Dealing with Low Voltage Errors

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rpbancroft
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Dealing with Low Voltage Errors

Post by rpbancroft »

Hey there!

On 1/16/22 and 1/20/22, our batteries threw low-voltage errors for the first time in our ownership of them (the lowest SoC I've seen is 52%, with only a handful of times below 55% in 3.5 years). It's a 24V system, and apparently the low-voltage trigger is 22.2V (I assume that's the default as I don't believe I've tinkered with that, and probably shouldn't). The batteries are inside our house, within two nearly sealed wooden boxes (physically separated from each other; one shows 5-degrees lower surface temperatures than the other; the colder one is against the outside, SE corner of the house, and the floor is insulated but poorly by design; it's on a steel trailer and recessed into the steel framing members I think). We have eight (8) 260Ah 12V AGM batteries wired to yield 1040Ah at 24V (though I'm sure at this point it's something like 85% or even less this capacity).

On 1/16, at the time of error: The SoC was 67%, reported battery voltage on the Mate3s display was 23.7. Outside temps were about 24, with as low as a 13 degree wind chill. I didn't get surface or surrounding area temperatures before I'd getting things going again.

On 1/20, at the time of error: The SoC was 72%, reported battery voltage on the Mate3s display was 24.0. Surface temperatures of the batteries with a temp gun read about 57 degrees, with some of the surrounding walls within the battery box as low as 52 - 53.

We have a 280V piece of heat tape on the system (gonna be deprecating this after this winter, crazy excited for that), and a 9.9 cu. ft. refrigerator. There are also about 80W of other passive loads in the house, plus two passive DC loads (only one which runs 24/7, a vent fan in a Separett toilet). In both cases, I would guess that 22.2V was only achievable when the heat tape was running (quite a frequent occurrence on super frigid nights) and the fridge kicked on.

I assume the problem here is temperature, lack of an RTS (posted a question about that separately), perhaps battery age (not sure if that changes their tolerance to cold and voltage variations related to those), and different temperatures affecting the two 4-battery banks. Lifting the top of the battery box to let in some warmer air and leaving the thermostat overnight 4 degrees higher did not prevent the 1/20 error, but there is a LOT more I could do to protect them (shim them off the floor, add passive and/or active ventilation holes on the sides and circulate in warmer air, etc.).

But am I barking up the wrong tree? Or is this A right tree and is there another tree I should add to my, um, barking?

Any other info you need?

Thanks SO much! Super excited to not break out the generator at 4AM again. :P

~Ryan
raysun
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Re: Dealing with Low Voltage Errors

Post by raysun »

As a veteran of the AGM wars, I'll share some observations.

AGM batteries are great, because they are maintenance free. AGM batteries are not-so-great, because you can't maintain them.

AGM has the highest cost per cycle, and the lowest cycle life of the lead acid battery family.

AGM is the "Goldilocks" of lead acid, not too little (charging, operating temperature), not too much (charging, operating temperature). Just right, or I'll just die (which I will do sooner than you want anyway.)

AGM tends to perform excellently, until it doesn't, and then it's likely to have cells fail catastrophically.

I truly hope I'm wrong on this conjecture, but sudden low voltage events (especially at SoC above 50%) is usually a sign of dead cells.

Watch for this event again. Note the SoC, its likely to be fairly consistent. Recharge and repeat the discharge. As the SoC event horizon approaches, use a voltmeter to measure each battery block. There's likely to be one or more lower than average. At the point of failure, the bad blocks will drop very low, and can even reverse polarity(!) The evidence will erase itself somewhat, fairly quickly as the quiescent battery will tend to equalize voltages with a surface charge on each cell.

Since there are 8 monoblocs, in 4 parallel strings ( best practices dictate 3 parallel strings max), you can do some battery triage and remove 2, (or 4) of the ailing blocs keeping the 6 (or 4) healthiest.

This is a "rear guard" action until the battery is replaced.

BTW, Temp Comp charging may help prolong the lives of healthy blocs a bit at this point, but it won't cure the ailing ones.

If you don't find sub-par bloc voltages, we can strategize rehab techniques.

