Installing a DC2DC on engine bay?

[GeekyGuy]

I've decided to go with LiFePo4 batteries. 2x100A Group 24, they are a direct replacement and fit perfectly.
I also am installing a Renogy 20A DC2DC charger.
I'm looking for a location to install said charger.
It looks like the engine bay, close to the existing BIM would be a good location: ability to use the existing wires for IN & Out, and the ignition control. There is not much space in the battery compartment under the stairs, rewiring would be required.
Has anyone installed a charger in engine bay on their Class C? Any comments or suggestions?
Thank you.

[Camper_bob]

Sub'd for content! I may be considering something similar...

[dvspl]

I haven't put one in the engine bay, seemed too crowded there already to me. I put mine on the forward wall of the compartment just behind the entry steps. Easy to re-route the wire and very close to the batteries.

[GeekyGuy]

Originally Posted by dvspl

I haven't put one in the engine bay, seemed too crowded there already to me. I put mine on the forward wall of the compartment just behind the entry steps. Easy to re-route the wire and very close to the batteries.

Well that is good info - I may have sufficient space too there, will see.

Guess I'm confused with the +&- IN and OUT needed for the charger and wonder if they're easy to identify. Can I simply connect both Neg- to the chassis ground or are all required cables there?

I know the Yellow taped one is to the converter, one to the genny and one to the solenoid/chassis battery.

[dvspl]

Originally Posted by GeekyGuy

Guess I'm confused with the +&- IN and OUT needed for the charger and wonder if they're easy to identify. Can I simply connect both Neg- to the chassis ground or are all required cables there?

I know the Yellow taped one is to the converter, one to the genny and one to the solenoid/chassis battery.

What I did is move the positive 4 AWG wire that comes from the aux start solenoid to the positive input on the charger. On my 2020, that wire shared a battery terminal with the 4 AWG wire with yellow tape that comes from the battery disconnect solenoid. So I had to separate them. Then I added a 4 AWG wire from the charger positive output to the battery. All of the negatives go the chassis ground. I found an existing ground right behind the steps that was easy to tie into. If you're not planning to add solar, there is also a solar prep package in that same compartment (behind a panel) and you could use those wires to connect from the charger to the battery. If you don't have an electrical schematic for your coach, you should ask for one here: https://www.jayco.com/contact-motorized-service/ That made the wires easy for me to identify.
Also, for convenience, I mounted the charger along with input and output circuit breakers on a piece of 1/2" plywood and then mounted that plywood on the forward wall of the compartment. Cut a small hole through the compartment inside wall to route wires through.

Edited to add: hooking up the charger this way will make your aux start solenoid non-functional as the DC-DC charger will only take power from it, not capable of providing power to it. So I carry a small lithium jump box that I can use if I need help getting the motor started.

[GeekyGuy]

I already have solar. I also did get my schematics from Jayco for my unit.

You gave me enough info to get started, I appreciate this very much.

I'm OK losing the Button under the dash functionality, as I don't think I'll ever need it, as my solar always tops the chassis battery off. I even read of some who removed the solenoid and just connected both wires together.

Best regards

[Camper_bob]

Originally Posted by GeekyGuy

I already have solar. I also did get my schematics from Jayco for my unit.

You gave me enough info to get started, I appreciate this very much.

I'm OK losing the Button under the dash functionality, as I don't think I'll ever need it, as my solar always tops the chassis battery off. I even read of some who removed the solenoid and just connected both wires together.

Best regards

Wouldn't you then run the risk of depleting the chassis battery?

I mean, I know that with a solar install, and/or plugged in there really isn't a high risk, but it could happen, right?

[GeekyGuy]

Originally Posted by Camper_bob

Wouldn't you then run the risk of depleting the chassis battery?

I mean, I know that with a solar install, and/or plugged in there really isn't a high risk, but it could happen, right?

The DC2DC is a 1-way device, the current only flows to the house battery, only when the engine is running, so I don't see how it could deplete the chassis battery... Or am I missing something?

[Camper_bob]

Originally Posted by GeekyGuy

The DC2DC is a 1-way device, the current only flows to the house battery, only when the engine is running, so I don't see how it could deplete the chassis battery... Or am I missing something?

No, I'm probably missing something.

Perhaps then it would be required to take the solenoid out of the system?

The entire purpose of that solenoid is to connect the house and chassis batteries temporarily. I have a device installed on mine that will read the voltage on either side of that solenoid, and will open/close it as required. This keeps one battery from killing the other, but still allows the house battery to be charged through the alternator, and the chassis battery to be charged through the converter.

If you close that circuit permanently, the batteries would be effectively connected.

