Using Lithium Ion Safely in without BMS situation

[numberonebikeslover]

I decided to start a new discussion about using lithium ion batteries in a situation where one could not find BMS. It includes the availability of resources and its efficient use.
After using SLAs for so long I have come to the conclusion with the following points:

EVs lose a lot of electric power dragging those heavy SLAs and lose expensive electric power.
Regenerative breaking is not fruitful in case of these batteries.
In case of climbing a single hill completely deprives the batteries of their charge and there is no more juice to complete the remaining ride. To overcome this problem one needs larger capacity. Larger capacity = more weight which is not good for EVs.
Acceleration and picking power is reduced due to weight.
As per my past experience I quote here: once I fell and was unable to pic my bike so I asked some people to help me pick it up.
To keep the life of the battery longer it needs to be charged at slower charge rate (c/8) rate which takes a long time. Some time we don’t have enough time for that.

For this reason I kept on studying Lithium Ion batteries and come to know the following qualities: (please correct me if you find any thing wrong with my statements)

Light weight
200 watt per Kg
Absorbs any regenerative breaking efficiently
Individual cell voltage are 3.7 therefore little amount of cells are required as compared to NiMh and NiCad.
Can bear higher discharge current rates even more than its capacity (in some types)
Little charging time required.

It has following draw backs.

They need a battery management system (BMS) which is expensive integrated device.
These batteries explode like a firecracker if heated due to over charged or discharged at higher rates than company specifications.
For the cells connected in series cell balancing is also an issue to arise in the absence of BMS.
The battery capacity is equal to the weakest cell in the array in the absence of BMS.

It means that in my situation, in the absence of a BMS a system needs to be developed which could do the following:
Check the battery for over charge
Disconnect the battery while terminals are shortened or discharged higher than company specification.
Cut off the battery while it reaches its limits of low battery (3.2 volt)
Shut off the battery when it heats up some how (due to over charge or during use)

Recently I have found a great source of Li Ion cells in the market for very little price (Rs. 200 = 2.1 USD). These are second hand cells from laptop batteries. They are quite abundant and the sales men said that he can provide about more than 500 cells. I bought one and tomorrow I will start the proper tests but in the mean time I checked it with a 12 volt 100 watt bike head light. The power is amazing almost feels like new I am conducting tests about which I will provide my statistical data later on.

Right now I want to share my ideas how to make a battery bank of 60 volt and a mechanism of using them safely without a BMS. I will also draw diagrams for what I am intending to do in order to take guidance from senior members.

Until next time please feel free to comment and suggest. It will be a great pleasure for me to read what you think about my plan.

With due respect and kind regards
Naeem

 

[Punx0r]

IIRC the main problem with laptop cells is you can only discharge them at 1C max, or they sag badly and become hot.

 

[CanadianWinters]

Recently I have found a great source of Li Ion cells in the market for very little price (Rs. 200 = 2.1 USD). These are second hand cells from laptop batteries. They are quite abundant and the sales men said that he can provide about more than 500 cells. I bought one and tomorrow I will start the proper tests but in the mean time I checked it with a 12 volt 100 watt bike head light. The power is amazing almost feels like new I am conducting tests about which I will provide my statistical data later on.

Right now I want to share my ideas how to make a battery bank of 60 volt and a mechanism of using them safely without a BMS. I will also draw diagrams for what I am intending to do in order to take guidance from senior members.

Until next time please feel free to comment and suggest. It will be a great pleasure for me to read what you think about my plan.

With due respect and kind regards
Naeem

Hi,

I recycled hundreds of cells from laptop batteries. Try to get a lower price on those cells, I paid as low as 1 USD per battery pack (6-9 cells each), and got lots for free. Of course they had to be tested.
Remember that laptop cells can tolerate a discharge of 1C continuous and 2C for a few seconds. They will heat (and get damaged) pretty quickly if you don't stay under those limits.
I am running without bms on my ebike with a 10s12p (36v 24Ah) pack and a bafang 500w rear setup.
If you run without bms have at least some kind of "alarm" or monitoring for LVC on each cell (they are cheap on ebay).