Good luck!
raysun
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Re: Dealing with Low Voltage Errors

Post by raysun »

One other (less sour) note - low temperatures can reduce battery capacity temporarily. A well-charged battery is unlikely to be damaged by sub-freezing temperatures, but a discharged battery can have its electrolyte freeze. Fortunately, AGM batteries have relatively little electrolyte, so can "thaw out" fairly quickly.
rpbancroft
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

Ha! I find myself somewhere between a resigned sigh and a cry of "let's just do this." While expensive and complicated to deal with, at this point I'm more excited about clarity and sleep than anything. :grin:

Thanks for the descriptions of AGMs. Ever since I've seen the promise of Lithium Ion, especially with the 8000+ cycles, beautifully forgiving DoDs, and excellent BMSes (some even are self-heating!), I've been dreaming of flipping my bank. I was HOPING to do that in about 5 years, but best laid plans and all that...

Several questions to give me a bit more of a framework based on what I was already thinking / potentially planning, and to make sure I'm understanding what all you said:
  1. Do you feel that the 5% variance between the two current trigger points I saw qualifies as fairly consistent? Or perhaps it's too early in data gathering to note a pattern?
  2. I used to obsessively keep the batteries at 80% or above (especially since I was aiming for that 3000+ cycles at 20% DoD reported in their lifespan chart), but fell off that wagon a bit. If we're looking at a bad-cell situation, any chance this strategy will stave off catastrophic effects, or have some chance of doing so, prolonging the bank as it is currently laid out?
  3. Could you expand on measuring a battery block? Can I measure individual batteries while they're linked together, or will I instead be seeing the voltage/readings from each linked set? I presume there will be four (4) linked sets in this particular design, if I'm interpreting what you said correctly? Which leads to...
  4. You mentioned not exceeding 3 parallel strings max. Am I correct in interpreting that, in my situation where I have 8 12v batteries wired to 24v, that means I have 4 parallel strings but ideally would not have exceeded 3? Sorry if that sounds super obvious, but I wanted to attempt rewording it to make sure I had the concept down. I didn't wire this system, and didn't have the knowledge to assess the quality of its wiring at the time it was bequeathed to me; I wanna make sure I do next time.
  5. Based on your experience, if you had to ballpark it, how long would you guess I have until the whole system goes belly up (if the situation is what you've mentioned could be happening)? I won't hold you to anything. Just want to get an idea if I need to act within a week or if I can probably save this until we're out of Winter (which makes EVERYTHING harder).
  6. Is there any way I can preemptively examine the batteries one-by-one (perhaps turn off the house power at an optimal time and isolate each battery one at a time) to determine if any is having a cell problem? If so, is there an SoC the batteries should be at for that process? Would that be done with a multimeter? And what voltages would I be looking for?
  7. How do I physically identify which batteries are in which parallel strings? Will that be obvious from the way they're wired together? The way they're separated (four in each physical wooden compartment) always made me think of each lump of four as a singular unit, but it's pretty obvious from what you've said that that's not the case. Trying to rewrite my faulty conclusion / assumption.
  8. If this all does show that two or even four batteries (or 1 or 2 parallel strings / blocs) are bad, would you recommend I only replace the ailing batteries? I've heard that will degrade new batteries down to the capacity of the older ones. Any best practices for handling situations like this?
  9. If I do have to do the rear guard approach, I assume I should adjust the values in the Mate3s to reflect the "new" battery capacity?
  10. Do you think there's any legitimacy to my conclusion that I should try to keep my batteries warmer? Or is that just not worth messing with? Just now (deep into composing this response) saw your note on a well-charged battery's ability to withstand cold - so is it worth investing the time and effort into ventilating them and keeping them warmer do you think?
Ugh, I'm gonna be a novice even in things I intimately manage until I DIE. But I guess that's fine - the more you know, the more you realize you don't know.

Just tiredness speaking. :wink:

Super appreciate your support. I'll try to gather data and report back. With any luck, it will take a while and this event won't occur again (or so says my undying optimism, which I love but don't put much faith in).

~Ryan
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Re: Dealing with Low Voltage Errors

Post by raysun »

[*]Do you feel that the 5% variance between the two current trigger points I saw qualifies as fairly consistent? Or perhaps it's too early in data gathering to note a pattern?
I think that's right on the money. With consistent temperatures and loads the same event should happen about the same SoC.

