I want to add more fets to cc25 ESC- how

[glofuel]

I have good electronic assy with lots of proto experience and general understanding of electronics. Also pcb layout aswell, I hope you guy's can help on the more technical side. :)

I wish to add more fets to a cc p25 esc to increase it to handle approx 120Amps using something like 29.6v (8cell li-po), I understand it could be a case of paralleling fets and adding extra drivers - is this possible with correct pcb layout and cooling. a seperate pcb maybe a good idea (weight not a problem).

:rolleyes: My idea is to power a 1/3 scale Diabolo rc aerobatic aircraft approx 8Kg be capable of extreme verticals/3D flying using a outrunner brushless motor.

Your feedback would be appreciated :D

[dj2u]

Not a good idea to use homebrewed parts inside an 8Kg plane for security reasons!!!!

Diego

[Comatose]

Erm, you could, but why not just use a CC P125? The heavy copper board (4 oz double sided with wiiiiiiiide traces, or thicker, or more layers) will cost more for one prototype than the P125 costs new. Just the PCB. 125 Amps is really a lot of current.

[Gary Warner]

I did this years ago with a brushed controller. I just added the gate leads to an external PCB and loaded up 10 IRFZ44's. It held up at 100 amps. Was used on a weight lifting plane and flew at 14 pounds for a 500 sq.in. plane.

Gary
--

[glofuel]

Thanks for the feedback guys

Hi dj2u, homebrewed parts are not necessarily bad or unreliable, depends on the level of skill building them, in some cases are proberly as good if not better than the one's bought from a retail outlet.

Hi comatose, I am trying this on a budget. Cost of RC products in UK are dearer than rest of the world, it seems we get ripped of all the time. The cost of pcb's/components can be alot cheaper to than you think. ;)

more feedback please :)

[The Other Dave]

The first question I would have is would adding
all of the circuitry you are planning to add screw
up the phase detection circuit that controls the timing.

If you mess that up by adding to much capacitance or lowering the drive output impedance you will have a modified brick not a motor control.

[dj2u]

Hi glofuel!
Sure you're right! just didn't want to just tell a bare newcomer how to do power electronics ;)
Basically if you don't change the voltage you just have to care about the fets and traces, not the back emf circuitry.
I wouldn't use a standard cc ESC but a cc master (cooler fets due to switching algorithm). You could just try to stack some fets and double the traces with some soldered on wires. Look for a low rdson and low total gate charge (need less driving power).

diego

[tino_j]

In most cases there's no problem parallelling MOSFET's. You'll gain lower RS-on, thus lower power loss. Keep in mind, the combined gate capacitance increases, that might need better driver circuit...

[Bruce Abbott]

Just slapping on some extra MOSFETs in parallel is not likely to work very well. Firstly, for good current sharing the extra FETs should have the same characteristics (esp. Rds-on, Gate charge, threshold voltage), so it's best to use identical parts. Secondly, the increased capacitive load on the Gate driver circuitry will slow down switching speed and may cause increased dissipation (esp. at part throttle).

An 8S Lipo puts out 33V fully charged. The existing FETs in the PHX-25 are only rated for 30V, so you will need to replace them with parts rated at 40V or better. Some capacitors may need to be upgraded, and possibly also the 5V regulator.

The PHX-25 drives its N-FETs directly from the MPU, and its P-FETs through a simple level convertor with limited drive capacity. You should add high-power drivers such as TC4428. Make sure the maximum Gate voltage is not exceeded. It might be better to use only N channel FETs, with a boosted power supply (or special driver IC) for the high-side FETs.

I am trying this on a budget
It may be cheaper in the long run (and certainly a lot easier and safer) to just buy an appropriate ESC for the job. Yes, I know they're expensive, but after blowing a few dozen FETs...

[GlowFly]

As Bruce says, the original PHX25 has a just adequate gate drive circuit for the existing FETs, and cannot readily provide sufficient gate charging current for additional devices. The very recent revision does use an external gate driver and in principle might be better able to support additional devices.

I would advise though that there's more to getting extra current than just adding more devices. Physical placement is important. You should really examine the switching waveforms to ensure the FETs are being driven properly. Then there's the issue of parasitic gate lead inductance, ringing, oscillation etc.

Is it really worth it? Could get quite expensive.
--
Steve

[minifly]

have you taken a look at the hyperion esc's? they are ALOT cheaper than CC, and can be ordered from http://www.aircraft-world.com, shipping is quick.

[glofuel]

Thanks once again guy's for the info

Its starting to look more complicated than I first thought, although I have the necassary tools (Oscilloscope etc) to do this I am not sure I can afford the time involved testing to make sure everything works correctly such as the FETs switching properly and capacitve loading on the gate's, parasitic gate lead inductance, ringing, oscillation and so on. This is now getting a bit beyond my knowledge.

Hopfully this was a worth while question originally which may answer other people's thoughts with the same idea in mind.

Many thanks :)