aasgardvidar avatar image

Victron/Simpbms/Tesla Setup Van build


Starting a new van build and have some questions regarding battery setup.

I have 1 Tesla model s module (might upgrade to 2 in the future), I'm using Victron Buck boost dc dc 100a for alternator charging and a Mltiplus 3000w inverter.

For BMS I want to use the SIMP BMS together with a Victron gx type, this is where I have some questions and in need of some tips.

Anyone in here that uses a similar setup? Experiences?

Do you use contactors, precharge contactors as fail-safe system or Victron battery protect?

Current sensor via simp bms or victron battery monitor?

Charge enable/disable for temperatur high low, any way to trigger a heating pad?

Anyone tried simp with the cerbo gx?

A lot of questions here. Not much info on the simp bms/victron setup.

MultiPlus Quattro Inverter ChargerBMScerbogx
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Just found your question. Am building something similar. Am also debating the current sensor question right now - did post a question here.

What sensor did you go for, and did you connect it to the Cerbo, or to SimpBMS. Any experience/thoughts an the sensor setup you currently use? Would you build it different in the future?

2 Answers
littlewiggler avatar image
littlewiggler answered ·

Updated Jun 18, 2020 for changes:

There are many folks using Tesla/SimpBMS/Victron. As Justin said you need to be careful. The SimpBMS makes it pretty straight forward if you have a complete Victron system.

NOTE - the information below is for informational purposes only. I won't give any settings, just an overview. I used the following article as a starting point - <edit> note that there is no BMS in this example - possible safety issue </edit> :

I consulted the SimpBMS and CCGX manuals for everything else. The only thing not really documented is how the entire system works. I try to explain that below.


  • Single Tesla S 233 AH battery
  • SimpBMS in ESS Mode
  • Main and PreCharge Contactors connected to the SimpBMS
  • 1 LEM-CAM300 Sensor connected to the SimpBMS
  • Victron CCGX
  • Victron 24v MultiPlus 3000
  • Victron Smart 150/35 MPPT
  • Victron Smart BP 100
  • Victron BMV 712 (not needed with the SimpBMS - left over from my prior setup)
  • Victron Orion 24/12/70 (overkill, I can only pull a max of 30amps)
  • DPST 24v relay
  • 24v Temp relay to power on a battery warmer

The SimpBMS is connected to the CCGX via VE.Can

The MPPT and BMV 712 are connected to the CCGX via VE.Direct

MultiPlus connected to the CCGX via VE.Bus (CCGX is also in DVCC mode)

MPPT battery line connected to the Smart BP100 (relay allows charging when closed) THIS IS IMPORTANT - it can only be used one way.

Relay on the CCGX drives the DPST relay

DPST relay enables charging on the MultiPlus and enables the BP to allow the MPPT controller to charge (see above)

With this configuration all battery voltage settings and alarms are done on the SimpBMS console. As a backup, I programmed the settings into each Victron unit.

How it all works:

The SimpBMS provides all voltages from the battery and sends any alerts to the CCGX while in DVCC mode. The CCGX relay is set to open when an alert is received and opens the DPST disabling MPPT Charging via the BP100 and stops the MultiPlus from charging as well.

While in DVCC mode the MultiPlus and MPPT settings are not used. The SimpBMS appears as a Smart Battery and directs the charging voltages and the CCGX prioritizes the MPPT over Shore power if both are available.

If anything goes critical SimpBMS will disengage the Contactors disconnecting the battery from the entire Victron system.

Connection Path:

Battery +


200 Amp fuse

Precharge Contactor (Connected to SimpBMS) -> Resistor

In parallel to precharge Contactor a Main contactor

Positive Bus Bar

  • MultiPlus (Charge enable monitored by Aux1 input from relay)
  • Relay Power
  • CCGX Power
  • BMV712 Power
  • 24v Temperature controlled relay for warming blanket
  • Orion 24/12 converter out to a 12v positive bus bar

Negative Bus Bar


LEM-Can 300 (Connected to SimpBMS)

Battery -


Battery +

BP 100 in

(Switch controlled by relay)

BP 100 Out to the positive bus bar

I am using a buck converter off of the Tesla to downstep to 12V and feed it to the SimpBMS unit. I added a cheap AC trickle charger for charging the generator battery.

Hope this helps.


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update: the post this reacts to has been edited, so not all remarks below are still relevant:


Hi @LittleWiggler

I like your setup...but...please mention that the link you gave is of an unsafe system without a bms.

on your system:

-you -do- need a pre-charge system, you -will- damage your contactor, and that is potentially dangerous (it either welds closed, and/or provide a higher resistance so it can overheat / melt.

please read:

about powering the BMS, you can use two diodes to feed from either the load (inverter) side (when there is shore-power) or the charge (MPPT) side to a smal dc-dc converter to power the BMS

instead of contactors, you can also use a shunt-trip instead, this is a manual reset situation (breaker with shunt trip attached), here you can also use a manual pre-charge btw.

littlewiggler avatar image littlewiggler Daniël Boekel (Victron Energy Staff) ♦♦ ·


Thanks for the replay. I will be adding a pre-charge contactor.

Thank you so much for the informative reply. This helps a lot! Good luck on your install..