[*]I used to obsessively keep the batteries at 80% or above (especially since I was aiming for that 3000+ cycles at 20% DoD reported in their lifespan chart), but fell off that wagon a bit. If we're looking at a bad-cell situation, any chance this strategy will stave off catastrophic effects, or have some chance of doing so, prolonging the bank as it is currently laid out?
The DoD v.s. Cycle Life charts are marvelous, lab-grown marketing tools that have passing resemblance to real world usage, but there's so many variables its tough to draw 1:1 correlations.

IME, the best course of action is to put the battery to use and have it last as long as it lasts. That and scour the family for a long-lost rich uncle you can buddy up to so he leaves you a bequest to pay for your lithium battery.
[*]Could you expand on measuring a battery block? Can I measure individual batteries while they're linked together, or will I instead be seeing the voltage/readings from each linked set? I presume there will be four (4) linked sets in this particular design, if I'm interpreting what you said correctly? Which leads to...
Yes, each 12V battery block in a series string can have voltage measured at its terminals, and that will represent the voltage for that block. Parallel connected battery blocks are more difficult to measure, as there will be interaction between the blocks.

In order to get accurate measurements with the battery at rest, each block may need to be isolated.

The easiest test is 'resting voltage' measurement. It would likely require disassembling the battery, letting the disconnected blocks rest for 8 hours (or more) then measuring voltage of each. With a battery under constant use, this is nearly impossible. The best than can be done is to remove two blocks at a time, and test. However, the rest of the battery will have continued to discharge/charge, so comparative voltages are impossible to record.

Under load, blocks with grossly degraded cells may show up as having a lower voltage. They should be flagged for the "resting voltage" method.
[*]You mentioned not exceeding 3 parallel strings max. Am I correct in interpreting that, in my situation where I have 8 12v batteries wired to 24v, that means I have 4 parallel strings but ideally would not have exceeded 3? Sorry if that sounds super obvious, but I wanted to attempt rewording it to make sure I had the concept down. I didn't wire this system, and didn't have the knowledge to assess the quality of its wiring at the time it was bequeathed to me; I wanna make sure I do next time.
Your interpretation is correct. Typically, four series strings, each a nominal 24V @ nnnAH. (You mentioned the capacity but I'm too lazy to look it up.)

The four strings would then be connected in parallel. In a parallel connection, the capacities add. So the total is 24V @ 4x(nnnAH).

20220121_000124.jpg
Simplified battery wiring diagrams.

Google series parallel battery connections and you will see more diagrams illustrating the wiring schemes. You should be able to take one of the visualizations and correlate it with the cabling on your battery.
[*]Based on your experience, if you had to ballpark it, how long would you guess I have until the whole system goes belly up (if the situation is what you've mentioned could be happening)? I won't hold you to anything. Just want to get an idea if I need to act within a week or if I can probably save this until we're out of Winter (which makes EVERYTHING harder).
IMO, you have time. Since you started with more capacity than is needed on a daily cycle, you can trade capacity reduction for service life. Permit me a long, not especially simple explanation.

Your battery consists of a total of 48 individual 2V cells. 6 cells per battery block (a monobloc in battery engineering parlance). 12 cells per series string. 48 total cells in the battery.

In the ideal battery all cells would measure, perform, and degrade, identically. There's no such thing as the ideal battery. Over time, some cells fall behind their battery mates. They lose capacity faster, they can't hold as consistent a voltage, their electrolyte leaks away. Anything that causes them to become weaker, causes them to die earlier. If the imbalance becomes pronounced enough in a given cell, or enough cells become somewhat more degraded than others, then they drag the entire battery's performance (and eventual health) down with them, but again, not in balance.

With an AGM, the best we can do to identify bad cells, is to measure the voltage of an entire block of cells (the 6 cells in the 12V monoblocs).

In a sort of "battery triage", the two monoblocs that measure the worst at the voltage failure point are the first candidates for removal from the battery. Why two? Because an entire two-block string must be removed. The two removed don't need to be from the same string, and likely won't be.

The hopeful end result will be four strings performing badly become three strings performing better, albeit at lower battery capacity. 36 cells working more closely in balance is better than 48 cells with a few bad apples spoiling the whole barrel.

