Electric Unicycle Specs sheet

[US69]

17 minutes ago, Carlos E Rodriguez said:

There are single cell that can store more energy than other cells. If you take two 4.2volt cells with different capacity as they are discharged, the lower capacity cell will start to run out faster. Then the higher capacity cell will be working harder to make up for the lower capacity cell. So it would not be healthy for the higher capacity cell longevity. The higher capacity cell will always be working harder lowering its life expectancy.

Also when charging the lower capacity cell will get overcharged waiting for the higher capacity cell fill up.

If you mix the individual cell types, it need to be engineered so you dont damage them.

In fact it is no big Problem to connect Batterie packs of different Watthours (range)....as Long as they have the same voltage

For example i have in my Msuper a 820wh pack and a 340wh pack....together 1160wh

As they are connected in parallel they are always on the same voltage. This is also when charging them, the lower pack will not get overcharged......

 

what you are not allowed to do is to put different type of cells in one seriell pack!

 

But what here was asked is to use different range/wh packs in parallel....

That's no Problem and is done by some sellers with no problem

[Carlos E Rodriguez]

2 minutes ago, KingSong69 said:

In fact it is no big Problem to connect Batterie packs of different Watthours (range)....as Long as they have the same voltage

For example i have in my Msuper a 820wh pack and a 340wh pack....together 1160wh

As they are connected in parallel they are always on the same voltage. This is also when charging them, the lower pack will not get overcharged......

 

what you are not allowed to do is to put different type of cells in one seriell pack!

 

But what here was asked is to use different range/wh packs in parallel....

That's no Problem and is done by some sellers with no problem

Agreed if the different packs are made with the same type of cells.  lets take two packs 1P same S.  If one pack is made with say 2900mah cells and the other pack is made with 3400mha cells it is not good to connect in parallel to discharge and charge. the Higher mah pack will work harder and the Lower mah will get overcharged if the packs are used/wired in parallel.

So if the cells making the packs are similar mah per cell then it does not matter.

[US69]

27 minutes ago, Carlos E Rodriguez said:

Agreed if the different packs are made with the same type of cells.  lets take two packs 1P same S.  If one pack is made with say 2900mah cells and the other pack is made with 3400mha cells it is not good to connect in parallel to discharge and charge. the Higher mah pack will work harder and the Lower mah will get overcharged if the packs are used/wired in parallel.

So if the cells making the packs are similar mah per cell then it does not matter.

Nope, Sorry!

i have a 820wh pack made of 3500mah cells, and a 340wh pack made of 2900 cells...

These are connected in parallel, and because of this parallel Connection they "equalize" themself all the time...that also happens while charging.

That is not stressfull at all for the packs....not while charging and not while working.

 

You can even buy such combinations in a new wheel....

[Mono]

On 4/26/2017 at 4:47 PM, Carlos E Rodriguez said:

Agreed if the different packs are made with the same type of cells.  lets take two packs 1P same S.  If one pack is made with say 2900mah cells and the other pack is made with 3400mha cells it is not good to connect in parallel to discharge and charge. the Higher mah pack will work harder and the Lower mah will get overcharged if the packs are used/wired in parallel.

Where do you have this information from? 

AFAIK, if you wire two identical packs in parallel, they behave like one pack with the same voltage and twice the Ah. From the electrical perspective (physical location aside) they are like one pack with twice the Ah. Also for a third pack added in parallel the previous two look and behave exactly like one pack with twice the Ah. For a forth pack added in parallel these three packs look exactly like one pack with three times the Ah...

[Chriull]

3 hours ago, Carlos E Rodriguez said:

Agreed if the different packs are made with the same type of cells.  lets take two packs 1P same S.  If one pack is made with say 2900mah cells and the other pack is made with 3400mha cells it is not good to connect in parallel to discharge and charge. the Higher mah pack will work harder and the Lower mah will get overcharged if the packs are used/wired in parallel.

So if the cells making the packs are similar mah per cell then it does not matter.

