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chobe2's avatar
chobe2
Explorer
Mar 10, 2016

Generator vs Battery/Inverter/Solar

We have just purchased our first truck camper - a used 2007 Lance 845 and have a couple questions that I hope you can help us out with. The camper is still at the dealer and we're considering having a couple modifications done before we pick it up. It has an empty generator compartment in the back that we could have a propane generator installed in. Or...I've seen online that another person used this space for 3 extra batteries and an inverter plus I believe they had a solar panel. What are the pros and cons of these two systems? Any thoughts?
Truck Campers

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  • DiploStrat's avatar
    DiploStrat
    Explorer
    Mar 16, 2016
    HMS Beagle wrote:

    It may be a little overboard, but I have considered adding the second alternator to the truck (an option on most 1T) but keep it off the truck electrical system, feeding only the camper house batteries through a good external 3 stage regulator. But in the sunny West, I find that 200W of solar on the roof is all that is every needed.


    Some comments/observations, if I may.

    -- I don't have a Ford shop manual, but I suspect that you will find that you already have a multistage regulator on your truck.

    -- The "trick" to getting your truck's alternator to step up and do its share of the charging is to lower the resistance between your starter and camper batteries. Most RV's are wired with tiny 6AWG runs between the two batteries. (Worse, some also use diode isolators.) With a wire that small, you can drive all day and never really achieve a decent charge of your camper batteries.

    -- You really need at least 50mm2 of copper (and a good ground) to make things start to happen. This means a minimum of 1/0 AWG cabling. I use a pair of 1/0 AWG cables, which comes out to 100mm2. Once you get the resistance low enough you will find that you start to get a significant bulk charge from your vehicle alternator, a charge that quickly (1 - 2 hours) gets you into the absorb stage where your solar controller can finish the job.

    This voltage drop calculator is a nice tool. I have preloaded it with the following assumptions as a starting point:

    -- 14v
    -- 1/0 AWG
    -- 100A alternator
    -- 20 feet of cable from the alternator to the camper battery.

    As you will see, the voltage drop is so such that you are actually starting to charge at a typical "float" voltage. That voltage will rise, however, as the amp flow decreases. (For giggles, reduce the wire size to 6AWG, a very common size, and the voltage drops to under 12.5v; essentially useless.)

    Voltage Drop Calculator

    Based on my experience, I would suggest that rather than spending money on a regulator to replace the one you already have, spend the money on good cabling, it will be expensive enough. If your camper is removable, you will have the additional cost of big Anderson Power Poles or similar detachable connectors.

    Best wishes.
  • HMS_Beagle's avatar
    HMS_Beagle
    Explorer
    Mar 16, 2016
    This is why I have 3 stage chargers with a voltage sense line and temp sensors at the battery terminal. Treat Lifelines right and they will last 10 years. Also it is a good argument for solar - after the weekend or week away, it sits and the solar brings it to a full charge and keeps it there (with a decent solar charge controller), keeping the AGMs happy. It even keeps them in float with the cover on the camper.

    It may be a little overboard, but I have considered adding the second alternator to the truck (an option on most 1T) but keep it off the truck electrical system, feeding only the camper house batteries through a good external 3 stage regulator. But in the sunny West, I find that 200W of solar on the roof is all that is every needed.
  • DiploStrat's avatar
    DiploStrat
    Explorer
    Mar 15, 2016
    HMS Beagle wrote:
    Higher voltage will not harm flooded lead acids, though they will go through water a little quicker. But it will eventually harm AGM batteries, and pretty quickly ruin gel batteries. For longest life you want a proper 3 stage charge, with set points for the battery chemistry being charged.


    To be sure, we agree completely. No one is proposing using a voltage higher than that specified by the battery manufacturer. The key point is that the charging voltages for modern batteries, of all types, are higher than many would expect and those voltages go higher still as the temperature drops to freezing or below. The classic "charge an AGM at 14.2v or 14.4v is only true at 20C/70F. The proper charge voltage will be lower for a battery under the hood in Death Valley and much higher camped up at Leadville in the winter. Thus temperature compensation is especially disable for your shore and solar chargers.


    Another peculiarity of AGM batteries is their life will be shortened by chronic undercharging - which is actually more likely in a camper. They need to be fully charged periodically to maintain capacity.


    Again, you are exactly right. This is the point drilled into my head by the folks at Lifeline. Most (camper) batteries die from never being fully charged. A quick boost charge from the engine or the genset won't do it. You need the long absorb stage that almost only ever comes from solar or shore chargers.

