Can i series these power supplies?

Thread Starter

Khaleef

Joined Mar 22, 2017
73
Good day AACians

I would like to know if I can connect 2 (12v 32A PS3 power supply) in series to make 24V to charge my 7s100p 18650 Battery powerwall.

I cant afford solar system now so I only depend on the local grid to charge. My inverter only gives 15A current so it takes very long time to charge the 180Ah battery and the FETS gets blown every now and then.

So I wish to support the inverter with the 32A charge.

What do I need to put in place to make this work? Also if possible, if I can make a circuit to boost the 24v to 28.6v which I wish to charge the battery to.

(Ignore the 23A PS in the attached image, I hope to use same 32A PS)
 

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Dodgydave

Joined Jun 22, 2012
8,674
Yes you can connect them in Series to make 24V, provided the outputs are Not Connected to the Earth Terminal, most Atx pc supplies have the Negative lead connected to Earth.

If they are connected to Earth, then remove the link inside from negative to earth, this will allow them to be floating.
 

Papabravo

Joined Feb 24, 2006
12,767
Any time you implement a conversion process from DC to DC, or DC to AC, or AC to DC there is an inefficiency which implies that the power out will always be less than the power in. Put two or three of these processes in series and thing get worse rapidly. There was another recent thread where someone wanted to string three or four conversion process together for some unknown purpose. My advice to you is to define your requirements and acquire the equipment that meets your needs and stop trying to hack a solution out of what you have in front of you. You're just wasting your time and ours.
 

AlbertHall

Joined Jun 4, 2014
9,009
Also put a 32A capable reverse diode across each supply. This will prevent damage to the supplies from reverse voltage in the event of an output short circuit or one supply reaching its current limit.
 

Thread Starter

Khaleef

Joined Mar 22, 2017
73
Yes you can connect them in Series to make 24V, provided the outputs are Not Connected to the Earth Terminal, most Atx pc supplies have the Negative lead connected to Earth.

If they are connected to Earth, then remove the link inside from negative to earth, this will allow them to be floating.
Thanks. The PS supplies I plan to use is from the Playstation 3 unit. The AC connect is just 2pins.

Also there a circuit that can boost the 24v to around 28v at same current?

Also put a 32A capable reverse diode across each supply. This will prevent damage to the supplies from reverse voltage in the event of an output short circuit or one supply reaching its current limit.
Can you please show a diagram how to connect the diodes? Thanks.
 

Tonyr1084

Joined Sep 24, 2015
4,028
Tried googling 7s100p 18650 but couldn't find anything. Since I'm not familiar with this I'm left with questions: Your battery wall - - - is it 24 volts or is it something else and you believe charging at a higher voltage will accomplish a faster charge time?
 

Thread Starter

Khaleef

Joined Mar 22, 2017
73
My read on your supplies is the large one has a 12 volt 32 Amp (MAX) output and the smaller unit 12 volt 23.5 Amp so placing them in series the best I see is 24 Volts @ 23.5 Amps maximum. I don't see 32 amps?

Ron
I stated in my first post to ignore the 23A unit. I am using exact same type of the 32A. The 23A is there because I didn't crop it out before attaching.

Tried googling 7s100p 18650 but couldn't find anything. Since I'm not familiar with this I'm left with questions: Your battery wall - - - is it 24 volts or is it something else and you believe charging at a higher voltage will accomplish a faster charge time?
7s100p is just the arrangement of the 18650 cells. Maybe you should google "18650 Powerwall"

7s100p means 100 cells was connected in parallel and 7 of the (100cells) was connected in series.

100cells (A pack) connected in parallel gives 4.2v 180Ah. Then 7packs connected in series to give 29.4v full charge.
 

Reloadron

Joined Jan 15, 2015
4,883
I stated in my first post to ignore the 23A unit. I am using exact same type of the 32A. The 23A is there because I didn't crop it out before attaching.
So if you have two 12 volt 32 Amp supplies supplies in series on a good day you will have 24 volts 32 amps. It's all in the details. The series current will always be the lesser of the two.

Ron
 

Tonyr1084

Joined Sep 24, 2015
4,028
Thanks for the explanation. So you have a 29 volt system. How do you plan to charge them using a 24 volt charger arrangement?

