Battery used while on shore power?

[onefiftyfour]

I know there are other threads about this, but I'm still not clear about this.


My situation. LifePo4 batteries with no low temp protection other than I have the temp sensor and all my charging units are set to not charge below 38 degrees F. All victron units. Last week we were camping below freezing temps and had shore power. I assumed that while on shore power, the batteries would not be used to power anything. But, I saw on my victron app from the shunt that the batteries were being used. I do have a battery disconnect switch installed, so I turned it to the off position. All my appliances and lights continued to work now on shore power.


Is this only a problem (the need to use the battery disconnect) while below my temperature cutoff? Is there something I'm not understanding about this? Not a huge problem, I just want to understand whats happening.


Thank you!

[PaulBristol]

I think you are correct. The Victron Multiplus or what ever you have will likely work fine with shore power, without the battery.

Check the owner's manual for specifics.

[jeffmc306]

onefiftyfour, what brand LifePo4 batteries do you have installed?

Low temp protection is pretty standard and is part of the BMS (battery management system) with a sensor. I would be very surprised if a LifePo4 battery sold today does not have this important safety protection.

Perhaps you’re confusing heated batteries with low temp protection? If that’s the case, you don’t have to worry about temps - your batteries will not accept a charge when the temp gets below their preset level. They will continue to discharge below this temp but won’t accept a charge.

For example, we have a Battle Born GC3 without heaters but do have solar installed. The battery will not accept a charge from the solar controller if the temp hits 25 degrees and won’t restart until the temp hits 32 degrees.

You might be fine with what you have!

[onefiftyfour]

jeffmc306, about a year ago I bought and installed 2 power queen group 24 lifepo4 100ah batteries. the BMS does not do low temp charging cutoff, but I'm being careful not to let charging happen via victron temperature sensing and configs. This setup works great as long as I'm fully charged when I head out for a 3-4 day low temperature adventure. And usually during the warm part of the day I can get some charging done with solar or dc/dc charger. If I have access to shore power, I will use it to conserve batteries. I was just unaware that I would have to use my disconnect switch while on shore power. Thanks!

[vanderwielen]

It depends on how the after market installation was done, but generally, the victron MP is wired to a bus which is wired to the batteries. The batteries have the disconnect between the bus and themselves....so with shore power present and the switch 'off' the MP will still provide a 12v output to the bus which in turn powers your DC panel.

[waninae39]

i use plant heating pads during the winter to cover my batteries. they are plugged into a temp sensitive controller

[JeffKim]

To be clear, you have a Victron temperature sensor connected to the batteries and all Victron chargers/controllers set to not charge below 38F?

Your observations make perfect sense to me, the batteries can discharge down to -4F or so but none of your chargers will charge them and all should be off, so you would see the shunt showing battery discharge. Hooked up to shore power the charger would ordinarily kick in and power the DC circuits, but it's off because of the temperature setting, so the batteries are being discharged.

To confirm, do you have Smart Victron components (I would assume)? When the low temperature is tripped there will be a message in the Victron app saying the charger or solar controller is off for low temp charging protection.

I have low temperature charging protection, but they're cheap batteries and I don't trust the BMS, so I installed the Victron temperature sensor and set my Victron charger and controllers to cut out - I think very similar to your situation. To use shore power in low temps I have to disable the temperature protection on the charger and disconnect the batteries (not trusting the BMS). Again, your observations fit this.

[onefiftyfour]

@JeffKim Yes to all of your questions. The Victron Shunt has the temp sense wire connected to one of the battery positives and all the Victron components are networked to receive that temperature info. And yes they say "off" below the low-temp cutoff setting.


But... All I did was turn the battery disconnect to off. I did not change the low-temp cutoff setting in the converter. but all appliances and lights still worked. I wonder if the lights and appliances need the converter at all while on shore power. Today I might flip the breaker for the converter and see what doesn't work.

[JeffKim]

Originally Posted by onefiftyfour

@JeffKim Yes to all of your questions. The Victron Shunt has the temp sense wire connected to one of the battery positives and all the Victron components are networked to receive that temperature info. And yes they say "off" below the low-temp cutoff setting.


