What's it called when larger capacity uses more Ah/Wh?

[Ykick]

How does larger capacity consume more AhWh?

Background - cold weather, I double my RC Lipo battery pack capacity in order to help offset the reduced capacity of cold temperatures. Actually, not so much reduced capacity as increased sag, but that's for another thread...

Basically, I convert the pack to 15S4P (20Ah) during winter and go back to 2P 10Ah as warm weather temps return.

The revelation comes from how the 20Ah pack was consistently using nearly 7Ah to recharge after a run to work and back but when scaled back to the 10Ah pack it's only taking about 5.5Ah over the same distance/terrain.

20Ah pack, the total pack voltage doesn't drop nearly as much as it does when there's only 10Ah available. Okay, logical and expected behavior but the crazy thing to me is how much difference it actually makes at the end of the run?

+20% is significant and it's almost as if you can squeeze more range by using a smaller capacity pack because it sort of self regulates performance? If so, this may appear to offer a method of stretching range by splitting your packs up? Crazy idea, eh?

Anyway, probably not worthy of a thread for such a "noob" discovery but I recently noticed it and wondered what is the term to describe higher operating voltage/wattage spread out over discharge curve?

 

[Arlo1]

Sure its not just the temperature causing the higher usage?

 

[Ykick]

Sure its not just the temperature causing the higher usage?

I thought that might be it too and went back to 4P under similar temps to compare. Nope, it goes back up close to 7Ah covering the same route.

The now apparent explanation is that I'm enjoying speedier performance over more of the distance covered while using the 20Ah pack as opposed to the lower average voltage experienced via the smaller pack.

You can do the same thing just backing off the throttle or limiting usage with a CA but I found it informative and self-regulating, as long as the smaller pack has enough C rate to handle peak amperage.

Recreational rides I often stretch range to it's limits - knowing the above, it makes perfect sense to do those rides on 1/2 packs instead of combining them into one large pack out of the gate. For one thing, it will allow me to self regulate the discharge as above but also when #1 pack runs out, that's merely an obvious, simple warning to switch over to #2 pack and head back home!

 

[amigafan2003]

You've already found the answer - larger packs suffer less voltage drop, thus when you factor in the pack voltage x amp draw it uses more watts.

I.e. Say the small pack drops to 55v. Amp limit is 15 amps. That's 825watts drawn. On a larger pack voltage would say only drop to 58v so that would be 58*15 = 870 watts drawn - 45watts extra. The effect becomes more pronounced the high the amp draw.

Hope that makes sense.

 

[Ykick]

You've already found the answer - larger packs suffer less voltage drop, thus when you factor in the pack voltage x amp draw it uses more watts.

I.e. Say the small pack drops to 55v. Amp limit is 15 amps. That's 825watts drawn. On a larger pack voltage would say only drop to 58v so that would be 58*15 = 870 watts drawn - 45watts extra. The effect becomes more pronounced the high the amp draw.

Hope that makes sense.

Thanks, 'appreciate your views and input about this. Hell of a math problem to solve precisely because it's a constantly moving voltage point along the discharge curve?

Oh well, 'certainly opened my eyes to a new way of approaching Safari trips when carrying the larger pack.

 

[SamTexas]

The revelation comes from how the 20Ah pack was consistently using nearly 7Ah to recharge after a run to work and back but when scaled back to the 10Ah pack it's only taking about 5.5Ah over the same distance/terrain.

That does not make sense at all. Same average moving speed for both cases? What does the Cycle Analyst say? Average speed, top speed, wh/mi for both cases?

The only disadvantage in using the larger pack is the additional weight (10lbs?). That should impact the consumption rate by at most 1%, all other things being equal.

 

[Ykick]

The revelation comes from how the 20Ah pack was consistently using nearly 7Ah to recharge after a run to work and back but when scaled back to the 10Ah pack it's only taking about 5.5Ah over the same distance/terrain.

That does not make sense at all. Same average moving speed for both cases? What does the Cycle Analyst say? Average speed, top speed, wh/mi for both cases?

The only disadvantage in using the larger pack is the additional weight (10lbs?). That should impact the consumption rate by at most 1%, all other things being equal.

You're not quoting all the information I've provided about the situation.

Unfortunately, I don't own a CA but I have very good power meters. I said I'm traveling at higher average speed over the same course because the larger battery simply holds it's voltage higher over the same time/load of discharge. It's obvious where the higher Wh usage is going. I'm trying to figure out proper terminology of what that's called?

 

[SamTexas]

How does larger capacity consume more AhWh?

Background - cold weather, I double my RC Lipo battery pack capacity in order to help offset the reduced capacity of cold temperatures. Actually, not so much reduced capacity as increased sag, but that's for another thread...

Basically, I convert the pack to 15S4P (20Ah) during winter and go back to 2P 10Ah as warm weather temps return.

The revelation comes from how the 20Ah pack was consistently using nearly 7Ah to recharge after a run to work and back but when scaled back to the 10Ah pack it's only taking about 5.5Ah over the same distance/terrain.

20Ah pack, the total pack voltage doesn't drop nearly as much as it does when there's only 10Ah available. Okay, logical and expected behavior but the crazy thing to me is how much difference it actually makes at the end of the run?

