How to configure Victron BlueSmart charger to ensure battery cycling between 40% and 90%?

[Atom Tan]

Iterative testing can be very informative, if you understand the results.

I am trying to understand how my BlueSmart charger configuration and the outcome are related. I’d appreciate some feedback on my conclusions.

I had a brief power outage (go figure) so the charger was reset and started bulk again, so I didn’t get to see what the end result of the above test would have been. I hypothesize that eventually, one of three things would have happened:

1. It would have hit the default (if no rebulk current is specifically configured) rebulk threshold of 15A for 4 seconds.
2. It would have fully charged the battery back up as the charger continued to pump more current into the battery to try to keep it at 13.2V. I don’t think this is likely, since I *think* that Storage mode would just try to keep it at 13.2V, not charge it fully.
3. I would have hit my low voltage shutdown threshold.


My Conclusions

I think that in disabling Float, the charger went from Bulk to Absorption and then straight to Storage mode. Once in Storage mode, the battery serviced all loads exclusively until the battery’s SoC hit the 13.2V threshold for the Storage setting, at which point the charger started to send current back into the battery to try to keep it at 13.2V. As load continued to draw the battery down, the current into the battery in Storage mode ramped up.

I suspect the charger may never have gone back into bulk, unless one of several external factors occurred: power to the charger is interrupted, a mode switch is pressed, or I forced it.

Once a week, the charger would run an absorption charge, which would fully charge the battery and balance the cells.

If I had had Float configured, the battery would have serviced all loads exclusively until the battery’s SoC hit whatever I configured the Float threshold to be, at which point the charger would have started to send current back into the battery to try to keep it at the configured Float voltage. Again, without a rebulk current configured, I’d be waiting for the default to trigger.


Scenario 1 - Some Battery Cycling
I think that if I want the battery to draw down to, say 50% SoC and then start a full charge cycle, I would set the Float voltage at a voltage approximating 50% SoC under load, keep Storage at 13.2V and set rebulk current to something like .2A or .3A. It should never hit Storage in this case. Alternatively, I could keep Float disabled, and set Storage to a voltage approximating 50% SoC under load.

I do understand that SoC is generally measured at rest, and that a measurement taken under load will not be accurate, so it will be an approximation.

Scenario 2 - No Significant Battery Cycling
Since y'all are telling me that cycling the battery isn't a meaningful exercise, I could just abandon any attempts to do so altogether, and configure Float to be 13.6V, Storage to be 13.2V and set a rebulk current of somewhere in the .2A to .5A range.

In either scenario, I probably need to observe what happens with different rebulk current settings to dial in getting bulk to start when I want it to.

Do I understand the charge process correctly? What is wrong with my conclusions and my understanding?

 

[RCinFLA]

Questions:

If I understand you correctly, @RCinFLA, you are recommending that I should re-enable float at a voltage below 13.7V, but relatively high, so probably 13.6V?

Not necessarily, but the biggest mistake folks make in trying to 'baby' there LFP battery is failure to keep the cells in SoC balance by periodically allowing the BMS to perform balancing. Most BMS's only balance dump when a cell gets above 3.4v. You should have a little more than 4x this voltage (for four series cells, 12v LFP battery). Something like 14.2v absorb charge level for couple hours once a month.

 

[Atom Tan]

Thanks, that is helpful.

My understanding of all of this is evolving as I continue to test, and I think I have ended up pretty much where ya'll originally suggested I should be. But now I (think I) understand why I'm there.

For one set of tests, I had Float set to 13.7V and rebulk current offset set to 1A. This caused very frequent, very short duration (measured in seconds) bulk, an hour of absorption (minimum duration settable in this Victron charger), and then a minute or two of float before rebulk fired again, repeating the same process. Some of this is inference, as the Victron logs have a decent amount data, but it's not comprehensive.

I didn't particularly like that the battery was nearly always in absorption, although it's my imperfect understanding that it won't really hurt anything. I really don't like that an hour of absorption is the shortest duration I can configure.

In an effort to reduce the frequency of cycles, I then set Float to 13.6V and rebulk current offset to 5A, with repeated absorption set to 7 days and it's closer to what I was looking for. The battery serves loads by itself until the Float voltage threshold is hit, at which point current begins to trickle in. I haven't been able to directly observe what is happening at the point at which Float starts trickling current, but I suspect that it either starts out or quickly ramps up to current more or less equal-to-or-slightly-higher-than the draw on the battery, to keep voltage at 13.6V.

