Parallel wiring..perhaps a unique scenario?

[ebike11]

Hi guys
At the moment my pack is 28s lipo 20Ah pack. Its connected to a 300A ANT BMS. I can monitor each cell because the BMS can handle 32s

Id like to keep the same voltage but wire another separate 28s pack in parallel to have 40Ah.

Its easier for me to mount to separate packs in parallel then make one large pack

If one pack has the BMS wired to it and the other pack is connected via a 3 way connector/spliter
(1 connector for each pack and then the 3rd connector which is main vtage OUT for the controller)
would it be ok?

 

[amberwolf]

There's a lot of threads that discuss the ins and outs of paralleling batteries; I recommend following the advice in them.


FWIW, it sounds like you want to use one battery with a BMS, and another without one, in parallel.

Doing this means that only the one with a BMS will be protected against cell damage.

The BMS cannot protect a pack it is not connected to all the cells of, so it cannot protect both packs.

If you have the packs separately wired in parallel at only their main outs to the controller, but only one BMS, the pack without the BMS is unprotected.


If you instead intend to wire the BMS's balance wires and the BMS's main power wires to both packs, so that they are completely paralleled at cell level, then the BMS will protect both packs.

Note that if the wires for balance are long, it is possible you can get electrical noise on them that will affect the BMS's ability to monitor the cells, and may cause you unexpected problems.

Hi guys
At the moment my pack is 28s lipo 20Ah pack. Its connected to a 300A ANT BMS. I can monitor each cell because the BMS can handle 32s

Id like to keep the same voltage but wire another separate 28s pack in parallel to have 40Ah.

Its easier for me to mount to separate packs in parallel then make one large pack

If one pack has the BMS wired to it and the other pack is connected via a 3 way connector/spliter
(1 connector for each pack and then the 3rd connector which is main vtage OUT for the controller)
would it be ok?

 

[ebike11]

There's a lot of threads that discuss the ins and outs of paralleling batteries; I recommend following the advice in them.


FWIW, it sounds like you want to use one battery with a BMS, and another without one, in parallel.

Doing this means that only the one with a BMS will be protected against cell damage.

The BMS cannot protect a pack it is not connected to all the cells of, so it cannot protect both packs.

If you have the packs separately wired in parallel at only their main outs to the controller, but only one BMS, the pack without the BMS is unprotected.


If you instead intend to wire the BMS's balance wires and the BMS's main power wires to both packs, so that they are completely paralleled at cell level, then the BMS will protect both packs.

Note that if the wires for balance are long, it is possible you can get electrical noise on them that will affect the BMS's ability to monitor the cells, and may cause you unexpected problems.

Hi guys
At the moment my pack is 28s lipo 20Ah pack. Its connected to a 300A ANT BMS. I can monitor each cell because the BMS can handle 32s

Id like to keep the same voltage but wire another separate 28s pack in parallel to have 40Ah.

Its easier for me to mount to separate packs in parallel then make one large pack

If one pack has the BMS wired to it and the other pack is connected via a 3 way connector/spliter
(1 connector for each pack and then the 3rd connector which is main vtage OUT for the controller)
would it be ok?

Hi thanks for your advice!
Yes I read many threads but didnt see one where 2 packs are in parallel with only 1 pack having a bms and other unprotected. I dont mind 1 being unprotected because I often monitor all my cells.

However as you said near the end of your post, do you mean running a second bms to the second pack the then connecting both packs at their main terminals?

I think it would be impossible to run a single bms to monitor both packs

 

[amberwolf]

However as you said near the end of your post, do you mean running a second bms to the second pack the then connecting both packs at their main terminals?

I think it would be impossible to run a single bms to monitor both packs

No, I meant using a single BMS to monitor both, because if you are truly wiring both completely parallel, then you would also wire the balance wires together, and then the BMS is monitoring both packs.

As noted, if the balance wires from one to the other are long, there may be electrical noise picked up by them that may interfere with BMS operation. There are various methods of shielding against this, but you can try it without first to see if it is necessary.


If you're running one pack without a BMS and don't care about the potential problems of that, then there's no reason to even use the BMS on the other pack, and you could just run with no BMS at all.

If you have a reason to use a BMS on one pack, then you have a reason to use one on both (or one on each, separately).

