Defined high/low state of charge limits

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saxofon asked Oct 4, '20

Defined high/low state of charge limits

I have a victron 48V bank (4x200Ah smart), bms, smartshunt, cerbo, BlueSolar Charger MPPT 150/45, batteryprotect, li-charge and multiplusII (yes, all in on victron stuff :) )

Goal is to have it autonomous as much as possible.

Currently when charging, the systems always tries to charge to 100% where the bms is shutting down multiplus and the li-charge relay where the solarcharger is connected. As I don't want the batteries to sit at 100% for long (which they then will do during summer months when we have plenty of sun) in order to keep battery lifetime as good as possible, I'd like to define a upper limit like 75% SoC perhaps. The system should then try to charge to 75% and at that level only add energy (via solarcharger and/or multiplus) as needed in case of load to keep it at 75%. And yes, I would need to now and then charge up to 100% so the SoC measure isn't drifting off. The manuals suggests once per month so can be a manual thing todo, perhaps with some notifier via VRM...

Similar for the lower limit... instead of bms shutting down load at battery protection level, would be nice with a definable lower level like 35% SoC. Have not so much experience of this part of the energy envelope as the system so far coped good with load :)

This would also allow one to test and make sure the protection mechanisms will work, without having to actually be at the edge of safe SoC range.

Haven't found howto do this, or should it be possible?
If no, perhaps add as a enhancement request?

SOC

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saxofon commented · Oct 05, 2020 at 06:50 AM

and to clarify the obvious... these defined upper/lower limit should of course be *in addition* to the battery protect levels that BMS sense on already today.

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Answer 1 · 2020-10-16T08:24:04Z

saxofon answered · Oct 16, 2020 at 08:24 AM

Ping! Anyone awake at Victron? ;-)

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Alexandra ♦ commented · Oct 16, 2020 at 08:52 AM

@saxofon

Are you off grid? On grid? Mobile?

This affects what programming can be done. Or advice that can be given.

And for the 100% on battery state of charge I think that the bms will handle the overcharge or held at high charge issues. Most bms designs never hold the internal cells at max anyway.l or even charge the that high.

For example winston cells can be charged to 3.85v but batteries that use them usually only keep then about 3.35v per cell and the bms tells the system it is at 100%. Even though technically they are not.

You could always program a load on ac2 to switch on and off if you really want the batteries to cycle if the system is unattended. Bit for the most part the system can run itself.

You can even program the multi on the charger page with the storage function so it 'refreshes' the system. When you are using ve configure you will see how the graph changes when you check the storage function .

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saxofon Alexandra ♦ commented · Oct 16, 2020 at 05:00 PM

Hi and thanks for reply! It is a boat, so mobile I'd say. Mostly off-grid but somes connected to shore-power so then on-grid I guess. Yes the BMS shuts charging off at 100%, which is good for the safety barrier. But as said, I don't like them to sit at 100% for longer period. I get substantial energy in on summer period, like 6-7kWh per day and I consume like 2kWh per day currently (more to be added of course along time). As I've been prototyping this year I've mostly balanced it with either 0, 1 or 2 solarpanels connected. Would be nice to not have to have the multi on all the time so when leaving boat I would prefer it to be off. Is assistants running in the multi even when it is in off state? I understand assistants runs in the multi, although with the cerbo and it's friends (gx etc) it feels more preferable to have them as the maintainer of state. But if assistants runs even in multi off state it doesn't matter from me as a user point of view. I don't say the batteries should be cycled automatically, just not charged above a userdefined level, like perhaps 70% or so. If they are at 70%, the system should just stop charging and only add energy when needed for ev consumption.

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