brushed dc motor ESC can i just add more MOSFETs to increase Amps?

[onercboater]

Today, 04:27 PM
hello this is my 1st post here, what I am trying to do it create a more powerful reversible DC motor controller to drive a 12v-14.5v DC brushed motor. The motor in question is a minn kota trolling motor that at 14.5v draws 49-50A at full throttle. I intend to control the device either through servos moving the potentiometers (or preferably through actuation direct from a joystick and would be absolutely tickled if i could control it via radio control receiver however I must 1st come up with an inexpensive controller circuit to build 1st before working on fancy controls) the schematic I am intending to follow is here...
https://www.electro-tech-online.com/custompdfs/2011/03/k166.pdf
located at the bottom of the page. I realize that asking this circuit to deliver 50A continuously in either forward or reverse would be a failure as the board it's self is unable to handle more than 5-10A even with the traces improved by layering solder on them. What I want to do is use this circuit in a modified form, I wish to triple or quadruple the MOSFETs by adding more in parallel, so instead of a total of 4 MOSFETs I am proposing that I use 16 which would give me 4x the capacity in ea direction. I also intend to use the circuit board only for the control portion and intended to fabricate my own separate board for the MOSFETs, which would allow me to use 4 gauge wire for the power in and power out of the driver portion of the circuit with a tap coming off of the heavy gauge connectors to feed the control portion of it. I realize I will need much greater heat sink capacity and am considering either very large fan cooled heat sinks or water cooled heat sinks. I have been warned of capacitance issues when adding additional MOSFETs and I am not sure if this will be a problem or not, if it is a problem how would I work around this. If someone has a better circuit design for me to follow that will not require programming I would be more than happy to follow it.

It has been over 20yrs since my last electronics class in HS, and I can still easily follow a schematic for assembly or bread boarding, I vaguely remember my electronics theory mostly just the basics needed for radio control toys such as wattage calculation.

Thank you very much.
Sean

 

[edman222]

Can you just use mosfets that are capable of more than 50amp? OnSemi Makes some that are around 120amps each.. ( will require some massive cooling) .. But in case you want to parallel them instead, I have found a circuit dealing with motor controllers with a description a while ago that shows you a bit about that (page 9)... "Half bridge from MIT".. https://web.mit.edu/first/kart/controller_rev1.pdf

 

[cr0sh]

My suggestion would be to purchase a motor controller sized for the application; unless you have a lot of experience in such controller design, what you could end up with is either a controller that works perfectly (or mostly perfectly), or something that eats thru FETs until you figure it out. If you are unlucky and it ends up being the latter situation, you might end up spending more money (on FETs, mainly) chasing down your problem(s) than you would have purchasing something already designed and built. A 50A motor controller won't be cheap, though; if it is your intention on gaining an education in such controller design, and money isn't an issue, then a custom design might fit the bill.

 

[onercboater]

best prices i have found for ready made controllers are in the $450-$600 range, as i need to control 2 motors, I figured i could fry several FETs trying to get there without exceeding that price. I really do like the idea of just using larger FETs.... do you have any suggestions, i will look myself but figured you might have more exp than I. Perhaps I could just use two much larger FETs to drive rather than several smaller ones... that might take care of the capacitance issue in the 1st place.

Sean

 

[onercboater]

I think i may have found the answer or part of it, unfortunately I am not savvy enough to understand it.... at least this late in the day... I'll read it again, sleep on it then try again in the morning. I found this PDF on paralleling FETs... I am just not up to snuff on this stuff anymore lol.
https://www.electro-tech-online.com/custompdfs/2011/03/para.pdf

 

[Dr_Doggy]

???? check ebay, there were lots of 60amp ESC's listed for like 30$

....and get one ESC per motor!

 

[4pyros]

Thare are hundreds of cheep controllers out thare, most of them for remote control robots. Here is a 80 amp unit for $120 for example.**broken link removed**

 

[Oznog]

What are you trying to do? Do you want this to be a trolling motor, or are you trying to retask it?

Do you want to simply have on/off control, or variable speeds?

Do you KNOW it draws 50A, for sure? Draw depends on load.

Adding more MOSFETs will (generally) help if it's not PWM'ed. If there is PWM, then there's a whole slew of problems in getting the gates to switch together, and quickly, and this could actually end up worse.

