Parallel vs Single performance.

Loginphp

10 mW
Joined
Sep 4, 2021
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Assuming the batteries are all identical, brand and all. What kind of performance difference is there between:


2x 10ah 48v Batteries (20ah total)
And
1x 20ah 48v Battery (20ah total)

Is it true that two batteries give less voltage sag as opposed to one?
 
No, certainly not significantly.

The fewer the cell count does favour longevity though, simplicity is always better for reliability.

Having multiple sub-packs that can easily be paralleled gives flexibility though

lighter weight for shorter trips

redundancy when a sub-pack goes bad

lower investments replacing at shorter intervals.

Having sub-packs in series lets you use Hobby balancing chargers, 6-8S common and cheaper.

Not relying on a BMS for balancing is nice.
 
Depends on your load.

A) Put two 48v batteries in parallel and you double the output current.
B) Put two 48v batteries in series and you double the output voltage.
In either situation, you double the potential wattage output.

A low turn count motor would operate best on A)
A high turn count motor would operate best on B)
 
it really depends, but if all else is equal and from my understanding it's goes a little something like this:

single lane vs dual lanes

single lane :
1. all energy needed can be consumed from one lane
2. so if it's BMS Controlled = limited by how man AMPS the BMS let's you draw

dual Lanes:
1. energy needed can be consumed from either battery
2. so if each BMS is set to xAMPS = xAmps are added to give you bigger AMP draw

this is all in theory and there is a little more to it, but that's the jist.

as far as voltage sag, it would really depend on the amount of Amps being drawn. if your motor wants 60 amps and each battery pack can only give 30 Amps max, the sag on each one will be able the same, but dual batteries will be able to help the motor perform to it's max. but if you go say a little less, say 15amps, single battery will sag as it's trying to draw that much on one battery vs dual will be sharing that draw and effectively halving the load taken from each battery(7.5amps each respectively). less draw, easier to maintain = less sag.
 
That's not how it works. Same number of the same cells, same number in series, same number in parallel-- the only thing that could be different between two small packs or one big pack is the capacity of the BMS or the cross-sectional area of the cables, and both those things are arbitrary.
 
If you run two similar packs in parallel, you will halve the current needed from each pack. Since the capacity is dependent on the level of current draw, on an ebike I would expect a little more range running in parallel as opposed to running one pack til it's flat and switching.

Anyway, I've got a few tiny 4AH and 5AH 10S packs I run in parallel and I think performance is better, as long as I run at the same speed.
 
Loginphp said:
2x 10ah 48v Batteries (20ah total)
And
1x 20ah 48v Battery (20ah total)

Is it true that two batteries give less voltage sag as opposed to one?

No

conceptually, the simplest version of your question; not sure where people are seeing BMS's in your description, but if you assume that, you have to assume whether the BMS discharge capacities are halved, etc. for the parallel pack scenario. In any case, wouldn't affect voltage sag, which is the question.
1s1p.jpg

scaled up to the next simplest. feel free to extrapolate up to 13S4P x 2 and 13S8P, or whatever the configuration of the 48V packs for your situation.
2s2p.jpg
 
E-HP said:
Loginphp said:
2x 10ah 48v Batteries (20ah total)
And
1x 20ah 48v Battery (20ah total)

Is it true that two batteries give less voltage sag as opposed to one?

No

conceptually, the simplest version of your question; not sure where people are seeing BMS's in your description, but if you assume that, you have to assume whether the BMS discharge capacities are halved, etc. for the parallel pack scenario. In any case, wouldn't affect voltage sag, which is the question.
1s1p.jpg

scaled up to the next simplest. feel free to extrapolate up to 13S4P x 2 and 13S8P, or whatever the configuration of the 48V packs for your situation.
2s2p.jpg

I suppose the reason I'm asking is because I have a battery setup nearly the same as I described and a single battery appears to push at least 1 volt less than a parallel setup. The bike goes 1 or 2 mph slower and slight less torque on startup throttle. I don't really know if its voltage sag or not I'm just assuming because I can't think of any other explanation why 2 give a more consistent voltage than 1 battery. Could it be because one is 10Ah and two are 20Ah combined? Does the amp hour really have anything to do with that?

This is what I'm actually using FYI

VISET Ebike Battery 48V 10Ah
https://www.amazon.com/dp/B0895J9SNF/ref=cm_sw_r_apan_glt_fabc_9W9HTVPVFJZBWV526CWB?_encoding=UTF8&psc=1

I have two of them. Two perform better than one and I can't figure out why. It could be that one is more defective than the other.

1x 10Ah 48v (10Ah total)
2x 10Ah 48v (20Ah total)
 
Loginphp said:
Two perform better than one and I can't figure out why. It could be that one is more defective than the other.

1x 10Ah 48v (10Ah total)
2x 10Ah 48v (20Ah total)
If the voltages are constant then yes doubling the Ah capacity of course vastly increases the max current output, thus reducing voltage sag by a lot.

Before it seemed you were asking about splitting a constant Ah in two then paralleling them, which does not improve performance in that sense.


 
You said cells are all the same, but voltage sag can be very influenced by "which" cells you use. High amp cells have little sag, but with low-amp cells, even a big pack can have noticeable sag.

Size and material of conductors can be an influence, since nickel buses have measurable resistance. Joining two packs can have a bottleneck at the connectors if undersized for joining two packs.

Many considerations to avoid voltage sag.
 
Loginphp said:
Assuming the batteries are all identical, brand and all. What kind of performance difference is there between:

2x 10ah 48v Batteries (20ah total)
And
1x 20ah 48v Battery (20ah total)

Is it true that two batteries give less voltage sag as opposed to one?

Loginphp said:
I have two of them. Two perform better than one and I can't figure out why. It could be that one is more defective than the other.

1x 10Ah 48v (10Ah total)
2x 10Ah 48v (20Ah total)

I'm not sure what the logic is for asking a different question than the one you want answered, but I guess Neptronix is a mind reader, since he was able to answer it before you asked it. Administrator experience I guess.

neptronix said:
Depends on your load.

A) Put two 48v batteries in parallel and you double the output current.
 
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