Generator vs Battery/Inverter/Solar

[chobe2]

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?

[zcookiemonstar]

DiploStrat wrote:

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.

Nice calculator. Thanks for that link. Just remember it's not just the size of the cable. The thinner the strands the more resistance you will have. If you were to use welding cable because it is nice and flexible you will not get as much voltage as with a heavy stranded cable/wire. Sorry don't have a link to prove that.

[DiploStrat]

Double GRR! Even excising percent symbols I cannot get the rest of the text to post. Anyone interested in the rest of the text after "Battery Sulfation Mode" should send me an e-mail or PM and I will send you a Word document.

If you want that the entire PDF, I will have to use Dropbox as it is huge.

[mkirsch]

rwiegand wrote:
I wonder if using a pair of step-up/step down transformers would be a better solution than having to run such massive wires? I'g guess that the stock wiring would be quite adequate if you stepped the voltage up to 48 V or so. I'm no electrical engineer, but that seems to be the general solution to voltage drop in power transmission.

Unfortunately, transformers don't work with DC electricity.

Even if it were an AC system, the transformers would be more expensive than cables for such a short run, and would introduce more points of failure in the system. When you're talking miles and miles, it makes sense, but for 20 feet, not so much.

[mkirsch]

DiploStrat wrote:
GRRRR! Having trouble getting RV.net to take a post.

Don't use the percent sign. The site is still choking on percent signs.

[billtex]

ticki2 wrote:
http://www.silveradosierra.com/electrical/voltage-fluctuate-on-the-dasboard-meter-t19680.html#p18011...

This may shed some light on the subject , at least as far as GM . Apparently my 02 is too old for this feature . t might also explain why some GM owners are having trouble charging coach batteries from the truck .

thanks Bob...I never knew that!
I stay in T/H most of the time...unless running really flat/long...

Not sure if it matters...but does this apply to gas/diesel or both?
I didn't see in the article.

Tx, Bill

[DiploStrat]

Not a big deal if you are carrying a camper AND the wiring between the starter battery and the camper battery is large enough (low enough resistance) for the alternator to "see" the camper battery.

Wire up with normal wire, like 6 AWG and the camper battery may not draw down the starter battery fast enough to prevent the truck going into econo mode.

To recap: to keep a camper battery happy, you need:

-- Constant voltage/variable amperage. (The voltage of your truck should be as close as possible to the absorb voltage of your camper battery.)

-- A low resistance party between the starter and camper batteries so that they appear to the alternator as simply one big battery.

And, of course, the batteries need to be isolated when not under charge.

[ticki2]

http://www.silveradosierra.com/electrical/voltage-fluctuate-on-the-dasboard-meter-t19680.html#p18011...

This may shed some light on the subject , at least as far as GM . Apparently my 02 is too old for this feature . t might also explain why some GM owners are having trouble charging coach batteries from the truck .

[DiploStrat]

GRRRR! Having trouble getting RV.net to take a post.

Begin extract from Chevrolet Manual
===========================

CHARGING SYSTEM OPERATION

The purpose of the charging system is to maintain the battery charge and vehicle loads. There are 6 modes of operation and they include:

• Battery Sulfation Mode
• Charge Mode
• Fuel Economy Mode
• Headlamp Mode
• Start Up Mode
• Voltage Reduction Mode

The engine control module (ECM) controls the generator through the generator turn on signal. It monitors the generator performance though the generator field duty cycle signal circuit. The signal is a 5 volt pulse width modulation (PWM) signal of 128 Hz with a duty cycle of 0-100
percent. Normal duty cycle is between 5-95 percent. Between 0-5 percent and 95-100 percent are for diagnostic purposes. The following table shows the commanded duty cycle and output voltage of the generator:

The generator provides a feedback signal of the generator voltage output through the generator field duty cycle signal circuit to the ECM. This information is sent to the body control module (BCM). The signal is a 5 volt PWM signal of 128 Hz with a duty cycle of 0-100 percent. Normal duty cycle is between 5-99 percent. Between 0-5 percent and 100 percent are for diagnostic purposes.

Battery Sulfation Mode

[DiploStrat]

ticki2 wrote:

Can you verify that your trucks voltage regulator has three stage charging ?

