BYD 24 volt Questions of Capacitance

[Ampster]

charge rate, settings are 27.5v/24v, stop and start. Amps can be set between 2 and 60. Charger hits the numbers, the battery's are coming up to 26.7v,

So, the question I asked earlier is what is causing your batteries to stop charging at 26.7 when the inverter is set for 27.5? Can you verify that is what they stop charging at with a multimeter the moment they stopped charging. Is the 26.7 the resting voltage after they have finished charging?

 

[thealaskan]

So, the question I asked earlier is what is causing your batteries to stop charging at 26.7 when the inverter is set for 27.5? Can you verify that is what they stop charging at with a multimeter the moment they stopped charging. Is the 26.7 the resting voltage after they have finished charging?

Yes, I have a separate meter on the system and I physically see the 27.5v, and yes I don't know why the batteries never go there and stop short. At 10a CR it was worse, and at 30a I thought I was burning them up.

 

[Ampster]

When you physically see the 27.5 I assume that is the setting. It beats me why it stops. Does your BMS have any logs.My Inverter has a calibration difference on .6volts so when I have it set for 55 it stops charging at 54.4, Have you calibrated the voltage the inverter is reporting and using for cuttoff versus a know good voltage meter.

 

[thealaskan]

When you physically see the 27.5 I assume that is the setting. It beats me why it stops. Does your BMS have any logs.My Inverter has a calibration difference on .6volts so when I have it set for 55 it stops charging at 54.4, Have you calibrated the voltage the inverter is reporting and using for cuttoff versus a know good voltage meter.

That is on the bus bar battery parallel main. This is just a pic. not at the 27.5v I have seen.

 

[Ampster]

It feels like we are going around in circles.
I asked you if you could verify that your charging is cutting off at 26.7 and you responded that that you have a separate meter on the system and you see 27.5. Maybe what it happening is the usual voltage sag after charging. Lets assume that is what is going on and not worry about anything.

 

[thealaskan]

If I see 27.5v on the meter, that means the charger went to 27.5v and quit. So it has been verified.

As of this morning the battery's have increased capacitance another .2v on the 20a CR.

 

[Ampster]

Problem solved. My theory os that your BMS was stopping charging early because one cell had reached the cutoff. As that cell became balanced the rest of the cells caught up and your pack could charge to the full 27.5. Lowering the charging Amps helped to give more time for the BMS to do its balancing..Now you can increase the charging Amps slowly to use more of your solar power. Enjoy your battery.

 

[thealaskan]

It will be over a week before I know if more capacitance has started come back, at the 20a CR. Would like to see under 1v difference.

When I first fired them up it was .3v.

 

[Ampster]

Are you missing a decimal? It seems you are below 1v difference if you were at .3v when you first fired them up. Besides editing your posts more carefully I would suggest you try to be more explicit in your description of what difference you are looking at. I could reread the entire thread again to jog my memory but it would just be easier to move on to another thread.

 

[thealaskan]

Are you missing a decimal?

No.

27.5v battery charge setting, batteries were only charging to 26.1v, have now increased to 26.5v. which is the 1 volt difference your system does, mine should be going to at least 27.2v. which is the .3v.

thanks for your time

 

[thealaskan]

What is the difference in-between top balancing or bottom balancing. I would imagine it means what it states. They either start together or they end together.

I would think that top balancing would be better in a parallel application.

 

[Ampster]

I would think that top balancing would be better in a parallel application.

Top balancing works better when there is a BMS because most BMSs are devices that top balance.
Bottom balancing was advocated by some that felt a BMS was not necessary. Years ago, when BMSs were expensive and not as reliable many in the EV conversion community felt it was the best because the risk with an EV was at the bottom if some one drove it too far and tried to limp home.

It all depends on your perspective and has nothing to do with whether the cells are in parallel. Either form of balancing can be done individually or as a group in parallel.

 

[thealaskan]

I believe I have found my Issues. I have learned after reading other articles that Capacitance is a constant, which is lets say physical.

The range of operation, in my case was balance.


I performed these tests and could not understand why they were not more uniform. Each line is a Battery.
So I decided to top Balance the 2 battery's that were acting different from the other 2, and have now increased my useful range .5v.

I have been doing them separately, doing the other 2 now, and then will do all at once. when I get more set up.

Added a new tool to the shop and it works great, Kaiweets 30v 10a power supply.

Amazon.com

 

[thealaskan]

I don't understand?
1. I topped all battery's for separate top balances, with intent to do a full parallel balance. I gained a total voltage to 26.7v relaxed.
A. Performed a load for a day, with a one time 15 minute 53% load, the batteries dropped to 26.2v, and after 3 days use the relaxed voltage only increased .1v per day?
B. After 3 days I shut off all inverters, 26.4v was the relaxed voltage, and setup the power supply for charging all 4 in parallel. (forgot to disconnect the solar)
When I realized what I had done when I found the power supply had topped out at the adjusted 28v, Battery 1 was at 27.8v? Battery 2 was at 27.6v? Battery 3 was at 27.2V? Battery 4 was at 28.9V? Isn't the installed BMS supposed to cut at 28v?
All battery's should of had the same reading?