Battery advice

in h

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748
Many State of Charge Battery Monitors, such as the Victron BMVs, will use the level of charge current as a way to tell if the Battery is fully charged.
Indeed. My B2B charger detects the current going down as an indication that the battery is fully charged. That's all very well, but it has no way of knowing whether that current is going into charging the battery, to charging your laptop or powering the fridge. For that reason, my three way AES fridge is powered from the starter battery.
I'm guessing that the complex Victron units have a shunt that can record all the current in and out of the battery and so they can tell that 3A is going to load and 4A is charging (or vice versa).
Most solar controllers are not wired to use their load terminals, and few B2B chargers even have load terminals.
 

wildebus

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2,873
Indeed. My B2B charger detects the current going down as an indication that the battery is fully charged. That's all very well, but it has no way of knowing whether that current is going into charging the battery, to charging your laptop or powering the fridge. For that reason, my three way AES fridge is powered from the starter battery.
I'm guessing that the complex Victron units have a shunt that can record all the current in and out of the battery and so they can tell that 3A is going to load and 4A is charging (or vice versa).
Most solar controllers are not wired to use their load terminals, and few B2B chargers even have load terminals.
The Victron BMVs just see a net current value, so if you had say 10A from Solar (which is a decent input), but 9A of it went to some highish load, so just 1A into the battery available, that could confuse and fool it potentially.
It is not a major thing as you just adjust and fine tune the settings to suit your installation. over something like 3 years, I have only seen a jump to 100% SOC incorrectly maybe a dozen times and from memory was related to solar charging on cloudy days.
Where you get the info from what is going to charge and what is going to load is when you introduce the Venus kit into the picture, which makes that kind of thing a lot clearer (although still doesn't prevent the 100% SOC jumps - each device is pretty much independent.)
 

xsilvergs

Full Member

Messages
115
The Victron BMVs just see a net current value, so if you had say 10A from Solar (which is a decent input), but 9A of it went to some highish load, so just 1A into the battery available, that could confuse and fool it potentially.
It is not a major thing as you just adjust and fine tune the settings to suit your installation. over something like 3 years, I have only seen a jump to 100% SOC incorrectly maybe a dozen times and from memory was related to solar charging on cloudy days.
Where you get the info from what is going to charge and what is going to load is when you introduce the Venus kit into the picture, which makes that kind of thing a lot clearer (although still doesn't prevent the 100% SOC jumps - each device is pretty much independent.)
I find the SOC inaccuracy with the BMV annoying, I wonder, and I haven't checked, if the point the MPPT switches from Bulk to Absorption is a more reliable indication of SOC?
 

nabsim

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2,396
I don’t seem to have any problem with SOC on mine, at least not since I set it properly, did have something wrong on solar setting initially
 

xsilvergs

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Messages
115
have you made the adjustments to take account of having solar?
I have watched the video in the past but have watched it again, thanks.

When left on the drive and the only drains are a Pi and the router it keeps synced but when away and running the inverter to power the fridge sync goes to pot.

For example, yesterday before the sun hit the panels the battery was just below 70% SOC. Sun comes up charges the battery to 91% at which point the inverter starts to power the fridge until the battery drops to 87% or the fridge gets down to temp. So as the fridge cycles the battery can see a discharge current of between 5 and 20 amps depending on the amount of solar. At a guess the battery sees the fridge cycle about 8 or 9 times a day. It seems this cycling and the differing load, dependent on solar strength, causes loss of sync.

Any thoughts?
 

wildebus

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2,873
I have watched the video in the past but have watched it again, thanks.

When left on the drive and the only drains are a Pi and the router it keeps synced but when away and running the inverter to power the fridge sync goes to pot.

For example, yesterday before the sun hit the panels the battery was just below 70% SOC. Sun comes up charges the battery to 91% at which point the inverter starts to power the fridge until the battery drops to 87% or the fridge gets down to temp. So as the fridge cycles the battery can see a discharge current of between 5 and 20 amps depending on the amount of solar. At a guess the battery sees the fridge cycle about 8 or 9 times a day. It seems this cycling and the differing load, dependent on solar strength, causes loss of sync.

