Electrical Hookups When Camping?

Originally posted by offgrid StephenH, let me first define what I meant by "high current". That depends on what your alternator can produce at idle, which is quite a bit less than at normal engine operating speeds. My alt produces about 120A at idle. Subtracting engine electrical demands (electronics, ignition, radiator fans, etc) a net of about 75-80A is available.  Beware of aftermarket high current alternators because they are typically designed to produce their max current at high engine rpm, which actually reduces their idle current capacity in most cases.

Are there any brands of alternators that would be suitable? Also, how do you measure the output of your alternator? Is the output affected by the battery's state of charge? IOW, if the battery is charged, does the voltage regulator then cut the current so the battery won't be overcharged? If so, how does this affect the ability to charge the trailer's battery/batteries? It almost seems like a separate alternator and charging circuit would be needed for optimal charging so the TV's charging is isolated from the trailer's charging.

The problem is that the alt won't produce that 80A at its max output voltage. I get the 80A at more like 12.5V, above which it tapers off to zero at 14.4V. On top of that there are the resistive losses in the cables connecting the TV to the trailer. You're fighting voltage drops between two circuits that want to be at the same voltage. So you can't directly float charge your trailer batteries from your TV alt, unless you want to idle your TV for many hours, which is both impractical and inefficient.

Agreed. I don't use the TV for that. My generator connected to the trailer and letting the converter charge the battery seems to be much better. I don't worry about float charging when I am not connected. If we are camping without electric, I have used the generator every second or third day to charge the batteries during the times when generator use is permitted. Most of the time, we are not in one place long enough to be concerned. The batteries charge while we are towing.

However, by using short runs of heavy gauge conductors you can directly bulk charge the trailer battery, and then use solar or occasional ac charger operation to complete the charging process. Doing it that way I'd suggest at least 2/0 (preferably 4/0 cable) and short runs directly from the alternator terminals to the trailer battery with the vehicles parked nose to nose. Anderson style connectors can be used to connect the two.

With short cables, it should not cost too much. I don't want to think about how much it would cost to run two 4/0 cables the length of our Frontier.

I plan to do something a little different to get around the voltage drop problem. My plan is to convert the trailer to 24V Li batteries and use dc/dc step up converters for charging. That eliminates the concern with voltage drops as well as eliminating the need for float charging entirely (Li batteries don't require it).

How do you plan to step that down for the refrigerator, furnace, and AC? To convert those for 24V use would not be inexpensive I would think.

But the simple way with short heavy gauge conductors and normal 12V PbA batteries should work fine as long as you have an alternative way to complete the absorption and float charge process, which does't need to be done every day.  Before doing away with your generator I'd suggest both measuring your TV alternator capacity and also its fuel consumption at idle. My TV burns about 1/4-1/3 gallon per hour at idle with no load so its really pretty efficient as long as I keep the charge rates high and then shut it off. And the biggest benefit is its very quiet, I can barely hear it 20 ft away, compared to the high noise level of even a "quiet" inverter-generator.

With the information you gave me here, I don't think I will be trying this any time soon. Perhaps when I upgrade TV's, I will make sure the output is sufficient. In theory, the Frontier's alternator is 110A. Whether that is the actual capacity given the age, I am not sure. When I clamped my meter to the positive terminal when the engine was running, it was not measuring anything near 110A. I don't remember exactly what it was, but it was a fraction of the 110A rated capacity.

Even if I could use my Prius to run my house here in the OBX in the event of a power outage, I wouldn't plan on doing it. My portable genny stays upstairs where its both above flood levels and accessible afterwards. A Prius is a bit heavy to carry upstairs . My cars end up parked on high ground somewhere away from the house during weather events so they don't get flooded.