Travel Trailer 24v LiFePo4 / Solar / Charger / Inverter system setup...

[CanadianEH]

Good afternoon fellow solar enthusiasts. I am new to the forum .. please go easy on me!

I am in the process of designing my ideal of grid Solar charger inverter system for my travel trailer. Any help and or guidance would be great. This isnt my first dive into the Solar pool, but I am no expert by any means. We also live in Alberta Canada which is a great solar potential area as we get ALOT of blue sky sunlight and the temperatures generally dont get extremely hot here.

The goal of the system is to allow my family more access to camp at sites and locations which do not have power hookups. My wife enjoys the outdoors as I do, but is a confessed "Glamper" she likes the niceties of home close at hand whenever possible. So far we have kept pretty well to camping at campground but limited ourselves to power only sites. This limits our availability as reservations fill up EXTREMELY fast around here. We have gone a few times using a friends Genny, but neither of us enjoy that. Even the quiet ones are too loud and annoying to turn on and off as required. We usually go for a 3-5 day maximum trip. But have taken a few 2 week hauls in the past. I did some basic calculations and added in about 20% for the unknown to be safe we would be around 3000wh a day. itll likely be MUCH lower. I would like to connect this to my current rv system to run all 110v plugs and the 12v items. as well as allow the 30amp power hook up the ability to charge the batteries when connected to power. ( im a little unsure about this part) The largest draw will likely be a Hair dryer, microwave or coffee maker..

Therefore.. rather than dumping $$ into a generator, I would like to install a system that would be available 24/7 with no noise and no campground restrictions on use ( ie only use between 8am and 9pm)

Here is my basic outline and thoughts on a system to suit the needs. Please feel free to let me know if you see any glaring errors in judgement or components.

Purchased: (from Shenzhen Basen currently enroute)
- 12 x 310ah CATL LiFeP04 cells. Will be used to make a 24v 310ah I ordered 4 extra cells incase of damage etc.. if all end up being good ill make another 12v 310ah battery and set it up for my dads trailer.
- Daly 8s 100a 24v smart BMS
- Daly 4s 100a 12v smart BMS

Ill likely have a buddy 3d print some nice cell holders if anyone has plans or ideas on this that would be great.

Had a friend give me a bunch of 8awg PV wire and mc4 connectors which he had left over.

Need to purchase:
- 2 x 400w Q-Cells Peak duo L-g7.2 Solar panels. ( connected in Parallel)
- Havent decided on flat vs manual tilting mounts yet.
- Victron 100/30 smart solar mppt
- Victron 500a Smart Shunt
- Wzrelb 2000 pure sine 24v inverter
- 24-12v converter

I am forgetting breakers, fuses, shut off switches etc.. as haven't got around to drawing this layout up yet.

Am I missing anything that I should have on that list, ie. for 2 panels in parallel do I need a combiner box?

 

[rmaddy]

Given the specs for those panels, your proposed charge controller might be a bit small. Those two in parallel with a 24V battery will produce over 33A at 25ºC. At -25ºC (you are in Alberta) they can produce over 37A. The Victron 100/50 might be a better choice to put those extra amps to use.

I know Victron's website based MPPT calculator recommends the 100/30 for those panels but their Excel spreadsheet gives the numbers I state above. Note on the website tool that if you click the Calculations button for the recommended charge controller, it is showing the "Max. current @ MPP min. temp." result in yellow because the panels will produce more amps which will just go unused with that controller. I don't know why Victron's website doesn't recommend the next size up.

You might need a combiner box. Someone with better experience can confirm the following - Those panels have an Isc of 9.7A. In 2P that's 19.4A. Multiply by 1.56 for a safety factor and that's just over 30A. Adjust for higher temps and it's slightly higher yet. MC4 connectors are typically rated for 30A.

 

[CanadianEH]

Given the specs for those panels, your proposed charge controller might be a bit small. Those two in parallel with a 24V battery will produce over 33A at 25ºC. At -25ºC (you are in Alberta) they can produce over 37A. The Victron 100/50 might be a better choice to put those extra amps to use.

I know Victron's website based MPPT calculator recommends the 100/30 for those panels but their Excel spreadsheet gives the numbers I state above. Note on the website tool that if you click the Calculations button for the recommended charge controller, it is showing the "Max. current @ MPP min. temp." result in yellow because the panels will produce more amps which will just go unused with that controller. I don't know why Victron's website doesn't recommend the next size up.

You might need a combiner box. Someone with better experience can confirm the following - Those panels have an Isc of 9.7A. In 2P that's 19.4A. Multiply by 1.56 for a safety factor and that's just over 30A. Adjust for higher temps and it's slightly higher yet. MC4 connectors are typically rated for 30A.

Perhaps I missed something?

I did the calculation on both Victron website using all the data off the datasheet which says to use the 100/30, as well as used the calculator on the Explorist.life website (https://www.explorist.life/solar-charge-controller-calculator/) Which says to use the 100/30.

Can you explain the 1.56 safety factor? and you mention that as the temperature goes up the output goes up? Isnt that the opposite? When the temperature decreases the output goes up?

