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06-28-2014, 04:07 PM
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#1
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Platinum Member
Join Date: Dec 2010
Posts: 2,058
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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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06-28-2014, 05:10 PM
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#2
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Platinum Member
Join Date: Aug 2007
Location: Minnesota
Posts: 5,967
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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
__________________
Davydd
2021 Advanced RV 144 custom Sprinter
2015 Advanced RV Extended body Sprinter
2011 Great West Van Legend Sprinter
2005 Pleasure-way Plateau TS Sprinter
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11-20-2017, 08:34 PM
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#3
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Platinum Member
Join Date: Aug 2016
Location: Northern VA, USA
Posts: 197
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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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11-20-2017, 08:39 PM
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#4
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Platinum Member
Join Date: Oct 2006
Location: New Brunswick, Canada
Posts: 8,828
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Explain the "couldn't handle" it part. Any breakers trip etc.?
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11-20-2017, 09:31 PM
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#5
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Platinum Member
Join Date: Aug 2010
Location: Minnesota
Posts: 12,456
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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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11-20-2017, 10:06 PM
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#6
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Platinum Member
Join Date: Aug 2016
Location: Northern VA, USA
Posts: 197
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Quote:
Originally Posted by markopolo
Explain the "couldn't handle" it part. Any breakers trip etc.?
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The inverter sounded an alarm that would not quit until I shut the fridge off.
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11-20-2017, 10:46 PM
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#7
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Platinum Member
Join Date: Oct 2017
Location: Ontario
Posts: 449
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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.
Brian
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11-21-2017, 12:12 AM
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#8
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Platinum Member
Join Date: May 2016
Location: LA
Posts: 1,551
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Quote:
Originally Posted by ManWonder
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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Plugged into shore power? Running the van's engine?
Bud
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11-21-2017, 03:24 PM
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#9
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Platinum Member
Join Date: Aug 2016
Location: Northern VA, USA
Posts: 197
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Quote:
Originally Posted by booster
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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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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11-22-2017, 03:03 PM
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#10
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Platinum Member
Join Date: Jul 2014
Location: Garland, Texas
Posts: 238
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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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11-22-2017, 03:34 PM
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#11
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Platinum Member
Join Date: Aug 2010
Location: Minnesota
Posts: 12,456
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Quote:
Originally Posted by gklugie
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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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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