diy solar

diy solar

Update. Replacement BMS? What's next?

Dirty surfaces or low torque on a nut could make a contact resistive.
In my AC breakers, I find the specified torque provides very little compression. If I just wiggle/rotate wire, it works loose and I can turn the screw further, so that's what I do.
Loose/bad connection would get hot, pushing breaker closer to tripping.

The breakers I'm used to can take 50% excess current for 10 minutes or so. I think 100% excess might trip in 1 minute.
Try to find current/trip curves for yours, see what would explain 1 minute trip.


Battery should supply approximately constant current. Capacitors in inverter should smooth out 60 Hz cycles, and the higher frequency PWM used to synthesize sine wave.
If the capacitors aren't enough to smooth out 60 Hz, each pulse of current will go through the breaker.
Try using AC Volts scale to measure voltage across breaker. Also across a shunt if you have one. Across a length of battery cable (you can look up resistance per foot and use it as a shunt).
Try DC Volts too.

The AC Volts would tell you how much ripple.

People say to derate the BMS, plan to use it for continuous current maybe half its rating.
If there is very high ripple current (zero to 200A instead of steady 100A) that would increase heating of both breaker and BMS (when back to using BMS in the circuit.)

Maybe added capacitors at the inverter would reduce ripple. It would also increase the current surge when closing DC breaker, so a precharge resistor might be a good idea.
My thinking is that invertor vendor might skimp on capacitors.

Bigger breaker/fuse would be a work-around. Just like getting a BMS rated twice what you need.

"I^2 R" or "I squared R" is the power dissipated in a resistor.

Pulses of 200A half the time would deliver same power as 100A all the time, but would cause more heating in the wires.
If wire, breaker, or another component was 0.001 ohm, power dissipated in it is:
100A x 100A x 0.001 ohm = 10W all the time
200A x 200A x 0.001 ohm = 40W half the time, 20W average.

Obviously if breaker dissipates 20W not 10W, it'll trip sooner. Can only carry 1/sqrt(2) = 0.7 times as much current
140A x 140A x 0.001 ohm = 20W half the time, 10W average
So 70A average current (140A half the time) would heat breaker same as 100A continuous.
 
Dirty surfaces or low torque on a nut could make a contact resistive.
In my AC breakers, I find the specified torque provides very little compression. If I just wiggle/rotate wire, it works loose and I can turn the screw further, so that's what I do.
Loose/bad connection would get hot, pushing breaker closer to tripping.

The breakers I'm used to can take 50% excess current for 10 minutes or so. I think 100% excess might trip in 1 minute.
Try to find current/trip curves for yours, see what would explain 1 minute trip.


Battery should supply approximately constant current. Capacitors in inverter should smooth out 60 Hz cycles, and the higher frequency PWM used to synthesize sine wave.
If the capacitors aren't enough to smooth out 60 Hz, each pulse of current will go through the breaker.
Try using AC Volts scale to measure voltage across breaker. Also across a shunt if you have one. Across a length of battery cable (you can look up resistance per foot and use it as a shunt).
Try DC Volts too.

The AC Volts would tell you how much ripple.

People say to derate the BMS, plan to use it for continuous current maybe half its rating.
If there is very high ripple current (zero to 200A instead of steady 100A) that would increase heating of both breaker and BMS (when back to using BMS in the circuit.)

Maybe added capacitors at the inverter would reduce ripple. It would also increase the current surge when closing DC breaker, so a precharge resistor might be a good idea.
My thinking is that invertor vendor might skimp on capacitors.

Bigger breaker/fuse would be a work-around. Just like getting a BMS rated twice what you need.

"I^2 R" or "I squared R" is the power dissipated in a resistor.

Pulses of 200A half the time would deliver same power as 100A all the time, but would cause more heating in the wires.
If wire, breaker, or another component was 0.001 ohm, power dissipated in it is:
100A x 100A x 0.001 ohm = 10W all the time
200A x 200A x 0.001 ohm = 40W half the time, 20W average.

Obviously if breaker dissipates 20W not 10W, it'll trip sooner. Can only carry 1/sqrt(2) = 0.7 times as much current
140A x 140A x 0.001 ohm = 20W half the time, 10W average
So 70A average current (140A half the time) would heat breaker same as 100A continuous.

Hedges,

I owe you an apology for the long delay in responding. Please accept my heartfelt "I am sorry." I've had several travel issues with my RV over the past few weeks.

I've read your last message at least a half-dozen times over the past couple of weeks, hoping a read on a different day would help me understand it better. I sincerely appreciate your effort to educate me. I think some of it is beginning to stick, but I have such low base knowledge, much is still beyond my grasp.

