Required Batteries

[dwaindablane]

Regarding batteries, does anyone know the exact requirements other than the documentation, I've linked a battery below but would be nice to get some feed back on suitable batteries.

Turnigy_1000mAh_3S_30C_Lipo_Pack

[Justin]

Here is the exact battery being used in the Opus 200:

http://www.hobbyking.co.uk/hobbyking/store/__11901__Turnigy_nano_tech_1000mah_3S_25_50C_Lipo_Pack.html

[Bapgood]

Battery needs to be a 3S lipo/lifepo4/imr lithium style battery capable of handling a constant load of the max 23 amps. Having some overhead is always a good thing.

[dwaindablane]

Bapgood,

Thanks for your reply I have already ordered the battery that Justin suggested as used in the Beta mods

[mamu]

The lipo pack Justin linked to is used in the Opus 200.  It is not the one used in the beta mod.

[dwaindablane]

Cheers manu, what do the beta units have in them?

[macz]

dwaindablane said:

Cheers manu, what do the beta units have in them?

If not mistaken they're using Fullymax 900mAh, 30C, 3S lipo pack, do correct me if I'm wrong

[dwaindablane]

In relation between a say 18650 2000mah and Lipo 900/1000mah what sort of differences are there in battery life?

[mamu]

You'll get a longer vape runtime with the 3S 900/1000 mAh lipo pack vs the single 18650 2000mAh.  With the way the DNA200 uses batteries, you can essentially triple the mAh of the pack.  So with 3S 900mAh, you'll have approximately 2700mAh and with the 1000mAh, you'll have approximately 3000mAh.

[dwaindablane]

Thanks

[mamu]

Well, Evolv is turning the meaning of mAh on its toes lol.

We traditionally think of series batts where the voltage is multiplied while the mAh of the pack stays the same. Meaning 3S 1000mAh 3.7v batts would have a nominal voltage of 11.1v, while the capacity of the pack stays at 1000mAh.

The DNA200 runs on the energy density of the batts with x amount of watts in, x amount of watts out, treating each cell as individual cells, so you effectively get 3x the capacity of the 3S batts. Not exactly 3x, but pretty darn close. Meaning the 3S 1000mAh batts will give you close to 3000mAh - which significantly increases the vape runtime before needing a charge.

[Cisco]

If you calculate the energy density/watt hr you can see the comparison between 3S LiPo pack @ 11.1v and a single 18650 @ 3.7v

3s 950mAh  lipo pack running @ 11.1v has a watt hr rating of 10.54 watt hrs
1x 2850mAh 18650 running @ 3.7v has a watt hr rating of 10.54 watt hrs

The actual "usable" watt hr is less for both, you wouldn't use more than 80% of capacity before reaching recommended cut of voltage.

-C

[Jakeatadvance]

dont know if this has been answered, or even thought about, but i understand you need a 3s lipo battery, but im assuming (hoping) you can wire another lipo battery in parallel? just thinking BIG here

[John]

Sure, you could run a 3s2p pack. You'd need to make sure both batteries are in the same condition (perferably new) and are fully charged before you pair them. Parallel the main output leads and parallel the tap connectors. 

Or buy an off the shelf pack built 3s2p, which the manufacturer will have done all of that when they were building the pack in the first place.

In power supply mode (or with a three resistor tap divider) it will run off a car battery if you're REALLY thinking big.

[VapingBad]

Rather than start a new thread I thought I would just ask this here.

Re max current and battery rating:  Strictly speaking shouldn't we looking at 28.75 A min current rating new if we want to run at 200 watts when the battery is near the end of it life (80% capacity)?

[John]

9 volts and 23 amps is 207 watts, which is the output power plus the board losses. Where do you get a different number?

Edit: I see what you did there. That's a valid concern (battery ampacity at end of life) but that will vary from cell design to cell design. Not as straightforward as adding 20%

The board, wiring, solder joints, fuses and the like, plus the pack in any condition need to be able to do 23.

[VapingBad]

John said:

9 volts and 23 amps is 207 watts, which is the output power plus the board losses. Where do you get a different number?

Lipo's max continuous discharge current rating is C times capacity, so if I get a new 23 C 1 Ah Lipo that has a max cdc of 23 A, but when it is near the end of it life it's capacity will only be 800 mAh so the max cdc would be 18.4 A.   So if we start with a battery with max cdc >= 28.75 A ti will still be at least 23 A when it is only at 80% capacity.

[John]

Sure, but it isn't that simple. Where did the capacity go, and more importantly, what side effects did that loss of capacity have? I am certainly not saying don't have extra margin. I'm just saying that an "add 20%" rule of thumb is too simplistic, because as the capacity decreases, the proper c rating changes as well. Not always intuitively. Also, it isn't unusual to see an identical cell rates as 20c from one place, 30c by another and 50c by a third. Or have a manufacturer understate capacity to inflate the C rating.

[VapingBad]

John said:

Sure, but it isn't that simple. Where did the capacity go, and more importantly, what side effects did that loss of capacity have? I am certainly not saying don't have extra margin. I'm just saying that an "add 20%" rule of thumb is too simplistic, because as the capacity decreases, the proper c rating changes as well. Not always intuitively. Also, it isn't unusual to see an identical cell rates as 20c from one place, 30c by another and 50c by a third. Or have a manufacturer understate capacity to inflate the C rating.

Thanks John, I knew it wouldn't be that simple, but I believe the capacity largely went by a proportion of the chemicals entering a state where they are not reacting during charge & discharge.  I wouldn't expect the healthier section of the battery to be able to provide more current to compensate either. I am over simplifying, but LiPos are new to me.

Is their a rule of thumb rate that is applicable to help us choose a battery spec?  I know that it would never be "accurate" in most cases, and the battery monitoring will protect us, but could be useful.

[John]

http://batteryuniversity.com/learn/article/bu_808b_what_causes_li_ion_to_die and others on the site are good reading. 

It is important to note that C ratings are based on the nominal capacity, not the measured capacity at that discharge rate or lifespan, but cycling cells to death certainly happens faster at higher discharge powers, so it is still a good discussion to have. 

[VapingBad]

Thanks John, I have read all of battery Uni, when it was on the Cardex site, but not really thinking at Lipos at the time. I was looking for something simple to tell folks that will never read it.  Not just for the DNA200 or even just LiPos, people tend to think of batteries as always happily supplying the cdc and in the last year they are more and more using the bdc and don't get that the output V is going to take a dive at these currents.  As you know the battery has to work a lot harder at lower SOC.  EG I tell people a good general rule for max current VW boards is wattage/2.5 to allow for sag and electronic efficiency of the converter, not strictly accurate, but a good rule of thumb for those that will never learn Ohms law.

I will have a reread of Batt Uni this week.

[John]

That's probably not a bad rule of thumb, all things considered.

[jimmy11]

Is it safe to use this connector installed for changing batteries?

[John]

Those are really only good for about 5 amps continuous and 10 amps peak, so unless you never intend to go above 100W I would go with something beefier. 

[jimmy11]

How about this sir?