Yet Another Lithium Conversion and Solar Addition

[Crabcakes-WO]

Hi all! Brand new here, but been a lurker for the last year. My wife and I bought a new 2023 Micro Minnie 2108FBS in December. We will be moving into it full time starting in September as my work will have me on the road constantly and we thought that sounded like “fun”

In the process of getting it ready to be home, I am working on a lithium battery conversion. We’ve worked out our power needs and we’ve settled on some components. HOWEVER, I’ve never really done an electrical project of this proportion, so I thought I would do a write-up so that:

1. I could see all the info in one place
2. If I screw up royally, I have a record of what I did
3. Others might be able to see the process if they’re doing this themselves and,
4. (or 3a) Those who know what their doing might be able to tell me if number 2 above is occurring.

I put some questions I haven't been able to sort out from searching the forums below, in hopes that someone might be able to provide some guidance. So here’s our plan, staring with the components we selected:

• 2x LiTime12v 230Ah Plus LFP Batteries with Low-temp protection
• 1x 400W Lightweight Portable Solar Suitcase (No charge controller)
  [*Progressive Dynamics PD4655V Converter Replacement
• DCC50S 12V 50A DC-DC Battery Charger with MPPT
• ]Renogy ONE Core monitor[/FONT]
  
  108FBS has 190W of solar on the roof. We are hoping that we can utilize the Go Power side port and rewire it to the new MPPT controller to give extra juice for our 460Ah battery bank. We are currently living in (and generally traveling around) Denver, so sunlight is at a surplus all year. I read that the general recommendation is to have 2-3x Watts of solar per battery Ah, but I don’t mind having to fire up our generator to top up if the solar is not quite sufficient.
  
  Battery Install
  The plan is to mount the two LFP batteries into the pass through, up against the interior wall. I plan to wall-mount the DCC50S and monitor to the wall beside them. I’ve found wiring diagrams and have had a look at the wiring, but I am not sure exactly how to physically route the wires into the pass through this quite yet, but I’m sure it’s doable.
  
  Converter Replacement
  With the PD4655V, I know a change in wire gauge is needed, I’ll be replacing the existing wires with 4AWG. I’m assuming this is just the wire running between the battery and the converter, so hopefully this is just a matter of following the wires as they traverse the underside of the TT.
  
  Portable Solar Addition
  This one I’m a bit fuzzy on TT feeds into the batteries, but looking at the forums here it sounds as though it feeds into the solar charge controller. My hope is to replace the existing solar charge controller and feed the existing roof solar AND the side portable into the new unit - making it just a plug-and-play system when we are stopped and the suitcase is deployed.
  
  Does anyone here know how to combine those panels into the solar charger? Is this a matter of attaching both panels to the same terminals of the solar controller? I’d love to avoid a combiner box if possible. I also suspect I’ll need to upgrade the wire coming out of the side port.
  
  Another option I would be happy with is to leave the existing solar controller in place for the roof solar and to utilize the new charge controller for the new portable solar. Is this possible? I'm not really sure how I'd marry them together to both serve the electrical needs of the TT.
  
  DC-DC and MPPT Unit
  I was excited to find this unit that can combine a few functions: solar charge controller and DC-DC charging. It came in a package with the Renogy monitor and the price was right. Less things to mount is a positive for me. I’m hoping a wiring diagram of the junction box will be a self-explanatory “connect this wire here, that wire there”, but I’m prepared for a little struggle.
  
  Until parts arrive, that's where things stand. I'm hoping to get most of the components this week and get started. If you kind folks see things I am missing or have insights into the above, please let me know. Otherwise, I'll provide some updates as things get done.

 

[Crabcakes-WO]

For those keeping score at home, I found what I think is a solid answer to the question of how to connect the solar panels to the battery bank. It seems from other forum posts and from other research, that you cannot wire both arrays into the terminals of the MPPT solar controller. It does seem that it is acceptable to have two charge controllers feed into the same battery bank.

There is some talk about the controllers competing and only one array charging the battery at a time because one controller sees the charging voltage of the other and thinks the battery is full. I found a great youtube video that suggests that might not be the case, linked below. Instead, he suggests that the charge controllers base their "decision" to charge on the internal resistance of the battery.