But... All I did was turn the battery disconnect to off. I did not change the low-temp cutoff setting in the converter. but all appliances and lights still worked. I wonder if the lights and appliances need the converter at all while on shore power. Today I might flip the breaker for the converter and see what doesn't work.

Since the lights, etc. are DC they need either battery or a converter/charger or solar. With the batteries disconnected, I'm not sure where the power is coming from. Can you check all the charging devices to be sure? Maybe it's not cold enough to shut them down.

Anyways, good questions.

[onefiftyfour]

@JeffKim,


Just continuing with this thread to satisfy my curiosity.



You are correct with the converter/charger off (via AC breaker) AND the battery disconnect off (disconnected) AND on shore power: None of the DC only circuits operate.


It is not cold enough to test if the converter charger provides DC to those circuits while in the low-temp cutoff state. But, I did this last week while camping. it did provide DC to the DC circuits while temps were below the cutoff. My theory is that the low-temp cutoff only cuts off "charging voltage" and still provides enough voltage to be a power supply for the DC circuits. OR maybe the converter/charger somehow sensed that the battery was disconnected?

[uncle_bob]

Hi

In a *normal* install (we never have all the details on any install ) the converter / charger hooks to a master 12V bus. That same bus wires to the batteries.

If the converter is on and supplying power, that power goes to the batteries along with everything else. There is noting anywhere in a normal install to stop that. The converter can only be on or off. There is no "on but not charging" mode in a normal install.

Batteries take a while to cool down in the evening and warm up in the morning. Knowing just what temperature the *insides* of the battery is at is not simple. There's no practical way to burry a temperature probe in the middle of a battery. There also is the basic question of what temperature you stop charging at. Depending on where you look there are a range of answers. In a lot of cases folks use a "higher than needed" cutoff temperature because of the temperature sensor location "problem".

Simple answers if the batteries do not have a low temp cutoff BMS:

1) Unplug the converter charger (flip the breaker or whatever). Wait untill things have warmed up to power it back up again. Do the same thing with your solar side of things.

2) Replace them with batteries that have a BMS that cuts off at low temperatures. These days, that's maybe a $130 battery. I haven't looked for a bit, the low price leader may be down under $100 by now.

3) Put in a full battery disconnect switch or relay. Use that to disconnect the batteries. This may not make your converter charger happy. It most certainly will not make your solar happy.

Anything other than that gets problematic. As you have noted, the converter chargers are not really going to do the job, even more so if you have solar.

Bob

[ricjones]

Originally Posted by jeffmc306

onefiftyfour, what brand LifePo4 batteries do you have installed?

Low temp protection is pretty standard and is part of the BMS (battery management system) with a sensor. I would be very surprised if a LifePo4 battery sold today does not have this important safety protection.

Perhaps you’re confusing heated batteries with low temp protection? If that’s the case, you don’t have to worry about temps - your batteries will not accept a charge when the temp gets below their preset level. They will continue to discharge below this temp but won’t accept a charge.

For example, we have a Battle Born GC3 without heaters but do have solar installed. The battery will not accept a charge from the solar controller if the temp hits 25 degrees and won’t restart until the temp hits 32 degrees.

You might be fine with what you have!

Our Renogy LifePOs stop charging when it gets cold. It seems to be more like 38 degrees on Renogies. And yes, even when plugged into shore power, the batteries are being used. If it is too cold to charge, on shore power, they lose charge.


And our Renogies show the battery temp in the app. They also show the current charge level as a percentage on each battery, and the current (volts and amps). This is how I figured out how much 12v things use when they come on, by watching the app.

The app also shows any abnormal condition (like low temp no charge notice) and it shows the voltage on each and every cell.

Between all that data and all the data you can see on an EMS with its own app, data geeks and be happy all day and night.

[gypsydad]

I leave my AS plugged in while in storage here in Texas, and flip the knife switch to "disconnect" on my LiTime batteries negative terminal. Got down into the 20's last month. After the cold spell, I engaged the knife switch and when I checked next day, using the Bluetooth with built in BMS, everything was 100% working. No issues. I have always kept my AS plugged in while in storage, even when batteries disconnected and all electric lights/fridge/water heater/furnace worked fine, even though batteries were disconnected, when I used to have 12V Lead Acid batteries.