The lower capacity (36 cell) battery will now be discharged more deeply on daily cycles.
[*]Is there any way I can preemptively examine the batteries one-by-one (perhaps turn off the house power at an optimal time and isolate each battery one at a time) to determine if any is having a cell problem? If so, is there an SoC the batteries should be at for that process? Would that be done with a multimeter? And what voltages would I be looking for?
Individual battery block capacity testing can be done, but it will require some external test equipment, disassembling the battery string-by-string. Unless the testing is done in a very controlled manner,, it may not be any more informative than the simple "in-situ" voltage measurements of each block as described earlier.
[*]How do I physically identify which batteries are in which parallel strings? Will that be obvious from the way they're wired together? The way they're separated (four in each physical wooden compartment) always made me think of each lump of four as a singular unit, but it's pretty obvious from what you've said that that's not the case. Trying to rewrite my faulty conclusion / assumption.
Each battery box may have two series strings, but the installer might have been "clever" and made all four in one box a 12V parallel bank, then cabled the two boxes in series to make a 24V battery. (It may be just me, but I dislike "clever").
20220121_000124.jpg
Repeating this simplified wiring diagram.

When in doubt, post some pictures clearly showing the cabling.
[*]If this all does show that two or even four batteries (or 1 or 2 parallel strings / blocs) are bad, would you recommend I only replace the ailing batteries? I've heard that will degrade new batteries down to the capacity of the older ones. Any best practices for handling situations like this?
If its necessary, replace bad blocks. The new blocks will have a service life equal to the remaining original blocks.

Best practice? Bite the bullet and know the best thats being done is staving off the inevitable.
[*]If I do have to do the rear guard approach, I assume I should adjust the values in the Mate3s to reflect the "new" battery capacity?
Correct. e.g. Three strings would be 75% capacity, and likely further derated to 80% of the original published C20 capacity (so 80% of 75%, if that makes sense.)
[*]Do you think there's any legitimacy to my conclusion that I should try to keep my batteries warmer? Or is that just not worth messing with? Just now (deep into composing this response) saw your note on a well-charged battery's ability to withstand cold - so is it worth investing the time and effort into ventilating them and keeping them warmer do you think?
AGMs are generally servicable from 14°F to 140°F, but the extremes come at a cost. 35°F - 90°F would be more in their comfort zone. I'd think you're OK if it isn't getting any colder.
rpbancroft
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

Beautiful, thank you - not only for your attentiveness but also your willingness to engage with so many questions at once! I think I have enough info to go off of for now. Time to get comfy with my multimeter and see what I can ascertain.

I'll report back and/or share diagrams if I hit a snag in figuring out what I'm seeing.

~Ryan
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Re: Dealing with Low Voltage Errors

Post by raysun »

My psychic abilities waned many years ago. However, I'm guessing there are 15 cables in total connecting the battery bank.

6 short cables in each battery box. 3 connecting the negative terminals of the 4 battery blocks, and 3 connecting the positive terminals. 6 x 2 boxes = 12 cables.

1 cable connecting the negative terminal of a battery block in one box to a positive terminal of a battery block in the other battery box.

1 cable connecting a battery positive terminal in one battery box to the equipment (hopefully through a fuse or circuit breaker.)

1 cable connecting a battery negative terminal in the other battery box to the FNDC shunt(s). The other end of the shunt(s) connect to the Bat - of the inverter, charge controllers, etc.

Are there any DC loads connected to the battery?
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

Ha, maybe those abilities will return with practice. :)

I have pictures and hopefully useful information! I have a feeling the way they did DC, and maybe even the whole way they wired it, is kind of a problem (or maybe not the greatest idea). A few interesting pieces of info, and then I'll drop the photos:
  • Every battery I tested with a multimeter read as a 12V unit, which surprised me; I figured they would read as 24V because of how they're wired up.
  • SoC as reported by the Mate3s when I tested was about 98%.
  • All batteries in the left/by-fridge box read 12.7v-12.8v (it fluctuated).
  • All batteries in the right box (which I couldn't get a full photo of, so it's split into two) read 12.3v. This is also the box to which the DC wires are connected.
  • If I'm understanding what I'm seeing, it looks like each of the four batteries in each box is wired in parallel (had to look up the difference), and then both 1040Ah parallel blocks are wired together in series to yield 24v. However, it looks like the DC loads are only drawing from one of the two sides of the in-series blocks.
  • Throughout all of this, the Mate3s seems to report the 24v equivalent of the voltage in the non-DC-connected bank. When they're at 100% and mostly load-free, it generally says between 25.2v - 25.3v. It may say a bit higher sometimes, but I can't recall clearly.
Full shot of the left box, voltages 12.7-12.8 measured on each of the four batteries.
left_box_full_shot.jpg
Zoom in on the left-box's uplink to the other box and the wiring that goes to the inverter.
left_box_zoom_on_external_link.jpg
Point near inverter where the wiring comes out of the indoor wall (about 25 feet from batteries). Also shown are the DC fuses.
wiring_near_inverter_and_DC_fuses.jpg
Looks like I can only do 3 photos per post. I'll add more.
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