Either way, I will plan on keeping my existing PWM controller for the roof solar and hook the new MPPT solar controller to the portable suitcase array. If someone has more info on the two controllers and how they work together to charge a single battery bank, I'd love to hear it.

 

[creativepart]

Instead, he suggests that the charge controllers base their "decision" to charge on the internal resistance of the battery.

You are aware that this internal resistance that you speak of is a Lead Acid battery thing, not applicable to Lithium Iron Phosphate batteries, right?

 

[Crabcakes-WO]

You are aware that this internal resistance that you speak of is a Lead Acid battery thing, not applicable to Lithium Iron Phosphate batteries, right?

I am not! But I'm here to learn, thanks for the info.

 

[creativepart]

A key difference between lead acid batteries and LFP batteries is that as LA batteries charge their internal resistance increases dramatically as they reach full charge. LFP batteries do not have this and continue to accept current up to fully charged.

LA battery chargers use this increasing resistance to limit current through the charge cycle. LFP battery chargers do not and they use voltage to end charging.

I’m not saying your two charge controllers will not work and while I’m not experienced with using two separate charge controllers I would think they will work fine together. I’ve certainly seen others that run this kind of system on YouTube.

You will be connecting multiple charge controllers to your LFP batteries regardless of adding the second controller for your portable PV panels. When you are driving the TT down the road your rooftop charge controller will be charging your batteries and your DC2DC charger will also be charging your batteries at the same time. This is perfectly normal and not an issue as both chargers will be aware of the battery’s voltage and charge accordingly.

So having multiple chargers connected to one bank isn’t usually an issue that I’m aware of.

 

[Crabcakes-WO]

A key difference between lead acid batteries and LFP batteries is that as LA batteries charge their internal resistance increases dramatically as they reach full charge. LFP batteries do not have this and continue to accept current up to fully charged.

LA battery chargers use this increasing resistance to limit current through the charge cycle. LFP battery chargers do not and they use voltage to end charging.

I’m not saying your two charge controllers will not work and while I’m not experienced with using two separate charge controllers I would think they will work fine together. I’ve certainly seen others that run this kind of system on YouTube.

You will be connecting multiple charge controllers to your LFP batteries regardless of adding the second controller for your portable PV panels. When you are driving the TT down the road your rooftop charge controller will be charging your batteries and your DC2DC charger will also be charging your batteries at the same time. This is perfectly normal and not an issue as both chargers will be aware of the battery’s voltage and charge accordingly.

So having multiple chargers connected to one bank isn’t usually an issue that I’m aware of.

That is great info, thanks creativepart! I never really thought of the DC-DC and solar as acting as two seperate charge controllers, but it makes perfect sense. Feeling a little more confident in this piece of the project, thank you.

 

[Crabcakes-WO]

Converter Replacement
With the PD4655V, I know a change in wire gauge is needed, I’ll be replacing the existing wires with 4AWG. I’m assuming this is just the wire running between the battery and the converter, so hopefully this is just a matter of following the wires as they traverse the underside of the TT.

I took a look around the TT this morning and have started to feel a bit daunted about replacing the existing 6AWG wire with 4AWG, mostly because it all just disappears under the trailer insulation.



The existing converter is 55amp, and the new one will be, too. Does anyone have any insight into whether the upgrade in wiring is required/recommended? If the existing 6AWG is sufficient on the existing 55amp converter, will it be sufficient with the new converter charging the LFPs?


Am I missing something?

 

[Fred 2106DS]

I took a look around the TT this morning and have started to feel a bit daunted about replacing the existing 6AWG wire with 4AWG, mostly because it all just disappears under the trailer insulation.



The existing converter is 55amp, and the new one will be, too. Does anyone have any insight into whether the upgrade in wiring is required/recommended? If the existing 6AWG is sufficient on the existing 55amp converter, will it be sufficient with the new converter charging the LFPs?


Am I missing something?

Hi Crabcakes,

Good luck on your LFP conversion. I'm not an expert on LFP conversions or charging LFP batteries but here's my take on what you are dealing with using the existing 6 AWG or upgrading to 4 AWG wiring.

Running the charging parameters listed for your Progressive Dynamics PD4655V converter/charger through a voltage drop calculator, you are probably going to struggle to fully charge your LFP batteries when using just the converter/charger.

Here are the results based on the charge parameters of the PD6455 (14.4V@55A). I estimate the wire run between the converter/charger and the batteries to be approximately 20 feet based on the way the 6 AWG wires were run in my 2106DS.

