House battery not charging while driving

[davismills]

You've been given great advice and I have only one "wild card" to throw out there.

My Aux Start switch was a 3 way that I found out about the hard way. I stopped at a gas station and the coach wouldn't start. I pressed down on the Aux switch it worked as advertised and I was on my way.

The problem was that my coach engine had quit charging the coach batteries and I just lived with it for a while. On a hunch, I pressed the aux start switch toward the 12 o'clock position and was surprised that the switch clicked into this position

My coach alternator was now charging my house batteries while underway.

This was a fluke in my coach and most likely is NOT your problem, but it's worth a check.

[THenne1713]

DAVISMILLS: That makes sense if you think about trying to BOOST in both directions? Trying to power a solenoid from a DEAD battery would not work, and at least, might disconnect under load, with associated voltage drop? You have BOTH battery sources right there, inches apart, which could also explain the dual FUSES on many solenoids coil circuit? I have had to boost engine only once, but had to Boost to start GEN several times.

[Jim_HiTek]

I didn't read all of the responses and I wanted to mention to the OP that 'smart' systems measure the voltage and health of the house batts BEFORE engaging the solenoid to charge it up from the alternator...in order to avoid damaging it. SO, if you're only reading 10 volts, that is below the safe voltage which is typically 11.3 Volts

What you should do, is borrow a battery charger and charge up the house batts so they are over 11.3 volts (and hold it) and THAN start the engine. There is a delay, and depending on the health of the house batts, it could be a few seconds or never if the house batts are bad. But typically, it takes a few seconds to 2 minutes for the solenoid to close and allow alternator charging to charge the house batteries.

IF you don't read higher voltage from the alternator on the house batts after a short delay, than you probably have a bad component. Like maybe that fuse. Kinda means you need a schematic.

And a suggestion. Next time you want to store the RV, just make sure the batts are charged up, and then just disconnect the ground wires from both sets. Sure they'll lose a bit of voltage over the months of storage but they won't be exhausted and pulled down to 10 volts by the phantom loads on the typical RV (engine, tranni, CO detectors, propane detectors, steps, inverters, etc., etc.). When ready to travel, just reconnect them, maybe give the chassis batt a jump if necessary, and off you go.

[rarebear.nm]

Originally Posted by THenne1713

DAVISMILLS: .... which could also explain the dual FUSES on many solenoids coil circuit. ....

If the type of solenoid you're speaking of looks like this:




The fuses are housed in the two rectangular "ears" on either side of the coil body.


The small post labeled Brown is used for the POS lead and the post labeled white would be ground. The coach batteries connect on the left and chassis battery on the right. If the coach batteries are too low to activate the coil you will not be able to get power across the solenoid.


This same solenoid may also be used as the master power on/off switch and the right side goes to the house circuits. You can wire these devices many different ways.



Then the fuses are not really involved with the coil at all. In the picture yo can see small bare wires extending from the two large posts to one side of each fuse. Those fuses get power directly from the main posts. The out going side of the fuses may be used in a variety of manners. Sometimes one supplies power to a DPDT switch that in turns activates the coil. The second can be used light an LED to show power is passing thru the solenoid. They may be used in other ways as well or not at all.

[twinboat]

Originally Posted by rarebear.nm

If the type of solenoid you're speaking of looks like this:


Attachment 359271

The fuses are housed in the two rectangular "ears" on either side of the coil body.


The small post labeled Brown is used for the POS lead and the post labeled white would be ground. The coach batteries connect on the left and chassis battery on the right. If the coach batteries are too low to activate the coil you will not be able to get power across the solenoid.


This same solenoid may also be used as the master power on/off switch and the right side goes to the house circuits. You can wire these devices many different ways.



Then the fuses are not really involved with the coil at all. In the picture yo can see small bare wires extending from the two large posts to one side of each fuse. Those fuses get power directly from the main posts. The out going side of the fuses may be used in a variety of manners. Sometimes one supplies power to a DPDT switch that in turns activates the coil. The second can be used light an LED to show power is passing thru the solenoid. They may be used in other ways as well or not at all.

Your displaying a latching relay ( solenoid )

It takes a momentary pulse of 12 volt power to the 2 small terminals to latch on. Once latched on, it needs a pulse of reverse polarity to the same terminals to unlatch. Magnetic fields created by the polarity cause it to latch/unlatch.

It uses a momentary, center off, double pole double throw, reversing power toggle or rocker switch.

It can not be used as a isolation/charging relay because of its unique design. Sending constant power to it will just burn the coils out in short time and it will never disconnect the batteries.

[papademuchos]

I finally got it working!

All of the fuses are good - those under the hood and those down by the driver's left foot. I bought a fuse holder:



Then I found a 15 amp fuse that was hot with IGN = ON. I pulled out the fuse and plugged this in, then put the fuse in it. Then I connected a 16 gauge wire and routed that down and under and around, following wire loom tubing that was already in place and going up to the solenoid under the hood. I was able to tuck my wire into the tubing all the way up.

Then I added a connection on the end and bolted that in to the small right terminal on the solenoid - the one that closes the connection when it receives power... and voilá! When I turn the key and start the engine, the solenoid "clunks" and I'm getting ~14.5 volts from the alternator flowing through. I verified the battery is registering the same voltage as well.

Thank you everyone for your help with this! I learned a lot about the setup and what my rig has and doesn't have and where things are. I really appreciate all the input and suggestions and guidance to help me figure it out. I'm a computer nerd and not a mechanic, but I'm not afraid to learn. I think I've learned more in the last year about car mechanics than I have in my life!

Anyways, I have a couple of follow up questions:

Does anyone see any concerns about the method I used? Will this blow out the 15 amp fuse? Is it ok tapping in to this fuse for this purpose? Any extra safety measures I should ask?

Also, I replaced the old solenoid under the hood with a new one, but it's 80 amp relay. I remember one person suggested a 200 amp relay instead. Any problems using this one? Should I expect it to overheat or go bad soon?

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

I see good and bad reviews on it.

As a side note - I got the latching relay cleaned up and reconnected everything in the back. As far as I can tell, it's all working as expected now.

[THenne1713]

I expect it will work fine, as solenoid you show is continuous duty, and suspect 15a should be fine, as you size Fuse to match the wire size, so 14ga or larger= fine. Maybe some day you will stumble across the original problem; took me 3yrs to find source of my video static on camera.