Auxiliary start vs Isolator solenoid

[Dmitry103]

Update:
I’m getting continuity across two small terminals on the solenoid when nothing’s connected to them. With this said, there’s no continuity across two large terminals. I believe that the solenoid went bad and needs replacement. Any recommendations on a heavy duty replacement?

Also, after more troubleshooting I’ve found that the Aux switch is not wired to the 12v ignition source (only to the house battery). I was able to find an empty ignition wire under the dash and going to wire that in using a 5amp fuse as Jayco recommends.

 

[JimD]

Update:
I’m getting continuity across two small terminals on the solenoid when nothing’s connected to them. With this said, there’s no continuity across two large terminals. I believe that the solenoid went bad and needs replacement. Any recommendations on a heavy duty replacement?

Also, after more troubleshooting I’ve found that the Aux switch is not wired to the 12v ignition source (only to the house battery). I was able to find an empty ignition wire under the dash and going to wire that in using a 5amp fuse as Jayco recommends.

The continuity you measured is correct. There should be continuity between the small terminals only. This is the "primary" side of the relay and is basically a coil that when energized will pull in the relay causing the 2 large terminals to be connected together. The 2 large terminals should not show any connectivity until the relay is energized.

If you can determine which small connector is connected to ground you could simply jumper one big lug to the other small terminal (the one not connected to ground. This would pull in the relay. Or just remove both small leads and apply 12 volts (+12 volts and ground) across the small terminals. Same end result. If this makes it "clunk" then try measuring across the large lugs. If no clunk, try reversing the wire connections to the small terminals and repeat the test.

The way a relay like this works is that a voltage across the 2 small terminals will energize the relay resulting in the other 2 terminals being connected together. The large terminals can be though of as an on/off switch the is controlled by the small terminals.

These relays/solenoids do operate a bit differently than a standard relay as these are latching relays. You do not need to keep 12 volts on the small terminal to keep it energized.

Lastly, if you hold the pushbutton in for more than a second, it can disable the relay. See the attached picture.

 

[craigav]

Just FYI, on those I have seen including mine, a "latching" relay is only used for the battery isolation and located near the coach battery. The relay for "AUX start" and charging from the engine alternator is a non-latching relay and needs continuous power in order to stay on. ~CA

 

[Dmitry103]

Thank you, Jim. The solenoid in question is of the type below (Powered by Aux switch under the dash), see image. I believe it does need continuous power in order to stay on.


Thank you, Craig. Looks like I’ll have to replace the relay as I’m getting continuity across two small terminals when they’re not powered.

 

[craigav]

Thank you, Jim. The solenoid in question is of the type below (Powered by Aux switch under the dash), see image. I believe it does need continuous power in order to stay on.


Thank you, Craig. Looks like I’ll have to replace the relay as I’m getting continuity across two small terminals when they’re not powered.

Latching or not latching, I should have also added that Jim is still correct. There should be continuity across the two smaller terminals. One small terminal is grounded and the other provided with 12v to turn on the relay. Once the relay is on, then both larger terminals will (should) have continuity as well. The absence of continuity on the two smaller terminals would indicate a problem, not the other way around. ~CA

BTW, on that relay should be two larger cables, one going toward the engine and the other going towards the coach battery(s). Do both cables indicate voltage (even when the smaller terminals do not have any wires connected)? They should, one being the coach battery resting voltage and the other cable the engine battery resting voltage. Generally speaking the engine battery will have the higher voltage when the engine is running and then the relay will connect the two cables (coach and engine source) which allows the higher voltage (engine usually) to charge the lower voltage source (the coach). The AUX start switch is for when the engine battery is too low so the coach source provides the engine starting battery with power in order to help start the big engine (also does the opposite if the coach battery is too low to start the generator). Sometimes you have to hold the aux start switch down for many minutes in order to get enough charge to start the engine but that topic isn't really relevant with your issue. ~CA

 

[Dmitry103]

Latching or not latching, I should have also added that Jim is still correct. There should be continuity across the two smaller terminals connected or not connected. One small terminal is grounded and the other provided with 12v to turn on the relay. Once the relay is on, then both larger terminals will have continuity as well. The absence of continuity on the two smaller terminals would indicate a problem, not the other way around. ~CA

