I see many people fret about using a low voltage power supply to configure their VESC. This is a good idea but it is not always necessary.
The only time I would say it is absolutely necessary is when powering up a VESC for the very first time, if you buy them from me you can count on this already being done. Sometimes a solder bridge will not be seen on the first visual inspection and you can fry a vesc if you attempt to spool up at higher voltages. Also if you are attempting to power an unusual motor that is not normally used, better to use caution and use low voltage.
Well sir… what low voltage supply should I use?
Lab power supplies will often have trouble or induce unknown variables so I recommend a basic 12v lead acid battery. Nothing fancy, you can get one delivered for less than $10. Again, if you buy one of my VESC’s this is not necessary unless you are using unorthodox motors.
I have run motor detection at 12s without issue on a 192kv motor. This brings up another point… motor KV and system voltage. Before running config divide 8600rpm by your system voltage. If the resulting number is lower than the KV of the motor you are going to use than your KV is to high and you need to get another motor or lower your voltage.
A 192kv motor is the absolute max you should use at 12s.
8600rpm/44.4v = 193.69KV
If you attempted to spool up a higher kv motor at 12s it could cause faults and return a bad detection. Same goes for lower voltages but with higher KV motors. Take 10s for instance. 8600rpm/37v = 232.43kv So we can see 230kv is the max kv we should use at 10s.
It should also be possible to power up the VESC for the first time with a 3s lipo battery right?
I would happily get myself a 12v lead acid battery if needed, but I do have quite a few 3s lipos at hand. This probably goes for quite a few people.
Thats a tricky question. Chances are those lipos are capable of some really high amps in comparison to a little 12v lead acid battery. Small lead acid batteries are not capable of high discharge currents while a lipo might give a fault all the current it needs to do some damage. Maybe I worry too much?
Edit: After giving this some thought I came to the realization that i have never breached 5 amps on my power supply when running detection at 12v… even with a faulty VESC. A 3s lipo should be fine.
@claudiofiore88 That should work but you will probably pop it if you try to reverse rotation at max rpm. Most of the time you can reset it by unplugging/plugging the power supply with the vesc disconnected. Using a SLA eliminates this nuisance when calibrating transmitters etc… again this is only necessary on a fresh untested VESC or when running an experimental or questionable motor.
@NNGG The VESC version 4.12 and under currently has a minimum voltage requirement of 8v.
Honestly, if you have an untested VESC your best bet is to look over the drv8302 legs in detail with a 10x jewelers loupe before running motor detection. I never test without first going over the entire board with 5x and legs with 10x magnification.
Most failures are actually due to uninsulated phase wires and bad connections. I personally have never killed a vesc. It is not for lack of trying but I mind my wires and I always look for things that might be wearing through cables or coming loose. I also use a bms so no more battery connection mishaps.
Don’t rush it, take your time and inspect everything before making your final connections and make sure everything will not come loose when you go for that first ride. Haste has killed more VESC’s than we will ever know.
Isn’t it safer to use a lab power supply with current limitation for the first times you power up your VESC ?
An battery of 12V has no current limitation and can deliver quite a big load in comparison.
Can you also elaborate a bit more on this statement ?
“Lab power supplies will often have trouble or induce unknown variables”
@akira You are correct but… three of my customers have killed vesc’s using lab power supplies. I don’t know if they reversed polarity, uploaded the wrong firmware or some other cause. It leaves a lot of questions and not many people have lab power supplies or know how to use them either. A thorough inspection paired with a low voltage power source has given me 100% success rate when testing fresh VESC’s. The main saving grace of using low voltage is that the motor will spool up softly compared to higher voltage. It is much less aggressive.
One little detail I did not mention earlier. Use the arrow keys to check the VESC before running detection. Just give it a quick tap. If everything sounds fine give it another longer burst and make sure it spools up before detecting parameters. If something is wrong it will let you know with either a drv8302 fault or jerky operation.
@Hummie using a nominal cell voltage for the max kv calculation is fine. In real world use, the pack will be under considerable load at max rpm and have considerable voltage sag unless it is an extremely large pack. 192kv @ 12s has proven to work without faults.
There really isn’t many reasons to go higher than 12s on a skateboard. 12s at 80 amps will give you 3500 watts. 80 amps being the limit “for me” when using 10awg cable. 3500 watts should propel a person to about 45 to 50 mph on a skateboard. If you use higher voltage you also need to use special cables and take some extra precautions like warning labels etc. Everything gets a lot more expensive too. Maybe someday when we have a fully fledged racing circuit will see systems like this in the open class but I would still caution against it for the average street rider.
Many thanks @chaka! It’s really helpful for me to understand the rationale behind the calculation. I always limit erpm to around 40-50k, just to keep top speed aligned with my personal speed tolerance (this gets me to about 24mph top).
Am I wrong but I remember someone saying that you may run a voltage and kv motor that keeps you under the 8600 limit on the bench, but if you get outside going down a hill/mountain and were to brake you’ll end up beyond the rpm limit and have a fault? That sounds like disaster.