[Saullman]

Pulling power from batteries in freezing temps isn't a big deal, LifePo4's can handle that just fine, its just you don't want to be charging in freezing temps.

Been doing that way for many years with no deleterious effects.

[SunchaserV]

I've used large inverter chargers for decades on boats. When off the boat, but on shore power, we'd turn the inverter off but leave the charger on. When on the boat with shore or genset power, we'd normally turn the inverter on as the design allowed pass through amps from the battery when a momentary heavy load would appear.

[JeffKim]

Originally Posted by onefiftyfour

@JeffKim,
It is not cold enough to test if the converter charger provides DC to those circuits while in the low-temp cutoff state. But, I did this last week while camping. it did provide DC to the DC circuits while temps were below the cutoff. My theory is that the low-temp cutoff only cuts off "charging voltage" and still provides enough voltage to be a power supply for the DC circuits. OR maybe the converter/charger somehow sensed that the battery was disconnected?

With the Victron charger you can check the Bluetooth app and see if there's an output when it is below the battery charging cutoff. With mine it does not provide any charging or act as a power source, it just says it's below the battery charging temperature and is cutoff - no output. If it did act as a power source, then it would still be charging the batteries since they are connected to the charger through the positive bus bar, so not good.

I'd guess the batteries are discharging at below the charging threshold, so the DC circuits are powered by battery. They can discharge down to -4F as I think I said.

[JeffKim]

Originally Posted by uncle_bob

Hi

In a *normal* install (we never have all the details on any install ) the converter / charger hooks to a master 12V bus. That same bus wires to the batteries.

If the converter is on and supplying power, that power goes to the batteries along with everything else. There is noting anywhere in a normal install to stop that. The converter can only be on or off. There is no "on but not charging" mode in a normal install.

Batteries take a while to cool down in the evening and warm up in the morning. Knowing just what temperature the *insides* of the battery is at is not simple. There's no practical way to burry a temperature probe in the middle of a battery. There also is the basic question of what temperature you stop charging at. Depending on where you look there are a range of answers. In a lot of cases folks use a "higher than needed" cutoff temperature because of the temperature sensor location "problem".

Simple answers if the batteries do not have a low temp cutoff BMS:

1) Unplug the converter charger (flip the breaker or whatever). Wait untill things have warmed up to power it back up again. Do the same thing with your solar side of things.

2) Replace them with batteries that have a BMS that cuts off at low temperatures. These days, that's maybe a $130 battery. I haven't looked for a bit, the low price leader may be down under $100 by now.

3) Put in a full battery disconnect switch or relay. Use that to disconnect the batteries. This may not make your converter charger happy. It most certainly will not make your solar happy.

Anything other than that gets problematic. As you have noted, the converter chargers are not really going to do the job, even more so if you have solar.

Bob

Some clarification: my understanding is that the OP has a Victron temperature sensor (same as I have) which runs from the positive battery terminal to the shunt. Yes, not as accurate as something internal to the battery, but still much better than nothing with batteries having no low temp charging cutoff.

Each Victron solar controller and charger can read this temperature. There is a cold temp cutoff setting on each device which switches off charging when the shunt read temperature drops below this value. The charger is still "on" and reporting to the Bluetooth app, it just says the charging and DC output is off because of temperature. My Victron Phoenix does this.

This seems to me to be a sensible solution in the absence of a cold temp charging cutoff in the BMS. I don't think anything else needs to be added. In sub-charging temps the batteries either can be run on their own or with shore power they have to be disconnected and the charger low-temp protection turned off.

[uncle_bob]

Originally Posted by JeffKim

Some clarification: my understanding is that the OP has a Victron temperature sensor (same as I have) which runs from the positive battery terminal to the shunt. Yes, not as accurate as something internal to the battery, but still much better than nothing with batteries having no low temp charging cutoff.

Each Victron solar controller and charger can read this temperature. There is a cold temp cutoff setting on each device which switches off charging when the shunt read temperature drops below this value. The charger is still "on" and reporting to the Bluetooth app, it just says the charging and DC output is off because of temperature. My Victron Phoenix does this.

This seems to me to be a sensible solution in the absence of a cold temp charging cutoff in the BMS. I don't think anything else needs to be added. In sub-charging temps the batteries either can be run on their own or with shore power they have to be disconnected and the charger low-temp protection turned off.