Really, you need some super-low rds-on MOSFETs. 50A from one MOSFET is not especially difficult.

That circuit is a problem. P-channel MOSETs have inherently lower performance than N-channel. It would be a fine idea to use N-channel in the + to motor "high side". The circuit will be all different though, because the N-channel will require a gate voltage higher than the + terminal of the batt. There's driver chips that DO that for you.

 

[OlPhart]

1> 4pyros' valid: cheaper to buy than guess & build. Unless you want to learn, then it's tuition.
2> oznogs' approach is 1 way. I've used similar, but put the N-channel on the motor low side. So: +supply -> motor -> N-channel -> ground(-supply) That way the gate voltage can come from the +supply above the motor.

Use a MOSFET driver (MCP1406 etc), they're made for it. I initially tried my own driver(s) and failed miserably. Took perfectly good silicon & returned it to sand, via smoke(teehee). Good Hunting... <<<)))

 

[onercboater]

ok, looks like i have more homework and some explaining to do...
1st off thank you very much for the feedback, and thank you for being active forum members (a dif forum i tried is apparently inactive)
Yes I was looking at Pulse Width Modulation, as it increases efficiency and maintains torque (from my understanding) I would be perfectly happy to use voltage regulation in place if that will be easier and will not cost me greatly in efficiency...and would prefect switching i think over linear.
Yes I am sure it was 50A I was looking at, I used an inline Watt meter rated for 75A to check it It moved between 49-50A at 14.5VDC.... 725watts... granted that was tested in a 55 gallon drum and the load would likely drop once the boat begins moving.... but for positioning and as a safety net I feel it wise to call it 50A so that whatever I wind up with can handle the draw for sure.
Yes I am trying to use a trolling motor as a trolling motor not as anything else. What I am trying to do is get a working electronic speed control unit that is reversible. The idea is that if i can get one unit to work then i can get two to work. I have a pontoon boat 20ft long that I am intending to put one trolling motor at the rear of each pontoon of, then I would like control the motors independently via a joystick (pulled from an old rc plane radio) through a mixer (got that unit standing by) so that full up on the joystick is full FWD on both motors....full down is full reverse on the motors, and left or right is full REV on one and full FWD on the other... with any combination of that capable for smooth tank like steering.
Here are a couple other options that I am considering...
Build a Versatile Miniature High-Rate ESC with BEC and Brake this is a description of the ESC, http://www.stefanv.com/quiet/escboth/figure1.gif this is a link to the schematic.
The issue with this one is that it does not have reverse otherwise perfect. i think... would it be possible to mirror the drive portion of the circuit to accomplish reverse....or use relays to flip the polarity as it goes to the motor to accomplish reverse?...
or am I much better off purchasing **broken link removed** this and just sucking it up with a $300.00 bill at the end... going to interesting explaining it to the wife.

I really would like to build the ESC, if for no other reason than pride... I am also trying to return to learning electronics... but as I said highschool was a long time ago...wish i would have been a better student. I use ESCs both brushed and brushless on almost a daily basis in the RC hobby, and would sure like to be able to upgrade and repair them as needed.

thank you all again for your time and patience.
Sean

 

[4pyros]

4pyros' valid: cheaper to buy than guess & build. Unless you want to learn, then it's tuition.

You can also find many DIY Controllers too. Andy

 

[onercboater]

ok ....after some serious soul searching, i decided on the sabertooth 2x50..... I feel a lil bit defeated.... but am essentially assured a working finished product. and at a good price.
So....now I am saving up my $$...should be ready to purchase in the next week or two.
Unfortunately....while perusing the different robotics forums..and electronics forums... i got the bug again. So two steps fwd 3 steps back.... I will buy and use the sabertooth unit for this project... and will look for a good ESC to build as well....hopefully I will be able to use the ESC i choose to build in a robot.... darn it.... this is going to be expensive lol.

Anyhow thank you all, and thank you for just telling it like you saw it.

Sean

 

[ronv]

Here are some ideas. Nice FET and driver. Just add a little pwm and stir well.

https://www.electro-tech-online.com/custompdfs/2011/03/FD2FFDP040N06.pdf


https://www.electro-tech-online.com/custompdfs/2011/03/an9405.pdf