 

[ebike11]

However as you said near the end of your post, do you mean running a second bms to the second pack the then connecting both packs at their main terminals?

I think it would be impossible to run a single bms to monitor both packs

No, I meant using a single BMS to monitor both, because if you are truly wiring both completely parallel, then you would also wire the balance wires together, and then the BMS is monitoring both packs.

As noted, if the balance wires from one to the other are long, there may be electrical noise picked up by them that may interfere with BMS operation. There are various methods of shielding against this, but you can try it without first to see if it is necessary.


If you're running one pack without a BMS and don't care about the potential problems of that, then there's no reason to even use the BMS on the other pack, and you could just run with no BMS at all.

If you have a reason to use a BMS on one pack, then you have a reason to use one on both (or one on each, separately).

Thanks...i didnt know that i could connect Cell 1 balance wire from pack A and Cell 1 balance wire from pack B together and then connect it to BMS cell 1.

One reason i dont have a second bms is lack of mounting space and also I didnt know I could use just a single BMS for 2 packs of 28s

 

[ebike11]

However as you said near the end of your post, do you mean running a second bms to the second pack the then connecting both packs at their main terminals?

I think it would be impossible to run a single bms to monitor both packs

No, I meant using a single BMS to monitor both, because if you are truly wiring both completely parallel, then you would also wire the balance wires together, and then the BMS is monitoring both packs.

As noted, if the balance wires from one to the other are long, there may be electrical noise picked up by them that may interfere with BMS operation. There are various methods of shielding against this, but you can try it without first to see if it is necessary.


If you're running one pack without a BMS and don't care about the potential problems of that, then there's no reason to even use the BMS on the other pack, and you could just run with no BMS at all.

If you have a reason to use a BMS on one pack, then you have a reason to use one on both (or one on each, separately).

Also, if were to wire both Cell 1 wires to each other from each pack and coonect it to the BMS cell 1, how would I see both Cell 1 voltages on the BMS app? Wouldnt it only display 1 of the cells voltages rather than 2?

 

[amberwolf]

If you have them wired together, they will be at the same voltage, assuming the wires used have low enough resistance and no electrical interference.

Also note that if they are not at the same voltage when you connect them together, current will flow thru the wires until they become the same voltage.

So they won't show up as separate cells, because they effectively are only one cell once wired together (though if the cells have wildly different internal resistances or other properties, and the resistance of the interconnects is high, they will be at different voltages while under a heavy enough load, and the BMS will read the average of the two voltages if it is "between" the cells).

If you want to see separate cell info, you need separate BMS and separate device to run another copy of the app (unless the app supports reading multiple BMSs at the same time, which I doubt).

 

[ebike11]

If you have them wired together, they will be at the same voltage, assuming the wires used have low enough resistance and no electrical interference.

Also note that if they are not at the same voltage when you connect them together, current will flow thru the wires until they become the same voltage.

So they won't show up as separate cells, because they effectively are only one cell once wired together (though if the cells have wildly different internal resistances or other properties, and the resistance of the interconnects is high, they will be at different voltages while under a heavy enough load, and the BMS will read the average of the two voltages if it is "between" the cells).

If you want to see separate cell info, you need separate BMS and separate device to run another copy of the app (unless the app supports reading multiple BMSs at the same time, which I doubt).

Oh thats very interesting! Thanks so much for your knowledge..ill learn from it for sure.
I also assume the the first and last cell wires +/- will also connect to the first and last +/- wires of the other pack that run to the main packs +/- ?

 

[eMark]

Id like to keep the same voltage but wire another separate 28s pack in parallel to have 40Ah.

As long as there's room for two packs why the need to parallel? Just disconnect one pack when discharged to cut-off voltage (or before) ... then connect the other pack for another 20Ah.

IMO, the best way to go about it is KIS. You're making more work for yourself than is necessary (IMO). Besides it's good to stop and take a break once in awhile than riding continually for 40Ahrs..

If you were delivering non-stop E-pony Xpress Mail could see the logic of paralleling the two. Even so you could use a 3-way protective switch. In a couple seconds you could switch from one 28s pack to the other 28s pack without exchanging a tired Mustang for a fresh Mustang (taking more than a couple seconds).

