Originally Posted by elind
When your figuring power usage the formula is: volts X amps = watts. So if you have 120v X 30a =3600watts, or 12v X 300a = 3600 watts. Watts is like gallons of water that came out of the hose depending size & pressure. When you have a 30 amp service in your RV means your max is 3600 watts. So if your a converter is 50 amp that means 12v X 50a = 600 watts output and input is 120v X 5a = 600 watts. The higher voltage means lower amperages or lower voltage means higher amps. So a converter input amp could 5 amps AC and the output would be 50 amp DC when you comvert the voltage.
True, and considering no losses a 30 amp converter, charging at a full 30 amps, should draw 3 amps 120 VAC. Below is the response I received this morning from one of Parallax's engineers. He did a good job of answering my questions, actually better than I expected !
1. How many amps does the 110 VAC charger draw?
A little over ¼ amp at no load, and about 9-10 amps at full 55 ampere DC output depending on the line voltage supplied.
2. Is the charger protected by a breaker or fuse, and if so where is it located?
This question can be interpreted several ways. The 120 to 12 volt converter module is protected against drawing excessive input current by a current limiting thermistor and a fuse in the primary B+ voltage circuit. If the fuse in the primary B+ circuit opens, it is typically the result of a high current failure of a power device and/or support components in the converter module. Simply replacing this fuse rarely restores proper operation.
The converter is not protected against high line voltage, line spike, lightning strike, etc. any more so than typically any other 120VAC appliance connected to the load panel. The load breaker in the load panel is only there to protect the wiring for the load circuit in that it limits the maximum current to the safe ampere capacity of the wiring suppling the load (converter module or module and GP branch circuit). There are companies that manufacture products that will provide surge and voltage protection products for your RV 120VAC electrical panel and appliances. A simple internet search for “RV surge protection products” should bring up several links to investigate and we highly recommend their use.
3. How many amps is the output of the 12 VDC charger? The converter only supplies a "pool" of available DC current for loads to draw from and can be anywhere from zero to 55 amperes DC depending on the 12 volt load system demand including the amperage required to charge the battery.
4. Is the charging output protected by the 30 amp fuses located at the top of the 12 VDC section of the panel? The two polarity fuses are there to help protect the converter in the event the battery system is reverse connected. The converter module provides internal safety circuits for over-current and over-temperature protection.
5. I do see an inline 30 amp fuse about a foot from the battery and assume it is to protect the charger, correct? The inline battery breaker or fuse is again only there to protect the wiring used by limiting the maximum current to the safe ampere capacity of the wiring according to the wire size (AWG), and insulation temperature rating, as determined by the NFPA70/NEC (National Electrical Code).
A very simple test you can do as an owner to confirm the converter module is working is to disconnect the battery system (at the batteries or turning a battery disconnect to "off" or "store"). Have the RV "plugged in" and see if your 12 volt loads function normally. Do not try to run slide rooms or power jacks however, those are high current demand loads and most converters will not power them without battery support. If 12 volt operation appears normal, the converter would be working normally.
If the test above does not indicate normal operation, a qualified technician (with a good quality DC volt and DC amperage meter capable of measuring the output capacity of the DC converter) is usually recommended to positively confirm a converter problem.