Bulk charging options prior to top balancing

BretS

Solar Enthusiast
Joined
Mar 30, 2021
Messages
169
I am trying to figure options for bulk charging my cells when they come in, before top balancing. I plan to get a 10A power supply for top charging, but realize it would take forever. The only charger I currently have is the one in my camper now. But, I don't believe I can configure my new cells in 12V and use it because it would take them to 14.4V (3.6 per cell). I am attaching the specs on it. Am I correct? And if so, what is a recommended bulk charger for this purpose without spending a bunch of money on something I will never use again?20210505_084951.jpg20210505_084951.jpg20210505_085052.jpg20210505_085052.jpg
 

Gazoo

Dumb Dumb
Joined
May 12, 2020
Messages
2,794
Location
Texas
I am trying to figure options for bulk charging my cells when they come in, before top balancing. I plan to get a 10A power supply for top charging, but realize it would take forever. The only charger I currently have is the one in my camper now. But, I don't believe I can configure my new cells in 12V and use it because it would take them to 14.4V (3.6 per cell). I am attaching the specs on it. Am I correct? And if so, what is a recommended bulk charger for this purpose without spending a bunch of money on something I will never use again?
You do not need to but another charger.

You will need to connect a BMS to your cells before you charge the cells in series. The charger in your van will work and the 10 amp PS will work as well. For example if your cells are 280ah's and they are delivered with a 50% SOC it would take apx. 14 hours to charge the cells connected in series using your power supply.

If connected in parallel it would take apx. 56 hours. This is of course assuming your PS delivers the full 10 amps and good cables and connections will be the determining factor.

The charger in your van charges to 3.6 volts per cell. But it will not be 3.6 volts per cell because the cells are not capacity matched and have not yet been parallel top balanced. You could use your vans charger, then connect the cells in parallel and parallel top balance using your PS set to 3.65 volts.

After the cells are series charged. connect the cells in parallel and start your top balancing. Just make sure you set the voltage of the power supply to 3.65 volts before connecting it to the cells.

When charging in series keep in mind the BMS's HVD will kick in if one of the cells reaches 3.65 volts, and it most likely will because the cells are not capacity matched. This is the reason to parallel top balance. And this is why it's very important to connect a BMS whenever charging cells in series.
 

BretS

Solar Enthusiast
Joined
Mar 30, 2021
Messages
169
You do not need to but another charger.

You will need to connect a BMS to your cells before you charge the cells in series. The charger in your van will work and the 10 amp PS will work as well. For example if your cells are 280ah's and they are delivered with a 50% SOC it would take apx. 14 hours to charge the cells connected in series using your power supply.

If connected in parallel it would take apx. 56 hours. This is of course assuming your PS delivers the full 10 amps and good cables and connections will be the determining factor.

The charger in your van charges to 3.6 volts per cell. But it will not be 3.6 volts per cell because the cells are not capacity matched and have not yet been parallel top balanced. You could use your vans charger, then connect the cells in parallel and parallel top balance using your PS set to 3.65 volts.

After the cells are series charged. connect the cells in parallel and start your top balancing. Just make sure you set the voltage of the power supply to 3.65 volts before connecting it to the cells.

When charging in series keep in mind the BMS's HVD will kick in if one of the cells reaches 3.65 volts, and it most likely will because the cells are not capacity matched. This is the reason to parallel top balance. And this is why it's very important to connect a BMS whenever charging cells in series.
I don't think I can use the charger from my 5th wheel then, because my BMS is a contactor type and has to be assembled along with my entire system (see my system diagram below). I wanted to get the bank top balanced before installing everything in the 5th wheel. I guess I will just have to use the 10 amp PS with some good leads, and do them one at a time. I guess that would give me the chance to see what voltage they all rest too as well - to make sure they don't self discharge too quickly?

system 3.jpg
 

Gazoo

Dumb Dumb
Joined
May 12, 2020
Messages
2,794
Location
Texas
I don't think I can use the charger from my 5th wheel then, because my BMS is a contactor type and has to be assembled along with my entire system (see my system diagram below). I wanted to get the bank top balanced before installing everything in the 5th wheel. I guess I will just have to use the 10 amp PS with some good leads, and do them one at a time. I guess that would give me the chance to see what voltage they all rest too as well - to make sure they don't self discharge too quickly?
I understand your dilemma now. Nothing wrong with topping the cells one by one except for the time it will take. Are you planning to capacity test each cell too?
 

