Update. Replacement BMS? What's next?

jesfl

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Thanks again to all. Had to take some time away from my electrical mess.

Yes, the 2 gauge wire is directly from the genset to the batteries. I never thought about it much (because it was the least of my worries), but, yes, the only purpose of that wire should be to start the generator. The other cable that I cannot see in the flooring seems smaller than the 2 AWG. It is, I have assumed the (1) connection to the power panel for the 12-volt system, and (2) the converter connection for charging the batteries when either connected to shore power or running the generator through the transfer switch. That converter charging of the batteries also has worked quite well in the past. I have not tried it with the new battery.

I've decided this. Tomorrow morning after the batteries are fully PV charged -- and my solar charging also is working quite well -- I am going to start the "process of elimination" by disconnecting everything and reconnecting ONLY the inverter to the battery. No SCC, No power panel connection, no genset connection, nothing else.

Either the inverter will run my coffee pot and microwave without problems, OR the problem is the inverter!!! I am taking that approach because I tried the microwave again this afternoon after checking EVERY wire in the system, and it crashed the system and blew another 175 amp AMG fuse. If it does that when the only thing connected to the battery is the inverter, bingo (I think), it must be a problem with the inverter?

The reason this test will work, I think, is because the entire system/the inverter is not wired directly into the power panel . . . yet. As I was building the system, I took an easy-way-out suggestion and bought two 10/3 gauge extra heavy-duty industrial extension cords and ran those from the 120V AC outlets in the back of the inverter to the RV. The microwave runs off one of those cords, so it is not running through the entire wiring system, at all. It is directly connected to the back of the inverter via an AC outlet there.

If the inverter works perfectly isolated and connected only to the battery, then I have eliminated the inverter and the (very short) 4/0 gauge wiring as the problem. After that I can rewire one element at a time (i.e., solar charge controller with the PV panels) and test each "segment" of the system that way.

The more I've thought about it as I double- and triple-checked all of the wiring and found absolutely nothing wrong. There simply is no wear/tear, loose connections, or discolored (overheated) wiring! Except for the long-installed wiring in the floor from batteries to the power panel, it is all new wiring (6 months or less).

Unless I am all wet with this approach and someone thinks it is futile or otherwise cannot work, there's no need to respond. I'll send the results tomorrow. It's a new starting point, I hope.

Thanks for all the support.

Jim
jesfl
 

GXMnow

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What is the input power rating on the microwave? My newer Samsung microwave can draw up to 1,600 watts. Figure an excellent 95% efficient inverter, that is 1,700 watts from the 12 volt battery. 1,700 / 12 = 142 amps in run mode. That would be pretty close on a 175 amps fuse. It should hold, but if it has much of a start surge, that could do it. If it is a less efficient 80% inverter, now we are up to 2,000 watts in from the battery, and if the voltage is dropping to 11 volts at the inverter, then it could be drawing up to 182 amps. It does not take much voltage drop in a 12 volt system to kick the current up even higher. Double check all of your connections, and measure the voltage at the inverter input while under load and see how much lower it is than the voltage at the battery bank. Do you have a load of about 400-500 watts you could plug in and run it? Big enough to cause voltage drop, but not enough to blow another fuse. Then measure across each connection with a meter. Each wire to lug, lug to bolt, lug to buss bar. All metal to metal connections should be just a few millivolts. If you find one a bit higher and one maybe getting warm, that could be your culprit. Modern sine wave inverters do regulate their output voltage. As the input voltage drops, they have to pull more current to still get the desired output voltage and power demanded by the load.
 

Just John

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I suspect that @GXMnow might be on the right track. The fuse and breaker might very well be undersized for the surge of starting the microwave. With inverter efficiency of 80%, you are looking at a surge capacity of 1600 to 1700 watts. The 4/0 gauge wire should have no problem handling that, but the fuse and breaker might need to be upsized. That is a drawback of having a 12v system.

Edit to add that other than esthetics, I don't think using good extension cords is a problem.
 

Hedges

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A graph shown here (expand the "More" section) indicates a Mega/AMG fuse should carry 250% of rating for 1 second, 150% for one to 10 minutes. That's assuming standard temperature environment, so no poor connections contributing to heating.


