How to charge and balance this LiPo pack?

[rg12]

Just ordered my Turnigy 8S 150w 7A charger.

I ordered x6 25.9v (7S) 20c 5000mAh Turnigy's.

Right now i'm going to connect two sets of x3 7S in parallel to get x2 25.9V 15A units
and then connect those two in series to get to a total of 51.8V 15A pack.

The question is how to charge this pack?

First of all, does this balanced charger set the charge current automatically or do i need to
tell it how many amps to charge at?

Also, How do i balance the cells? each 7S unit has a balanced charging plug, so do i need to charge
6 different packs each time?
Or do i need to somehow charge it all at the same time? sounds weird as the balancing process won't exist i guess
and i also don't think i can charge a 51.8V pack with this charger.

Please help,
Thanks
Roy.

 

[pwd]

Hi Roy,

What kind of balance plugs do the 7S packs have? Last time I saw a 7S pack; it had one 3S plug and one 4S plug.

You will need to know what the max charge current of the pack is. It will most likely be listed as a 'C Rate'. I recommend you read up on that first before attempting to charge, it is important to understain what you are doing before charging LiPO.

If it is an 8S charger, you can only charge a maximum of 8S batteries.

 

[dnmun]

if you use a balancing charger it would be best to use the 1420 since it is 14 channels wide.

or you could use a 14S lipo BMS and bulk charge to 58.8V with a lifepo4 charger.

i used the Bestechpower D126 14S lipo BMS on mine. but it has a limit of about 22A, like most controllers.

cost was about $20 for the BMS and $25 for the charger.

 

[rg12]

The charge rate is 5 (C)

I already ordered the 8S charger, so a new charger isn't relevant for me.

This is what i ordered, i accidentally wrote a different model with very similar specs
https://www.hobbyking.com/hobbyking/store/__41316__ZIPPY_Compact_5000mAh_7S_25C_Lipo_Pack_EU_warehouse_.html
Its a 25c Zippy and not a 20c Turnigy.

It looks like the balance plugs are 3+4 like you mentioned.

 

[rg12]

bump...

 

[wesnewell]

Well since you've already bought this stuff, which I would not have recommended btw, you'll need to make or buy if you can find them, some balance adapters cables that will turn the 3s and 4s balance plugs on each pack into a single 7s balance plug. One way to do this is the buy 2 7s plugs, 2 6x 3s parallel balance cables, and 2 6x 4s parallel balance cables. now starting one 7s bank, parallel the 3s plugs together and then the 4s plugs together, giving you just one 3s and one 4s plug. Now do the same thing for the other 7s bank. That should leave you with a 3s and 4s plug on each 7s bank. Now unplug all the batteries and then adapt the 3s and 4s plugs to either a 3s+4s to 7s cable adapter you bought or cut one each 3s and 4s receptacle and use them to make the the 7s plug using one you bought. once you've done this for both banks, you can then balance charge each bank as a single 7s battery. A little more complicated than you expected I assume.
They also make adapter boards you could plug the 2 plugs into and do a balance charge that way. But having 2 balance cables per battery really makers it a pita. I'd probably carefully cut the 2 balance plugs off one wire at a time and replace them with a real 7s balance plug. There's really not a good option with what you bought. That's probably why you won't get many responses.

 

[dnmun]

yep, bad screw up. if you don't wanna use the right charger then you should go to 16S for the pack so you can use that 8S charger and then rewire the packs with 9 pin plugs on each 8S section. the ground of the upper 9 pin plug will overlap the channel 8 of the lower 8S section. this is gonna turn out bad imo.

you can find the 9 pin plugs on ebay and then you can use the 8S cellog on the 9 pin plugs.

 

[dogman dan]

I would say his next charger might be a 14s one. Or he could just bulk charge with a kingpan type charger. But right now he's got a bargain 8s charger. So let's help him with that

First of all, you won't need to balance that pack every single ride.

Second, that 150w charger will never be able to charge even a 5000 mha pack too fast. So forget about that issue.

To charge the whole pack without balancing it, you will need to parallel the two 7s sections into one huge 7s pack. Just the main wires. Then select regular charge on the menu. It will take awhile, on 150w.

Remaining, how to balance the whole pack? Is the whole pack actually out of balance? I bet it's not. Once in a while, as actually needed, separate out the pack that actually needs balancing, and run a balance charge on just that pack.

