Bleeding boards mod help

?

 

OK I''ll bite, what is a bleeding board. I will assume it is some sort of voltage regulator set for 3.7v? If you want a lower voltage I would think changing the values of the board resistors maybe the way to accomplish this.
A schematic sure would be nice!

 

A bleeding board is a BMS for a single LifePo4 cell, in this case it is a A123 20ah pouch cell. It just top balances but it has no voltage protection.

I guess you can call it a poor man's BMS top balancer.

 

This is a break off from FWD's other thread.
Elcon Charger End voltage and other mods | Page 2 | PriusChat

He said he would start a separate thread about modifying his bleeding boards.

Basically the boards bleed off extra energy when charging to prevent a cell from getting charged too high.

Right now it sound like these do not start their bleeding off process until the cell's voltage reaches 3.7v.
This is higher than FWD wants.

Instead he wants to lower it to something like 3.45v, 3.5v or maybe even 3.6v.

 

A simple Ohms Law will suffice with the equation to help alleviate that offending voltage.
- - - Yeah, the schematic will simplify a lot

 

Need better photos. Focus is bad. They need to be taken closer using the macro function. Cannot read SMD resistor values, cannot trace PCB tracking etc.

 

Hi Dutch,

It looks like R1/R2 is your voltage divider for U1A shunt regulator.
To lower yor shunting (bleeding) voltage you need to decrease R1 or increase R2.
R1 is probably parallel R1A, R1B, R1C, R1D and R2 is parallel R2A, R2B, R2C, R2D.
I can't give you the exact value as the resolution of your photos is too low.

BTW: Hope charger upper voltage limit and this bleeding boards are not the only protection
you have in your system - it's definitely not enogh.

Jacek.

 

According to my calculation your bleeding should start at 3.66V. If you just remove R2D (105 = 1MOhm) you will get 3.61V for start bleeding voltage.
The rule is: whenever voltage at R2 (ABCD) is above 2.5v this circuit start shunting.
So:
Vshunt/R1+R2 = 2.5V/R2

Regards,

Jacek.

 

Hi Jacek,

Can it be modified to start bleeding at 2.5v.

Thanks.

 

Hi John,

When you open R2 or short R1 then it in theory should start bleeding at 2.5V. But U1B regulator has some accurracy (lets say 5%) so thats why they provide 4 positions for each of the R1 and R2 - for final tuning.

Regards,

Jacek.

 

Hi Dutch,
Removing any of R1 will increase bleeding voltage. I gave you the rule...
You can replace R1C (475 = 4.7MOhm) with lets say (225 = 2.2MOhm) to go further lower with the voltage.
Some checking is needed.

Jacek.

 

You can not remove R2A - if you remove it you will get about 2.5V bleeding voltage.

Jacek.