If battery voltage holds up, a marginal wattage overload shouldn't blow it (but continuous operation should be limited to 80% of rating)

As GXMnow said, if voltage drops then current draw by inverter will go up. Can you measure voltage at inverter during your test?

I would rather have a larger, possibly oversize fuse that will blow only for a short circuit, and a breaker that protects against overloads.
Still thinking there is an intermittent short somewhere. But it only appears under load??

It takes a period of time for a moderate overload to overheat a wire. Somewhat larger fuse could be used for a limited time to test. If the entire battery to inverter circuit is 4/0 awg, then considerably higher than 175A use can be used to protect that wire as a permanent solution.
 

jesfl

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OK, folks, I sincerely appreciate the education and information. I've conceded a kindergarten-level beginner hasn't got a snowball's chance in h--- of getting everything correct when setting up, and especially finding problems!!!

Questions answered:
-- microwave power input rating is 1550 watts = about 130 amps in run mode; but, I see 90 amps on the inside voltage meter near the microwave when it is running, before it alarms and shuts down
-- the 3000-watt inverter claims 85% to 90% efficiency in specs, which I suspect, as you suggest, might be closer to 80% efficiency in reality

Other questions:

-- "Do you have a load of about 400-500 watts you could plugin and run it?"

Yes, probably, but can you give me a clue what typically might use 400-500 watts so I don't have to start plugging in everything I have to find that level of voltage. I don't look at electrical appliances and see volts, like some of you pros might. It's harder for me.

-- "Can you measure voltage at inverter during your test?"

Not really. At least I don't know how? The inverter is in the RV "basement forward locker" about 22 feet from the microwave. The microwave only runs 30 seconds before the inverter alarms and powers off. I don't have a remote multimeter or one that connects to a phone by Bluetooth or anything like that. My inside voltmeter which I can see from the microwave shows a startup surge of about 120 amps and then settles to 90 amps for 20-40 seconds before the inverter alarms and shuts down. That's as close as I can get to measuring voltage.

Having said all that . . . I ran my test today before I read all of your thoughtful and helpful comments.

But, I think I was on track with the test, unknowingly. Sometimes I do blunder into things like the larger-sized breaker and fuses.

My new, high-quality "Blue Sea/Bussman" 200 amp breaker ($80, ouch) and my 200 amp Littelfuse AMG fuses arrived late morning.

I installed those and simultaneously disconnected EVERYTHING in the system except the 100% fully charged battery @ 200 Ah with battery voltage showing 14.4V on my inside voltmeter (before disconnecting solar) AND the connected inverter.

I have attached a hand-scribbled drawing of what I left connected. Very simple.

I went inside and turned on the microwave. The inverter again ran about 30 seconds before alarming. I quickly shut it down to save another fuse. Keep in mind the voltmeter showed about 120 amps when the microwave/inverter started up, and then settled to bout 90 amps when running . . . before alarming. So, 90 amps is making the inverter convulse? What is going on?

Then I disconnected the one thing remaining on the negative side -- the shunt for the inside voltmeter. I tested again. Same result. Alarm and shutdown.

Now I will check each small segment of the 4/0 wire and the connections. (I didn't see the above comments until after my little test.) But, remember, we are talking a total of 20 inches of 4/0 wire on the positive side and about 28 inches on the negative side (to allow for the shunt connection). Not much room for shorts or other problems in that 4/0 wire at those very short lengths.

NOW, I must ask, IS IT POSSIBLE ALL THIS IS A PROBLEM WITH THE INVERTER?

Here's why I ask. I bought the inverter in August of 2020 and installed it in September 2020 (still under warranty, thankfully). The inverter, like everything else in my system worked perfectly until about February 2021. Then crap started happening.

I now see a chicken-or-egg conundrum here:
(a) did some short or other freak event cause a system-wide surge of some sort that fried all three BMS units in all three of my batteries simultaneously (and maybe damaged the inverter at the same time)?
OR,
(b) did the inverter somehow fail and cause a system surge of some sort that fried the BMS?

I am sending the facts about my test today along with my drawing to the distributor from whom I purchased the inverter. I am asking for a simple solution. I've also asked the distributor how to test the inverter to find what is causing this alarm and shutdown. I'm not yet 100% blaming the inverter, but after my inverter-only test today (no breaker flipped, no fuse blown) it seems an increasingly likely problem-causing candidate. There just ain't nothin' else to blame other than the inverter, through my eyes? Process of elimination leads to it.

