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shockbroker avatar image
shockbroker asked

How to avoid victron charger return to bulk during float

I have a MultiPlus (two in parallel) connected to a large LiFePo4 bank. When not in season I want toe keep the bank at a float voltage to keep it approx 50% charged. After a full charge it takes a few days of power consumption before this voltage is reached.

Then, all is well until the MultiPlus believes the voltage has been 'low' for a minute or so, and starts a new bulk cycle. This results in a very length, high power charge cycle that negates the advantage of keeping the bank at float.

How can I avoid this bulk cycle and just keep the bank at float voltage during winter?

At this time I am wondering if I should just bypass the MultiPlusses and use a DC power source at the float voltage but that would really be suboptimal since I prefer keeping the boat in 'ready to go' condition at all times.

I would be very happy for suggestions.

battery charging
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regman54 avatar image
regman54 answered ·

Does the manufacturer give specific instruction on how they should be stored? If not just disconnect the batteries. From what I've read it's safe to do so as long as they are stored in a proper environment and their voltage monitored occasionally.

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shockbroker avatar image
shockbroker answered ·

I tried to keep my question short but I suppose I kept some information out. The boat needs AC power over the winter e.g. for heating and pumps and I definitely want the back-up of the batteries in the case of shore power failure. Float voltage as supplied by the victron would be perfect, it is just that the MultiPlus insists on recharging the batteries back to FULL after just a very short time of low voltage. Instead of it just getting back to the float voltage. So e.g. should a pump start and run while the float voltage has been reached and it causes the voltage to sag to a 'too low' value (no mention anywhere of what the values are) then it is back to BULK charge which does not stop until the batteries are 100% full.

So I would really like to undo this -for LiFePo4- anti-feature of keeping the batteries topped up (if that is what it is), or otherwise be able to radically adjust the limits of what Victron believes is 'too low' .

A solution I thought of would be adding a separate DC supply and set it to my current float value while reducing the MultiPlus float voltage to a much lower value so that voltage sags don´t impact it any longer. Not an attractive solution because it requires installing additional equipment. Plus, what that supply at float would do when the MultiPlus would start charging to above its float is another issue.

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pwfarnell answered ·

While away you could set the absorption voltage to be the same as the float voltage at around 50% SOC and then it would not increase in voltage when it goes to bulk. The MPPT chargers have a setting for rebulk like 0.4V so it has to drop thst much below float to rebulk. The Multiplus value for this is not configurable. On teturn you would need to reprogram the Multiplus. If you have a GX device in VRM then you could have 2 settings profiles and upload these through VRM as the easiest option.

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shockbroker avatar image shockbroker commented ·

Thanks for this info. I'm on board quite often so changing the settings (and break float with it) is not a very good option. However I didn´t know 'rebulk' was a thing and thanks to you, I found

https://community.victronenergy.com/questions/65096/multiplus-rebulk-voltage-threshold.html

and


https://community.victronenergy.com/questions/102344/multiplus-frequent-rebulk-while-on-shore-power.html

No for-certain solutions as yet, but if the rebulk offset is different based on the battery type settings, what is the offset with a VEconfig custom type? Perhaps I can get a larger offset than .4V?

What I really want is an open source charger/inverter...

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