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Old 05-26-2004, 10:11 AM   #1
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Solar vs generator vs nothing?

Here's my question.

I've read all the posts about generators, solar, boondocking, and batteries. What comes to mind is; why all the trouble? Can't you just hook up your tow vehicle and recharge your battery(s) when need be?

Here's my personal assumptions:

1) Everything of "importance" runs on 12V or propane (i.e. fridge, accessories, lights, television, etc.)

2) I have no need to run 110V when boondocking other than for a blowdryer (us pirates usually wear a hat or bandana tied on our heads anyway, so itsa moot point...).

So, what gives? Is there a problem with this scenario?

Thanks, as always, for your heartfelt insight!
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Old 05-26-2004, 11:05 AM   #2
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Why using the tow vehicle is not really a good idea

xray,
you can use the tow vehicle to charge the battery, but the problem is the rate of charge is typically only about 10-20 amps by the time it makes the trip from the alternator to the trailer battery. Although modern alternators can output 80-120As at highway rpms, they drop to about 30amps max at engine idle. So figure that you have drained the batteries down 50%, which on a dual battery setup amounts to about 100AH. At 20amps charge rate, you would need would have to charge for 5hours, not exactly the best thing for the tow vehicle engine or remaining good neighbors. I think you can see that using the car is really just an emergency fallback. With solar, you are depending on the fact that the panels can output power all day. With a genset, you are depending on using the internal battery charger on the A/S which can output 55A.

Hope this sheds some light.

david
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Old 05-26-2004, 12:19 PM   #3
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My alternator is rated at 190A/95AH.

Can you help me with the calculations again?

Thanks,
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Old 05-26-2004, 02:37 PM   #4
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no magic formula

xray,
Even though you have a high output alternator, more than anything else, the wire size (both charge and negative return) dictate the max current you can deliver to the trailer batteries. Also, regardless of the max output capability of an alternator, they all output about 30amp max at engine idle. To charge a battery, you must raise the voltage until the desired charge current is produced. Insufficent voltage, no charge. As a battery charges, its voltage rises, which means that if you want to maintain a given charge current, you must increase the charging voltage. But as you near capacity on a battery, you must reduce the charging current to avoid boiling or buckling the lead plates. All wire drops a portion of the available voltage...the larger the current and the longer the wire length, the more the voltage drop for any given wire size. As an example 30ft of 10gauge wire as is typical in most tow vehicle charging circuits will limit the max charging current to around 10amps due to the voltage drop of the wire alone and that is regardless of the alternator output. One solution would be to run 4 gauge charge and negative wires from the alternator (thru a battery isolator) to the rear of the tow vehicle ending in insulated terminal blocks (one for each wire). 4 gauge wire has LESS voltage drop at 30amps than 10 gauge wire exhibits at 10amps. From the terminal blocks you would attach the charge and negative wires from the trailer umbilical jack. On the trailer side of things, the existing umbilical terminates inside the A/S at a terminal block. You would want to make sure that the wires from the trailer side terminal block back to the trailer batteries were also 4 gauge. Although you still have a section of wire that is smaller (ie the umbilical), you have minimized its length so that the overall voltage drop is greatly reduced. If you are a good DIYer this would not be all that difficult, but if you are unfamiliar with electricity, then have a professional do the work. 12V is not high enough voltage to electrocute, but a car's charging circuit produces enough current to arcweld, so you need to know what you doing to avoid fires and damage to the system. By all means you would want to ensure that a 60amp fuse was located in the charge line near the connection to the alternator.

Even after all this, you are still looking at a several hours to put back 100AH of capacity as batteries do NOT have a linear charge curve. The first 80-85% can be done quickly, but as mentioned the last 10-15% has to occur at lower currents. As a battery charges, its voltage rises and its internal resistance to charge increases. The regulator in the alternator sense these changes and it reduces its output as a battery nears a full charge so it takes longer to get that last 10-15%

Hope this helps. I have been accused of offering a fire hose when all someone wanted was a drink, but I tried to make it concise and accurate and hopefully understandable.

david
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Old 05-26-2004, 03:45 PM   #5
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X,

I thought the same thing at one point. David is right. I have a 140a alt. At idle it kicks out about 75a. If just keeping the batts happy is the goal, then I'd get a Honda 1000. If you're looking for AC use, then depending on how large the AC unit is, I'd get a larger Honda.

Me, I like A/C and if I want it when boondocking, I'll need 2 2000s to do it with the 15k BTU AC unit.

Eric
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Old 05-26-2004, 04:35 PM   #6
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Hi X,

I'm having a custom battery bracket/shroud fabricated to carry a 212 AH Douglas Deep Cycle Scrubber battery instead of the wimpy 85 AH Group 24 that came with my 22' CCD. This will last most long weekends boondocking without the need for charging. When I get it installed, I'll send pix and info if you want to get one.