There is already a discussion you may find interesting here:

http://endless-sphere.com/forums/viewtopic.php?f=3&t=26383

I made a video explaining how to recycle those cells with minimal testing equipment:

http://endless-sphere.com/forums/viewtopic.php?f=3&t=26383&start=435#p620698

8)

 

[dnmun]

your assumptions are wrong.

ping sells a cheap BMS, BMS battery sells a cheap BMS. there is no way to build a battery pack of lifepo4 cells without one.

it is not a "weakest" cell. they are all the same capacity, but they have to be balanced and only a BMS can do that.

 

[dogman dan]

Hogwash. (" only a bms can do that")

A single cell charger that shuts off completely when done can balance a pack beautifully. One cell at at time, eventually. But it will be perfectly top balanced.

One good cheap way to get it done a bit better, would be a bottom of the line RC lipo charger. This would charge and balance six cells at a time, allowing you to build your battery in 6s modules. RC chargers have a balancer built into them, so they include the charging part of a bms.

Both methods balance fine without a bms on the pack.

That leaves dicharging. Assuming your pack got balanced, a very conservative depth of discharge could allow monitoring of the pack with one cheap voltmeter. Or, 6s modules could be monitored at that (22v) voltage. 8 modules could be monitored by one fairly inexpensive cellog 8.

This assumes of course, that some of these items can be imported to Pakistan.

The "hard way" would be to build 12v modules and charge them with a cars 12v charger. You'd have to monitor voltage closely, and take off the charger at the right time since a lead charger never completely shuts off. Then to balance, use a light bulb to drain any high cells, and if needed, put on the charger again. Lots of work to do the charging of course.

Lots of people have made ebike batteries out of recycled laptop cells. It's not ideal, you need large capacity to get much amps. But it does work.

If you can do an import from China, a cheap (to us) bms would make things much easier. But not a stock ping bms, since those laptop cells are likely to be lico, not lifepo4

 

[dogman dan]

Now that I'm about done ranting, You go dude. I have to think Dnmun didn't realize who he was talking to. You are an inspiration to many of us "experts" and allways will be. You are very very capable of building and monitoring a homemade battery pack safely!

A few more simple things even I understand. You will put lots of cells into paralell connections to get the capacity you need, to keep the discharge rate where you need it to have a safe battery. Once you do paralell all those cells, they will balance with each other. So the paralell group then acts like one big cell. Only each group needs to be monitored for voltage. So for 60v fully charged, you'd do 14 or 15 groups.

Likely you knew that, but I hope that helps you realise that it's not that complicated to monitor a 60v pack. Three voltmeters, each watching a 20v section would be adequate I bet. Or even just one, if you leave plenty volts in them when you stop.

 

[etriker]

Dnmun says strange stuff a lot.

I am not sure what he thinks a bms is.

It really can be as simple as a B6 charger and some hobby king lipo alarms.

Before I was blessed to have the Hyperion charger I used a B6 charger to test laptop cells for laptop cell ebike pack builds.

That and some packing tape, electrical tape, heat shrink, solder and soldering iron, wire, fuse and fuse holder, xt60 connector and balance leads.

A good meter is nice too.

 

[dogman dan]

Likely he just didn't notice the join date, and was thinking noob. He's the Amberwolf of Pakistan. Big question is, can he get an RC charger in country?

If he can get mail from the USA no problem, I have two 50w RC chargers I'll give him. He can power supply them with his old sla's. Postage would be a bit high, but I'll just ask for a hand with it.

Other stuff can be thrown in the box. I have spare 5s low voltage alarms, and we could buy him two cellog 8's, and a bag of Jst extensions.

Let's set him up with everything he needs. 8)

 

[etriker]

Likely he just didn't notice the join date, and was thinking noob. He's the Amberwolf of Pakistan. Big question is, can he get an RC charger in country?

