I bought a Hobbywing ESC - Is this our Holy Grail?

I think you could come close to 17kW from the Castle/Hobbywing setup. I'm sure you could get to 14kW fairly easily (you just need to make sure duty cycle on the motor is maxed - which means finding the pulley sweet spot (one advantage of a belt/pulley setup)). Basically you want phase current to match battery current as closely as possible. If you have a high phase current, but a low battery current, your duty cycle is low.
 
17 kW is 22.8 HP. T=HP*5252/rpm. So 22.8 HP at 85000 rpm is 1.41 ft-lbs which is 1.91 newton-meters. The torque constant (nM/amp) for a BLDC is approximately Kt = 8.3/KV. The Castle 1721 is a 2400 KV motor so the torque constant is approximately 0.00346 nM/amp. For comparison various high speed offerings from NeuMotor with a KV of 2400 have a torque constant of 0.00394. This is true regardless of how the motors are wound. Using the NeuMotor data 1.91 / 0.00394 gives 485 amps. Assuming 92% efficiency for the motor this becomes 527 amps. So if a Castle 1721 is directly connected to a GT3582R compressor wheel with 8S you need a very big ESC. Otherwise every time the motor starts at full throttle you are going to hit an amp limit in the ESC. How many times can that be done before the ESC goes up in smoke?
 
I would say 12s should be a minimum requirement for any ESC one would consider for any full-size automotive application. Also, while kv and torque constants can be used as a guide, I wouldn't go by them. Too many variables. In practice you'll find things change. Sometimes by a lot. That's what I've found empirically and why my sig says what it says. Also, most ESCs have a punch or ramp-up function. Right now I can tell you, under load on a running car, it takes the LMT motor about 1.8 seconds to spool up in the sledgehammer. That's slow enough to minimize any sort of serious spikes; though on the first hit pretty much every time I see a phase current spike of about 1,800 amps. But that's not repeatable and I've only seen that twice. Actual current spikes (of any real, repeatable duration) are in the low 700 amp range; and running current is around 680-690 amps.

In the real world, full boost in 1.8 seconds would result in loss of control of a car at any serious power level. That's coming on hard and fast. Almost as hard as the Whipple and Eaton pd blowers I had on there before. With the power set to 100%, I can blow off the street tires at will at any speed. It's like having a 200-250 shot of nitrous come on hard.
 
Thank you for all of the thinking here. It is a lot to ponder and a lot to learn.

I did get this back from Hobbywing tech service regarding the Hobbywing max4 ESC. I noted in their specs that you should not run a motor over 600KV at 12A. So I asked if it could run a castle 1721 2400KV motor at 75,000-80,000 RPM. Below is their reply.

The ESC has no "limits" or safety for those areas (RPMs), so "it should work" fine overall. It dosen't have an RPM limit that is reasonable for any motor to acheive. The ESC's can fire significantly faster than required to operate the motors at their given ranges. In theory, the ESC's can operate well above 100,000 RPM​
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So, I am going to give it a go. I am wrapping up the design work on the GT 3582, which I surmise is too big. I’ll start a thread on my build. I ordered my stainless steel shaft extender. I am also ordered the parts for a LiFEPO4 battery. I will take it easy on the beginning and not hammer it too hard as it is spooling up and be sure to have plenty of cooling. Also I am a data hound, so will data log and learn.

I think I have a similar compressor to WB and he was able to make some boost. also have a small turbo to try KO4. That one has a friendly CFM for my engine, but requires a higher rpm, so may need gearing / pulley and belt.
 
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I just had a short talk with a rep at NeuMotor. The torque constant for a motor is solely a function of the KV. The KV is determined by the number of poles and how the motor is wound. If the torque requirements for the load is known then the motor constant can be used to determine the amps. The torque constant is the same across motor brands assuming it is defined the same way - peak or RMS current. A motor should be chosen with a safety margin vs max amps. At max amps the motor is saturated and the operations goes to hell in a hand basket. An ESC should be chosen that will accommodate the max amp requirement of the motor. Relying on the ESC to protect itself by limiting amps is not a good practice. and generally leads to ESC failure. He equated this to trying to control peak amps by flipping on and off a switch.
 
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GTHound said:
Similar to the motor summary, I am seeking a short list of ESCs to consider that are in the <$500 realm given the experiencial knowledge and collective wisdom of the forum.

What other specific models should be on the list? What should be crossed off this list? Are there other considerations? Country of manufacture? Other safeguards? Data logging? Are there any advantages to matching motor and esc manufacturers for a perfect pairing?

ESC Description​
VoltageProgrammableCont AMPt / Peak AMPPrice
Hobbywing EZRun Max46S-12S300A / 2000A$450
Castle3S-12SCastle link160A$315
APD$209
MGM
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Last week I bought the Hobbywing EZRun Max4 HV for $301 included shipping from Aliexpress. There was a Back to School sale on Aliexpress and you got a $40 discount on items over $200. Unfortunately it needed 1 week that my forum membership was confirmed so the discount is now expired...
Anyway if you don't need the Hobbywing US Warranty there are sometimes good deals on Aliexpress for the EZRun Max4 HV.
BTW I bought it for a different project but maybe one day it will be used for an E-Supercharger...
 

