ElectricBeam wrote: ↑
Jul 23, 2018 6:30 pm
Since I don't plan to let the motor reach insane speeds, I am hoping it will not self-destruct.
That really only happens to brushed motors, but some brushless inrunners aren't built very well and magnets can come off the rotor at really high speeds.
I am really only aiming to increase the efficiency of the system while maintaining a high power level. Of course, that is not to say I won't ever run it at high speeds.
Well, higher voltage vs higher current doesn't necessarily mean higher efficiency.
It depends on the exact problem, and the reasons it's happening.
There've been a number of discussions about it, but basically it comes down to losses inside the electronics at higher voltages, vs losses inside teh wires at higher currents, vs the winding of the motor vs the speed it's run at vs the gearing of the motor-to-ground system.
Thicker wires will fix those wire losses.
Electronics losses cant' really be fixed that easily, at least not all of them.
As an example: often, FETs for higher voltages have higher internal resistance vs those for lower voltages. So there's more heat generated in them whenever current is flowing. Not much to do about that but find the best match for FETs for your needs, that will still work with the existing gate drivers/etc., or get a controller that is already optimized for it by a good engineer (this is probably not cheap).
Similarly, if a controlelr's LVPS is not a switching unit, or even if it is and it uses a resistive input like the non-SMPS ones do, then the higher the voltage the more heat it'll generate. This can be fixed by using a controller that has an SMPS LVPS in it, or installing one in the controller and bypassing the existing LVPS, as a couple of ways.
Those losses are not on the scale of making things super hot, but they do exist.
But...since it's a brushless motor, you may want to look into the phase/hall wiring combo first. If it's a false positive, it may run forward, even at normal speed under load, but it will take way more power than it should, and everything will get hot (wires, motor, controller) because the timing of the system is wrong.
That might fix everything without all the complexity and hassle and expense of tripling your voltage and replacing or modifying all those things.
As for the battery, I was able to locate some 32s BMSs that appear to be suitable on Aliexpress. I know there are millions of BMSs on these sites, but I am not sure what the consensus is on buying them.
The consensus generally is that you get whatever they send, and it does whatever it does, and you pay whatever the cost is. Whether it does what you want, or instead just produces smoke, well, that's the gamble.
Sometimes sellers are honest, and sometimes they are not, and sometimes they have no idea what they actually have or sell. There's unlikely to be any kind of real support or warranty, honest or not.
I couldn't tell you if either of the linked BMS are what you need (even assuming the sellers have accurate info on the page, which is not a given).
You might have to look around the forum at the various BMS threads, and see if anyone has a recommended seller that's proven reliable. Then see if that seller has a BMS that does what you want.
With a BMS, I suppose I could get away with lower quality batteries such as these on sale now
I suppose, but remember that the battery is the heart of the system, and if it can't supply the power you need when you need it to, for as long as you need it to, the system cant' do anything to make up for that.
But besides that, what is a source of high-quality lipo batteries? I would not be against using them if the price is not insane.
I don't know anyplace to get guaranteed tested quality RC LiPo--it's cheap for a reason: there's really no QC of the cells, assembly, wiring, or completed packs, regardless of source, AFAICT.
The main advantages are that tehyr'e easy to hook together, there are common balancing chargers for them, and they can put out some pretty high currents (for a short time).
But tehy have short lifespans, and when they have more severe quality problems, or are abused in the wrong way, they tend to go out in style, as it were.
That said, various reports here on ES have said that the Turnigy version of a pack can be better than the Zippy, IIRC. (you could search for those two terms together and see what comes up).
I've used RC LiPo on CrazyBike2 and it worked pretty well while I did, but it didn't last all that long before it began puffing up; I doubt I could get the packs out of the ammocan they're in now wtihout damaging them. :/ (been sitting a few years now without much use since they started to go).
I've also used a cheaply made 18650 pack, and with low demand it works ok, but high currents it'd need a lot more parallel cells. Mostly this is not used much nowadays except for bench testing stuff cuz it has a wierd BMS problem.
I've used an old A123 pouch cell pack, and it worked pretty well. Still in use on the Raine Trike.
What I really like and use heavily are EIG NMC pouch cells but they aren't cheap and are hard to get hold of. If they were easier to find and get, I'd recommend using them. The only "easy" place to find them is used Zero motorcycle packs from the year or so they made them with that cell.
Others use various repurposed cells and pack sections from large-EV packs, like the Nissan Leaf, etc.