+20% is significant and it's almost as if you can squeeze more range by using a smaller capacity pack because it sort of self regulates performance? If so, this may appear to offer a method of stretching range by splitting your packs up? Crazy idea, eh?

Anyway, probably not worthy of a thread for such a "noob" discovery but I recently noticed it and wondered what is the term to describe higher operating voltage/wattage spread out over discharge curve?

You're not quoting all the information I've provided about the situation.

Unfortunately, I don't own a CA but I have very good power meters. I said I'm traveling at higher average speed over the same course because the larger battery simply holds it's voltage higher over the same time/load of discharge. It's obvious where the higher Wh usage is going. I'm trying to figure out proper terminology of what that's called?

If I knew you were traveling at a higher speed, I would not have made a comment at all. But how could I know? Where exactly did you say that?

 

[neptronix]

Peukert's effect comes to mind here.

Here's the thing though - you don't really lose capacity on a lithium pack when it's sagging quite a bit. It always springs back up to whatever the voltage should be, over a long period of time. What you lose is watt hours, because you have a lower voltage as you apply a load on it.

You can understand how this works with a cycle analyst, turnigy watt meter, or whatever other device you have for monitoring volts and amp hours.

Lithium batteries' internal resistance increases dramatically the colder they get.
So a bigger pack really minimizes the problem.

I like myself a good 20AH 20C RC Lipo pack.. stands up to my 36A / 36v load all day long. drops about 0.5v on a 1.8C load.. in the winter i get all of 1-2 voltage drop.. how awful.. :lol:

 

[Ykick]

If I knew you were traveling at a higher speed, I would not have made a comment at all. But how could I know? Where exactly did you say that?

Sure its not just the temperature causing the higher usage?

I thought that might be it too and went back to 4P under similar temps to compare. Nope, it goes back up close to 7Ah covering the same route.

The now apparent explanation is that I'm enjoying speedier performance over more of the distance covered while using the 20Ah pack as opposed to the lower average voltage experienced via the smaller pack.

You can do the same thing just backing off the throttle or limiting usage with a CA but I found it informative and self-regulating, as long as the smaller pack has enough C rate to handle peak amperage.

Recreational rides I often stretch range to it's limits - knowing the above, it makes perfect sense to do those rides on 1/2 packs instead of combining them into one large pack out of the gate. For one thing, it will allow me to self regulate the discharge as above but also when #1 pack runs out, that's merely an obvious, simple warning to switch over to #2 pack and head back home!

My wording sucks and I'm sorry for any confusion. Thanks for your input.

 

[Ykick]

Peukert's effect comes to mind here.

Here's the thing though - you don't really lose capacity on a lithium pack when it's sagging quite a bit. It always springs back up to whatever the voltage should be, over a long period of time. What you lose is watt hours, because you have a lower voltage as you apply a load on it.

You can understand how this works with a cycle analyst, turnigy watt meter, or whatever other device you have for monitoring volts and amp hours.

Lithium batteries' internal resistance increases dramatically the colder they get.
So a bigger pack really minimizes the problem.

I like myself a good 20AH 20C RC Lipo pack.. stands up to my 36A / 36v load all day long. drops about 0.5v on a 1.8C load.. in the winter i get all of 1-2 voltage drop.. how awful.. :lol:

I do understand but more of a terminology and limited Algebra skills challenge for me. There's no "magic" capacity here, but based on how it's being discharged (yes, higher average speeds) it would appear to offer interesting configuration options for some of my riding purposes.

Thanks buddy!

 

[dogman dan]

Reminds me of past threads where the question was why a more powerfull motor uses more power even when pedaling just as hard as before.

Answer, baisicly if you have it it gets used. The pedaling might well be at the same cadence, but the motor was doing more for sure when the motor got upsized.

I think in this case, the wh went into snappier acceleration, slightly higher avereage speeds and such, much like the other case.

 

[scoot]

Glad you did post this Ykick... a new twist on familiar theme I hadn't fully thought about until now. And that's why I still lurk around out here.... besides the other obvious reasons 8)

 

[auraslip]

Less voltage sag means more power. More power means you burn more. Basically what dogman said.

 

[spkpn]

Peukert's effect comes to mind here

First, I think that this effect would affect a smaller pack more than a larger pack. Second the peukert effect is not something that causes dramatic capacity decrease in lithium batteries (at "normal" use) afaik (much more relevant for lead batts).

 

[TylerDurden]

We used to call it: "swelling of the right foot". I don't know if there is a commensurate term for hand throttles.

 

[Ykick]

I'll just call it "thinking the really weird stuff..."

I've always believed one method of reducing range anxiety when riding unknown routes might be dual packs? Similar to dual fuel tanks. Now that I better understand this discharge behavior, I'll definitely configure 1/2 packs from now on!

Thanks for the good thoughts and ideas!

 

[auraslip]

With packs of smaller capacities you'll actually be seeing more I^2R losses as the pack resistance will be double. And the pekuert effect will be double. Keep your pack in parallel. The effect you are seeing is solely the creation of the rider and the throttle.

 

[999zip999]

I agree with Dogman you are just harder on the throttle.