Custom Battery Charger HELP and questions from a noob

[jeremy85]

Hi Guys. I'm quite new at this stuff. I've read a lot and learned alot.

My current bike has a custom shaped 48 volt samsung 18650 battery pack with 192 individual cells that I made myself.
This is the third and largest pack I've made for my bike. It's big so I have lots of range on a single charge.

But now MY PROBLEM IS CHARGING.
I've been useing 2 imax b6 24 volt chargers and charge my 1 48v pack in 2 separate 24v packs.
Buutttttt, for whatever reason, the imax b6 will not put out more than 2.1 amps during charging. (any idea why?)
Now that my pack has a lot of capacity, it takes about 12 hours to charge from empty till full, which i would like to quicken up a bit if possible?????

I'm looking for a 48volt charger or bms that is simple to adapt to charge my battery.
I'm also looking for the cheapest option without it being junk.
Something like this maybe http://www.amazon.com/dp/B00VB2BXGG
but under $100???

Thank you in advance for your help!! =]

 

[Jon NCal]

The imax b6 can charge at a maximum of 50W, ie 24x2.1=~50W.

You can order a "custom" Kingpan charger to charge to your desired voltage. For example 12S x 4.2V = 50.4V. Some of the common aluminum shell chargers have a potentiometer inside that you can adjust the output voltage to your desired level.

There are also hobby R/C chargers that can do 12S.

 

[MrDude_1]

keep the RC chargers for balancing, but do most of the charging with a single bulk charger.
and with lithium, a bulk charger is just a CC/CV power supply.

So the endgame for you, would be a simple cheap power supply.

But first, you need to understand how everything works, how to set it up, the risks... you need to know exactly what you're doing.
However once you know, no one can take that away from you, and a world of easy charging and EV understanding awaits.

I would start by looking at the meanwell power supply thread on here...

 

[jeremy85]

keep the RC chargers for balancing, but do most of the charging with a single bulk charger.
and with lithium, a bulk charger is just a CC/CV power supply.

So the endgame for you, would be a simple cheap power supply.

But first, you need to understand how everything works, how to set it up, the risks... you need to know exactly what you're doing.
However once you know, no one can take that away from you, and a world of easy charging and EV understanding awaits.

I would start by looking at the meanwell power supply thread on here...

Is there a specific thread you are talking about? I've read a few.

So I could use something like this? http://www.ebay.com/itm/Adjustable-Power-Supply-60V-5A-110V-Precision-Variable-DC-Digital-Lab-w-clip-/262142645425?hash=item3d08eb54b1:g:qUsAAOSwMTZWRY2g
Set the voltage to 50.4 volts, and the current will automatically taper off as the battery nears full?

 

[dogman dan]

Just get a good bulk charger, which can be fine tuned to the voltage you desire.

My favorite charger in the house, of about a dozen, came from EM3ev. This one is for 14s, but you can turn it down for 13s. http://em3ev.com/store/index.php?route=product/product&path=35_37&product_id=120

Next fave, the ol kingpan type, because it's also easily adjusted for both voltage and amps.

But if you have the bucks, the satiator is a GREAT CHARGER! Definitely worth the money for a permanent, mounted on the vehicle charger. I want one, but too much for me at this time.

 

[MrDude_1]

So I could use something like this? http://www.ebay.com/itm/Adjustable-Power-Supply-60V-5A-110V-Precision-Variable-DC-Digital-Lab-w-clip-/262142645425?hash=item3d08eb54b1:g:qUsAAOSwMTZWRY2g
Set the voltage to 50.4 volts, and the current will automatically taper off as the battery nears full?

That power supply is limited to 5A. I dont know anything about your pack, but I would call that too small for myself.

What size is your pack, and what C rate are your batteries rated for? Knowing this, you can figure out the size charger you need for the fastest charging rate... and then you can step it down a tad if you like.


As far as the taper goes, its pretty simple.

if you connect full power from the power supply to the battery, it will try to make the battery reach its voltage level...
if the PS and the battery were the same voltage, no power would flow.
if the battery is a little lower than the PS, a small current would flow, raising the battery to the PS level.

however if the battery voltage is much lower than the PS voltage, it would take alot of current to raise it to the level of the power supply.
if the current goes higher than the current limit, it cuts voltage down until it is below the limit.... the voltage is low, but as the battery charges, the voltage rises.
eventually the battery, with that current flowing into it, reaches power supplies set voltage. its not fully charged yet, but its voltage, plus that current is the PS max... so the voltage stays the same...
but the current starts dropping... once it drops to a very low level, the battery is fully charged.

I dont have one specific thread, but a search on here about the meanwells, or bulk charging will get you the info you need. There is plenty of info on just this site to get you started.

 

[jeremy85]

That power supply is limited to 5A. I dont know anything about your pack, but I would call that too small for myself.

What size is your pack, and what C rate are your batteries rated for? Knowing this, you can figure out the size charger you need for the fastest charging rate... and then you can step it down a tad if you like.

It has 16 18650s per cell, 12 cells in series. 192 total for 48 volts. C rating? no clue. THIS IS WHERE I REALLY STRUGGLE. I also don't know the true ah of my battery. or amp output at all.
I just soldered it all together(carefully) and went riding! B)
How can I calculate these things?

