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Fusing, isolating batteries and CAN questions

Hello, I have some questions about a build I’m working on. It’s mostly Victron equipment and I wanted to make sure everything is communicating the way it should be, I also have some questions regarding isolators, fuses and cable sizing.


Victron SmartSolar MPPT 250/100

Victron MultiPlus-II 48/5000/70-50

Victron Smart BatteryProtect 48V-100A

Victron Lynx Distributor (Power distribution board)

Victron BMV-712 Smart Shunt (500A)


x2 PylonTech US5000B 48V 100AH LiFePO4 batteries

PylonTech cables = 4x 2M Power Cables (4AWG, Peak Current Capacity 120A, 100A constant)


wiring-diagram.png


// Batteries


1. Where do I define the max discharge limit in software? Is this part of the PylonTech BMS and can I change it using the Cerbo or do I have to interface with the BMS itself? I would like to hard limit it to 160A (0.8C on each battery)


2. The batteries have a max discharge current of 100A each but should be run at 80A or below. When run in parallel this discharge current will be 200A-160A. Is this correct?


3. I have set up DVCC. As far as I know, it’s just a way for the BMS to control the MPPT output into the batteries, is this correct? What are the advantages of using the PylonTech batteries BMS to control the MPPT as opposed to entering the charge parameters into the MPPT manually? Do they have inbuilt temperature sensors that guide the charging profile or something?


4. Is the cable configuration on the batteries correct? Should they be paralleled using the PylonTech parallel cable or is this a weak point that is under rated for the current going through it? Would I be better off ditching the short parallel cables and running both batteries independently to the Lynx distributor?


5. Should the PylonTech batteries be part of the same CAN network as the Inverter and MPPT or are the batteries better directly connected to the Cerbo by a separate VE CAN to CAN-Bus RJ45?



// Fusing and isolation


1. Should I be using x4 Class T fuses on all the battery outputs?


2. Regarding battery isolators. Are they just another point of failure and a waste of money considering the batteries themselves have a circuit breaker? If they are required, should I use them after the Class T fuses and combine the two positives and two negatives to x2 isolators, or do I need x4 isolators?


3. Post BatteryProtect I intend to have a fused 48VDC distribution board. Should I stick with MEGA fuses here like I have in the Lynx distributor? The BatteryProtect is only good for 100A so should I put a 100A fuse between the BatteryProtect and 48VDC distribution board? Or does the BatteryProtect have it’s own fuse and/or current limiting?


4. Should I fuse the MPPT battery positive and negative cables to the Lynx Distributor even though it’s a source and not a load? I guess it would protect everything else attached to the Distributor in the event the MPPT epicly fails. Should this 48VDC fuse be in the range of 120A-140A? Does the PV max current on the MPPT PV input come into play here at all for calculating the fuse value of the MPPT output? The PV input is coming in at 50A max.


I got the 120A-140A value from section 4.2 of the MPPT manual

https://www.victronenergy.com/upload/documents/Manual_SmartSolar_MPPT_150-70_up_to_250-100_VE.Can/29694-MPPT_solar_charger_manual-pdf-en.pdf#page=15


5. Fuse size for DC inverter input = 200A (9000 / 48 = 187.5A) - Is this calculation correct or is it undersized for peak loads?


Inverter manual: https://www.victronenergy.com/upload/documents/Datasheet-MultiPlus-II-inverter-charger-EN.pdf



// Cable sizing


1. Do the PylonTech battery cables have to take the collective loads of MPPT charging, inverter charging and battery discharge at the same time or will it be split between the four cables? If I were to turn the circuit breaker on one of the batteries off, would that overload the second battery's cables in a max current situation?


Battery max discharge = 160A-200A

Inverter max charge = 70A

MPPT max charge = 100A


Total = 330A-370A


2. Does lug positioning on the bus bar matter? Should I put the MPPT lug closest to the battery IN on the Lynx distributor?




// Communications


1. Is the Cerbo itself running VenusOS?


2. What is the ‘Battery Monitor’ setting? Should I set this as the PylonTech BMS?


3. Can I connect a VenusOS RasPi directly to the Cerbo Wi-Fi network or is it only for setup and I’ll need a real network that the Cerbo connects to?


4. What does the HDMI output of the Cerbo do? Can I hook this up to another 7” screen for a second display next to the Cerbo? Does the Cerbo accept touch input over USB?