 

[eMark]

opps - deleted

 

[ebike11]

Id like to keep the same voltage but wire another separate 28s pack in parallel to have 40Ah.

As long as there's room for two packs why the need to parallel? Just disconnect one pack when discharged to cut-off voltage (or before) ... then connect the other pack for another 20Ah.

IMO, the best way to go about it is KIS. You're making more work for yourself than is necessary (IMO). Besides it's good to stop and take a break once in awhile than riding continually for 40Ahrs..

If you were delivering non-stop E-pony Xpress Mail could see the logic of paralleling the two. Even so you could use a 3-way protective switch. In a couple seconds you could switch from one 28s pack to the other 28s pack without exchanging a tired Mustang for a fresh Mustang (taking more than a couple seconds).

Hi!!
Ah yes..thats what i have been doing
However Im assuming Ill be able to double my battery input current going up to 40Ah. Im looking increase the
power because my motor is qs273.

If i run 20Ah x 12C rating then (240amps continuous)
But doubling the capacity would allow me to increase the controller to 480 battery amps

 

[eMark]

However Im assuming Ill be able to double my battery input current going up to 40Ah. Im looking increase the
power because my motor is qs273.

By paralleling you double the Ah capcity, but the power remains the same. You can go twice as far by paralleling the two packs, but power remains the same (28s). For example two 28s12p packs when paralleled are now 28s24p (double capacity riding range), but the available power remains the same at 28s.

If i run 20Ah x 12C rating then (240amps continuous)
But doubling the capacity would allow me to increase the controller to 480 battery amps

You may be confusing your packs' 20Ah capacity with the cells Maximum Continuous Discharge rating (20A MCD). That's why some are using salvaged pouch cells with a higher amp rating than cyclindrical cells ... https://endless-sphere.com/forums/viewtopic.php?f=14&t=116108

Instead of "28s12p with twelve 20A rated cells in parallel (20A MCD x 12 = 240A) you need cells capable of a MCD rating of 40amps (40A MCD x 12 = 480 amps) to increase available power while still a 28s pack.

One advantage of paralleling your two 28s12p packs is if you can't afford to buy another Charger :wink:

 

[ebike11]

However Im assuming Ill be able to double my battery input current going up to 40Ah. Im looking increase the
power because my motor is qs273.

By paralleling you double the Ah capcity, but the power remains the same. You can go twice as far by paralleling the two packs, but power remains the same (28s). For example two 28s12p packs when paralleled are now 28s24p (double capacity riding range), but the available power remains the same at 28s.

If i run 20Ah x 12C rating then (240amps continuous)
But doubling the capacity would allow me to increase the controller to 480 battery amps

You may be confusing your packs' 20Ah capacity with the cells Maximum Continuous Discharge rating (20A MCD).

Instead of "28s12p with twelve 20A rated cells in parallel (20A MCD x 12 = 240A) you need cells capable of a MCD rating of 40amps (40A MCD x 12 = 480 amps) to increase available power while still a 28s pack.

One advantage of paralleling your two 28s12p packs is if you can't afford to buy another Charger :wink:

Hi...yes I understand that basically doubling the Ah will just double the driving range.
Oh i forgot to mention that Im using 12C continuous lipo packs, not 18650 etc

I thought I read in multiple places that increasing the overall Ah capacity allows you to draw more current

 

[eMark]

After your latest post i made an edit to my previous post by adding the following ... https://endless-sphere.com/forums/viewtopic.php?f=14&t=116108

For your power requirement you might consider building one pack using salvaged EV pouch cells.

I thought I read in multiple places that increasing the overall Ah capacity allows you to draw more current

Yes & Maybe ... definitely more Ah capacity current, but not necessarily power current (depends). For example 8p groups with cell MCD of 20A (8 x 20A MCD = 160A MCD). 16p groups with cell MCD of 20A (16 x 20A MCD = 320A MCD).

Ah capacity (riding range) is diminished faster pulling say 160A MCD instead of 80A MCD with same number of parallel groups. In other words the two go hand-in-hand. Amp Capacity (riding range) is affected by rate of amperage drain.