Just thinking about the arrangement; 100 batteries (18650) in parallel? I suppose each battery has its own Battery Management Board. I lack experience with that many 18650's and am having a hard time wrapping my head around 100 batteries. But then again, like I said, I lack the experience.
 
Are you trying to charge your "powerwall" of many battery cells without using a battery charger designed for Lithium cells?
The Instructable shows seven groups in series of eight 18650 Lithium cells in parallel. Then the fully charged voltage is 7 x 4.2V= 29.4V, not anywhere near the 24V your series power supplies will give and there is no charging current limit so the battery cells might explode. Lithium cells in series are supposed to be charged by a balanced charger so that the group with the best cells do not become over-charged and explode.
 

Tonyr1084

Joined Sep 24, 2015
4,028
This project should be rethought with an eye toward proper equipment. Unless he likes his home/garage really really warm. For a few hours. Good news is that the fire would go out eventually.
 

Thread Starter

Khaleef

Joined Mar 22, 2017
73
Are you trying to charge your "powerwall" of many battery cells without using a battery charger designed for Lithium cells?
The Instructable shows seven groups in series of eight 18650 Lithium cells in parallel. Then the fully charged voltage is 7 x 4.2V= 29.4V, not anywhere near the 24V your series power supplies will give and there is no charging current limit so the battery cells might explode. Lithium cells in series are supposed to be charged by a balanced charger so that the group with the best cells do not become over-charged and explode.
Yes you're rigth about the cell calculations. I am not just starting to learn to build this battery. I have built and been using it since months back. My problem is simple not good charging system yet.

Having 7 packs in series, yes I know each should be monitored to charge correctly, that's why there's a BMS. Yes, I know about that and even though i already have one, i haven't been using it since months back my battery is been in use. Simply because the packs were built properly and voltages are very similar (Attached a voltage display of my 7 packs) and also, i am not charging each pack to the exact full voltage.

Why i asked if the 24v series would work is to be sure I can achieve that series connection with power supplies. I have an inverter which I have set to charge the battery to 28.6V full charge but it charges at just 15A which is very low for the lithium cells.

This project should be rethought with an eye toward proper equipment. Unless he likes his home/garage really really warm. For a few hours. Good news is that the fire would go out eventually.
Dont worry Tony, remember you said earlier you aren't familiar with this 18650 battery thing. I am, I have built it and know when it's going to warm my home or not. ;)
 

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Tonyr1084

Joined Sep 24, 2015
4,028
Yes you're rigth about the cell calculations. I am not just starting to learn to build this battery. I have built and been using it since months back. My problem is simple not good charging system yet.

Having 7 packs in series, yes I know each should be monitored to charge correctly, that's why there's a BMS. Yes, I know about that and even though i already have one, i haven't been using it since months back my battery is been in use. Simply because the packs were built properly and voltages are very similar (Attached a voltage display of my 7 packs) and also, i am not charging each pack to the exact full voltage.

Why i asked if the 24v series would work is to be sure I can achieve that series connection with power supplies. I have an inverter which I have set to charge the battery to 28.6V full charge but it charges at just 15A which is very low for the lithium cells.


Dont worry Tony, remember you said earlier you aren't familiar with this 18650 battery thing. I am, I have built it and know when it's going to warm my home or not. ;)
From your mouth (keypad) to God's ear (monitor).

To be perfectly honest, my impression is 100 parallel batteries times seven of them. In reality what you have are seven batteries in series. These are 3.7 volt batteries. 3.7V x 7 = 25.9 volts. I may not know much about 18650's but I do know that you can't charge a 26 volt battery with a 24 volt charger. Unless I missed something in your statement(s).
 
For an ordinary 18650 lithium battery cell, 3.7V is half the full charge voltage of 4.2V and 3.2V is when the discharge should be disconnected. The average voltage of about 3.83V shown is close to half a full charge.

When a lithium battery has more than one cell in series then it has each cell fully charged to 4.20V with a balanced charger and the balancing prevents the best cell from becoming over-charged.

Cells in parallel must be matched so that the best cell does not hog most of the charging current then explode. Temperature measurements can detect an unbalanced current in a parallel cells pack.
 

Tonyr1084

Joined Sep 24, 2015
4,028
OK, so 4.2 x 7 = 29.4. Suddenly I remember someone saying that. So I reiterate, how do you fully charge 29.4 volt batteries with 24 volts ? ? ? If you've figured that one out then you're a genius and potentially a billionaire.
 
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