I've spent far too much time on all of this. I'm frustrated, exhausted and, frankly, gettin' plain old-fashioned irritated about it all.

I will let you know what the distributor says, if I get a response.

Thanks again for your patience, incredible assistance, and amazing knowledge!

Jim
jesfl
 

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Bob B

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You really need to know what the voltage into the inverter is when things fail ..... is the inverter shutting down because of excess current .... or low voltage?

The good new is you will know a lot about your system by the time you resolve this.
 

Hedges

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Inverter alarming - that is a key. I would expect to alarm for low battery voltage. Got extension cords? Bring the microwave with you to the inverter (oh, it's probably built in?) OK, two extension cords, one from the outlet and one back to the microwave? Probably an electronic model. You could start the microwave, run outside to read voltmeter at DC connection of inerter, unplug.

Easier to extend wires from the battery. You could even use an extension cord, if careful not to short. Then use meter to read voltage of battery from far end of extension cord while running microwave.

Hopefully something like a bad connection, dropping voltage. If so, it will also start to get hot, so you might find it by touching things.

LiFePO4 battery - it is possible for busbars to have bad connections. But I would expect BMS to detect voltage drop and disconnect.
Assuming you built the battery, have access to it, check all busbars and cable connections for heat.

With a lower load that doesn't trip it (e.g. radiator heater, 600/900/1500W) drawing a moderate current, you can use a meter to check voltage drop across each length of cable, each connection between cell terminal & busbar, each switch or breaker.
 

GXMnow

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The 90 amps you are seeing should not be a problem by itself. 90 amps x 12 volts = 1,080 watts. Maybe a bit less true watts, but I won't bother complicating this more with power factor. This is enough info to realize something else is going on.

As Hedges said, w do need to get the voltage reading at the inverter input. What other AC powered devices do you have to try putting a load on the inverter? Each device should have a power consumption label. We don't need a specific amount of power, we just need enough load to put some stress on the system, but not so much that it shuts down. The idea is to allow it to run long enough for you to be able to measure a few things.

Here is my hypothesis.
The inverter is probably okay, but there is a poor connection somewhere between the battery and the inverter. When the inverter is heavily loaded, the resistance from either a bad connection, or maybe just too long of wire is allowing the voltage to drop down to where the inverter is going into a low voltage shut down. When you find a device or two, maybe 3, to get a load in the 400 watt range, then you can use your meter to measure the voltage at the battery terminals and again at the inverter input under this load. Also note the battery current from your shunt monitor. 400 watts should pull about 40 amps. If the battery is still at 13 volts, then the battery is doing fine. But if it is down to 11, the battery is not holding up to the current. But let's assume the battery is still good at 13+ volts, but the input of the inverter is showing just 11, then we found our smoking gun. Losing 2 volts at 40 amps would be a total resistance of 0.050 ohms, or 50 milliohms. That is not a lot, but it is enough to cause what you are describing. A 4/0 cable would need to be 1,000 feet long to have 0.050 ohms. So the wire should be fine. Even 100 feet, 50 on the negative and 50 on the positive, would only be 0.005 ohms, and should only drop 0.2 volts at 40 amps. This is why the loaded voltage measurement is important. We need to see what is going on and where. If the inverter input is within 0.5 volts of the battery voltage, then the wiring is all fine. At that point, the focus would move to a problem with the inverter.

A friend of mine relocated his battery in his car to the trunk. He ran two 8 foot long 2/0 cables from the front where the battery was to the new battery box. The car would crank a bit slow and was very hard to start. He tried grounding the battery at the back, but it didn't seem to help. When we did a load test we found the voltage at the front of the car was dropping 2 volts at 50 amps. Obviously we had a problem somewhere. All of the connections checked fine. He had bought new cable from a local welding supply company, so we never suspected bad wire, but the positive cable was dropping all the voltage loss. We didn't see any problem at first, but after having a 50 amp load on it for 10 minutes, the wire was very warm in a 1 foot length. As we inspected the cable closely in that area, we finally found it. There was a slice into the wire. Probably from a razor knife opening the box of cable. The wire had a slice nearly 2/3 of the way through the cable. Of course when he brought it up with the cable supplier, it could not be their fault, we must have cut it during the install.

