Lipo 6s pack voltage

[Geebee]

Just a quick basic question, what is the actual voltage of a Battery pack such as ZIPPY Flightmax 5000mAh 6S1P 25C whilst in use, max draw less than 15a.
Reason for the question is that my Tongxin controllers cut off around 22.4 volts, I dont mind losing some usable capacity as long as I can use say 70 % of capacity before cutoff.
Thanks.

 

[ZOMGVTEK]

You can expect the 3C loaded voltage to be around 1-2V lower than resting. I'd say right around 1.5V drop at the controller including all the wire and contact losses.

That would put your cutoff a bit high, assuming you are at peak current draw when LVC is triggered.

 

[jmygann]

24V

 

[E-bike4life]

Actual voltage of a 6s zippy pack fully charge is 25.2 volts. Each cell charged to 4.2 volts. So assuming the voltage sag of 1.5 volts you will only get to use about 30-40% of the battery before it would go into LVC.

 

[wesnewell]

Just a quick basic question, what is the actual voltage of a Battery pack such as ZIPPY Flightmax 5000mAh 6S1P 25C whilst in use, max draw less than 15a.
Reason for the question is that my Tongxin controllers cut off around 22.4 volts, I dont mind losing some usable capacity as long as I can use say 70 % of capacity before cutoff.
Thanks.

I don't know the exact sag with a 15A draw on a single 6s pack, but if your controller is 15A max, it will only draw that for a short time during takeoff or when going up a steep hill. Ease up on the throttle and you will get about 70-80% use of the power. Which is a good safe usage. BTW, 22.4V cutoff sounds too high for a 24v controller. It should be lower than that, around 21-22v

 

[neptronix]

Get a turnigy watt meter or cycle analyst. You can see the numbers yourself.

What everyone pretty much said was accurate.

But i'll tell you this:

fully charged: 6 x 4.2v = 25.2v
half charge: 6 x 3.8v = 22.8v
fully discharged: 6 x 3.3v = 19.8v

Your controller will cut off before you are 1/2 way done discharging your battery, with 70% or more left in the pack, because you will get about 1-3V of voltage sag, as the others mentioned.

If you sag 3 volts at initial throttle, you will hit LVC immediately, lol.. Not much headroom here

What you really need is a 7S pack.

 

[wesnewell]

I think he needs 2 (or more) 6s in parallel. that will cut his sag down and the controller lvc will still protect from over discharging. If he goes 7s, he's got to get a charger that does 7s, and if he stays light on the throttle, he will over discharge a 7s pack. 22.4/7=3.2V per cell. I limped home the other day running 10ah 18s on a controller with a 60v lvc. I had one cell at 3.5x and others at 3.6x. Charger showed 5% left. If I'd been running 20s and done the same thing, I would have over discharged every cell in the pack. 7s would be a big mistake if he depends on the controllers lvc to protect from over discharging.

 

[neptronix]

No matter how many 6s he uses in parallel, his battery will always die with about 50% left.
There are plenty of 8s chargers that will happily accept a 7s battery.

His LVC will never be ideal for lipo. It's probably meant for lead acid or lifepo4. That's why the majority of us run programmable infineon controllers... so we can change this stuff and not worry about it.

A watt meter would also prevent overdischarge. That's how i roll. watt meter near the handlebars..

 

[wesnewell]

I think you are mistaken. But if he decides not to use 6s, he might as well go to 8s using 2 4s packs. 7s packs are hard to find, and very expensive when you do find them. He will surely want some way to monitor the voltage if he goes with 7s or above.
Yes, most default LVC's are set for lead, but that's just a voltage. One can adapt any voltage they want to meet the controllers LVC. LVC is 42V on all the 48V controllers I have. 12s lipo fits that perfectly, 42/12=3.5v. That's also one of the reasons I normally run 18s on my 72V controller even though I have a voltmeter on it.

 

[neptronix]

What do you think i am mistaken about?

7S can be made by putting a 4S and 3S pack in series. Many 8s chargers are designed to handle it.
Yup, straight 7S batteries ARE hard to find, so you get to make your own.

