question

Kevin Windrem avatar image
Kevin Windrem asked

MK3-USB can't be used on Cerbo

I've been working with someone transitioning from a Raspberry PI to Cerbo and he reported that Cerbo is not fully detecting a Multiplus which is connected through a MK3-USB adapter. The device shows up and the device's values populate, but those managed by system calk are not populating.

However, everything works after downgrading to Venus OS v2.94.

I found code in the multi.py part of systemcalc:

# If platform has an onboard mkx, use only that as VE.Bus service.

This appears to prevent use of a MK3-USB adapter with Cerbo.

@mvader (Victron Energy) This was obviously an intentional move but not sure it's documented anywhere. Was there a reason for this change? I know there were changes to the MKx interface as part of v3.0. Could it be that the MK3-USb can't be updated and is not compatible?



Venus OSmk3-usb
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klim8skeptic avatar image klim8skeptic ♦ commented ·

@Kevin Windrem if you have the Cerbo, why not connect the multi to the Cerbo's VE Bus port? No Mk 3 needed.

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4 Answers
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @Kevin Windrem,

The Venus OS only supports a single fully featured VE.Bus inverter (except where they are programmed and synchronised via parallel or 3 phase).

This limitation is documented in the Cerbo GX manual here - https://www.victronenergy.com/media/pg/Cerbo_GX/en/connecting-victron-products.html#UUID-45296fbc-6298-b29c-2e54-7730edc3d313

Where a system has hardware VE.Bus ports, additional VE.Bus inverters can be added via the MK3-USB - but they will be very limited functionality, basic energy meter data only.

If previous version functionality existed to allow the MK3 to be the primary VE.Bus (instead of the built in VE.Bus ports), it was unintentional, and I could see how that could cause issues and be considered a situation to be avoided.

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aph avatar image
aph answered ·

Because before the Raspi solution could only use USB type of connection. As Raspi and display were in only one housing it sits in the other corner of the campervan away from Multi, MPPT and shunt. In order not to have to pull another cable al the the way from one to the other end of the vehicle I just did use the existing USB based wiring.

Overall, if I have a already have an MK3 why not use it?

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nickdb avatar image nickdb ♦♦ commented ·

Because it isn’t required and you can just connect the RJ45 cable you used to the mk3 directly to the cerbo.

I would imagine there is a conflict when the cerbo sees two ve busses (busi?), something a PI doesn’t have.

Probably related to why the two can’t be connected simultaneously to the same bus.

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Kevin Windrem avatar image
Kevin Windrem answered ·

Just my two cents:

The logic used in v2.93 and earlier was to select the first inverter/charger found as THE managed one. All ports were considered equal. I know order of discovery is not a good mechanism to select one device from many but in 99% of the systems there is only one inverter/charger so this isn't a factor.

Like the @aph system, there may be cabling issues that make it difficult to run the necessary VE.Bus cable. This is often the case in RVs and boats where cabling is installed during construction and changes can't be made later. Locking out the use of the MK3-USB adapter for THE inverter/charger on Cerbo, etc. which began in v3.00 will make such systems difficult to maintain.

I think it's fair to check the on-board VE.Bus port first but then check the USB and CANbus for inverter/chargers if none are found on the on-board VE.Bus port.

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aph avatar image
aph answered ·

I can follow your argumentation, but it as as @Kevin Windrem did state. I will most likely have not the chance to pull a RJ45 cable from Multi to the panel where Cerbo and display are located. As it would need large scale dismantling of a lit fixtures. There is also no good place next to the Multi to place Cerbo or display.

Will try to somehow pull the cable, but I’d that won’t work I will have to sell the brand new cerbo and go back to a PI based solution, which doesn’t have the issue.

Please consider though if the solution proposed by @Kevin Windrem can be a valid alternative.

CU, >>> Arne <<<

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Related Resources

Victron Venus OS Open Source intro page

Venus OS GitHub (please do not post to this)

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