Aux start solenoid -> DC2DC 2 questions!

[barnz333]

So I have a new-to-me 2021 Melbourne prestige LP (so the Mercedes 3500 chassis) and I am working through a changeover from the auxiliary start solenoid to a DC to DC charger. For the most part, it seems straightforward to me, but there are two things I’m unsure about. So I’m checking to see what the folks who may’ve also done a similar changeover may have done.

1) there is a 16 gauge red/white wire from the solenoid to the power step. My assumption is that pulls the step in when the engine starts or the boost button is pushed. So it’s a safety feature so you don’t go driving off with your step out. For those who changed from a solenoid to a DC to DC charger, how does that work? I bought a Victron DC to DC charger, and I don’t see anything in the manual that might point to a replacement for that type of functionality.

2) there is a 16 gauge red wire from the auxiliary start switch (not the solenoid) to the battery disconnect solenoid. My guess is that this makes sure the battery connection is open when boosting or running. On the flip side, not sure if it then shuts down the battery connection when you’re no longer boosting or running. Regardless, not sure a DC to DC charger has the capability to replace this functionality? If I can’t do anything, I’ll just need to remember to make sure to turn on the battery disconnect switch when going somewhere. The worst that can happen is alternator charging would not happen.

Anyone have any experience with replicating these two pieces of functionality with the DC to DC charger?

One last thought. I did see mention from one or two people on other forums that they just added the DC to DC charger after the solenoid (leaving the solenoid in there). So maybe the solenoid can then continue to perform those two functions. And then for its initial intended purpose it just passes through power from the alternator side to the house side, and the DC to DC charger can handle doing the proper Charging of a lithium battery set up. Thoughts on that?

 

[Kevin Cooper]

Unless you buy a dc to dc charger that is Bidirectional, you will loose the auxiliary start function if wired after the relay.
Someone else will need to give you their experience since I do not have one.

 

[barnz333]

Unless you buy a dc to dc charger that is Bidirectional, you will loose the auxiliary start function if wired after the relay.
Someone else will need to give you their experience since I do not have one.

Understood. I have a ln easy workaround should I ever need to ‘jump start’ the chassis batts

 

[dvspl]

One last thought. I did see mention from one or two people on other forums that they just added the DC to DC charger after the solenoid (leaving the solenoid in there). So maybe the solenoid can then continue to perform those two functions. And then for its initial intended purpose it just passes through power from the alternator side to the house side, and the DC to DC charger can handle doing the proper Charging of a lithium battery set up. Thoughts on that?

This is what I did. Mine is a Ford E450 chassis but the functionality is the same. I just put the DC-DC charger at the end of the heavy gauge wire to the battery and everything works fine. Well, except for the aux start function, of course, but you already expect that. I just carry a jump box with me in case I need help starting the engine.

 

[Kevin Cooper]

There is an easy way to fix the Aux start.

 

[barnz333]

This is what I did. Mine is a Ford E450 chassis but the functionality is the same. I just put the DC-DC charger at the end of the heavy gauge wire to the battery and everything works fine. Well, except for the aux start function, of course, but you already expect that. I just carry a jump box with me in case I need help starting the engine.

Sounds like I’ll be giving that a go. It sounds logical enough!

 

[barnz333]

There is an easy way to fix the Aux start.

What is your solution? I was going to use (YouTuber) Tito’s solution. He put anderson connectors on both incoming battery cables to the DC2DC. When he wants to have the house batts help the low chassis batt, he connects the 2 Andersons together and starts the engine.

 

[Kevin Cooper]

Just so you are aware, I have not done this, but I can read electrical schematics. I did building electrical construction design for 35 years.
Before anything can be done, you must understand that lithium batteries should not be used to start an engine. The current draws are too high and can damage them. But, they can charge LA batteries. That means Aux start button must never be engaged when starting the engine, only for charging.
Having said that, if you still want to know, if you connect the DC TO DC input to the chassis post on the Aux start relay, and the output on the house post on the Aux start relay, leaving the batteries connected too, you can remove the two ignition conductors and the step conductor from the control posts on the relay. Now the relay will only close when the Aux power button inside the cab is pressed.
If anyone sees anything wrong with this post, PLEASE feel free to comment.

