Mysterious issues ~ please help! (pics included)

[fratermus]

I thought it was weird to wedge a flat washer between the fuse and cable termination lug but saw that method recommended by other electrical companies.

I'd never thought about it before, but last week I saw a video with Nigel Calder and another gentleman talking about it. IIRC they remarked how easy it is to get a stainless steel washer in the wrong spot in the stack, and the effect on resistance/heat. I'm paying closer attention now.

 

[fratermus]

....Aaaaand I believe I found the culprit.

Thank you for reporting back what you found. Sometimes we don't hear back and are left wondering.

 

[jessicadavis]

Hi everyone -
I'm away from the rig all day today but plan to do some voltimeter testing first thing tomorrow + address the battery protect questions

I had a spare fuse and fuse holder that I attached yesterday with the recommended alignment until I can get my hands on the recommended blueseas fuse holder. It was immediately working better - the blueseas switch worked correctly in the OFF position and once everything was turned back on, the inverter appeared to be struggling less than before and everything seemed to be flowing properly.

Now a new issue emerges! This morning, as soon as the sun hit the solar panels, the DC power shut off. What's weird is that the inverter kept running properly and according to the app and lights on the front of the unit, the battery is not low. It's about an hour later and the DC is still not working (the AC is working great) and the MPPT app shows the charging is in float (pic attached)

All I can think is that I reattached something incorrectly when I was messing with the fuse yesterday. I'm going to go over everything tomorrow but if anyone has any ideas why the DC would be shut off while the AC continues (and why this would've happened this morning when the sun came out) in the meantime please let me know -
Thanks for everyones input, this is a huge help and is def helping me feel safer about the electrical!

 

[Rocketman]

Get your digital multimeter (DMM) out:
Get basic readings on batteries, and on the mppt battery screws.

Look over your wiring job to make sure you got everything back correctly.

 

[mikefitz]

You need to explain how the Victron battery protect operates in your system.
I am not surprised you are still having issues, to be blunt your wiring is a mess, wire nuts are very unreliable. It's not clear if the cables used are multi stranded automotive grade or house wiring grade.

When commissioning a system it's useful to evaluate sections of the system separately taking voltage and current measurements along each circuit. The first thing you need to evaluate are the voltage readings on the battery compared to readings on the solar charger terminals.
The solar history you have shown indicate a low battery voltage of around 1.5 volts and a high of 30.6 and 28.8. This suggests one or more of the batteries BMS has shut the battery down. Note the BMS can shut down the charge path and still allow discharge. Also even with the battery completly disconnected the Victron Solar Charger can still put power Into the DC circuits .
These things would help,
Charges settings in the Victron Solar Charger.
How the Victron Battery protect is wired in the system.
Circuit diagrams.
How the Renogy monitor is wired.

Most issues can be identified by systematically testing each element of the system and comparing what you have to what you expect.

Mike

 

[jessicadavis]

Ok all -
Thank you for your patience. I was able to finish up the updated diagram of the full system when I got back today. It is attached

I just went to test the batteries & the MPPT with a multimeter as @Rocketman and others suggested and there were little sparks that freaked me out and I didn't want to push it. The multimeter (a cheap $7 harbor freight unit) was set to DCV and i started with the negative lead. I hope I didn't damage anything.

Please let me know what you think and if you have any questions about the schematic. I'll try the multimeter again tomorrow around high noon as suggested. If anyone knows how to avoid a spark please let me know - it was small but alarming!

EDIT: I had the positive lead plugged into 5ADC on the multimeter - I believe this was the issue behind the sparks.

 

[jessicadavis]

I want to add if it’s easier and it probably is shade a panel in series instead of disconnecting. If wattage goes down the string is good. If it stays the same it’s bad. Each side should go down just as much.

Tried this - the wattage dropped as expected when shading each set. I think the issue is something else! Feel free to take a look at the diagram I just posted

 

[jessicadavis]

Are you charging thru the Battery Protect? According to Victron that is not allowed and has been seen to fail catastrophically (e.g. melts). Perhaps that is contributing to charging woes?

No I'm not - feel free to take a look at the schematic I just posted to see how it's hooked up

 

[jessicadavis]

You need to explain how the Victron battery protect operates in your system.
I am not surprised you are still having issues, to be blunt your wiring is a mess, wire nuts are very unreliable. It's not clear if the cables used are multi stranded automotive grade or house wiring grade.

When commissioning a system it's useful to evaluate sections of the system separately taking voltage and current measurements along each circuit. The first thing you need to evaluate are the voltage readings on the battery compared to readings on the solar charger terminals.
The solar history you have shown indicate a low battery voltage of around 1.5 volts and a high of 30.6 and 28.8. This suggests one or more of the batteries BMS has shut the battery down. Note the BMS can shut down the charge path and still allow discharge. Also even with the battery completly disconnected the Victron Solar Charger can still put power Into the DC circuits .
These things would help,
Charges settings in the Victron Solar Charger.
How the Victron Battery protect is wired in the system.
Circuit diagrams.
How the Renogy monitor is wired.

Most issues can be identified by systematically testing each element of the system and comparing what you have to what you expect.