If he can get mail from the USA no problem, I have two 50w RC chargers I'll give him. He can power supply them with his old sla's. Postage would be a bit high, but I'll just ask for a hand with it.

Other stuff can be thrown in the box. I have spare 5s low voltage alarms, and we could buy him two cellog 8's, and a bag of Jst extensions.

Let's set him up with everything he needs. 8)

Cool, got to find out about shipping.

I have a bunch of connectors. A B6 too for that matter.

 

[dogman dan]

Yeah, I'm just not sure if there are diplomatic reasons we can't mail him stuff. I'm sure he can find out, and if he'll send me the address, I'll get a box of goodies to send him. At most, it would cost him customs duties or something. Free stuff.

 

[numberonebikeslover]

What can I say about you guys?

THANKS FOR GIVING ME SO MUCH LOVE. No doubt; I feel like I have come back home after a long time due to my back problem and some official engagements.

Thanks for the complements, specially, Dogman said Amberwolf of Pakistan. I like that but I think of Amberwolf as my teacher and I respect him so much that I feel a bit disrespectful to call my self Amberwolf of Pakistan. I believe no one can be like him. I have learned so much in this Institution we call ES and for Free.

About the price of these cells the salesmen said that as I buy greater number of cells the price will go down so I hope it is below 1 USD. I would bargain with him.

ES is my family and I respect what ever is suggested to me or said to me. Positive and creative criticism pushes me harder to think of another way around. There is always another way around in science. It is just that we stop striving to discover further. It may not be right in front of us but it is always around. I believe that sky is the limit to discover more ways of doing a number of simple things. Our thinking must be an out of the box type. And that can bring a dramatic change in our lifestyle.

Naeem

 

[The Mighty Volt]

Hi Naeem, I used to look at your videos on youtube, they made me feel very inadequate. Well done.

 

[dogman dan]

Well, who's the best I couldn't say. But like AW, you are really creative, and willing to work at truning a junkpile into an ebike. I know you are up to the task of building your own battery from cells many of us would consider inadequate and a waste of time. You'll do fine provided you can find a cell count that matches your power supplys voltage. You aren't a careless type.

By contrast, I just buy a hubmotor and slap it on a bike. I'm a fair bike mechanic, but that's about it. I haven't used those B6 chargers in nearly two years if you want em.

 

[numberonebikeslover]

Now Back to the topic:
Discharging at one C; hmmm ….. well it is ok because I have checked my e-bike peak amps drawn @ 60 volt as follows:
No load current 1.25 amps
Normal straight road (maximum speed) = 3.6 to 4.8 amps
Uphill (normal) = 6 to 7.3 amps
Tough hill = 7.5 to 8.1 amps
Suppose the motor gets stuck might draw 16 to 20amps I guess. (For this situation I have found a mechanical reversible cut off switch which cuts off at certain amps load would be a great addition)

My office ride is about 13 to 14 km a total of 28 km approximately and hardly a 30 min ride from one side (Unless there is a traffic jam).

I guess a 12 Ah battery having 15 to 16 cells in series (technically speaking 16s5p) would be fine with me having a cut off mechanical switch to prevent the battery from over load and a LVC cutt off for every series of 4 cells at around 2.9 volt per cell (2.9 x 4 = 11.6). Cutting off will be in such manner that any of the 4 cell series reach the 11.6 mark; the entire battery would stop working.

For charging I have already made and tested a LA741 IC circuit with Lead Acid Battery I can adjust it to be used for 4 of these cells to cut off charging at 4.25 volt each cell (for 4 cells 4.25 x 4 = 17 volt).

Moreover, for every 4 cells the charging transformer will be separate so it would make every 4 cell series to be regardless of the remaining pack during charging.

I will attach the diagram and also the picture of the LA741 IC circuit little later which includes the relay on PCB. This circuit works for LVC and HVC both (with little adjustments)

The lithium cell I bought few days back (green in colour) there is no statistical data on it just codes which reads as:
SE US18650GR
T GP11JPG09C A trade mark RJ (R is inverted like it looks in the mirror)

One internet source says it is Sony laptop battery cells with Nominal Capacity 2200mAh Nominal Voltage 3.78V.

