[Renny_D]

Hi I am thinking of using a quick charge charger for a lithium pack. The 96 volt charger charges at 2.55/cell or 122.4 volts then switches to 2.26v/cell or 108.5 volts for it's float charge. What would be the right cell count of TH 100ah cells to match this charge algorithm? I was thinking 30 as this puts the max charge voltage at 4.08v/cell and a maintainence charge of 3.6v/cell. Maybe this is doing it backwards but I have a limited budget at this moment and price wise this works. Please let me know your thoughts.

Thanks
Renny

[bruceme]

Originally Posted by Renny_D

Hi I am thinking of using a quick charge charger for a lithium pack. The 96 volt charger charges at 2.55/cell or 122.4 volts then switches to 2.26v/cell or 108.5 volts for it's float charge. What would be the right cell count of TH 100ah cells to match this charge algorithm? I was thinking 30 as this puts the max charge voltage at 4.08v/cell and a maintainence charge of 3.6v/cell. Maybe this is doing it backwards but I have a limited budget at this moment and price wise this works. Please let me know your thoughts.

Thanks
Renny

I just converted my PbA EV to TS 100's. I used the miniBMS connected to my existing PFC-20. I set the charger to 3.7v/cell (163v for 44 cells). I believe you can use up to 3.8v/cell safely, but others that watch this thread can say better.

You should plan to take full advantage of the BMS, let it turn off the charger. Your charger installation likely will require a relay to do that. Fortunately the PFC has the "Reg-Bus" interface, which miniBMS already accommodates.

But yeah, it can be done, I did it.

[bruceme]

Btw... you can get away without a management system on flooded PbA (over-charging just gasses off), but anything sealed (especially expensive LifePo4's) MUST have something that proactively keeps any one battery from getting beaten on by the pack.

[ewdysar]

Originally Posted by bruceme

I just converted my PbA EV to TS 100's. I used the miniBMS connected to my existing PFC-20. I set the charger to 3.7v/cell (163v for 44 cells). I believe you can use up to 3.8v/cell safely, but others that watch this thread can say better.

You should plan to take full advantage of the BMS, let it turn off the charger. Your charger installation likely will require a relay to do that. Fortunately the PFC has the "Reg-Bus" interface, which miniBMS already accommodates.

But yeah, it can be done, I did it.

I've charged 4 TS 160Ah cells with a Black and Decker "smart charger" on the "wet" (not AGM or Gel) setting. The max voltage was right at 15V (3.75V/cell). While I do have stand alone EV Works shunting modules (they start shunting at 3.65V) on each cell, no individual cell exceeded 4.0V. I monitored voltages manually with a multimeter since the batteries were sitting on my workbench.

If you're going to run without any BMS protection, I would recommend a max voltage of 3.65V/cell for the entire pack, which put you at 33 TS cells for your given peak charging voltage. This should give a reasonable amount of headroom for the "faster" cells. You should still manually balance the cells periodically with either a single cell charger (top balancing) or a small resistive load (bottom balancing).

Eric

[Renny_D]

Originally Posted by ewdysar

I've charged 4 TS 160Ah cells with a Black and Decker "smart charger" on the "wet" (not AGM or Gel) setting. The max voltage was right at 15V (3.75V/cell). While I do have stand alone EV Works shunting modules (they start shunting at 3.65V) on each cell, no individual cell exceeded 4.0V. I monitored voltages manually with a multimeter since the batteries were sitting on my workbench.

If you're going to run without any BMS protection, I would recommend a max voltage of 3.65V/cell for the entire pack, which put you at 33 TS cells for your given peak charging voltage. This should give a reasonable amount of headroom for the "faster" cells. You should still manually balance the cells periodically with either a single cell charger (top balancing) or a small resistive load (bottom balancing).

Eric

Thanks actually I was planning on using the Mini BMS system. Thanks for the feedback.