8S could work too, as long as his controller can handle it. Should be able to do it .. but then you don't even have a semblance of a LVC. At least at 3.2v, you do have *some* protection.

Not having something like a watt or voltage meter is like driving a car without a fuel gauge. But on a car, you run out of gas. On an electric bike, you ruin those batteries you just bought. We can both agree on this.

I'm surprised at how few people have watt/volt meters hooked up to their bikes.

 

[Geebee]

Thanks for all the replies.
I decided to recheck the cut off in view of the comments well it is 22.5v to turn on by slowly increasing voltage but it cuts off at 21 volts (actually 20.92v ), I do have a Hk watts up meter on the bike and check ah and volts often as I am running a low quality 6 ah sla pack at the moment and at 3ah she's pretty much done.
I was going to run 2 parallel packs and the original idea was 7s but 6s is neater, easier and cheaper.

In view of the revised cut off is the 6 s acceptable, oh normal use is 4 to 10 amps 15 is rare and very short periods (steep hills).

 

[wesnewell]

I think you are mistaken about the amount of power he can pull from the 6s packs. 2 6s packs in parallel won't sag much at all at cruising speed. It's also unlikely that his LVC is actually 22.4V. It should be 21-22v. And controllers LVC works great to protect lipo if you match the pack to the lvc. Built a 12s pack for a kid that runs it to lvc every day and it's always around 90% dod. That's 10ah 12s on a 48v system. 10ah 6s should work even better on a 24v system.

 

[neptronix]

Dude, you got a watt meter.... run 8S. You can get 8S batteries as 1 unit.

http://www.hobbyking.com/hobbyking/store/uh_listCategoriesAndProducts.asp?idCategory=86&LiPoConfig=8

Bump up the amps by soldering that shunt a little.
Have some fun fer once in your life. :lol:

 

[neptronix]

I think you are mistaken about the amount of power he can pull from the 6s packs. 2 6s packs in parallel won't sag much at all at cruising speed. It's also unlikely that his LVC is actually 22.4V. It should be 21-22v. And controllers LVC works great to protect lipo if you match the pack to the lvc. Built a 12s pack for a kid that runs it to lvc every day and it's always around 90% dod. That's 10ah 12s on a 48v system. 10ah 6s should work even better on a 24v system.

Oh i'm not doubting that he can pull 15A out of them. 1 pack would easily do 30 amps constant all day without getting much more than lukewarm, it's just that it will sag 1-3v ( temperature and state of charge dependent ).

I was only sayin.. if his LVC really *was* 22.5 or so, he'd hit it pretty dang quick. Now we know it's not. So the argument is null 'n void, i suppose.

 

[wesnewell]

Thanks for all the replies.
I decided to recheck the cut off in view of the comments well it is 22.5v to turn on by slowly increasing voltage but it cuts off at 21 volts (actually 20.92v ), I do have a Hk watts up meter on the bike and check ah and volts often as I am running a low quality 6 ah sla pack at the moment and at 3ah she's pretty much done.
I was going to run 2 parallel packs and the original idea was 7s but 6s is neater, easier and cheaper.

In view of the revised cut off is the 6 s acceptable, oh normal use is 4 to 10 amps 15 is rare and very short periods (steep hills).

2 6s packs should work out great for you. The controller should let you run them down to at least 70-80% dod. You should get twice the range of your current sla pack.

 

[NeilP]

1 pack would easily do 30 amps constant all day without getting much more than lukewarm,

hey, have you been keeping quiet on those packs ?? A single packs that puts out 30 amps all day...I want one..my packs go flat after about 1 to 2 hours riding

 

[neptronix]

Well i'm done holding the secret, Neil. I am now a reseller for >9000AH leaderhobby lipos, only 1000g.. 20C rate.. :lol:

 

[NeilP]

Yes, i read your write up on them on your site..they are lovely aren't they. Hope paypal comes up for you on this one. Not that I personally hold out any hope.

The only dealings with them that I have had, they always side with the vendor and expect you to pay for registered shipping to the seller, and only give a refund once the seller receives the item back and you have proof d delivery from the postal service