WheelchairDriver

Posted: **22 Jun 2020, 07:38**

It balances ALL of the time. Theres no way to stop that as far as I know. And if you could then the whole BMS isnt needed at all since you are using non of it.

What you need isnt a BMS at all. You need a CELL MONITOR. And again, if a couple of cells are a little higher or lower it wont tell you anything. The voltage of a LiFe cell does not tell you its state of charge for almost the entire charge.

Let me put it this way. Removing 10Ah from say cell or cell group 8 wont show anything on your cell monitor till the last few miles. Because they all stay at pretty much the same voltage from 95% doen to 30% give or take a few fractions of a volt. And those fractions may be reversed! The lowest cell might be the most charged. And thats because the actual changes are tiny. And theres always some calibration error on each cell reading, and some natural variation between identical charged cells.

All you really need is a cell log that warns you if a cell starts to drop after a days use before the rest.

Posted: **22 Jun 2020, 09:09**

Returning to that balancer board linked by Steve. Agree completely that we, or the manufacturer, would have to find a way to shut it off EXCEPT during charging. As it is now, that could be done manually (there's a software switch), but that defeats the possibility of "plug-and-play" use with a dumb charger. Given that it is computerized, the question then becomes whether the firmware can be updated to balance only at charging voltage.

Posted: **22 Jun 2020, 09:41**

Using voltage as SOC reference is viable on Li-ion, but not on LiFePO4.

Just doing a discharge of a170Ah pack , 26.48V → 26.34V after 85Ah taken out .

Posted: **22 Jun 2020, 09:51**

EXCEPT during charging.

And then only above 3.50V!

I dont thinl it can be shut off though. Its its main claim to fame. It does it all the time. Maybe hard wired. That would cause little if any issues on LiPo or on Lion cells. as the voltage only drops with discharge level.

Posted: **22 Jun 2020, 09:54**

Shirley beat me to it. And the problem is that the voltage of some cells, AFTER that 85Ah is removed, may still be higher than some cells were before... So balance gets screwed up by the balancer all day. And something like the warmth of the cells due to use, increases volts more than discharge drops it... So your SOC fuel gauge will increase and become more full as you drive depending on load! So climbing a hill will give you more fuel!

So if you want a fuel gauge, you need something that measures and counts current rather than volts so it can measure Ah or watt hours removed, and compare that to capacity. And leave a safe 10%.

Fit a big enough battery and its a non issue.

If not then thats why thse sorts of devices exist. The only way to do this. Some cheap. Some expensive. http://www.antares.co.uk/battery-gauge.html

Posted: **24 Jun 2020, 07:25**

This one worths a look.

Over volt
Under volt
Balance triggering volt

All adjustable 2.40V----4.40V

Balance method (2-3A): dumping / transferring .

WiFi monitor and remote control. Fuel gauge .

Posted: **24 Jun 2020, 17:32**

Thanks Shirley, Do you have a link or an English manual?

Posted: **25 Jun 2020, 16:24**

shirley_hkg wrote:
This one worths a look.

Over volt
Under volt
Balance triggering volt

All adjustable 2.40V----4.40V

Balance method (2-3A): dumping / transferring .

WiFi monitor and remote control. Fuel gauge .

Interesting. What's the price?

Posted: **26 Jun 2020, 01:51**

https://m.tb.cn/h.VK7PqUF?sm=535cb3

Posted: **26 Jun 2020, 08:25**

Here's a Google translate of part of that link:

Product basic parameters

1. Integrated management system for lithium battery, BMS03B can monitor 3-8 lithium iron phosphate ternary and polymer, BMS03C can monitor 10-16 lithium iron phosphate 10-14 ternary and polymer, BMS02X can monitor 3-5 12V single cell 36-60V lead-acid battery pack (BMS02X only balanced without overvoltage and undervoltage protection)

2. Use the MODE button to switch parameters, and + and-to add or subtract parameters. 3. Single-cell voltage monitoring and management of the battery pack (overcharge and overdischarge voltage values can be set by themselves).