Since you live in NM, solar is more of an option than here in VA. That might be worth some investigation. I won't run AC, but if you have Fantsatic fans, they work pretty good.

I have a Honda EU-3000i that I use to recharge the battery and it also starts my 13.5K A/C! If you don't require AC, you can get by with a 2000 or 1000 watt generator to recharge.

Bob
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Old 05-26-2004, 05:00 PM   #7
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Generator/Battery/Solar

The generators come in handy at final destination if it isn't an integeral part of your AS. Boondocking for a nite here and there doesn't call for big measures but as SilverTwinkle indicated....when the AC is needed in the heat of the summer, that Honda EU3000 sure comes in handy.


As you travel a while, you'll be better able to make a choice one way or the other...

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Old 05-26-2004, 05:38 PM   #8
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Excellent feedback all!!!

You can start taking this advice stuff for granted!

Before I go on >>> Thanks!!!!!

Twink, where do you carry your generator? I know your TV. I, like you, do not have a pickup truck. Gasoline gives me a headache...

I think a Honda 1000 would do the trick so long as I can bring it along. It's dry out west - no A/C needed most of the time.

One final Q, is there a feasible way to use propane to power your Honda?

Danka!
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Old 05-26-2004, 08:30 PM   #9
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Ford uses 12AWG for the charging wire, and it's fused at 20A. IIRC, the charging line on the Airstream plug is also 12AWG.

DON'T use an isolator in the charging line. It reduces your charging voltage by about 0.6 volts, turning a charging voltage into nothing but a low float voltage. Ford has a relay that only sends connects the truck (charging system and battery) to the trailer when the key is in the Run position. If you don't have that, instead of an isolator, use a a voltage-sensing high-current relay, which won't reduce your charging voltage. At normal battery voltage level on the input, it is open. When the input rises to typical charging level, it closes. You can find them at marine supply stores.

You CAN convert a Honda to propane. Pick posted a link to a supplier of a kit for that. Just be aware that propane has less energy, so your generator's output and maximum run time go down. Even with the converter unplugged, an EU1000 is already marginal for a 600W cooking power (900W magentron on power) microwave oven at sea level.
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Old 05-26-2004, 08:47 PM   #10
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BTW, if you're going to be boondocking in sunny, shadeless desert in Arizona, without air-conditioning, go ahead and spring for a Shell/Siemens SM-110 or Kyocera KC-120 (a bit longer) and a Solar Boost 2000 controller, to run the Fantastic Vent.

This is one of those applications, like pumping water through a solar collector, that electrical solar panels are ideal for. As power produced by the panel goes down from lower angle, shorter days, or cloudy skies, so does solar heat gain (in your case in the trailer), so you need less power.

These panels will produce about 27.5-30AH/day, or enough for 11-12 hours of one Fantastic Vent on medium speed, in the summer, and about 2/3 that in Spring and Fall, when the days are shorter and you need the vent less fast and for less time. This can save you as much as an hour or so of generator run time, depending on the state of battery charge.
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Old 05-26-2004, 09:40 PM   #11
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Where do you carry the generator?

We are thinking of getting the Honda 1000 too but we do not have a pickup truck. Is there a safe way to do this without making a mounting on the trailer for it?
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Old 05-26-2004, 10:27 PM   #12
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Not all battery isolators are bad

RoadKingMoe,
I totally agree that typical solid state isolators are not worth throwing in the trash, but there are some excellent units, such as made by Hellroaring (www.hellroaring.com). Their units have typical voltage drops in the .001-.005V @ 150amps. Granted the cost of these unit is in the $150 range, but they certainly don't affect the charging circuit capacity like the cheaper diode based isolators. I also have qualms with relay isolators as the contacts in those things tend to fail and there is NO notice to the owner that anything is wrong.

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Old 05-27-2004, 08:04 AM   #13
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I used 2 of the Hellroaring SSRs to control all my chassis power, voltage drop and reliability were my concerns. Relays do have a voltage drop as they age, the contacts pit as they arc when closing and opening. Eventually the contacts become so pitted they don't pass current.

John
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Old 05-27-2004, 08:19 AM   #14
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Relays are mechanical devices and will eventually fail, over a long period of service, however, saying they "tend to fail" is misleading, as is saying they do it without the owner's knowledge. That's true if the owner doesn't monitor charging voltage periodically.

If you're willing to spend that much on the Hellroaring equipment, then yes, it's better than relays. However, just telling readers to use an isolater is bad information. The most common isolators use diodes and are like BADLY pitted relays from brand new on.
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