Powering trailer with an alternator

Our small Itasca Class C came with a dash switch to gang all three (coach,engine) batteries together if needed.

(FWIW, since we go offroad rockhounding we also carry the "ultimate dead battery backup" ... a small portable generator for charging the batteries when all other options have been exhausted.)

McZippie wrote:
...and I've said many times... IMHO RV's should get rid of separate house and starting batteries and have only one large AGM bank that is charged with high output alternators.

For example; change normal 2 starting and 2 house batteries
into one 4 battery AGM bank, with automatic low voltage disconnect.
House would have the 2 additional batteries added to its bank, that were previously used only for engine starting.

Sounds good- most of the time. But that one time when something unusual happens and you are stranded because you don't have a dedicated starting battery...

Also consider the different chemistry needs of starting and true deep cycle batteries.

Having said that, the ability to tie all the batteries together when needed...priceless! I've seen many MHs and boats with this feature. The Perko switches are very nice on the boats.



A bit trickier for MH- I'd prefer a dash switch and use relays to keep the wiring short, close to the batteries, and neat ;)

Funny thing about bacon. It can sit out in the sun for quite a while, but it much prefers to be saved :B

MrWizard wrote:
i have said many time that IMO rv's should come with (2) alternators
one for the chassis one for the house, individual regulators and a 'cross connection system' for backup IF one fails

...and I've said many times... IMHO RV's should get rid of separate house and starting batteries and have only one large AGM bank that is charged with high output alternators.

For example; change normal 2 starting and 2 house batteries
into one 4 battery AGM bank, with automatic low voltage disconnect.
House would have the 2 additional batteries added to its bank, that were previously used only for engine starting.

pnichols wrote:
Speaking of high 12 volt power output from an idling RV engine ... I'm surprised that not much/any mention has been made of using dual alternators. Many vehicles have this - often offered as an option when buying new or installed later by their owners.

.

Yep spec'd dual alternators on our Ford E350, with fast idle and 225amp AGM battery bank.
After batteries are drained to around 11.9 volts, see +200 amps charging for the first few minutes. After about 15 minutes fast idle kicks down RPMs to normal and alternators output is around +40 amps with no load.

I've turned off the fast idle controller and alternator amp output is about the same as with fast RPMs.

The fast idle is mainly for running the seperate Bus system 40,000btu Air Conditioner while parked.

i have said many time that IMO rv's should come with (2) alternators
one for the chassis one for the house, individual regulators and a 'cross connection system' for backup IF one fails

pnichols wrote:
Speaking of high 12 volt power output from an idling RV engine ... I'm surprised that not much/any mention has been made of using dual alternators. Many vehicles have this - often offered as an option when buying new or installed later by their owners.

Why, for instance, wouldn't a couple of 200 amp alternators easily provide at least 250-300 amps with the engine at full idle?

A couple of 200 amp alternaters would probably also cost way less $$$ than some exotic 400 amp alternator. With two alternators, you also get redundancy for backup in case of failure of one while on an RV trip.

Earthroamer even touts their use of double alternators for idling-engine charging of their large battery bank when the sun isn't shining enough to do it.

KEEP IN MIND, many high-power alternators ARE NOT DESIGNED to run at higher outputs under the hood of an AUTOMOBILE (pickup truck). I freakin' do not care what the fluorescent tie boys say about their product, silicon rectifiers are designed to operate within a STRICT temperature/amperage limit. A 125 ampere rectifier is a 125 ampere rectifier but boost its temperature to 150C and what do you get? Anyone willing to do a little research and get a cyber gold star?

One of the best jokes in the industry was Leece-Neville and it's 2800JB series of alternator rated at 160+ amperes using (3) Motorola 5020 rectifiers (absolute maximum of 150 amperes capacity at 20C). I made A LOT of money rebuilding these alternators.

If I were north of the border I would seriously consider manufacturing remote rectifiers for RV's. Included would be avalanche rectifier protection and a high voltage capacitor. Some of what I see these days is entirely silly-stupid.

I recommend GOOGLING

HAIR PIN ALTERNATORS

For more information.

PapPappy wrote:
Are you taking into account the amount of gas that engine is going to use to run that alternator, as compared to the gas that a smaller generator will use?

Keep in mind, your numbers suggest that you'll have to run that alternator at 1200 rpms. What does that mean the engine has to be turning? Are you going to sit there with your foot on the gas pedal to bring the RPMs up from their idle speed?

Just thinking about the setup on my vehicles, the alternator pulley is less than half the diameter of the crank pulley. At a 600RPM idle, the alternator will be rolling at more than twice the engine RPM (i.e. greater than 1200 RPM) I don't see a problem provided that the alternator is, in fact, putting out its rated output at that speed. (most don't.)

Reading the info in this thread with great interest, keep it coming!

A few things to add, some relevant to the OP directly, some just informational on the topic.

1. If idling for long periods, keep an eye on your engine temp, especially in hot weather. You can add a water misting system to the front of the radiator to help with cooling if necessary. Or spray it with a pump spray like found at a garden center for spraying insecticides. NO HIGH PRESSURE! Misting is the key. Pressure can damage the radiator.

2. If you want to add a second aux alternator, perhaps you want to consider using a mag clutch on it, like the one on your air conditioner compressor. Add a dash switch to turn it on. The switch can also control other conditions, such as a mister, monitors, any other items that should only be enabled when it is turned on.

3. BEWARE of carbon monoxide if you are planning to idle for long periods. Did I miss it- This is on a coach or travel trailer?


Are you looking for a permanent installation, or just playing around with it? Either way, it is an interesting idea.

Speaking of high 12 volt power output from an idling RV engine ... I'm surprised that not much/any mention has been made of using dual alternators. Many vehicles have this - often offered as an option when buying new or installed later by their owners.

Why, for instance, wouldn't a couple of 200 amp alternators easily provide at least 250-300 amps with the engine at full idle?

A couple of 200 amp alternaters would probably also cost way less $$$ than some exotic 400 amp alternator. With two alternators, you also get redundancy for backup in case of failure of one while on an RV trip.

Earthroamer even touts their use of double alternators for idling-engine charging of their large battery bank when the sun isn't shining enough to do it.

THE NEW "HAIR PIN" STYLE OF ALTERNATOR HAS AN UNBELIEVABLE HIGH OUTPUT ESPECIALLY AT IDLE. Some models can put out almost 180 amps at a dead slow idle. These are for AUTOMOBILES, not over the road big rigs or buses, they are not the size of a washing machine.

My issue is with rectifier cooling, the "diodes". With a separate rectifier box, mounted away from engine heat, using adequate heat sinking, and a stator to stator lead AC fan for cooling, this would be one impressive setup. Run THREE stator wires from the alternator stator connections to the box. The box powers the AUXILIARY LOAD, the regular alternator output takes care of the vehicle chassis just like normal. Three 150 ampere 600 PIV rectifiers on the positive and three 150 ampere 600 PIV rectifiers on the negative. One CS 144 parallel bridge with avalanche rectifiers to clamp transients. This is a hell of a system, got a dozen on cruising sailboats. Some have gone circumnavitation (around the world). Throw a couple of electrolytic capacitors in to smooth ripple and wowee. Change the field over to type B add a Cruising 3-stage voltage regulator (totally adjustable) and you have a World Class charging system.