Parallel connection is by far not as critical in regard to cell specifications as series configuration of cells. However If different cells are directly paralleled as worst case the weaker cell deteriorates until it could be pushed by the stronger cells to reverse polarity -> desaster  Also nicely selected cells deteriorate differently and can end in the same desaster...

For paralleling cells with different specifications it's best to build packs of this different cells and parallel the whole packs and not every single cell. The higher capacity cells should in such a configuration be able to nominaly deliver more current (?imho direct proportional to the capacities?)

Unfortionately not to detailed sources in regard to this topic: 

http://batteryuniversity.com/learn/article/bu_803a_cell_mismatch_balancing

http://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations

 

[Slaughthammer]

2 hours ago, Chriull said:

However If different cells are directly paralleled as worst case the weaker cell deteriorates until it could be pushed by the stronger cells to reverse polarity -> desaster

I disagree. If you parallel two cells, they will per definition always have the same voltage, and thus will always balance each other! You can parallel any cells you want, as long as they have the same voltage specs. This polarity reversal only occurs serial arrangements.

[Chriull]

13 hours ago, Slaughthammer said:

I disagree. If you parallel two cells, they will per definition always have the same voltage, and thus will always balance each other! You can parallel any cells you want, as long as they have the same voltage specs. This polarity reversal only occurs serial arrangements.

I tend to believe to people from http://batteryuniversity.com/learn/article/serial_and_parallel_battery_configurations (plus some other articles there mentioning this possible incidents in more detail - just did not find them again by scanning the index...) - my own knowledge or experience about this details are not really existing

Edit:

Which does not mean, that paralleling (especially selected ones) cells is critical and should be avoided. As far as i remember this possible incident mentioned at batteryuniversity in more detail in the other article was at highest risk/mainly with aged cells, high load situation and cold temperatures...

So with some "supervising" of the battery state there should be no real dangers to expect.

[Mono]

Maybe you don't talk about the same situation? To parallel cells with different voltage is rather detrimental, as it will overcharge the cell with the smaller voltage (it will be charged until no voltage difference is left), no?

[esaj]

On 4/27/2017 at 11:08 PM, Mono said:

Maybe you don't talk about the same situation? To parallel cells with different voltage is rather detrimental, as it will overcharge the cell with the smaller voltage (it will be charged until no voltage difference is left), no?

AFAIK, neither cell will get overcharged, but there will be lots of current flowing (the actual amount depending on the resistance of the wiring and the internal resistances of the cells, which are both very small, plus the voltage difference). The wires might melt and the cells could get damaged, and/or overheat, possibly ending up catching fire or exploding. That's why the voltages should be as close to each other as possible before paralleling (single) cells or batteries.

When paralleling packs, probably the easiest way is to charge both packs to full (as they should then be at or very near the same voltage). Another trick is to use a (power) resistor of "suitable value" in between, so the current will stay low until the voltage reaches equilibrium.

As for paralleling packs with different capacities/cells, I think hobby16 once mentioned it should be ok (of course taking care that the voltages are the same when they're first connected). Don't know if it can cause issues further down the line, like maybe the "weaker" pack might age slightly faster.

[Carlos E Rodriguez]

20 minutes ago, esaj said:

AFAIK, neither cell will get overcharged, but there will be lots of current flowing (the actual amount depending on the resistance of the wiring and the internal resistances of the cells, which are both very small, plus the voltage difference). The wires might melt and the cells could get damaged, and/or overheat, possibly ending up catching fire or exploding. That's why the voltages should be as close to each other as possible before paralleling (single) cells or batteries.

When paralleling packs, probably the easiest way is to charge both packs to full (as they should then be at or very near the same voltage). Another trick is to use a (power) resistor of "suitable value" in between, so the current will stay low until the voltage reaches equilibrium.

As for paralleling packs with different capacities/cells, I think hobby16 once mentioned it should be ok (of course taking care that the voltages are the same when they're first connected). Don't know if it can cause issues further down the line, like maybe the "weaker" pack might age slightly faster.

Guys! Let's be careful here. 

So 1p3500mah another 1p2900mah. 

The milliamps is the water in the bucket. Now you pare all el the cells. Both cells start at 4.2vdc. No issues. 