BretS

Solar Enthusiast
Joined
Mar 30, 2021
Messages
169
I understand your dilemma now. Nothing wrong with topping the cells one by one except for the time it will take. Are you planning to capacity test each cell too?
No, because I don't want to spend the money on a tester that I won't use again too. This project has really added up... I am just going to top balance, and make sure they all stay about the same, and above 3.5x after 24 hrs of resting to make sure I didn't get any really bad ones.
 

Gazoo

Dumb Dumb
Joined
May 12, 2020
Messages
2,794
Location
Texas
I didn't capacity test my cells either. I tested the pack and am very satisfied.
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
7,688
Location
Somewhere South of Denver
I didn't capacity test my cells either. I tested the pack and am very satisfied.

Same here. My eight cells (4s2p) are looking great!

OP, I used only a benchtop power supply to do my top balance. It didn't take that long. If you ordered the cells from China and it took the usual 45 days, what's another three days to do the top balance?
 

Gaze

Solar Enthusiast
Joined
Nov 4, 2020
Messages
51
I didn't study everything in this thread before reply, but I connected the battery cells in series to an all-in-one unit with over-voltage setting protection, fast charged (20A/30A/40A...adjustable on-the-fly), however fast you want to go) to a bulk-charge limit set just below the max safe voltage threshold while monitoring the individual cells with BMS app. Then disconnect to fine tune a slow, careful top balance using whatever is your favorite method. It worked fine, fast.
 
Last edited:

Stepandwolf

Solar Addict
Joined
Nov 14, 2020
Messages
620
Same here. My eight cells (4s2p) are looking great!

OP, I used only a benchtop power supply to do my top balance. It didn't take that long. If you ordered the cells from China and it took the usual 45 days, what's another three days to do the top balance?
I connected my 10A bench charger to a single cell and was going to bring them all up to 3.5 and then put them in parallel to top balance. After having the PS connected to the first cell for 2 days, it only went from 3.3 to 3.4V. When I started to charge the second cell the PS died...no output now so I am waiting to hear back from Dr. Meter on how to proceed for a warranty repair.
 

HRTKD

Boondocker
Joined
Apr 24, 2020
Messages
7,688
Location
Somewhere South of Denver
I connected my 10A bench charger to a single cell and was going to bring them all up to 3.5 and then put them in parallel to top balance. After having the PS connected to the first cell for 2 days, it only went from 3.3 to 3.4V. When I started to charge the second cell the PS died...no output now so I am waiting to hear back from Dr. Meter on how to proceed for a warranty repair.

Sorry to hear your power supply died. It seems that the failure rate of power supplies is fairly high, like more than 5%. But we tend to hear only about the failures, so it's hard to tell.

The charge rate improves if you ditch the leads that came with the power supply. Make your own out of heavier gauge wire and use ring terminals instead of the alligator clips.
 

Stepandwolf

Solar Addict
Joined
Nov 14, 2020
Messages
620
Sorry to hear your power supply died. It seems that the failure rate of power supplies is fairly high, like more than 5%. But we tend to hear only about the failures, so it's hard to tell.

The charge rate improves if you ditch the leads that came with the power supply. Make your own out of heavier gauge wire and use ring terminals instead of the alligator clips.
I have since seen the heavier wire tip, but even the wimpy factory leads should have charged more than .1V in 2 days considering it is just once cell.
 

Gazoo

Dumb Dumb
Joined
May 12, 2020
Messages
2,794
Location
Texas
I connected my 10A bench charger to a single cell and was going to bring them all up to 3.5 and then put them in parallel to top balance. After having the PS connected to the first cell for 2 days, it only went from 3.3 to 3.4V. When I started to charge the second cell the PS died...no output now so I am waiting to hear back from Dr. Meter on how to proceed for a warranty repair.
You are not the only one who had a bad experience with that power supply.
 

Sanwizard

Photon Sorcerer
Joined
Feb 2, 2021
Messages
1,705
I connected my 10A bench charger to a single cell and was going to bring them all up to 3.5 and then put them in parallel to top balance. After having the PS connected to the first cell for 2 days, it only went from 3.3 to 3.4V. When I started to charge the second cell the PS died...no output now so I am waiting to hear back from Dr. Meter on how to proceed for a warranty repair.
After sitting for days charging cells in parallel, I bought an expertpower 12V 20 amp charger from Amazon, together with a battgo monitor. Hooked up 4 cells at a time in series, and brought them to 3.6V.
Then back to parallel to top off.
The battgo is needed, unless you have a 12V BMS.
 
Top