Generator and Solar

[Redrider007]

I just purchased my 2015 Bighorn 3010re and am having a 5.5kw lp generator installed. I do a good amount of dry camping and am looking for advice on what watt solar system to purchase. My concern is that I haven't owned a new unit this extreme and want to make sure I keep battery power. I will use the generator for all the high wattage items like the AC, microwave, blenders, hair dryers and such. I'm really looking at running some lights and occasionally Tvs-I'm just not sure how long the batteries will last being charged through the converter. My previous trailer was a 2000 Salem and we could last a good 7-10 days off 2 6 volt batteries and occasionally running my Honda 3000 but this rig as quite a few more amenities. I haven't ha power slides (3) ad power leveling system before.

 

[Jim.Allison]

Look up the parts I have listed in my signature. That system cost about $5k, but I got a tax credit of 30% for installing the solar on my second home which is lawful, i dont care what the naysayers say. Net cost $3500.

You can try to charge a battery system ALL day with a generator and not fully charge your batts. The best way to charge batts is with solar. I will get you the charging time for batts from cummins onan. And you will see why using generators to charge batts is a worthless effort and serves no purpose except to make everyone in the camp upset at you.

Later I will describe the features of my system so your can see what a little extra money can do as far as performance. I think you may be interested. I can run everything off inverter except AC and the 120v water heater. I stay fully charged and what I use at night is fully charged by noon. With Solar your batts will live 8 years instead of 2.

Now that Im more familiar with my system, I can probably cut $1000 off and have just as good of a system. 4K with 30% tax credit is not bad for a pure boondocking rig that requires no generator. I only use my generator when I need air conditioning.

 

[porthole]

Why use the genny's low output 12 volt DC feed to charge house batteries?
Run the genny and use the trailers converter.

 

[branson4020]

Duane,

Don't think anybody is suggesting you use the 12V output from a portable genny to charge the batteries. Its just a fact that it takes a long time for the coach's converter to push that last 20% of charge into the batteries.

 

[Jim.Allison]

I did not know that a generator had a DC feed, mine does not, it does operate a PD9280 (my standby charger or my Xantrex inverter charger (3012) , but at any rate when the generator is charging through the onboard charger, the charger charging curve forces you to run your generator for 8 hours or more to achieve 100% charge. This is why solar works so well, it is constantly charging.

As Porthole and I have discussed in the past, there is but about 1.5 v. between a fully charged battery at 12.7 and a dead battery at 11.4. The idea is to push the battery to about 13.4 to maintain the max charge. All your battery capacity is represented in the voltage present between 12.7 and 11.4. You will have more capacity if you can push your batts to 13.4. These various dead and charged batteries come from different sources so its hard to be consistent without knowing exactly which batts are being used, but generally speaking I believe these comments to be on target as far as concept.

[SUB]On the chart on page 12[/SUB] of the Onan owners manual, Cummins has given an illustration of a 100 amp charger charging various amp hour battery banks from 0% charge which is 11v according to them.

http://www.westerncanada.cummins.com/LiteratureRetrieve.aspx?ID=100192

A typical onboard progressive charger PD9200 charging curves is shown on page 3 of this PDF

http://www.fishhousesupply.com/images/PD9200.pdf


As you can see charging from 10.5v takes an incredible amount of time. What makes solar desirable and the best charging method is that it provides power for the rig and charges simultaneously . if the rig exceeds the charging output the solar charger will be interrupted or continue it charging curve depending on how deeply the battery was discharged during the interruption.

In my case the Trojan T 1275 should only be charging from 12.1 volts (50% discharged) or so. My inverter is set to shut off at 11.9v and my auto gen start is set to start at 12v. With solar, I have never shut down, nor had the auto gen start come on to run the charger.

It takes a lot of LP to charge a battery via a generator that you used to watch TV, run medical equipment, microwave, and the demands that the 12v system requires of the battery when boondocking. Converting LP to rotary motion to generate 120v to run a progressive dynamics charger for a few DC volts is incredibly expensive and inefficient.

http://www.trojanbattery.com/pdf/TRJN0109_UsersGuide.pdf

Illustration 7 gives the state of charge for Trojan batteries.

