I am new to the R-Pod forum and glad you guys have brought this up.  My last RV, a 28' Dutchmen, had a three stage charger.  If I left the shore power plugged in 24/7/365, the batteries would go dead every other year.  Reason being is a three stage charger has a "float" or trickle charge that never really shuts off. Even topping off the water level, the batteries would eventually end up cooked.  I ended up installing a 4 stage smart charger that actually shuts off when the batteries are charged.

Folks on this forum seem to think it's ok to stay plugged in 24/7/365.  Are the R-Pod 3 stage chargers smart enough to keep from cooking the batteries?

I'm curious because I wired in 30 amp service to my house and would LOVE to just keep the R-Pod plugged in.  Oh, it's a 2015 RP178.

 

fred

A quick note first: inverters and converters are different things.  We've been discussing converters, which take AC to DC.  Inverters take DC to AC and are all after-market.

The maximum amperage of the WFCO converter/charger (it's both and quite pricey) is a very good question, and I've not been able to find out the precise answer despite searching.  I was surprised to see several reports that it's anywhere from 45 to 55 amps, which is quite large for a 12 volt charger.

The WFCO model is a 3 stage charger.  In the process of monitoring the battery's voltage it determines that the battery's capacity is below about 70-80%, it does 'bulk' charging at the highest amperage rating it can.  Once the battery reaches around 70-80% capacity, it switches to 'absorption' charging and significantly fewer amps are sent to the battery, usually 5-8.  Once the battery reaches 93-97% capacity, it finally switches to a 'float' or 'trickle' charge that is usually 1-2 amps or even less.  This overall process is the 'healthiest' way to recharge lead acid batteries, though it can easily take 8-12 hours, depending on the size of the charger, the size of the battery, and the battery's capacity.  I apologize if you already know all of this, but I'm sure that some reading this will not.

However, this process does create some issues to be aware of when you're recharging the battery via a generator.  Mainly, it is a waste of fuel to run the generator to recharge the Pod's battery unless the battery's capacity is low enough for the charger to run in bulk charging mode.  Otherwise, you're producing a minimum of 20% of your generator's rated capacity in power (i.e. 2,000 watt generator can't produce less than about 400 watts) when your charger only needs a fraction of that to charge the battery; the excess power is wasted unless you're using it for something else.

The easiest way to determine this is to monitor the battery's voltage.  There are lots of posts on this site showing various ways of installing a permanent voltmeter for this purpose.  When the battery's voltage drops to around 12.2-12.3 volts, the battery is at about 50% capacity, and it is at this point that you should recharge the battery as letting it go below 50% does excessive, irreparable damage to it (keep in mind that any use of a lead acid battery reduces it's lifespan to some degree).  When the charger is bulk charging, the voltage will be around 14.4.  When it switches to absorption charging (70-80% battery capacity), the voltage drops to around 13.6.  At this point, you should stop running the generator.

So running the generator more often with the charger doing bulk charging each time is far better in terms of minimal overall cost than running it less often and the charger switching to absorption charging for a part of that time.  But once you're doing camping or when you can plug into shore power, you should bring the battery back to 100%.  A battery should never be stored at less than a full charge.

 I'm not sure what the maximum charging amperage is of the converter, but my guess is it's either 10 or 15 amps.  That would be 120 to 180 watts plus what the converter itself uses, so I'm guessing the total draw would be around 200-300 watts.

fred

It will probably go up a bit when you get indoor plumbing! 

fred

The fridge does seem to draw about 140 Watts AC when cooling (converter on also). I have it set at the midpoint for cooling, it's empty and inside temp is @ 30 degrees measured with analog fridge thermometer. Doesn't take much opening and closing to make it work and from my overnight measurements I think it's safe to say you will use 85-100 AC watt average running converter and fridge. Of course ambient temp and midnight fridge raids will effect usage. All in all the fridge does seems pretty efficient on AC at our current temps 75/50.

fred

I haven't been able to find out exactly how much propane the refrigerator uses, but I can figure out a break-even point.

If the refrigerator consumes 14 watts after its cooled down, that's 336 watt hours per day.  At current electrical rates (~$.10), that's $.0336 per day, just over three pennies.  With propane at $1.29 a gallon, the refrigerator would need to run on one gallon of propane for a little over 38 days to equate to the same cost as shore power.

Given my experiences, a 20 lb. tank will last somewhere around 30 days, plus or minus a week.  That would cost $1.01 with electricity and about $25.80 with propane.

So even if the propane lasts twice as long as my estimate and the refrigerator consumes twice as much electricity as I'm calculating, it's still FAR more expensive to run the refrigerator on propane than shore power.

I don't think so. The fridge on 12 volt is not very efficient. The converter kicked on almost immediately. We're measuring AC watts and since the converter needs to run almost full time to keep up with fridge (12 volt) load, I doubt that it would drop below 250 watts. I really just wanted to measure converter load when charging instead of float.

I think what the numbers best demonstrate is that if you have well maintained and fully charged batteries, it is very reasonable to keep the pod plugged in 24/7. Someone here, smarter than me, may wish to do the math regarding the relative cost of running the fridge off propane or shore power. BTW, I did just have a new 1000 gallon propane tank filled - 850 gallons @ $1.29/gallon. Bet that would run the fridge for a while!!

fred

More great data!  Thanks again Fred!

I'd be willing to bet that your last scenario (or bulk charging the batteries, see below) is how techntrek got his 240 watt number.  Based on your numbers running the fridge from shore power, the 12 volt power draw would probably drop by 80-90% after it was cooled down.

I think that the last data point that would be really interesting would be how much current the converter draws when it's bulk charging the batteries.  I'm not sure what the maximum charging amperage is of the converter, but my guess is it's either 10 or 15 amps.  That would be 120 to 180 watts plus what the converter itself uses, so I'm guessing the total draw would be around 200-300 watts.

Reefer on shore power. Startup from warm => 140 watts.

After 4 hours and cooled down to about 30 degrees => 13.8 watts 

Forced converter on by opening fridge and switching to 12 volt. Battery voltmeter dropped to about 13.1 and kicked the converter on quickly (hear fan running) => 250 watts!

fred

At the 24 hour mark The Kill-A-Watt measured 0.26 Kw. Calculated to 10.83 watt average over 24 hours.

fred

fred