Airstream Basecamp LiFePO4 Conversion System Feedback

amm

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Hi All,

Just starting my build design for our new Airstream Basecamp 20x. The trailer already has 180W of solar on it but I want to convert from AGM to LiFePO4... See attached diagram as my starting point. I think I still need to add some fuses for protection. I plan on putting in an inverter charger to be able to use the AC outlets from the battery. I also plan on connecting the inverter output into the existing converter charger. Should I disconnect the converter portion of the converter charger since it will always see AC power and convert? Anything else major that I am missing?
 

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HRTKD

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If you're going to buy the Multiplus then you don't need the converter. You can leave the converter in place if you want, but you will want to disconnect both the AC and DC wires attached to the converter. If the converter is on a dedicated breaker then you can just turn off the breaker and put a label on it telling people to leave it off.

If you're going to stick with 180 watts of PV then that solar charge controller is way overkill. Use the Victron MPPT Calculator to find a solar charge controller that is more appropriately sized for that PV.

 

Rocketman

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How many watts is the microwave? Is it also a convection oven? That is usually the largest single item and you need to make sure you have the watts to run it plus a little left over.

The Victron 12/2000 max watts are 1600 and if it gets to 104 degrees F it will derate to 1400w and hotter it will be down to 1100 watts.

A couple of other items I have found useful…

Victron Smart Battery Protect - just before your fuse box. That way if something gets left on - it shuts down the 12v loads at ____(you pick) voltage. That way you can stop most loads at around 10% to 15% of battery - instead of waiting until the bms stops at 0%.

Victron Dc-Dc isolated charger. (You will need the isolated one). This way the alternator is charging up between campsite.

Batteries. You have chosen a great (but expensive) battery. Will they be mounted indoors?

Wire and fuses. A class T fuse on positive wire next to the Smartshunt and a high quality on/off switch to power down the system.
You will also want fuses on the wire going to the mppt and the fuse box (rated for the wire size). Also a circuit breaker or switch between the mppt and the panels. (So you can turn the sun off).

Good luck
 

amm

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If you're going to stick with 180 watts of PV then that solar charge controller is way overkill. Use the Victron MPPT Calculator to find a solar charge controller that is more appropriately sized for that PV.
That is the charge controller that came on the trailer. Not sure I will upgrade the solar on the rooftop yet but I do have 3x200W renogy suitcases that I run through a bluetti AC200 to provide power to the trailer (left from my old setup).

How many watts is the microwave? Is it also a convection oven? That is usually the largest single item and you need to make sure you have the watts to run it plus a little left over.

The Victron 12/2000 max watts are 1600 and if it gets to 104 degrees F it will derate to 1400w and hotter it will be down to 1100 watts.

A couple of other items I have found useful…

Victron Smart Battery Protect - just before your fuse box. That way if something gets left on - it shuts down the 12v loads at ____(you pick) voltage. That way you can stop most loads at around 10% to 15% of battery - instead of waiting until the bms stops at 0%.

Victron Dc-Dc isolated charger. (You will need the isolated one). This way the alternator is charging up between campsite.

Batteries. You have chosen a great (but expensive) battery. Will they be mounted indoors?

Wire and fuses. A class T fuse on positive wire next to the Smartshunt and a high quality on/off switch to power down the system.
You will also want fuses on the wire going to the mppt and the fuse box (rated for the wire size). Also a circuit breaker or switch between the mppt and the panels. (So you can turn the sun off).
Microwave is 1150 input watts so I am guessing I just need to keep that compartment coolish... For the DC-DC charger I was going back and forth on it. Since it is only 20A that should work with existing 7pin wiring? I would prefer not to have to run a dedicated line from the TV (2017 F150) battery/alternator. Battery will be located in the existing battery compartment inside the TT.


Thanks for the inputs, they really help.
 

amm

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Also since max wattage is 1600 for the inverter I was thinking a 200A fuse would be sufficient. Peak power of the inverter is actually 4000W I'm not sure the characteristics of the fuse but should I fuse to hit 4000W peak (~400A when accounting for efficiency losses)?
 

amm

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The owner's manual will have guidance on the size of fuse to use. My Multiplus 12/3000 specified a 400 amp fuse.
Weird. I see it in the 12/3000 manual but not the 12/2000 manual. Based on the ratio of power between the 3000/2000 ~250A should be sufficient.
 

HRTKD

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Weird. I see it in the 12/3000 manual but not the 12/2000 manual. Based on the ratio of power between the 3000/2000 ~250A should be sufficient.

