that is my understanding–less cells, less torque. @MysticalDork has a better way of explaining this than me
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I second that. He’s got a better grasp of the mumble jumble of it all
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Okay, I’ve been summoned to smack some knowledge on you guys.
Watts is watts, yes, but only if you can actually use it. If you keep all your parts the same and go from 10s4p to 12s3p, your board will theoretically go 20% faster. But, since you have less available power, your top-end torque will be less.
You’ll still be just as fast off the line because that’s limited by your motor current, not your battery current. There’s a point during your acceleration where the limiting factor switches from being the motor current to the battery current. It’s above that threshold that you’ll notice the lack.
Basically, with BLDC motors, voltage = RPM, and phase current = torque.
More phase current, AKA motor current, gives you more torque.
More voltage gives you a higher maximum RPM.
Since RPM X torque = horsepower, and horsepower = watts, it all maths out.
At low RPM and high load (think accelerating from a stop), the motor has a very low electrical resistance, and it’s not producing much back-EMF. This means it has very low impedance to current flow, so a lot of current can flow at a very low voltage. It wouldn’t be uncommon to se 80 amps flowing, but only see 5 volts. The vesc is at a low duty cycle, stepping the battery voltage down, and the current up to match this low impedance, acting kind of like a DC-DC converter.
As the motor speed increases, it starts to behave like a generator, generating an opposing voltage in its windings (AKA back-EMF). As the back-EMF increases, so does the impedance of the motor, so to get the same 80 amps from before to flow, you’d need 20 volts, not 5. The vesc will increase the duty cycle to raise the voltage accordingly, and all is well.
Except on the 12s example above, there’s only 1512 watts on tap, and 80 X 20 is 1600. So the vesc will reach the battery current limit before it can raise the duty cycle high enough to get the full 20 volts and 80 amps.
As you reach full speed, the back-EMF from the motor is almost as high as the battery voltage. This means the impedance increases dramatically, and less and less current can flow, because there’s less and less voltage drop to be had. Since the voltage of a 12s battery is higher, there’s more oomph to go faster, but your acceleration will be lower.
/mic drop
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@MysticalDork Amazing summation. I just learnt heaps. Thankyou very much for for that succinct explanation. Legend.
I’ll wait until I can get some higher output cells to go 12s, as I’m not sure I can fit 12s4p.
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This is a ride and charge I got off of @DerelictRobot awhile back.
The solar charger does its MPPT thing well enough off of the 10s5p guts. Can charger both 10s and 12+ packs from it at specified amps.
Samsung 30q pack. No more than 400Watts get pulled out it by the MPPT at max (I charged a 10s battery at 6-8a without noticeable temp increase 5-6 times, I watched potential points of fail with thermal cam)
There is a step down to 12v transformer (Silver Heatsink on bottom). I’ve used an automotive 750W inverter to power lights with.
It can power my TS100 iron.
Pending retractable corded MPPT to externally pack for charging external pack.
The original a123 lifepo cells from the black enclosure with nifty handle (batteryhookup.com) ended up Making 2, 4s4p packs I use in parallel for spot welding (blue shrink wrap pic, 2 cubes in center). ~20ah for welding. Never gets hot.
Smart switch from old 10s board, harvested Anker 3 port at 2.4a each USB hub. green and black gauge is overall pack monitor.
@Agressivstreetlamp This is the most recent experiment I didn’t catch anything on fire with or even dead short. I’ll post guts and build schematic after you do of your banggood special 
.
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If you’re looking for perfect series connections, this is the thread you’re looking for. I used the same technique @Skyart outlines in his thread and it worked beautifully.
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Dude. I love this thing.
I just ordered that mppt converter
I would love to see the guts.
You guys meeting at your place today again? I can ride today
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Doood 
come ride
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So I bought an 18650 charger to charge up all my p packs before i get to soldering all the series connections together. Buuut it takes about 24 hours per pack. So I bought a power supply instead to charge them at a higher current; didn’t work, since it needs to be a constant current and constant voltage power supply.
So I was wondering, could i wire something like this to my power supply charge them? or better yet, just connected it to my wall charger and step it down to 4.2v @ 4A? (I have a 4p pack)
Along similar lines, do you guys build your packs at storage voltage as shipped, charge to full volage before building, or even do a full cycle before building? Last time I made sure individual cells were within 0.01 v shipped before welding in parallel, is there more to consider than that?
If I order cells new, I always check the voltage, which should be 3.7-ish, and if they are all indeed around that voltage I will build the pack at that voltage. For salvaged cells, like breaking them out of used old packs and refurbishing them, I charge them to 4.2 again because they’re usually well below nominal (2.8-3.2V) by the time I’ve broken them free from their old packs.
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is it normal to get cells at 3.46V?
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yeah that’s fine, I’ve had some at that V as well. @iamasalmon I think your HG6 cells were at that V?
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I think most mine come at that voltage. But I charge mine all to full and then monitor each one after a couple days to see if I have any bad eggs
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Are you checking to see that they don’t lose voltage during that time?
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If you have cells within about 0.03v you can also match them so the group comes out at the right voltage
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I need to add a JST connector (similar to the one pictured above) to a battery I purchased, that didn’t come with one. Would it be safe for me to use one like this 20awg silicone wire to splice/solder? It claims that it’s for 1amp or less. My charger is 2 or 3 amps. I can’t find a similar JST product with thicker wires.
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Note that “JST” is the brand name, not the connector type. I believe the one you have pictured is a JST-RCY type connector, whereas the link you provided is to JST-SM, which is a click lock connector. Either way these are meant for connecting signal wires and are only rated for 5volts 1amp. I’d use instead an xt30 or xt60 for charge cables.
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Thanks for the connector facts. I learned something! I’ve bought 3 or 4 batteries and they’ve all had a low-profile connector on the charge cable (likely RCY type), so that you can easily feed the wire through a hole you’ve cut into your enclosure. If I used an XT30 it would be too large to feed through this hole in order to mount the female power connector.
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