    One problem with many of the "converters" installed in many RV's, even a few touted as being "multistage" or "intelligent," is that they drop the voltage too much during the absorb stage. This isn't a huge problem for a camper plugged in overnight, every night, but those of us whose camper may go for more than a year without ever plugging in, a charger that did not complete the absorb stage would be a major problem.
  • HMS_Beagle's avatar
    HMS_Beagle
    Explorer
    Mar 15, 2016
    Higher voltage will not harm flooded lead acids, though they will go through water a little quicker. But it will eventually harm AGM batteries, and pretty quickly ruin gel batteries. For longest life you want a proper 3 stage charge, with set points for the battery chemistry being charged. Another peculiarity of AGM batteries is their life will be shortened by chronic undercharging - which is actually more likely in a camper. They need to be fully charged periodically to maintain capacity. There is a new type, carbon foam AGM, which does not suffer this effect, but they are expensive.
  • chobe2's avatar
    chobe2
    Explorer
    Mar 15, 2016
    Oh my gosh...you guys are pretty impressive with your electrical knowledge. Thank you for the information...I'll see if somebody local can make some sense out of it!
  • DiploStrat's avatar
    DiploStrat
    Explorer
    Mar 15, 2016
    You are misreading my post and misunderstanding a bit of what is going on.

    All of this discussion assumes that you are using roughly similar batteries, specifically lead acid and not lithium iron.

    -- You DO want shore/solar power to reach your starter battery. If you use an intelligent relay (aka, voltage sensing relay, automatic charge relay, etc.) this will happen automatically and you will not have to use an additional product like the AMP-L-START or similar. While my truck actually uses a Magnum Energy "Smart Battery Combiner" driving a Blue Sea relay, I rather prefer the Blue Sea ACR.

    -- GM alternator/regulators are very sophisticated, even going to full alternator shutdown as a fuel saving measure under certain circumstances. This is very, very rare, however when you combine air conditioning and the various loads of a camper. Under those circumstances you almost always have so much drain that the voltage will never drop to a classic float voltage.

    In my case, the refrigerator, and often the heater, are enough to assure a background drain of as much as 5A, peaking to 15A. Thus I want the voltage to stay around 14v whenever the engine is running. The AMPERAGE, however, will drop and thus there is no danger of the starter or the camper battery overcharging. I do have the charge voltage on the solar controller capped at 14.9v as my heater will fault if it sees 15v.

    My solar controller will drop to a true float, but only when I have all of the loads (e.g. heat, fans, refrigerator, composting toilet, etc.) shut off and the engine shut down.

    So basically you need a higher voltage to assure a full charge. That voltage will not harm your batteries unless the amperage is too high.

    Two years in, running massive loads, and without a genset, my batteries still perform like new.
    As always, YMMV.
  • ticki2's avatar
    ticki2
    Explorer
    Mar 14, 2016
    DiploStrat wrote:
    ticki2 wrote:

    I choose to feed the solenoid from a lighted switch on the dash so I could manually control the charging times and the connection between the TC batteries and truck batteries . I didn't like the idea of continually pumping 14+v into a fully charged deep cycle battery which is what happens when the solenoid feed is connected to an ignition-on feed. Comments ?


    Two comments:

    -- Manual switches get forgotten. Ignition controlled switches prevent a charge from solar/shore power ever reaching the starter batteries. (Can be important if your camper ever sits for very long.) An intelligent relay, such as those made by Blue Sea, solves all of these problems very elegantly. Like others, I like Blue Sea products.

    -- You won't be pumping current into a fully charged battery. Your vehicle's voltage regulator will throttle back as the internal resistance of the battery rises.

    Basically, you want the batteries combined when under charge and separated when discharging.


    Yes manual switches can be forgotten , that's why I use a lighted switch to help me remember.

    Why would you not want solar/shore power from reaching starting batteries if you have 3 stage charging ?

    Have you ever checked the voltage going to the starting battery after the engine has been running for several hours ? It's usually close to 14v , not near float charging.

    Basically you want the batteries combined under charge and separated under discharge , but not always .

    A more sophisticated system than mine would be better for sure , but at what cost .
  • DiploStrat's avatar
    DiploStrat
    Explorer
    Mar 14, 2016
    ticki2 wrote:

    I choose to feed the solenoid from a lighted switch on the dash so I could manually control the charging times and the connection between the TC batteries and truck batteries . I didn't like the idea of continually pumping 14+v into a fully charged deep cycle battery which is what happens when the solenoid feed is connected to an ignition-on feed. Comments ?


    Two comments:

    -- Manual switches get forgotten. Ignition controlled switches prevent a charge from solar/shore power ever reaching the starter batteries. (Can be important if your camper ever sits for very long.) An intelligent relay, such as those made by Blue Sea, solves all of these problems very elegantly. Like others, I like Blue Sea products.

    -- You won't be pumping current into a fully charged battery. Your vehicle's voltage regulator will throttle back as the internal resistance of the battery rises.

    Basically, you want the batteries combined when under charge and separated when discharging.
  • ticki2's avatar
    ticki2
    Explorer
    Mar 14, 2016
    HMSbeagle

    I have looked into that Balmar product and it does what I'm looking for . The problem is the cost , it is more than my entire unsophisticated electrical system , batteries included . On a six figure yacht it would be a no brainer .
  • 2oldman's avatar
    2oldman
    Explorer II
    Mar 14, 2016
    Dr. Feelgood wrote:
    When you're talking about adding a 1000W-2000W inverter is that so you can run the heavy wattage appliances?
    It's to run appliances that fall into the 1000-2000w range.

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