When you are dealing with 90 amps, it does not take much to cause a voltage drop. At just 12 volts, voltage drop becomes critical. A 5% drop is just 0.6 volts. The 30 seconds from the microwave is probably not long enough to get anything hot. So check what you have for a smaller load.
 

jesfl

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Good morning,

To the best of my ability, I've completed all the tests I'm capable of. The results are below.

Is it possible I am learning that a single 12-volt 200 Ah LiFePO4 battery does not have enough start-up oomph to run a 3000-watt inverter with an 1100 watt microwave (rated 1550 watts)?

If I understand the calculations correctly, that means at 80% efficiency, the inverter needs to provide 1860 watts of power for the microwave to run? It should be able to do that without alarming and shutting down, shouldn't it? But, can the battery provide that?

I am curious about one thing. Does the (small) 6 AWG wire to/from the Daly BMS play into this "voltage drop" equation? The customer support engineer from the company that sold me the 3000W inverter once told me "you may have a problem with that" when I told him of those 6 AWG connections to my (previous, now dead) batteries. Is that 6 gauge wire strangling the power outflow from the battery for higher draw use like the microwave?

So do I start shopping for a smaller inverter, or a lower-powered microwave, or both?

The battery/inverter handled the 860-watt test load with no problems and the voltage only dropped to 11.8 volts from 12.2 at the battery when running with the load.

Along this often futile road I am wandering, this morning I recalled two comments different helpful folks posted:

-- lithium batteries have steady power capability with long duration, but not instant high voltage power like vehicle "cranking power" in lead-acid batteries, and

-- it may be possible that attempting to start the 3600 kw generator using lithium battery power is what killed the BMS in the batteries?

My test results from this morning are below.

I'll be out of play for a few days because I will be on the road beginning tomorrow. Since everything else seems to be working well, I can do without the microwave for a few days, But, I still hope to get one working somehow.

Thank you again for any/all comments and/or ideas.

Your help continues to be incredible;e ! ! ! I am awed by your graciousness.

Jim
jesfl


Wire/Connections Testing Battery To Inverter* (Battery & inverter ONLY connected, per the previous drawing)
*Using a heat gun (low setting) + ice maker for “load” = 860 watts with 65 amps draw on voltmeter

Wire/Connections Check** (Positive wire 18” 4/0 with 3 sections, negative wire 4/0 26” with 2 sections)
+ @ battery out = 12.17V
+ battery to on/off switch = 12.16V
+ battery switch to 200 amp breaker = 12.09V
+ breaker to inverter = 12.04V
+ @ inverter input terminals = 12.01V

- @ battery out connection after BMS = 12.08V
- battery to inverter connection = 11.98V

(Note: I did not test two wire segments through the voltmeter shunt because it is so difficult to reach)

With 860 Watt Load**
@ battery terminals = 12.24 volts
@ battery after BMS = 12.13 volts
@ inverter +/- connections = 11.78 volts

With Microwave Running** (Inside shunt-connection voltmeter reading of microwave volts @ startup = 138V)
Battery/microwave running = 11.54V
Inverter input/microwave running = 10.87 volts

(Note: I had to reconnect and turn on solar charging (PV panels & charge controller) to get the microwave to stay on long enough to rush outside and get the readings. The SCC meter showed a charge of 20+ amps when the microwave test was conducted. Without the solar charging assist, the microwave would run only 10 seconds.)

** Battery was not 100% charged during these tests. It was approximately 90% charged. The readings were voltage = 13.7V; Amp hours remaining = 179.6; Percent of charge = 89.9%


Other Relevant Facts
-- 12-volt 200Ah battery is brand new, put in service about 10 days ago
-- as stated, wire lengths are very short and the tests indicate no huge current loss battery to inverter
-- for the tests, everything in the system was disconnected except battery and inverter; UNTIL I had to reconnect the PV panels/charge controller to get the microwave to run long enough before shutdown to get readings
 