In regards to the mc4 connectors vs combiner box.. if anyone can chime in on this that would be great

 

[Whinny]

With a 2000w inverter there is not much reason to go to a 24v system, smaller wires allowed but 24-12 conversion efficiency offsets that. Your trailer emerg. braking needs 12v as well.
Hard to say on the connections-is 1 panel forward, 1 to the rear,or side by side. are you thinking paralell or series?

 

[CanadianEH]

With a 2000w inverter there is not much reason to go to a 24v system, smaller wires allowed but 24-12 conversion efficiency offsets that. Your trailer emerg. braking needs 12v as well.

I figured id go with a 2000 watt as I dont really need anything higher. I believe the highest draw would be a hairdryer at around 1500w. I am not looking to run air conditioner or anything of the like.

Please do correct me if I am mistaken.. but If I go with a 12v system, wouldn't I need to to size up the wires and every other component? the cost escalates pretty quickly. I would need to jump into a victron mppt 150/60 which alone is almost triple the price of the victron 100/30

In regards to the electric brakes, are they not run off the connection to my trucks battery and brake controller?

 

[rmaddy]

Perhaps I missed something?

I did the calculation on both Victron website using all the data off the datasheet which says to use the 100/30, as well as used the calculator on the Explorist.life website (https://www.explorist.life/solar-charge-controller-calculator/) Which says to use the 100/30.

Can you explain the 1.56 safety factor? and you mention that as the temperature goes up the output goes up? Isnt that the opposite? When the temperature decreases the output goes up?

In regards to the mc4 connectors vs combiner box.. if anyone can chime in on this that would be great

I pointed out the issue with Victron's MPPT website calculator. Again, click on the "Calculations" button for the recommended 100/30 controller. Download their Excel spreadsheet and enter your panels and plug in your setup. You can see so much more detail.

When you look at the spreadsheet calculations tab you can see that the PV current goes up with temperature. But at the same time the voltage and current at the battery go up with decreasing temperature.

See https://diysolarforum.com/threads/pv-array-breaker-switch-size.15212/ for an explanation of the 1.56. The whole thread is relevant for you but posts 6 & 7 address that specific question.

 

[Whinny]

The running brakes do, but the breakaway switch requires a power source if the trailer becomes disconnected.
Sorry didn't see you stated panels in parallel, The only fusing/wiring that needs to be bigger is the inverter to battery and controller to battery. But yes, you would have to upgrade the controller or use 2 smaller ones...

 

[rmaddy]

With a 2000w inverter there is not much reason to go to a 24v system, smaller wires allowed but 24-12 conversion efficiency offsets that. Your trailer emerg. braking needs 12v as well.

The 12V needed by the trailer brakes should be coming from the tow vehicle via the 7-pin connector, not the trailer's house electrical system.

I'm building a cargo trailer camper conversion. It's a 24V setup with only a 2000W inverter. All components are cheaper. All wiring is smaller and cheaper (and lighter). The water pump, fridge, and all lights are 24V. The only 12V components are the ceiling fans and the 12V power sockets. The trailer's brakes and taillights get their power from my tow vehicle and the little 12V battery on the tongue that came with the trailer. That's all separate from the electrical system I'm adding to the trailer.

 

[John Frum]

I suggest you leave the 7 pin tow cable including the breakaway separate and isolated.
The breakaway needs a battery btw.

 

[ereams65]

Usually the brakes are tied into the camper's battery. It's a safety protocol in the event the trailer comes disconnected from the truck, all the stopping power is applied to the brakes.

 

[John Frum]

Usually the brakes are tied into the camper's battery. It's a safety protocol in the event the trailer comes disconnected from the truck, all the stopping power is applied to the brakes.

Its my understanding that this usually destroys the battery in the process.

 

[CanadianEH]

OK, gotcha. The break away I will keep connected to the 12v power.

 

[CanadianEH]

I pointed out the issue with Victron's MPPT website calculator. Again, click on the "Calculations" button for the recommended 100/30 controller. Download their Excel spreadsheet and enter your panels and plug in your setup. You can see so much more detail.

When you look at the spreadsheet calculations tab you can see that the PV current goes up with temperature. But at the same time the voltage and current at the battery go up with decreasing temperature.

See https://diysolarforum.com/threads/pv-array-breaker-switch-size.15212/ for an explanation of the 1.56. The whole thread is relevant for you but posts 6 & 7 address that specific question.

So.. End result just size up to the 100/50 as I am slightly over paneled? i have the potential to be creating power with nowhere to go with the 100/30

 

[rmaddy]

So.. End result just size up to the 100/50 as I am slightly over paneled? i have the potential to be creating power with nowhere to go with the 100/30

That's my understanding of the numbers. I just went through this for my own setup. Victron's website was recommending the 150/35 for my panels (3 330W in series). But the spreadsheet showed my panels would be producing more than 35A in cooler temps. Your panels could produce over 30A in warm temps (and more in cold). Apparently the smaller controller will just "ignore" the extra amps and work safely. But to me it seems a waste to throw out the extra amps. But maybe with the reality of actual numbers due to sun angle, shading, etc., you'll never quite reach those higher amps so maybe you'll never actually break 30A. Your setup is close so it's a question of whether you want to spend the extra $100 for the 100/50.