Using the existing 6 AWG you would see 13.5V to 13.6V (6% drop) at the batteries.

Upgrading to 4 AWG you would see 13.8V to 13.9V (4% drop) at the batteries.

...and just for fun, upgrading to 2 AWG you would see 14.0V to 14.1V (2.5% drop) at the batteries.

Based on what I've read none of these options will get your batteries to 100% charge just by using the converter/charger. You will probably see a charge of 95% to 98% if left on charge long enough. It's my understanding to fully charge a LFP battery, you need a minimum voltage 14.2V -14.4V to get that last 1-2% and allow for top balancing. You should be able to accomplished this last 1-2% by using your solar or DC/DC charger.

This is why when I converted to LFP, I mounted my 14.6V chargers within 3 feet of my batteries. This kept my voltage drop to less then 1% using 6 AWG wiring.

 

[No1Hunter]

This is why when I converted to LFP, I mounted my 14.6V chargers within 3 feet of my batteries. This kept my voltage drop to less then 1% using 6 AWG wiring.

Same here. I bypassed the whole converter (actually removed it) and ran my AC up front to an inverter/charger. From the inverter, I ran 4/0 copper cables to my 400ah battery bank through a Victron Lynx Distributor as well as ran AC from the inverter back to the breaker panel. I also used the existing 6awg cable to power the DC section of the 12v distribution panel.

My batteries are charged by the inverter when connected to shore power or generator, two solar charge controllers (one for the 380w roof panels and if used, one for my portables) and a DC to DC charger.

 

[Crabcakes-WO]

Thanks Fred and No1, I think at some point I may end up installing a new converter closer to the battery bank. I may have to look into an inverter/charger down the road.

A few updates since the last. The wife and I decided that an inverter would really improve the quality of life for us while boondocking, so that is going in, as well. I wired a 30amp plug to the frame of the trailer that will eventually be wired to the inverter in the through storage once it is installed, so our shore power can plug into the inverter. Really happy with the result.



Our combo DC-DC charger and solar charge controller arrived today. But I must admit I'm kind of perplexed about the connection from the alternator to the dc-dc charger. I assumed that this would come from the 12v power on the 7-pin connector from my truck, but now that I'm looking into it, I'm seeing people run new 2 AWG cables from their truck battery to a connection near the hitch to plug directly into that.



Is this really how it is done? I assumed that because my truck could charge my trailer before the existing wiring would be sufficient.


I'm second guessing the DC-DC charging altogether. I'm not sure it's THAT important for me to charge while I travel. What do you all think about this? Originally I was going to install the DC-DC charger because I had heard that adding lithium was wrecking alternators, but now that I dive deeper, it sounds like that might just be a motor home issue, not so much a travel trailer issue?


Can anyone help shed some light on this?

 

[No1Hunter]

I'm second guessing the DC-DC charging altogether. I'm not sure it's THAT important for me to charge while I travel. What do you all think about this?

I haven't used mine yet! My DC to DC converter is a Victron 30amp and I ran 6awg from the battery to an Anderson connector receptacle and then another 6awg cable from the converter to the tongue, terminating it with an Anderson connector.

I also install a set of Anderson connectors on the leads to my portable air compressor for adjusting my TT tires. That way, I don't have to turn the truck around and open the hood. I simply plug it into the receptacle at the rear of my truck.

On a side note, I haven't used my generator since upgrading to lithium, but I still take it. I guess it is the Boy Scout in me!

 

[Crabcakes-WO]

I haven't used mine yet! My DC to DC converter is a Victron 30amp and I ran 6awg from the battery to an Anderson connector receptacle and then another 6awg cable from the converter to the tongue, terminating it with an Anderson connector.

I also install a set of Anderson connectors on the leads to my portable air compressor for adjusting my TT tires. That way, I don't have to turn the truck around and open the hood. I simply plug it into the receptacle at the rear of my truck.

On a side note, I haven't used my generator since upgrading to lithium, but I still take it. I guess it is the Boy Scout in me!

I've got a bit of that Boy Scout tendency, too.



It looks like a really clean install. If you park and don't disconnect the DC-DC connector, does it drain your vehicle battery? Or is it smarter than that?

Do you have any thoughts on whether the alternator damage is or is not an issue for travel trailers?