 

[barnz333]

Just so you are aware, I have not done this, but I can read electrical schematics. I did building electrical construction design for 35 years.
Before anything can be done, you must understand that lithium batteries should not be used to start an engine. The current draws are too high and can damage them. But, they can charge LA batteries. That means Aux start button must never be engaged when starting the engine, only for charging.
Having said that, if you still want to know, if you connect the DC TO DC input to the chassis post on the Aux start relay, and the output on the house post on the Aux start relay, leaving the batteries connected too, you can remove the two ignition conductors and the step conductor from the control posts on the relay. Now the relay will only close when the Aux power button inside the cab is pressed.
If anyone sees anything wrong with this post, PLEASE feel free to comment.

Please refer to my uploaded diagrams.

Original Setup:
============
-When chassis batt is good (& engine starts), relay opens, alternator charging occurs, and step closes.
-When chassis batt is bad, user pushes boost button, relay opens, house batt helps chassis batt to start engine (but not good for lithium house batts), step closes, and aux start switch pings the batt disconnect solenoid (presumably to ensure electrical system is open (or closed?!? still not sure about that function.
-Bottom line: everything works as designed.

Your solution:
============
*Not sure I grasp your intent, but I drew it out and this is what I see.
-When chassis batt is good (& engine starts), ignition signal doesn’t reach relay (so original alternator charging is not kicked off), but your DC2DC placement ensures a new path of alternator charging). The step is disconnected, so it never closes (ignition OR boost)
-When chassis batt is bad, user pushes boost button, relay opens, original design alternator charging works, AND the DC2DC path opens as well. Step does not close but the battery disconnect ping still works as designed.
-Bottom line: upon ignition start, alternator charging happens (good), step doesn’t close (not good), and battery disconnect solenoid is pinged (good). BUT aren’t TWO separate pathways of alternator charging (through relay and through dc2dc) opened? is that ok or not ok.

My latest solution:
==============
-I disconnect the Boost, and add DC2DC after the relay.
-When chassis batt is good (& engine starts), relay opens, step closes and charge moves on to dc2dc charger. Dc2dc then ensures proper lithium charging to house batts.
-When chassis batt is bad, I would use a jump box to help the chassis batt start the engine. That would then send ignition signal to relay and start the functionality lates out in the previous bullet.
-Bottom line: alternator charging pathway opens , dc2dc then ensures proper lithium charging, step closes as designed (whether chassis batt is good or bad), and I no longer use lithium batteries to help the chassis battery start the engine. Only drawback is the battery disconnect solenoid is never pinged during my ‘replacement boost’ procedure. Not sure how critical that is yet.

Thoughts?

 

[craigav]

After reviewing the post here I can say that knowing what is right or wrong is hard to do without having the actual schematics for a 2021 Melbourne on a Mercedes chassis (or a very similar model with the same wiring).

On the GreyHawks for example (that I do have schematics for and it may or may not be the same), the power conductor to the steps is just that, a power in connection which is the main power for the steps controller (and motor) and the solenoid chassis battery terminal connection on the solenoid is simply a convenient location to obtain power for the steps but that wire does not control the steps at all. The steps are controlled in a couple of places (manual switch and magnetic switch) along with a signal from the key on connection that is also tied into the aux start switch.

I will also add that on the GreyHawks the solenoid remains closed all of the time when the key is in the on position assuming there is 12v chassis power to start with and if there isn't (dead chassis battery), then pressing the aux start button will provide the solenoid with power to close the contacts.

So with that what Keven stated sounds correct but at the same time I would want to see the actual schematics if anyone has them to share, and\or if not then perhaps a few pictures of the solenoid and the connections to it.

@barnz333 Which Victron DC2DC charger did you purchase and a qq would be where you plan to locate it and does it have a "trigger" connection to turn it on whenever a signal (key on perhaps) is sent to it.

I will also add that in the past (year or two ago) I created a diagram that would work well for at least the GreyHawks that would allow one to choose between the DC2DC charger or the existing Solenoid however what would also be needed would be another switch (SPDT center off) located near the aux start switch which I haven't done even on mine, although perhaps one day I will. If the Melbourne has the same wiring setup as the GreyHawk and if that would be of interest to anyone then I can find that post or recreate a quick diagram explaining how to do that. ~CA

 

[craigav]

Original Setup:
============
-When chassis batt is good (& engine starts), relay opens, alternator charging occurs, and step closes.
-When chassis batt is bad, user pushes boost button, relay opens, house batt helps chassis batt to start engine (but not good for lithium house batts), step closes, and aux start switch pings the batt disconnect solenoid (presumably to ensure electrical system is open (or closed?!? still not sure about that function.
-Bottom line: everything works as designed.

