Do you disconnect solar from battery when your RV is not being used?

[sunrise]

Hello,
I am wondering if folks disconnect solar charger(or panel) or lithium battery after each use of your trailer (I am not talking about winter storage)?
Asking as per this article, keeping LiFePo4 battery at high SOC isn't good for the battery life:
https://www.solacity.com/how-to-keep...tteries-happy/

Let's say I use my trailer mostly during weekends, for the rest of the week, if I don't disconnect either solar or battery, what's going to happen -
1. Say battery started at low SOC after weekend use. during the weekday, solar charger controller would slowly top it off at 14.4v which is ~100% SOC (high SOC)
2. During night, parasitic current will bring the voltage slightly down.
3. Next morning when the sun comes up, since the voltage is below 100% the solar charger controller would top it off again at 100% SOC.

So I think the battery is cycle between 100% SOC and maybe ~99% (depends on parasitic current amp), this seems to be bad for Lithium battery life if I read that article right.

So do folks disconnect one of these 2, when you are not using the trailer? I am not talking about winter storage, just in camping season but when you are not using your trailer.

BTW, I have a Victron MPPT charger.

Thanks!

 

[HRTKD]

No, I don't disconnect the charge controller. What I may do once the battery warmers don't need to be on, is lower the absorb/float values.

 

[sunrise]

No, I don't disconnect the charge controller. What I may do once the battery warmers don't need to be on, is lower the absorb/float values.

Thanks! What lower value do you use?

 

[HRTKD]

I'll probably start with 3.4v per cell (13.6v for the battery).

 

[Tgmontague]

The charge controller should keep your batteries charged using float mode which is actually good for Lithium batteries I think. Not sure what kind of batteries you have and LION is all I know.

 

[MisterSandals]

I'll probably start with 3.4v per cell (13.6v for the battery).

I let my RV sit with the solar disconnected and the battery at 13-13.2v between trips. I think this is the recommended charge for storage. I monitor the SCC via bluetooth once a week or so just for peace of mind.

At the very least if you are in storage mode, i would set the float voltage below where the cells tend to settle after a few hours. My cells settle to 3.35v within minutes of charging to 3.6v. So if i were to set the float to 3.4v, I would be micro-cycling the charge process several times an hour. To me, its absolutely pointless and definitely wear and tear on the batteries and charger (Victron 100/30).

A few days before a trip i will turn on my solar and charge up to my max charge voltage of 13.8v and its always ready to go at 13.4v.

So if you know what YOUR cell settle voltage is, i'd recommend a similar strategy with float just below that.
And if you have a lot of things in your RV discharging your battery, you may need to keep your solar connected (i pulled fuses on satellite radio, entertainment center clock, ... so phantom draws very minimal).

 

[sunrise]

@Tgmontague @HRTKD
Not according to this post: https://diysolarforum.com/threads/how-to-quickly-kill-a-lfp-battery-part-2.3703/

Most charger float at 3.4v, according to varies voltage -> SOC table thats somewhere between 90% and 99%

 

[sunrise]

I let my RV sit with the solar disconnected and the battery at 13-13.2v between trips. I think this is the recommended charge for storage. I monitor the SCC via bluetooth once a week or so just for peace of mind.

At the very least if you are in storage mode, i would set the float voltage below where the cells tend to settle after a few hours. My cells settle to 3.35v within minutes of charging to 3.6v. So if i were to set the float to 3.4v, I would be micro-cycling the charge process several times an hour. To me, its absolutely pointless and definitely wear and tear on the batteries and charger (Victron 100/30).

A few days before a trip i will turn on my solar and charge up to my max charge voltage of 13.8v and its always ready to go at 13.4v.

So if you know what YOUR cell settle voltage is, i'd recommend a similar strategy with float just below that.
And if you have a lot of things in your RV discharging your battery, you may need to keep your solar connected (i pulled fuses on satellite radio, entertainment center clock, ... so phantom draws very minimal).

Thank you @MisterSandals, that's what I plan to do, I was planning on using breaker as switch, but I have changed mind and added 2 marine switches (1 for battery disconnect, 1 for pv disconnect) for easier access.

 

[HRTKD]

I let my RV sit with the solar disconnected and the battery at 13-13.2v between trips. I think this is the recommended charge for storage. I monitor the SCC via bluetooth once a week or so just for peace of mind.

In non-winter time, that would be OK. I work on the trailer almost year round. In January, it's friggin cold in there, so I run a space heater through the inverter and if that can't keep up, I'll run the furnace.

 

[sunrise]

To add to the confusion, the company that makes my trailer's converter also makes a Lithium version of it. here are the charging profiles

If my understanding of LiFePo4 is accurate (I admit, probably not) , then this is more of a marketing move actually does more harm -
1. Since most batteries aren't perfectly balanced, when you charge to 3.65, most likely one cell would have reached 3.65 (or whatever the BMS sees as overcharge voltage), and triggers a BMS overvoltage protection and the charging stops.
2. Even your battery is *perfectly* balanced, like the delta is < 0.001v - charging battery to 3.65 won't bring any meaningful additional energy - my battery goes from 3.6 to 3.65 in a couple of minutes during charging - the curve is almost vertical once you get to 3.6 .
3. But the 13.6 (3.4v) absorption is the exactly the voltage that kill you battery quickly according to the article. I'd much prefer it floats at 13.2(3.3v)

 

[sunrise]

In non-winter time, that would be OK. I work on the trailer almost year round. In January, it's friggin cold in there, so I run a space heater through the inverter and if that can't keep up, I'll run the furnace.