But that's completely ignoring where the DC2DC charger exists in the circuit, and whether it will allow current back to the chassis battery from the house battery/converter.

If that's the case, I'm probably not going to be installing a DC2DC charger, and would install a Li-BIM in place of the solenoid instead... I want/need the chassis battery to get a charge from the house somehow. I don't care so much about the solenoid/button connecting them since I carry a jump pack, but because all batteries are always being charged from somewhere, I've never needed it.

[GeekyGuy]

Yep. I hear you.

I was confused as well.

In my many year's of RVing I have never had truck battery issues. Also my solar panel charges both the coach and chassis batteries, that gives me comfort.

I'd rather have an automated charger start/stop charging as needed than the rather manual LiBIM 40 min ON, 20 min OFF idea. That is what had me go with a DC2DC.

Not Installed yet, at the planning stage still ��

Balancing my 2 LiFePo4 right now.

Always open to ideas and suggestions.

[Camper_bob]

That's the same reason I'm even considering a DC2DC charger. I don't like on/off, non-"smart" charging anywhere.

But since I don't have solar panels, it doesn't look like I have a lot of choice?

My chassis battery is very likely to discharge to flat in storage if I can't figure a way for it to charge from the converter... I mean, I could put in some kind of disconnect? But that's not an optimal solution either...

[craigav]

Just for thoughts, the very simplest solution would be to replace the 100A solenoid under the hood with the DC2DC charger as every wire you need is already there. I looked at mine and I don't recall right now but I believe with the solenoid removed there is enough room to place the DC2DC charger there and if not there was a couple places nearby that would also work but you would need to extend the wires a foot or so. Doing this will not keep the chassis battery charged though, but then again neither did the factory setup. If I was to go this route I would likely permanently wire in a trickle charger for the chassis battery. As it is now, I use a waterproof marine charger maintainer to keep the chassis battery charged although it is not permanently wired in.

I had considered installing a Single Pole Double Throw Switch which would allow me to switch from the factory setup (keeping the aux start) to the DC2DC charger (one or the other at a time), along with a center off (so no chassis to coach charging in that position). I would have to look and see if I still have that drawing, it is not all the complicated really but would require installing a switch next to the aux start switch and running a couple of wires. ~CA

[GeekyGuy]

Originally Posted by craigav

Just for thoughts, the very simplest solution would be to replace the 100A solenoid under the hood with the DC2DC charger as every wire you need is already there. ..... ~CA

That was my idea to start with - also I could use the Aux start switch wiring to connect the DC2DC D+ post to turn it off if I wished.

Food for thought. Wow, all great feedback.

THANKS

[Camper_bob]

I agree, great feedback!

My goal is to keep this as "passive" as possible. I don't want to have the potential to forget a switch here or there. And while I'm perfectly capable of doing so, I don't feel like laying in additional circuits or re-wiring a bunch of things.

That's the attractive part about a Li-BIM in my case. I can get away with JUST replacing the solenoid, wire for wire (mostly), with the Li-BIM. Then the only disadvantage is that the charging that happens through the BIM is not "smart", it's just "on/off"...

It probably wouldn't be terribly difficult to plug in/hard wire a float charger though... I like that idea. I have Noco Genius installed in my YJ and my boat...

But thinking about all of this, and some of the other things I would like to accomplish is leading me down a very dangerous rabbit hole...

[craigav]

I had mentioned last that the simplest thing to do would be to change out the charge solenoid with a DC2DC charger however, and to circle back around, the absolutely easiest thing to do is do nothing. You may find as I did that doing nothing still allows for the LifePo4 battery and everything already in place to work very well and I have years of time now to base this comment on. I don't remember exactly what the charge current was with doing nothing (maybe I will test again in the near future) but I do remember it was lower than what many on the internet claimed it would be (seems like I remember ~40 amp with a very low LifePo4 battery).

With doing nothing, I would still highly recommend using a dc clamp style ammeter and to verify the charge current, I had a helper throttle up the rpm while testing. I suspect the reason the charge current wasn't all that high is for two reasons, first being I only have installed a single 100ah LifePo4 and that the charge voltage was around 13.8 volts. ~CA

Another thought to add, by not fully charging a LifePo4, it will last a lot longer and while many may not know this, a 12V LifePo4 will still become fully charged even at 13.8 volts although it takes longer and more often it will be less than 100% charged but still very close, perhaps 80~90% and because you can safely run it down completely, it will have more usable capacity than a 100% fully charged 100ah lead acid battery (assuming you don't fully discharge the lead acid battery as commonly recommended to only discharge it to 50% max, or 50Amps).

