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Old Jun 01, 2009, 04:19 PM
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Question
increasing brushless esc power

1st thank you for your time,

Can an brushless esc be made to handle larger amperages just by increasing (in other words adding) to the number of fet chips in parallel and increasing the heatsink as well? if not why not, and if so would you have to increase the trigger signal for the fets at the same time?

Sean
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Old Jun 01, 2009, 05:18 PM
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Paralleling FETs is an option, but the circuitry driving the FET gates, has to change too. Otherwise FETs will switch too slow, ruining them very quickly.

ESC cooling
www.mgm-compro.com
-> tech.info
-> controllers COOLING in models [pdf, 166 kB]

Vriendelijke groeten Ron
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Old Jun 01, 2009, 07:01 PM
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Thank you for the quick reply,

Why would they switch slower as you add more fets? And what would be needed to speed up the switching?

I'm not doubting your answer just trying to wrap my mind around it a bit better.

I have a bit of electrical knowledge but most of it is....well almost 20yrs old from highschool, and the rest is either job related (control systems) or gleaned from books and places of wisdom such as this site. I'm pretty sure that i can purchase new speed controllers cheaper than repairing the collection of dead and used ones, unfortunately I am one of those people that feels the continuous compulsion to fiddle with things. If it is easier you are more than welcome to direct me to a book or website and I will assimilate as much data as possible before posting again.

Thank you again.
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Old Jun 01, 2009, 07:10 PM
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Quote:
Originally Posted by ONERCBOATER[QUOTE
]Thank you for the quick reply,

Why would they switch slower as you add more fets?
Ettra gate capacitance demansds more current to switch fast.

Quote:
And what would be needed to speed up the switching?
More current
Quote:
I'm not doubting your answer just trying to wrap my mind around it a bit better.

I have a bit of electrical knowledge but most of it is....well almost 20yrs old from highschool, and the rest is either job related (control systems) or gleaned from books and places of wisdom such as this site. I'm pretty sure that i can purchase new speed controllers cheaper than repairing the collection of dead and used ones, unfortunately I am one of those people that feels the continuous compulsion to fiddle with things. If it is easier you are more than welcome to direct me to a book or website and I will assimilate as much data as possible before posting again.

Thank you again.
Its fairluy simple. There is a parasitic capacitor - and a bloody big one, like several hundred pF or even a nF or two across the gate/source junction, formed basically by the uber thin insulation between the gate and the FET channel..

The bigger the FET /more FETS there are..the bigger that capacitance is..and it has to be slammed full of electrons to get the FET fully ON or OFF. Half on FETS are bad news. half current and half voltage = LOTS of power to make them fry. So you want the transit time in that state to be as fast as possible. BUT there is an even worse possibility, that they will go unstable and oscillate as they switch if you drive them from TOO low an impedance. So its all a bit of a compromise. Which is generally optimised for a particular number of FETS and the type they are.

Which is why Ron is urging caution. You MAY be OK. Or not. Doubling up? probably. Slapping in ten times the current devices of entirely different spec? No way.
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Old Jun 01, 2009, 09:58 PM
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If your ESC has a standard FET driver like the IR2130 you can look in the data sheet and see if it can drive more FETs. In any case it is always possible to calculate the drive capabilities to see how much more load that can be added. All ESC's have resistors between the FET's gate and driver to limit the switching current. Too fast a switching time causes oscillations. In most cases with a driver like the IR2130 it is possible to drive huge loads. Also the IR2130 can handle 600 volts so if you modify the zero cross detect circuits it may be possible to up the voltage. In my experience the IRF drivers such as the IR2130 are indestructible.
In all cases it is possible to add a driver circuit to drive any size load you want.
Another possibility is to replace all the existing FETs with something that has more current and less capacitance. This is a way to repair those smoked ESC's you have piled up.

Just about all ESC's use the same generic circuits, the manufactures such as IRF and Atmel have application notes that explain the circuits. They are simple enough so they can be modified as needed.
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Old Jun 04, 2009, 12:39 AM
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wow....i'm absorbing a big chunk of info....thank you very much!
Let me see if I understand this right, I can add more fets, but it would be better to replace all the fets so that they are all the same type. If I increase the fets then I most likely should increase the power for the driver.
As I increase the size or the number of fets I will increase the capacitence and this could cause the fets to open and close too slowly causing damage to them (heat build up?) In order to minimize this damage, I would wish to up the available amperage and if I over do this portion then they could wind up in an unstable state constantly shifting on and off which would also damage them.

The resistors that are inline with the fets are there to limit current as it is and if I am not askinf for too much more power from the esc I should be able to tap in prior to the resistors and add more fets in parallel with their own resistors, this could in theory allow me up to double the esc's amperage as long as I provide enough power to the source pole of the fets by a jumper from battery (?) and provide adaquate additional heatsink material. The resistors are there to control or buffer the capacitence...or is it current?

If I also understood correctly I can use the portion of the speed control prior to the fets to control a larger driver circuit and by doing this essecially build a much larger esc as long as the capacitance doesn't get too great and there is enough amperage available to the fets source pole.

also what type of fets are best suited to this type of application as there seems to be a plethora of different fet designs.

and last but not least are there any pics or diagrams available to assist with this? or books I should read on it?

Thank you all again and it always amazes me with the amount of info available here....I have a feeling that a greater than average portion of our members is at or above the 95th percentile

Sean
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Old Jun 04, 2009, 07:10 AM
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Quote:
Originally Posted by ONERCBOATER
Can an brushless esc be made to handle larger amperages just by increasing (in other words adding) to the number of fet chips in parallel and increasing the heatsink as well?
You can always increase power by adding more heat sink and, as mentioned, sometimes by parallel FETs. I was able to almost double capacity of Turnigy 6a by adding more of same FETs (no driver chip on that one). Made it the lightest controller in it's class.
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Old Jun 04, 2009, 11:10 PM
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A good place to start is to get an application note for the IR2110, IR2111, IR2130, etc. They all have about the same information. Next get the application note for the On semiconductor MC33033 or MC33035. Next get an application note from one of the microprocessor manufactures such as the AN1160 from Microchip, Atmel also has a bunch of good application notes.
There are other application notes but those will get a good start.
FETs come in three main types, low voltage (under 30 volts), high voltage (55 volts) and either logic level or high voltage control. The main concern is the voltage driving the bootstrap circuits. If it is 5 volts you will have to use logic level FETs. If the bootstrap circuits are high voltage (12 to 20 volts) then you can use cheap FETs such as the IRF3205 ($.95) or IRL3803 ($.90). These are 110 and 140 amp FETs so two or three in parallel can take out just about any battery pack. You will never smoke one of these unless you apply too much voltage.
Also the bootstrap circuits have to have enough current to drive the upper FETs, since the bootstrap circuit is just a diode and capacitor they can be made any size needed. In some cases the BEC or 5 volt processor supply drives the Bootstrap so that can be overloaded.
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Old Sep 01, 2014, 09:04 AM
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hi guys just having a brain storm along this thread

pleas let me know if im wrong (witch i probably am)

if the fet driver board emits a on/of signal to drive the fets

could you use the output from the same fets to simply drive bigger fets?
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