Hi

There's *always* other ways to do things

With a setup like that, you have both wiring and programming "fiddly details" that can easily go wrong, You also have fun stuff like firmware updates that randomly clear this or that setting. While *some* of the Victron stuff can "play along" if set up properly, not all of their devices can join in.

Since the OP *is* charging cold, there's a very long list of things to go over that are highly specific what he does or does not have. Without a full breakdown of *everything* in the install .... There are a lot of permutations and combinations. What does he need to add to get to a system like you describe? Who know ...

Can a full up install with a central controller handle this sort of thing? Sure. That's after all the link stuff (possibly involving wires) gets worked out. Once you get it all programmed, away you go. In this case, replacing the batteries is cheaper / quicker / easier than just the controller.

The down side of *any* of these "shut off the converter" approaches is that you now are dependent on the batteries for all your 12V gear. You are on shore power .... but you aren't when it's cold. It's *really* easy to forget grubby details like that .

So it's evening and it gets cold, the converter cuts off or you manually cut it off until morning:

Run the furnace (they can pull quite a bit on 12V)

That compressor fridge chugs along all the time

Some turn on the water tank heater pads

Now toss in battery capacity that drops noticeably when it's cold.

There will always be the "normal use" stuff like water pump and lights.

You might have weird stuff like a Starlink that hooks into the 12V buss. Everybody has their own set of "add on" gear that's impossible to guess.

That *could* be more that you can handle with the battery in this or that condition (wear and tear as well as charge state).

Bob

[onefiftyfour]

Thanks, all!


The mystery sill remains that I had shore power in temps below my cutoff setting. And with the batteries disconnected, the converter was powering all the 12V units. I did not have to turn off the low temp cutoff setting. With the batteries connected, I was drawing power from the batteries (not charging).



I'm pretty happy with my situation. I understand all the components and settings and I like checking the app to see what is going on. We don't love camping in cold weather and I think we will do less of it. We have the 16footer so it's nice to be able to sit outside and enjoy the outdoors if the weather is decent. Inside the small camper can get a little cramped with the two of us and a small dog. I could go on about why we don't want a larger camper... We are mainly camping this time of year just to travel between New Mexico and Michigan. We are thinking of moving our travel to later in March or April.


(A lot of campgrounds and RV parks are closed until April) I like to use harvest hosts so I do need to make sure we have enough battery power for the days we don't have shore power. I definitely don't want to draw down the batteries if we have shore power. It's easy enough to use the disconnect switch. Usually during the day time it gets warm enough to charge via solar while driving. I guess the problem would be 3 or more days of no shore power and freezing temps during the daytime. I'm not sure how many days 200ah of LifePo4 is will power overnight running of the furnace and a little of the fridge and lights.



With that top of the battery temp sensor, what setting do you think is appropriate for the low-temp cutoff to allow for the difference between internal and external temp? I'm sure it depends on how low the temps got during the night.


And I think I read somewhere that the danger is just damaging the batteries if you try to charge at 32 or below. There is no chance of some kind of fire or explosion?

[Wazbro]

Originally Posted by onefiftyfour

And I think I read somewhere that the danger is just damaging the batteries if you try to charge at 32 or below. There is no chance of some kind of fire or explosion?

With that top of the battery temp sensor, what setting do you think is appropriate for the low-temp cutoff to allow for the difference between internal and external temp? I'm sure it depends on how low the temps got during the night.

From what I've read you are correct about just damaging the batteries not causing danger of fire or explosion.

It is very hard to come up with a certain temp to compensate for the sensor being external, so many variables, how much airflow at the sensor compared to the rest of the batteries, how much load which (creates heat), how quickly the temp changes (drops from 60° to 30° or drops from 40° to 30°).

Also something nobody has mentioned, the temp that damage starts at is not actually one temp, in an interview with someone at Battle Born that person said that as the temperature drops the rate the batteries can be charged without damage goes down. I don't remember any actual rates or if he actually said any, which would depend on the size and make/construction of batteries so these numbers may be complete BS, just to give you an idea of the concept; charging at 100amps might start causing damage below 38°, 50amps below 34° and 15amps might not start causing damage until below 30°.