Renny

[dexion]

There is no need to float the cells (and it may be a problem as well but i am unsure on that point.) You can set the profile to shut off when its done charging and not float. Id say size the pack to max at about 3.6V so you may be able to get 34 cells in there with that charger. Thing about that charger is when it gets to "80"% of the charger it lowers its output and is timed (or atleast my 120Volt model did) so it may take some time to get the cells to 3.6V or 4.08 if you go with 30 you may have to restart the charger for another +80% timed cycle. Id rather have 4 more cells more range, lower sag etc but of course more cost too.

[Renny_D]

Originally Posted by dexion

There is no need to float the cells (and it may be a problem as well but i am unsure on that point.) You can set the profile to shut off when its done charging and not float. Id say size the pack to max at about 3.6V so you may be able to get 34 cells in there with that charger. Thing about that charger is when it gets to "80"% of the charger it lowers its output and is timed (or atleast my 120Volt model did) so it may take some time to get the cells to 3.6V or 4.08 if you go with 30 you may have to restart the charger for another +80% timed cycle. Id rather have 4 more cells more range, lower sag etc but of course more cost too.

So Lithium don't do the same self discharge that lead does? Also looking at the mini bms, if I go that route the bms will start shunting current as soon as the majority of the batteries are at full charge the shunts will run out of place to shunt power to then the voltage in one cell will rise triggering the HVC shut down - it that correct?

Thanks
Renny

[ewdysar]

Originally Posted by Renny_D

So Lithium don't do the same self discharge that lead does? Also looking at the mini bms, if I go that route the bms will start shunting current as soon as the majority of the batteries are at full charge the shunts will run out of place to shunt power to then the voltage in one cell will rise triggering the HVC shut down - it that correct?

Thanks
Renny

First, Lithium batteries have similar self discharge to high quality AGM, < 3%/month. FLA self discharge at 3-5%/week.

With BMS modules, each module will start to shunt when its cell reaches the shunting voltage (3.6 - 3.65V/cell for TS batteries) The excess energy (less than 1A) is dissapated as heat (not much). With 30 cells, the BMS modules can easily shunt 15A combined, even though your charger should be ramping down in amperage by then. I've never had my BMS modules trigger an HV shutdown.

There are active BMS systems that can direct energy from one cell to another, but that requires many more wires and a master control unit that can manage that process. These systems are more complex, more $$$ and only contribute a small percentage to overall charging efficiency.

Eric

[bruceme]

Originally Posted by ewdysar

With BMS modules, each module will start to shunt when its cell reaches the shunting voltage (3.6 - 3.65V/cell for TS batteries) The excess energy (less than 1A) is dissapated as heat (not much). With 30 cells, the BMS modules can easily shunt 15A combined, even though your charger should be ramping down in amperage by then. I've never had my BMS modules trigger an HV shutdown.

Eric

miniBMS can burn up to 750 mA into the shunting resistor. I manually floated the pack the first couple charges to get everything in sync. That went quickly and it's now very very closely balanced. I backed the PFC down from 163v to 160v. LiFePo4 are very different than PbA at end of charge. PBa just steadily go higher. LiFePo4 barely change at all, then "pop-off" at 3.6v and will sky very high. You have to protect against that by either knowing that the pack is very closely balanced or put some type of protection in the charging circuit. miniBMS accomplishes both for me. But I am going to put in a _crazy_ simple battery balance monitor.

http://www.evdl.org/pages/battbridge.html

[Renny_D]

Originally Posted by bruceme

miniBMS can burn up to 750 mA into the shunting resistor. I manually floated the pack the first couple charges to get everything in sync. That went quickly and it's now very very closely balanced. I backed the PFC down from 163v to 160v. LiFePo4 are very different than PbA at end of charge. PBa just steadily go higher. LiFePo4 barely change at all, then "pop-off" at 3.6v and will sky very high. You have to protect against that by either knowing that the pack is very closely balanced or put some type of protection in the charging circuit. miniBMS accomplishes both for me. But I am going to put in a _crazy_ simple battery balance monitor.

http://www.evdl.org/pages/battbridge.html

Thanks, that battery bridge indicator looks good.

I see two different mini bms, my understanding the 3.8 was for the TS and the 3.6 was for the Calb batteries. Am I misunderstanding this?

Please let me know.

Thanks
Renny