5. Where can I confirm how the devices are communicating? I want to run everything off a daisy chained CAN. I want to confirm some devices aren’t using Bluetooth or VE.Direct for example.


6. Do I have to manually activate ‘Power control’ and ‘PowerAssist’ in software or is it enabled by default?



// Miscellaneous


1. For the 48VDC distribution side of things I’m thinking of getting one of these:


https://www.bluesea.com/products/5196/MRBF_Surface_Mount_Fuse_Block_-_Common_Source


Are there any good quality 48V capable fused distribution boards that have both positive and negative bus bars integrated into the one unit other than the Victron Lynx Distributor? I had a look at BlueSea and couldn’t find one. Extra points if it has M8 studs


2. I’ve really struggled trying to get voltage ranges and charging parameters for the PylonTech batteries. The best I could get from the battery datasheet is:


Depth of discharge 95%

DischargeVoltage (VDC) 43.5~53.5

ChargeVoltage (VDC) 52.5~53.5

RecommendedCharge/Discharge Current 80A

Max Continuous Charge/DischargeCurrent 100A


How can I use this information to set some reasonable values for low voltage disconnects in both the BatteryProtect and MultiPlus-II Inverter?


What kind of DoD should I use? 90-95%?

Should I set the Inverter LVD to kick in at a slightly higher voltage than the BatteryProtect remote LVD tells it to turn off?


What bulk, absorption and float values can I use with these batteries?


3. With the BatteryProtect, should I be using mode B (relay mode)? Also how does the remote on/off for the inverter work, does it just short the wire or send a pulse?


4. Is it possible to configure AC OUT 2 on the MultiPlus II Inverter so it acts like AC 1 OUT? As in it’s always on and not contingent on there being AC incoming ie: from a generator.


5. Where can I set generator remote start parameters? I want the genset to kick in when the batteries get below 50% and keep going until they are fully charged. That way the generator won’t be stopping and starting all the time. Is this a good idea? Should I set the genset to only charge to 90% of capacity?


6. The BMV smart shunt and Cerbo have temperature sensing. Should I buy a temperature probe or would the temperature sensing do nothing on the Lynx distributor? They have weird SurLok connectors on the PylonTech batteries, not standard studs so I can’t see a way to get it on the battery terminals.




Thanks heaps :)

cerbo gxBMSPylontechVE.Canisolators
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kevgermany avatar image
kevgermany answered ·

Batteries. Follow the guide linked below. And use this in conjunction with the Pylontech manual.

Any settings you make are generally overridden by the batteries. But things like charge rates should be set as a safety measure. Personally I'd connect each in parallel with the 2M cables to the distributor or a power in. This takes care of your cable size concerns. Pylontech cables are rated for 130A, 4 batteries with the short interlinks can easily blow that.

Batteries have a separate connection to the Cerbo with special cable..

Depending on local regs you may or may not need isolators as well as the battery switches.

DVCC is overridden by the battery BMS.

You probably don't need the battery protect or BMV, the Pylontechs handle this.

Cerbo runs Venus.

Battery monitor is Pylontech

One GX per system. No Venus RPi. Cerbo needs an internet connection for VRM. This can be WiFi, Ethernet or both.

Cerbo hdmi is picture plus touch. Standard is to use GX touch screen, but other screens combining touch with hdmi will work. USB nearest to hdmi is power only.

Bluetooth network is only used if you configure it. Ve.direct only if you plug the cables in.

Temp sensing not needed, Pylontechs handle this.

I hope this answers all questions that aren't in the manuals.


Given the number and level of questions, it would be good to consult an experienced installer.





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confusion avatar image confusion commented ·

Thanks so much for your reply, I appreciate you taking the time.


Any settings you make are generally overridden by the batteries. But things like charge rates should be set as a safety measure. Personally I'd connect each in parallel with the 2M cables to the distributor or a power in. This takes care of your cable size concerns. Pylontech cables are rated for 130A, 4 batteries with the short interlinks can easily blow that.


That's a good idea and I'll be manually setting the following parameters for the MPPT. After which point I'll let the BMS call the shots.

Bulk charge voltage 52.5V

Absorbtion time to 1 hour

Float voltage to around 49.5V

Low voltage disconnect on the inverter at 45V


DVCC is overridden by the battery BMS.

I was under the impression that DVCC was the mechanism the BMS uses control to the MPPT?