 

[Jim.Allison]

Right you are Bob.

That 20% is the top 20% as well, those are the amps you need the most. One should not exceed 50% discharge of his battery bank to begin with, so when the charger senses the 80% charge level and cuts back from bulk charging the last 20% is forced in with low and lower charging amps because of the charging curve. 100% is difficult to achieve. Its even harder to achieve for me because I'm pushing to 13.4 as 100% charged and my batteries go to 14.8 daily to maintain battery health. Lord help you if you were to try to equalize using your generator. My battery bank would laugh at depositing DC pennies from a cigarette lighter adapter, LOL. The more batts you have in your battery bank the harder it is for a PD charger to force that last 20% of course if you had a large battery bank you may not have been so deeply discharged to begin with, But then you have 400 lbs of battery on board. I find that 300 amp hours (150 at 50%) is about right and that 3000 watts of inverted power is a nice luxury with a good solar array.

Duane,

Don't think anybody is suggesting you use the 12V output from a portable genny to charge the batteries. Its just a fact that it takes a long time for the coach's converter to push that last 20% of charge into the batteries.

 

[Jim.Allison]

On the charging curve for a 3 or 4 stage charger, when the charger senses 80% it cuts back the charging amps and they diminish to float as the bank reaches 100%. That last 20% represents 40% of your usable power considering 50% max discharge to maintain battery health. On some chargers there is a "forced charge setting" which is what I would use if I was using my generator to charge batts, but its hard on the system/batteries. My batts are about $400 and I expect to get at least 8 years out of them. I do not mind running them to 60% discharged here and there, and I would run them to 80% discharged if it was necessary. But battery life suffers exponentially the deeper they are discharged. 50% has been determined to be optimal for RV battery banks. Some industrial applications are designed to only discharge 10 or 20 percent to achieve exponentially better battery life.

 

[porthole]

Jim, have you tried starting the generator at 12 volts yet? Enough reserve to get at least two 10-20 second start attempts?

I haven't yet and I guess how quick it starts would be dependent on how long it has been since last run.
My monthly or so run cycle takes a bit of time to get running, and usually takes two starts to get running.

 

[Jim.Allison]

I do not have that problem as solar always has me charged. But I think that 12v (50% charge) would definitely start my Onan even if I had to start it several times. Where I might get bit is if it was blistering cold. That would present a 2 fold problem in that the generator might be hard to start, and the batts would be reluctant to give up enough amps to turn it. But I could always jump it from the RAM truck if I had to. The coach hydraulic system is a capacity burner, I can start off with 13.4 volts and loose .2 volts just putting out my sliders. The generator does not even use that to start.

Jim, have you tried starting the generator at 12 volts yet? Enough reserve to get at least two 10-20 second start attempts?

I haven't yet and I guess how quick it starts would be dependent on how long it has been since last run.
My monthly or so run cycle takes a bit of time to get running, and usually takes two starts to get running.

 

[Redrider007]

I was hoping for some answers on what solar wattage to consider buying.

 

[Jim.Allison]

I have 488 watts going to a solar controller that supplies all the power I need to run my rig and charge batts through the entire charging curve by noon each day. considering normal usage during the day and night.

But when it comes to sizing your system, you have to consider what your usage would be what size your battery bank needs to be, then how many solar watts you need to charge that bank.

If you are only using the DC systems on your rig, then an affordable 300 amp hours will run several days without any charging. And can easily be recharged each day with a small solar array.

But when you add an inverter, you must size up the solar array, and maybe the amp hours of batts. Its a balance.

a device that draws 4 amps AC, is drawing at a rate of 40 amps per hour in DC current, then add 3 dc amps internal inverter usage. That comes to 43 DC amp hours to run a 4 amp AC appliance for one hour.

Fortunately, microwave ovens only run for 3 minutes, TV run for hours but require very little AC amps, hair dryers run only for short periods.

You must do an energy survey to figure out your needs. I have already done one and you can look at my signature to see what it takes to run a rig like yours.

Here is a link that Sums it up,

http://www.macandchris.com/IntroToDryCamping.htm





So using my rig as an example, I can run everything

I was hoping for some answers on what solar wattage to consider buying.