13-2011, 01:19 PM   #11
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Old 08-13-2011, 03:34 PM   #12
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You are all wrong. An amp makes my music louder!!!

Seriously though, amperes, which is current is the flow of electrons. You have to install the ammeter in line ( in the circuit) to measure the draw. Motor start up current (in rush current)is typically 1.5 to 1.7 time full load amps. You can use a clamp on meter but they are expensive. Resistive loads (heaters, lights) do not have start up currents.

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Old 08-14-2011, 01:15 PM   #13
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Good point, and I should have noted that "NOT ALL" meters function at high current loads, however, many do.

AC amps can be measured via inductive meters, but like the aforementioned, one should be cautious on just what instrument we use, and we should always observe proper safety precautions.

Nevertheless, many high and low-end DC meters, both analog and digital, can measure up to 10 amps. Fluke - can be a high end, Micronta (from Radio Shack) low end, and others may require one to change the input leads, yet still others can measure the load differently.

As mentioned, an approximate load calculation given from the standpoint of the manufacturer will help determining the exact load-- if that's important. But, simple light bulbs and most products are less than 10 amps, suggested by the wire size. When in doubt, ask.

In the lead connections (not all-- so be ware), the curious will remove the hot lead, then connects the two meter leads, one to the lead just removed and the other to the lug where he/she just removed the wire. Some meters, by the way, are polarity conscious so be careful to read the manual before connecting, else---.

What may not be obvious is this warning: ONE should NOT connect the entire RV to the meter without observing the statement about approximate load calculations, and following simple safety precautions. Turning the entire RV on at once may fry your meter, or at least blow the overload prevention mechanism in your meter, cause a fire, or hurt oneself.

Therefore, calculate each item independently-- and for the total add them all together.

Also, as in a car, house, boat, etc, be sure to disconnect the AC current bush and RV battery before fussing with wiring. If you are wiring something, determine the proper wire gauge based on the following: wire length means from the source to the product AND back, and that heat (southern climate) forces larger wire sizes and lugs. Your product will give you an apprximation on it's requirements in amps or watts.

While I'm at it, Romex is not DC wire, and visa-versa, and proper fused links MUST be installed at the battery side. See codes for the maximum distance from the battery or buss bar.

Finally, several books are available to help one understand RV life to the fullest. One notable title, "Living off 12 Volts," comes to mind. I don't remember the others. But, after living aboard our boat for many years while traveling the Pacific Ocean, knowing what works and what doesn't made our adventure enjoyable.

Hope this helps,

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Old 08-16-2011, 06:45 PM   #14
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Old 08-16-2011, 09:28 PM   #15
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All that being said, this is good information that I'm getting a real "charge" out of!!!!
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Old 08-16-2011, 09:38 PM   #16
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I guess this is as good a place as any to ask the question- has anybody ever seen an in-line meter that shows how many watts a 12 volt appliance is drawing?

I know they make them for 120 volt AC:
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Old 08-16-2011, 09:54 PM   #17
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A quick search on the WWW with the conditions "inline dc amp meter" resulted in several alternatives. You might check the listings.

If you are inclined, you could use a panel meter and appropriate shunts. Panel meters are readily available and one may serve your purpose. But, I tend to measure the actual items and do the simple arithmetic. My sea-going experience taught me that more connections make more headaches with potential outages, no matter the attachment.

Good luck,

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Old 08-17-2011, 07:12 AM   #18
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The voltage drop is caused because the the battery has a small internal resistance.

This resistance value is not constant, it can change with many factors (battery charge state, temperature, etc).

So to answer your original question...No you cannot determine the amp draw by the voltage drop.

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Old 08-17-2011, 07:37 AM   #19
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Something I stole

One night, when his charge was pretty high, Micro-Farad
decided to seek out a cute coil to let him discharge. He
picked up Milli-Amp and took her for a ride on his Megacycle.
They rode across the Wheatstone Bridge, around the Sine Waves,
and stopped in the Magnetic Field by a flowing current.
Micro-Farad, attracted by Milli-Amp's characteristic curves,
soon had her fully charged and excited her resistance to a
minimum. He laid her on the ground potential, raised her
frequency, and lowered her reluctance. He pulled out his
high voltage probe and inserted it in her socket, connecting
them in parallel and began short circuiting her resistance
shunt. Fully excited, Milli-Amp mumbled "OHM-OHM-OHM". With
his tube operating at maximum and her field vibrating with
his current flow, her shunt overheated, and Micro-Farad was
rapidly discharged and drained of every electron. They fluxed
all night trying various connections and sockets until his
magnet had a soft core and had lost all it's field strength.
Afterwards, Milli-Amp tried self-induction and damaged her
solenoids. And with his battery fully discharged, Micro-Farad
was unable to excite his field, so they spent the rest of the
night reversing polarity and blowing each other's fuses.
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Old 08-17-2011, 09:03 AM   #20
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Half the posts here should be moved to the "Jokes" forum.

Maybe when I get a "Round Tuit"


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