[Archived]

Setting the charge rate on inverters is a balancing act and it requires an understanding of both the 120VAC current draw and the 24 (or 12) volt loads.

In the heat of summer when the 120 VAC loads are all the normal stuff such as water pump, HW tank, AC units, battery charging through inverters, TV, aux air compressor, etc. an owner has to recognize the current draw on 50 amp service is finite and loads have to be shed or juggled. The obvious loads that can be turned off might be the HW heater and the aux air compressor (if it is not needed to keep slide seals inflated), or the inverter battery charge rate can be reduced. The theory behind reducing the inverter battery charge rate is that if it is insufficient to keep the batteries charged during the day, at night when most DC loads such as lights are off, the inverters will top off the battery charge.

What most owners do not recognize is the lights (unless LED) and the tivolis are huge power consumers. So when operating with reduced inverter charge rates the use of those has to be minimized.

It is possible to cope with juggling loads but it requires attention to details. Select a greater charge rate for the inverters, but offset that by using 2 AC units to keep cool, turning off the HW tank until the evening, reduce the use of lighting, especially the tivolis, and monitor the loads and the voltage on the house batteries.

The inverters have variable charge rates so when dry camping, with the inverter charge rate set at the highest, the auto-start on the generator will kick in as needed and slap a good charge on the house batteries quickly. But when on shore power our coaches really have a limited power supply and we are obligated to manage that power.

And to be very clear we actually do not have 50 amp service available on shore power. We have 2 50 amp rated legs of 120 volt power. The theoretical total is 100 amps. But in our coaches we must limit the current draw to a continuous 40 amps on each leg. If we exceed that it is probable we will trip the shore power breaker because most of the time we can only rely on having 80% of the rating available. Beyond that we risk tripping the breaker on the shore power.

Keep in mind when watching loads. We have several loads that cycle on and off and we don’t control when that happens so in managing power we have to plan on those loads and leave capacity for them. A good example is the HW tank. Let’s guess it draws 10 amps. We first have to know which leg the HW tank draws power from and then we have to make sure when the HW tank is in the heating cycle the 10 amps it draws will not put the load on that leg in excess of 40 amps. The same applies to water pumps, aux air compressors, and any other intermittent loads including AC units when they cycle.

The above does not apply specifically to all coaches because not all coaches use 120 VAC water pumps for example, but the concept applies to all coaches. Almost all of us can exceed the available shore power and management of the power is necessary.

[Jim/Chris]

Jon,

Good explanation.

[Archived]

Jon,

What John said.

[Archived]

Delicious, meaty discussion, Jon!

In the summer we had a terrible time popping breakers. Three campgrounds in a row needed new breakers before we could even manage two A/Cs, let alone the other power draws. I contemplated carrying my own spares to take care of any others we came across but decided that I really didn’t want to be an electrician.

So, the decision was made to cut the inverter/charger max charge, because that was really taking us over the top. Like quick. The choices were 20 amps or 5. Or higher. 10 amps may have been ideal, but wasn’t an option.

Things were better over the summer after that. We went pole to pole and had no problems. Until this episode.

We did replace all of the lights with LEDs, it was day time so no tivoli lights were on, and we were plugged into shore power. I am at a loss to say what was pulling so much power that it drained the batteries. Still, changing the charge rate back helped alleviate the problems, so we will leave it there. This summer I presume we will just switch off one of the chargers during the day.

Will one charger charge all batteries equally, or is it only one bank of batteries that are serviced per charger?

[Archived]

Take this as a guess based on my 97 coach. I think it applies to the present one, but I don’t know enough to be sure.

Both inverters function as chargers, but if you have the Liberty set up with two remote panels you will note that one inverter tends to show charging load only unless the house batteries have been drawn down. Then both will show a rate of charge. I would periodically verify both inverters were able to function as chargers by turning one off at the remote panel. Then after a short delay I would see the second one pick up the charge. I would first verify both are working as chargers just to be sure that is not your problem.

Why your batteries went down even though you have LEDs is likely because your total loads on the batteries exceeds the set charge rate. Because you were on shore power you were not inverting so 120 volt AC phantom loads such as the TV had no impact, but the 12 and 24 volt DC loads were still there drawing from the batteries. If you fully charge your house batteries, and turn off all 120 volt breakers except the two for the inverters with all the lights off your electric panel will show your coach with no apparent loads still has a current draw of about 3 amps on one leg, and perhaps 1 or 2 amps on the other leg. That is the load your inverters are drawing to maintain the batteries and compensate for the phantom loads imposed on them. Those loads may be your clocks, alarms, power to maintain memory in the dash radio, plus a load due to the efficiency loss of the inverters.We also have loads for all of the devices in our coach that are sitting there apparently doing nothing, such as the satellite or TV antenna booster. I cannot begin to list all of the small phantom loads. Add in all your lights and you have loads that likely exceeded your set charge rate.

Our coaches have a lot of ceiling lights. Even if you have all LEDs that still is a draw on the batteries.

Early conversions were not energy hogs, but each succeeding generation of conversions has required more and more electric power to keep the coach working. That just requires us to do a lot of juggling when we want to run heavy loads such as our air conditioners or our cooktop or grille.

[Bill]

l

I keep one of the inverters set at 5 amps and the other at 20. If i need to have the power for the AC units I turn off the inverter set for 20 amps at the remote panel and only run the one set for 5 amps. Once the day has cooled down I turn the second inverter back on. The newer coaches probably have the inverters talking to each other and it may not be possible to do.