 

[No1Hunter]

My Victron unit auto disconnects if the internal switch isn't hardwired to the vehicle and the vehicle is turned off. You can see the red wire in my picture that goes to the internal switch, but it is not connected to the tow vehicle. I put the 6awg inside solid (not split) wire loom tubing and decided to include the switch wire in it while I was at it. I made the mistake when doing my truck wiring, again inside wire loom, not to include some wire in it for the DC to DC switch. I did the truck before the trailer.

 

[Crabcakes-WO]

My Victron unit auto disconnects if the internal switch isn't hardwired to the vehicle and the vehicle is turned off. You can see the red wire in my picture that goes to the internal switch, but it is not connected to the tow vehicle. I put the 6awg inside solid (not split) wire loom tubing and decided to include the switch wire in it while I was at it. I made the mistake when doing my truck wiring, again inside wire loom, not to include some wire in it for the DC to DC switch. I did the truck before the trailer.

Good to know. At this point, I'm thinking of maybe returning my DC-DC charger. That may be a project for the future. It seems like most of what I'm reading online is that the alternator damage isn't really a problem for TTs.

 

[No1Hunter]

I think it boils down to how much charging you want when moving. I believe I read somewhere on here the plug charging is limited to 10 amps, or less.

 

[Crabcakes-WO]

I think it boils down to how much charging you want when moving. I believe I read somewhere on here the plug charging is limited to 10 amps, or less.

Thanks for the input!


I'm less worried about charging while towing and more concerned about damaging my alternator, but it sounds like its not so much of an issue. The DC-DC charging can be a future project if needed.

 

[creativepart]

I'm less worried about charging while towing and more concerned about damaging my alternator, but it sounds like it’s not so much of an issue. The DC-DC charging can be a future project if needed.

There is a significant difference between alternator LFP battery charging in a motorhome and in a travel trailer.

In a motorhome it is important to protect the alternator from overheating. There is a very direct connection between the alternator and the chassis and house batteries in a motorhome.

However, in a travel trailer the output of the alternator is reduced by the long run of thinner gauge wire between the alternator and the trailer battery. So. The possibility of overheating the alternator is greatly reduced, if not eliminated.

 

[Crabcakes-WO]

There is a significant difference between alternator LFP battery charging in a motorhome and in a travel trailer.

In a motorhome it is important to protect the alternator from overheating. There is a very direct connection between the alternator and the chassis and house batteries in a motorhome.

However, in a travel trailer the output of the alternator is reduced by the long run of thinner gauge wire between the alternator and the trailer battery. So. The possibility of overheating the alternator is greatly reduced, if not eliminated.

Reassuring, thanks creativepart!

 

[creativepart]

By the way, I have the Victron D2D charger setup in my motorhome. It works great but really hasn't been very needed at all. It seems when I leave one campground to travel to another the batteries are not all that low and my solar panels would likely do the job of topping them up while driving.

I guess it's more of an insurance device. In case we're leaving one dry camping spot and heading to another and it's a cloudy/rainy day. A circumstance we have not yet encountered.

 

[Fred 2106DS]

...I'm seeing people run new 2 AWG cables from their truck battery to a connection near the hitch to plug directly into that.

Is this really how it is done? I assumed that because my truck could charge my trailer before the existing wiring would be sufficient.

I'm second guessing the DC-DC charging altogether. I'm not sure it's THAT important for me to charge while I travel. What do you all think about this? Originally I was going to install the DC-DC charger because I had heard that adding lithium was wrecking alternators, but now that I dive deeper, it sounds like that might just be a motor home issue, not so much a travel trailer issue?

Can anyone help shed some light on this?

Yes, You will need to run separate wiring to install a DC/DC charger.

I mainly installed a DC/DC charger to run our 2-way fridge on AC while traveling. To do this I need to run the inverter while traveling and use the DC/DC charger and solar to keep the LFP batteries charged so when we arrive at our destination our LFP batteries are not depleted.

To control the DC/DC charger I tied its trigger wire to the clearance light circuit on the trailer which allows me to turn it on/off with the light switch in the truck.

As far as the DC/DC charger putting undue strain on the trucks alternator, I haven't seen any issues.

Here's a link to my DC/DC install.
https://www.winnieowners.com/forums/f267/micro-minnie-thread-290423-23.html#post3882902