geomz avatar image
geomz asked

Feature Request: BMV should show time-remaining as time to full charge, when charging

Would really like to see the BMV time remaining calculation shift from time left on discharge to time-to-full charge (instead of infinite).

Could be done without a lot of display changes, simply by placing a minus (-) sign next to the number showing -hh:mm left till batteries are full, or perhaps even better have that "ceiling" be user configurable to a certain percent. For example I rarely charge my lithium batteries beyond 90 percent so having that ceiling be set to precent 90 (just like the time remaining floor is user settable) would be double bonus.

VRMBMV Battery Monitorfeature request
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Mark avatar image Mark ♦♦ commented ·

While I think that this would be a very nice/useful feature & information - in practice I think that the calculated time will be deceiving in many applications.

I say this because even if you have a constant & sufficient power to charge at the full current limit, the charge profile is such that full current can only be used during the 'bulk' phase.

Once the 'absorption' phase commences the charge current decreases gradually over time.

The issue with this is that the proposed 'time to full charge' would be CALCULATED only from the instantaneous charge current (subject to the averaging period set) & the amount of Ah remaining to be replenished into the battery.

The issue with this is that the time calculated during the bulk phase charging conditions will be MUCH shorter than the real time to full charge (basically to the end of absorption phase), and the same issue would occur during absorption as the current is constantly decreasing over time.

I would instead very much like to see the time remaining to the end of the absorption phase, but this data is probably better to be provided/displayed by the MPPT or MultiPlus since they are the components that calculate & control this (providing that low charge current is not the absorption phase end trigger).

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geomz avatar image geomz Mark ♦♦ commented ·

I appreciate your input and that might be true for some batteries/chemistries. But With my lithium batteries I can calculate, with pretty darn good accuracy, when my batteries will be full.

I've been testing them under highly variable charge conditions from 110A to ~8A. I can basically take AHs drawn, divide by current charge rate and get quite close. It's not perfectly accurate of course, but it's certainly way better than deceiving or worthless ;)

I rarely, if ever, put my batteries in absorption. I have my BMV setup with Peukert and CE correctly, and it tracks with the batteries' BMS SOC within a percent or two.

It will, of course, over time, deviate a bit. And that's when I run a bulk charge till they "absorb" for a few minutes, then I turn off the charger and everything is back in sync again.

So for me, and I anticipate a not small % of other users, this would be extremely handy -especially with variable/multi charging conditions under solar/wind/hydro, if the BMV did the same math it does now, but in reverse ;)

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Mark avatar image Mark ♦♦ geomz commented ·

I agree with you - that if the charge cycle does NOT include an absorption period at all OR if the absorption period is very short (ie. for lithium batteries) then this will work & should work well (with only the simple calculation).

But when you have up to ~6h of absorption to finish off the last ~15% (such as for an AGM, Gel, etc) then it would NOT be accurate or useful at all.

So how to best handle this (to avoid confusion) would be difficult.

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geomz avatar image geomz Mark ♦♦ commented ·

I would think that Peukert and CE (which would be substantially different for lead) could be used as a guide for that calculation. Perhaps below a certain setting/limit of either/both values, that calculation just goes back to infinite -as it does now -which is definitely not very useful at all ;)

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technomadia avatar image technomadia Mark ♦♦ commented ·

Estimated time until the end of bulk is what really matters - for LFP batteries Absorptions really isn't a factor.

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Mark avatar image Mark ♦♦ technomadia commented ·

Hi technomadia,

Yes, as per my reply to Geomz above - I agree that this will work well if 100% SOC is achieved at the end of bulk (with no absorption phase at all or if its very short/negligible). So for lithium batteries I agree & support.

But if the same logic is used with lead acid based based batteries (or any battery type where a lengthy absorption period is included to achieve 100% SOC), then it would be highly inaccurate for 2 reasons;

1- The 'basic' time calculation would work out time to achieve 100% SOC based on the Ah drawn & current charge current, but the bulk phase would only replenish the Ah lost up until ~85% SOC

2- The 'basic' time calculation assumes that there will be full/constant charge current that continues up until 100% SOC, but once in absorption phase the charge current gradually reduces with time

Accordingly, in THIS case (which would represent a large proportion of users) the initial time calculation provided during the bulk phase would be highly inaccurate.

This does not mean that such a change should not be implemented, but if it was then it would need to be structured in such a way that Victron would not receive a bombardment of complaints about 'inaccurate time to full charge calculation'.

Maybe the solution could be a logic change triggered by a simple YES/NO answer to the question of 'is an absorption period used for charging?'...