As far as the taper goes, its pretty simple.

if you connect full power from the power supply to the battery, it will try to make the battery reach its voltage level...
if the PS and the battery were the same voltage, no power would flow.
if the battery is a little lower than the PS, a small current would flow, raising the battery to the PS level.

however if the battery voltage is much lower than the PS voltage, it would take alot of current to raise it to the level of the power supply.
if the current goes higher than the current limit, it cuts voltage down until it is below the limit.... the voltage is low, but as the battery charges, the voltage rises.
eventually the battery, with that current flowing into it, reaches power supplies set voltage. its not fully charged yet, but its voltage, plus that current is the PS max... so the voltage stays the same...
but the current starts dropping... once it drops to a very low level, the battery is fully charged.

This was pretty much how I understood it. I just like to hear someone tell me I'm correct. =]

I dont have one specific thread, but a search on here about the meanwells, or bulk charging will get you the info you need. There is plenty of info on just this site to get you started.

Yes, there is plenty of info. But man is it overwhelming. At least to me. I've been on here for 2 years, just started to post. Read a ton. But sifting thru it all is an undertaking.

Thanks for your help thus far!!!

 

[Jon NCal]

Do the power supplies and meanwell chargers have auto shutoff at the end of the charge cycle when the current gets low, like the RC chargers do?

 

[MrDude_1]

Do the power supplies and meanwell chargers have auto shutoff at the end of the charge cycle when the current gets low, like the RC chargers do?

not by themselves.
some people use simple timers... others just leave them trickling in. You can also make simple shutdown circuits if you like.
assuming you have no BMS and set the voltage correctly, there is nothing wrong leaving it plugged in, but it does waste a little power. It doesnt hurt the battery or anything like that.
If you have a BMS, it can slowly overheat the power resistors, if they are not matched exactly the same. A simple plug timer can fix this... or a fun circuit.

what you're really doing is trading off plug and play for cost and possibly more power.

 

[MrDude_1]

It has 16 18650s per cell, 12 cells in series. 192 total for 48 volts. C rating? no clue. THIS IS WHERE I REALLY STRUGGLE. I also don't know the true ah of my battery. or amp output at all.
I just soldered it all together(carefully) and went riding! B)
How can I calculate these things?

Well first you need to find the spec sheet of your batteries, OR you can just use rules of thumb... its not something that has to be perfectly accurate, but it does have to fit your chemistry.

C is capacity. If your battery is 5 amp hours, then 1C for you would be 5amps. if your battery was 15amp hours, then 1C is 15amps.
.5C would be 2.5 and 7.5amps respectively.....

The larger your battery is, the more you can put into it at once. thats it. once you get the hang of it, its not hard to follow.

Your rule of thumb would be no more than .5C..... this is by my guesstimates, and not to be taken as a golden rule or anything. :lol:
if you have these cells, then .5C would be the way to go according to this randomly googled spec sheet: https://www.powerstream.com/p/INR18650-25R-datasheet.pdf

so.. what is the amp hour rating of your pack? tell me that in amp hours. then divide the number in half. that is your max amp rating to shoot for, but not go over.

Yes, there is plenty of info. But man is it overwhelming. At least to me. I've been on here for 2 years, just started to post. Read a ton. But sifting thru it all is an undertaking.

Thanks for your help thus far!!!

I know what you mean. I lurked here for years before posting. there was always more stuff to read.

 

[jeremy85]

My batteries say the following exactly like this:
IRC18650-28A
SAMSUNG SDI
2 2E72

I do know each battery is 2800mAh 20.7Wh

From what I've gathered around the web(may be incorrect) they:
Will put out about 5 amps...
Should be charged to 4.3 volts... (is this weird?)(I still never have gone over about 4.15v)
And ICR's use unstable chemistry that vent very violently and explosively. Haha!

So I understand my total pack has 44.8Ah. And 331.2Wh. Right?
But what is this "C"? 22 amps? And total available amps?

Currently I have a 48v 13amp rated controller, 26amp peak. If it matters for calculating..

 

[jeremy85]

Your controller is well suited to your pack.

C has already been answered at least twice. Here is another though. If you have a 20Ah pack it should put out 20A of current for one hour (Ah is amp-hour). With a 20Ah pack, 1C is 20A and might last 1 hour. 0.5C is 10A and might last 2 hours, 2C is 40A and might last 30 minutes.

So your 12S16P pack is 16x2.8Ah= 44.8Ah as you said. At one C your pack can give 44.8A for one hour. If your controller peaks at 26A, your pack is seeing 26/44.8=0.58C peak. Great usage rate of those high capacity cells- they will live longer that way. You can also charge them to 4.2 or 4.15 and sacrifice a little capacity while gaining a lot of longevity.

For wh, your cells should be roughly 3.7Vx2.8Ah= 10.4wh. if you have 192 cells, you have nearly 1996wh, so ~2kwh.
The math is similar if you look at the pack as a whole. i.e. a 48V20Ah pack is ~48Vx20Ah= 960wh.

This link tests them well but appears they might be a little less than 2800mAh: http://lygte-info.dk/review/batteries2012/Samsung%20ICR18650-28A%202800mAh%20(Purple)%20UK.html

Thank you thank you thank you!! This is all very clear to me now. So I could reasonable charge this pack with a 20 amp charger and still be charging at less than .5C
In the future, I could also get a higher amp controller. Say 20 amps, with a 40 amp peak. I would gain acceleration, speed would be the same, and my motor would get hotter and might be smoked out if abused too much, like off road low speed full throttle when it's pulling peak amps.