Looking to design/ build a pair of H Bridges

someone can either explain this kind of stuff or knows of any good resources.

If you actually will look at those sites, you will find 100s of them are describing the
design considerations of BJT or MOSFET, or comparing both. They're not just
printing diagrams.

Honestly, people tend to think this stuff is trivial, and can be explained in a sentence or
two, but with h-bridges in the 15A range, you have no idea what you're getting into.
Do some legwork.

For a homemade H Bridge of that calibre, you could do it with 2x SPDT relays. If you need PWM control, you need 1 MOSFET between the relays and power source.

oric_dan(333):
Honestly, people tend to think this stuff is trivial, and can be explained in a sentence or
two, but with h-bridges in the 15A range, you have no idea what you're getting into.

You would do well to heed this advice. Designing an h-bridge that works properly and doesn't self-destruct after you get past about 5 amps or so of current-capability gets difficult quickly. If your goal is to learn how to design and build such an h-bridge, and money isn't an issue, then go for it; you will learn a lot. If, however, your goal is to implement an h-bridge for some other project, you will probably find it cheaper to just purchase such an h-bridge that uses a proven design. Otherwise, in testing/experimenting with building your h-bridge, you may find yourself blowing expensive MOSFETs left and right - ultimately spending more money than if you had bought a properly-sized h-bridge in the first place...

You would do well to heed this advice.

Wow, someone actually agreed with me this week! LOL.

That's why I'm asking here is someone can either explain this kind of stuff or knows of any good resources.

below is some quick reading on DIY H-bridges. ebay has some affordable h-bridges available.

http://www.ebay.com/itm/43A-DC-Motor-Driver-Drive-Module-H-Bridge-PWM-Contro-For-Robot-Smart-Car-Arduino-/300818612987?pt=LH_DefaultDomain_0&hash=item460a2fc2fb

http://www.ebay.com/itm/30A-H-bridge-Coreless-Motor-Driver-Forward-Reversion-Brake-For-Smart-Car-Arduino-/180983568079?pt=LH_DefaultDomain_0&hash=item2a237616cf

http://www.ebay.com/itm/Dual-H-Bridge-Optoisolate-ATMEL-ATTINY-2313-based-Motor-driver-Arduino-PIC-/271028808736?pt=LH_DefaultDomain_0&hash=item3f1a936c20

http://www.ebay.com/itm/50A-Single-H-bridge-Motor-Driver-Module-PID-for-Arduino-Intelligent-Car-Robotic-/230888425765?pt=LH_DefaultDomain_0&hash=item35c205c925

zoomkat:

That's why I'm asking here is someone can either explain this kind of stuff or knows of any good resources.

below is some quick reading on DIY H-bridges. ebay has some affordable h-bridges available.

Arduino Forum

http://www.ebay.com/itm/43A-DC-Motor-Driver-Drive-Module-H-Bridge-PWM-Contro-For-Robot-Smart-Car-Arduino-/300818612987?pt=LH_DefaultDomain_0&hash=item460a2fc2fb

http://www.ebay.com/itm/30A-H-bridge-Coreless-Motor-Driver-Forward-Reversion-Brake-For-Smart-Car-Arduino-/180983568079?pt=LH_DefaultDomain_0&hash=item2a237616cf

http://www.ebay.com/itm/Dual-H-Bridge-Optoisolate-ATMEL-ATTINY-2313-based-Motor-driver-Arduino-PIC-/271028808736?pt=LH_DefaultDomain_0&hash=item3f1a936c20

http://www.ebay.com/itm/50A-Single-H-bridge-Motor-Driver-Module-PID-for-Arduino-Intelligent-Car-Robotic-/230888425765?pt=LH_DefaultDomain_0&hash=item35c205c925

I love you.

Also how did you find these on ebay? When I search H bridge on ebay all I get was a bunch of garbage and L298N's. Thank you so much though!

dhenry:
At 14-15amp range, you need fairly beefy mosfets and you will need to use a mosfet gate driver for those things at moderate switching frequencies (1k or up).

Large motors have a lot of inductance. Running the PWM at 1 KHz will make the motors absorb most of the power.

Probably 30 to 60 Hz would be a better range for a large motor.

Looking at the maximum rating on the drain, 72A peak, 18A continuous I should be fine right?

Those ratings are typically for pulsed current (5us for example) into a resistive load, and with the case at 25c.

So I typically derate them 50% for my applications. For 15amp current, I use a 30amp (continuous) mosfet.

