Designing Victron System for Keystone RV Travel Trailer

[SendIt]

Hey everyone, happy Thanksgiving! This is my first post on the forum -- found it after watching some of Will's videos. I'm a Mechanical Engineer who changed careers to software development so that I could work remote. I've done a decent amount of industrial automation and microcontroller work in previous positions.

I recently purchased a Keystone Springdale travel trailer that I plan on doing some extended off-grid living/working in with my wife. It has a WFCO power distribution system with a built-in 12V converter, 120V breaker panel, and 12V fuse panel. It accepts power from a 30A Shore power hookup and from the aux input on the trailer hitch. The battery is crap and barely holds a charge.

My plan is to add a large DIY LiFePo4 battery and equipment to charge it from shore power and eventually solar. We will plan on charging off a generator a few hours/day until we eventually install solar panels.

Requirements​

I'd like to build out a 48V DIY battery with 16 x 100ah cells and an overkill solar BMS and I'm trying to decide what components to add which can:

• invert 48V to 120V
• convert 48V to 12V
• charge the LiFePo4 from the shore hookup
• disconnect automatically when the cells are low or it's too cold
• Eventually charge from solar.

Loads​

The loads I'm working with are relatively small. AC Loads (two people working remote):

• Starlink, 2 laptops, and a monitor 8-9 hours/day

12V loads (a 26' keystone RV with two people inside):

• Lights
• Awning
• Propane Furnace Fan
• Propane water heater
• water pump

Initial Design​

I'm thinking about going with Victron components, since it seems like they are high-quality and have a good re-sale value. There's a local distributor in town that I can purchase everything from. I have a few questions about how the BMS interfaces with the Victron components and how to size the fuses. I'm also wondering if someone recommends going with a less expensive brand than Victron.

Future Work​

Initially, I'm just doing the battery storage system, but in the future I'm expecting to add the following

Battery Temperature Controller​

I still need to figure out how I'm going to heat the battery. We expect to be in some cold areas. I've seen a few custom controllers with Arduino hardware. I'm not sure if I can tap into the BMS or the Multiplus to get the battery temperature or I'll need a separate temp sensor for the heater. Regardless, I'm not going to worry about this until later.

Solar Charge Controller​

Initially, I'm planning on charging the system with a portable generator that I already own. At some point in the future, I'll be adding rooftop solar. It's winter here, so I don't want to climb around on the snow-covered roof until it melts off

Open Questions​

• Any safety concerns you can see with this setup?
• Is it a bad idea to run the charging and discharging through the BMS? Should I have a separate battery protect to switch the high current AC Inverter load?
• How large should the fuses be on the shunt, inverter, and dc charger?
• Is Victron overkill? Anyone recommend less expensive components?
• I'd like to be able to fully disconnect the battery when storing the trailer. Do I need to add a circuit to charge the multiplus capacitors when reconnecting the battery so I don't trigger the over-current protection on the BMS? Any posts you recommend about that if so?
• Can I use the Cerbo + Multiplus to switch the inverter off in a low-voltage situation or do I need an additional battery protect?

Thanks and I appreciate any feedback. I have a lot of experience working with 12 and 24 volt system, but I've never built a 48V system. I understand that fully charged, these batteries can kill me.

Happy Holidays and thanks in advance for any advice.
SendIt

Edit: removed A/C requirement from energy storage system

 

[MisterSandals]

but I'd like to size the system to run an A/C unit that's on the roof of the trailer.

100Ah of LiFePO4 sounds small for A/C especially if running while not connected to shore power, generator or solar.

How many Wh will your A/C require per battery charge?
RV A/C are usually ~1500W so 5h is 7500Wh

3.2V x 16 x 100Ah = 5120Wh battery power

Do a power audit with what you expect to run daily or per battery charge to see how realistic your numbers are.

 

[SendIt]

100Ah of LiFePO4 sounds small for A/C especially if running while not connected to shore power, generator or solar.

