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Old 12-06-2020, 05:44   #1
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123 Sm art BMS gen3 - voltage accuracy - opinions

This BMS has 4 boards, one attached to each cell in a 4s config.

Voltage measurements are made by each individual board and are used for HVD, LVD and balancing.

The spec states +/- 20mv measurement accuracy.

In my case the between boards are measuring -30mv from actual. I've confirmed this and swapped cells around and the between board readings remain the same regardless of cell placement.

I would expect the tolerances to be better.

I can adjust the HVD and LVD to compensate for this, but balancing will consistently push the middle cells higher by 30mv.

Is this a problem?
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Old 12-06-2020, 10:36   #2
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Re: 123 Sm art BMS gen3 - voltage accuracy - opinions

I suspect I have the same problem. One of my cells is always 0,02 to 0,04ish below the others when looking at the bms app. But when measuring with my normally very accurate voltmeter I canít see any differences at all between the cells. I donít know if it is possible to calibrate the boards regarding voltage in any way.
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Old 12-06-2020, 11:59   #3
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Re: 123 Sm art BMS gen3 - voltage accuracy - opinions

I double checked what my 2 matching mutilmeters were telling me by swapping the cells around. All cells measured 3.27v with the multimeters, The BMS reported 3.27v for the first and last cell and 3.24v for the two middle cells.


When I swapped them the BMS readings stayed the same. The specs say accuracy should be +/- 20mv. They way I interpret this is both between boards are -30mv out of whack and not in specification.


What I don't know is if this a significant problem and if so I don't want this equipment.


I hope some of our real techie members will weigh in.
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Old 16-06-2020, 10:57   #4
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Re: 123 Sm art BMS gen3 - voltage accuracy - opinions

Well,

After sitting connected over the weekend with no load or charge the BMS and multimeters are reading 3.27v on each cell.

I just don't trust this hardware. And the more I look at it the more I dislike the exposed circuitry and inter-cell wiring. I'm going to toss it and get something else.

YMMV
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Old 26-06-2020, 13:31   #5
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Re: 123 Sm art BMS gen3 - voltage accuracy - opinions

I'm still looking at BMS options. I'm considering Rec ABMS, but want to see what else is out there.

Any suggestions?

I installed the 123Smart BMS after is apparently corrected itself and cycled the batteries. When I left the boat last week all cells were sitting at 3.3V. I shut the main switches so only the BMS and SG200 were on the battery.

Got to the boat today and saw this. SG200 and my multimeter report this is wrong. Cell 3 is really 3.3v. I checked and cleaned all connections. No change.
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Old 28-06-2020, 06:23   #6
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Re: 123 Sm art BMS gen3 - voltage accuracy - opinions

The 123 Smart BMS continues to exhibit bizarre behavior. The SOC history shows when the Between Board for cell #3 started to die late last Tuesday. It spiked a couple of times then died for good on Wednesday.
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I need to disable cell balancing before I can charge the batteries. To do this I need to remove the Begin Board to access the micro switches and change that setting..... Effectively disassemble the whole system as loose wires will short things out. So, I might as well just remove it to the wheely bin.

I checked the error log before doing this and see that Between Board for cell #2 reported high voltage of 4.03v. That would have been when I turned the inverter on to make coffee.
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So, it looks like that board is borked too.
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Old 28-06-2020, 07:21   #7
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Re: 123 Sm art BMS gen3 - voltage accuracy - opinions

It certainly looks like one or more of your boards are faulty. I have used mine for almost 2 seasons now and have to say that I am overall very satisfied with the product. Especially the app is a nice feature and it is very addictive. You can buy a single board and replace the faulty one if you like. But maybe you donít want to go down that road.
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Old 28-06-2020, 11:37   #8
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Re: 123 Sm art BMS gen3 - voltage accuracy - opinions

I'm not going throw parts at it. When I reported the voltage issue that started this thread tech support told me the boards were within tolerance. Then they wanted to see the installation, all cell voltages, etc. etc. I didn't do anything because it looked like the problem resolved itself. Now, it's one thing after another. Bottom line - I don't trust the equipment.

I like the App also and the current sensors. But there are too many board connections, too tiny & too close to other board components. Fact is it is poorly designed from a mechanical standpoint.

I don't want to cut another shunt into the negative cable. I already have the SG200. But it seems like the only other option is the Rec ABMS.

I don't have the background to interpret what all it can / should do. I've read everything I can find on them.

I don't understand the relays. Seems they will not work with bistable relays like the Bluesea 7700 without messing around with programming and/or more equipment. I have no idea what the optocouplers do or how they can be integrated into what I have other than, maybe alerts.

Oh well. Vent over. I'll find something to KISS.
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Old 28-06-2020, 12:55   #9
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Re: 123 Sm art BMS gen3 - voltage accuracy - opinions

Quote:
Originally Posted by Wood View Post
I'm not going throw parts at it. When I reported the voltage issue that started this thread tech support told me the boards were within tolerance. Then they wanted to see the installation, all cell voltages, etc. etc. I didn't do anything because it looked like the problem resolved itself. Now, it's one thing after another. Bottom line - I don't trust the equipment.

I like the App also and the current sensors. But there are too many board connections, too tiny & too close to other board components. Fact is it is poorly designed from a mechanical standpoint.

I don't want to cut another shunt into the negative cable. I already have the SG200. But it seems like the only other option is the Rec ABMS.

I don't have the background to interpret what all it can / should do. I've read everything I can find on them.

I don't understand the relays. Seems they will not work with bistable relays like the Bluesea 7700 without messing around with programming and/or more equipment. I have no idea what the optocouplers do or how they can be integrated into what I have other than, maybe alerts.

Oh well. Vent over. I'll find something to KISS.
Not intending to pick on you Mr Wood, but your experience is one more data point indicating what more boaters will have to deal with as they move to new technology batteries and charging systems. There is another thread I was reading today about a mysterious problem with an Balmar regulator trying to charge Lithium batteries.

With Lithium batteries which come in small, rather delicate and dangerous if not properly handled, low voltage cells, each of which must be monitored with a BMS and balanced, as well as requiring specific charging profiles, etc, owners must have very complex systems of multiple monitoring charging and balancing devices.

All of the components of these systems are electronic and therefore subject to failure. And on typical Li installs, there are many components. Everything is well and good when they are new and all working, but when one or more go pear shaped it becomes difficult to diagnose or remedy.

Even with all of the advantages of Li, the complexity and difficulty of diagnosing problems (in addition to the consequence of certain failures) puts these installations in the "not recommended" category for me.

Myself and all of my friends and neighbors (all cruisers) spend ungodly numbers of hours keeping our simple systems running. I can't imagine one of these complex systems after about 5 years of ocean cruising.

Those of you who charge gung ho into giant Li battery banks and giant solar systems, and even worse, electric main engine installations...well I wish you luck when it breaks down in Papua New Guinea.

Me, I don't mind if my toys are complicated and complex, but I want my important systems to be dead simple.
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