how does a battery boost switch operate?

The word SOLENOID is often used cause that's what FORD calls the relay that makes the starter whine.

Another term is CONTACTOR.. but that is usually used for very high power stuff.

Relay is of course what they are

For the O/P if it helps

Have you ever jump started a car or other engine? You hook a cable Positive to positive then negative to engine block (if you do it right most folks do not) and varoom

Well the negative cable is already connected.> Both the house and the chassis systems use the chassis as a common negative terminal

The boost simply acts like the POSITIVE jumper cable.. Hooks house to chassis and may work both ways to crank up ye old generator.

Side note.. Once had to jump start both a truck and the stumper it was (towing Machine that grinds up stumps)

They had tried to jump the stumper from the truck, still connected. They were somewhat insulted when I ask if they had paid attention to positive an negative they said We hooked Hot to Hot and Ground to Ground how much more positive to positive can you get.. I said 24 volts the stumper is positive ground.

Yup. they did it bass ackwards.

MrWizard: You must have come same school as me. Solenoids in my school was a device to change types of energy. Vacuum to electrical, electrical to mechanical, mechanical to electric and the like.

solenoid is an old term
and technically was an electric coil with a throw arm, that could be used for anything an engineer wanted, like opening a gate valve, or closing a large electric switch. it was a separate component that could be disconnected and replaced, with out changing the mechanical parts, or the mechanical parts could be replaced with out replacing the electric solenoid

you won't find any true solenoids in an RV

what some people here call a solenoid is an enclosed relay
metal can start type or plastic multi-contact
makes no difference , these are ALL relays, they switch electric power

now in the past, cars had a solenoid on top of the electric starter
the solenoid would push the starter gearing into the bell housing to engage the ring gear
my 53 chevy i had back in high school , had that type of starter
now days starters are built with a different mechanical design
where the spin action of the start motor moves the starter gear out to engage the ring gear

Mile High wrote:

Clay L wrote:
Also on Winnebagos the RUN terminal on the ignition switch activates the boost solenoid so the house batteries are charged while driving. The boost solenoid is a continuous duty solenoid.

Do they still do that?

I understand that some diesel pushers have a different system but house batteries are still charged when driving I think.

Solenoids are relays!

garym114 wrote:
Not all systems that connect the chassis and house batteries have a relay involved. Some operate a regular battery solenoid that connects the two battery systems.

People are using Relay and Solenoid as the same item. Battery Boost---It takes a COACH battery system fully charged to activate the Battery Boost. If your Coach batteries are dead or below 11.5 volts the system will NOT activate. And if it does close the solenoid nothing will happen because the Coach batteries are below 12 volts. Remember, IF the CHASSIS batteries are fully dead, the Battery boost may not work on a Diesel Motorhome. THE AMP DRAW for a Diesel battery system is to great for some boost solenoids to transfer enough amps to start the engine. The dead chassis battery will "draw" some of the current that is needed to the starter. GAS engines will usually start with a dead Chassis battery and using the Boost. Doug

Not all systems that connect the chassis and house batteries have a relay involved. Some operate a regular battery solenoid that connects the two battery systems.

While all the above answers are correct, to give a quick answer to what the OP may have been asking,
When pressed it basically acts like connecting jumper cables from one battery (or batteries) to the other.

Clay L wrote:
Also on Winnebagos the RUN terminal on the ignition switch activates the boost solenoid so the house batteries are charged while driving. The boost solenoid is a continuous duty solenoid.

Do they still do that?

All of the above are possible configurations of how it might be wired
All configurations use at last one relay
Some systems use more relays
Make model and year of RV , will help us be more specific
Someone may have the same RV