Any thoughts?
I don't think that should be a problem if setup right. The calculation is very straightforward ... the monitor knows how many Ahs are in the battery, sees how much current is being drawn through the shunt, works out the Ah based on the time and that use (or provision of Ah) as a percentage of the total battery is taken/added to the SOC value.
The only thing that could make that value incorrect is if the Peukert exponent is wrong - where the Total Battery Capacity is adjusted depending of the C rate of the current discharge. Maybe your battery has something different needed there? There are defaults for different battery types, but they are only defaults.
I know when I have taken the numbers from VRM to compare Ahs against SOC it has been correct.
 

xsilvergs

Full Member

Messages
115
I don't think that should be a problem if setup right. The calculation is very straightforward ... the monitor knows how many Ahs are in the battery, sees how much current is being drawn through the shunt, works out the Ah based on the time and that use (or provision of Ah) as a percentage of the total battery is taken/added to the SOC value.
The only thing that could make that value incorrect is if the Peukert exponent is wrong - where the Total Battery Capacity is adjusted depending of the C rate of the current discharge. Maybe your battery has something different needed there? There are defaults for different battery types, but they are only defaults.
I know when I have taken the numbers from VRM to compare Ahs against SOC it has been correct.
I agree. When the battery regularly sees Float and sits at 100% SOC it works fine, but when it rarely sees more than 91% and has 60 plus charge discharge cycles it dries. I wish I knew how to set better accuracy.
 

wildebus

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2,873
it seems to go wrong when the inverter is in use - so I definately would adjust the peukert value. If you think the SOC is dropping too fast, make it smaller; if too slowly, make it larger.
 

xsilvergs

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Messages
115
it seems to go wrong when the inverter is in use - so I definately would adjust the peukert value. If you think the SOC is dropping too fast, make it smaller; if too slowly, make it larger.
Thanks for comments, I have been adjusting the Peukerts and charge efficiency over the last month but with few opportunities to get the battery to 100% SOC for a period of time, hasn't helped I feel.

As I mentioned in a previous post I hope to get a 12v 200Ah LifePo4 from Alpha when they're in.
 

wildebus

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2,873
Thanks for comments, I have been adjusting the Peukerts and charge efficiency over the last month but with few opportunities to get the battery to 100% SOC for a period of time, hasn't helped I feel.

As I mentioned in a previous post I hope to get a 12v 200Ah LifePo4 from Alpha when they're in.
I was looking at the sizes of those batteries yesterday actually ... seeing best combos for the space :) Peukert for those is virtually zero (or 1.0x in the settings in BMV).
I wonder if it could be your battery aging and doing weird things on load?
 

xsilvergs

Full Member

Messages
115
I was looking at the sizes of those batteries yesterday actually ... seeing best combos for the space :) Peukert for those is virtually zero (or 1.0x in the settings in BMV).
I wonder if it could be your battery aging and doing weird things on load?
You're possibly right about aging, Varta AGM, 3 years old, this is the excuse the get LiFePO4 😁, B2B too 😁😁😁.
 

wildebus

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2,873
You're possibly right about aging, Varta AGM, 3 years old, this is the excuse the get LiFePO4 😁, B2B too 😁😁😁.
kind of getting off the original topic, but I think the batteries in my new MH might be 12 years old! Checked with John at Alpha Batteries to help identify them and they are (were?) good batteries, so be interesting how they perform (installed a BMV yesterday and a RPi running Victron Venus OS this morning so I can monitor them. Hoping they will be ok for a few months until the Lithiums have landed :) )
 

svenontour

Free Member

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1
We are going to upgrade our single 110 amp lead acid battery to two 110 AGM batteries.but have noticed you can get larger capacity batteries so was wondering which is best two 110 batteries or a single 220 any advice greatly appreciated
Hello, (in my capacity as a non-expert) I can tell you when I was looking for a replacement battery I thought about AGM's butsaw plenty of info suggesting they might not be totally the business. For one thing it sounds like they need a particular type of charger so I would guess it might be worth looking at that side of things? And for another, I seem to recall that AGM's might need more in the way of ventilation. Sorry to be vague but I have the impression that battery technology can be a bit tricky and it would probably be worth clarifying whether this is a good move before you plump for one of the other?
 

wildebus

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2,873
Hello, (in my capacity as a non-expert) I can tell you when I was looking for a replacement battery I thought about AGM's butsaw plenty of info suggesting they might not be totally the business. For one thing it sounds like they need a particular type of charger so I would guess it might be worth looking at that side of things? And for another, I seem to recall that AGM's might need more in the way of ventilation. Sorry to be vague but I have the impression that battery technology can be a bit tricky and it would probably be worth clarifying whether this is a good move before you plump for one of the other?
Sorry to say, but there is a fair bit of incorrect info above, and a lot of misinformation on the internet (including sadly on a particular website that seems very renowned).
One key one is ref ventilation .... The typical wet cell Lead Acid battery should be vented externally - so either fitted externally in a battery locker, or if fitted inside, the vent pipe connected to the outlet provided on those batteries.
With an AGM there is NO equivalent need to ventilate and this is why they are so useful for campervan type installtions where they are fitted within the living space.
In terms of chargers, as has been mentioned, the typical AGM battery needs a charging voltage higher than wet cell batteries, but TBH it is not a very special charger, just a reasonably modern one. Any smart charger from the last, oh ,8 years?, will charge a variety of batteries correctly, including AGMS.

In fact, as far as trouble-free simple-as-it-gets installations, an AGM is probably the most fool-proof battery technology available.
 

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