Following up with more photos:

Right box, voltage per battery read as 12.3v (all 4 identical, no dynamic fluctuation). Has DC loads attached.
right_box_DC_links.jpg
Other two batteries in this box.
right_box_other_batts.jpg
Close-up of the link between the boxes, which also shows how the wires go into the wall and bridge between the two boxes.
close_up_of_link_btwn_boxes.jpg
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

And the last one! Maybe not important, but just in case:

Here's a full shot of the link between the two boxes.
link_between_two_boxes.jpg
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Re: Dealing with Low Voltage Errors

Post by raysun »

The battery wiring is as described. Each box has four battery blocks wired in parallel, creating a 12V bank. The two 12V banks are wired in series to create a 24V battery. Both banks must be series connected (and in use) to provide 24V.

Measuring across the +/- terminals of one battery block will always yield 12V nominal reading. The individual battery blocks in a box will measure the same (or nearly so) as the parallel connections of all four blocks "averages" the voltage.

The two battery box average readings- 12.3V in one and 12.7V in the other- is an issue. It speaks to an imbalance in the manner in which current is distributed between the boxes, both on discharge and charge. IMO, its a partly a result of the manner in which the battery is wired.

I cannot tell for sure, so will ask here - does the house have any 12V loads? A water pump perhaps? 12V lighting? I'm suspicious that there is a 12V "tap" off the 2nd battery box. If so, this would also contribute to the imbalance between the two battery banks. Determining the presence of 12V loads is a "critical path" factor in deciding next steps for addressing the battery issue.
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

Yes, I have two DC loads - a water pump (good guess!) and an always-on vent fan for our separating toilet. The pump is under the kitchen sink and kicks on every time we use any water in the house (after about 1/8 gallon or so of water is used; it pressurizes the internal piping to 40psi). Those are the only two currently.
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Re: Dealing with Low Voltage Errors

Post by raysun »

Trace the wiring for those two loads. I believe it will lead directly to battery box two. (The thin grey wire on the battery positive terminal and thin black wire on the negative terminal in the photo raises suspicions). If so, that direct tap off the 12V battery bank (box two) is a major no-no. If its in place there, it is a substantial contributor to killing the battery.

The proper way to drive 12V loads would be a 24V to 12V DC-DC converter. The 24V tap draws from the whole battery, in balance, and the 12V tap feeds the loads. Is such a device installed in the system?
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

If such a device is present, I've never seen it or known about it. I'll have to look more closely, but I'm fairly certain the answer is no. Is this an example of that unit? Or this (changed URL a few minutes later as I realized the originally linked one was a 24V to 12V unit)?

I'm almost positive you're correct, and that the thin wires are DC taps; the fact that they're only on battery box 2 probably suggests there is no such device installed? I can't really think of anything else they would be, and I'm fairly sure they correspond well with the wires that go into the DC fuse box in one of the photos.

Would I be correct to assume that a 12-24V converter would require physical wiring to both battery boxes, so that it can tap them simultaneously? And do you think it would be feasible to install something like that near the battery boxes, DC wire to both boxes, and use the wiring that runs through the walls to the inverter (unit) to link back to the overall control system? That's what my rough understanding is suggesting, but I'm not sure if I'm on the right track.

If all that's on point, is there anything I should do to recondition the right battery box's batteries before correcting the wiring issue?

And how do I proceed safely? I'll definitely watch some videos on doing this, but was curious about your recommendations.