Personally, I never put a whole pack on balance anymore. I charge 1s through the balance plug as needed, or discharge one cell that's way high with a 12v car light bulb.

If you wish to charge to 4.1v, select the lilo setting rather than the lipo. It's a bit hard to find that on that charger. (I have two of them)

You will need some kind of balance wire adapter to use the balancing function, if the packs don't come with a 7s plug.

 

[rg12]

Thanks alot guys for the help!

If i connect two let's say 7s packs in parallel, how will the charger balance each cell individually inside each pack?
The charger can only balance 7 cells at the same time, so how can it balance two 7s packs at the same time?

I thought everyone charge with a balancer each charge...How often then should i balance?
Do most people use the balance chargers just for balancing and also use a powerful simple charger for most charges or
do they charge each time with the balancer?
I have seen people combine a big DC charger with a balancer together...what is that about?

Few Q's since you guys are so helpful:
How long approximately will it take to charge the two 7s sections on a regular charge with my 150w 7A charger? the two 7s in series are 30A!

Does it matter how fast you charge your battery if im concerned about battery life ?

Why do some people buy a low voltage alarm to connect to the balance plug? I thought the controller takes care of that...

Why do people use the discharge option in their charger?


Hope i didn't kill you with all my questions, im a newbie but im learning fast.
Thanks again,
Roy.

 

[dogman dan]

First of all, if you have a pack with a cell that needs balancing every cycle, GET RID OF IT. Like the one you mentioned, it's unfortunately pretty normal to have to toss up to 10% of RC packs.

Once you sort to all good ones, they will stay remarkably well balanced if you are not hammering them too hard. Try to carry enough to not need to 100% discharge often, and carry enough to not have lots of sag under load. Personally, I tend to balance only about once every 3 months.

Some people just love to fuss, and balance and fret over .01v off. I worry only if a cell is more than .05v off, and may only keep an eye on it till it's close to .1v off. Since I don't charge to 4.2v, I have more headroom for a high cell. I will put the discharge on the high cell if it's going over 4.25v.

I DO check voltages often. I just don't see cells that need balancing often. Nothing wrong with running a balance charge every cycle, other than it takes time and is inconvenient. Since you need to monitor cheap RC lico while it charges, I don't like waiting an extra few hours for a balance charge I don't really need. Investing in a faster 14s charger will of course make balncing easy. I only have the same thing you have, so balance charging a huge pile of lico is a pain in the ass with the little charger. That's why I just find the ONE cell that needs it, and attack it manually.

To make your whole pack balance at one time with an 8s charger, you will need to make parallel adapters for both the main wires and the balance wires. So you have the whole thing connected into 7s.

Then it will take a LONG time to balance it. You will have to reset the time out on the charger for sure. 30 ah x 25v is 750 watt hours. 5 hours to charge at 150wh per hour. But it will slow at the end, adding about an hour. Balancing could take another three hours. MUCH faster to separate out one pack that actually needs a balance, and run balance charge on that pack all by itself.

You are no where near charging too fast for a 750wh pack.

The controller may shut off the pack before the whole pack gets too low, but one cell may already be too low. (but not going to happen if you sorted your cells)

A low voltage alarm, of the right type, can warn you when just one cell gets too low. I rarely use mine, but when I am on a very long ride that I know will very deeply discharge my pack, I will put an alarms on the pack so I can run it down to the very end. 99% of the time, I stop sooner and have no need for alarms. I just watch my CA, and don't let my 14s pack get below 48v.

 

[rg12]

Thank you again for the detailed response!

What did you mean about 750w pack? It will be a 51.8V 15A pack when connected so that means i have 777w pack, that i get.
But, would i have problems powering my 2000w motor with my 48V 40A controller? the LiPo's are 25C.
At which watt draw will they start to sag if for example i had a very big controller like 80A?
I'm concerned because i did this lipo order after i thought i could get away with 18650 cells for a 2000w motor. :lol:

Roy.

 

[wesnewell]

Hope i didn't kill you with all my questions, im a newbie but im learning fast.
Roy.

