Golf Cart Soild State Controller

Thread Starter

Keldeck Knight

Joined Jul 28, 2016
5
Hi Everyone!
I've been dong a heck of alot of research and wanted to confirm on a couple of things as I step through building a Golf Cart Controller. First of I understand I will not get it right the first time and will more then likely burn through a couple if not several hundreds of dollars before I start to geting the hang of things.

So heres my goal, After reading alot of PWM Mosfet examples I find myself to have a couple of questions and thoughts in mind. It appears a large amount of examples show that they only support the motor going in one direction and to have the mortor have a back and forth I need to build an "H" bridge type circut. Now if that's the case then the "H" Bridge examples I see normally have One MOSFET on each side. I myself need to have the ability to support a Burst of 300AMP's and a CONST value of ~50AMPs for the motor to run. Does that seem around right for a 2 HP motor? I know its hard to guess but I just wanted to confirm that I am somewhat warm.

2nd, I plan on making this controller compatible with motors with up to 700AMP's burst, and a build that can support 700 AMPS should be able to support 300 AMP's just find, The only difference would be cost, Correct?

How during the Time I am creating an "H" Bridge controller it appars the idea is that you have an uC that connects to a Driver that drives a MOSFET Drive to enable fast HIGH / LOW switching and after that the MOSFET then after that a fast switching diode to stop the motors Magnetic fields from classping and shooting a voltage back into the mosfet correct? I know this is very highlevel and it can get as granular as the traces on the PCB being able to handle the current traveling through it but I just wanted to make sure I have the general Idea.

Thanks everyone!

POSTSCRIPT: I will post some parts here shortly and see if I am getting the right idea.
 

crutschow

Joined Mar 14, 2008
23,545
Mosfets have a built-in substrate diode that usually can handle the current transient in a bridge when the motor is turned off.

To handle such high currents you may have to put several MOSFETs in parallel in each leg of the bridge.

To minimize switching requirements you could control all 4 MOSFETs in the bridge to reverse the motor polarity, but switch only one of the lower MOSFETS rapidly for the PWM speed control signal.

You might also consider using large contactor type relays in the bridge to switch the motor direction and use just one MOSFET(s) in series to control the PWM to the motor.
 

tcmtech

Joined Nov 4, 2013
2,868
The 300+ amp draw on your 2 HP rated motor is likely in a stalled condition so that why it can be so high for a 50 amp nominally rated unit.

Also unless your motor is a permanent magnet type (two leads or lug terminals) simply reversing the power to it won't make it go backwards. More than likely it's a series wound type (four leads or lug terminals) so you have to reverse the power going through either the field winding set or the armature set to make it spin the other way.

As for basic PWM circuit design that fairly easy. I would recommend starting with an old school control device like an LM3524 PWM regulator IC or similar being they are fairly easy to work with.

Now as for burning up hundreds of dollars doing this unless you have money to burn and want this entirely for a learning project you will be money and time ahead to just buy a stock golf cart speed control module being a good 36 - 48 volt 300+ amp plug and play unit can be had for $200 - $300.
 

Thread Starter

Keldeck Knight

Joined Jul 28, 2016
5
Thank you for your help!!!
Now what do you think about this mosfet for this application. It seems that I will need to make sure the board it goes on is rated to handle the current but what are your thought's on this? Its a TO-220 package. I don't need one rated for handle 330 continue amps but hey, Downside is just cost right?

http://www.mouser.com/ds/2/149/FDP020N06B-108818.pdf

In the Datasheet do you see the internal Diode you spoke about in your above post?

I think I need to have a driver to pair up with this mosfet as well to protect the IC as the Mosfets also have a Kickback?
 

crutschow

Joined Mar 14, 2008
23,545
It's an odd thing but sometimes the MOSFET chip can handle a higher current than the leads in the package can.
I would not try to push more than about 150A through a single TO-220 and thus recommend you use a least two transistors in parallel for reliability.

The internal diode characteristics are listed in the table titled "Drain-Source Diode Characteristics" at the bottom of page 2 in the data sheet.

No, MOSFETs do not have kickback.
A MOSFET driver is used to provide a high current to rapidly charge and discharge the large gate capacitance of a MOSFET.
A driver may also have a bootstrap circuit to all the use of an N-MOSFET in a high-side circuit such as those transistors in the top of the bridge.
 

Thread Starter

Keldeck Knight

Joined Jul 28, 2016
5
Thank you Crutschow. After your input I recall reviewing youtube and he went over talking about MOSFETS on the TO-220 being able to handle about 300 AMPs, However I'll take your word for it. That being the case, I found this MOSFET instead.

http://www.mouser.com/ds/2/196/irfb3256pbf-937544.pdf

It has a 4V trigger on the gate and handles about 172AMPS (More then 150) Plus it cost about 1/3 of the price. with a 5V uC I can just throw a resister on it for PWM to pulse the MOSFET for speed control (If the motor handles it) Is this where the driver for the MOSFET is needed as talked about in your post for PWM for the switching to occur fast enough?
 

tcmtech

Joined Nov 4, 2013
2,868
At 300 amps the leads will melt right off those if the solder joints don't first. When sizing switching devices look at their continuous current ratings, not peak which with TO-220 case style 50 - 75 amps is their limit.

The general rule I use is to use switching devices is that should have at least a minimum of 2x the systems peak working voltage and 4x the systems peak working amps.

Personally, I would spend the money and just use a large body type switching device that has screw or bolt type lug connections, not anything that is circuit board mounted unless there are 10 or more being used in parallel.
 

jpanhalt

Joined Jan 18, 2008
8,139
4QD Tech has been in the business of making solid state drives for golf carts and other mobility aids for years. There is a wealth of detailed theory and design information in its sites. This should get you started: http://www.4qdtec.com/

John
 

BReeves

Joined Nov 24, 2012
410
Good thread, I have an old Cushman 3 wheeler plus an old Cushman Minute Miser industrial cart. Have been thinking of converting both to solid state for quite some time but just never seemed to make it a priority. Hope you come up with something workable and post the details in the Completed Projects area. Going to take allot of work and research I can't seem to find the time to do.
 

tcmtech

Joined Nov 4, 2013
2,868
I've got literal buckets full of those things in the 200 - 600 amp 600 - 1200 volt range now. Many new old stock and many more as good used take offs from industrial power supplies and massive VFD units.

If you need some for experimenting let me know. I have a bunch of these I will never use , https://www.galco.com/buy/Powerex/KD621230 Half bridge NPN Darlington pair 1200 volt 300 amp and I tend to let the used take off units go for cost of shipping to guys haven't acted like a total asshat on the forums. ;)

Give me a good sob story about how you need them and I will send a pair. They are a bit dirty and what not but guaranteed to work good.
 

tcmtech

Joined Nov 4, 2013
2,868
Guess we got the same bucket. I had a bunch of them at one time they where used in big h-bridges
Yea it's always amazing to see what a guy can get from scrapping out big industrial power and control systems. Best score I got so far was a dozen of these 1200-volt 300-amp Half H-bridge power transistor units from one huge VFD drive. :D

I think I have given away at least 8 of them so far in grab bag boxes to new guys on these forums wanting to play around with bigger stuff while they learn about power electronics. :)
Popping TO-220 and TO-247 case switching devices is pretty easy but so far I have yet to ever hear of anyone blowing the guts out of one of these because they hooked something up wrong and caused a dead short. :p
 
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