How many Wh will your A/C require per battery charge?
RV A/C are usually ~1500W so 5h is 7500Wh

3.2V x 16 x 100Ah = 5120Wh battery power

Do a power audit with what you expect to run daily or per battery charge to see how realistic your numbers are.

Thanks for the reply. I'm not expecting to ever run the A/C off shore power prior to installing solar and/or expanding the battery bank. The spreadsheet you linked to is pretty good, thanks for posting it. I'm coming in at around 1.7 kwh / day excluding the A/C. Max Inverter draw is ~600 W no A/C.

I'm gonna update the original post to exclude the A/C, since it's sort of irrelevant to the first version of this I'm building.

 

[John Frum]

Since you don't a lynx module to the left of the lynx shunt I suggest you use a smart shunt instead and save your self some cash.

SmartShunt - Victron Energy

The SmartShunt is an all in one battery monitor, only without a display. Your phone acts as the display. The SmartShunt connects via Bluetooth to the...

www.victronenergy.com

These are handy for connecting things to lynx backplane.

Victron Lynx Adapters

These custom-cut copper Lynx Adapters are designed to connect the Victron Lynx Distributor to the Victron BMV-712 Shunt and Master Disconnect.

shop.explorist.life

What this video how to turn add fuses to a lynx power-in to save a bit of cash

The battery should have a class-t fuse as close as possible to the positive terminal.
Since the Victron manual suggest 1 awg which is kind of odd I suggest 1/0 awg with a 250 amp fuse for the battery(feeder) circuit.
Use 1/0 awg with a 200 mega fuse for the inverter circuit.
The battery disconnect switch should include a pre-charge circuit to protect the bms from the in-rush current to charge the inverter capacitors.

Inverter Disconnect Switch with Precharge

To get the paper, click on the orange button at the top of this page. This circuit is designed as a disconnect switch that allows the user to pre-charge the inverter capacitors before turning the switch completely on. 26 June 2020 update: At...

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For the buck converter use the Orion-Tr 48/12-30

https://www.victronenergy.com/upload/documents/Datasheet-Orion-Tr-DC-DC-converters-isolated-100-250-400W-EN.pdf

Hopefully that will be big enough.
For the dc distribution circuit use 6 awg all the way to the dc distribution panel.
Put a 100 amp mega fuse at the power-in.
Put a 50 amp inline maxi fuse between the converter and the distribution panel.

Don't forget to disable the ac2dc converter in the ac/dc distribution panel to avoid a power loop with the inverter.

 

[SendIt]

Awesome info. Thanks! I appreciate the cost savings recommendations. I’ll redo my diagram in the morning. Probably going to have questions then.

 

[Ahjwinth]

You can also consider to use a multiplus II GX 48/3000. Then you have the functionality of the Cerbo included in the multiplus. It saves a few cable’s and a device.

The BMS can also measure the SOC and other parameters identical to the smartshunt. So why not keep the money in your pocket from the shunt and use the BMS information. This can also be connected to the GX device so you can read the SOC. This can be either the Cerbo or the multiplus. If it doesn’t work as you wanted then install the smartshunt later on.

And why the battery protect device between the battery and Orion, the battery protection is also in the BMS to shutoff the battery when SOC gets to low?

 

[John Frum]

The BMS can also measure the SOC and other parameters identical to the smartshunt. So why not keep the money in your pocket from the shunt and use the BMS information.

The Victron shunt in combination with the Cerbo GX allows the Victron charge sources to easily terminate charge on tail current.
In other words they can know what amount of current is going into the battery and what is going to the loads.
Despite appearances I'm not really a Victron guy but that is my understanding.
@sunshine_eggo am I correct on this?

This can also be connected to the GX device so you can read the SOC. This can be either the Cerbo or the multiplus.

Cool, I didn't know that this integration existed.
Please point me to the code repository.

And why the battery protect device between the battery and Orion, the battery protection is also in the BMS to shutoff the battery when SOC gets to low?

