Building lipo Pack Question

Simonvtr

100 W
Joined
Sep 23, 2015
Messages
217
Location
USA, Harrisburg PA
Hi ES members.

Please don't be mad at me if this info is already been posted somewhere on this forum.
I've been reading a lot up on battery and how to run them in series and parallel.
I have a trike I am working on.
My hub motor is a mxus 6t on a 17" moped rim.
My controller is a 12fet.
I will have a CAv3 installed with this setup.

So 1st question is about volt vs amp.
I used to run pro 4wd rc.
My understanding back then was higher amp gives you more run time while high voltage makes you go faster.
But with my trike build what will be more better?
Running 48volt with a combine amp of 20ah or 72volt 10ah.
Which of the 2 will give me more run time.
I know speed will be a question so if all being equal 25mph which of the 2 packs will give me a longer run time and which of the 2 will be easier to maintain.

2nd question is about lipo pack configuration.
My current battery I have are 8x 6s lipo 5000mah.
I've seen people first parallel a pack then put them into series.
example they would take 3x 6s 5000mah and tape them in parallel which would give them 6s 15000mah pack.
Then they will twist all the balancing wires together from each pack. so pack1, pack2 and pack3 1st pin are all twisted together etc... which will give me a single balancing connector for a 3p battery pack.
How does that help with balancing?
Like if pack1 cell-1 is 4.1, pack2 cell-1 is 4.0 and pack3 cell-1 is 4.04 how does the balance charge the set of cells?
What is the benefit of having them setup in pack of 3p before making them serial to get the voltage you want?

Thank you for your time.
Simon
 
1. You've got amps (A) and amp hours (AH) confused. A is a current amount, while AH is a capacity amount. And AH capacity is relative to voltage. When measuring capacity of different voltage packs, you need to find the watt hours (wh) of each and compare them. A 20ah 48V pack has (20x48) 960wh, and a 10ah 72v pack has 720wh. So at the same speed, the 48v pack will have more rang, while the 72V pack ill have the highest top speed. With the same charging method maintenance will be about the same.

2. Parallel first or series first really doesn't matter as long as all packs are balanced to about the same voltage. All paralleled cells will always have the same voltage, so your last scenario is impossible. if one drops to 4.001V, they all do. The only exception to this would be if you pulled a massive amperage from one string that the paralleled leads were to small to handle, but I doubt you'll ever see that scenario.
Lots of info here.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=39666
 
where has he mixed up Ah and A?
the question was "Running 48volt with a combine amp of 20ah or 72volt 10ah.
Which of the 2 will give me more run time."
and as you said: there is a clear answer. the first one as it's 960Wh versus 720Wh.
and i prefer parallel first and series after. makes balancing much easier.
 
After reading some more I am going to parallel 4 packs of 6s 5000mah which would give me 24volts 20000mah.
I will make 2 of these packs and join them serially giving me 48volt 20000mah = 960 wh I think.

Question now is how should I charge them.
I have a imax b6ac charger
14volt 10amp powersuplly = 140wh?

When I charge each parallel pack 24v 20000mah my charger never goes above 3.5amp even when I have it set to the max 6amp.
Is there a reason for this?

I've read other post where people have used a powersupply to charge the lipo without a charger and have a lipo medic to even out the cells.
Is this a better/faster way to charge without spending a lot of money?

I just bought the imax a few months ago and I don't want to go and buy another charger.
What would be the best way to charge my lipo setup?
If I did parallel charge the 2 packs it will still take double the time @ 24v 40000mah.

Thanks
Simon
 
Another question is how low can i drain the pack.
I've read people say 3.5v each cell, some say 3.7v and other have said as low as 3.0v.

If my pack of 12s4p turnigy lipo = 49v 20amp hot off the charger
@ 3.7 I can drain a fresh pack to 44v
@ 3.5 drain down to 42v
@ 3.0 down to 36v

I would love to drain it from 49v to 36v which would give me more run time but is it safe?
What would be safe?

