lifted club cars - lifted ezgo
Home FAQDonate Who's Online
Go Back   Buggies Gone Wild Golf Cart Forum > Modified Golf Carts > Extreme DC! > All things Lithium


Post New Thread  Reply
Thread Tools Display Modes
Unread 11-18-2019, 09:24 AM   #11
Gone Wild
 
Sergio's Avatar
Club Car
 
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 7,671
Default Re: Adding 2nd set of 7 module

I still think my recommendation on how to add the new "capacity mismatched" pack in this post still stands as the best approach:
Want 7 more Leaf Modules...knew this would happen
As far as pre-balancing all the modules without an adjustable voltage power supply, I think the best approach is to use the Zeva BMS to fully charge each 7S1P modules pack individually.

You can then disassemble the packs and reconfigure them as 7S2P per the mentioned schema.

Since there is a good possibility the new pack will not be an exact match in capacity, the top voltage is the best method to reduce the load on the BMS and get the entire new pack in balance.

Definitely do not do "dynamic balance" as it makes no sense unless the cells are a perfect match to each other and then it would only benifit the intial balance.

Make sure You have a clean and tight connection on that cable that will tie the two packs together to minimize the "sampling" error on the first module pair on the smaller pack during high current discharge.
Sergio is offline   Reply With Quote
Alt Today
BGW

Golf car forum Sponsored Links

__________________
This advertising will not be shown in this way to registered members.
Register your free account today and become a member on Buggies Gone Wild Golf Cart Forum
   
Unread 11-18-2019, 01:17 PM   #12
Gone Wild
 
DaveTM's Avatar
 
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 3,584
Default Re: Adding 2nd set of 7 module

I guess another option (just thinking out loud) would be to sell the existing 7 module pack and purchase a 14 module pack that have come from the same set.
DaveTM is offline   Reply With Quote
Unread 11-18-2019, 01:31 PM   #13
Gone Wild
 
Sergio's Avatar
Club Car
 
Join Date: Sep 2012
Location: Charlotte, NC
Posts: 7,671
Default Re: Adding 2nd set of 7 module

The "have come from the same set" is always an unknown when buying used modules.

The original pack has 48 modules, so depending how many sets of 6, 12, 7, 14, etc they sold from that pack there would be left over modules.

I think the only advantage is that the modules would be closer in voltage to each other, but once you get the pack top balanced, just like any other pack the overall pack AH would be that of the lowest AH cell in any module.
Sergio is offline   Reply With Quote
Unread 11-18-2019, 02:47 PM   #14
Gone Wild
 
Join Date: Mar 2019
Posts: 210
Default Re: Adding 2nd set of 7 module

Quote:
Originally Posted by DaveTM View Post
I guess another option (just thinking out loud) would be to sell the existing 7 module pack and purchase a 14 module pack that have come from the same set.
I could but noone around me is gonna want the set. No golf carts around me. For now just toying around and seeing how feasible it is to do if i need to this summer. Hoping with the new motor, alltrax controller and new tires its not gonna drain the battery any faster than stock

Sent from my SM-G960U using Tapatalk
cmysstailights is offline   Reply With Quote
Unread 11-18-2019, 04:16 PM   #15
Gone Wild
 
DaveTM's Avatar
 
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 3,584
Default Re: Adding 2nd set of 7 module

Well, I "bantered" it about as posted on my thread, but after this hunting season...or after Jan 2020, I plan on making the upgrade\addition.
DaveTM is offline   Reply With Quote
Unread 11-18-2019, 06:28 PM   #16
Getting Wild
 
Join Date: Nov 2018
Posts: 78
Default Re: Adding 2nd set of 7 module

Another string of 7 modules can be parallel-connected to existing string of 7 modules.

Let's say existing modules are charged at 4.1 volts per cell and newly acquired modules are at 3.7 volts per cell. If say they were paralleled using 1Ohm resistor, that's I = 0.4V / 1Ohm = 400mA, correct ? P = 0.4A * 0.4V = 0.16W. Given that voltage difference amounts to some 12-14Ah, it would take about 40 hours to equalize, thus going with a smaller resistance and more wattage could be more practical. Once the two cells are equalized via the resistor, resistor is removed and the permanent jumpers or bus bars can be put between the two. Then next cell is likewise equalized. Once the process is complete for all 14 cells, you got a balanced pack. No changes to BMS.
cricketo is offline   Reply With Quote
Unread 11-18-2019, 07:18 PM   #17
Gone Wild
 
DaveTM's Avatar
 
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 3,584
Default Re: Adding 2nd set of 7 module

Quote:
Originally Posted by cricketo View Post
Another string of 7 modules can be parallel-connected to existing string of 7 modules.