Having the loads disconnect before the bms disconnects allows the Solar charge controller and possibly the multiplus to charge the battery even after low voltage disconnect.
Typically a solar charge controller has to see battery voltage in order to charge.

 

[HRTKD]

You don't need a 48v converter in your RV distribution panel if you have a Multiplus. The converter would be redundant.

You could skip the switch between the Lynx and the Battery Protect. I have the Smart Battery Protect and use the Bluetooth connection to turn the Battery Protect off with the Victron Connect app. You may also be able to skip the Battery Protect altogether if you can program the Orion to cut off the 12 volt feed when the 48 volt side reaches a low voltage. That's a guess on my part.

If you get the Cerbo GX, you'll probably want the Touch 50 also. The Victron Connect app doesn't have the same capability to work with the Cerbo GX that the Touch 50 does. Maybe that will change in the future, but right now, it's limited.

 

[John Frum]

You don't need a 48v converter in your RV distribution panel if you have a Multiplus. The converter would be redundant.

He doesn't need an ac2dc converter but he does need a 48->12 dc2dc converter.

You could skip the switch between the Lynx and the Battery Protect. I have the Smart Battery Protect and use the Bluetooth connection to turn the Battery Protect off with the Victron Connect app.

Nice.

You may also be able to skip the Battery Protect altogether if you can program the Orion to cut off the 12 volt feed when the 48 volt side reaches a low voltage. That's a guess on my part.

Nice.
The orion has a remote on/off contact points which might be controllable via the Cerbo.

 

[HRTKD]

He doesn't need an ac2dc converter but he does need a 48->12 dc2dc converter.

Yeah, but he has the label under the RV Main Distribution Panel, where the AC-DC converter is typically located.

 

[SendIt]

Thanks for the reviews @Ahjwinth, @John Frum, & @HRTKD!

You can also consider to use a multiplus II GX 48/3000.

My local distributor does not have a Multiplus GX in stock, but it looks like a good option. Will poke around online.

This can also be connected to the GX device so you can read the SOC.

I too was unaware that the Overkill solar BMS can talk to the Cerbo GX. Would love to see an example and save $ if I can. Are you aware of any posts about it?

And why the battery protect device between the battery and Orion, the battery protection is also in the BMS to shutoff the battery when SOC gets to low?

As @John Frum pointed out, I'd like to disconnect loads before triggering the BMS in order to allow for charging at low voltages. For extended life, I'd also like to have the Cerbo set prevent getting to a low state of charge. Am I correct in that if the BMS low-voltage triggers then I can't charge the unit until it's been reset?

He doesn't need an ac2dc converter but he does need a 48->12 dc2dc converter.

Yup, I'd like to go 48v ->12v, not 48v->120v -> 12v

You could skip the switch between the Lynx and the Battery Protect.

awesome.

If you get the Cerbo GX, you'll probably want the Touch 50 also.

good to know, will add that to the BOM.

Here's an updated schematic based on your feedback:

 

[Ahjwinth]

For the BMS integration in VENUS OS / GX device see this discussion.
https://diysolarforum.com/threads/v...-daly-ant-jkbms-heltec-renogy-tian-ecs.17847/

For the battery protect, I have checked my own Orion 24/12 in my camper. I have the smart version and this has the option to switch on/off depending on the input voltage. See the screenshot below. So using a battery protect is double up as you have the function also in the Orion.

 

[John Frum]

As @John Frum pointed out, I'd like to disconnect loads before triggering the BMS in order to allow for charging at low voltages. For extended life, I'd also like to have the Cerbo set prevent getting to a low state of charge. Am I correct in that if the BMS low-voltage triggers then I can't charge the unit until it's been reset?

If the bms low voltage disconnect triggers, a solar charge controller will not resume charging until the trigger clears and the system voltage is above the scc's threshold.
Not sure about the mp2.