BTW, on that relay should be two larger cables, one going toward the engine and the other going towards the coach battery(s). Do both cables indicate voltage? They should, one being the coach battery resting voltage and the other cable the engine battery resting voltage. Generally speaking the engine battery will have the higher voltage when the engine is running and then the relay will connect the two cables (coach and engine source) which allows the higher voltage (engine usually) to charge the lower voltage source (the coach). The AUX start switch is for when the engine battery is too low so the coach source provides the engine starting battery with power in order to help start the big engine (also does the opposite if the coach battery is too low to start the generator). Sometimes you have to hold the aux start switch down for many minutes in order to get enough charge to start the engine but that topic isn't really relevant with your issue. ~CA

Yes, two large cables are connected. One toward chassis battery, other’s the coach battery. 12V on the chassis terminal (14V with engine on), 12.5 on the house terminal. Logically speaking, I expect to see around 14V on the coach battery when the engine is on AND solenoid engaged. Doesn’t seem to be the case though. Going to test the solenoid next.

 

[craigav]

Yes, two large cables are connected. One toward chassis battery, other’s the coach battery. 12V on the chassis terminal (14V with engine on), 12.5 on the house terminal. Logically speaking, I expect to see around 14V on the coach battery when the engine is on AND solenoid engaged. Doesn’t seem to be the case though. Going to test the solenoid next.

Correct, with the relay engaged, both sides should show similar voltage (if not then the relay is not powered on or not working). On my setup, I have often used a small jumper from one of the larger terminals to the + (Positive) smaller terminal which should engage (click) the relay. This allows for me to charge the chassis battery when plugged into shore power. You should be able to so something similar for testing the relay, just use a small jumper from either larger terminal to the + smaller terminal. Once you hear the click, then the voltages should be close to equal on the larger terminals. This will help to tell you if the relay works or doesn't. ~CA

 

[Dmitry103]

Correct, with the relay engaged, both sides should show similar voltage (if not then the relay is not powered on or not working). On my setup, I have often used a small jumper from one of the larger terminals to the + (Positive) smaller terminal which should engage (click) the relay. This allows for me to charge the chassis battery when plugged into shore power. You should be able to so something similar for testing the relay, just use a small jumper from either larger terminal to the + smaller terminal. Once you hear the click, then the voltages should be close to equal on the larger terminals. This will help to tell you if the relay works or doesn't. ~CA

No voltage across the solenoid when I jump the small terminals. As a matter of fact, house battery drops to 11.6V and the jumper wire becomes very very warm.

 

[craigav]

No voltage across the solenoid when I jump the small terminals. As a matter of fact, house battery drops to 11.6V and the jumper wire becomes very very warm.

Don't jump across the smaller terminals, jump from one of the larger terminals to the one smaller terminal that is the + (not grounded). If the wire gets warm or hot when doing this, then you are likely on the grounded smaller terminal which you shouldn't do for long, the correct smaller terminal should give a distinct click sound. ~CA

 

[JimD]

Just FYI, on those I have seen including mine, a "latching" relay is only used for the battery isolation and located near the coach battery. The relay for "AUX start" and charging from the engine alternator is a non-latching relay and needs continuous power in order to stay on. ~CA

My mistake. For some reason I was thinking this was an issue with the cutoff relay. Must have been thinking about some other post.

If this is indeed the charge relay, they fail all the time. If there is no click when power is applied to the small terminal, the relay is bad, guaranteed.

 

[JimD]

I have attached my troubleshooting guide that has a section on this relay.

 

[Dmitry103]

Don't jump across the smaller terminals, jump from one of the larger terminals to the one smaller terminal that is the + (not grounded). If the wire gets warm or hot when doing this, then you are likely on the grounded smaller terminal which you shouldn't do for long, the correct smaller terminal should give a distinct click sound. ~CA

I powered the solenoid with an independent 12V supply. It clicks and voltage evens out between both large terminals. I fired up the engine and house battery shows 14V. So far so good.