Since I now have picked up the replacement BMS I ordered (AliExpress), I am hoping that I can get one of the old batteries working again and the extra power will solve the system deficiency that keeps the converter/microwave from operating?

Of course, the new BMS came with no installation instructions. Further, it looks like I'm going to have to learn to solder again. It's been since about 1968 when I last soldered anything . . . then assembling a Heathkit receiver.

Again, thank you for your continuing support and information. I'll let you know when I get to the next stage of my restore-my-solar-system process.

jesfl
Jim
 
No problem, we all work on various other things, can sometimes get by with a system that's halfway working.

Breaker tripping could be one of the following, maybe something else I haven't thought of:

1) Just too much current
2) Breaker bad, not able to carry its rated current
3) External heating, especially connection to wire getting hot
4) Current cycling high/low rather than being constant.

That last one is tricky. I've realized that calculating inverter battery current based on wattage isn't sufficient. Battery current has a large ripple because the AC current produced varies as a sine wave between peak, zero, opposite peak.

Power delivered from battery to inverter is voltage x average current. Heating of breaker is proportional to RMS current, calculation includes square of current so the peaks cause more heating.

After thinking about your problem I decided to measure my system. I have current transformers which clamp around wires and show the AC (but not DC) current through them. I have an oscilloscope which can capture a waveform. I was expecting some ripple current but was surprised at how large it was.
I found that for an average 217A battery current, it showed a ripple going as low as 125A and as high as 309A.
As large as that ripple sounds, I calculated it was 227A RMS, only 5% more current, 10% more heating.
This was with particularly high-end inverters, which probably have more capacitors than less expensive ones.
The load was only 40% of inverter rating. If running at full load the ripple would have been higher, RMS current and heating maybe much higher.
If essentially no capacitors at all, entire AC current comes directly from battery, my calculations indicate 12% higher RMS current, 26% more heating.

Our usual practice of oversizing breakers/fuses 25% might cover that, but the 12% effect of ripple uses up half that safety margin. I think the fuse/breaker for inverter battery connection ought to be increased another 12% due to ripple.

That alone isn't enough to explain yours tripping, but contributes to it.


Let me know what you find measuring voltage drop and checking for hot connections.
 
No problem, we all work on various other things, can sometimes get by with a system that's halfway working.

Breaker tripping could be one of the following, maybe something else I haven't thought of:

1) Just too much current
2) Breaker bad, not able to carry its rated current
3) External heating, especially connection to wire getting hot
4) Current cycling high/low rather than being constant.

That last one is tricky. I've realized that calculating inverter battery current based on wattage isn't sufficient. Battery current has a large ripple because the AC current produced varies as a sine wave between peak, zero, opposite peak.

Power delivered from battery to inverter is voltage x average current. Heating of breaker is proportional to RMS current, calculation includes square of current so the peaks cause more heating.

After thinking about your problem I decided to measure my system. I have current transformers which clamp around wires and show the AC (but not DC) current through them. I have an oscilloscope which can capture a waveform. I was expecting some ripple current but was surprised at how large it was.
I found that for an average 217A battery current, it showed a ripple going as low as 125A and as high as 309A.
As large as that ripple sounds, I calculated it was 227A RMS, only 5% more current, 10% more heating.
This was with particularly high-end inverters, which probably have more capacitors than less expensive ones.
The load was only 40% of inverter rating. If running at full load the ripple would have been higher, RMS current and heating maybe much higher.
If essentially no capacitors at all, entire AC current comes directly from battery, my calculations indicate 12% higher RMS current, 26% more heating.

Our usual practice of oversizing breakers/fuses 25% might cover that, but the 12% effect of ripple uses up half that safety margin. I think the fuse/breaker for inverter battery connection ought to be increased another 12% due to ripple.

That alone isn't enough to explain yours tripping, but contributes to it.


Let me know what you find measuring voltage drop and checking for hot connections.

(1) Since I have none of your (sophisticated-to-me) tools, I have not tried to test and make the checks you suggested above. But, I kinda' understand what you are saying.

And, since I am now in an RV park with 30 amp power, I am not microwave-less.

But, I will test this weekend with shore power off -- at least for connection heating and the breaker flipping off when I try to use the microwave on battery only.

Thank you once again.

Jim S.
 
Got a DMM?
DC voltage drop across a connection (e.g. battery terminal to cable clamp of a car battery) is often where I find a problem at high current.
Heating takes time, but voltage shows up immediately.

If not a connection at the breaker/fuse it doesn't contribute directly to heating of the OCP. But if it drops a percentage of battery voltage, inverter draws that much more current to produce same watts, and current squared is what trips OCP.

If inverter terminals are much lower voltage than battery terminals (e.g. 11V vs. 12V) then you chase down where the drop occurred, like 0.5V across a single connection.
 