Now even if an absorption period is used, it would not be impossible to make a similar/useful calculation for time to reach 100% SOC. However, the calculation would be a bit more involved, there would need to be some assumptions made & it would probably need to be handled by a Venus device with inputs from BMV & MPPT or Multi (since even absorption duration is a calculated duration & it can be different for each individual charge cycle).

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geomz avatar image geomz technomadia commented ·

One solution could be, just like time remaining has a floor to calculate down to, time-to-full could have a ceiling to "desired" charge. (Heck, it's practically already there since the Low SOC relay is the current floor trigger for time to go. The top number could be used for that purpose in the other direction. Although, I think there's probably a better way to do that).

I rarely charge my batteries to 100% (I actively avoid it, whenever possible).

That way, lithium users can set a desired time-to-charged of say 80-90% and lead users can put in a number that matches the end of bulk.

The issue would arise again if users elect 100%, but I still don't think that'll be an issue.

The time remaining calculation is still based on a sample of time (time to go averaging period) and it is not as an absolute number. Meaning, it's constantly changing anyway, all the time, based on load. It could easily be doing the exact same thing, the other direction, and nothing would have to change other than math and a + or - sign on the same display.

Lead users would see the number continue to climb as absorb hits (as they should, as charge rate decreases) and lithium users can see the same numbers, based on their charge rate, to their desired fill level.

Everyone's happy :)

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leo avatar image leo commented ·

Just wanted to say that I would also like this feature. I am in the same situation, chargeing my lithium batteries using a generator from time to time. I would be great to know how long I will have to run / when to come back and shut it off. I have only a BMV712 so no workaround using Venus.

Of course I can calculate it myself but it would be nice to have.

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Paul B avatar image Paul B leo commented ·

you could set the venus to turn off your generator when it gets to a set voltage using the venus or ccgx relay.

by using the generator stop start function, even if you dont start the gen using it it could always be stopped that way

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1 Answer
Paul B avatar image
Paul B answered ·

Thanks for your suggestions,

but keep in mind this is a forum to help others with issues and suggestions on how to set things up, and general help, these sorts of feature requests should be best sent direct to victron energy development area as we here cant do anything inregards to this sort of request.

These sorts of things would be nice, but there are far more important things that should be added.


Voltage history

SOC History

Input output history

better colour screen

(were do you stop)

the list goes on and on

I think all these sorts of things are great including your suggestion and others would have many more

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geomz avatar image geomz commented ·

Hmm, while I respect your opinion, as far as I know it's not the only thing this forum is designed for and it's not how it was "sold" to me by Victron when I was directed to go here to share with the community such items -including- ideas and suggestions.

I have no way to contact Victron directly (without a s**tload of hassle) and this is the first time Victron has centralized their formerly hodge-podge forum solutions of old.

And the site even has an "ideas" section, although it appears currently non-functional.

So, if you would like to see the features you listed above, added, then perhaps you should create a post listing them.

And in my opinion, we "stop" when the product is 100% perfect, which is not likely to be anytime in my (or several) lifetime ;)

But thank you none the less.

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JohnC avatar image JohnC ♦ geomz commented ·

Hi Geo. There is actually a 'feature request' topic in the full topic list. And it's been used a few times. You could edit that in to your original post, so perhaps some Victron boffin will look there one day when he's got nothing to do (ha) and find maybe multiple requests for the same thing..

That actually seems to be editable by anybody, but I haven't tried it to see if it will stick.

I'm sure Victron values your contribution(s).

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geomz avatar image geomz JohnC ♦ commented ·

Thanks John, I added 'Feature Request' as a topic to the post. Not holding my breath they'll "hop right on it", but we can hope for the someday bored engineer with time on his/her hands :)

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ben avatar image ben ♦ geomz commented ·

You can also just implement Time-to-full yourself, and stick it onto the Venus dbus, and then modify the QML to have it show up on the UI at the right point.

Probly a ten hour or less project if you’ve worked in the system before.

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geomz avatar image geomz ben ♦ commented ·

I have not worked, at this level, in the system before. But seeing what you, and @Kirb B, and others, have done with it so far has me really jealous :)

It's been on the eternal "list" for a while.

But right now it'd be completely new and I'd have to start from scratch -like pushing a new bolder up-hill. I have no doubt I can do it, but I have to overcome the overwhelming inertial forces of laziness first :D

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Paul B avatar image Paul B geomz commented ·

I maybe wrong but have a read, you were suppose to read this when you joined

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Paul B avatar image Paul B geomz commented ·

Also I was not trying to offend if if I did I am sorry,

I was just trying to point out that putting the request here wont help much. as I dont think the Victron development section reads this forum.

Best to send it direct to the support people at victron who have the request list at hand and can add it to it . well one would hope so anyway.

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