Now, when I use AUX Switch wire coming from house battery to power the same solenoid (like seen in schematics), the wire quickly gets very hot and there’s no clicking of the solenoid. Any ideas?

 

[craigav]

I powered the solenoid with an independent 12V supply. It clicks and voltage evens out between both large terminals. I fired up the engine and house battery shows 14V. So far so good.

Now, when I use AUX Switch wire coming from house battery to power the same solenoid (like seen in schematics), the wire quickly gets very hot and there’s no clicking of the solenoid. Any ideas?

With the wire getting hot and not clicking the solenoid, both indicate a short (connection to the ground somewhere) which could be because of a miswired setup. Have you moved or reconnected any of the wires that are from the RV and goes to the solenoid's smaller terminals? That would be my first suspicion. Other than that, I would trace the wire from the aux switch to the relay. ~CA

 

[JimD]

Is there only one wire connected to each of the small terminals? If there are multiples maybe the wire coming from the aux start is connected to the side that the ground wire is connected to.

Try pressing the aux start button with the wires disconnected from both small terminals. If it still gets hot then it must be connected elsewhere in the system.

 

[bucko-JAY]

Good morning- I have a 2016 Melbourne 27D My battery charge isolator is on the firewall on the drivers side.

All responses have been good ones, but yours actually addressed the OP's question as to where the isolator is located!

 

[DNMakinson]

The solenoid coil receives voltage to close the relay from the pushbutton. It is a 2-pole button, one N/O contact set, and one N/C contact set. The N/C set is connected to the engine running circuit (not sure how that works, but KOEO will not activate it). The purpose of that is to send alternator power to the coach battery. This is what seems to be not working per the OP. The N/O contact set comes into play to supply power to the relay coil from the coach battery, when the button is pushed. The two input circuits never mix.

I replaced my bad relay with a Yandina Combiner 200. I removed the input to the pushbutton that came from the Engine Running circuit and isolated that wire (near the pushbutton). The N/O contact of the Pushbutton is still operative, and the Combiner will connect Chassis with Coach on command. However, the Engine Running circuit is not needed because the Combiner will automatically close when Chassis electrical comes to about 13.2 (IIRC) V. This usually takes about 15 seconds after a start (the Chassis battery needs to be replenished right after a start.
The other advantage of this set-up, is that, when on shore power, when the converter / Coach battery gets to 13.2V, the Combiner will also automatically close, and the Chassis battery will be maintained. Thus no second tender is needed.
One caveat: The Manual and ground studs need to have 2 nuts each, with the wire (ring terminal) captured between them (use a Lockwasher also). Else, those terminal joints will loosen over time. DNM

 

[Dmitry103]

With the wire getting hot and not clicking the solenoid, both indicate a short (connection to the ground somewhere) which could be because of a miswired setup. Have you moved or reconnected any of the wires that are from the RV and goes to the solenoid's smaller terminals? That would be my first suspicion. Other than that, I would trace the wire from the aux switch to the relay. ~CA

Red supply wire from coach battery to Aux switch had 12V and also continuity with the ground. I did find that it shorted out in the battery bay from rubbing against a piece of metal. I replaced it and it’s now inside a corrugated conduit. No continuity between that wire & ground after that.

I pressed the Aux button this time and the wires quickly got hot.

Now, the white ground wire at the solenoid is fed back into the cab and secured there. Why? I’m not sure. On a hunch, I jumped the negative terminal directly to the frame and everything works. Aux switch engages the solenoid, none of the wires become hot.

Not sure how jumping the ground terminal directly to the vehicle frame made all the difference vs ground wire being fed inside the cab and secured there. But things now seem to work as they should. Thank you all for your suggestions and recommendations!

 

[Dmitry103]

I replaced the momentary pushbutton switch with ON-OFF-ON type. It allows me to keep the house battery charged during those long hauls. Also, I can jump/charge the chassis battery directly from the house battery while camping. There are two independent power sources (house battery and ignition). This project has been on my “to do list” for a while now and I can finally cross it off lol. Thanks again to everyone’s insight and recommendations.