Finally, you'd suggested that this wiring config might be problematic for AC as well. Anything I should consider fixing there?

Thank you!
Last edited by rpbancroft on Mon Jan 24, 2022 10:08 am, edited 1 time in total.
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

Oh yeah, we also see a sort of DC brown-out situation whenever running DC loads. For example, I used to have three things on DC. I had to take the UV-light water filter off because the drop in voltage that occurred whenever the water pump would kick on caused the unit to throw an error. We bypassed this by connecting to a DC-to-AC converter for that unit. But the vent fan still slows down whenever the water pump kicks on. I'm guessing it's a pretty heavy device requiring a lot of amperage.

Would the 12v-to-24v device you mentioned correct this problem do you think? Also, does this particular problem give you any more hints about what's happening here overall?
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Re: Dealing with Low Voltage Errors

Post by raysun »

Yes, those DC-DC devices are of the type needed. I don't use such devices so don't have specific recommendations, but the circuits are fairly simple, and whats needed is one that can handle the startup load of the pump. Wiring would be across the 24V tap. It can be taken on the "load" side of the battery fuse that's marked as inverter feed.

Now the tough issue.

After 3.5 years of a "parasite" sucking the lifeblood out of bank two, the bank is likely seriously ailing. (Its too harsh for a Monday morning to say its dead, but that's likely the case.) It might be revived a bit, but will always be weaker than the other bank.

My recommendation is to reconfigure the battery to use the four blocks in box one only. That entails:
Disconnecting box two
Wiring the blocks in box one as two 24V strings
Connecting the 24V strings in parallel
Connecting the battery feed cables, the heavy cables: Battery + going to the fuse, and Battery - going to the shunts; to the + terminal of string one and the - terminal of string two.

While it cuts the apparent capacity of the battery in half, in practice the battery will deliver better performance.
Last edited by raysun on Mon Jan 24, 2022 10:27 am, edited 1 time in total.
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REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Dealing with Low Voltage Errors

Post by raysun »

Would the 12v-to-24v device you mentioned correct this problem do you think? Also, does this particular problem give you any more hints about what's happening here overall?
In the "Who dunnit?" battery murder mystery, the battery wiring is the mastermind, but the 12V tap pulled the trigger.

The brown outs are a symptom of bank two's demise.
rpbancroft
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

:lol: Hopefully we're getting closer to solving the mystery! At least they've made it this far with weird wiring. I can be happy about that. :P

I should mention also, those brownouts have been happening since day 1, so I figured they were somehow related to the wiring itself (could even be the gauge used, from what little I've read). Maybe them being linked to just bank 2 has something to do with it? Was just curious if somehow that was related. I remember hearing that the electrician who set all this up wasn't very familiar with DC wiring, so... this is a good lesson showing how dangerous, especially over time, such a problematic gap in knowledge can be. If only I'd been more suspicious and curious earlier and checked with you all about how that box was wired. Eh, hindsight.

I'll have to give some thought to rewiring and completely removing bank 2 from the system. I can definitely see your logic - having four solidly healthy batteries, even at 1/2 capacity, would bring some serious peace of mind, especially overnight in deep cold. And our system actually was delivered to us with the stock 400Ah configured (in the Mate3s) as the batteries' capacity rather than the true 1040Ah they have, so, for the first several months, we worked with a bank that was acting like it was that size. We do have some familiarity with running our house at that capacity.

Finally, in your step-by-step, would it be appropriate also to add acquiring one of those 12V to 24V DC devices and wiring them up to use the two 2 battery units evenly?
raysun
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Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Dealing with Low Voltage Errors

Post by raysun »

20220124_084131.jpg
A very crude drawing of a 24V battery using the blocks in box one.

The brown outs from day one suggest a wire guage too small.

Check the pump specs, it should give a hint as to startup current demand. A 24V to 12V converter should be sized to meet the startup current.

As suggested, wire the converter to the load side of the battery fuse. (Though now that I look at the photo of the wiring panel, I don't recognize a battery fuse in line with the battery + lead. Does the heavy cable from the battery go directly to the inverter?) The "fuse box" in the picture looks to be AC out from the inverter, I guess.