I started out using similar logic, thinking I could get by with a 300 amp fuse. I probably could have, but I ended up switching to 400 amps of fuse, just to be on the upper end of the spectrum. It would never get that high since my LiFePO4 battery bank is currently fused for only 225 amps, but that could change. My BMS is rated for 240+ amps, so I have some room to play with there.
 

amm

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@HRTKD Do you have a schematic of your system? After doing some more research I may want to go with 560Ah of eve 280 cells (4s2p). Seems like it is a similar footprint as the GC3.0. Essentially all I will need to do is build the battery, top balance and install (still doing research)? Should I go with the 3000VA multiplus? My A/C draws about 1200W so it would be close on the 2000VA system. Would be nice to run that for a couple hours in the afternoon if we need to put the kids down for a nap.
 
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amm

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I don't have an updated schematic for my system. There are old schematics in my plan review thread: https://diysolarforum.com/threads/gut-check-time.10751/

I can run my rooftop air conditioning for a bit. I think that having two BMS that each can handle 120 amps is key.
Thanks. Still evaluating my options here. I think the dimensions of the space and climate are complicating things for me a bit. I think I am still planning on going with the EVE 280Ah cells but just trying to make sure I do my due diligence. It sounds like I will need to build some sort of enclosure to give some mild compression to the cells. In terms of storage we are in Phoenix so the batteries will likely see some pretty high storage temperatures throughout the summer. Obviously the best thing would be to take them out but in all likelihood they will stay in the trailer. I am guessing the tradeoff is capacity/lifetime?
 

HRTKD

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Monitor your internal trailer temperatures. If the temperatures are too high, I would pull the batteries. @chrisski is in that area and he pulls his batteries in the summer.

My batteries stay in the my trailer all year, but I have to worry about subzero temperatures, not 100°F+.
 

chrisski

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Monitor your internal trailer temperatures. If the temperatures are too high, I would pull the batteries. @chrisski is in that area and he pulls his batteries in the summer.

My batteries stay in the my trailer all year, but I have to worry about subzero temperatures, not 100°F+.
I opted not to pull the two batteries made of eight 280 ah cells. Too much work risk to disassemble that 200 lbs with 50 screws and wires.

I store them at 50% in the trailer which reaches 105f and don’t use the system at all during those 5 or 6 months

For a schematic, you can see my signature block part 1 and part 2.
 
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HRTKD

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I opted not to pull the two batteries made of eight 280 ah cells. Too much work risk to disassemble that 200 lbs with 50 screws and wires.

I store them at 50% in the trailer which reaches 105f and don’t use the system at all during those 5 or 6 months

For a schematic, you can see my signature block part 1 and part 2.

Thanks for the update. I guess I won't use you as a "pull the batteries" reference any more. :)
 

amm

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I opted not to pull the two batteries made of eight 280 ah cells. Too much work risk to disassemble that 200 lbs with 50 screws and wires.

I store them at 50% in the trailer which reaches 105f and don’t use the system at all during those 5 or 6 months

For a schematic, you can see my signature block part 1 and part 2.
Thanks for the info. It seems there is a large disconnect between storage conditions from cell manufacturers to battery vendors. Both BB and SOK say storage to 140F whereas the cell storage from EVE is much less. At the end of the day it is the same chemistry right? It almost makes me want to purchase the battery with a warranty that says to store less than 140F just in case I run into degradation issues. The trailer will eventually be stored in a covered space but for the time being it is sitting in the Phoenix summer sun... I am guessing ~120F in the trailer? At the end of the day I am sure the reliability will be better than AGM.

It would be a nice to have to be able to run the A/C off grid for a set amount of time while we are boon docking but I may just settle for ~400 Ah with the smaller inverter and I will run a generator if we get too warm, which is pretty rare.
 

chrisski

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Thanks for the info. It seems there is a large disconnect between storage conditions from cell manufacturers to battery vendors. Both BB and SOK say storage to 140F whereas the cell storage from EVE is much less. At the end of the day it is the same chemistry right? It almost makes me want to purchase the battery with a warranty that says to store less than 140F just in case I run into degradation issues. The trailer will eventually be stored in a covered space but for the time being it is sitting in the Phoenix summer sun... I am guessing ~120F in the trailer? At the end of the day I am sure the reliability will be better than AGM.

It would be a nice to have to be able to run the A/C off grid for a set amount of time while we are boon docking but I may just settle for ~400 Ah with the smaller inverter and I will run a generator if we get too warm, which is pretty rare.
When I took my two or three measurements on the hot summer day, the inside temps were 105, outside up to 115.

I don’t believe covered parking would help with internal temps that much. Just my opinion based off a study of a piece of equipment we had at work where a study showed an insignificant lower temp with the equipment under the tarp versus uncovered. I think it helps for UV and water damage, not heat.