 

[Whinny]

Trailer breakaway won't hurt the batteries, it should be tested occasionally as well. Total current for a 4 brake system is around 16amps.There is no fusing allowed in the circuit, there is debate as to whether a BMS is allowed in it. I would like to know the answer...
Some RV's on this site are running a lead battery for the 12v stuff and charging it if required with the existing converter through the inverter
There are other high quality options to Victron controllers.....

 

[CanadianEH]

Trailer breakaway won't hurt the batteries, it should be tested occasionally as well. Total current for a 4 brake system is around 16amps.There is no fusing allowed in the circuit, there is debate as to whether a BMS is allowed in it. I would like to know the answer...
Some RV's on this site are running a lead battery for the 12v stuff and charging it if required with the existing converter through the inverter
There are other high quality options to Victron controllers.....

Safety redundancy isnt the worst idea, ill have it connected to 12v anyways in one way or another...

Even though my thinking would be that if my trailer hitch somehow disconnected, the chains would still be attached holding the trailer and 7pin to the truck but would likely pop the Ebrake break away, at least until the whole thing flipped and the brakes wouldn't matter anyways.

 

[Whinny]

It's a requirement-all trailers have to have a breakaway.....

 

[HRTKD]

When the tow vehicle's brake pedal is applied, the power at the trailer brakes is coming from the tow vehicle.

Should the trailer's breakaway cable get pulled, all power applied to the trailer brakes comes from the 12v power source on the trailer. The 7-pin cable has nothing to do with the breakaway system.

I have separate 12v systems on my trailer. The breakaway brake is connected to a 12v battery on the tongue of the trailer. @Whinny is correct that the breakaway will consume about 16 amps. It depends on system though. 12 amps is usually called for as a minimum on a dual axle setup.

@CanadianEH, a 24v system isn't warranted based on your requirements. All you're doing by going 24v is making for a more complicated system.

 

[CanadianEH]

When the tow vehicle's brake pedal is applied, the power at the trailer brakes is coming from the tow vehicle.

Should the trailer's breakaway cable get pulled, all power applied to the trailer brakes comes from the 12v power source on the trailer. The 7-pin cable has nothing to do with the breakaway system.

I have separate 12v systems on my trailer. The breakaway brake is connected to a 12v battery on the tongue of the trailer. @Whinny is correct that the breakaway will consume about 16 amps. It depends on system though. 12 amps is usually called for as a minimum on a dual axle setup.

@CanadianEH, a 24v system isn't warranted based on your requirements. All you're doing by going 24v is making for a more complicated system.

Do you mind to elaborate on why?

One of my requirements is lower cost. 12v seems more expensive for everything, from wiring to charge controllers etc.

 

[HRTKD]

Do you mind to elaborate on why?

One of my requirements is lower cost. 12v seems more expensive for everything, from wiring to charge controllers etc.

When you put in a 24v system you now need adapters to handle both 12v output and 12v input. That right there adds cost for the adapters (converters, chargers, whatever you want to call them), cost for the wires, lugs, heat shrink, etc.

Since you do not have a generator, I'll assume you don't have a fifth wheel trailer. The landing gear and leveling systems in a fifth wheel have very high amp loads. A travel trailer may have a powered tongue jack. My tongue jack has a rated 25 amp draw. Your 24v-12v buck converter needs to be rated for at least that amount. With wiring distance from the LiFePO4 battery to the tongue jack the amp draw may be even higher.

That buck converter isn't 100% efficient so you have to take that into account. It also has a standby draw. It isn't much, but over time, it could draw down your LiFePO4 battery bank. But you say you'll put in a switch to turn off the buck converter when it isn't needed? Fine, more complexity, more wiring, more work, more expense. Oh, and you'll need to instruct everyone that uses the trailer on what that not so little switch does. Don't forget that the switch needs to be rated for the same amps as the converter.

To charge the LiFePO4 battery bank from the tow vehicle, you'll need a 12v-24v DC-DC charger. The naysayers will point out that you'll need a DC-DC charger even in a straight 12v system and they are correct. However, you need a slightly more complicated DC-DC charger that most likely is more expensive because it's a boost converter to go from 12v to 24v.

The same issue comes up with the AC-DC converter. You need a new one that supports a proper LiFePO4 charge profile, but you also need one that is 24v. Just for giggles, I compared two IOTA Engineering AC-DC chargers. 45amp 12v and 25amp 24v. Prices on Amazon are $150 and $225, respectively. I didn't look too hard, so those prices may not be good examples. But you get the idea.

I have a Victron 100/50 MPPT solar charge controller connected to my 640 watts of solar on the roof of the RV. The controller can handle more watts if the system was 24v, but I don't have room on the roof for more panels. So it's a good fit for a 12v system.

24v sounds sexy. The added complexity is not.