Power to Fridge

[Stan Simpson]

We're getting ready to head out for a spring shake down trip on Thursday. Went to the coach today and turned on the fridge. I don't have shore power there, so I set it on LP.

After awhile, the fault code came up reading "DC Low". Since I didn't hear the fridge come on, or any flow of propane, I'm guessing the chassis batteries are what run the fridge on propane.

I ran the engine for about a half hour, and turned it on again. Same settings. I waited for a half hour, and no fault codes came up, and I could definitely hear the fridge running.

Does the DC just power the circuit board to get it running? Or does it require DC to continue running? Do you think my half hour of running the engine charged the chassis batteries enough until I leave?

As always, thanks for the help.

Stan

[Joel Ashley]

You should have used the genset, Stan.  Charging low batteries with the engine alternator is a good way to ruin it, as several threads on this forum have explained.   It should be the house batteries that run the fridge.  It is likely also that the gas valve didn't turn on at the tank if the batteries were down.

The gas valve, burner ignition, and most if not all fridge control circuitry are 12 v.  If you have an ice maker on the fridge, that is AC.

If you park the rig where it has no solar battery upkeep or AC available, then turn off master battery switches before leaving it, and always use the genset, not the engine, when you return, even if you have to use the boost switch or portable jump unit to start the genset.

Joel

[Jim Nichols]

Needs 9 volts to comp. board.

[Stan Simpson]

Now I'm confused. When I'm going down the highway, the fridge is running on LP. It switches automatically when I unplug from shore power. There is no 12V power except from the chassis battery, yes? I have had the fridge on for about 3 hours. I just ran over to the coach to see if everything was okay. The fridge is still running, however, the inverter is on. The panel said I had 11.7 volts in the house batteries. I shut everything off.

What does the fridge run off when I'm driving down the road? Stored energy from the house batteries? The chassis batteries? I never looked...the inverter comes on?

I can't wait until we get to our first Beaver Rally in Gillette in June. I hope someone there can walk me through the electrical system...especially the inverter/charger...in layman's terms. I'm not an engineer...just an end-user.

[Jim Nichols]

The 9 volts I mentioned is from house batteries and what the lowest voltage the frig can have before it shuts off while on propane. The only time it runs on 110 house current is while pluged to shore power or the gen is running suppling house current.  The computer board for the fridge needs DC voltage of no less then 9 volts to decide what is needed. Do you have manuals for the fridge?

[Joel Weiss]

Stan:

Your house and chassis batteries form two (relatively) independent 12V systems.  The chassis batteries power the starter motor and the electrical needs of the vehicle (ECM, headlights, etc).  The house batteries power everything else, including the 12V side of the fridge.  

When you are going down the road your engine's alternator is charging both battery banks which is why Joel cautioned you not to try to re-charge a discharged house battery set using just the alternator; it will significantly shorten its life. If your house batteries are reading only 11.7 volts then they are barely charged so trying to charge them with the alternator is definitely not a good idea.  Plug the MH into shore power or turn on the generator to charge the house batteries before using the engine again.

You inverter has no role in the 12V electrical system; it's only job is to turn 12V into 120V when you are going down the road or dry camping.  The inverter does not need to be on for the fridge to operate on propane.  Most fridges are wired so that they cannot access the 120V being created by the inverter because they would be too large a load if permitted to run off of it.  But simply having your inverter on creates a power loss that is unnecessary if all you wish to do is run the fridge on propane.

Based on what you have written unless you leave your MH plugged in your fridge will only run for a relatively brief period of time given the discharged condition of your batteries.  If you have left the fridge running I seriously doubt it will still be on when you return.

Joel

[Stan Simpson]

Thank you Joel, and Jim. So, I should set the inverter to Disabled? And the charger to Enabled? How long do I need to run the generator to get the house batteries back up to speed? I will go tomorrow and run the generator for the required length of time.

I shut everything off, so except for parasitic draw, there should be no more drain on the house batteries.

This has been very helpful, thank you.

