proper charging methodology for series connection

[ThinkFab]

Hi there, I want to build a battery that is comprised of two 24v batteries run in series most of the time to get a 52v pack for my bike, but sometimes change to a 24v parallel configuration to run my 24v inverters. the question I have is this.

Can I charge both of the 24v packs while in series connection with a 52v charger, or would I need to run two 24v chargers separately to charge the battery? I am about to purchase two 24v 60a BMS's to start the build, but since I only have36v, 48v, and 52v chargers, I want to know if I will need to purchase 24v chargers as well to charge everything up properly.

Is there a specific type of BMS I should buy in order to charge two 24v packs in series? I am planning on purchasing a common discharge/charge port BMS.

thanks for your help ES team!

 

[john61ct]

First off, specify your cell count, voltage is vague and 24+24 does not = 52

When the two sub-packs are connected in series, that **is** a single 52V pack and can / should be charged as such.

Obviously when the two are paralleled, you charge as a 24V pack.

Satiator model# 4808 "24V-52V" output range 24-63V @8A (manual states 12-63V) would be excellent, one charger for bulk charging either setup.

Or charge as 52V with your existing rig, then (carefully!) change the configuration for parallel use once charged

I would keep the balance leads accessible from the outside so BMS can easily be removed/replaced / reconfigured as needed,

this lets you test different models / configurations without those decisions olding up the project

and you definitely want to regularly verify / calibrate voltage accuracy with known-good instruments.

I would ensure proper safe charging is well handled by the chargers, if the protective BMS is hooked up as well, that is just a failsafe backup for if/when the charger fails. A standalone HVC cutoff can do the same job.

Balancing gear better than what you get from cheap BMS may be needed as the pack ages.

PS parts comprise the whole, the whole is composed of parts

 

[ThinkFab]

7s 24v, so in series, 14s 52v. maybe I should simplify. is it safe and common practice to charge 2 7s series packs making 52v, with a 52v charger, or do I need to separate the packs and charge them with 24v chargers?

will the BMS's be able to handle that without something going wrong?

 

[john61ct]

Again, 2x 7S sub-packs in series **is** a 14S pack, nominal "52V" actual 50.4-51.8V, em3ev calls it a "50V"

Charges at 56-58.8V.

Obviously a higher voltage is "less safe" than 24V, but just be more careful.

You do not "need" to charge them as 24V, but as I stated, you can if you want to, just divide above actual voltage ranges by two.

The ability to easily switch from a 14S BMS to a 7S model would be the straightforward solution if you really felt you need BMS functionality forboth use cases.

 

[ThinkFab]

okay, thank you. I still have one question unanswered. I hope I am not frustrating you, but it isn't clear to me.

is it safe and common practice to charge 2 7s series packs making 52v, with a 52v charger?

thank you for the help. I am sure this is a noob question, but this is the first time I have tried to series a couple of packs like this.

 

[john61ct]

By stating **there is no difference** between a 14S battery and 2x 7S batteries connected in series

I thought I made it clear, that even if you were the first person on planet Earth to "try" it, there is no problem inherent in doing so.

I also addressed the safety part, which is just a subjective value judgment, in multiple ways.

Of course, most "normal" people would say that no amount of messing about with these dangerous LI chemistry batteries could ever be called "safe".

But it is, if you know what you are doing and take the proper precautions.

Those that don't (yet) can educate themselves by reading past threads and asking specific questions that have more objective answers.

Where there is disagreement, then it is up to you to figure out which members are more knowledgeable than others, or if there are just different ways of looking at things.

I really don't know how else to answer further at this point. Maybe others could (please) chime in with their opinions?

 

[ZeroEm]

Knowledge is safety!
Gasoline at one time had a high flash point, spark 20ft away or more could set it off. It's still not safe to smoke while filling your tank.
Power outlets in you wall are not safe. Power lines are not safe.
Tires are not safe mostly big truck tires.

Batteries "DC" is not safe, but below 60V is safer because it has a hard time going thru dry skin. Above that, treat it as high voltage.
Learn as much as you can about what you are working with.

 

[ThinkFab]

great, thank John. I will order parts for the 7s setup and get to work building this new battery. much appreciated.

 

[999zip999]

What 7s . 7s recycle computer batteries 7s Samsung 40t ? What's this for ?

 

[999zip999]

Plus put on proper dial in between just so you could feel better.