You can see the difference between using 10A MCD rated cells and 20A MCD rated cells with two 14s7p packs. If both packs use 3000 mAh cells both packs are rated at 21Ah capacity, but a difference in MCD amp drain of 70amps (70amps MCD vs 140amps MCD).

 

[eMark]

If i run 20Ah x 12C rating then (240amps continuous) But doubling the capacity would allow me to increase the controller to 480 battery amps

That's where it gets a little dicey (pack Ah capacity rating vs pack maximum continuous discharge A rating).

Theoretically one 28s24p pack with MCD cell rating of 20A (480amps Maximum Continuous Pack Discharge) should be the same as two 28s12p packs in parallel with MCD cell rating of 20A (480amps Maximum Continuous Pack Discharge).

Theoretically twice the Ah capacity (riding range) for a 28s24p (40Ah pack) in comparison to a 28s12p (20Ah pack).

 

[amberwolf]

Given a single pack of a particular power output, paralleling a second identical one does double the current output capability of the set of packs, as well as doubling it's capacity; this is exactly like simply having twice as many identical cells in the same pack.

Because current is doubled, so is power, since power is voltage multiplied by current.

(this disregards whatever limitations any BMS might have, or controller, it is strictly regarding the current-delivery-ability of the paralleled cells).




Doubling the current draw of such a paralleled set of packs vs a single one doesn't change the available capacity of either pack; it's the same as if you used the original current draw with a single pack, so you still get doubled capacity as well as the doubled current-delivery ability.



How much range you get out of it with this increased capacity depends on the usage to which you put the system; if you then go a faster speed with it then you'll use up power faster because of the increased air resistance, so you won't get double the range that way.

 

[ebike11]

Given a single pack of a particular power output, paralleling a second identical one does double the current output capability of the set of packs, as well as doubling it's capacity; this is exactly like simply having twice as many identical cells in the same pack.

Because current is doubled, so is power, since power is voltage multiplied by current.

(this disregards whatever limitations any BMS might have, or controller, it is strictly regarding the current-delivery-ability of the paralleled cells).




Doubling the current draw of such a paralleled set of packs vs a single one doesn't change the available capacity of either pack; it's the same as if you used the original current draw with a single pack, so you still get doubled capacity as well as the doubled current-delivery ability.



How much range you get out of it with this increased capacity depends on the usage to which you put the system; if you then go a faster speed with it then you'll use up power faster because of the increased air resistance, so you won't get double the range that way.

Thanks for the reply again!
So would this be correct after all? :
If i run a pack with a total capacity of 20Ah x 12C rating then (240amps continuous)
But doubling the capacity with another identical pack would allow me to increase the controller to 480 battery amps

 

[amberwolf]

So would this be correct after all? :
If i run a pack with a total capacity of 20Ah x 12C rating then (240amps continuous)
But doubling the capacity with another identical pack would allow me to increase the controller to 480 battery amps

If what you are doing follows the guideline you quoted, it will behave as noted in the quote.

 

[ebike11]

So would this be correct after all? :
If i run a pack with a total capacity of 20Ah x 12C rating then (240amps continuous)
But doubling the capacity with another identical pack would allow me to increase the controller to 480 battery amps

If what you are doing follows the guideline you quoted, it will behave as noted in the quote.

Ok thanks...the other posted has a different opinion on it so wanted to get more input. According to him the battery capacity output isnt increased

 

[amberwolf]

Well, it's just like any other paralleling: anything that adds because of paralleling, meaning anything to do with current (Amps, Amp-Hours), would double if you parallel two identical units, whether those are individual cells or entire battery packs.

Anything that uses Amps or Amp-Hours as a base to multiply from (like Watts or Watt-Hours) also then doubles if you parallel two identical units....


If you parallel three, it triples; four, quadruples, etc.


If you *series* them, then Volts go up, not Amps or Amp-Hours, but Watts would still go up by the same factor because Volts went up by that factor.



Again, none of this considers anything other than the cells themselves (wiring, interconnects, connectors, BMS's, controllers, motors, etc).

 

[amberwolf]

Now...the question is, what kind of system do you have (or need) that uses that much battery current?

 

[ebike11]

Now...the question is, what kind of system do you have (or need) that uses that much battery current?

