Electrical problem

[Ron in BC]

Originally Posted by HABBERDABBER

I had a 5W solar panel trickle charging a small sailboat lead acid battery. I recall that a charge controller was not needed at that system size. I recall reading that at night, the panel could discharge the battery, but not enough to make a big difference and the next day would be back to snuff.

Besides the parasitic load of your control electronics, it is possible you have a "gone bad" blocking diode.

This is just mere speculation, and I am no solar guru.

https://solarenergyhackers.com/can-s...harge-battery/

That's pretty much my experience. In the very early days of solar panels, early 90s, I left a small panel connected to my sailboat batteries for months, without a charge controller, at a time when it was stored overseas. I simply soldered in a diode to prevent loss overnight. The batteries lasted for many years. Now, with built-in blocking diodes, that's not necessary any more.

Ron

[John in Santa Cruz]

I keep a 10W (0.5 amp) Solar Battery Tender on the windshield of my diesel truck when i'm not driving it. this has a simple regulator integrated onto it.

[kavm]

Originally Posted by rubicon327

Good article on winter lithium battery storage from Battleborn…
https://battlebornbatteries.com/faq-...our-batteries/

Thanks Dave! That article gives us the path forward.

[John in Santa Cruz]

we use our trailer at least once a month year around, so I'm just leaving my solar enabled and set to fully charge it. We might get a few mornings a year below 32C, I'll rely on the BMS to stop any charging below that point.

[Brian B-P]

Originally Posted by rubicon327

The BMS should shut the battery off at a low voltage cutoff but it can still self-discharge over time to complete destruction.

Even worse, while the cells will self-discharge, the BMS is still connected within the battery case and is itself a small additional load that can't be disconnected by any external method.

[kavm]

Originally Posted by Brian B-P

Even worse, while the cells will self-discharge, the BMS is still connected within the battery case and is itself a small additional load that can't be disconnected by any external method.

So, what's the advice on how to proceed? I was converging to the plan for disconnecting both terminals - negative followed by positive - of both our lithium batteries before storing in the winter. But, now I am not as clear.

Our camper is parked in a remote covered storage location. So, solar panels are not going to charge it. We can request that it be plugged in but not sure how reliably the support staff will do that. We do not have access to the camper while it is parked in the storage facility.

[Brian B-P]

Originally Posted by kavm

So, what's the advice on how to proceed? I was converging to the plan for disconnecting both terminals - negative followed by positive - of both our lithium batteries before storing in the winter. But, now I am not as clear.

Our camper is parked in a remote covered storage location. So, solar panels are not going to charge it. We can request that it be plugged in but not sure how reliably the support staff will do that. We do not have access to the camper while it is parked in the storage facility.

Externally disconnecting will reduce the chance of discharging the battery so far that the BMS shuts it off, but can't do anything about the internal BMS causing more discharge. The only absolute fix is to provide charging power for a while (ideally long enough to reach mid-charged) occasionally, but it sounds like that isn't feasible in this case; hopefully something external is running it down, and with that disconnected the state of charge will never get low enough for there to be a problem with the BMS.

[kavm]

Thank you very much, Brian! We will do it like that. During the summer, we plan to use it frequently enough to avoid the scenario. So, it is something we only have to do once we are storing it for the winter.

[Vermilye]

For what it is worth, I stored a pair of unconnected Battleborn lithium batteries in an unheated garage (down to 32°F many nights) - from January 28th to February 20th they dropped from 13.55V & 13.64V to 13.32V & 13.34V or around 3/10ths of a volt over a month.

[kavm]

Thank you Jon!

Is it fair to project 0.5 volt per month during storage? Even if it were slightly higher with a higher average temperature, the batteries should only drop 3-5 volts in 6 months of storage. Is that a reasonable projection?

[BobG]

I stored a couple lithium 170 Ah batteries from November 4, 2020 to May 23, 2021 and they dropped about 0.1 volt each. It was in a heated garage. They were delivered to me at about 13.15 volts each. That is a little over 6 months they sat unused. They were stored in the foam packaging they arrived with and were turned off. They have an on off switch that I do not know everything it does. It may disconnect the BMS as well as the terminals when off. The voltage meter on each battery turns off when I push the on/off button to turn then off.