Other three that I bought yester day are red in colour and the codes read as:
JAGFH35
069564 This is something that could not find on the internet



One more feature that I would add would be to disconnect the entire battery from the bike while parked and take it to my office desk for charging. (I have learned my bitter lesson last time when school kids messed up everything).

The other feature of the battery would be that all the cells could be taken apart (in minutes through mechanical screw type points holding all the series of 4 together) on week days for checking them for any unbalanced cells in series and manually charging them for balance. How will that happen I am still drawing in my imagination. Just need some calm and spare time for my self to think

Test Result during Charging:
I charged the red cell for 9 hours @ 500mAh it reached 4.17 volts. I stopped as I felt the battery getting hot (about 35 Degree C I guess). Tomorrow I will put this cell to the test after noting down the voltage at rest.

My post is getting a bit lengthy so I will continue the remaining some other time when I find some.

God bless you all.
Naeem

 

[amberwolf]

your assumptions are wrong.

ping sells a cheap BMS, BMS battery sells a cheap BMS. there is no way to build a battery pack of lifepo4 cells without one.

it is not a "weakest" cell. they are all the same capacity, but they have to be balanced and only a BMS can do that.

I am not sure if you fully read his first post.

He's talking about using recycled laptop (and/or other consumer electronics) cells, which are hardly ever LiFePO4. Neither of the BMSs you refer to could be safely used (for LVC, at least) with the cells he proposes to use. Those BMSs would also not allow them to fully charge, as their HVC and balancing circuitry would cut off charging long before they got full.


As an aside: There certainly are many ways to build and charge a battery pack of LiFePO4 cells without a BMS. Or to use yourself as the BMS, to manually monitor the pack and cells, during charge and discharge. Even balancing can be easily done manually. It is just time-consuming.


Regarding balancing, all the "cheap" BMSs simply make the cells all the same voltage, which does not necessarily mean charging them each to the same capacity, depending on the cells' internal condition, age, possible manufacturing flaws and variations, etc. So a BMS does not necessarily even give you the best capacity from a pack, unless it is designed to coulomb-count each cell's charge and discharge, as well as monitor it's LVC and HVC.

A BMS *can* give most people an easy way to balance their packs and monitor them for LVC and HVC without much time spent on it, but it is not required. For many people I think it is a very good idea for them to have some sort of automatic system for these things, as they dont' know enough (or care enough) to do it manually, but it is not an absolute requirement for anyone to have one in order to build a working and useful battery pack.

 

[CanadianWinters]

My office ride is about 13 to 14 km a total of 28 km approximately and hardly a 30 min ride from one side (Unless there is a traffic jam).

I guess a 12 Ah battery having 15 to 16 cells in series (technically speaking 16s5p) would be fine with me having a cut off mechanical switch to prevent the battery from over load and a LVC cutt off for every series of 4 cells at around 2.9 volt per cell (2.9 x 4 = 11.6). Cutting off will be in such manner that any of the 4 cell series reach the 11.6 mark; the entire battery would stop working.

For charging I have already made and tested a LA741 IC circuit with Lead Acid Battery I can adjust it to be used for 4 of these cells to cut off charging at 4.25 volt each cell (for 4 cells 4.25 x 4 = 17 volt).

God bless you all.
Naeem

Hi Naeem,

great ideas and a lots of data. In my experience with li-ion laptop cells is that below 3.4-3.6 Volts the cells holds very little energy so if you discharge them too low (2.9V is too low in my experience, I would go 3.2-3.4v if continuous discharge and 2.7-2.9 for peak during stop & go) you risk damaging the cell (you will notice that they will heat up quickly if "stressed" too much and retain the heat for quite a bit).
Every brand & type of laptop cell has a different charge/discharge curve so, if you can, try to get the same of type/code so that will be easier to monitor them. Personally I will go 16s6p (or more) with your setup but I understand it's not easy to get those cells for cheap where you live.

