New 100a reversible car esc on hobbycity - Page 2 - RC-Monster Forums

lutach · 04.27.2009, 05:08 PM

Quote:

Originally Posted by BrianG

Let's see:

- Two MMMs: yes, I do use the fans. But I would rip them out in a heartbeat if it wasn't for that warranty issue.

- One HW80: no fan.
- Four MM's: no fans.
- Two Quark 125b: no fans.

. Just messing with you Brian. I spoken with a few knowledgeable people and they said is not that difficult to make a very strong ESC that would stay cool without fans (Easy for them to say, some work for the largest EMS companies in the world). One of those people saw a design I have in mind and it was exactly what he was talking about. Now all of them said if all the MOSFETs are saturated (I've heard this before, but still having trouble figuring out what it actually means. All know is if a driver can switch a lot of MOSFET, why not make a humangodango of a ESC, people will buy the them if one builds them) it would definitely handle what ever R/C motor available. I'm actually testing something out to see if they are right and from the initial test, I think they might be specially with a driver that I was told wouldn't be able to switch all the MOSFETs. I wish I knew what I was talking about, but I don't. So feel free to fill my head with goodies.

BrianG · 04.27.2009, 05:27 PM

Saturating a MOSFET simply means driving the gate with enough voltage that the drain and source has as little resistance as possible. An "ideal" FET would have infinite gate resistance, zero gate capacitance, zero on-resistance, and infinite slew rate. No losses means 100% efficiency.

Anyway, less resistance equates to less voltage drop, which equates to less power wasted as heat on the FET for a given current. However, aside from an FETs rdson value, it takes time (albeit small) from when the FET turns off to fully on, and back again. This is called the slew rate and is measured in volts per second (or milli-second). During that time, there is variable "resistance" (increasing as the FET approaches "off", decreasing as it approaches "on"). Since a PWM signal switches on/off many many times per second, it makes sense that at those times is where you have the majority of the losses. OK you say, so why not simply reduce the on/off cycles? Well, you can, to a degree, but then you have motor inductance and the role it plays with the PWM "A/C" to worry about.

Paralleling enough FETs reduces the total rdson value and also reduces the voltage drop during the on/off cycles. If a FET can be totally saturated AND have a very very fast slew rate, losses are greatly reduces. Then, the FET current rating is pretty much limited by the package wiring.

I hope I explained that for you; I tend to ramble.

lutach · 04.27.2009, 05:50 PM

Quote:

Originally Posted by BrianG

Saturating a MOSFET simply means driving the gate with enough voltage that the drain and source has as little resistance as possible. An "ideal" FET would have infinite gate resistance, zero gate capacitance, zero on-resistance, and infinite slew rate. No losses means 100% efficiency.

Anyway, less resistance equates to less voltage drop, which equates to less power wasted as heat on the FET for a given current. However, aside from an FETs rdson value, it takes time (albeit small) from when the FET turns off to fully on, and back again. This is called the slew rate and is measured in volts per second (or milli-second). During that time, there is variable "resistance" (increasing as the FET approaches "off", decreasing as it approaches "on"). Since a PWM signal switches on/off many many times per second, it makes sense that at those times is where you have the majority of the losses. OK you say, so why not simply reduce the on/off cycles? Well, you can, to a degree, but then you have motor inductance and the role it plays with the PWM "A/C" to worry about.

Paralleling enough FETs reduces the total rdson value and also reduces the voltage drop during the on/off cycles. If a FET can be totally saturated AND have a very very fast slew rate, losses are greatly reduces. Then, the FET current rating is pretty much limited by the package wiring.

I hope I explained that for you; I tend to ramble.

Info like this is like giving a chocoholic free chocolate for life

.

BrianG · 04.27.2009, 05:56 PM

mmmm, chocolate.

Uh, yeah, anyway... I'm sure there is more to the story, but you can ask your engineer friends for all the sordid details. It's been a loooong time since I've done any kind of tinkering with FETs...

lutach · 04.27.2009, 06:10 PM

Quote:

Originally Posted by BrianG

mmmm, chocolate.

Uh, yeah, anyway... I'm sure there is more to the story, but you can ask your engineer friends for all the sordid details. It's been a loooong time since I've done any kind of tinkering with FETs...

The problem is all the engineering lingo and complexity that messes my poor non engineer brain

. One day who knows, I might see the design I have come true.

BrianG · 04.27.2009, 06:13 PM

lol, let's hope it is smaller than the average office desk though.

lutach · 04.27.2009, 06:31 PM

Quote:

Originally Posted by BrianG

lol, let's hope it is smaller than the average office desk though.

One of the designs for a 8th scale ESC has a MOSFET (Power Board) board measurement of 44mm (length) x 33mm (width) with 10GA wires. With the FET 30A rating it gives about 180A or 360A if double MOSFET board is used. I have other more powerful designs, but they are somewhat complex.

crazyjr · 04.27.2009, 08:55 PM

Quote:

Originally Posted by lutach

Castle Mamba Monster, Castle Mamba Max Pro, Tekin RX8, Losi 10th and 8th scale ESC, Hobbywing (Speed Passion and Orion), Novak, Traxxas, Ko Propo (Orion), Tamiya, Quark Plasmas and a few others that I might've missed. Brian, which one do you use

.

Sorry lutach, traxxas has an option for a fan, but its not mounted or included with the esc

lutach · 04.27.2009, 09:01 PM

Quote:

Originally Posted by crazyjr

Sorry lutach, traxxas has an option for a fan, but its not mounted or included with the esc

My fault, I gave my Traxxas away.

Styx · 05.20.2009, 04:41 AM

Anyone tested one of these ESCs yet?

Unsullied_Spy · 05.20.2009, 06:09 AM

Those are similar to the older 60A and 35A ESCs, right? I've got a pair of the 60A Marine ESCs (same thing as the land ESC but sealed up and water cooled) and they've been excellent so far.

BL_RV0 · 05.20.2009, 11:17 AM

I read a few of the reviews on te esc and they say that it will not work with spektrum radios, as it shuts down the motor at full throttle. Is this because the spektrum rx needs a higher voltage to stay on, and the bec on the esc can't keep up at full throttle?

lutach · 05.20.2009, 11:28 AM

It could be a switching BEC problem. Someone in the Brasilian forum got one and he said it works good.

BrianG · 05.20.2009, 11:41 AM

Does it have a switching BEC? Would make sense if it was linear and running on 3s+. Either way, an external BEC solves that problem. Although, sometimes simply adding a 1000uF+/10v cap on an unused receiver port provides enough buffer for momentary high servo loads.

05.20.2009, 12:02 PM

Quote:

Originally Posted by BrianG

Let's see:

- Two MMMs: yes, I do use the fans. But I would rip them out in a heartbeat if it wasn't for that warranty issue.

- One HW80: no fan.
- Four MM's: no fans.
- Two Quark 125b: no fans.

I still don't get why you hate fans, could you explain it please?