The problem with sealed batteries is from the outside, a dead battery looks as good as a healthy one.
rpbancroft
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

Oh man, I just had a thought. What if the electrician wired everything intentionally to a single block to get 12v, bypassing the rest of the 24v system, so that he could directly supply these loads to the DC appliances? That would "simplify" things for him because he wouldn't have to worry about going 12v > 24v (apparently, as you've said, essential for battery health to keep the DC loads balanced across both strings within the whole 8-unit battery bank) and then back to 12v when he hit the appliances themselves. I would assume that the appropriate design in this case would be to use a 12v>24v converter between both battery blocks (if that's the right word), and then use a 24v>12v converter at each DC appliance. Unless the Outback equipment we have has some means of handling a 24v DC link and pushing 12v to devices (and why would it? It's designed as an inverter for standard AC I thought), I can't see how else this would work.

I'm gonna have to do a lot more tracing to see exactly what is going on here; I hope nothing wacky was done within the walls, but at least I have photos before the insulation and wall boards were put on. I need to see if the DC wiring even interacts with the rest of the Outback equipment at all. I have a sinking feeling it's 100% it's own thing, by design. If that's the case, this was BUILT to fail. Sigh. Either way, I'm learning a ton though (don't trust what you're given without healthy skepticism, double and triple check wiring even if it was done by a "pro", etc.). That's invaluable.

Thanks for the drawing! I'll give it a good study once I'm back with the batteries pondering my next move.

I suspected wire gauge could be an explanation for the brownouts. Not sure what else I can do about too-small wiring since it's in the walls, though, and they didn't have the grace to use conduit. I may just have to convert to AC, though I hope I can avoid that (not really sure how heavy the pump would be if it is AC).

Right on, will check the pump specs; I want to investigate the whole system and see what needs doing.

I think the heavy line does go directly to the inverter. The fuse box in the photo is only for the DC loads; I found that out the hard way when we kept blowing a fuse because of the brownout/voltage issue.
raysun
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Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Dealing with Low Voltage Errors

Post by raysun »

Measure the battery voltage at the inverter and you will surely find it is 24V. That voltage is derived from the series connection between the two 12V battery banks in the two battery boxes.

If you want to prove it to be as described above, simply remove the series cable connecting the two. The inverter will shut down. (Actully, take my word for the configuration. Do not try that test without turning the inverter off first.)

The configuration in your supposition is too complex to pull off. Nobody that "doesn't really understand DC" could pull it off. Nobody that understands DC would do it.

You MUST HAVE a fuse or circuit breaker in the Battery + line. Otherwise, a real safety issue is lurking in your house.
raysun
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Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Dealing with Low Voltage Errors

Post by raysun »

I recently purchased one of these pumps: https://www.amazon.com/gp/aw/d/B076TGWYDK

Seems decent enough for the task. Not sure if the flow rate is enough for your purpose, but yes, you should switch to an AC pump.
rpbancroft
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

I think I didn't describe what I'm thinking of very well (poor command of the terms is mostly likely the culprit). I just meant the wiring of those tiny cables that run power from the batteries to the DC fuses to the DC appliances. I have a theory that the electrician just went directly from the batteries to those appliances (with the fuses in the middle). As for the main, big power that all AC loads use, I'm reasonably confident that the big cables that run to the Outback equipment are good, or at least functional (if not optimal).

I'll not touch anything though without powering things down, just want to see how it's all lined out. Especially the stuff I was calling DC (which I can see being confusing since it's all DC where batteries are concerned).

Thanks for the pump recommendation. I don't know much about pumps, but the one we have is a variable-speed one that's apparently fairly fancy (at least it retailed for almost $500 if I remember the original quote correctly). I may have to do some research if it won't be as simple as acquiring a DC-to-AC converter of some kind. Lots to learn still.
raysun
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Joined: Tue Jul 26, 2016 5:57 am
My RE system: Flexpower Two: (2) FXR3048A-01, (2) FM80, MATE3s, FlexNetDC
6 SimpliPhi 3.8-48 (48v @ 75AH. 450AH total)
Outback IBR3 battery enclosure
REC Alpha 440W panels - 2 arrays: each of 4 strings of 2 in series
Honda EU7000is gas fuel generator

Re: Dealing with Low Voltage Errors

Post by raysun »

No worries. Sounds like a pump you want to keep, fed by wiring not up to the task. The issue is, for a given amount of power (to run the pump), the lower the voltage, the higher the amperage required, which in turn means heavier wires. The skinny "Romex" house wiring the electrician used is not up to the task at 12V.