Keep us posted with your project and tests, it's very interesting.

8)

 

[amberwolf]

The battery capacity is equal to the weakest cell in the array in the absence of BMS.

Even with a BMS this is still true.

It means that in my situation, in the absence of a BMS a system needs to be developed which could do the following:
Check the battery for over charge
Disconnect the battery while terminals are shortened or discharged higher than company specification.
Cut off the battery while it reaches its limits of low battery (3.2 volt)
Shut off the battery when it heats up some how (due to over charge or during use)

Basically what you are proposing *is* a BMS, even if it is not a commercially-produced one. It just isn't a "balancing" BMS, but it is still doing all the monitoring and cutoff functions a BMS would do.


What you are wanting is something essentially identical to Methods' LVC/HVC system, for which there are a few threads around the forum, including in the For Sale section, and they include schematics and discussion of why specific components were chosen. The difference is that his system's cutoff limits are an emergency-cutoff, intended only to prevent fire or battery destruction, not to be used as everyday limits. You can get the parts needed in other voltages, though, so you can build it in just about any variation you want. It is the very simplest of the cutoff systems I am aware of that can actually be built into the battery packs and left there without worrying about them draining the packs just sitting there.


The Fechter/Goodrum BMSes can also be built with different voltage references than those it usually uses (whcih are for LiFePO4, if you want to use one of those designs for your base unit. You can leave out the balancing circuit/resistors if you like, and only use it for LVC / HVC.



One thing you may wish to do is retitle the thread a bit, though: "Lithium Ion" is a generic term that includes many kinds and voltages of battery, and if you are going to be using laptop cells then you are probably going to be using LiCoO2 or Lithium Cobalt Oxide; this is the same chemistry in "RC LiPo" packs (like the blue Turnigy packs in my AmmoCan pack on the Fusin Test Bike), and it can be volatile, as you note.

There are other Lithium Ion types that are less volatile when damaged or overcharged or overdischarged, including the LiFePO4 Dnmun referred to, which uses a different voltage range than the cells you are probably using.


That "RJ" mark you see is actually not a trademark, but rather a certification mark:
http://www.stollerinc.com/scripts/news.cfm?id=6

The RU, with the backwards "R," is what UL calls a Component Recognition Mark. It is used only on components that later will be included in a complete product that will subsequently be tested by UL. Such a recognition limits the use to certain conditions only. Plastics are Recognized Components, as certain uses would be safe and some not safe. The UL Component Recognition Mark, RU, limits the use to what is safe.

 

[amberwolf]

I guess a 12 Ah battery having 15 to 16 cells in series (technically speaking 16s5p) would be fine with me having a cut off mechanical switch to prevent the battery from over load and a LVC cutt off for every series of 4 cells at around 2.9 volt per cell (2.9 x 4 = 11.6). Cutting off will be in such manner that any of the 4 cell series reach the 11.6 mark; the entire battery would stop working.

I think cutting off at more like 3.6V/cell would be safer, though you will get less usable energy from them, by a little bit.

For charging I have already made and tested a LA741 IC circuit with Lead Acid Battery I can adjust it to be used for 4 of these cells to cut off charging at 4.25 volt each cell (for 4 cells 4.25 x 4 = 17 volt).

You would want to cut off below 4.20V on each cell.

I would recommend putting a separate voltage monitor circuit on each group of paralleled cells, rather than on a group of seriesed cells. It is not *required*, but it is a good idea.

I myself do not run my lithium stuff with an LVC other than monitoring the whole pack voltage, and very occasionally checking the individual cell voltages at rest, during charging, and under a heavy load simulating a ride. But I would still recommend cell-level monitoring if it's practical. I do have some of the Methods' boards for doing the LVC/HVC, but they are just for emergency cut-off if things go way too low or way too high, not for everyday knowing-when-to-stop-your-ride.


