JBD-SP04S020 120A BMS Charge and Discharge Currents Inaccurate

ptmac

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I have just finished putting together two 12V x 280AH LifeP04 battery packs using JBD-SP04S020 BMS's and the charge and discharge currents are way off. Paid the $10 for the Xiaxiang BMS app and run the idle, charge and discharge calibrations. Measurements changed but are way off. They are in parallel and at the moment my Victron shunt shows 48a going in but the BMS app is showing 5.8a on each battery. Saw pretty much the same when I checked it while discharging. Any suggestions and what the issue might be.
 

HRTKD

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Are there any other devices between the shunt and the batteries? Have you checked all your connections? A bad connection can result in some very odd readings.

I have an almost identical setup. When I look at my Victron numbers it is almost exactly the sum of what the two BMS are showing. I'm looking at this on my Android phone. It takes some time to switch between the three devices and the amp numbers can change.
 

mikefitz

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I find the JBD BMS ( as supplied) current values closely match other current monitoring readings in the system. A diagram of your system showing how the chargingsystem, batteries, BMS and shunt are connected together would be helpful.

Mike
 

ptmac

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Picture of my battery pack and a drawing of how they are connected. Lead lengths on each BMS are the same as is +ve cable to the +ve and -ve terminals. Have tried disconnecting one battery and calibrating idle, charge and discharge. Still a large difference between what Victron shunt and app are indicating. I had to assemble inside a storage compartment to get them into the space in my motorhome. Will disassemble one and put it back on bench for further investigation. Have been in touch with JBD and so far no solution.


2 x 280ah Battery.jpg1626908457453.png
 

Bob B

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I think I'm seeing a third connection to the negative battery terminal ... that isn't consistent with your drawing.
 
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ptmac

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I think I'm seeing a third connection to the negative battery terminal ... that isn't consistent with our drawing.
Ah yes, I have active balancer's which are the extra leads you can see in picture. I have disconnected them at the balancing board end.
 

Bob B

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Do you have a clamp meter that you can use to see what the actual current is at various places?
 

Bob B

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It doesn't seem likely to me that you would have 2 JBD BMS with the same problem. I think some actual current measuring is going to be required to troubleshoot.
 

ptmac

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I just went and purchased a DC amp clamp and some interesting results. Inverter with heatgun pulling 48amps. Check the positive lead to each battery and show 24amps. I have 3 x 8awg cables to an from BMS on negative side. All three in amp clamp and I see 24amps. Each one individually I see 8amps which all makes sense. I then calibrated BMS discharge using 24000 and it shows ~5000ma discharge. I then tried using 8000ma (current through one of 8awg cables and it is displaying 8000 ma in the app. I would think that the connection points on the BMS for these cables is paralleled but wondering if that is not the case as it appears to be reading only one of the three leads. I guess next step is to run load through only one of the negative leads, and see if I get a different result.
 
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ptmac

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Mystery solved. Been going back and forth with JBD in China and asked what the Current mR setting should be. I assume this is the shunt resistance. Was set at 2.5mR when in fact it should be .2 mR. All makes sense now. Sucks a bit as it needs to be plugged into UART box as not available over Bluetooth. Which means disassembly of other battery to get at BMS. Thanks for the suggestions.
 
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HRTKD

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Mystery solved. Been going back and forth with JBD in China and asked what the Current mR setting should be. I assume this is the shunt resistance. Was set at 2.5mR when in fact it should be .2 mR. All makes sense now. Sucks a bit as it needs to be plugged into UART box as not available over Bluetooth. Which means disassembly of other battery to get at BMS. Thanks for the suggestions.

I'm impressed that you got a response out of JBD. Did you get it working with one of your batteries already?
 

ptmac

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I contacted them via Ali Express and they were very responsive. Communications did get confused and while they were trying to help, we weren't getting anywhere. Just seemed to me that there was some sort of issue with the current/shunt. So I started looking at parameters and asked them about the mR value. They came right back with the value it should be and it was not what was programmed into the boards. So they certainly helped in that respect. This parameter is only visible in the JBD Tools windows program. Changed both battery packs. The one on the bench looks pretty accurate so assume the other one will be fine once I get it all back together.
 

WingNut

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Good info. It may affect others also so it's a value they can check.

Under Parameter View, the Android app lets you change the "Galvanometer resistance" mR value which is further described as current sense resistance.
 
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HRTKD

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Good info. It may affect others also so it's a value they can check.

Under Parameter View, the Android app lets you "Galvanometer resistance" mR value which is further described as current sense resistance.

Is that a confirmation that the Android app allows you to change that parameter?
 

Bob B

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First I've heard of that problem ... but if you have 2 BMS that had that .... there is probably going to be more.
 
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