GXMnow

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Going down all of your tests, it looks like your voltage drop issue is between the BMS and the inverter. The BMS is dropping 0.11 volts with the 860 watt load, but then you are losing another 0.35 volts by the time it gets to the inverter input. That is a bad drop. And the microwave load pulled the inverter input all the way to 10.87 volts, that explains the shut down. Just under 11 volts is a common lower limit on inverters. The battery dropping to 11.54 volts with the microwave on is not good. You are certainly at or near the load limit for the battery. Having another in parallel might fix that part. Getting your old batteries back up with new BMS units will probably do the trick there. But the question here is still where are we losing the other 0.35 volts before the inverter at 860 watts? And with the microwave on, you have a total drop of 0.67 volts between the battery and the inverter. That is way too much. Something is making a bad connection. At nearly 90 amps, 0.67 volts is still 60 watts of power being turned into heat wherever that loss is happening. How long are your cables? I see the 18 inches with 3 sections, and 26 inches with 2 sections. Is that spliced in a row making an 18 x 3 = 54 inch run and a 26 x 2 = 52 inch run? Is that the total between the battery and inverter or is there more? 106 inches of 4/0 cable should be no problem at all, but that does imply at least 7 connections. I am reading that correct? Any connection point is a possible failure point. Run the 860 watt load for a bit and carefully feel all of the cables. Check near the connectors as well. If you feel something getting hot, you may have your culprit. How difficult would it be to move the inverter and/or battery to have them right next to each other and just use the best looking short cables to connect them together. See if that will then run the oven without shutting down. If you know the batteries are well charged, you could also try bypassing the BMS for a couple minutes to see if it's drop is adding to the issue. But don't run it that way long because it would have any protection if a single cell is dropping.
 

Just John

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I am curious about one thing. Does the (small) 6 AWG wire to/from the Daly BMS play into this "voltage drop" equation? The customer support engineer from the company that sold me the 3000W inverter once told me "you may have a problem with that" when I told him of those 6 AWG connections to my (previous, now dead) batteries. Is that 6 gauge wire strangling the power outflow from the battery for higher draw use like the

I'm curious about what the rating is for the Daly BMS? Mine is rated at 250 amps and has 2 gauge wiring.

Your measurements certainly indicate that between the battery and the inverter you have a very significant voltage drop that is causing your problem. Oddly enough, your BMS is the likely culprit without further measurements.

I only have a Victron 1200va inverter in 12v, but at 100A I am not having this problem. Are you still in AZ?
 

jesfl

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Good morning,

Thanks to both of you for the responses. Have to hit the road this morning (6:30 am here) so this info quickly . . .

Yes, you are misreading my wiring. Total "runs" in test configuration with everything else disconnected are 18" (w/ 6 lug connections + bolt-on 200 amp fuse at battery) and 26" (w/ 4 lug connections and 200 amp bolt-on fuse at battery). Distance from center between battery posts to center between connections on inverter is 13.5" In my limited space, I can't get the battery any closer than that to the inverter. The drawing is accurate.

Re: the BMS. I don't know what the Daly BMS rating is because it came "bundled" with the 4 LiFePO4 cells I purchased. I will look that up in a couple of days when I am stationary again. Not surprised that might be the problem or at least part of it. If that IS the problem, I assume there is no solution other than a new BMS? Will you please tell me the model of yours with the 2 AWG wire so I can look and learn? No, not in AZ, in NM near Albuquerque headed north.

Again and again, your comments and direction are incredibly valuable and helpful.

Thank you.

Jim
jesfl45
 

Hedges

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Re: the BMS. I don't know what the Daly BMS rating is because it came "bundled" with the 4 LiFePO4 cells I purchased. I will look that up in a couple of days when I am stationary again. Not surprised that might be the problem or at least part of it. If that IS the problem, I assume there is no solution other than a new BMS?

One possibility would be to bypass BMS with a relay to feed inverter directly from cells, and have BMS power coil of the relay.

This likely means BMS doesn't get to measure current. Some BMS prevent charging below freezing by disconnecting only when they detect charge current, so you would want charge controller connected to BMS and only inverter to relay.

This might be an SSR of higher current that the FETs in the BMS, or mechanical. Some people have had problems with mechanical relays getting welded.
 

GXMnow

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My 200 amp rated JK BMS only has a pair of #7 awg wires in parallel for the high current DC path. I was a bit worried they would be too thin. The used very high temp silicone insulated wire and claim it is good for the current, but I still shortened them as much as practical to reduce the resistance. The B- side goes to a buss bar where I attach the cables from the battery bank. The P- is crimp spliced to a 2/0 cable to my output side buss bar. Measuring across the between the 2 buss bars, I calculate just about 0.001 ohms (1 milliohm) of resistance, dropping 0.080 volts at 80 amps. The drop seems very linear, with 1 mv per amp, so even at 150 amps, it should still only be dropping 0.150 volts. That is more than I would like, but not enough to cause the issue you are having.