One GX per system. No Venus RPi. Cerbo needs an internet connection for VRM. This can be WiFi, Ethernet or both.

Can I just use the Raspi as a remote screen then? Or will it mess with everything?


I'll be running a couple of 125A Class T fuses on the positive leg between the batteries and the Lynx distributor. Do you have any recommendations on brands or sensible ways to do this? I've looked at some from Blue Sea but they aren't available in Australia. Everything else seems to be M10 studs (M8 would suit the PylonTech cables) and terribly expensive at 200AUD+ for a single fuse and holder.

Thanks again mate, have a good one

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Alexandra avatar image Alexandra ♦ confusion commented ·

@confusion

Probably best to follow the guide for the bulk/abs and float settings. And cut off settings. Also pylons don't want you to discharge over 90% so set the low SOC shut down to 10%

https://www.victronenergy.com/live/battery_compatibility:pylontech_phantom#veconfigure_settings

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confusion avatar image confusion Alexandra ♦ commented ·
Thanks for the link. Any ideas about fusing the batteries?

Appreciate the time, cheers.


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pwfarnell avatar image pwfarnell confusion commented ·

@confusion I have seen some discussion that Class T fuses are widely available at reasonable cost in the US but not here in Europe where Class NH can be easier and cheaper to find. The same might apply in Australia. Have a look at Swe-Check of Moorabbin, Melbourne for example.

https://www.swe-check.com.au/

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nesswill avatar image nesswill pwfarnell commented ·

I have used these if it's of any help?

https://mou.sr/3MGRN1L


EDIT

and these

https://www.fischerpanda.co.uk/e-store/mastervolt/Fuse_Class_T_300_Amp_160VDC.html

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kevgermany avatar image kevgermany ♦♦ confusion commented ·
DVCC/BMS. Correct. What I meant is that the BMS will override your DVCC settings (unless you set lower values than the BMS wants)
1 Like 1 ·
confusion avatar image confusion kevgermany ♦♦ commented ·

Thank you for the response,

I'm pretty comfortable going forward but would like some confirmation on three things


1. Is the cable configuration on the batteries good? Should they be paralleled using the short PylonTech parallel cables or is this a weak point that is under rated for the current going through it? Would I be better off ditching the short parallel cables entirely and running both batteries independently to the Lynx distributor (Using 2x positive and 2x negative cables). What do the parallel cables even do? Help balance the batteries or something?


2. Do the four PylonTech battery cables have to take the collective loads of MPPT charging, inverter charging and battery discharge at the same time? How is it split between the four cables? If I were to turn the circuit breaker on one of the batteries off, would that overload the second battery's cables in a max current situation?

Battery max discharge = 200A

Inverter max charge = 70A

MPPT max charge = 100A

Total = 370A


3. Is it possible to configure AC OUT 2 on the MultiPlus II Inverter so it acts like AC 1 OUT? As in it’s always on and not contingent on there being AC incoming ie: from a generator.


Thanks mate

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kevgermany avatar image kevgermany ♦♦ confusion commented ·

1 your equipment list is 4 batteries in your first post. Paralleling using the short supplied cables between the batteries gives the opportunity to overload the cables. They're only good for about 120A. Taking sets to a busbar such as the distributor spreads the load across the cables and avoids overloading.

However it looks as if you're only installing 2 batteries from later comments.

2 Draw up a block diagram showing the currents between each component. If you have MPPT and multi charging at the same time you will put that total into the batteries. So if there's a single connection (pair of wires) between the distributor and batteries it must be sized for this. Usually the BMS will set a max charge current of 80A or less per battery.

Loads will be served from the distributor not the battery until total load exceeds DC inputs to the distributor from multi and solar.

The BMS in each battery limits output from that battery. Switching one battery off will halve the available output(assuming 2 batteries). Best to leave all batteries on to avoid imbalance between the batteries.

Heavier loads are distributed equally across the batteries. What I've seen from the indicator LEDs on the batteries are that light loads may be supplied from a subset of the batteries, and the subset changes over time. Guessing this is the BMSs balancing the batteries.

3 No. If you only need permanently on power, use AC out 1 only. This must have suitably sized cables and be connected direct to a suitable consumer unit with RCD, breakers etc.


It would be a good idea to get advice/a consultation from a qualified professional. This would cover your questions, raise others you might not have thought of as well as making sure your installation is safe and complies with regulations. Otherwise big shocks, post installation changes and serious risks to life and property...

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