The lower in votlage you go before LVC, or the higher before HVC, the less times you will be able to charge and use the cell. If you ahve lots of cells, that's not a big deal, but it means having to fairly often start testing many or all the cells in a pack for problems, and replacing individual cells.


There is a good thread by DrkAngel that has lots of information about building packs out fo laptop cells, including various ways of interconnecting them.

 

[docnjoj]

Also kfong has a LVC cutoff switch that is programmable. Certainly worth a look at his thread. I use one for Fatpacks (Sony cells) and it works fine. He has posted schematics fo his device.
otherDoc

 

[numberonebikeslover]

My Dear friends;
I am finding little time to work on my thread therefore it is becoming difficult for me to respond to the valuable suggestions and discussions, for which accept my apology.

Dogman; Thank you very much for your offer but this time I want to make this battery from the parts that I can resource here easily because I want to create a model which could prove beneficial and could be reproduced in how many numbers I want. If I accept your kind gifts, it will take the challenge away from my project and I like challenges. Every one can buy the parts and make I want to make every part my self and then assemble the whole thing together. Though it may not be a high tech product which could compete against a product from an international company but it would work for me.
Moreover, as I mentioned earlier I would use a relay cutoff mechanism through LM741 Circuit that I designed my self and would works just fine for a series of 5P4s cells.
Keeping in mind the high density of LiIon cells, I guess that long before my pack is half empty my ride will be complete.

Etriker: Thanks brother but I have to test my own wings to fly this time and after resting this long I seriously need a challenge. Besides, ES funds are still a very long way to go for my projects. Big thanks to every body that donated those funds for my work. May God bless you all.

There is one more thing I must mention that sending stuff here is way too costly. I tried to import a hubmotor from China which is the nearest country to us but I dropped the idea when I found out about the shipping costs. Total cost of goods was about 160 USD while shipping costs were 213 USD so a total waste of the funds. Some day I will turn my Axial Flux Alternator to a Brushless hub motor of which I am sure. Here is the thread I hope you have seen this one of mine: http://endless-sphere.com/forums/viewtopic.php?f=41&t=33468

The Mighty Volt: Thanks man, what ever I do, I take the time to share the pleasure with every body in world through youtube.

Amberwolf: Sir, it always gives me great pleasure to see your comment or response to my post. It is always full of knowledge and I take serious time to read it with much care, as I learn a great deal. I completely agree with what you said about charging each cell to the same capacity through a BMS is not necessary possible due to the aging factor of the cell and other aspects. My battery may not be a state of the art type but keeping the voltage levels in safe margins, it would definitely work.
Regarding re-titling the thread is a good suggestion how about “Using Laptop batteries safely without BMS Chips?”
About setting the cutting off at 3.6; It might cut off when the motor starts or a little hill climb will temporary bring the battery to 3.6 then after when load is out it will rise back again. What do you think?
About HVC below 4.2: I noticed while charging one of the cells yesterday that when it reached 4.15 it started to generate a little amount of heat. I left it there then at 4.17 the heat increased but very little. So I guess cutting off at 4.1?
Putting a voltage monitor on every parallel unit means 16 units is very difficult and will take some energy to run all those.
I completely agree about stopping further discharge before LVC would require little time for re-charging the pack, so, having bigger capacity would be better solution. I hope the supplier has the number of cells I require.
Spuzzete: Thanks for the correction in LVC 3.2 it is then. And of course I have noticed that every brand and so many aspects are different I would try to have one brand cells. If I could not then I would at least try that every 4 cells series (5p4s) is of the same cells. Thanks for taking interest.

docnjoj: Thanks I will check the thread some time.

 

[dogman dan]

OK, I get it now. You want to be able to do it more than once, not just charge your own pack safely.

The main thing is, it is a more dangerous chemistry, so I don't like to see shortcuts taken with it. Perhaps you can do something homebuilt very much like the methods lvc hvc boards. I see charging as the big danger. Overdischarging is easy enough to avoid with monitoring and conservative stopping point.

