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by zombiess
Mar 07 2020 7:34pm
Forum: Motor Technology
Topic: Does adding more cap to the DC bus on a controller help? Look in here for the answer.
Replies: 10
Views: 522

Re: Does adding more cap to the DC bus on a controller help? Look in here for the answer.

Something to think about is that when you have a battery disconnect event, it could be a short somewhere that is tripping a fuse or contactor, and they trip at currents quite higher than your thermal-limited peak current figure. If you can deliver a 400A burst to the motor, maybe your main fuse tri...
by zombiess
Mar 07 2020 4:26pm
Forum: Motor Technology
Topic: Does adding more cap to the DC bus on a controller help? Look in here for the answer.
Replies: 10
Views: 522

Re: Does adding more cap to the DC bus on a controller help? Look in here for the answer.

Marcos, I've simulated the battery disconnect in various scenarios as posted below. There is quite a bit going on the graphs, so here is the secret decoder key. Top graph: Green = max recorded voltage into 25uH load inductor Red = Voltage pulses into 25uh load inductor Yellow = DC bus supply (batter...
by zombiess
Mar 07 2020 12:36pm
Forum: Motor Technology
Topic: Does adding more cap to the DC bus on a controller help? Look in here for the answer.
Replies: 10
Views: 522

Re: Does adding more cap to the DC bus on a controller help? Look in here for the answer.

I'm going to take a stab at sorting out what is needed on a sudden disconnect with back of the napkin calcs. Energy stored in an inductor is 0.5 LI^2, so 150nH has: 0.5 * 150nH*400A^2 = 12mJ Capacitance overhead required to absorb 12mJ = 0.6uF (calculated at 200V because of device avalanche and assu...
by zombiess
Mar 07 2020 12:18pm
Forum: Motor Technology
Topic: Does adding more cap to the DC bus on a controller help? Look in here for the answer.
Replies: 10
Views: 522

Re: Does adding more cap to the DC bus on a controller help? Look in here for the answer.

Does a large inductance between battery and DC link change the voltage situation? For example during normal operation and also when the BMS disconnects the battery at peak current. Yes, it does change things. As simulated above, the battery to DC link was 150nH. I just ran it at 15uH and 150uH batt...
by zombiess
Mar 07 2020 12:00pm
Forum: Motor Technology
Topic: Does adding more cap to the DC bus on a controller help? Look in here for the answer.
Replies: 10
Views: 522

Re: Does adding more cap to the DC bus on a controller help? Look in here for the answer.

So is it possible to make your own snubners or they have to be embedded on the pcb itself? Ive heard a few things about them but not much on how to make one, if the speed controller pcb design does not have it. Seems like major safety improvement, which has not been widely enough been executed Sent...
by zombiess
Mar 07 2020 11:38am
Forum: Motor Technology
Topic: Ceramic Capacitor, adding some to controller DC rail
Replies: 44
Views: 3981

Re: Ceramic Capacitor, adding some to controller DC rail

I simulated adding more cap to the DC bus at different locations.
viewtopic.php?f=30&t=104994
by zombiess
Mar 07 2020 11:36am
Forum: Motor Technology
Topic: Does adding more cap to the DC bus on a controller help? Look in here for the answer.
Replies: 10
Views: 522

Does adding more cap to the DC bus on a controller help? Look in here for the answer.

This was inspired by a resurrection of Doctorbass's old thread about adding ceramic caps. Adding caps to the DC rails can provide some minor improvement, but it often will not solve major turn off overshoot. Here are some simulations with relevant parasitic RLC parts modeled. This layout has ~45nH o...
by zombiess
Feb 12 2020 12:24pm
Forum: Motor Technology
Topic: Cheap FOCer 2 (Open-source, Low-cost, VESC 6 based ESC) (Prototyped. Materials have arrived for a test batch)
Replies: 45
Views: 5519

Re: Cheap FOCer 2 (Open-source, Low-cost, VESC 6 based ESC) (Prototyped. Materials have arrived for a test batch)

shaman wrote:
Feb 11 2020 11:02pm
How do I know everything is waterproof up in that motor?
By running it underwater of course! Motor runs = waterproof, motor fail = not waterproof :mrgreen:
by zombiess
Feb 04 2020 1:01am
Forum: Motor Technology
Topic: Cheap FOCer 2 (Open-source, Low-cost, VESC 6 based ESC) (Prototyped. Materials have arrived for a test batch)
Replies: 45
Views: 5519

Re: Cheap FOCer 2 (Open-source, Low-cost, VESC 6 based ESC) (Prototyped. Materials have arrived for a test batch)

I'll be interested to see what your results are. Based on my math, both FETs should be able to handle close to (or even over) 100A phase with good heatsinking, assuming you don't spike over 60V of course. Here's hoping you might achieve something close to that. In one of my own thermal tests I foun...
by zombiess
Jan 10 2020 4:48pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

What I do not follow is predicting motor efficiency from impedance matching, nor BEMF dictating motor output. I was using the efficiency to demonstrate where maximum power is transferred, that is all. When you tell someone that an electric motor makes the most power when it's loaded to 50% efficien...
by zombiess
Jan 10 2020 12:33am
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