[Camper_bob]

Originally Posted by craigav

I had mentioned last that the simplest thing to do would be to change out the charge solenoid with a DC2DC charger however, and to circle back around, the absolutely easiest thing to do is do nothing. You may find as I did that doing nothing still allows for the LifePo4 battery and everything already in place to work very well and I have years of time now to base this comment on. I don't remember exactly what the charge current was with doing nothing (maybe I will test again in the near future) but I do remember it was lower than what many on the internet claimed it would be (seems like I remember ~40 amp with a very low LifePo4 battery).

With doing nothing, I would still highly recommend using a dc clamp style ammeter and to verify the charge current, I had a helper throttle up the rpm while testing. I suspect the reason the charge current wasn't all that high is for two reasons, first being I only have installed a single 100ah LifePo4 and that the charge voltage was around 13.8 volts. ~CA

Another thought to add, by not fully charging a LifePo4, it will last a lot longer and while many may not know this, a 12V LifePo4 will still become fully charged even at 13.8 volts although it takes longer and more often it will be less than 100% charged but still very close, perhaps 80~90% and because you can safely run it down completely, it will have more usable capacity than a 100% fully charged 100ah lead acid battery (assuming you don't fully discharge the lead acid battery as commonly recommended to only discharge it to 50% max, or 50Amps).

Thank you Craig,

You put this in my other thread on the topic, and I really appreciate this, and am glad you included it here.

Keeping me near the top of the rabbit hole is much appreciated!

[GeekyGuy]

Originally Posted by craigav

.... first being I only have installed a single 100ah LifePo4 and that the charge voltage was around 13.8 volts. .

I installed my 2 x 100Ah LiFePo4, but have not received my DC2DC charger to install, Renogy had a sale, will only ship next week.
So I may measure the current flow to see if doing nothing would work... Clearly that would be an easy solution.

Thank you.

[Camper_bob]

Am I looking at this right? If you have solar panels, then doing nothing between the alternator and the batteries is more likely to be an option. Your batteries will not demand high current from the alternator, right? I mean the BMS on the batteries themselves will regulate charge current, and if they don't need it (because they're staying charged up through the panels), they won't ask for it, right?

Personally, I'm nervous enough considering running just one 100AH lithium in the system, 2x would make me even more nervous. I don't need to be burning up an alternator...

But then I guess I'd be in a similar situation? I'm almost always plugged into shore power (even in storage), so my battery should always be relatively well charged, and wouldn't necessitate a lot of amperage from the alternator. I guess then I might just be worried if I was in a position to discharge the house battery significantly...

[craigav]

For many electrical issues with an RV you really need to purchase one of these. (not necessarily this one, just that it showed up first on my search, just be sure DC is listed for measuring amps). A meter is the only way to determine how much output from your alternator and chassis battery is being supplied to the coach battery. You would set this for DC and clamp the cable at the disconnect solenoid and measure the current. Have someone help by increasing the rpm ~2500 rpm to make sure you are measuring the full alternator output.

A LifePo4 battery BMS does not regulate or control the charge current. It will disconnect the battery at the extremes of over charge or if the battery is extremely low. This is a protection feature and not a control feature.

A fully charged LifePo4 will not pull any charge current, this concept is similar to having an air pump that can only produce 45 psi and the tire already has 45 psi in it. When the LifePo4 battery is low for example 12V, then the engine alternator will commonly output 13.8 (some more than that) and the current will flow into the coach battery. The amount of current that flows is based on the resistance (nothing you need to measure) which is basically speaking how easy can the current flow. In this case the wiring itself from the front of the RV to the Coach battery(s) will offer some resistance as well as the battery itself. LifePo4 batteries however have very low resistance which means they will often pull as much current as they can compared to a lead acid battery so for the most part it is the wiring itself that keeps the current low enough to not be a concern. Also, in the charge circuit are circuit breakers (I believe 80A but perhaps 60A, I don't remember off hand) which will prevent the alternator from outputting more than that for any extended period of time. When the wiring is capable though a LifePo4 can overwhelm an alternator and the wiring which is why it is important to have such a meter as I described.

Just to add, two batteries have less resistance than one, so with two it is more likely to have a higher charge current than with one battery, however it still may be low enough not to be a concern.

Also, if you follow this guidance, do so with the Battery(s) not fully charged (perhaps around 50%) otherwise you can't measure the maximum charge current. If you find the charge current to be over 60~70A or there about, then you should move forward with other options such as a DC2DC charger. ~CA

[Camper_bob]

Yeah, I definitely need one of those. I hate the thought of guessing how many amps are going where...