16 phone chargers, combined with 16 hvc boards should work well. Even where you are, I bet phone chargers are found in the trash. Not simple, especially if you have to disconnect all your series connections. But that disconnecting could be handled by multiple plugs similar to what Icecube 57 makes. With such a harness, you could also paralell some of the 4v sections to use less lvc boards and chargers during the charge. So then you only need 8 lvc boards or 4 lvc boards, or perhaps, just one as you charge the whole assembly as one huge 1s battery. The set your cutoff to 4.1v for longer cycle life and increased safety.

 

[etriker]

All laptop cells are not the same voltages.

Some are called 3.6v and some 3.7v and such.

Find the factory data sheet to be sure.

You may see in the data sheet the temps may seem warm.

They will get warm in the bottom of my laptop.

If you charge them too fast they will get warm or hot and if you discharge them too fast they will get warm or hot.

Sometimes used cells will get warm or hot when charging because of shorts inside the cell. Watch out for those cells.

The more cells in parallel in your pack the less sag you will have and the cooler the pack will run.

I use simple lipo alarms to alert lvc.

It is easy to adjust.

If you get on the gas and they start to beep set at 3.2 then set them to 3.0v and see if they beep.

If they beep off at 3.0 when you get on it then set them to 2.7v and see if they go off.

If you can get enough cells in parallel so that the alarm does not go off at 3.0v when you get on it then that may be ok depending on how much you like to get on it.

You want a pack that stays cool and doesn't sag too bad when you get on it or go up hills.

When the pack is built I use the Hyperion charger to cycle it and I get to rate the amp hours.

If I rate it at 10ah it really will put out 10 ah.

On rides I use the watts up meter and when the pack has used up about 8 amps hours I know it is time to recharge.

That is the cutoff point for me. Not a voltage.

I cycle and test every cell before it goes in a pack.

http://www.hobbyking.com/hobbyking/store/__18588__Hobbyking_2_8S_Cell_Checker_with_Low_Voltage_Alarm.html

 

[999zip999]

I would build them in three 24v blocks of 15-18ah. 73v. charge, if your motor can handle it. This way if a parelle string goes out you could replace that block and fix it later. This way your put a 6s balance wires on for monitoring. As 6s is common. Plus it will have a BMS and it will be you.
With low c-rate cells you need more AH for headroom and life.
Nice to read from you again. Thanks

 

[numberonebikeslover]

I would build them in three 24v blocks of 15-18ah. 73v. charge, if your motor can handle it. This way if a parelle string goes out you could replace that block and fix it later. This way your put a 6s balance wires on for monitoring. As 6s is common. Plus it will have a BMS and it will be you.
With low c-rate cells you need more AH for headroom and life.
Nice to read from you again. Thanks

thanks man but my motor can't handle more than 60v. I agree with what you said about low C rate cells. Need to have more Ah for sure but that depends on availability of the cells again.
The limit for my LVC and HVC circuit is 4s not more.
thanks again.
Naeem

 

[numberonebikeslover]

Ok. I have found these cell phone chargers called as Desktop chargers for the fact that one needs to take out the battery from the cell phone and fix the battery onto this charger in a clamp where it gets connected with the contacts of the battery. Some LEDs show it is charging by blinking. When the charge is complete the LEDs stop blinking and fully lit. I plugged in one cell and found out that it really works well but it takes the cell to full 4.2 and secondly it gives pulses of voltage going and up and down instead of stable voltage to the cell for charging. Moreover, it took an entire day for a single cell to get charged (approximately 11 hours). For a 5p it might take days to charge them. I opened the charger and found out that it is some chopper type charging unit with some micro chip installed also a transistor and some LEDs. I will post a video later on.

I just did a diagram (self explanatory) tell me would it work having only one side, either A or B charging which both the sides A & B connected all times?

I think I will keep the Desktop chargers as a part of battery with a 220 plug to charge the battery at the office which will also balance the pack, while quick series chargers (4 of them for all 4 series of 5p4s) for home charging. (Total of 5p16S).