@Hedges @Just John
I just bought two cheap BTR batteries and have been reading to learn what I need to know to preemptively purchase two appropriate replacement BMSs. I found what I needed early in but had to keep reading.

Just wanted to say thank you for the incredibly thorough education you have provided for the readers, here.

@jesfl - so how did it pan out?
 
@Hedges @Just John
I just bought two cheap BTR batteries and have been reading to learn what I need to know to preemptively purchase two appropriate replacement BMSs. I found what I needed early in but had to keep reading.

Just wanted to say thank you for the incredibly thorough education you have provided for the readers, here.

@jesfl - so how did it pan out?

The above follow-up message just popped up in my email, so it seems appropriate to add an update more than a year later . . . should anyone else read/skim through this long thread?

Yes, amazingly helpful, gracious, giving and patient is all that can be said about all here on the Forum who contributed to helping me solve my failed LiFePO4 battery problem.

(1) I got the system wired and working with the one 200 Ah replacement battery I was forced to purchase. That was only because of the education and assistance I received on this forum.

(2) As scary as it was for this novice, I have now carefully repaired the three dead 150 Ah el-cheapo Chinese batteries with the new BMS (recommended previously in this thread).

(3) Ultimately, I installed only 2 of the repaired 150 Ah batteries because I could not get one of them to even come close to being near-balanced cells. I did not/do not know what effect that would have on the two "good batteries" when connected in parallel. So, to be safe, The un-balanceable battery is just stored. As I think about it while writing this, I might try again to completely discharge and then re-charge that battery to see if I can get the cells closer to being balanced?

(4) The 2 repaired 150 Ah batteries have been working fine since the installation was completed last fall. Thank you again to all here who helped. I cannot say that often enough.

(5) After raising h--- with eBay, PayPal and the original seller through the eBay system, that seller sent me a "replacement" 200 Ah battery. (Obviously trying to appease me and, I imagine, hoping to stop my bad reviews. So, so I got 200 Ah vs. the 450 Ah I originally purchased. Oh, well.)

(6) At first I was reluctant to install that 200 Ah freebie, not knowing what it might do to the other installed batteries that are working fine giving me between 450-470 Ah of total battery capacity. Later, I decided to take the risk and added the freebie 200 Ah battery, and it has been working, too, now giving me 650-670 Ah of capacity. The system is working well. My normal daily boondocking usage seldom takes me below 80% of total capacity, except after a string of 3-4 cloudy, rainy days. I am still uneasy about using the "replacement" 200 Ah battery, but so far so good.

(7) "btrPower" was the company from which I bought the original three (3) 150 Ah batteries via eBay. DO NOT BUY FROM THEM ! ! ! There are far too many other choices for batteries from more reputable companies. Among many other reasons, the batteries I received from btrPower were USED! When I fibnally opened them, I saw previous BMS soldered-on connection wires cut off and on 2 of the 3 batteries a piece of tape saying with handwritten 128Ah and 132Ah, which I can only assume means their tested Ah capacity of the used batteries I was sold as new. Chinese crooks, for sure.

(8) Someday, if I ever have the money (retiree here), I'd like to replace at least the 200 Ah freebie btrPower battery because I don't know what the BMS inside the plastic case might be, or whether it can mess up my system if another of their cheap BMS units fails. I've also considered tearing it apart and adding a good BMS, like the others I purchased. I haven't cut open battery's case to see the cells, but the battery is considerably larger and heavier than my 200 Ah prismatic cells (blue plastic outside), so they must be an older, cheaper cell generation.

But, as is, I do have a decent solar system for a single RVing full-time, mostly-boondocker that serves my purposes well.

That is true ONLY because of the time, brainpower, and graciousness of everyone here who helped me out of a serious dead-batteries jam.

With all my heart, again, thank you, Thank You, T H A N K Y O U ! ! !

jesfl (now a slightly more knowledgeable solar system user)
 
Nice to hear.
I did buy the BTRs.

I’ve never capacity tested any batteries before. Reading this thread and BTRs 3-month return policy and inspired by Will’s videos I may purchase (I might have one already) a 100A shunt and run a 1100W space heater on both individually and see what exactly sugars off!

I’m most likely going to order a couple BMS’ to have on hand anyway. While they will be located inside, the new BMS’s add charging protection with a programmable set-point curve that feels like an insurance policy at about the same cost as amazonian’s 4 year protection plan I wouldn’t buy.

Realistically at $397/each for 140Ah they only have to last four or five years to cost out at what my lead acids did. I expect 8-10 years and at that they’re inexpensive to the extreme.

Again- thanks for the update.
 
