Researching and going to build an RV Solar system.

[DIDDLYV]

I am researching putting a solar system on my Elkridge Extreme Light E282 Fifth Wheel.

Planning on building my lithium battery 12 v 280 or 270 ah cells with 4s 2p configuration. with a 250 or 300 amp daly bms. Will be putting in a 3000 inverter onto the system. I may possibly use the vitron energy 3000VA multiplus as i rather like its ability make up current when driveway surfing off a 15 amp circuit to allow AC to be run etc. Looking at 4 210 watt solar panels wired 2s 2 p with a 100 50 Amp solar controller.
I am reticent to build a 24 volt system as I would have to not only step down the 24 volts to power all the 12 volt systems for the rv but also step up the 12 volt charging circuit from the tow vehicle from 12 to 24. Given the rather short distances I will have from the battery bus to the inverter/converter the heavy cable will not be that much of a problem.

Am I heading in the right direction?

 

[geoffire]

Sound very similar to the path I'm on. Right at the boundary of what still makes sense for 12v. I keep going back and forth, but 12v is I believe the better answer. Sure have to upsize or multiply the electrical items to get the required current capacity, but it's simpler and 12v is just so much more common that if there are issues while on the road it would be easier to find replacements.

 

[geoffire]

How were you planning on solving the charging from alternator problem? That's the vexing one for me. I almost convinced myself to just order a pair of Orion-Tr Smart 12/12-30's today and be done with it, but I kind of want to DIY some sort of current limiting/alternator saving device.

 

[DIDDLYV]

Leaving the system 12 Volt there should not be an alternator problem will there be one?

 

[HRTKD]

Leaving the system 12 Volt there should not be an alternator problem will there be one?

Direct charging of LiFePO4 from the alternator (through the 7-pin connection) is generally discouraged. The LiFePO4 battery can draw more than the 7-pin circuit is often fused/relayed for. The charge profile isn't ideal either.

The solution is to put in a DC-DC charger. However, don't forget that your trailer's breakaway brake system still needs to get power from the battery bank.

 

[geoffire]

Well, that's a ~540ah low internal resistance battery you got there. If you hook that directly up to your vehicle alternator if it doesn't pop a fuse or melt a wire it will almost certainly overheat and fry the alternator as it will pull a nearly unbounded amount of current. Then if the system did somehow manage to survive it would overcharge the batteries (the BMS limits are best as a safeguard, not the main overcharge protection). As your in a trailer such as that you want you might want to isolate the grounds as well (I'm no expert there).

After looking at the options I'd suggest the Orion-Tr DC-DC Converters. You can get them isolated or non-isolated (cheaper) and you can run a bunch of them in parallel to get the power you want. They are actually reasonably priced (for Victron) as well. The smallest one can just about work through the 7-pin, but likely needs a 25A fuse.

 

[the_colorist]

If you're going with Victron, 12V makes the most sense generally, cheaper overall IMHO. And if you're able to get discount on components from myself or another installer/dealer, that will help as well.

 

[the_colorist]

To second what is said above, you definitely need a DC-DC that is programmed for LFP to charge the house bank. How precisely the charging is controlled will have an impact on the lifespan of your bank.

The Orion definitely will work but they don't have VE.Direct (Victron knows this) so you lose DVCC (Distributed Voltage Current Control) and monitoring which would enable more precise charging. But again, they do work.

If you are using a REC BMS, I would recommend looking at Wakespeed. The configuration would be much more advanced for lead starter+lithium house bank but also more ideal in the long run with alternator protection etc.

The main issue you would have is wiring the CAN communication between the fifth wheel and the host vehicle.

 

[geoffire]

The question is how seriously you need to charge from alternator. A few hundred watts just throw on a DC-DC or two. If not open your wallet wide!

 

[geoffire]

they don't have VE.Direct (Victron knows this) so you lose DVCC (Distributed Voltage Current Control) and monitoring which would enable more precise charging.

I was looking at that. I'd love something like the Smart BMS CL 12/100, but don't run Victron batteries.

 

[DIDDLYV]

One should think with a Solar system and the RV being stored a lot more than it is used generally when I hook the vehicle to the trailer the 540ish AMP battery will be fully or nearly fully charged at all times, is that still going to draw a ton of current and potentially damage the alternator of the dodge ram 3500 tow vehicle. Not trying to be argumentative rather wanting to be educated.

 

[geoffire]

One should think with a Solar system and the RV being stored a lot more than it is used generally when I hook the vehicle to the trailer the 540ish AMP battery will be fully or nearly fully charged at all times, is that still going to draw a ton of current and potentially damage the alternator of the dodge ram 3500 tow vehicle. Not trying to be argumentative rather wanting to be educated.

If you don't really need it then don't hook it in. If you find you need just some then add a little DC-DC charger. Hooking it in without any sort of current limiting is asking for trouble. You might be able to get away with that with a battery Ah < alternator amp output capacity, but you're way beyond that.