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Overvolting ESCs is never a good idea, getting them to run reliably at their rated voltage is already tricky.

The Max5 is designed for a smaller class of RC cars, I would expect the Max4 to be a better choice / have better ratings
 
wkerstens said:
Overvolting ESCs is never a good idea, getting them to run reliably at their rated voltage is already tricky.

The Max5 is designed for a smaller class of RC cars, I would expect the Max4 to be a better choice / have better ratings
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This thing is rated at even more Amps than Max4
1748389153275.png
 
Spec-wise, it looks better than the MAX4. However, it is significantly smaller and lighter than the MAX4. FWIW, I wasn't over-volting the ESC. They are rated for 12S; with each cell having a max voltage of 4.2 volts - which gives you 50.4 volts. The caps inside are rated for 63 volts. I also just checked the price on Amazon for the MAX4 - it's still at $379; perhaps they're raising prices due to tariffs? I don't know.

The one thing that does catch my eye is not only is the continuous current higher on the MAX5, but (more importantly to me) is the kV motor limit is almost 3 times higher - which indicates better MOSFETs are being used. Higher kV = faster switching which means switching losses (gate capacitance mainly in a MOSFET) should be lower (or better handled). I guess it's also possible that it uses GANFETs. I dunno.

BUT - I just checked on Amazon for the MAX5. The price is low - $219 usd. It gets pretty poor reviews from people who are pushing it hard - it tends to blow up. Could the low Amazon prices be counterfeits? Seems doubtful since it's sold from the Hobbywing store.
 
AlexLTDLX said:
BUT - I just checked on Amazon for the MAX5. The price is low - $219 usd. It gets pretty poor reviews from people who are pushing it hard - it tends to blow up. Could the low Amazon prices be counterfeits? Seems doubtful since it's sold from the Hobbywing store.
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That's for "small" Max5. G2 Plus is 330$
 
AlexLTDLX said:
Spec-wise, it looks better than the MAX4. However, it is significantly smaller and lighter than the MAX4. FWIW, I wasn't over-volting the ESC. They are rated for 12S; with each cell having a max voltage of 4.2 volts - which gives you 50.4 volts. The caps inside are rated for 63 volts. I also just checked the price on Amazon for the MAX4 - it's still at $379; perhaps they're raising prices due to tariffs? I don't know.

The one thing that does catch my eye is not only is the continuous current higher on the MAX5, but (more importantly to me) is the kV motor limit is almost 3 times higher - which indicates better MOSFETs are being used. Higher kV = faster switching which means switching losses (gate capacitance mainly in a MOSFET) should be lower (or better handled). I guess it's also possible that it uses GANFETs. I dunno.

BUT - I just checked on Amazon for the MAX5. The price is low - $219 usd. It gets pretty poor reviews from people who are pushing it hard - it tends to blow up. Could the low Amazon prices be counterfeits? Seems doubtful since it's sold from the Hobbywing store.
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Confused about voltage. So are there battery packs with 3.7V and there are with 4.2V?
 
For a normal Lithium (polymer) battery the nominal voltage is 3.7 V, the maximum, fully charged voltage is 4.2 V.
Generally 3.3 V is considered empty
 
AlexLTDLX said:
Spec-wise, it looks better than the MAX4. However, it is significantly smaller and lighter than the MAX4. FWIW, I wasn't over-volting the ESC. They are rated for 12S; with each cell having a max voltage of 4.2 volts - which gives you 50.4 volts.
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So there is no such thing as "4.2V batteries" or 50.4V batteries? This is max voltage when freshly charged, and it quickly drops to ~3.7V?
If so, than after initial full-charge is gone, I would need to switch to 13S instead of 12S, to keep max possible voltage (assuming 12S system)? Also I see voltage drop is usually significant so it may be necessary to go upto 14s to use full power?
 
Think of nominal voltage as the 'average' voltage of the battery over its useful range. For best results you need to keep battery charged up - but you shouldn't go over the rated cell count for the ESC/motor if you want it to survive.
 
Vetal said:
No way to add couple of cells in series while voltage is low under load?
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I think you would be better off having more amps in battery pack than trying some complicated system to dynamically adjust the number of cells in the circuit. People have a lot of mixed feelings about elon musk and spacex but I think their philosophy of the best part being no part is a step in the right direction. The less complex a system is the greater its reliability assuming quality parts and work when building it
 
Vetal said:
No way to add couple of cells in series while voltage is low under load?
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I'm afraid this is a really really bad idea. One of the most important factors of battery health is cell balancing, adding cells with a different state of charge to a battery pack under load will result in uneven load of the pack with unbalanced cells as a result. When doing this with common Li-ion based cells this can get dangerous quickly. I would suggest reading some more about lithium-based batteries, and how to take care of them.
They're great, because of their huge energy and power density, but that's also the reason they can be very dangerous, when not used properly. LiFePO4 / LTO are inherently safer, but the power required to run these compressors can still burn down your car if not taken care of properly.

Just make sure to use properly dimensioned batteries, that can take the load of the BLDC motor, and you'll be fine. The performance will be slightly better when fully charged, but will drop pretty quickly to the nominal performance, where it wil stay for most of the time, until the battery needs to be recharged again.
 
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