A 120VAC to 12VDC power supply situated near the pump could do the job.

If wishing to remain in the DC realm, a 24V to 12V converter, also situated at the pump end, *might* do it, as it cuts the feed amperage requirement in half.

That "Romex" looks to be 14AWG, which can carry about 20A. 12V x 20A = 240Watts, likely not enough to start the pump without voltage sag (brown out). 24V x 20A = 480W. Maybe enough (when converted to 12V by the 24v - 12v gizmo, probably 400W delivered to the pump.)
rpbancroft
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Re: Dealing with Low Voltage Errors

Post by rpbancroft »

Sorry for the lapse in communication; been intensively researching and trying to get more context on this, assessing options, understanding DC low-voltage wiring (if I'm even phrasing that correctly), planning my next move once I have the equipment I've ordered in hand, etc.

One interesting and somewhat concerning detail I've noticed, I determined that the electrician used 18 AWG HoneyWell Thermostat wire for wiring up all the loads (can't yet tell if he also used that to run the low-voltage line between the batteries and the fuse box, still investigating; you'd suggested it could be 14 AWG ROMEX, which is pretty much assuredly undersized, especially for an almost 30-foot run where some of the appliances need <3% voltage swings). From what I could tell, we need 10 AWG for both the UV filter (3% voltage swing tolerance) and the pump (10% voltage swing tolerance). So that seems like a ringer to explain the brownout issues. I'm exploring rewiring (already installing some conduit for another related project, could use it to re-run the cable since all the loads are on the same side of the house), considering 10 AWG THHN, stranded cable (though I don't know a lot about the differences between cable types just yet).

For the pump, failing the ability to get DC where I want it, just going with an AC-to-DC converter is attractive. I'll keep it in my back pocket.

I've seen some other recommendations that seem a bit odd, but maybe have some minor merit. Do you have any thoughts on these?
  1. One person in a FB group commented that he has a similar build (two 12V banks pushing to a 24V inverter, with DC loads tapped to one side of the bank) and handles the issue by having a voltage meter with an LCD wired up that tells him where each bank's voltage is at dynamically. He then uses alligator clips on the two DC wires, and swaps them back and forth between the two periodically (as he observes 0.5V swings between the two). Is there any legitimacy to this approach, in your estimation? I'm thinking I'm gonna at least give it a try in the short term, as it'll shift the load to the other, healthier bank and give me a few days to put a solid charge into the overall bank to see how the undercharged side responds (I gain lots of data this way, and I can't really see how short-term tapping the other side of the bank with these relatively minor loads could hurt anything). If its voltages rebound (and hold that rebound overnight and into the next morning), I would have more confidence I'm not yet facing a deal cell. At that point, there may be some legitimacy in digging into how to restore them all together.
  2. I just learned about Battery Balancers, like this one (which seems to be exactly the right thing, built for 24V batteries across two 12V banks wired in series). I doubt it would be smart to install one of these now that the batteries are as out of balance as they are (unless I can find a way to restore them), but do you think this is the kind of thing that could have made the way these are hooked together work properly? It sounds like, when charging is occurring, this device detects voltage inconsistencies between the two banks and strives to move power between them to balance them. But could something like this be wired up to the bank without interfering with what the Outback system does? Can these two systems work in tandem?
  3. In reference to your description of the DC voltage conversion, I'm still not sure how to even wire that up. If I'm converting from two 12V banks, and trying to draw power from them equally, I assume both will need to be tapped on both their positive and negative. That's four (4) wires total coming out of the battery banks. These step-up and step-down converters seem to have two inbound wire links. It seems these converters are designed more to convert the voltage from a single battery (or string) from one voltage to another. Does that mean maybe I'd need a 24V to 12V step down converter, wired to the positive in one 4-battery 12V bank and the negative in the other 4-battery 12V bank - essentially bridging between the two banks? Somehow that seems wrong to me (how can it pull power effectively without engaging both terminals in both 12V banks?), but I don't yet know enough to say why. Let me know if that doesn't make sense... still fighting the terminology. :P
Thanks!
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