basic battery question, or not so basic.

[Dreams]

Not sure where this fits so it is here for now.

I am remodeling/rewiring a 76 superior and came to a dilemma. I have removed all the house wiring and will be running it completely separate from the starting batteries. My question is do I really need the constant duty solenoid since the battery is only going to the starter relay, or can I eliminate it now?

I don't have the monster onan generator or anything that will be hooked up to the starting batteries, so I figure it is just a waste of space and extra connections that aren't needed.

Let me know if I am missing something with the purpose of the solenoid. Thanks, Jen

 

[Lou Schneider]

The constant duty solenoid engages when the engine is on so the engine alternator can charge the house batteries while you're driving, then disengages to seperate the engine and house batteries when the engine is off. 

It also lets you use the house batteries to boost the engine battery by manually engaging it via a Boost switch on the dashboard if something drains the starting battery too low to start the engine. 

I'd keep it in place.

 

[Dreams]

Right now the way it is wired it has 1 cable going from starter relay to solenoid then from the same terminal a cable goes to the positive on the battery, the second terminal has a wire going to the frame, the 3rd terminal has a cut wire to no where and the 4th terminal is empty. The house batteries go to solar battery bank. Have a dual fuel generator  can use if needed to charge batteries.

So if I keep the solenoid I have to replace it and how would I connect it?

 

[Henry J Fate]

It sounds as though a solar charging system was installed and to isolate the solar charge to the house batteries only, they disconnected the solenoid that combines the batteries. Just a guess but here are a few things to think about as you put together a wiring design.

1) The engine alternator should charge both the chassis battery and the house batteries.

2) The solar panel should only charge the house batteries. (you could elect to change this if  chassis battery charging is needed)

3) current should not flow from the chassis battery to the house batteries or from the house to the chassis.

This gets a little tricky and requires a combination of isolators (diodes) and solenoid switches. There should be many wiring designs available using a google search.

 

[Ex-Calif]

It doesn't have to be that complicated unless you want it to be. It boils down to what you want the batteries to do, how you want to charge them and how much automation you want...

You don't have to follow conventional wisdom but you do have to follow correct design if you want it to work as you expect.

 

[Matt_C]

Jen,

Your plan is very good.  No, you do not need that contactor (what a big heavy relay gets called), but it can be nice to have when you need it. 

There is also a device that would be essential in your case, it is called a battery combiner. 
These are devices that, when charging voltage is detected, connect the banks so both get charged.  When the voltage slips below that level, the banks are again separate.  Having that continues duty solenoid (aka contactor) there can be an asset if either bank is down and you need it up enough to risk it. 

Before the abrogation, I made a good living converting aged racing boats into performance cruisers.  A racing boat has as little accommdation of crew comfort as can be managed as it is not essential for speed.  A performance cruiser is the same sailboat but now with a five star hotel below.  So, before the carpentry, there came the massive increase in hotel electrics and plumbing.  I put in more than a few isolators and combiners.

Matt   

 

[Dreams]

Thank you all for the input. I am still gathering info on this before I commit to anything. It is a slow expensive work in progress. Figuring out no matter what I need on this motor home (76 Superior 2900) I have to search everywhere and then still have to use my imagination to fix things because parts are non existent  and even the chassis build (76 dodge m500) is missing from most searches. Ebay pictures have come in very handy when looking for parts that may be compatible. Just rebuilt the harnesses and the original fuse box and traced all the wires, about 1/2 went to nowhere.

For now I will keep listening to input and hope I can put everything together to get a good functioning solution. Amazing some of the wiring people come up with in older motorhomes...several times I have said OMG! How did this not burn...lol

Anyway keep adding ideas please and Thank you all!

Jen

 

[Lou Schneider]

Basic info:  The House batteries connect to the empty large terminal, then with one of the small terminals grounded you apply +12 volts to the other to close the solenoid and connect the two battery sets together.

Usually the +12 volts comes from a dash switch so you can energize the solenoid when needed to boost the chassis battery.  In this case get the energizing voltage from the house battery so you can pull in the solenoid even if the chassis battery is dead.

Winnebago back in the early days used a clever arrangement, with a rocker switch that was momentary in one direction and latched on in the other.  The momentary side was fed from the house batteries so you could boost a dead starting battery by holding the switch on in that direction.

The other side that latched on came from the ignition circuit and was energized only when the key was in the Run position.  This energized the relay whenever the engine was running so the alternator could charge both batteries.

 

[Ex-Calif]

The biggest question in this system design is whether you want the ability to combine the banks to start the chassis engine. If you do then the connection (via relay/solenoid/manual etc) has to be made with battery cables. This means ideally the banks are near each other and preferably near the starter motor.

If you only want to charge the house bank with the engine alternator there are simple Automatic Charge Relays that will combine the banks only when the chassis bank is about 13V (i.e. engine running and alternator producing) - then you can run probably 10ga wire to the house bank.

If you want to charge the chassis side with a charge source on the house side it gets a little more complicated. This would include your charger/converter, solar, wind etc...

On the simple end of things you could put 200W solar on the roof to charge the house. This supplements alternator charging and charger/converter when plugged in.  Then add a 40W Chassis battery maintainer wired on the chassis side. You should not need a charge controller for a 40W maintainer.

 

[Dreams]

For now I am still setting up power. If I keep the constant duty what amp should I use? I will have 12v 400w solar with possible upping in future. If it matters I am running a 440 with sniper efi. Have to check what the starter and alt are.

Thank you all for the valuable info. All info is appreciated. Jen