What to do with my leftovers... Should I cascade them ?

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iammotorhomeless asked Jun 6, '23

What to do with my leftovers... Should I cascade them ?

Hi
I have had my pair of Multiplus II 48/5000 (240V) running in Parallel for a couple of weeks now, and they are working fine. (other than a dodgy fan in one of them)

but I have a load of parts leftover !

when I started my Victron solar journey, I bought loads of stuff that I thought I'd need and then bought other stuff that was 'better' (differant)

So. I have four Epoch 12v 105Ah LiFePO4 batteries (that I was going to connect as a 48V pack)
a 500A SmartShunt, a SmartSolar MPPT 150/35, a heavy duty DC isolator (Icu 85kA)
loads of 50mm2 and 75mm2 cables and Lugs.
A Raspberry Pi with Venus OS and a load of USB to VE Direct DIY Cables, set up and ready to go.

I can't hook the 4 Epoch batteries up to my main (BYD battery) system.
But I could buy a small Multiplus 48/1600/20 and cascade them ?
Thinking of setting up a second "separate" system that just powers my office (using about 2kW per day)
that part is not that complicated

MY QUESTION
is how to set up charging and pass-thru

I don't really want to set up more solar... so would like to only charge the 4 Epoch batteries, from the main system, once the BYD batteries are full, and we have excess solar.
and would like the Multiplus 48/1600/20 to go into passthru if the 4 Epoch batteries are low

And I just can't work out the best way to do it.

I was thinking of using a Shelly 4 Pro to switch power to the Multiplus 48/1600/20 once the main batterys were full, but then how would I work the passthru, if both sets of batteries were low.

and how would I stop the Multiplus 48/1600/20 from drawing power from the BYD battery to charge the 4 Epoch batteries (that would just be a waste)

there must be a way... anyone :)

thanks in advance

battery charging Venus OS virtual switch cascading inverters dc isolators in parralell system

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Answer 1 · 2023-06-06T14:18:57Z

matt1309 answered · Jun 06, 2023 at 02:18 PM

Hi @IamMotorHomeless

Just out of curiosity why can't you connect the Epoch to main system battery as well? Both LiFePO4 aren't they or is one 15 cells vs 16 cells?

If it's inrush current you're worried about and the BMS don't have built in current limiters I think I've seen some companies offering separate devices to limit current (although if you're not turning the packs off you might be fine without assuming all fused anyway).

Seems like a shame to cascade having to split loads etc.

I suppose you could just use node red or equivalent to turn off 1600 multi if main batteries starts discharging.

Another options maybe: Not sure if this would work but could you put the smaller multi before the grid meter and parallel it with the grid to "catch" the excess energy as it's being exported to the grid.

grid -> grid meter 1 -> mutliplus 1600

grid -> grid meter 2 (after grid meter 1) -> main multiplus

Sperate Venus OS and ESS running on multiplus 1600.

So the ACIN of multiplus 1600 and main system ACIN are paralleled. but Grid meter 2 is before main system only. and Grid meter 1 is a true grid meter.

Have the main system operate normal ESS but when it exports it thinks the "grid" is at grid meter 2 (so grid data on main system will be wrong but i'll ignore that for now).

However multiplus 1600 will see grid meter 1 is negative as the main system is exporting and it'll turn on charging if possible through it's ESS settings.

The part I'm not sure on is if the multiplus 1600 ESS will need to see amounts coming from main system. Or if it can work just having the grid meter 1 data and outputing power based on that number alone. (I'm guessing it does, as that configuration is almost like AC coupled PV but on ACIN but rather than have AC Coupled PV you've got the entire main system)

If that does work then the multiplus 1600 would "catch" some of the power as it was exporting to the grid and also be able to export power back through grid meter 2 into the main system if the main system ever drew power from the grid. Or you have seperate consumer unit on the mutliplus 1600 like you mention.

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iammotorhomeless commented · Jun 06, 2023 at 06:09 PM

HI @matt1309

I got a MCS Certificate for my system... (and I am not 'allowed' to modify it) so if I add anything to it, the warranty that comes with the Certificate becomes nullenvoid. Plus BYD are a little funny in their warranty about pairing their batteries with other batteries.
Else, my Epoch batteries would just be getting wired in :)

The other reason behind a Multiplus 48/1600, was although I am MotorHomeless at the moment, I could 'disconnect' it all, load it in the back of the car and take it camping, maybe.

I do like the idea of using the Energy Meter to control the 48/1600,
I have an ET112 in the consumer box. It is connected to my Cerbo GX
what's the best way to share that data with my Raspberry Pi Venus OS ??

and I could add a second clamp energy meter, to give me grid 1 and 2 meters
the Shelly EM only connect with Wi-Fi, I can't find an ethernet version (is there one)
thinking that I could pull that data into both the Cerbo GX and the Ras Pi ??

all food for thought, need to do some more reading

And thanks for putting me onto node red... having loads of fun

but not as nice as some :(

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matt1309 iammotorhomeless commented · Jun 06, 2023 at 06:58 PM

Ahh i see, that makes sense not to mess with. Don't want to ruin warranties although would be a nice solution.

Yeh I've noticed that a lot in battery community, in my opinion if BMS have sufficient safety features + a fast acting fuse then it's safe but I see their arguement, more risky to allow it.

I'm not a big MCS fan, as a (filthy) DIYer it feels like a paywall. For insurance/warranties it makes sense, the bit i dont like is that you can export to grid with just DNO approval but you can't get paid for it without MCS.

"We'll take your excess power if it's a dodgy install but we wont pay you for it"

I'm only bitter after being charged me 1500 to sign off as MCS when all the work was done before hand, just "reviewed".

Thinking about it I think your solution was cleaner. Especially if potentially installed in a motorhome.

I would get a second Venus os for the motorhome connected to the multiplus 1600, have that query the main system Cerbo for how much is being exported to the grid. (Using amount exported will prevent any concerns around main batteries being drained as multi 1600 is only charging with the exported amounts)

I would try to do this using node red on venus os in motorhome. Read via MQTT on the main systems cerbo GX the Grid meter data to see how much is being exported) And then set charging limit in multi 1600 to match how much is being exported. (I think you can do that by setting current limit in DVCC via node red also, think this is in amps rather than watts though)

I think the MQTT topic would be:

'N/{vrmid}/system/0/Ac/Consumption/Total/Power'

replacing vrmid with your vrmid. Here's some more detail on MQTT that might be useful if you go that route.

https://github.com/victronenergy/dbus-mqtt

In terms of using that power in the house from the motorhome might need to be more creative. (I'm not sure on how easy the earthing configurations are when coming from the motorhome, that's beyond my knowledge), However using motorhome power in the house is likely a problem folk have already solved.

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