Generally speaking I have cut back on pointing out things of less importance to the questions asked , but in this case it is important for clarity of what I was saying above that the relay closes with the key on (closes mean power flows through the relay, the contacts are connected). Not that I didn't understand your meaning but for others and to avoid confusion I thought I would mention this. Open = off and Closed = On

~CA

 

[barnz333]

Generally speaking I have cut back on pointing out things of less importance to the questions asked , but in this case it is important for clarity of what I was saying above that the relay closes with the key on (closes mean power flows through the relay, the contacts are connected). Not that I didn't understand your meaning but for others and to avoid confusion I thought I would mention this. Open = off and Closed = On

~CA

Thank you for that clarification, and for that detailed response above that. I’ll need to re-read a time or two to let it marinate in my addled brain, but in the meantime I am adding my unit’s electrical wiring diagram.

 

[craigav]

Thank you for that clarification, and for that detailed response above that. I’ll need to re-read a time or two to let it marinate in my addled brain, but in the meantime I am adding my unit’s electrical wiring diagram.

The diagrams you shared do have value for the knowledge they contain however, if you received them from Jayco I would ask Jayco if they have a similar schematic for yours as I attached here for the GreyHawks. The one I attached shows you all of the wires sizes and colors going to each component and provides more detail for the aux start wiring setup that I suspect is the same as in yours.

In particular and looking at what you shared, I highly suspect that the Melbourne Aux Start Solenoid and the Aux Start Switch would most likely be the same as it is for the GreyHawks (in the attached schematic). I wouldn't necessarily believe that everything in the schematic I attached though for a GreyHawk would be a match for the Melbourne so be cautious in that regard, but I do suspect a lot or the wiring setup would be exactly the same seeing how this is Jayco's wiring and is common for many Jayco Class C's over many years. ~CA

 

[barnz333]

Thank you for that clarification, and for that detailed response above that. I’ll need to re-read a time or two to let it marinate in my addled brain, but in the meantime I am adding my unit’s electrical wiring diagram.

…and sorry, the DC2DC is a Victron Orion XS 12-12v | 50a | Non-isolated

And also interested to hear why you believe Kevin’s solution may be right even though it removes the connection to the steps, and opens two parallel pathways to alternator-sourced charging.

Thanks all!

 

[craigav]

…and sorry, the DC2DC is a Victron Orion XS 12-12v | 50a | Non-isolated

And also interested to hear why you believe Kevin’s solution may be right even though it removes the connection to the steps, and opens two parallel pathways to alternator-sourced charging.

Thanks all!

There are a multiple people here that are very familiar with electrical systems and Kevin tends to be consistently correct with his responses however, there have been a few times when we have gone back and forth for the most part regarding a few non-relevant details <lol>. With that in mind, I have a complementary career background to Kevin's although I focused more on controls and automation.

In any case, I don't like to suggest a solution that I can't in some part verify myself with what already exists (should exist) which is why I said that what Kevin stated "sounds" correct but I left it open so to speak because... (and I like to be careful with my words here so that they come across in a very friendly and positive manner as I always intend for them to be), I am not confident that the information you provided regarding the power steps being connected to the aux start solenoid is completely correct, which in turn lowers my confidence level for any solution so to speak based on that understanding.

While it may appear that the Aux Start solenoid has a red\white wire connected to it for the steps, that is not what is indicated in the diagrams you shared nor what I would expect (which a few pictures of the solenoid may help in determining this better, also the aux start switch if possible). If you notice in the snippet below, (35) is the aux start solenoid and has a black (x2 but not indicated) and a 10awg Red and a 16awg orange wire (no red\white), which is the same as what the GreyHawks have. The red\white wire is part of the Dual Diode setup (36) which is used to provide a reliable "control" signal to the steps from either the coach or chassis battery(s) and likely a few other items, (not the main step power as that comes from the 10awg red wire that is connected to the solenoid). It may be that the dual diode setup is also attached to the aux start relay (or built-in? perhaps) so I am not saying that you don't see a red\white wire going to it, but for sure the dual diode functionally would be a separate component than the aux start relay, the GreyHawks also have a dual diode setup but it is separate and located under the dash commonly near where the radio is connected and provides the radio with either coach or chassis battery power, perhaps the steps as well along with the CO\propane leak detector (I believe it does the steps for mine as well).

