Very simple parallel/series wiring questions

[CGameProgrammer]

I want to create a 2s4p configuration. Would the below diagram work? Is there a better method?

To describe it, the right side has a string of four batteries in parallel, connected in a straightforward manner. But while the left side also has four batteries connected in parallel, those batteries' ground terminals are connected to the positive wire and the batteries' positive terminals are connected to the ground wire.

Would that work? I like it because it's simple.

 

[xyster]

That's a simply massive short-circuit! Kaboom!

Primer on series/parallel connections:
http://www.batteryuniversity.com/partone-24.htm

2S2P:

 

[xyster]

2S4P (with wire between the parallel subpacks for balancing and charging):

 

[CGameProgrammer]

Ha ha. Well then how do I hook them up correctly? It seems like anytime you connect batteries in parallel, then hook them up in series with other batteries, you could be forming a short circuit.

Is the solution to do the opposite and hook series in parallel, as in the below picture?

EDIT: Ah, you edited your post. Yeah that's the same thing as the picture I drew. It was my second guess! It makes sense as I see there are no closed loops here. BTW each "battery" (really a subpack of 10 cells in series) already has a BMS for its cells and will be charged individually, not in parallel with the others.

 

[fechter]

That would work if they are charged independently.

See this thread:
http://endless-sphere.com/forums/viewtopic.php?t=1312

I'd suggest using the 'lead/lithium' arrangement.

 

[CGameProgrammer]

They are being charged independently. I'm going to make a thread on the modification I made to the charger, even though I probably have no credibility now and will only be laughed at.

 

[xyster]

They are being charged independently. I'm going to make a thread on the modification I made to the charger, even though I probably have no credibility now and will only be laughed at.

Nobody else here lets that stop them.

 

[Drunkskunk]

They are being charged independently. I'm going to make a thread on the modification I made to the charger, even though I probably have no credibility now and will only be laughed at.

Nobody else here lets that stop them.

I don't have any credibility, but I did stay at a Holiday Inn Express last night :lol:

 

[CGameProgrammer]

I have a new question: Say I want to create a 5s5p cluster, to be charged by a charger expecting a 5s pack. Is this a correct method for doing it? (Sorry for small size.)

The leftmost column, tinted blue, is the original 5s pack (blue lines are series connections). Now what I'm also wondering is, if each column of cells is also connected together in their own series, would that adversely affect charging and discharging? I ask because it would be easier not to have to break the tabs connecting the batteries together in series.

The cells are A123. Another thing I'm unclear on is if this 5s5p cluster is itself connected (by the two output wires) either in series or in parallel with other identical clusters, can they still safely be charged individually or would I have to physically disconnect the clusters before I can charge each? In other words, might current "leak" outside a cluster to its neighbors?

 

[fechter]

That looks like it should work.
If each column is connected in its own series, it should not matter. In fact, it should reduce the series resistance, which would be good.

The charging time will be longer, but the BMS should still keep all the cells balanced.

 

[CGameProgrammer]

Excellent. That makes things simpler.

I have another unrelated but stupid-newbie question (hypothetical): If a battery is rated for 2C discharge and it has a maximum capacity of 25 Ah, does that mean its maximum discharge is always 50A, or does it mean it's 50A when full, 20A when there's only 10Ah remaining, etc.? Is it based on maximum capacity or current capacity, in other words?

 

[xyster]

Excellent. That makes things simpler.

I have another unrelated but stupid-newbie question (hypothetical): If a battery is rated for 2C discharge and it has a maximum capacity of 25 Ah, does that mean its maximum discharge is always 50A, or does it mean it's 50A when full, 20A when there's only 10Ah remaining, etc.? Is it based on maximum capacity or current capacity, in other words?

The former: If a battery is rated for 2C discharge and it has a maximum capacity of 25 Ah, that means its maximum discharge is always 50A. Battery operated devices would require even more massively oversized packs if this weren't the case.

 

[CGameProgrammer]

I have another question: When a charger expects a 1p arrangement of cells (i.e. Xs1p) and you have Y cells in parallel, isn't it theoretically perfectly safe to multiple the charger's output current by Y? If so, is there a simple way to do this?

 

[xyster]

I have another question: When a charger expects a 1p arrangement of cells (i.e. Xs1p) and you have Y cells in parallel, isn't it theoretically perfectly safe to multiple the charger's output current by Y? If so, is there a simple way to do this?

If I'm understanding your question correctly:

Yes it's safe to multiply the charger's output current by Y. The simple way to do this is to add chargers in parallel, just like you'd add batteries in parallel to increase current output capability.

 

[CGameProgrammer]

That doesn't sound safe; they're balancing chargers and I'd think they could conflict with each other.

I've hooked up my batteries in a 10s4p configuration but I'm not positive if it's correct. I've drawn an MSPaint of a similar 10s2p configuration; can anyone tell me if there are problems with it?

There are two pre-tabbed 10s packs. One of them has both the output terminals, and the charger also only deals directly with that one (using the same terminals). Then there's another 10s pack, and 11 wires are used to connect them in parallel instead of 20 like you'd expect. Each number is connected in parallel with the same number. Is there anything wrong with this assumption?

The only issue I'm currently aware of is that ground and positive should not be on the same pack, so I could keep the ground terminal but rewire the positive terminal to the top pack instead of the bottom one. Is that important? It's very easy for me to do if so. What difference could it make? The only thing I can think of is that, due to wire resistance, the child pack might not get as much power as the one directly connected to the charger/output.

 

[CGameProgrammer]

bump... I'm hoping to know the answer to the above question before I connect the packs to the bike.

 

[xyster]

I'm having difficulty understanding your questions. And even if I did, I have no familiarity with the dewalt charger and balancer. Hopefully somebody else here can help you.

 

[fechter]

I think you got it right.

Both packs would be paralleled, along with parallel connections between each cell so the balancing funciton of the BMS works for both packs. The two main + and - wires need to be heavy, but the wires that go between cells can be smaller since the balancing current will be much less.

The charger should be happy, but just take longer to charge.

I don't know if you can put more than one charger in parallel to speed up the charging. In theory, this should work, but I don't know what would happen to the BMS in a parallel charger configuration. You could possibly use two chargers and charge two 10s2p halves of the pack separately, then combine them for discharge.

 

[CGameProgrammer]

But what I was really wondering about was if it's bad practice to have both output terminals on the same pack. Compare the attached picture to the last one I posted (at the very end of the first page); this one is functionally identical except that the positive lead is directly attached to the second pack instead of the first. So the ground and positive leads are directly attached to different packs instead of the same one. Would this make a difference?

 

[xyster]

You omitted the balancing wires between the packs and the terminal (main power) leads on one of the packs -- so it's a little hard to understand your diagram and your question. If I'm reading you right, no, it won't matter because the terminal leads of both packs are electrically common no matter which pack those leads are connected to, so long as each lead is connected to both packs.