batteries in Fivers?

[BigDad]

The wife and I just signed the lease on the site for our yet to be purchased Fiver and I was wondering why there is a dual battery compartment as standard equipment?  I have a 50amp hookup and a 5k generator, why the need for batteries?

 

[Ned]

The batteries run all the 12V devices in the RV.  This includes lights, control boards for the hot water heater, refrigerator, furnace, thermostat.  You can get along without 110AC but not without 12VDC.

 

[Gary RV_Wizard]

You need 12V but your trailer's 12V converter/charger will supply that. If you never disconnect from shore power, you could easily get by with a single 12V battery, which sort of acts like a ballast for the 12V converter/charger. 

They used to make a thing called a battery eliminator or battery dummy for situations such as yours but I couldn't find a reference to one online. The eliminator doesn't store any 12v power, but it provides a dummy load for the converter to help stabilize its output.  They may no longer be needed for todays vastly improved solid state converter/chargers.  You could probably wire the converter output leads direct to the 12V power lines on the battery when your batteries eventally wear out, but it would probably be a good idea to check with the manufacturer of the converter first to be sure it will still function properly. Meanwhile, check the water in the batteries periodically and they should last 3-6 years. Do it monthly at first until you establish its  pattern for water consumption.

 

[Lou Schneider]

A trailer needs at least one 12 volt battery - in addition to everything Ned listed  it provides power to activate the electric brakes via the break-away switch if the trailer ever breaks free from the tow vehicle.  That's probably why the battery eliminator was, well... eliminated.

 

[Ned]

Lou, thanks for the addition.  I forgot about the trailer brakes, being a motorhome person.

 

[woodartist]

The tow vehicle doesn't supply the power for the brakes and break away switch???? Requires a battery? Don't understand that.

 

[Alaskansnowbirds]

The tow vehicle doesn't supply the power for the brakes and break away switch???? Requires a battery? Don't understand that.

The tow vehicle DOES supply the power for the brakes as long as the tow vehicle is hooked up. BUT, if the trailer breaks away (read no tow vehicle) and the break away switch is pulled then the battery on the trailer is used to supply power to the brakes.

 

[woodartist]

Thanks..kind of makes sense. Seems like an odd design that requires power to engage a safety device. I'm not disputing what you say...just that the concept is something I don't understand. I would think the brakes would require power to release and if the power went away, or the switch was pulled, then the brakes would engage. Better minds have apparently thought this out.......

 

[Alaskansnowbirds]

Thanks..kind of makes sense. Seems like an odd design that requires power to engage a safety device. I'm not disputing what you say...just that the concept is something I don't understand. I would think the brakes would require power to release and if the power went away, or the switch was pulled, then the brakes would engage. Better minds have apparently thought this out.......

Most trailers have electric brakes. When the brakes are activated you are supplying power to electromagnets. The magnets grab the brake plate and apply the brakes. Now if the trailer has hydraulic brakes then we're talking a whole nuther animal.

 

[woodartist]

Yea, I understand the electric brakes but wasn't sure about the failure mode when the brake switch is activated.......but what you say makes sense. Hate to have a safety device that needs power

 

[Karl]

Hate to have a safety device that needs power

Think of it this way: Assume your car or tow vehicle requires that you step on the brake pedal to keep the brakes OFF. That requires constant energy while driving. You could never relax your 'brake' leg. Same with a towed vehicle, plus now you have to rely on the total electrical system to be intact to keep the brakes from coming on. That means fuses never blow, connectors always maintain good contact, switches never fail, wires never get damaged by stones or mice, etc. or else your trailer brakes could come on at any time. There's also the engineering aspect of how to modulate the brakes by introducing the proportionally correct resistance into the circuit.

 

[Lou Schneider]

The hydraulic brakes on your car or truck require hydraulic pressure to operate.  If the hydraulic system fails, you lose your brakes.  Loss of pressure does not activate the brakes.

Electric trailer brakes operate in the same manner, substituting electricity for hydraulic pressure.  If you lose the source of electricity, the brakes will not apply.  However, you do have a backup source of power in the trailer's storage battery and the breakaway switch, which apply the brakes if the trailer sedperates from the tow vehicle.  In this respect, it can be said that the trailer brake system is actually safer than the hydraulic brakes in the tow vehicle, which do not fail-safe.

Air brakes work the same way.  An increase in air pressure causes the brakes to apply.  Loss in air pressure means loss of braking.

One axle, usually the rear, does have a backup system.  Here air pressure from the main reservoir feeds a seperate piston, which keeps a spring compressed.  If main air pressure is lost, the piston relaxes and lets the spring apply that wheel's brake.  This system is seperate from the service brakes, although some components like the brake shoes and drums are common to both.

 

[GaryB]

Question regarding Alaskasnowbird's comment shown below (I haven't figured out how to insert quotes yet, just smily faces? :? Does the breakaway switch activate automatically whenever the trailer and tow vehicle  separate?? Otherwise, I guess the driver would need to activate it using some type of remote-control button, etc.

"The tow vehicle DOES supply the power for the brakes as long as the tow vehicle is hooked up. BUT, if the trailer breaks away (read no tow vehicle) and the break away switch is pulled then the battery on the trailer is used to supply power to the brakes."

 

[Tom]

I haven't figured out how to insert quotes yet...

Gary, just click the Quote button instead of the Reply button , then edit out what you don't want.

 

[GaryB]

Gary, just click the Quote button instead of the Reply button.

Thanks Tom!  I'm trying your advice with this post - hopefully it works.  I also edited my last question since it was worded rather confusingly (it even confused me and I wrote it 
Gary

 

[Tom]

Hi Gary. Move to the top of the class!

 

[Alaskansnowbirds]

Question regarding Alaskasnowbird's comment shown below (I haven't figured out how to insert quotes yet, just smily faces  :  Does the breakaway switch activate automatically whenever the trailer and tow vehicle  separate?  Otherwise, I guess the driver would need to activate it using some type of remote-control button, etc.

Gary,

Most breakaway switches have two contacts inside them that are held apart with a plastic plug. The plug is attached to a lanyard that is attached to the tow vehicle. When the trailer departs the tow vehicle the lanyard pulls the plug out of the switch. The contacts close electricity flows and the brakes are applied.

 

[woodartist]

Thanks for all the clarifications....Obviously the concept is different than I would design it, but must have been proven over time to be the best way. Requiring power, to brake in an emergency seems counter intuitive. However I have a Ford truck ( diesel) that requires a vacuum pump to work in order to have brakes Seems odd, but that is what they did....

 

[Alaskansnowbirds]

Thanks for all the clarifications....Obviously the concept is different than I would design it,....

How would you design it?