I'll try and answer these one at a time.
Anytime you parallel cells, they equalize voltage in effect becoming a single cell. If you charge one, you charge both. So if you parallel at cell level 2 or more 7s packs, then it like one bigger 7s pack. So if you parallel all your 7s packs you charge them all at once as one big 7s battery. See this post where I parallel charge 6 6s packs at once.
http://endless-sphere.com/forums/viewtopic.php?f=14&t=39666

I balance charge mine every charge, even if I use external balancers, like battery medics. I don't recommend bulk charging at all, but it can be safe if you know the condition of your pack and don't overcharge. How lucky do you feel?

To determine approximately how long a charge will take, divide total WH of the pack by the watt rating of the charger. A 5ah 7s pack is 129.5wh, so about 1 hour per 5ah 7s pack with a 150W charger.

Typical recommended charge rate for rc lipo is a 1C charge. For a 5ah pack that would be 5A. Your charge won't do much more than that on a 7s pack.

Controller lvc only monitors total pack voltage. The cell alarms monitor each cell. To me, they aren't needed and I've never used one, but some may like the extra safety. Too much hassle to put them on and remove them for every ride. Don't leave then on if you use them. They use power from the battery.

You might use the discharge option to test your battery or make charts or whatever else you can think of.

 

[rg12]

Thanks alot again for the great responses.

So my last question is about the sagging thing.
With a 25C 15Ah 51.8V pack and lets say i have a big a$$ controller with 100A, how big a motor can i run without sagging?
Right now this pack is going to power a 2000w hub motor.
I just wanna know my limits.

Thanks again,
Roy.

 

[wesnewell]

You can't run a motor, even a little one, without some sagging, even if it's just a little. With 25C lipo the sagging will be a lot less than with say 2C lifepo4, or sla, or about any other battery. Don't worry about it. BTW, the battery pack doesn't power the hub motor, the controller does. The battery pack powers the controller. The hub motor behind the controller doesn't matter one bit as far as the battery pack is concerned.

 

[dogman dan]

I should have said, sagging a lot. By that I mean, sagging 4v or more under load. If that's happening, regardless of the controller amps, you need more battery, or the battery had gained a lot of internal resistance.

Your setup, when new, could theoretically run at hundreds of amps, so you can expect only a volt or two of sag under the load, depending on the load. A slow cruise will have sag almost too low to measure, but leaving a stop sign, you should see something on your voltmeter. When it starts to sag a lot, you will know it's time to save up for new packs.

I find that even 30c packs perform a lot better if not asked to pull more than 5 c. Your setup should pull just over 3c max. So you have a good size pack for your controller.

Get a voltmeter on the bike, First choice a cycleanalyst, second, a blue ebay wattmeter, third, just a volts readout for 3 bucks.

You will want to get a better (faster) charger. A second one like your first is one option, giving you 300w to charge in 3 hours if you stopped early. Wes is correct that bulk charging is dangerous. But your RC charger has several bulk charging settings. Use them to charge in a place you'd build a fire. In my case, I charge in my fireplace. You can't plug in lipo chargers and go to bed, so you need to charge faster so you can go do other things.

But the MAIN thing you can do to charge safe, is get rid of shitty packs. Good packs stay balanced, and don't overcharge. ALSO, don't continue to use packs with damage. Big dings, crushed corners, and for god sake, not leaking. Don't carry the battery unprotected!!! Keep it undamaged.

 

[rg12]

What do you mean by bulk charging? bulk balancing?
or just connecting the two 7s packs in series to charge a 25.9v 30a pack?

 

[BikeFanatic]

On your RC charger there are several charge modes.
One is called Lipo charge another is called Lipo balance and another is called Lipo fast charge.
Any mode where you do not have to connect the balance wires will work for bulk charging.
For example on my rc charger I select" Lipo charge"
Mode, hook up the red and black main battery wires only, then charge that way. My charger see the battery as one big Battery, not a bunch of cells in series. I have cell monitors that I can check each cell before and after charging to make sure my RC charger is not overcharging or my pack out of balance. I feel cells vary like some are 4.16 others 4.20 and 4.18- and I don't worry or try to balance unless there is a large discrempency.
So that is the "bulk charge" procedure using an RC charger. Is that clear?
Some charger don't charge without the balance leads plugged in, but that is like the little chargers, the 50 watt chargers. Most have bulk charging modes. Hope that helps.

 

[rg12]

Alright so i guess i will mostly bulk charge and keep an eye on cell balance and do a balance when needed.

Thanks alot guys!

 

[BikeFanatic]

your welcome from the girls.