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Old 06-28-2014, 04:07 PM   #1
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Default amp calculator

I ran across this calculator and dc amps to Ac i could never really understand. after studying this and playing with figure entries i finally really understand how dc batteries get drawn down with AC devices-this shows what happens with inverters






http://www.batterystuff.com/kb/tools/ac ... erter.html
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Old 06-28-2014, 05:10 PM   #2
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Default Re: amp calculator

This website has been a good source for grasping RV electrical as it is written for the novice. It explains amps, volts and watts and conversions between AC and DC and how to calculate. It also has some bubble diagram charts of how various systems are put together in RVs. It also has some clickable references to other sites.

RV Electrical Systems
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Old 11-20-2017, 08:34 PM   #3
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here's what i don't get... i plugged a small fridge rated at 1.3amps (115v) into my 700 watt inverter in my 2004 RT190P and the inverter couldn't handle it. Why not? 1.3 times 115 is less than 150 watts. So, what am I missing?
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Old 11-20-2017, 08:39 PM   #4
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Explain the "couldn't handle" it part. Any breakers trip etc.?
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Old 11-20-2017, 09:31 PM   #5
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That could be a problem with the electronics in the frig not liking the modified sine wave out of your (probably) Tripplite inverter/charger, or the Tripplite kicking off because it didn't like the frig wiring. You might want to get a 500 watt pure sine wave inverter to try. Compressors take a lot of power to start, and depending on what the native power of the frig is, it may have sensitive to dirty power issues.
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Old 11-20-2017, 10:06 PM   #6
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Explain the "couldn't handle" it part. Any breakers trip etc.?
The inverter sounded an alarm that would not quit until I shut the fridge off.
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Old 11-20-2017, 10:46 PM   #7
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If it is a compressor fridge, they can draw a lot more than the "rated" current when the compressor starts up- maybe that could be the problem.

I have a couple of small freezers at home that I have converted to fridges for my beer home brewing hobby. I control them with an external thermostat. I measured the current and found that while they barely draw 2 amps when running, they can draw around 13 amps momentarily when the compressor starts up.

The contacts in my external thermostat were only rated for 10 amps - probably that would have been ok, but to be sure, I used a secondary relay in the circuit with 30 amp contacts.

In other words, the thermostat switches the secondary relay which in turn switches on the fridge/freezer.

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Old 11-21-2017, 12:12 AM   #8
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Quote:
Originally Posted by ManWonder View Post
here's what i don't get... i plugged a small fridge rated at 1.3amps (115v) into my 700 watt inverter in my 2004 RT190P and the inverter couldn't handle it. Why not? 1.3 times 115 is less than 150 watts. So, what am I missing?
Plugged into shore power? Running the van's engine?

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Old 11-21-2017, 03:24 PM   #9
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Quote:
Originally Posted by booster View Post
That could be a problem with the electronics in the frig not liking the modified sine wave out of your (probably) Tripplite inverter/charger, or the Tripplite kicking off because it didn't like the frig wiring. You might want to get a 500 watt pure sine wave inverter to try. Compressors take a lot of power to start, and depending on what the native power of the frig is, it may have sensitive to dirty power issues.
So, am a little embarrassed to admit but... I was wrong about my inverter being 700w - I checked the specs sheet and it it a 300w pure sine inverter that is installed in my rig. And the fridge having a compressor was clearly too much to for it to run. I think all it was meant to power was the TV and DVD player. So, I'm shopping for a new inverter.
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Old 11-22-2017, 03:03 PM   #10
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Glad you figured it out. Wingeezer is correct though. Appliances with compressors (refrigerators, freezers, etc.) draw a LOT more current on startup than they are rated for.
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Old 11-22-2017, 03:34 PM   #11
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Glad you figured it out. Wingeezer is correct though. Appliances with compressors (refrigerators, freezers, etc.) draw a LOT more current on startup than they are rated for.
Many of the inverter manufacturers will have a table with various appliance types listed, with the "allowance" you should figure in above their rated watts. Things like compressors can be 3-5 times on some of the charts. Modified sine wave models will also not deliver the full rated power some things like motors because of the wave form, so that can also be an issue
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