question

geomz avatar image
geomz asked

Force a Quattro into Float?

Is there a way (switch, assistant, setting) that allows me to force a Quattro into Float -regardless of state of charge on the batteries?

I hope this hasn't been asked before, but search is not working at the moment (internal server error) so,

Here is my scenario, this deployment is in an RV.

I have a Quattro 24/5000/120 connected to a pair of 12V lithium batteries in series, with a BMV 712 monitoring them.

For half the year, this vehicle is spent "off grid", meaning no constant source of shore power (a generator is used to recharge the batteries).
In that scenario I manually manage the charge of the batteries to ~90% SOC (because evidence is showing it increases their lifespan over a constant 100% SOC). I do that by turning off the generator, and the batteries are allowed to discharge with regular day-usage. Then the recharge cycle is repeated.

That works great, however,

For the remaining half of the year, this vehicle is spent on-grid and has a constant AC input. That, of course, triggers the Quattro's charger functionality and it happily tries to recharge the batteries to 100% (with a *mandatory* and unnecessary 1 hour absorption as a bonus). And it repeats this cycle, anytime powerassist is triggered and the batteries are used temporarily (however little), thus discharging them enough to restart the whole cycle over and again.

I don't want it to do that :)

I believe that to be deleteriously burdensome on my batteries (or any lithiums for that matter), who would be much happier at ~50-60% SOC when operating in this "storage" mode.

And that's my issue.

I want to discharge the batteries to 50% and leave them there, while keeping the Quattro happily plugging along doing its other functions like passing power and power-assisting from the batteries as needed.

Is there a way to accomplish this with my Victron equipment?


I've tried a series of hacks to simulate this behavior. Primarily by using the charge rate assistant with an aux1 trigger switch. But even that, even though the assistant is set to 0 amps, when active, still isn't really 0 amps. It keeps a creeping 1.5 to 2 amps going, regardless - which eventually charges the batteries up anyway. Just slower.

Thoughts?

Thanks in advance for your help.

battery chargingcharge current limitfloat
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2 Answers
ben avatar image
ben answered ·

There are open feature requests to (a) remove the 1h absorption minimum and (b) add a "hold charge" feature to do exactly what you describe.

There is no way to force float programmatically that I am aware of.

If you have a BMS that can determine when your desired holding SOC is reached, you can use its enable/disable charge control line to instruct the Quattro to stop charging.

If no BMS is available, you can simulate a lower SOC by setting a lower absorb voltage threshold and a lower float. This is not something you would want to do every week, but if you're parked for six months, breaking out VEconfigure is not so bad. Getting the exact voltage dialed in to achieve 50% will take some experimenting, but you can get there. (I hold mine at around 70% this way.)

Finally, if you really want to start hacking, I suspect it is possible to write a Venus driver that watches the BMV state and sets a hardware control line somewhere that you then use as a quais-BMS -- and you go back to the earlier paragraph then, wiring that logic signal back in as a charge-enable control.

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Mark avatar image
Mark answered ·

Yes you can do this quite easily by using the '2 signal BMS assistant' and configuring it appropriately.

https://www.victronenergy.com/upload/documents/Manual-Connecting-other-lithium-battery-systems-to-Multis-and-Quattros-EN.pdf

You can assign one of the aux inputs to control this and select the charger to go into float rather than turn off if the related aux input is opened or closed.

If you have a BMV you could also set the BMV relay to trigger based on SOC% and wire it into the Quattro aux input to automate the process.

I am on my phone at the moment, but if you need some more pointers or screen images just let me know. The link I attached should explain the functionality quite well.

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geomz avatar image geomz commented ·

That’s brilliant Mark, thank you!

I hadn’t loaded that assistant before. I was faking things a bit using the charge current control assistant, bound to aux 1. When closed it set the charge rate to 0 and back to normal when open. But even at zero, there was still a trickle current of 1.5 amp.


A couple of questions, if you don’t mind,

1) are the other 3 options for triggers (the ones that use just one input) operating as an on/off switch? Or do they need to be unset/reset (to reactivate charging), elsewhere?

2) does the ‘disable charger’ selection turn the charger off completely? And do you know if works similarly to the checkbox option in the charge current assistant about “turning off the charger when current should be 0”?

3) if I force it into float, and have the batteries at say 50% I should assume that a trickle charge will be applied unless I set the float voltage really low?


Thanks a lot again! That gives me some new things to play with :)


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Mark avatar image Mark ♦♦ geomz commented ·
  1. Yes all control options are triggered by an aux input or temp input being either opened or closed. The Multiplus / Quattro has inbuilt pull up resistors so that one side of the aux input is ~5v in open circuit condition. When the circuit is closed it will pull the ~5v side down to ground. The trigger threshold is probably somewhere ~2v.

There is no need for any additional reset elsewhere, the aux input simply acts as an on/off switch.

Per the 4 control options - you can choose to respond to a theoretical;

  • battery full/over voltage condition by disabling the charger or going to float - - battery empty/under voltage condition by disabling the inverter

  1. I have tested the 'disable charger' option and the Multiplus goes into 'Passthru' mode, so I can only assume that the charger is totally off but I didn't take any actual measurements. Also note the the Multiplus / Quattro processor is powered from the battery, so if the charger is truly off there will be a power draw of ~3w and this will eventually deplete the battery.

  2. Forcing the unit into float phase just means that the charger will target the float voltage - there is no form of additional charge current control. If the batteries open circuit / resting voltage is below the float target voltage then a charge current will be provided to lift the voltage and hold it there. If the battery open circuit / resting voltage is at or above the float voltage then no charge current should be provided.

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ben avatar image ben ♦ commented ·

Thanks, Mark, I had no idea there was a "float" hiding in that wizard.

Have you found that installing it has any impact on regular bulk/absorb/float voltage-based charging (i.e., when not using the override)?

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Mark avatar image Mark ♦♦ ben ♦ commented ·

Hi Ben, No it shouldn't impact the regular charge settings, however this assistant does disable temperature compensation and set the absorption type to fixed in the background... (which is a bit unclear based on the prompts and user visible settings)

If your running lithium this should be your regular settings anyway and no issue.

But for me it meant that I unfortunately can't use the neat functionally in this assistant, since I have a bank of AGM batteries and need to keep the temperature compensation and adaptive absorption active...

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