 

[the_colorist]

I was looking at that. I'd love something like the Smart BMS CL 12/100, but don't run Victron batteries.

A buck-boost DC-DC with current-limiting stepping voltage up into a SCC is an idea. Needs to be done carefully tho, several things to consider. Disconnect the DC-DC or disable the SCC when the engine is off etc. A few ways to do that correctly.

One should think with a Solar system and the RV being stored a lot more than it is used generally when I hook the vehicle to the trailer the 540ish AMP battery will be fully or nearly fully charged at all times, is that still going to draw a ton of current and potentially damage the alternator of the dodge ram 3500 tow vehicle. Not trying to be argumentative rather wanting to be educated.

Yeah you definitely still need a DC-DC to prevent the low internal resistance of the LFP over loading the alternator and to prevent the alternator from ruining the lithium bank. It's a common issue. Check this out:

DIY LiFePO4 Batteries On Boats - Marine How To

DIY LiFePo4 On Boats Last edit;3/26/23:The base of this article was written a number of years ago (2010) but this does not mean the information here is outdated. We have been keeping it updated and have added to it when ever we had the time. This article deals

marinehowto.com

 

[HRTKD]

One should think with a Solar system and the RV being stored a lot more than it is used generally when I hook the vehicle to the trailer the 540ish AMP battery will be fully or nearly fully charged at all times, ...

This is why my LiFePO4 battery bank receives no charge from the tow vehicle. So far, there simply is no need for it. The PV satisfies 100% of the charge in storage just fine.

 

[k3nny]

For a 5ver with enough PV on the roof I second @HRTKD approach. Just leave the alternator out of the equation. On a Sprinter or anything with limited mounting options ( or briefcase solar ) I'd bring the alternator back into the system. I suppose if you don't get enough sun where you are at it might also make sense to charge up the batteries while you are on the road. For my personal rig I'd try it without it and see if it's necessary.

 

[HRTKD]

I've stated it elsewhere and I'll state it again here (just to add more confusion and further the discussion), I think the Victron test was deeply flawed and represents the height of spreading FUD (Fear, Uncertainty and Doubt). Shame on Victron for this. I expect better of them.

1. 70 amp alternator
2. Pulling 65 amps
3. No external air flow

Pushing a dinky alternator at its limits with no air flow? Sure, it's going to smoke. Run that same test on my F-350 (397 amp alternator setup) while on the road and I suspect my truck would just laugh.

I don't disagree with the idea that a LiFePO4 battery can suck the living daylights out of an alternator. Charging a LiFePO4 battery at idle, where the RPM of the alternator is low and airflow from the engine's fan could be non-existent is certainly not a good idea.

I simply disagree with the testing method used by Victron. Switch to a 180 amp alternator, add a fan to blow air across the alternator and I think the results would be unspectacular. I also find it very suspicious that Victron turned off comments for that video.

 

[Q-Dog]

I don't see the test as flawed at all.

The alternator has a built in fan. That's why it overheated at low RPM and not at high RPM. And air circulation inside an engine compartment is not guaranteed at low RPM.

 

[Cdkipp]

Hi, I am a Fulltime Rver in my sixth year with Lithium. My advice will sound an awful lot like HRTKD's.

1. I do not use my truck charging even though I have an F350 with two heavy-duty alternators. Could I? I think so but with solar you really don't need it. If I did I would use a dc-to-dc to control the amp draw. Redarc is known for making a product. https://redarcelectronics.com/
2. I started with a Magnum hybrid inverter 3012 (I love the power-sharing function). After 5 years I added another Magnum inverter the 4024. If I was starting over today I would probably go with a 24 volt system and maybe to a 48. The wiring size, efficiency, is just so much better. You can run your 12 volt system using one or more of these guys. https://www.victronenergy.com/dc-dc-converters/orion-dc-dc-converters-12v-24v-48v-110v

 

[DIDDLYV]

It may make sense to go 24 volt and I may do that if I end up with 800 100 watt panels current thinking is going 4 210 watt pannels 2s 2p to avoid shading issues. I guess my first decision will be what to do with the Batteries. I could build 2 12 volt batteries and use 2 controllers or will probably do a 2p 4s single battery with the 8 cells in 4 parallel groups run in series with on 250 or 300 amp controller. That set up will be approx 7 x 21 inches and fit in my current battery compartment albeit with a different battery box than the current group 27 lead acid battery

 

[k3nny]

North of 800 watts of PV you start to see some savings going 24V and stepping down 12V where needed. I might stick 12V at 800-ish and keep it simple. If you think you will want more PV then I'd go ahead and make the switch to 24V. If you can run the rig and bank happily on 800 then stick with 12V. It totally depends on how much you think you will use / need. Since your bank is DIY you can configure it both ways with a change in the BMS or use an external BMS that can do both.