(3) Ultimately, I installed only 2 of the repaired 150 Ah batteries because I could not get one of them to even come close to being near-balanced cells. I did not/do not know what effect that would have on the two "good batteries" when connected in parallel. So, to be safe, The un-balanceable battery is just stored. As I think about it while writing this, I might try again to completely discharge and then re-charge that battery to see if I can get the cells closer to being balanced?

Balancing typically involves charging each cell, whether individually or in parallel, using a CV/CC power supply set to 3.65V
When current tapers off to about 1% of initial current, disconnect cells and let voltage settle. See if they are similar (if one is low, typically after charging in parallel, could have been poor contact so charge it again.)
Charging them individually is probably the way to go, if assembled in a pack.
Set power supply voltage to 3.65V before connecting, and do not change while connected (most supplies show present voltage, not setpoint.)
There are top-balancing instructions under Resources of the forum.
 
The above follow-up message just popped up in my email, so it seems appropriate to add an update more than a year later . . . should anyone else read/skim through this long thread?

Yes, amazingly helpful, gracious, giving and patient is all that can be said about all here on the Forum who contributed to helping me solve my failed LiFePO4 battery problem.

(1) I got the system wired and working with the one 200 Ah replacement battery I was forced to purchase. That was only because of the education and assistance I received on this forum.

(2) As scary as it was for this novice, I have now carefully repaired the three dead 150 Ah el-cheapo Chinese batteries with the new BMS (recommended previously in this thread).

(3) Ultimately, I installed only 2 of the repaired 150 Ah batteries because I could not get one of them to even come close to being near-balanced cells. I did not/do not know what effect that would have on the two "good batteries" when connected in parallel. So, to be safe, The un-balanceable battery is just stored. As I think about it while writing this, I might try again to completely discharge and then re-charge that battery to see if I can get the cells closer to being balanced?

(4) The 2 repaired 150 Ah batteries have been working fine since the installation was completed last fall. Thank you again to all here who helped. I cannot say that often enough.

(5) After raising h--- with eBay, PayPal and the original seller through the eBay system, that seller sent me a "replacement" 200 Ah battery. (Obviously trying to appease me and, I imagine, hoping to stop my bad reviews. So, so I got 200 Ah vs. the 450 Ah I originally purchased. Oh, well.)

(6) At first I was reluctant to install that 200 Ah freebie, not knowing what it might do to the other installed batteries that are working fine giving me between 450-470 Ah of total battery capacity. Later, I decided to take the risk and added the freebie 200 Ah battery, and it has been working, too, now giving me 650-670 Ah of capacity. The system is working well. My normal daily boondocking usage seldom takes me below 80% of total capacity, except after a string of 3-4 cloudy, rainy days. I am still uneasy about using the "replacement" 200 Ah battery, but so far so good.

(7) "btrPower" was the company from which I bought the original three (3) 150 Ah batteries via eBay. DO NOT BUY FROM THEM ! ! ! There are far too many other choices for batteries from more reputable companies. Among many other reasons, the batteries I received from btrPower were USED! When I fibnally opened them, I saw previous BMS soldered-on connection wires cut off and on 2 of the 3 batteries a piece of tape saying with handwritten 128Ah and 132Ah, which I can only assume means their tested Ah capacity of the used batteries I was sold as new. Chinese crooks, for sure.

(8) Someday, if I ever have the money (retiree here), I'd like to replace at least the 200 Ah freebie btrPower battery because I don't know what the BMS inside the plastic case might be, or whether it can mess up my system if another of their cheap BMS units fails. I've also considered tearing it apart and adding a good BMS, like the others I purchased. I haven't cut open battery's case to see the cells, but the battery is considerably larger and heavier than my 200 Ah prismatic cells (blue plastic outside), so they must be an older, cheaper cell generation.

But, as is, I do have a decent solar system for a single RVing full-time, mostly-boondocker that serves my purposes well.

That is true ONLY because of the time, brainpower, and graciousness of everyone here who helped me out of a serious dead-batteries jam.

With all my heart, again, thank you, Thank You, T H A N K Y O U ! ! !

jesfl (now a slightly more knowledgeable solar system user)
Thank you for the follow up.
The good news is you now have the understanding and ability to guide future decisions, that's what this forum is all about. Congratulations!
 
This is as good a place as any to leave this and ask the question:

I contacted BTR power asking them to provide their recommended charging parameters. I mentioned I just received my class T fuses finally and wanted to get them configured with my Inverter. They responded, “you can just connect the cables directly to the battery”

So did OP or anyone above ever get definitive answers that 14.6 bulk and 13.2V(????) float/absorb are good to use with these batteries?
( Or should I just run with a default LiFePo setting in the 1012LV-MK or Epever Trirons?)
 
Back
Top