I think that rebulk will never fire in this configuration, since the current in should never exceed current out, and the loads are pretty steady state at about 3.5A, which is below the configured rebulk threshold. Even so, the battery is at a high enough SoC that any bulk phase would be very short. Once the 7 day timer for absorption fires, it'll get to 100% SoC again, cells will balance, and the cycle will repeat. This would, I believe, be a perfectly fine state of affairs from a battery health and safety perspective.

The charger will never enter Storage mode, since entering that mode requires 24 hours without discharge, which will never happen. I could set the Storage voltage to just below the Float voltage if I wanted to, just in case, or disable it if I can do so.

I can play with the Float voltage to run purely off battery for longer periods of time, play with the rebulk offset to trigger rebulk more frequently, and play with the repeated absorption frequency as well.

Regarding those variables:

1. Reducing the Float voltage to draw the battery down a bit more is probably not a useful exercise, except to the extent that it makes ME feel like I've accomplished something, because it will only run off battery for the first N minutes/hours of a cycle until SoC hits the Float threshold, after which point the Float program will keep the battery at whatever voltage I have set, and loads will be served from the charger until absorption fires and the cycle repeats.

2. Tweaking rebulk to fire isn't really useful since the battery will already be at a high enough SoC that bulk will only last moments anyway.

3. Absorption more frequently than a week is probably totally unnecessary and may even be less optimal from a battery health/safety perspective than a longer interval. It was suggested earlier in this thread that a month would be perfectly fine too. Since the battery will be kept at a relatively high SoC via Float, the only real purpose of absorption in this case is to balance cells.

I think I've arrived at a decent understanding of how charging parameters affect outcome, and appreciate both the advice I’ve been given and the ability to talk this out in this thread. Thanks.

It seems to me that for the use case I have originally laid out, the following settings are a good place to be, keeping in mind that I will be 2 days away from this setup with pretty much zero visibility into what is happening, except for a camera pointed at the devices:


BlueSmart Charger
Absorption: 14.3V
Float: 13.6V (Maybe 13.4V)
Storage: 13.5V (Maybe 13.3V)
Bulk time limit: 24 hours
Rebulk Current: 6A
Absorption Duration: Fixed
Absorption Time: 1hr
Repeated Absorption: Every 30 days

BatteryProtect
Shutdown: 11.8V
Restart: 12.8V

 

[Atom Tan]

The charger will never enter Storage mode, since entering that mode requires 24 hours without discharge, which will never happen. I could set the Storage voltage to just below the Float voltage if I wanted to, just in case, or disable it if I can do so.

Well, I was wrong about this, or I read docs for a different charger. I'm in Storage now after exactly 8 hours in Float.

Sitting at 13.2V (which is what I set Storage to), BMV reporting 95% SoC, no current from the charger. We'll see how it does overnight.

 

[Atom Tan]

Probably my final update on this question, posted only in case this comes up for anyone else and my experience might be useful.

To sum up, my steady-state 12V load on this battery is between 3.5A and 4.5A. My goal is to serve the loads full time from the battery/charger, keep the battery (mostly) charged, and recover gracefully from any utility power outage that results in battery depletion past the configured low voltage shutdown.

After some testing, this has emerged as my optimal configuration. It keeps the battery at 13.4V to 13.5V, or a BMV-reported 97-98% SoC.

After a bulk/absorption cycle, it goes to Float for 8 hours, and then to Storage, where it has been sitting steady for a couple days straight, so I think it'll keep going.

The charger continually puts between 3.5A and 5A into the battery during Float/Storage, effectively serving the connected loads. Absorption for an hour every 30 days should keep the cells balanced.

It shouldn't rebulk or absorb between those 30 day intervals unless there's a utility power outage that causes the charger to drop.

BlueSmart Charger
Absorption: 14.2V
Float: 13.5V
Storage: 13.5V
BatterySafe: Disabled
Bulk time limit: 24 hours
Rebulk Current: 6A
Absorption Duration: Fixed
Absorption Time: 1hr
Repeated Absorption: Every 30 days

BatteryProtect
Shutdown: 11.8V
Restart: 12.8V