In your case, your trailer is considered in active use, I think that's a different story.

 

[MrNatural22]

When my trailer is idle i leave the system connected. I keep an led light on inside and have a small 12v digital timer connected that turn the light on when it’s dark and off at dawn. I know the cc load connection would also do this but I like the convince of a separate timer and don’t use the load side of the cc. It draws very little power and the battery charges back up to 90% each day then goes to 13.4 float. This give the LiFePo a small workout each day.
Small discharge cycles each day seem to work very well at maintaining a great balance between the cells and <3000> Shallow cycles is many years of service.

 

[MisterSandals]

To add to the confusion, the company that makes my trailer's converter also makes a Lithium version of it. here are the charging profiles

I have encountered the same with my PD 4650 (10 years old, pre-lithium version for sure). I saw that the new lithium version charged up to 14.6 when plugged in and I wanted no part of this so i stuck with the lead acid original.
Almost all my battery charging comes from solar so its no loss that i only charge to 13.2v (?) from shore power.

If someone comes out with a programable wire for wire replacement (this PD was replacement for WAFCO original POS) i would consider buying it.

 

[sunrise]

When my trailer is idle i leave the system connected. I keep an led light on inside and have a small 12v digital timer connected that turn the light on when it’s dark and off at dawn. It draws very little power and the battery charges back up to 90% each day then goes to 13.4 float. This give the LiFePo a small workout each day.
Small discharge cycles each day seem to work very well at maintaining a great balance between the cells and <3000> Shallow cycles is many years of service.

Thanks for sharing your practice, depends on how much the lights draw I guess, but the post I was quoting basically says very shallow cycles (voltage > 3.4) would kill your lifepo fast.

 

[sunrise]

I have encountered the same with my PD 4650 (10 years old, pre-lithium version for sure). I saw that the new lithium version charged up to 14.6 when plugged in and I wanted no part of this so i stuck with the lead acid original.
Almost all my battery charging comes from solar so its no loss that i only charge to 13.2v (?) from shore power.

If someone comes out with a programable wire for wire replacement (this PD was replacement for WAFCO original POS) i would consider buying it.

Yep, my trailer has the WFCO 8955-Pec not WFCO 8955-LIS (Lithium version), I would not 'upgrade' even they give it to me for free. I agree if the voltage is programmable it would be nice and I will consider.

 

[MrNatural22]

In the morning my readings are usually at 3.3v which is 13.2v resting or 70% SOC before the solar changes back up to
13.35v just a hair higher than 90% SOC.
So a 20% cycle. Time will tell if this is bad. So I just leave it connected to do it’s thing and it’s ready to go when we head out.

 

[MisterSandals]

I keep an led light on inside and have a small 12v digital timer connected that turn the light on when it’s dark and off at dawn.

So a 20% cycle.

That seems like an awful lot of power for an led light and 12v timer.

 

[MrNatural22]

According to the BMS BT monitor The light I use draws .6a 7-8w on for 12 1/2 hrs. 5:30pm - 6:00am. That’s light and timer. The timer has it’s own internal battery for the clock so it draw is very small.

 

[MisterSandals]

According to the BMS BT monitor The light I use draws .6a 7-8w on for 12 1/2 hrs. 5:30pm - 6:00am. That’s light and timer. The timer has it’s own internal battery for the clock so it draw is very small.

.6a x 12.5h = 7.5ah
If that is a 20% cycle, that makes your battery capacity 37.5ah?

 

[HRTKD]

To add to the confusion, the company that makes my trailer's converter also makes a Lithium version of it. here are the charging profiles
View attachment 32026
If my understanding of LiFePo4 is accurate (I admit, probably not) , then this is more of a marketing move actually does more harm -
1. Since most batteries aren't perfectly balanced, when you charge to 3.65, most likely one cell would have reached 3.65 (or whatever the BMS sees as overcharge voltage), and triggers a BMS overvoltage protection and the charging stops.
2. Even your battery is *perfectly* balanced, like the delta is < 0.001v - charging battery to 3.65 won't bring any meaningful additional energy - my battery goes from 3.6 to 3.65 in a couple of minutes during charging - the curve is almost vertical once you get to 3.6 .
3. But the 13.6 (3.4v) absorption is the exactly the voltage that kill you battery quickly according to the article. I'd much prefer it floats at 13.2(3.3v)

I don't think the IOTA Engineering converter is much better. I have yet to see mine produce over 14 volts, but I'm probably not running it long enough to see that.

A programmable AC-DC converter is sounding better and better. These fixed charge profile converters are losing their appeal.