Advice on Big Battery shutdown issue. Is my design at fault?

[IC_Phyer]

Hello. I am hoping to get some advise on my solar system and wiring. I recently installed the solar system displayed in the attached diagram in my travel trailer. This is the first time I have worked on such a system. I did purchase and read Will Prowse’s solar power book and Explorist.Life Solar Wiring Diagram, and used many online sources, including this forum, to educate myself as much as possible and design what I believe to be an appropriate system for my needs. It has been a challenge!

Initially everything ran as expected on and off shore power while stationary, but after travelling from Washington State to Colorado I began experiencing shutdowns of the Big Battery 24V HSKY Elite. Some seemed to be caused by low temperatures (25oF to 33oF ambient in Wyoming and Colorado), others possibly a combination of low temps and vibration while driving, others when a large load (electric teapot, 64A/1575W) was applied to the battery, but only when it was cold outside (35oF and below). The same teapot would work mid-day when it was 65oF to 70oF using the inverter. Voltage was always good, 26 to 27+V. At first I could get the battery to ‘wake up’ using the charger I purchased from BB and running it off my trucks inverter. Then it would take multiple attempts with the charger. Three times I woke it up by giving it a firm slap. I believed I had multiple issues: bad temp sensor and/or BMS settings, and loose connections.

I have been in contact with Big Battery and Growatt tech support for the last two weeks trying to determine the cause for the shutdowns. Eventually BB tech support, which has been very helpful, and I determined the shutdowns were the fault of the battery itself. Since I am full time living in my trailer I travelled to BB in LA to have the battery repaired. They found the only issue was a possible faulty temperature sensor causing the shutdowns at higher than normal temperatures. They replaced the temp sensor and checked all connections in the battery. They found no loose connections. They also tested the new temp sensor down to 13oF and shook the battery, pretty aggressively by their description, and deemed it good to go. I reinstalled it today and have been load testing it with a microwave (1100W), electric teapot (1500W), Furrion AC Unit (1650W w/ soft start), and my wife’s hair dryer (1100W). Both with and without being connected to shore power. No shutdowns so far. Ambient temps are in the 80’s to 90oF. I have not travelled with the trailer yet.

I would like to ask the many experts here to look over my system just to make sure that I have no other issues that may have caused the shutdowns. I am camped in an area with no cell service so I can only post once or twice a day, but I will attempt to answer any questions or supply more data if requested.

Thanks ahead,
David

 

[acdoctor]

Looks pretty good, I would not have 12 awg connected to 225 amp fuse on 24 to 12 converter. It should have a 20 amp on the input side as should the one in the trailer. 20 amps in 40 amps out. I would eliminate the one for the brakes and replace with a sealed trailer battery. If you turn off your battery switch or bms opens or that very reliable battery goes to sleep while on the road then the breakaway circuit is dead. The sealed battery can be charged from the constant hot in the 7 wire harness. 14 feet one way is a long way and you know that battery does not like temperature extremes. I assume you have done the voltage drop calculations on 28 ft round trip. I used 1/0 on mine it is 6 ft. #1 was my choice but couldn’t find it in welding cable.

 

[IC_Phyer]

acdoctor: Thank you for the reply. The 12awg and 10awg wire is hardwired into the converter. No way to change that though I would have liked larger gauge wires. I will look into changing the fuse layout. Would you consider in-line spade fuses adequate. That would be an easy fix.

I did consider a separate battery for the e-brakes. I am _very_ tight on space in the tongue box as it is now.

I used the wire calculator at the Explorist.Life website. According to those calculations 1/0 wire is adequate. I did a full power audit of my trailer and appliances and I over calculated my power consumption to give myself a safety buffer. I have been monitoring for hot wires. No issues there so far and no fault codes/alarms on the Growatt.

 

[acdoctor]

Amazon.com

This is what I used down stream of the big breaker.
https://www.amazon.com/dp/B07Q76M4QS/ref=cm_sw_em_r_mt_dp_9XXSRKHD0ZHYRZG665PP
This mounts to the tongue I have this one.

 

[RF_Burns]

Maybe I am missing something here, But it would seem that since your issues are happening at around the freezing temperatures I would expect it has to do with the BMS cold temperature charging cut-off. You can discharge an LiFePO4 (LFP) battery below zero, but not charge it. Is the battery outside the living area where it is exposed to outdoor temperatures? If so you could move the battery into the living area where the temperatures are warmer. LFP batteries do not off-gas so there are no issues there.
Since you have solar panels, the BMS may be cutting off the cold battery to prevent charging, but then you don't have enough solar power to run your devices.