Start discharching with say 2.1 ohm resistor.  That is the 4.2/2.1 is 2 amps.

that mean at the beginning each battery will be pumping out 1 amp.  Now at some point the 2900mah will have emptied its bucked of electrons. Because it only holds 2900mah worth of electrons. At that point the 3500mah still has electrons in is bucket. Since the load resistance is still the same the 3500mah will continue to dump higher and higher currents. At some point the 2900mah will put 0amps and the 3500mah will be putting 2 amps. Electrically this is not detrimental for the 2900mah cell put it is clear the 3500mah cell is working harder. 

Now say it is time to charge. So power supply goes into current mode and starts charging cells. At the programmed voltage it will go into voltage mode. At this point the lower capacity cell will be fully charged sooner that the 3500 cell because that cell is still not full. Not I believe this is when the 2900mah is getting excessive charge. The power supply is in voltage mode and as long as the charge milliamps are in excess of 250ma the power supply will stay in voltage mode damaging eventually the 2900mah cell.  

So if I am wrong please explain. It's just not a good idea to parallel cell of different capacities. 

 

[esaj]

20 minutes ago, Carlos E Rodriguez said:

Guys! Let's be careful here. 

So 1p3500mah another 1p2900mah. 

The milliamps is the water in the bucket. Now you pare all el the cells. Both cells start at 4.2vdc. No issues. 

Start discharching with say 2.1 ohm resistor.  That is the 4.2/2.1 is 2 amps.

that mean at the beginning each battery will be pumping out 1 amp.  Now at some point the 2900mah will have emptied its bucked of electrons. Because it only holds 2900mah worth of electrons. At that point the 3500mah still has electrons in is bucket. Since the load resistance is still the same the 3500mah will continue to dump higher and higher currents. At some point the 2900mah will put 0amps and the 3500mah will be putting 2 amps. Electrically this is not detrimental for the 2900mah cell put it is clear the 3500mah cell is working harder. 

No, the 2900mAh cell or pack won't drop to 0amps, the voltage over the paralleled batteries should stay the same at all times. Due to the internal resistances, the actual currents flowing through each pack probably differs somewhat, though, so the one or the other pack is probably giving a larger "share" of the 2amps than the other, but that's nitpicking. That's how parallel circuits work, refer to  https://www.allaboutcircuits.com/textbook/direct-current/chpt-5/simple-parallel-circuits/   for example. It says pretty much in the beginning the very basic law of paralleled circuits (or components, or battery packs...):

"The first principle to understand about parallel circuits is that the voltage is equal across all components in the circuit. This is because there are only two sets of electrically common points in a parallel circuit, and voltage measured between sets of common points must always be the same at any given time."

->  The same polarity poles of the batteries are connected together (negative -> negative, positive -> positive), so the batteries are in parallel. There cannot exist two different voltages between the same two points at the same time. As a bad analogy, kinda like you can't have two different distances between two objects at the same time, or something...

 

Quote

Now say it is time to charge. So power supply goes into current mode and starts charging cells. At the programmed voltage it will go into voltage mode. At this point the lower capacity cell will be fully charged sooner that the 3500 cell because that cell is still not full. Not I believe this is when the 2900mah is getting excessive charge. The power supply is in voltage mode and as long as the charge milliamps are in excess of 250ma the power supply will stay in voltage mode damaging eventually the 2900mah cell.  

So if I am wrong please explain. It's just not a good idea to parallel cell of different capacities. 

The voltages of both batteries are still the same. Slightly different portion of the total current might flow through one or the other pack, but again, they will reach the fully charged voltage at the same time.

[Mono]

On 2017-4-28 at 10:19 PM, esaj said:

AFAIK, neither cell will get overcharged, but there will be lots of current flowing (the actual amount depending on the resistance of the wiring and the internal resistances of the cells, which are both very small, plus the voltage difference). The wires might melt and the cells could get damaged, and/or overheat, possibly ending up catching fire or exploding. 

That's right, the current is not limited in a controlled way. Then the weakest element in the chain is likely the battery with the smaller voltage experiencing an overvoltage and overcurrent under charging.