These look like a fairly decent design. They know enough to place a large reservoir cap across the battery
lines [presumed location]. zoomkat, have you actually ever used any of these things yourself?

http://www.ebay.com/itm/30A-H-bridge-Coreless-Motor-Driver-Forward-Reversion-Brake-For-Smart-Car-Arduino-/180983568079?pt=LH_DefaultDomain_0&hash=item2a237616cf

I do like it how so many CN companies include Arduino in the product title even though the thingies have
nothing at all whatsoever to do with Arduino.

You do appear to need 2 different PWM signals to the board, and what are the parameters of the current
and voltage signal out? Unfortunately, they rarely seem to have much documentation.

V + Power Input +
GND Power Input -
EN Driver Enable, high enable, low off
RPWM Forward PWM input, high active
LPWM Reverse PWM input, active high
CT Current signal output,analog signal
VT Voltage signal output, analog signal

A discrete h-bridge is fairly difficult to design, primarily to get it to switch fast and to allow for the appropriate dead time.

If you are starting now, I would recommend that you look into h-bridge drivers (high/low-side drivers). They come in many different shapes, depending on your needs.

Generally, you need to decide if you want to have braking / motor hold; if you want to be able to drive high/low sides separately; if you allow enable signaling or not; your desired voltage ratings and if you want under/over voltage protection, etc.

Many firms offer such chips and they are generally easy to use. IRF, Fairchild and On would be good starting points.

oric_dan(333):

You would do well to heed this advice.

Wow, someone actually agreed with me this week! LOL.

Well add me to your list. Playing about with this sort of current is not trivial.
One thing that it is hard to get over to beginners is that electronics do not scale up easly.

John_S:
For a homemade H Bridge of that calibre, you could do it with 2x SPDT relays. If you need PWM control, you need 1 MOSFET between the relays and power source.

This is an interesting option I hadn't considered. Mostly because I have never used relays. Is there anything to really know about them? Working with an relay seems kind of not ideal because the coil in the relay is going to suck a lot of current isn't it?

Also, I found this:

http://www.openservo.com/moin.cgi/Schematic2?action=AttachFile&do=view&target=OpenServo_2.0_032706.pdf

Is this a good approach/ alternative to designing a motor controller? I found it in another thread on these forums and it seems to get around a MOS buffer (or something, I still kind of a wet match in a dark room here). Obviously not using these MOSFETs and I don't really care about the current sensing portion either, just the H bridge (-like) part.

because the coil in the relay is going to suck a lot of current isn't it?

Depends on the relay but 20 to 100 mA is not a lot.

You do appear to need 2 different PWM signals to the board, and what are the parameters of the current
and voltage signal out? Unfortunately, they rarely seem to have much documentation.

Pretty much standard H-bridge operation. Typical h-bridges either pwm individual foward/reverse lines, or have a single pwm pin and a single foward/reverse direction pin.

Grumpy_Mike:

because the coil in the relay is going to suck a lot of current isn't it?

Depends on the relay but 20 to 100 mA is not a lot.

Are these typical relay currents? I'm looking at automotive relays because they seem to be whats needed to go up to 15 A (Most seem to be 30 or 40 A). I am making this up as a go with part selection. Also with regard to controlling a relay, I'm guessing I just connect it to my 12V lead acid battery and switch it with like a 2N2222. Do I need some kind of resistor? Or is the coil resistor typically enough to get the current down? They seem to show coil resistances of like 10-50 Ohm, so I'm kind of raising an eyebrow to this 20-100mA range.

If you are considering using relays, you might instead get two switches like below (one for each motor).

zoomkat:
If you are considering using relays, you might instead get two switches like below (one for each motor).

RadioShack.com Official Site - America's Technology Store

Lol, I'm trying to build a robot, I want to electronically control my motors, not physically switch them.

Here is an interesting relay that is really two independent relays in one package. 25 amp contact rating, dual SPDT contacts and 53 ma for each coil current. so in this one package a arduino using two digital outputs controlling two small NPN transistors to power the coils, one could program control to go forward, reverse, and break. Add a power N-channel mosfet in the negative side of the external DC power supply for the motor and you can add variable speed via an additional arduino pwm output pin. Lot cheaper and smaller then a 25 amp H-drive. And compared to a solid-state H-Drive you only give up a little on the speed with which you can switch from forward to reverse, which for a robot main drive is probably not an issue? I suspect this is used in electric window motor drive, seat control motors, door lock solenoid, etc.

Datasheet:

http://www.worldproducts.com/pdfs/ep2.pdf

So high current H-drive on a budget, what's not to love about that. That lets you put more $$$ into sensors and other cool stuff. I may have to pick up a couple of these.

Lefty

14A without a heat-sink. A bit spendy, but no design or testing struggles.