Electrical wiring question

Hey everyone, currently in the planning stages to start work on Kaizen 2.0 as a HW this time around and I need someone to validate a wiring idea before I jump into this.

At the moment, I've got a pair of Ampflow A28-400s rated for 24v and a LEM (I think a LEM 170-127, will need to check) rated for 48v. From what I've seen and heard, Ampflows aren't particularly good for being overvolted. I therefore need to find a way of powering both sets of motors to their full potential without falling foul of the FRA rules, running the LEM at half power or overvolting the Ampflows by 100% (as much as I do this with the CIMs in Jibril at any rate).

Given a source of 12S LiPo batteries, if I was to have two circuits from the batteries with two links for drive and weapon, the ESCs on the drive circuit wired in series so they only see 22.2v each and the weapon see 44.4v, would this work? I suspect it will from my reading, the ESCs are effectively variable resistors in this arrangement but I would like to make sure this is the case before going ahead.

I would just use two battery packs, i have to on Apex as i run 14s on the weapon and either 6s or 12s on drive (ive used ampflows and brushless on drive), I wouldn't recommend using the same battery pack for drive and the weapon, especially with the current draw the LEM will take.

I'd second Chris's suggestion on running 2 battery packs.

I would also like to add you absolutely CANNOT run ESC's in series like that. Labelling them as a variable resistor is far too oversimplifying of what's going on inside them. To also add if it were the case the voltage would be split by how loaded the motors/ESC's are, it wouldn't always be a neat 50:50 split and would likely overvolt the ESC's extremely often in the course of a fight.

Thank you Chris and Alex for your input.

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I would just use two battery packs, i have to on Apex as i run 14s on the weapon and either 6s or 12s on drive (ive used ampflows and brushless on drive), I wouldn't recommend using the same battery pack for drive and the weapon, especially with the current draw the LEM will take.

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Ideally yes, I would prefer running the two circuits separately but I cannot reconcile that and the fact that rule 7.5 of the FRA build rules states that for either LiFe or LiPo, the maximum number of cells in series is 12. Does that rule only therefore apply to a single battery pack or does that apply to the whole robot (the latter being my interpretation at the moment)?

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I would also like to add you absolutely CANNOT run ESC's in series like that. Labelling them as a variable resistor is far too oversimplifying of what's going on inside them. To also add if it were the case the voltage would be split by how loaded the motors/ESC's are, it wouldn't always be a neat 50:50 split and would likely overvolt the ESC's extremely often in the course of a fight.

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I used the label of variable resistor as I couldn't think of a better way to describe the way in which it worked at 4am in the morning :P I do recognise that it is a gross oversimplification to label ESCs as such.

I don't claim to be an expert in electrics (my background is computer sciences) but it was my understanding that the voltage seen by each component in a circuit was the total voltage of the circuit as supplied by the batteries divided by the number of components in said circuit, least to the ESCs themselves. I can see how the motors running would potentially affect the amount of current each ESC receives, I suppose that would be the same for voltage as well but I don't see how that would lead to one of the ESCs overvolting.

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Originally Posted by Ocracoke

Thank you Chris and Alex for your input.
I used the label of variable resistor as I couldn't think of a better way to describe the way in which it worked at 4am in the morning :P I do recognise that it is a gross oversimplification to label ESCs as such.

I don't claim to be an expert in electrics (my background is computer sciences) but it was my understanding that the voltage seen by each component in a circuit was the total voltage of the circuit as supplied by the batteries divided by the number of components in said circuit, least to the ESCs themselves. I can see how the motors running would potentially affect the amount of current each ESC receives, I suppose that would be the same for voltage as well but I don't see how that would lead to one of the ESCs overvolting.

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I'm afraid that's an incorrect understanding. It's their resistance compared to each other that decides the voltage they see which is not constant with ESC's. When things are all the same resistance it can work as a rule of thumb.

To take it to the extreme one wheel free spinning while one at stall would result in one ESC seeing the majority of the voltage (And promptly breaking itself).

Remember that with V=IR it is all interconnected.

EDIT: I'm still quite oversimplifying myself here. Electronics can be weird!

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To take it to the extreme one wheel free spinning while one at stall would result in one ESC seeing the majority of the voltage (And promptly breaking itself).

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This was along the lines of the issue I was thinking of, hence the original post though I was perhaps thinking about it from the wrong angle (I was concerned about the arrangement from an amperage perspective). So OK, that idea is out of the window. This leads me back to my question about rule 7.5 and wherever it applies to the whole robot or per battery pack when wired in series.

7.5 is functionally a voltage limit but phrased by cell count. If you are using 2 batteries you wouldn't be wiring them in series, they would be separate circuits (With a max of 12 cells in series so fine).

Basically as long as you aren't arranging your battery packs in any way that puts more than 12S in series you're fine. You could have 6 12S packs and as long as they are all in parallel it's fine.

Ah, OK, thanks for the clarification. I'll work that into my CAD designs later on this week.