Yes, from the system documentation (extract copied to a new post) and from direct observation over two years. As a practical matter, however, you only need two stage charging from your alternator:

-- Bulk or Boost charging, and,
-- Absorb or Acceptance charging.

And, in reality, this corresponds to constant voltage/variable amperage operation. You will never run your engine long enough to need to drop to float and you probably don't want to attempt an equalization charge with the engine alternator. (Even if Chevrolet does offer both of these modes.) With a lead acid battery you do want float from shore and solar. Scholars differ on equalization of AGM batteries.

N.B. None of this applies to Lithium Iron.

[Fisher_Bill]

billtex wrote:

Fisher Bill wrote:
So we started out with a used setup that has two deep cycle batteries and a 1000W inverter in the Genny cabinet.

I have a 3500 propane generator and I strap it on a cargo rack and I haul another 7.5 gallons of propane if we think we're going to end up boon docking but really all we need is coffee (coffee maker) in the morning.

Wow...all that for a pot of coffee.
Our French press weighs maybe 1#...just sayin'

Yeah I know, if we needed the AC or the microwave it might come in handy but the biggest fear in the tiny house hold? Not having an electric blow dryer thus not being able to be seen in public.

Just so y'all know my hair is less than an inch so you know how these things happen...:R

[billtex]

Fisher Bill wrote:
So we started out with a used setup that has two deep cycle batteries and a 1000W inverter in the Genny cabinet.

I have a 3500 propane generator and I strap it on a cargo rack and I haul another 7.5 gallons of propane if we think we're going to end up boon docking but really all we need is coffee (coffee maker) in the morning.

Wow...all that for a pot of coffee.
Our French press weighs maybe 1#...just sayin'

[Fisher_Bill]

So we started out with a used setup that has two deep cycle batteries and a 1000W inverter in the Genny cabinet.

I have a 3500 propane generator and I strap it on a cargo rack and I haul another 7.5 gallons of propane if we think we're going to end up boon docking but really all we need is coffee (coffee maker) in the morning.

Boon docked twice but never fired up the genny so if we're on the road and there are hook ups we don't bring the gen.

If I was going off grid I would be going where there ain't no neighbors to bother, even then just to run some appliances and charge a battery for a couple hours so not all night by any means.

But no neighbors (or did I say that already).


Bill

[DiploStrat]

HMS Beagle wrote:

I haven't checked the new truck, the old one certainly did not have 3 stage charging. Regardless, having the start and house batteries connected directly means one or the other is not getting charged correctly, since they are unlikely to have the same State of Charge, or chemistry, or voltage.

With an isolated alternator/regulator and remote voltage sense, these problems go away and extra large cables aren't necessary. #8 or #6 is adequate to carry the current, and the voltage drops are accounted for.

Parthian shot, but:

-- You may be exaggerating the differences between AGM batteries.
-- I suspect that your Ford comes with an AGM starter battery(s).
-- I think you will find that your new Ford is at least as sophisticated as my older Chevrolet.
-- Connected on the same bus, the state of charge will tend to equalize.
-- Assuming that you want to harvest the full 100A+ that your Ford can produce, you are going to need big cables, whether you attach to the starter battery or a separate alternator.

Another alternative, of course, would be something like the CTEK D250S/SmartPass, but again, for a modern US truck, I can't see the need.

Best wishes whatever you do!

[HMS_Beagle]

DiploStrat wrote:


Some comments/observations, if I may.

.....

I haven't checked the new truck, the old one certainly did not have 3 stage charging. Regardless, having the start and house batteries connected directly means one or the other is not getting charged correctly, since they are unlikely to have the same State of Charge, or chemistry, or voltage.

With an isolated alternator/regulator and remote voltage sense, these problems go away and extra large cables aren't necessary. #8 or #6 is adequate to carry the current, and the voltage drops are accounted for.

[ticki2]

DiploStrat wrote:


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.

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.

Can you verify that your trucks voltage regulator has three stage charging ? This was the issue , charging from the trucks alternator , not solar or shore power . I have not found this to be the case , it is either on or off at a set voltage above 14v .

Your solar and shore power converter both have 3 stage charging so are not part of the equation .