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Does the Vruzend BMS really balance?  

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kyletom415
(@kyletom415)
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05/07/2018 3:44 pm  

Hello,

I bought multiple of the 52V, 14S battery management systems ( https://vruzend.com/product/52v-14s-battery-management-system-bms/) from your website and wanted clarification on what it does.

 

For charging, I plug my 52V charger into the BMS and notice that everything will charge until one of the batteries in series hits ~4.2V. Once this happens, the charger shuts off and stays off. I've waited a day and measured each battery voltage in series and the battery pack still seems unbalanced.

 

Before I checked the BMS, I charged each battery to 4.2V. I discharged 1 battery to 3.8V, 12 batteries to 3.7V and 1 battery to 3.6V. After the test, the battery voltages will become: 1 batteries = ~4.2V, 12 battery = ~4.1V, and 1 battery = 4.0V.

 

Can you please let me know your thoughts? I've read both books your company sells and can't figure out what might be going wrong.


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Micah (Vruzend Rep)
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09/07/2018 12:21 pm  

That behavior does sound strange. Is it possible to share some photos of your connections so we can verify that it is all connected correctly? It's easy to miss a wire somewhere and that can (and has) led to incorrect BMS behavior in the past. You can either post the photos here by attaching them or feel free to email them to us at contactatvruzenddotcom.


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kyletom415
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11/07/2018 2:26 am  

Sorry for the delay - currently traveling but will post photos as soon as I get back.


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kyletom415
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15/07/2018 11:41 pm  

Not sure how to upload an image to the forums so I attached a link.

The electrical diagram is as follows:

https://ibb.co/eoahpJ

How do you think I should upload photos of the connections? Not sure how to make it easy for you to trace out 15 wires


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kyletom415
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CortisCooper
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27/07/2018 9:50 am  

Is your 52 V charger putting out 58.8V?  A BMS typically won't balance the cells until the very last step of the charging process, or in your case, when the 14s group is nearing 58.8 V.  If the charger is weak this could be the problem.  


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garolittle
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28/07/2018 11:25 pm  

Just for reference, I used a Vruzend BMS for my 14S 9P pack several months ago the pack was used on a kids go kart and had many charge/discharge cycles.  It sat in my garage during a long conversation led winter and  I recently tore down the pack and checked the voltage on each of the 126. All excep one were within 2 one hundredths of the same change for each cell. This gave me great confidence in the Vruzend product. 


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kyletom415
(@kyletom415)
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29/07/2018 11:03 pm  

Hello Garolittle. 

 

Were all of your batteries the same voltsge when you installed them?

 

i did a test where I made a pack of different battery voltages to see. So for example, on my 14s,3p pack, some rows were 4.2V. Others were 4.1. And some were 4.0. The BMS didn’t balance in this case. 


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garolittle
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04/08/2018 5:02 pm  
Posted by: kyletom415

Hello Garolittle. 

 

Were all of your batteries the same voltsge when you installed them?

Actually, I need to correct my statement.  The BMS was not from VRUZEND but every cell was almost identical in voltage.  I am now tearing down a pack that did in fact have a VRUZEND BMS and I will check the voltage on that one.  I suspect that the voltage will be the same because every VRUZEND product I have purchased has been of high quality. 

To answer your question, yes each cell had the exact same voltage when the pack was made.  I always double check this since a pack that starts out "out of balance" will only get worse over time.

 

 


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kyletom415
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05/08/2018 5:20 pm  

Hi garolittle,

i don’t quite understand what you mean when you say:

I always double check this since a pack that starts out "out of balance" will only get worse over time.”

When I built my test pack, I purposely made sure the cells did not start out with the same voltage because I wanted to see if the BMS balances the cells. 

 

If the BMS balanced the cells, why would it matter if the cells all had the same voltage? The BMS would make sure they become balanced.

 

This did not happen during my test! The BMS charged until one of the groups hit 4.2V. This then caused the charger to shut off. The BMS did not balance the cells. 


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garolittle
(@garolittle)
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07/08/2018 8:13 pm  

You are correct.  I am not sure what I was thinking when I responded but I should have been thinking/saying that the BMS would balance the cells.  My apologies.  It must have been a long day.  : - )


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