Let's say existing modules are charged at 4.1 volts per cell and newly acquired modules are at 3.7 volts per cell. If say they were paralleled using 1Ohm resistor, that's I = 0.4V / 1Ohm = 400mA, correct ? P = 0.4A * 0.4V = 0.16W. Given that voltage difference amounts to some 12-14Ah, it would take about 40 hours to equalize, thus going with a smaller resistance and more wattage could be more practical. Once the two cells are equalized via the resistor, resistor is removed and the permanent jumpers or bus bars can be put between the two. Then next cell is likewise equalized. Once the process is complete for all 14 cells, you got a balanced pack. No changes to BMS.
I'm pretty sure I did this when I received my initial 7 module pack. I wired 'em up and let 'em sit for 5 days or so.
DaveTM is offline   Reply With Quote
Unread 11-18-2019, 07:35 PM   #18
Getting Wild
 
Join Date: Nov 2018
Posts: 78
Default Re: Adding 2nd set of 7 module

Quote:
Originally Posted by DaveTM View Post
I'm pretty sure I did this when I received my initial 7 module pack. I wired 'em up and let 'em sit for 5 days or so.
If I understand correctly, you did that to 7 modules to get them to the same voltage prior to assembling the pack. Above I was talking about incrementally connecting existing string of 7 modules to another string of 7 modules.

In such scenario there may be some voltage variances in the new modules, but they don't matter as the goal is to prevent rapid transfer of energy from cells with higher voltages to cells with lower voltages, which is achieved by using a resistor to restrict the current. Once the every N-th cell in old string is matched to the N-th cell in the new string, there may be slight voltage variances between cells in the new pack, but those variances will get balanced out by the BMS during charging - at this point the pack will be at some 70% of the charge.

More over, one could connect new string of 7 modules when the old string is at 50% of the charge, reducing the voltage difference and speeding up balancing of paralleled cell groups.
cricketo is offline   Reply With Quote
Unread 11-18-2019, 10:32 PM   #19
Gone Wild
 
DaveTM's Avatar
 
Join Date: Oct 2012
Location: Southwestern Pa.
Posts: 3,584
Default Re: Adding 2nd set of 7 module

Quote:
Originally Posted by cricketo View Post
If I understand correctly, you did that to 7 modules to get them to the same voltage prior to assembling the pack.
Yes. I did that to get all cells in balance with each other.


Quote:
Originally Posted by cricketo View Post
Above I was talking about incrementally connecting existing string of 7 modules to another string of 7 modules.
Forgive me.....but I don't see the difference. You still want to "balance" all the cells so that each cell.....new and old....have the same voltage. Then, from that point on, whatever BMS system you use, will keep the cells in balance with each other.
DaveTM is offline   Reply With Quote
Unread 11-19-2019, 12:20 AM   #20
Getting Wild
 
Join Date: Nov 2018
Posts: 78
Default Re: Adding 2nd set of 7 module

Quote:
Originally Posted by DaveTM View Post
Forgive me.....but I don't see the difference. You still want to "balance" all the cells so that each cell.....new and old....have the same voltage.
That is unnecessary. Once again, the goal is to prevent large current from a cell with higher voltage from going into a cell with lower voltage - something that will happen when you connect two cells with different voltages in parallel. Cell that has higher voltage will gladly give what it has, but the cell with lower voltage won't be as happy to accept the gift, hence the resistor.

Now voltage differences in the series configuration is BMS'es problem, there is no need to get them to any specific voltage as long as BMS can balance them out during charging. In fact at the bottom of SoC there will always be variances in voltages given most cells in these setups aren't perfectly matched, so BMS deals with balancing every time you charge.
cricketo is offline   Reply With Quote
Reply
Go Back   Buggies Gone Wild Golf Cart Forum > Modified Golf Carts > Extreme DC! > All things Lithium


Thread Tools
Display Modes


Similar Threads
Thread Forum
HEI module + new coil= no spark...HEI module + original coil= very weak spark Gas EZGO
HEI Module Gas EZGO
HEI Module Help Gas EZGO
hei module help Gas EZGO


All times are GMT -5. The time now is 05:54 PM.


Club Car Electric | EZGO Electric | Lifted Golf Carts | Gas EZGO | Used Golf Carts and Parts

Powered by vBulletin® Version 3.8.6
Copyright ©2000 - 2020, Jelsoft Enterprises Ltd.
Content Relevant URLs by vBSEO ©2011, Crawlability, Inc.