Hope the next leg of your trip goes well. Let us know when you are docked again and want to look into this further.
 

Hedges

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One possibility would be to bypass BMS with a relay to feed inverter directly from cells, and have BMS power coil of the relay.

This likely means BMS doesn't get to measure current. Some BMS prevent charging below freezing by disconnecting only when they detect charge current, so you would want charge controller connected to BMS and only inverter to relay.

This might be an SSR of higher current that the FETs in the BMS, or mechanical. Some people have had problems with mechanical relays getting welded.

If your inverter has a remote on/off switch (or if you can open it and add one), skip the power relay and let BMS enable the inverter.
As a test, you can bypass BMS and wire inverter directly to cells, see if it can carry the load then.
 

jesfl

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Good evening, folks,

The break I took was good for my mental attitude, but I need to get my system running correctly so I am starting up again. Everything is working well except the microwave which will not run, as before.

Please note it is not the "start-up" of the microwave that causes the inverter to fault and shut down. The error typically occurs after 30-seconds to one minute of microwave runtime. (Maybe that is still considered "start-up?)

My motivation to start working toward a permanent fix is that I got notice one replacement BMS (for the previous 150 Ah lithium batteries) I ordered is in the U.S. and on the way to my mail forwarding service. I should be able to pick it up along my route in about two weeks. IF I can get one of the previous batteries working again, I am (slightly) hopeful that extra battery capacity might eliminate the one problem with the microwave? Perhaps wishful thinking, but I need to grasp for something positive . . .

Three things are on my mind tonioght:

(1) I shortened the 4/0 negative wires by a few inches by moving my shunt for the interior voltmeter closer to the battery. In the next few days, I will take new readings of the wire loss from the battery to the inverter. Hopefully, there is some marginal improvement. I am not expecting miracles.

(2) Since the BMS is suspect as the limiting factor for running the inverter/microwave, I would like to try to bypass the BMS and connect the battery directly to the inverter as a test, as was suggested. Is there any risk in me doing so? I don't want to damage the new battery.

(3) The Daly BMS came as part of the battery package. I don't know what to look for re: "rating?" (I got no details about the BMS with the battery.) The label says it is Model R05A-GC12. I looked for this model on the Daly AliExpress website; but I could not find it among the hundreds (?) of choices.

The seller's listing said this:

"The 4S 200Ah Daly BMS with Bluetooth / Low-Temperature Cut Off allows batteries to be wired in Parallel or Series. System Specifications: Power balancing 2.65V, Balance Release Volt 2.65V, Balance Current 40+/-5mA, Over-Discharge Detect Volt 2.8+/-0.05V, Over-Discharge Detect Delay 0.5V, Over-Discharge Volt Release 3.0+/-0.05V, Over Current Detect Volt 150mV, Over Current Detect Delay 9MS, Short Circuit Detect Delay 250uS, Main Circuit Resistor ≤10mΩ, Working current ≤100uA, Working Temp Range -20/+80ºC."

That's all I could find.

What is the model # for the Daly BMS with the 2 gauge wiring (vs. the 6 gauge on my Daly BMS)?

Thanks again for everything everyone has contributed to help me out.

Jim
jesfl
 

Just John

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I am actually pretty confident that you can get the old battery pack working with a new BMS. Then order two more!

I know the Daly BMS rated for 250A have 2 gauge wire, but I don't have a clue how their numbering scheme works.

I did figure out why mine doesn't count cycles, they sent me a lithium ion BMS, so it won't count a cycle unless you charge to over 3.7v per cell. Other than that, it works fine. So you don't want the part number from mine.

Especially with the 6 gauge wires, I think the BMS just can't sustain the current, so another battery pack will probably do the trick.
 

jesfl

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Good afternoon,

Thanks, again, especially for the encouragement.

I ran the inverter/microwave test this afternoon wiring the battery directly to the inverter.

The microwave ran for 1 min 10 sec and then the system shut down. It turns out my brand new ($80) 200 amp breaker (Blue Sea/Buss brand) had toggled off. I was watching my internal meter and it showed 122-123 amps being drawn from the battery when the microwave was running via the inverter.