[John in Santa Cruz]

Originally Posted by kavm

Thank you Jon!

Is it fair to project 0.5 volt per month during storage? Even if it were slightly higher with a higher average temperature, the batteries should only drop 3-5 volts in 6 months of storage. Is that a reasonable projection?

3 volts is a LOT, thats the difference between FULLY charged and FULLY flat.

[Brian B-P]

Originally Posted by BobG

... They have an on off switch that I do not know everything it does. It may disconnect the BMS as well as the terminals when off. The voltage meter on each battery turns off when I push the on/off button to turn then off.

That could be useful, if it does more than just turn off the meter. Most of these "drop-in lithium replacements for lead-acid batteries" have nothing on them but the positive and negative terminals. What brand and model of battery is this?

[BobG]

Brian, They are 2x 12v 170Ah BigBattery sold by BigBattery.com. I don't think they sell the BigBattery model anymore. They sell the 12v 170Ah OWL which visually looks like the same battery. I don't know about the specifications. I connected them in series. They each have an internal 300 amp mega fuse that is serviceable. The continuous amp rating is 175 amps.

[The M&M’s]

Originally Posted by SWCO

You could install an inexpensive manual disconnect on the ground side of your battery (or batteries), just a knob you turn by hand to connect/disconnect the battery from the system. I used this successfully to keep the battery up on an old farm tractor that had an electric drain I never did diagnose. Much more convenient that disconnecting a cable.

To the best of my memory, on my 2021 5.0, even with my Battery Disconnect switched off, my landing gear, the front outside light, and the Carbon Monoxide Detector, continue to function. So I’m thinking the Disconnect is not disconnecting everything.

[CE Vogel]

I converted my trailer to Lithium last spring, and had a similar experience last fall. Fortunately my batteries were not harmed. I now disconnect the batteries and have no further problems. My Renogy batteries have a built-in disconnect switch, but a terminal mounted switch as others suggested will work. If the batteries are nearly fully charged when switched off, the internal BMS will not fully discharge the battery over the winter; mine lost 5% charge over the three coldest months. The phantom discharge can be several items: backfeed through the solar charge controller, backfeed through the DC-to-DC converter, and backfeed through the RV converter. All these are tiny currents, and normal, but will obviously discharge a battery over time.

[kavm]

Originally Posted by CE Vogel

I converted my trailer to Lithium last spring, and had a similar experience last fall. Fortunately my batteries were not harmed. I now disconnect the batteries and have no further problems. My Renogy batteries have a built-in disconnect switch, but a terminal mounted switch as others suggested will work. If the batteries are nearly fully charged when switched off, the internal BMS will not fully discharge the battery over the winter; mine lost 5% charge over the three coldest months. The phantom discharge can be several items: backfeed through the solar charge controller, backfeed through the DC-to-DC converter, and backfeed through the RV converter. All these are tiny currents, and normal, but will obviously discharge a battery over time.

Thank you! We will do this in the future...

[alanmalk]

Originally Posted by kavm

...
So, solar panels are not going to charge it.

...

If there is enough light to see by you should get a small charge from your roof panel.

The photo below is a 150 Watt panel covered with a flannel sheet. It is producing 49 milliamps into a 8 ohm load (the white square resistor). That should be more than enough to offset the BMS and internal self-discharge. It is NOT enough to offset any parasitic loads.

[John in Santa Cruz]

that meter looks like its reading 499 ma, not 49 ma. eg, 0 .499 amps. 1/2 amp at 8 ohms is about 2 watts.

[kavm]

Originally Posted by alanmalk

If there is enough light to see by you should get a small charge from your roof panel.

The photo below is a 150 Watt panel covered with a flannel sheet. It is producing 49 milliamps into a 8 ohm load (the white square resistor). That should be more than enough to offset the BMS and internal self-discharge. It is NOT enough to offset any parasitic loads.

Thank you, Alan! I did not know that.