 

[IC_Phyer]

RF_Burns: Thank you for the reply. Yes the battery is outside the living qts. The BMS should stop charging the battery at freezing, but it should not shut the battery off according to Big Battery. The temperatures at which I experienced shutdowns were well within the operating perimeters of the battery, again according to BB. They replaced the temp sensor, as noted, and tested to 13oF. No shutdown. The question was concerning my overall system. Big Battery did not test the old temp sensor and found nothing loose in the battery connections thus could not replicate the shutdown. I'm just trying to verify that some of my shutdowns were not being caused by how my system is set up. So far load testing has not produced any issue. Today is first day back on the road. We're not going too far out of the LA area just in case.

 

[RF_Burns]

RF_Burns: Thank you for the reply. Yes the battery is outside the living qts. The BMS should stop charging the battery at freezing, but it should not shut the battery off according to Big Battery. The temperatures at which I experienced shutdowns were well within the operating perimeters of the battery, again according to BB. They replaced the temp sensor, as noted, and tested to 13oF. No shutdown. The question was concerning my overall system. Big Battery did not test the old temp sensor and found nothing loose in the battery connections thus could not replicate the shutdown. I'm just trying to verify that some of my shutdowns were not being caused by how my system is set up. So far load testing has not produced any issue. Today is first day back on the road. We're not going too far out of the LA area just in case.

I'm new to LiFePO4 batteries, but I was in radio communications systems for public safety for 40 years, so I am familiar with battery backup and charging systems. I installed LiFePO4 batteries in our motorhome this summer, so I'm just getting my feet wet here.
I understand the BMS should disconnect the battery if below zero and it detects a charging current. I'm not sure how the BMS and the solar charge controller reacts if it shuts down the battery from charging due to low temps, but then the SSC sees no charge current, except the 12V loads. Then you turn ON a load which is more than the SCC can provide and the voltage drops, then I assume the BMS will reconnect the battery cells once the external voltage is less than the total cell voltage (discharging). Our motorhome is put to bed for the winter now and is stored in our heated shop, so I won't get to experience cold weather operation.
Does your GroWatt unit provide any logging of status? My Samlex EVO inverter/charger/transfer switch has logging which helped me understand why my batteries were disconnecting while charging and how to setup my charge parameters to get around the fixed BMS parameters.

 

[IC_Phyer]

The Growatt does have a WIFI module available. I had one but returned it due to not having a persistent internet connection while traveling and incompatibility with my 5G phone.

 

[acdoctor]

I have a battery disconnect with the growatt but, with separate SSC the battery voltage is the basis used as reference. If it is lost while charging SSC shuts down like there’s no sun but, there is a second that the system voltage can get high. Anything connected to the system that can’t handle that burn up. I have lost a few things that way.

 

[IC_Phyer]

So I started having issues again with the repaired battery. Similar as before but adding discharge of up to 3v overnight with very little load (0.5 to 2.0A). Big Battery replaced it with a new battery. So far its working good. It definitely acts differently on the charger and with the Growatt. I think the old one had a bad BMS.

 

[acdoctor]

Please keep in mind if you are inverting 27-7 with the growatt my personal analysis is it will self consume 1.25 kw. 1 kw of panels flat and winter sun could be that low of production.

 

[IC_Phyer]

I'm not following you. Don't you mean it self consumes 1.25A? My background load is closer to 2A with fridge fans, lpg detector, etc running all night.

2A * 26V * 8hrs= 416W. That load shouldn't drain the battery 2.9V. It went from 25.9 to 23V in 8 hrs overnight. Twice. While this new battery drops about 0.4V overnight with the same load.

Another matter: Have you had any success with Program #4 Power Saving Mode? When I used it it did turn off the inverter, but a load on the AC outlets in my trailer (electric teapot, 1600W) would not wake up the inverter. No power at all. I thought the inverter should come back on. I had to disable program #4 to get it to turn back on. I haven't tested it again with the new battery. What is your experience with program #4?

Have you tried turning the Growatt off at night via the power switch on the bottom? I was thinking this may save some power since I have no loads on the inverter at night.

Thanks ahead,
David

 

[acdoctor]

I haven’t tried the power saving mode yet. But idle consumption with no load is around 55 watts times twenty four hours is 1.32 kw per day. That could be a larger part of your battery consumption than you are figuring with winter sun.