Someone previously suggested 225 amp bolt-on fuses. I am using 200 amp MEGA/AMG fuses at the battery, but the breaker flipped before a fuse blew? I'm wondering if the next step is another breaker of 225 amps, if there is such a thing? Then higher amperage AMG fuses, too?

However, I can't comprehend how only 122-123 amps from the battery caused the 200 amp breaker to flip?

Any thoughts will be appreciated.

I surely am eager for the new BMS to, hopefully, fix the first of the old batteries so I can see the result of that addition to my system.

Jim
jesfl
 

Hedges

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The microwave ran for 1 min 10 sec and then the system shut down. It turns out my brand new ($80) 200 amp breaker (Blue Sea/Buss brand) had toggled off. I was watching my internal meter and it showed 122-123 amps being drawn from the battery when the microwave was running via the inverter.

Someone previously suggested 225 amp bolt-on fuses. I am using 200 amp MEGA/AMG fuses at the battery, but the breaker flipped before a fuse blew? I'm wondering if the next step is another breaker of 225 amps, if there is such a thing? Then higher amperage AMG fuses, too?

However, I can't comprehend how only 122-123 amps from the battery caused the 200 amp breaker to flip?

Couple thoughts cross my mind:

1) High resistance connection between cable and breaker. If that is the case, should be hot enough to burn your finger.

2) Current draw comes in pulses, due to insufficient filtering in inverter. Meter may or may not read that accurately.
If 100A average is drawn as 200A pulses half the time, I^2 is 4x as much half the time, twice the heating.
Not that current draw should be that jerky but maybe it is.
Because I have a scope, I would look at it.

If this is the case, BMS will suffer same heating.
 

jesfl

Solar Enthusiast
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Couple thoughts cross my mind:

1) High resistance connection between cable and breaker. If that is the case, should be hot enough to burn your finger.

2) Current draw comes in pulses, due to insufficient filtering in inverter. Meter may or may not read that accurately.
If 100A average is drawn as 200A pulses half the time, I^2 is 4x as much half the time, twice the heating.
Not that current draw should be that jerky but maybe it is.
Because I have a scope, I would look at it.

If this is the case, BMS will suffer same heating.


Thank you, once again.

1) High resistance connection between cable and breaker. If that is the case, should be hot enough to burn your finger.


I'm not sure I truly understand "high resistance connection?" (Beginner here.)

I have 4/0 AWG with heavy copper lugs. There is a total of 18" length for positive cable to inverter via this route: battery to master on-off switch/ to 200 amp breaker/to inverter. What in the world might cause a high resistance connection in that short, heavy-gauge wire run?

The negative 4/0 AWG connection is from the B- wire on the Daly BMS/to shunt (inside voltmeter)/to the inverter. Of necessity, this wire run total is recently reduced to 25 inches.

In the case of yesterday's test, I bypassed the Daly BMS and wired the negative wire directly to the negative battery post.

I will try the test again today and try to dash outside to check the heat of the connection before/as the breaker flips or the inverter shuts down.

2) Current draw comes in pulses, due to insufficient filtering in inverter. Meter may or may not read that accurately. If 100A average is drawn as 200A pulses half the time, I^2 is 4x as much half the time, twice the heating. Not that current draw should be that jerky but maybe it is. Because I have a scope, I would look at it.

No scope here obviously. I do kinda' understand the pulses of Alternating Current. The inverter is Pure Sine Wave (supposedly) 3000W.

So, are you saying the pulses -- with 123 amps draw showing on my inside meter -- could be 246 amps half the time? (I^2 is 4x . . . ?)

In my plebeian thinking, does that mean a 250 amp breaker and 250 amp AWG fuses at the battery might solve the problem? If yes, is there any risk of damage elsewhere in the system (battery, inverter) if I changed to a larger breaker and fuses?

3) If this is the case, BMS will suffer same heating.

BMS was bypassed for the test yesterday. But, are you saying if I tested the microwave with the BMS connected, it would get hot, too? Any risk of damaging the BMS?

I'll disconnect the BMS and test gain later today to try to feel for heat (if I am fast enough to the battery/inverter).

Thanks for your continuing assistance. It is sincerely appreciated.

Jim
jesfl
 
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