I don’t worry too much about manufacturer specs for the same chemistry. Mostly because I noticed the same discrepancies you did.

My batteries got used 60 - 90 days last year. I have plenty of capacity for me. If there is degradation, I won’t notice it. Some people think these cells will last long enough to Will our kids when pass.

Maybe they won’t make it 35 years, but I’m betting it will more likely last me 10 years for my needs, but taking them apart 10 summers and reassembling in the fall, I’m betting is more likely to damage them.
 
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chrisski

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run the A/C off grid for a set amount of time while we are boon docking but I may just settle for ~400 Ah with the smaller inverter and I will run a generator if we get too warm, which is pretty rare
My 15 k BTU runs at 1700 watts and never shuts off. I have the internal temp set to 74 and outdoor temp can be 85 - 90. I can do this for 6 hours at least.

Except for the first two weeks and last two weeks, In the cooler months around the Phoenix valley I don’t use AC if I boondocking; not needed.
 

amm

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Based on the feedback I think I am going to give the EVE280Ah Cells a go. I updated the schematic with important wire sizes and stuff. I think 4AWG should be sufficient for each battery right (150A BMS)? Since the space I have is relatively small 25-27" W x 16-18" D x 17" H I plan on cutting a hole or two in the side to ensure good ventilation for the inverter charger. Maybe a 12v fan with a thermostat? Take a look and let me know if you spot anything that doesn't look right. Appreciate all of the help.
 

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chrisski

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I would not use 4 AWG on a 12 volt system. Wire may be good for voltage loss, but not wire amp limit. Here is an ampacity chart:

1657232387672.png
Here are my calculations on how I got the 400 amps. A Inverter Low Voltage Cutoff off 10.5 volts, with a 3000-watt rating. Fuse and wire should be 410 amps, but that is the difference between finding a 400-amp fuse and going to the next step with 500 amps and I don't know what that is.
1657232550689.png

Just to show you some differences and smaller fuses when the system runs at 12 volts and then the system runs at charging voltage of 14.5 volts.:
1657232720695.png


1657232736593.png
I can guarantee you there are few if any people in the world who use a 500 MCM wire for a 3000-watt 12-volt inverter, but this is the reason I jumped up to 24 volts. I did fuse my 24 volt, 3000 watt inverter at 250 amps and used 4/0 welding wire.

Some caveats to the calculations are wire ampacity rating is off the manufacturer spec sheet for the type of thing it was designed for. That is pretty clear with THHN building wire where that means it can run at the max rate for long lengths of time, but I'm unclear about the usually higher rated welding wire being used for the rated ampacity with brief surges to those amps when welding or to run an Air Conditioner maxing the inverter out for hours on end. Those higher ratings usually involve higher insulation rating on the wire. My Overkill/JBD BMS uses 200° C insulation. That could get very hot, so with those higher temp rated insulation, just need to be the stuff around it can take the heat.
 

HRTKD

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1. If you use the temperature sensor that comes with the Multiplus on the Cerbo GX you can use the Cerbo GX to control a fan. That allows you to skip adding a separate thermostat.
2. Assuming the worst case scenario that you pull a full 150 amps out of the BMS @ 12 volts (that voltage is bit low, but we tend to use that as it's worst case) and have a round trip distance of 8' (4' one way x 2) then 4 awg is the smallest wire you should run. It gives you just under a 3% voltage drop. But like Chris said above, bigger is better. I'm using 2/0 for a 120 amp BMS.
3. The Multiplus 12/3000 has two posts for each DC leg. That means you can run two 2/0 positive cables and two 2/0 negative cables. That gives you a very safe set of cables.
4. The 300 amp bus bar between the BMS and the shunt isn't necessary or is simply in the wrong position. The bus bar should be located downstream of the shunt. You can easily double up 2/0 lugs on the shunt. That's how I did my initial install. In the picture below, I put copper flat bar on the input side of the shunt to give my cables a better mounting surface.
1657233856224.png
5. Similarly, your positive bus bar should be downstream of the switch and fuse. Battery->BMS->Fuse->Switch->Bus Bar.
6. All connections are then made on the common bus bars. Inverter, solar charge controller, Trailer DC distribution panel, Cerbo GX, etc.
7. Your solar charge controller and the Multiplus will both have separate ground (not negative) connections. I put in a separate ground bus bar that those tie into and then there is a cable that goes from the ground bus bar to the chassis/frame.
8. You also need to decide what you're going to do with the 12 volt charge coming in from the 7-pin cable.
 
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