Thanks
Simon
 
3.0v under load is SAFE. but not advised. the lower you go from around 3.65V the more unbalanced the pack will be. and if you don't monitor each cell carefully some cells will be below 3.0V once your pack's voltage is 36V.
so i personally avoid going under 3.6V, maybe 3.5V under load maximum.
and if you look at discharge graphs you will notice that there is only very little capacity left below 3.5V.
 
Generally speaking, higher LVC (low voltage cutoff) values you employ, the better.

The problem with applying V/cell thinking in a series string is that unless you’re using something to monitor Voltage of each cell you cannot just assume all cell’s reach empty at the same time when measured by overall pack voltage.

Take a look at this golden oldie discharge graph:
1-8DischargeZend.jpg
As you see, one cell reaches 2.8V which is the protection cutoff of the BMS used. Trouble is, some cells are still around 3.5V. Few more in the lower 3’s but meanwhile a couple are hitting 2.8V.

Applying RC Lipo averages to a 12S pack with a controller LVC of 36V, it should be obvious some cells will drop well below 3V long before the overall pack voltage ever reaches 36V.

So, advice kinda depends. If you’re running naked without an active BMS or some form of cell voltage alarms, you should stick to resting voltages of around 3.6-3.7V/cell.

If you’re lucky, that should keep you out of trouble.
 
A 12s4p pack of 5000mah 6s packs is 888wh. You really don't want lvc on the controller below 3.3V per cell, or 39-40V. I consider 3.5V per cell or 42V ideal if you want to make sure you don't over discharge.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=47294
You can do a parallel charge of all 6s packs with your 6s charger, but it's going to take ~18 hours to fully charge an 888wh pack to 50.4V. which is the fully charged voltage of a 12s pack. The imax b6 is only a 50W charger. If you don't want to use a bms, then you can cut that in half with another b6 charger, or get a 300W 12s charger and charge the whole pack in ~3 hours.
 
wesnewell said:
A 12s4p pack of 5000mah 6s packs is 888wh. You really don't want lvc on the controller below 3.3V per cell, or 39-40V. I consider 3.5V per cell or 42V ideal if you want to make sure you don't over discharge.
https://endless-sphere.com/forums/viewtopic.php?f=14&t=47294
You can do a parallel charge of all 6s packs with your 6s charger, but it's going to take ~18 hours to fully charge an 888wh pack to 50.4V. which is the fully charged voltage of a 12s pack. The imax b6 is only a 50W charger. If you don't want to use a bms, then you can cut that in half with another b6 charger, or get a 300W 12s charger and charge the whole pack in ~3 hours.


OH WOW!

That is crazy I guess I need to get myself a more powerful charger.
Thank you for pointing that out to me Wes.

Thanks IZ and Yk for all your input as well.

I will be installing a HK low voltage buzzer on each of the parallel back and will be setting it to 3.6.

Thanks
Simon
 
.
.
I am having issues with the 6s4p lipo hk pack I build. I balance charged them yesterday took me all day to charge them with my b6 charger 25v 20amp.
I let the pack sit over night and checked the balance this morning and here is what I got.
Here is the pack

4ab58e0c16.jpg



c9f162b043.jpg


If I am reading this right so top left is cell 1? and bottom right is cell 6?
This morning after sitting for 12hrs cell 6 was at 4.22v.
ES member wesnewell said this couldn't happen.
I tested the balance again with my HK buzzer.

Reading from left to right. All Cell 1-6
5340260764.jpg
1289962804.jpg
42c9c091f8.jpg
7f3f21bf55.jpg

85662bc6d0.jpg
d2c632dcf0.jpg
5de759bc07.jpg


As you can see cell 4 on my charger and hk reader is different and also cell 6.
So I took a multi meter to the balance cable.