3. Two equalization modes: active energy transfer + passive resistance energy consumption, intelligent balancing and forced real-time energy transfer balancing

4. The monomer overvoltage monomer overvoltage range 2.40V-4.40V can be set freely

5. Support free setting of balanced starting voltage 2.40V-4.40V, and free adjustment of balancing precision pressure difference interval 6mv-108mv (color screen version)

6. With temperature protection function, collect the temperature of the whole machine and the equalization module to reach the over-temperature value, pause equalization and over-temperature, stop charging and discharging, and shut down the protection function

7. With a complete power off function to protect the battery safety.

8. Relay protection board (high and low voltage shutdown is to control the relay coil relay to control the overall positive on and off of the battery pack to achieve undervoltage and overvoltage protection) When the undervoltage protection is detected, the charging access automatically opens the relay to charge the battery pack, overvoltage After the protection, the return value of the overvoltage protection is automatically turned on by the monomer fall or the trigger relay discharge is triggered manually

9. The voltage display accuracy is 0.01V, and the charging and discharging parameters are set by the user.

10. Active energy transfer balanced current 2-3A peak 4A

11. Rich parameter display, battery pack voltage, total voltage, battery pack real-time charging and discharging power, current and capacity display

12. The full-platform Internet of Things remote monitoring supports Android/IOS smart phone tablets and various computers

13. Over-current and short-circuit protection methods: fuse blowing type and open circuit combination

14. The charging voltage of 3-8 strings does not exceed 30V, 10-16 strings does not exceed 60V, and the balance of 3-5 strings of batteries does not exceed 75V. Voltage overvoltage may bring certain risks.

Looks promising, especially #5. Not clear whether it can be set to balance only during charge, but #7 could be hooked to a switch at the charger Anderson.

Posted: **26 Jun 2020, 08:59**

Set 5 to 3.6v or more and it shouldnt interfere during the day.

Posted: **27 Jun 2020, 12:07**

Tried to shop for a board on Taobao, but got locked out trying to login :cussing

Even with translate on Chrome it's really hard when a lot of the info is displayed as untranslated graphics

Posted: **28 Jun 2020, 10:31**

3S……8S @ ¥338 CNY plus shipping.

Posted: **28 Jun 2020, 10:33**

10S……16S @ ¥348 CNY plus shipping.

Posted: **28 Jun 2020, 10:43**

Further information from seller :

Balance current via resistor dumping is 1.5A

BMS is meant for stationary installation, need to connect to internet for remote monitoring.
Not applicable to mobility devices.

Still interested ? Let me know. cheers

Posted: **28 Jun 2020, 10:50**

Does the app support English?
Does the app require manual fee? If so, how much for a year?

Posted: **28 Jun 2020, 12:09**

Doesn't support English.

App fee @￥15 CNY a year.

Posted: **28 Jun 2020, 23:51**

Thanks Shirley but if it's only for the chinese market It's not going to be of use to me

Posted: **03 Jul 2020, 09:05**

English version is under construction. :clap

Posted: **03 Jul 2020, 10:12**

Ah Ha! That's good,

Balance current via resistor dumping is 1.5A

It is better to move from the high cell to the low cell rather than dump into a resistor, is it not? I would like the balancer to :-

1. balance by moving charge from highest cell to lowest cell

2. balance current of at least 1 Amp, the more the merrier

3. balance to within a few mV

4. No balancing except when charging

5. No balancing until highest cell is >= 3.5V

Some form of wireless monitor would be nice, bluetooth to phone etc

Posted: **03 Jul 2020, 11:53**

stevelawiw wrote:
It is better to move from the high cell to the low cell rather than dump into a resistor, is it not?

That will be doing one cell /group at a time , whereas dumping will be all cells simultaneously.

Posted: **03 Jul 2020, 13:19**

4. No balancing except when charging

Theres no point in that unless the balancer can move charge faster then the charger can charge. So if you are charging a big pack like the 176 to 220Ah ones we are now using, say 30Amps charge, it needs to be able to balance ALL cells at above 30A. And it needs to PROPORTIONALLY reduce charger output until its a few mA. The place to do this is inside the charger...