[Joel Ashley]

That parasitic draw can be enough to hurt, Stan.  If the coach has a solar panel and is out in the sun, that should be enought to overcome the parasitic load.  Just turn off both master switches above your battery tray when you leave the coach in storage.  This does not keep the solar supply from charging the batteries.  Do not mess whatsoever with the black rocker switch in the group by the entry door;  that is called a salesman's switch and is not meant to be flipped on and off regularly by owners to "shut everything off inside" - leave that always in the ON position and don't use it.  Use the battery bay master switches to shut things down.

You don't need to mess with the Magnum panel either, other than as a monitoring device so you know the state of charge.  I have rarely touched the inverter or charger buttons there since when you run the generator, (or plug in to shore) the inverter automatically begins a charge cycle.  It may take a few hours to get from Bulk Charge to Float Charge or Full.  Fuel use will be in the neighborhood of 1/2 gallon per hour.  

As the batteries come up, you will notice over time that the current flow into them (amps) slowly drops, as read on your Magnum screen in terms of 14.2 to 14.6 volts eventually dropping toward 13.3;  in other words the rate of charge and voltage is higher in the initial Bulk Charge phase.  The charger notes the low battery state and really throws juice at them.  Somewhere below 14 volts it goes into the Absorb Charge phase until the voltage reaches around 13.7, then it should settle into kind of a trickle charge state called Float Charge.  You are at about 80% of a complete charge cycle there, and fairly safe in shutting down the genset.

Be aware that contrary to laymen's belief, a battery at a charge state of 12 volts has dropped significantly from being fully charged.  Try to keep things above that - at least 12.5 to 13+ volts is better for most so-called 12 volt DC devices.  

[Stan Simpson]

I understand about turning off the batteries in the battery bay. I did that when it went in to storage last November. When we got it out on the 11th of this month, it started right up. I recently retired, and we sold our house and bought a smaller one. The old house had a place for us to park the coach when we were home, and we installed a 30 amp outside receptacle. The new house has none of that, so it is being stored outside for now, about 5 miles from home. If its not raining, there is a solar panel that works. At least the Aladdin screen says so.

So much to learn, so much to see, so little time  

Thanks all.

Stan & Becky

[Joel Weiss]

Correct, set the charger to Enabled and the inverter to disabled (off).  I'm not the best one to answer the "how long should I run the genny" question, but I would expect that you will need to run it for at least ~6 hours. A fully charged battery will have a voltage of at least 12.7V but when you first turn off the genny the voltage displayed will not be the same as when the battery is at reast.

Even with fully charged house batteries there is a limit as to how long the refrigerator will run on propane.  Four fully charged 6V batteries have ~1000 amp-hours of stored energy and, I believe, a Norcold fridge draws ~50 amp-hours/day when running on propane.  You shouldn't discharge a battery past the 50% point so, in reality, you have ~500 amp-hours available to you.  So that means that a fresh set of four fully charged batteries can provide ~10 days of running a refrigerator assuming there are no other loads.    This, of course, isn't true, but it gives you a rough idea what you are dealing with.

[Stan Simpson]

Thanks Joel,

I'll be hooked to 50 amps on Thursday, so it will charge me up good I think. I needed to know on a go forward basis, what I need to do to run the fridge prior to departure, this time and in the future, so it will be cold when we leave.  I have the information I need now!

Stan

[Joel Weiss]

Thanks Joel,

I'll be hooked to 50 amps on Thursday, so it will charge me up good I think. I needed to know on a go forward basis, what I need to do to run the fridge prior to departure, this time and in the future, so it will be cold when we leave.  I have the information I need now!

Stan

Stan--

Please note that I just corrected a math error in my previous post.  The fridge should be able to run no more than ~10 days off a fully charged battery bank assuming there were no other loads.

Joel

[LarryNCarolynShirk]

Stan,

When using your generator, watch your amp charge rate.  When it drops from about 100 amps to 20 amps, you can shut off the gen set.

Larry