In any case, I can think of a few different ways to set this up and the way you described in your hand drawn diagram (the third entry) should work just fine accepting that you will lose the aux start "boost" functionality and you don't need to change anything else (no need to disconnect the "boost" wire you diagrammed) and just add the DC2DC charger downstream then everything (except the boost aux start functionality) including the steps should still work just fine. If you wanted the additional functionality and keep the ability to have a switched aux start boost then you could do that as well with what Kevin described and you diagrammed in the middle diagram however, there would still need to be more of the current setup understood before I would recommend that as you need to make sure that you don't have both the DC2DC charger and the solenoid on at the same time (which I believe Kevin was implying that as well by removing the solenoid's "trigger" connections except for the boost wire).

My suggestion would be to follow your plan, keep it simple as possible and enjoy the RV accepting that you will lose the aux start boost functionality, for me I would likely do something similar to Kevin's thoughts as I have had my chassis battery run down a few times already, very irritating when that happens and in fact I have a plan in place and I have already purchased what I need in order to accomplish my plans but due to several different things that have happened over the past few years (health and otherwise), I still haven't installed my DC2DC charger as of yet. Maybe this spring . ~CA

 

[barnz333]

Thank you once again for your replies… both to you and Kevin. I had asked Jayco for all schematics, but I did not see one in the group that looked like yours. That would’ve been very helpful to have! I will reach out to them though and ask for that specific type of diagram.

As for moving forward, it’s good to get more confirmation that my proposed solution will work. I am also very interested in understanding Kevin‘s design however, as it’s evident that I don’t truly understand how it would work. As mentioned, I would’ve thought that having current flow through both the old and new pathways would not be the best approach. It just seems like having the old solenoid/relay (with its inability to perform proper lithium charging protocols) in play my interfere with the DC to DC charging.

And I will get a picture of the relay posted as soon as I get my unit back from getting worked on..

 

[Kevin Cooper]

Thanks Craig! Was going to explain that too. Very sure that only closing the contractor (relay) with the button would work except for, you must only charge the chassis battery with it. With ignition wires removed, it will close pushing the button.

 

[Kevin Cooper]

Barnz, I reread your last post. You said you didn’t think it wouldn’t think current flowing through the old and new pathways.
I’ll try to explain. The solenoid with no control voltage is called normally open. No volts to the coil, contacts open. By removing the ignition trigger voltage, the relay will stay open when not running and when the ignition is turned on and engine running. Power from alternator is sent through DC2DC to house battery, contacts still open. So current direction is alternator/chassis battery to house battery for charging when house battery voltage is lower. There is a diagram somewhere in the forum that was discussed in the past about a wire coming from the step to the Aux solenoid that can cause parasitic amp draw. That is where the step wire came from.

Now, let’s say your camping and chassis battery gets low because you left a light on. Now chassis battery is hopefully lower than house. If you push the aux button, the contacts close and the higher voltage from house battery flows to chassis battery. Typically 50 amps totally dead and less if not. The DC2DC will not allow reverse flow so, no dual path. This is for charging the chassis battery only and must be held long enough to give chassis battery enough power to start the engine on its own again. Lithium batteries cannot supply the high amps required by starters.
But as Craig suggests, if you do not desire to have that, your setup will be fine. The new jump starter boxes have made it easy to do without the Aux Start.
I didn’t say it was the best solution, but it is a solution to get power from house to chassis when you need it.
Go camping and enjoy life!

 

[craigav]

This is how I plan to wire mine up. Two items to install which are the SPDT switch (w\center off position (the center off is not shown in my diagram here)) and the DC2DC Charger. With this setup I can turn off all Coach charging from the Chassis (with the switch in the off position), or choose between DC2DC charging or the original setup. I would use the original setup for example when a boost was needed (remember the boost could boost either the generator start or the main engine start), and I would plan to use the DC2DC position most often. This is simply a diagram as where the components are physically installed is another topic. I plan to place the spdt switch next to boost switch which is on the lower left of dash on mine, although I could place the switch under the hood and just open the hood if I need to change the switch position. That may be a better option for others that don't want to drill a switch hole inside the cab.

BTW as mentioned earlier, you don't want to pull too much current out of the Lifep4(s) for the main engine starter and it would be best to allow the chassis battery to build up a charge over ~10 minutes or more.

 

[craigav]

BTW, I haven't verified if the Victron DC2DC charger can use a single "trigger" wire although I believe it can but it may need another ground as well as I only quickly looked at the Victron manual (something to verify if you use this plan).

In the above diagram, only the Solenoid or the DC2DC charger can ever be enabled at any given time, and both will never be on at the same time. ~CA