The mp2 has configurable low voltage disconnect.
Probably can also be controlled including administrative disconnect via the cerbo device or venus os.

 

[John Frum]

For the BMS integration in VENUS OS / GX device see this discussion.
https://diysolarforum.com/threads/v...-daly-ant-jkbms-heltec-renogy-tian-ecs.17847/

That is a huge long thread and since my eyes are already worn out for the day I didn't read it.
I'm guessing that the cerbo is replaced by a pi running venus os and the "driver" enables communication with the overkill bms.

Is the communication just gets or is it sets and gets?
Or is it even more sophisticated?

 

[John Frum]

This design is looking better and better.

We have not yet talked about chassis bonding, dirt bonding and n-g bonding.

 

[SendIt]

That is a huge long thread and since my eyes are already worn out for the day I didn't read it.
I'm guessing that the cerbo is replaced by a pi running venus os and the "driver" enables communication with the overkill bms.

Is the communication just gets or is it sets and gets?
Or is it even more sophisticated?

From what I read on the github repo, you can actually install the driver directly on the Cerbo via SSH (which also runs Venus). Looks pretty quick to do and gives the Cerbo the same information it would have if you used the Victron BMS. This integration is actually giving the Cerbo more info than if you used a SmartShunt. Good find @Ahjwinth.

This design is looking better and better.

We have not yet talked about chassis bonding, dirt bonding and n-g bonding.

Thanks for the help. RE: Grounding I am planning on bolting a 1/0 AWG wire to the steel chasis under the RV (first sanding off the paint, then re-painting over the connection) and attaching that to the negative bus bar on the power-in.

The A/C outlets in the trailer are GFCI, so I'm not sure if they will trip because of the neutral - ground bonding though? This is a topic I don't know much about and have just started googling. Do you know of any good threads/articles addressing ground in a trailer + generator + 48VDC setup?

 

[HRTKD]

The low voltage disconnect is set on the Multiplus, not the Cerbo GX. To do the low level programming of the Multiplus you'll need either the MK3 (connection to USB devices) or the Bluetooth dongles. You don't need both.

To make all this integrate with the Cerbo GX, you'll need the correct Victron cables. VE.direct, VE.CAN, etc. The Cerbo GX does not integrate with other Victron devices through Bluetooth - that would be too easy. It all depends on which interface each device has. For my install, the MPPT did not use the same cable as the Multiplus. Be sure you get the right length. I had to re-order one because it was too short (my fault, bad estimate).

You're using the Overkill Solar BMS, which is an excellent choice. Should the BMS disconnect due to Low Voltage, the charge side is still open, so no big deal there as long as you get a charge.

 

[Ahjwinth]

the multiplus II GX doesn’t need all the cables and has the same functionality as the Cerbo to my understanding. It also runs venus os.

more info on the integration of the BMS into the venus os you can find on below 2 links.
https://community.victronenergy.com...nusos-driver-for-serial-connected-bms-av.html

https://github.com/Louisvdw/dbus-serialbattery

i noticed you have a 100a fuse towards the Orion, this is a bit overkill. probably 20a is enough that is already 1kw of power, which seems to me a bit to much for the 12v system.

 

[John Frum]

Should the BMS disconnect due to Low Voltage, the charge side is still open, so no big deal there as long as you get a charge.

Have you tested this?
I mean administratively open the discharge path on the bms.
isolate the panels from the scc to simulate night.
re-connect the panels to the scc to simulate daytime and see if the ssc will charge.
Many sccs need to see voltage on the bat side so that they can detect the system votlage before they will charge.

 

[John Frum]

Do you know of any good threads/articles addressing ground in a trailer + generator + 48VDC setup?

This series is good.

Grounding Made simpler - Part 1: AC/houshold grounding

To get the paper, click on the orange button at the top of the screen. The subject of grounding is a complex, multifaceted subject, that is often treated as an after-thought but needs to be considered from the beginning of the design and build...

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