81a0825d12.jpg


Am I doing this correctly?
So I put negative on pin1 and positive on pin2
then the next set pin2 is used as negative reading and pin3 is positive and so on and so on?

Here is what I got if I assumed I did it correctly
From right to left
C1-6
25245643a2.jpg
1ad6733a42.jpg
dd47defd71.jpg
f876916be9.jpg
aa7b4097fa.jpg
c792a54ec2.jpg


Cell 4 is 4.18 on the meter while the hk lvc is 4.17 and my b6 is 4.20.
Am I doing something wrong?
When I build my balance cable I just took all the colors of the same type and twisted them together and solder/shrink wrap them.
I double checked and none of the colors got crossed.
Unless its internal like inside the pack.
They changed the order of how the assemble the pack and solder the balance leads on.
Or am I overthinking this to much?

Thanks for any advice to help me understand what I can do or if I had done something wrong.
Simon
.
 
I said if you paralleled cells they would always be the same. Those cells aren't paralleled. It's a 6s pack, not a 6p pack. Still, it's not out that far. When they get .10V out, it's time to look at them. .01V is nothing to worry about.
 
Simonvtr said:
Sorry then I don't understand what do you mean by .10 out.
When I look at cell 1 at 4.18 and cell 6 is 4.22 to me that is over .10?

But then again I do not understand why 3 different device reading is so different from each other?

4.22 - 4.18 = .04
 
all fine simon. nothing to worry about.
there is a german saying: "wer misst, misst mist". it means: what every you measure is wrong. it depends on the device you measure with how accurate the measurement is. but it will never be 100% spot on.
so first: your charger is junk. they are not really calibrated and give you wrong readings.
second: those hk beepers are the same. if you buy 5 of them the all show different readings.
third: a good dmm gives best readings. and you get readings all equal within the accuracy of the meter. even with only 1% off a voltage of 4.20V can be 4.16-4.20V.
what wesnewell was saying is, that an overall delta voltage of 0.01V is nothing to worry about. you should worry if they are 0.1V apart. so one cell showing 4.10V and the other 4.20V. everything in the single digit mV area is best you can get.

off topic: last week i bought some grade A 18650 cells. THOSE are amazing. all 6pcs showing EXACTLY the same voltage 3.642V. measured with a fluke dmm.
 
wesnewell said:
I said if you paralleled cells they would always be the same. Those cells aren't paralleled. It's a 6s pack, not a 6p pack. Still, it's not out that far. When they get .10V out, it's time to look at them. .01V is nothing to worry about.

Please accept my apology Wesnewell. I don't know what was going thru my head yesterday but to me I thought it was .14 off >.>.
Thanks for all the help you guys have provided me and showing me my mistake. If it wasn't for you that pack would have been torn apart.

Thanks again
Simon
 
Can anyone recommend a lipo charger that can charge my pack faster then my current charger?
the back is made of 6s 5000mah lipo in 4p configuration x2 to make 48 volts.
I currently have a b6 imax but it takes a very long time to change the pack and it never charge higher then 2.1 amps. even when I have it set to 5amps.
It is running off a 12 rail on a power supply that said it can output 850watts on the rail.

I don't have any knowledge in bms setup so I would rather stick with a regular charger.
I was looking at the Thunder 1220 but they are out of stock.
Same with the Hyperion EOS 1420i they are out of stock.

Any recommendation?

Also who was it on our ES forums that sells converted dell server power supply to charging power supply?

Thanks
 
Get a 300-600W 50.4V charger and a couple of battery medics. If you decide to use a bms later, then you've already got the charger.
 
wesnewell said:
Get a 300-600W 50.4V charger and a couple of battery medics. If you decide to use a bms later, then you've already got the charger.

Yes I have 2 battery medics for each pack, but can you give me a few names so I can do a search. I know I want a 300w+ charger but unable to find any here in the US.
Do I have to go thru aliexpress to find these charger?

Thanks Wes
 
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