Im using a high rpm qs273 motor...its quite hungry so 20Ah doesnt go to far haha
Thought id double the packs in parallel to get me to around 40ah or close to it

 

[eMark]

...the other posted has a different opinion on it so wanted to get more input. According to him the battery capacity output isnt increased.

have previously posted that the capacity is doubled (20Ah to 40Ah) by paralleling your two identical 28s packs.

By paralleling you double the Ah capcity, but the power remains the same. You can go twice as far by paralleling the two packs, but power remains the same (28s). For example two 28s12p packs when paralleled are now 28s24p (double capacity riding range), but the available power (voltage) remains the same at 28s.

If i run 20Ah x 12C rating then (240amps continuous)
But doubling the capacity would allow me to increase the controller to 480 battery amps.

Oh i forgot to mention that Im using 12C continuous lipo packs

You are confused in thinking you can multiply the Ah capacity of your pack (20Ah) times the contiuous discharge rating (12C) and arrive at an amp rating for a 240amp Controller. Using a 480amp Controller with both 28S packs paralleled could result in your 28S 40Ah pack going up in flames.

Now...the question is, what kind of system do you have (or need) that uses that much battery current?

In other words 1 pack that could use a 240amp Controller or 2 paralleled packs that could use a 480amp Controller.
Photos of your 28s pack with description of lipos and number of lipos in your two identical packs would be helpful.

 

[ebike11]

...the other posted has a different opinion on it so wanted to get more input. According to him the battery capacity output isnt increased.

have previously posted that the capacity is doubled (20Ah to 40Ah) by paralleling your two identical 28s packs.

By paralleling you double the Ah capcity, but the power remains the same. You can go twice as far by paralleling the two packs, but power remains the same (28s). For example two 28s12p packs when paralleled are now 28s24p (double capacity riding range), but the available power (voltage) remains the same at 28s.

If i run 20Ah x 12C rating then (240amps continuous)
But doubling the capacity would allow me to increase the controller to 480 battery amps.

Oh i forgot to mention that Im using 12C continuous lipo packs

You are confused in thinking you can multiply the Ah capacity of your pack (20Ah) times the contiuous discharge rating (12C) and arrive at an amp rating for a 240amp Controller. Using a 480amp Controller with both 28S packs paralleled could result in your 28S 40Ah pack going up in flames.

Now...the question is, what kind of system do you have (or need) that uses that much battery current?

In other words 1 pack that could use a 240amp Controller or 2 paralleled packs that could use a 480amp Controller.
Photos of your 28s pack with description of lipos and number of lipos in your two identical packs would be helpful.

Hi here are the packs.
https://hobbyking.com/en_us/turnigy-high-capacity-battery-20000mah-6s-12c-drone-lipo-pack-xt90.html?queryID=82e067fdf0390db0dbdf000d8d28360b&objectID=78412&indexName=hbk_live_products_analytics&___store=en_us

2 x 28S packs. At the moment they arent connected together.

I was assumption that Ah x C rating gives max. Current ouput. I thought ive read that many times

These packs have a 12c continuous and 20c 10 sec.burst

 

[amberwolf]

You are confused in thinking you can multiply the Ah capacity of your pack (20Ah) times the contiuous discharge rating (12C) and arrive at an amp rating for a 240amp Controller. Using a 480amp Controller with both 28S packs paralleled could result in your 28S 40Ah pack going up in flames.

Could you please detail exactly how using the packs within their capabilities is going to cause them to "go up in flames"?

Unless there is some other exacerbating factor not accounted for, if using two paralled packs at twice the current would do so, then so would using a single unparalleled pack at the original current.


The "C rating" is exactly that--a multiplier for the capacity rating that gives you the max current the cells / batteries can support.

If the cells (or packs) are rated at 12C, then the output current capability of a single 20Ah pack is 12 x 20, or 240A.

If you parallel two of those packs, you can then output a max of 2 x 240A, or 480A.

The math has the same results if you use the 12C x 40Ah of the total of two paralleled 20A packs: 480A.



Note that there *are* scenarios with two paralleled packs with *separate BMSs* that could cause various problematic situations in the event of one pack shutting down, but if two packs are fully paralleled at the cell level and monitored by the same BMS, they are effectively one pack (assuming no electrical interference with balance leads if they are long) and those scenarios dont' apply.