Thank you for all the details.I'm switching from lead acid batteries to LiIon and I'm building almost the same setup like you (the difference is in the inverter which is a Phoenix 24/3000 not Multiplus).

I also have 4 questions regarding simpBMS:

1. What pins do you use for commanding contactors? (the simpBMS documentation is not very straight forward, and in my opinion I believe I need to use pins 4 and 5 for main contactor and precharge and a pin for command of BP100)

2. Do you use contactors with economizer?

3. Do you use diodes for contactors?

4. Did you find a way to power the simpbms directly from the charger?

Thank You

1, Yess pin 4 for Main and pin 5 for Pre Contactors. Tom changed this a few months ago - i will update my post.

2. Yes

3. The contactors I have do not require diodes.

4. I ended up using a buck converter off the Tesla battery to step down the voltage to 12v for the SimpBMS.

sacx avatar image sacx littlewiggler ·

Thanks for the answer, still I need 1 more clarification, On on what pin is negative contactor connected ? Or is enough to use 2 contactors?

Thank you again!

You only need the Main (pin 4) and Pre. (pin 5) The Main will open if any alarms/error happens. The changes Tom made simplified it a bit.

sacx avatar image sacx littlewiggler ·

Thank you very much!

I am also looking at the SimpBMS. The manual is terrible. I really wish they would explain things in more detail. I am building a system with 4 Tesla modules, 2S 2P, and I really wish I had a wiring diagram for a system like this. For example, the pins diagram talks about charge enable and discharge enable. Yet it doesn't explain what this means. What do these wires go to? I also can't figure out if there is anyway to turn on a heating system when the battery temp is too low. Does anyone have additional documentation that can help me with this?

The documentation is not so awful, but you need to read it slow and try to understand step by step. For a photovoltaic system you can used Main and Precharge (pins 4 and 5), from what I understand this is the new way for ESS mode. Regarding heating system I didn't find a way to do that from SimpBMS without changing the source code and event that I don't know if are GPIO unused on J4. How LittleWiggler describe his connection is enough to build a system, personally I didn't need more documentation to upgrade my existing system from LeadAcid to LiIon.

You might want to try reaching out to Tom on the heat question.

I chose to do it with an external temperature relay and a desktop heating pad.

I may get around to using fancy pictures and diagrams. My wife needs it for documentation if I'm not there and she needs to trace something down.

I am fairly certain that I can setup a relay on a Cerbo to start the heating system when the battery temp gets too low. I am using a couple heat pads on an aluminum fluid reservoir. This will maintain the temp above freezing, but if the batteries are cold soaked, I will have an inline heater to really warm things up.

I have a good idea how to wire up the SIMP BMS. The only that I am not 100% sure of it the precharge system. But I am sure I can figure it out once I have it and can play with it.

When you configure the Battery Capacity did you put the entire capacity like 232Ah or you just go lower a little bit ?

Not just a little bit. As the capacity is one of the variables for SOC calculation at SimpBMS and you are only able to use roughly 70 % of the whole capacity, you have to enter the 75% value of 232 -> 174 Ah there. Otherwise you will never get a proper SOC. (0-100%)

Hope it helps


I have mine set to 230 AH.

I have the charging set to only charge to 24v so 4000mv in the charge menu. SimpBMS will use that to calculate as 100% charged.

sacx avatar image sacx littlewiggler ·

4000mV I think is the correct value ....

Fixed in my post. Thanks for catching that.

yes and no .... if you use the cab300 current sensor (CAN Bus) the simpbms will use an other algorithm to calculate SOC. If you use "Voltage based SOC" you are right. The Current Calculation with the sensor is far more accurate then the volatge based and also no that bumpy -> if you apply lots of load to the tesla pack.

The capacity setting will not be used without a current sensor.

So .... it depends :)



As listed in my build I do have the CAB300 sensor.

Hmmm .... so you get a linear SOC from 100% to 0% with 230 AH ? From my understanding of the SimpBMS Code this is not possible with you settings. If so: would love to see the rest of you settings.


Justin Cook - Bay Marine Supply USA avatar image
Justin Cook - Bay Marine Supply USA answered ·

@aasgardvidar, Victron will not support (for obvious reasons) any used battery system; neither Tesla batteries nor the SIMP BMS to which you refer are supported devices, so although you may or may not be able to get them to work within a Victron system, you also may or may not void some or all of the connected-devices' warranties by so trying.

For a complete list of Victron-supported batteries/battery systems, please see this list. Using any battery or other component outside of this list may or may not work, but will be unsupported by your Victron distributor and, as mentioned, runs the risk of causing unexpected behavior within the system and/or voiding warranties, so regrettably you're very much on your own if you choose this route.

Furthermore, given the very high possibility of thermal runaway in Tesla batteries, since they're not the safe and stable LFP chemistry that is the current standard in mobile use, you're definitely running several very significant risks by doing this and I very strongly advise that you re-evaluate your current planned system.

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I looked up all the batteries on that list but hard to find many that are in the US and also a decent price. There were a couple options that looking interesting but they are 48V. What is the best way to charge a 48V system with the alternator? I dont see any 12V to 48V converters through victron. Anyone have any product suggestions?