Have I missed something? This discussion is about theory, money is irrelevant. :) Before coming to any conclusions you need to have a solid understanding of the problem which needs to be solved and any limitations. It's difficult to make generalizations for application. There are usually multiple w...
by zombiess
Jan 09 2020 6:04pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

Punx0r, what conflict do you see in my example trying to show the relationship between KV and MPTT?
by zombiess
Jan 08 2020 12:28pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

Punx0r or anyone, could you write a quick explanation of how BEMF works from your understanding? Keep it simple, use an ideal motor (no loss) and treat it as an impedance. We have a miscommunication happening and I'm not quite sure where it's at. How does BEMF limit input power? Where do the voltage...
by zombiess
Jan 07 2020 5:42pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

The 5V of BEMF is caused by the RPM of the shaft which is performing work on something. That work requires power which it is receiving from the shaft. Power at the shaft is voltage times current. There is 15V of voltage headroom left to add more power to the motor. Nope, that’s still not clear. BEM...
by zombiess
Jan 07 2020 1:20pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

I'll be honest I find your post hard to follow and I'm not sure if it's because there are mistakes or if it's correct but I can’t understand it. Or maybe it’s right but for the wrong reasons. For example, maximum power transfer theorem is about matching load to source and is generally unrelated to ...
by zombiess
Jan 06 2020 2:43pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

BTW, I know my title was click-bait :) I just wanted to talk nerd with other nerds for a bit, test out the explanation of the relationship between KV and and Power.
by zombiess
Jan 06 2020 2:41pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

Unless I'm missing something, motor efficiency is being muddled up with impedance matching: Output wattage: 150A * 5V = 750W of output power We are inputting: 20V * 150A = 3000W of power to the motor. It is outputting: 5V * 150A = 750W of work. Efficiency is output/input: 750W/3000W = 25% efficient...
by zombiess
Jan 06 2020 2:01pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

But but but :confused: he stutters. @zombiess: BEMF is the voltage resisting the input voltage, not the voltage doing mechanical work.. In your calc it’s all backwards or the motor would output max power at max back emf.. that is at noload where efficiency is zero. If your calcs above would be corr...
by zombiess
Jan 06 2020 12:32pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

If you only have 1V of headroom over the BEMF, then how are you getting 20A into your 0.1 Ohm motor? Do you mean 18V BEMF? For 19V BEMF, I think you have 0W output power, 190W iron loss, 10W copper loss, and you are 0% efficient. What I'm trying to illustrate is that when the motor is run at 19V, w...
by zombiess
Dec 31 2019 3:29pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

One of the times I was talking to Luke, it sounded like one of the reasons he preferred a high Kv motor at half-throttle compared to a lower Kv motor of the same type and size at full throttle (with both resulting in the same speed)...is that the high Kv motor had thicker wire and less resistance. ...
by zombiess
Dec 31 2019 3:22pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Re: Why more KV = more power, the Maximum Power Transfer Theorem

Dauntless wrote:
Dec 31 2019 2:18pm
We're going to have lower performance with hubs, but what is the real story comparing it to a middrive? Should we really want a high gear ratio?
You design for your needs, there is no one size fits all solution as they are all constraint dependent.
by zombiess
Dec 31 2019 1:17pm
Forum: Motor Technology
Topic: Why more KV = more power, the Maximum Power Transfer Theorem
Replies: 51
Views: 3794

Why more KV = more power, the Maximum Power Transfer Theorem

I wrote this up some time ago when I was trying to understand the Maximum Power Transfer Theorem in relationship to sizing a motor and choosing a KV for driving a propeller at high RPM and high load for several top speed quad copters I built. Some basic electronics knowledge is needed to  understand...
by zombiess
Dec 02 2019 7:33pm
Forum: Motor Technology
Topic: Cheap FOCer 2 (Open-source, Low-cost, VESC 6 based ESC) (Prototyped. Materials have arrived for a test batch)
Replies: 45
Views: 5519

Re: Cheap FOCer 2 (Open-source, Low-cost, VESC 6 based ESC) (Prototyped. Ordering materials for a test batch)

Of course I won't be able to out China China. You can totally out China, China. Just take someones money, send them a defective product, or the wrong product, or even better an incorrect defective product! Then when they ask for a refund, tell them sorry, but you'll provide them credit on their nex...
by zombiess
Nov 30 2019 9:33am
Forum: Motor Technology
Topic: STSPIN devboard
Replies: 5
Views: 864

Re: STSPIN devboard

TI's Instaspin on their C2000 chips is really nice, but the code bas a fairly steep learning curve when you start using your own hardware. FOC Sensorless startup has worked on every motor I tried with a little tuning.
by zombiess
Sep 19 2019 8:29pm
Forum: Motor Technology
Topic: 100A through a MOSFET? FLIR video
Replies: 1
Views: 485

100A through a MOSFET? FLIR video

This is part of a series of tests I ran to quantify some maximum parameters of various MOSFETs. The one in this video is an IRFP4568. Turns out my setup was able to handle a maximum of about 120W of dissipation. Not going to happen once an insulator is in place, I only managed 66A when it was instal...