So 4 is pretty pointless.

Posted: **03 Jul 2020, 14:50**

If I set psu cv @28.2V , current will reduce to quite low after passing 27V. And say if the cells are not way of unbalanced , would these help ?

No over charge at least, but switches on/off several times.

Posted: **15 Jul 2020, 15:23**

Active balancing while charging is a misnomer. An active balancing charger stops charging when the balancer is in operation. While voltage is not an absolute measure of SOC, cells that are weaker charge to a higher voltage and discharge to a lower voltage relative to others at the same charge/discharge rates. The active balancer moves charge from the weaker (fuller) cells to the not so full cells time multiplexed with the charging. So if balancing set to start at 3.55v the first cell to reach that voltage is discharged actively, ideally into all other cells, though the more simplistic approach is into the one above or below (top goes to bottom or vice-versa). Once the voltage in the higher cell has reduced by a specified amount (or after a certain Ah has been extracted), charging resumes across all cells. Obviously the higher the balancer rate the faster the pack balances.

I've been working on the design for a light-weight onboard mains-powered (initially) 40A charger with active 10A balancing and a Bluetooth battery capacity monitor (Columb counter) after scrapping my previous battery monitor as the functionality didn't justify the likely end-user price in quantities of 100s and the TI chip pricing was not good. Now using Analog Devices chips, based on some info about the EV charger for a certain fast paced cat

. Background info here.

Posted: **16 Jul 2020, 23:07**

Thanks Irving.
I was writing a longer than usual post for me in reply to your very interesting post and got timed out and lost it :cussing

So for now I'll just say your post is very interesting and it's encouraging that you and the Chinese are both working on active balance boards which is all good in my book.
I think they look like a very attractive solution to the problem which is currently being dealt with by the PL8, but I think it would be great if there was a choice of solutions.
For me personally working on a chair I'm going to power with 16 cells and a nominal 48v I don't really want to have to use two PL8s in parallel or split every charge into two separate 8s charges and use one PL8 twice!,
So an active balance board capable of balancing 16 cells in one go that is being charged using a ZXD psu is an attractive solution to me.

Steve

Posted: **16 Jul 2020, 23:13**

I was writing a longer than usual post for me in reply to your very interesting post and got timed out and lost it

Click back, and if needed twice, and the page you typed is still there. At least in firefox it is. If you are using anything else then you should get the same thing? So copy/past into new post after logging back in.

Posted: **16 Jul 2020, 23:20**

Didn't work this time for some reason. I use Firefox. I never intended to write a big reply! I'll try again tomorrow maybe :roll:

Posted: **22 Aug 2020, 03:45**

Posted: **27 Sep 2020, 09:45**

Does anybody know how PL8 or BMS get cell volts from balance wires? Do they use a chip or volt sensors or a special module? Or do they just use some special methods to calculate cell volts?

Posted: **27 Sep 2020, 12:06**

The PL8 does not charge continually. Even though it appears to do so. It measures several lots of voltages.

During the breaks several times per second it reads all the cell voltages.
During the charge periods it also reads the (higher incorrect) cell volts - due to cell resistance this is higher. It uses the difference in readings to give cell resistance.

During this time it also reads the difference between unloaded cell volts and charge cable volts, so it can read the charge cable resistance... And so it has:

Peak charge volts (higher than the average because of the gaps in charging) and the pulsewidth used to control voltage. Thats 3 different battery volts.
Averaged charge voltage, measured during charge periods
Battery voltage measured while in the unloaded gaps...
Battery voltage while on charge load, also averaged to remove the gaps... And displayed.
Measure cell voltages that are actual during the gaps that are displayed on screen. So cell volts added together may not = battery voltage displayed.

Theres lots of measurement and corrections and averaging and peak values known. Its not so simple.

At least thats what I was told by the beta developer guy I was emailing...

A bms? God knows.

WheelchairDriver

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