question

Martin Gasthuber avatar image
Martin Gasthuber asked

Recommended DC cabling/fuse/breaker BYD LVL to 3 x MPII 48/5000 and 3 MPPT

Hi,

What is the recommended DC interconnect between:

2 x BYD LVL 15.4,

3 x MPII 48/5000 and

up to 3 MPPTs ?


The Lynx systems (with the 600A internal fuse in the Lync shunt) looks OK, but the related documentation is focussing on other batteries.

According to the BYD/Victron documentation I expect problems with the BYD BMU and Lynx Shunt VE.Can connection to the CCGX.

What are the recommended fuse levels and breakers (if required) ?

Is the Lynx Shunt required at all with the BYD BMU is use anayway ?

best regards,

Martin

Multiplus-IIoffgridBYDdc system
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1 Answer
Guy Stewart (Victron Community Manager) avatar image
Guy Stewart (Victron Community Manager) answered ·

Hi @martghh,

The Lynx shunt is not required when using the Lynx Power-In or the Lynx Distributor.

You could use a Lynx shunt, that wouldn't cause any problems. But it is quite redundant and unnecessary with the BYD BMU on the LVL batteries, which is very accurate.

Just using the Lynx shunt for it's 600A fuse is a very expensive way to do it.

For so many DC bus interconnections I would suggest using a couple of Lynx Distributors with individual circuit fusing on the MPPT / MultiPlus side, and then running the battery take-offs into another Lynx, with an HRC fuse (like an NH fuse) between the two.

Cable sizes and fuse ratings are specified in the product manuals for each of the Victron products. Unfortunately I don't have an exact web link for section 4: Installation 5k product, but you can see it here for the 3k.

A nice safe rule of thumb is fusing sizing is 20% over what is required by the load or charge source, and cable sizing is 20% over what is required by the fuse sizing.

That's only a suggestion, and there are other ways to do it safely. LOTS MORE and far better information is available in the Victron book Wiring Unlimited, section 4 - DC wiring.

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Martin Gasthuber avatar image Martin Gasthuber commented ·

Hi Guy,

thanks - i've gone through the 'wiring unlimited' and some of the remarks looking a bit contrary to the way its done with the Lynx Distributor, especially the way of intermixing battery feeds with MPPT/Multiplus connections - the Lynx way will end in separating both. For a 'shunt' integration, the same applies to the '-' part of the circuit.

Using the Lynx Distributors only, i will not be able to use the LED/fuse monitoring LEDs, right ?

Still unclear to me is the receommendation to ground the 'minus' pole - is that recommended also for the BYD batteries ?

Are there other (simpler) ways to connect 35 and 70 mm2 cables to the Lynx Distributor compared to cable eye lugs ? Some of the typical NH boxes allows direct cable mounting - according to the specs, this should result in similar 'low resistent' and minimize connections throughout the cable run.

I have two of the BYD LVL systems already here, but still have to wait for the BMU/CCGX CAN cable to connect, so i was not able to see what monitoring information the BYD BMU will provide (except the SOC and charge/discharge limits) - will it be similar to what the BMS+shunt provide ?

best regards,

Martin



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Guy Stewart (Victron Community Manager) avatar image Guy Stewart (Victron Community Manager) ♦♦ Martin Gasthuber commented ·

There are many ways to do DC wiring, so information will be contradictory at times.

Where items are on the BUS comes with various implications.

Generally speaking the ability to isolate the batteries from the rest of the system is a requirement (and a really good idea).


Rules and requirements around grounding the Negative in a DC system vary with regional wiring rules and standards.

Your battery distributor will be able to assist with what is required in your region for safe installation of their battery system.


I have not heard of any issues with the Lynx cable lug mounting system.


The LVL BYD BMU connected will provide vastly better and more specific monitoring information than the Lynx Shunt.

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