Mike

Feel free to take a look at the diagram I just posted.
I left off the Renogy charger cus I've disconnected it and will likely get a Victron smart shunt as someone suggested earlier, but when it was connected it had its main lead plugged into the port behind the shunt going to the monitor display and it's positive lead in the 24v fuse block + the negative 2/0 cable coming from the batteries on P-of the shunt while the B- is affixed to the negative busbar with a copper bar.

Honestly re the battery protect it was suggested to me by someone with more expertise and I took their advice. They said it would help protect from excess discharge on the load side. It's detailed in the schematic

All the wires are marine grade and stranded

Attached are the charge settings from the charge controller (recently changed absorption to 28.8 as per a suggestion on this thread)

 

[jessicadavis]

First - raise the absorption to 14.4 per battery 28.8 on the mppt. That will help get more power into the batteries.

Here are several important tests
1. Battery to mppt voltage: about noon when good sun and your system is in bulk.

Find the digital voltage of the batteries. Say 26.98v
Then find the voltage at the mppt’s terminals. My guess is it will be much higher than the batteries. (If not this isn’t your problem - but it needs checked).

If this is a issue - your batteries are not getting fully charged - even though the mppt thinks they are.

A couple of solutions:
Figure out how much difference and raise your absorption voltage that much.
Second (an expensive option) replace the shunt with a Victron Smartshunt or BMV712. Then setup the VE.Network- the shunt will send voltage, current and temperature(if you buy the optional temperature sensor) to the mppt via Bluetooth. This will correct the differences and the mppt will be using the battery voltage to make the decisions of when to go into absorbing and float.

2. Batteries at different voltages. When charging in absorption (or late bulk), read the voltage of each of your four batteries. Are they all the same? They should be very close. Do this test several times, late absorption would be ideal. Also, first thing in the morning before any solar - if there are significant differences you need to re-balance the batteries.

Good luck with your system.

Just tested the Battery to MPPT voltage as suggested initially, system is in bulk with good sun conditions, bringing in around 425W. Here are the readings:

Battery voltages:
Individually -
13.1 - 13.2
13.1 - 13.2
13.1 - 13.2
13.1 - 13.2

Pairs -
26.3
26.3

MPPT voltage:
PV - 77.6
Battery - 26.3-26.4

If the discrepancy was predicted to be between the battery voltage of the mppt and the batteries themselves, it appears they're operating properly at the same voltage.

I plan to get a smartshunt as suggested but it will be a little bit til it arrives and is installed. Down to keep troubleshooting but honestly the system has been working fine since replacing the ANL fuse between the batteries and the bluesea switch. Let me know any thoughts, thanks so much

 

[Rocketman]

That’s good that your batteries are basically in sync in bulk mode at a lower charge level 13.1v. Now do the same test at the end of bulk - beginning of absorption mode - hopefully it will also be all batteries in sync. Should be 14.2 to 14.4 depending on where you set your mppt.

 

[jessicadavis]

That’s good that your batteries are basically in sync in bulk mode at a lower charge level 13.1v. Now do the same test at the end of bulk - beginning of absorption mode - hopefully it will also be all batteries in sync. Should be 14.2 to 14.4 depending on where you set your mppt.

Thanks - I'll try it again when it gets to that state.
Question: What's the lowest voltage they should be discharged to aka when the system reaches 0%?

 

[rodrick]

Thanks - I'll try it again when it gets to that state.
Question: What's the lowest voltage they should be discharged to aka when the system reaches 0%?

2.5 volt per cell is absolute max so a 24 volt system would be 20 volts assuming all cells are perfectly balanced which isn’t real world, many set the min on a 24 volt system to 22.5 to 24 (2.8 to 3 volts per cell) running them down to rock bottom isn’t good for longevity and risks pulling one to low bms should catch it but not worth the risk for what little extra you will get out of the battery

 

[jessicadavis]

2.5 volt per cell is absolute max so a 24 volt system would be 20 volts assuming all cells are perfectly balanced which isn’t real world, many set the min on a 24 volt system to 22.5 to 24 (2.8 to 3 volts per cell) running them down to rock bottom isn’t good for longevity and risks pulling one to low bms should catch it but not worth the risk for what little extra you will get out of the battery

Thank you! How do people generally design a system to ensure this discharge voltage is met without a battery protect? Is that just the internal BMS in the batteries at work?

 

[rodrick]

a lot of inverters can be set to shut down at a predetermined voltage on my mpp 2424 i can choose from 20 to 24 volts for my low voltage shutdown you will have to look at your inverter setup if your inverter will not do this or within the ranges you want then a battery protector is a good option

 

[jessicadavis]

I have more data for anyone following the thread

System shut off last night. Was running inverter and a small AC fridge as well as 2 maxxfans on low
It came back on this morning. It's a cloudy day, mppt has brought in about 460Watts so far.
About an hour ago (while the system was running) I used the multimeter and got these readings:

batteries: 24 & 23.9
mppt: 24.1

A few minutes ago, everything shut off. Battery Protect was flashing E3 (under voltage) and inverter's low battery light on.
multimeter readings:
batteries: both 21.8
mppt: 21.9

Heard the inverter attempting to click back on and got the attached notifications via the app (low battery/battery voltage ripple). Set from "on" to "charge only" (not plugged into shore, just want to keep it from continuing to try to fully power back on)

Not sure if I'm over thinking all this and the system is simply depleted, but it still seems like it gets to that point way too easily for the loads I'm putting on it. Any thoughts are welcome!