I am designing a new system for the house bank on our powerboat and plan on using some new components and some existing, as follows:
Existing Components:
Multiplus 24v/3000 120v AC located approx. 7-foot cable run to battery bank. This does and will act a the boat’s inverter and as one of two chargers.
A 24v Mastervolt Mass Charger 24v 100-amp charger 230v AC located approx. 20-foot cable run to battery bank
New Components:
Victron Smart Lithium (or the new NG) batteries in series/parallel to create a 24v bank of 800-900Ah for house loads.
Lynx BMS
Cerbo GX
And possibly a new Multiplus 24/3000 as a secondary charger-only if incorporating the MasterVolt is problematic and we delete it.
Wakespeed WS500 alternator regulator for our 200A Balmar alternator
Assumptions:
I program my older MasterVolt charger with the proper charging profile for the Victron batteries and of course do the same on the Multiplus. The Multiplus would be the inverter/charger, plugged in to the Cerbo GX and the Mastervolt would simply be a “dumb” additional, paralleled charging source which I would manually manage (turn on/off) for use when running our generator to recharge the batteries after sitting at anchor overnight, for instance. I simply need more charging amperage in that scenario than the Multiplus alone can supply.
The Wakespeed regulator would be provisioned with the proper Victron charging profile and is used as the only charging source when we are under way. Plugged in to the Cerbo GX.
Shunts installed at battery bank and alternator in recommended locations for proper sensing.
There is insufficient room to mount both chargers equidistantly near the battery bank, but adding DC cable to the closer inverter/charger to achieve equal length cabling is possible if absolutely necessary - but our cabling is large, 3/0 and 4/0.
Questions:
Is keeping my older Mastervolt and using it as described as an additional “dumb” charging source an acceptable scenario?
If not, and I replace the Mastervolt with a new Multiplus 24/3000 120v from my dealer will it be “model identical” enough to my existing Multiplus so that I can daisy-chain them and use synchronized charging and/or DVCC? They would be paralleled in terms of charging, but only one would be used as an inverter. (my current Multiplus is SN HQ1946JPJBP)
What other important considerations might I be missing?
The Lynx BMS manages charging from the Multiplus and the Wakespeed telling them how much to charge and shuts them down on cell overvoltage, high temperature etc. through the DVCC function in the GX. Your Mastervolt charger would not have any safety cut off. If you keep it you need to investigate if you can connect the allow to charge signal from the Lynx BMS to a remote on/off input on the charger, or add a Victron battery protect on the charger outlet with the battery protect operated by the allow to charge signal.
I can not answer paralleling inverters. If you install a second Multiplus as standalone then you can monitor it if you connect it to USB via a mk3 dongle but it will not be controlled by DVCC so it would still need all the Lynx BMS allow to charge connections for safety.
btw, if 24V, why not use 24V batteries as series balancing is no longer an issue.
Hi pwfarnell and thank you so much for the response.
My apologies…I misspoke: I am in fact going to use 24v volt batteries in parallel (nothing in series). My bank will have either 4 x 200Ah or 3 x 300Ah batteries if I go with the new NG variant.
When using multiple Victron chargers, the requirement that they be of the exact same model, firmware and have the exact same DC cable lengths is quite restrictive. But I assume this is only if you want to configure them in a Master/Slave arrangement and/or(?) enable DVCC to work?
I am not opposed to replacing my Mastervolt with a new Victron unit. Is there a way I could have a new Multiplus-II and an older original Multiplus with different length DC cabling (since they are in different locations) work well together if they were both plugged in to the BMS? And why must one be plugged in using a mk3 instead of having them both connected via ve.bus?
It seems like a dual charger situation like this would not be uncommon, but it is seeming uncommonly complicated to me!
You can only have one VE Bus system connected to the Cerbo that is under control. The VE Bus system can be multiple units set up as a single system in parallel which means identical units and identical cabling. You can have a second inverter that is separate but it HAS to be separate to the VE bus system because if it was on VE Bus the control would go awry, hence using the mk3 dongle. As the 2 inverters are separate and not synchronised outputs you would have to have them on separate ac output circuits, there would be problems on the same ac output.
OK, thank you - I think I’m beginning to get a grasp here.
So…assuming identical inverters and parallel DC cabling of same length BUT with only one inverter doing inverting and the other acting as just a charger, does this qualify for a master/slave configuration and could DVCC be enabled?
No, because they are not acting as a parallel pair. In parallel they work as if they were 1 larger inverter equally sharing charging and inverting and being fully synchronised. The output ac is also connected and the output ac cabling also has to be symmetrical.
The Victron page on parallel states
Parallel and Multiphase systems are complex. We do not support or recommend that untrained and/or inexperienced installers work on these size systems.
Thank you again pwfarnell for sticking with me here. Your comment is fair - although when I read that section as part of my research and viewed a related training video I felt it answered what would surely work but not what similar setups ‘might’ work which is why I asked.
So, in the end I suspect my system will end up having two dissimilar inverters (although both Victron Multiplus I’s and/or II’s), located in different locations, both plugged in to a Cerbo GX via VE Bus and a MKIII on the other. A Lynx BMS will be part of the system.
The inverter closest to the battery bank will act as my daily use inverter/charger and the further away Multiplus acting as a charger only and used to dump additional current into a depleted battery bank after a night at anchor in order to speed charging. Obviously both will be programmed with the proper charging profile.
The further away inverter will obviously see a relative DC voltage drop due to the wire run, but am I correct to assume that a Smart Shunt at the battery bank plus the BMS and Cerbo can communicate effectively enough to both chargers that they can function properly and efficiently together? (Not in perfect sync of course per all the above discussion).
I will try another response, I believe you are being optimistic, the second Multiplus will work only as a standalone charger, the mk3 to USB provides one way traffic allowing it to be monitored in a limited way.
See the answer provided by Victron staff in the old community.
Additional systems, connected to the GX device using an MK3-USB, are not controlled by DVCC and will charge and discharge according to the configuration made in those units.
So the second Multiplus will not get battery voltage from the SmartShunt to compensate for voltage drop. Neither will it get charge control from a Lynx BMS nor will it get charge disconnect via DVCC and will need ATC via remote switching as I said earlier.