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RV Converters, actually have a very simple task, supply 12-volt when your motor home is operating on 120-volt (generator or a public utility). It will also run all of your 12 volt appliances (lights, pumps, fans, etc), and charge your battery at 2 amps. You do not want to use this to charge a very low house battery as it is only charging it at 2 amps. If you are not plug in (i.e. you are dry camping) you want to run your engine for about a half an hour to an hour each day to keep your house battery charged up.
But because their basic function is shrouded with fuses, and circuit breakers, converters appear to be more formidable than they actually are. Most RV converters are composed of the following parts:
- Battery substitution power supply, and relay.
- D.C. Fuses
- AC circuit breakers
- Battery substitution power supply. Chew on this description for awhile "Battery Substitution?" "Power Supply?" Yep! That's all that it is, a humming transformer that reduces 120 volts AC down to 12 Volts, and a couple of Diodes, to convert the 12 volts AC to 12 volts DC. When the converter is connected to shore power, is makes it own 12 volts DC to a limit of about 30 amps of power, and your rig's coach battery is switched out of the circuit by a relay. But, what about the fuses?
- The converter box is a handy place to hang all of the 12 volt DC fuses.
- And it's also a handy place to hang all of the AC circuit breakers (one of which is used to switch the converter AC inlet power on and off).
The relay only operates when you plug your rig into shore power. The relay closes off your house battery and allows the battery substitution unit to power everything in the coach. When the rig is disconnected from shore power the relay clicks back to a different set of contact points, and your rig will then be operating off of your house battery once again. Shore power is transformer power, house power is battery power, as far as your lights, heater, and pumps are concerned.
Battery charging occurs because the converter manufacturer, installed a "Bleeder Resistor", which acts like a trickle-down reducer valve, between the converter-to-house power connection (the one that feeds all of the DC fuses in the face of your converter box), and the battery connector, located right before the relay. When the converter is humming away on shore power, the bleed resistor allows a small fraction of the converter's 30 amp potential to be siphoned off to "keep the house battery charged". Most converters only allow 2 amperes to "bleed" through to feed the house battery. This is a primary reason that attempts to recharge a flat house battery using an on board generator, fail miserably. Flat batteries require a minimum of thirty to forty amperes of power to recharge quickly. A 2 amp charge rate would take forever (and it usually does - most people give up after three or four futile hours of running a thirsty generator to recharge a flat battery). To charge a really low battery you use your engine's alternator. This gives an 85 amp charge which will charge your battery in 30 to 40 minutes.
For the technically inclined, the transformer and diodes, are connected to a large AC condenser (capacitor), Don't ask how it works, be satisfied that the condenser is necessary to regulate or throttle the transformer so that it produces the correct amount of voltage.
Trouble Shooting the Converter
- Switch on a couple of lights on inside the coach. Unplug your shore power. If your lights go out, the house battery is discharged, bad, or there's a dirty or corroded connection (usually near the battery or at the terminal posts). Older converters sometimes fuse the battery separate from the converter. So check all of the fuses.
- Plug in your power cord to shore power, switch on a couple of lights, and disconnect the ground cable from the house battery. If the lights go out or get dim, you've got a problem in the converter transformer, diodes or relay contacts. But first, check all of the AC breakers to make sure that one hasn't tripped or was shut off. You can hear a electric hum when the converter has shore power (the hum comes from the transformer).
- Converters are only capable of supplying the rated amount of power (usually 30 amps).
- Converters are sloppy about voltage level. When the load is low voltage is high, and vice-versa.
- Batteries are subject to the effects of No. 2 above. The bleed resistor is too crude to regulate voltage.
- Converters are not designed to recharge flat batteries or even partially discharged batteries, quickly.
- Regulated battery chargers are much kinder to batteries and your rig's electrical components (we'll discuss regulated chargers in a future tech tip article).
NOTE: This online manual is a work in progress and is subject to change at any given time. It is also a generic peace of work and is meant only as a general guide. Each Caravan/RV is distinct and individual in it's own right, do not take anything written here literally as it may or may not apply to the exact Caravan/RV you will be using.