If I'm following the schematic, the 1k and 10k are forming a voltage divider. If using a DPDT center-off switch, when in center off position, the Pmos is partially on with about 2.2 volts on the gate.
The Nmos will have about 21.8 volts, on the gate.
I think a re-design is in order.

 

Here's an idea.

1. Change the 1k on the Pmos's to 10k.
2. Use the 24Vdc supply through the DPDT switch to control the gates.
3. Connect a series 680-1k resistor from the gates to the respective gate drive connections.
4. Connect a 1 watt 12-15 volt zener from gate to source on each of the 4 bridge mosfets.

The idea is to switch the gates using 24 volts through a current limiting resistor/zener diode.

I hope this makes sense. I'm guessing I may have missed something.

 

I have drew the new circuit, but only modified the important part, you can try to figure out what's different from yours, and using the methods that I described on #18 to explain by yourself.

 

Nice drawing Scott.

Yep, I missed something in my post #22. The connections between the gates on each 'side' should be removed.

Scott, your drawings always look so good. What drawing software do you use ?

 

Nice drawing Scott.

Yep, I missed something in my post #22. The connections between the gates on each 'side' should be removed.

Scott, you're drawings always look so good. What drawing software do you use ?

I'm using the paint on windows xp, I had designed some basic ee symbols and connecting the wires, I'm not done the formal translation, but you can see the translation from google, basicly is to look the symbols, I have some new symbols but not update yet.

I always saved as 256 color bmp file and using AcdSee to transfer to gif or png.

How to using the paint software to draw the circuits at here.

Bill_Marsden(PaintCAD.zip) also using the paint to drawing the ee symbols, and he drawn more and more, you can download them from his blog.

 

Hello again, I tried the circuit but I used BC547 instead of 2N3904 and the PMOS that was getting 0V burned....=S

 

The Vceo of BC547 has 45V, so it should be OK when it is turn off.
When the Q1 is turn on then the Vgs of FET1 is close to 12V, also When the Q2 is turn on then the Vgs of FET2 is close to 12V.

So you may check the pins direction of MOSFET and the values of 4 12K resistors that they connected to c of Q1 and Q2.

 

What about this schematic?

I want to run my motor at 4A and 24V, so from the output characterstics I found out that the VGS should be -5V for the PMOS and +4.5V for the NMOS. That's why I placed 5V zeners instead of 15V. Hope this schematic doesnt have issues......please point out the mistakes.

 

5V zeners are definitely not enough, you need at least 10-12V one the gate otherwise the mosfet will not turn fully on, leavig around 1.5 W dissipation in the mosfet which is unnecessary. Don´t forget the resistor in series with the supply and some light load before running it on full power.

 

What about this schematic?

I want to run my motor at 4A and 24V, so from the output characterstics I found out that the VGS should be -5V for the PMOS and +4.5V for the NMOS. That's why I placed 5V zeners instead of 15V. Hope this schematic doesnt have issues......please point out the mistakes.

As mentioned those Mosfets need at least 10 volts on the gate to turn on fully or they will heat up too much. The maximum gate voltage is 20. Above that, damage will likely occur. Thus the need for ~ 10-15 volts on the gates.

I believe you were using a center-off DPDT switch, correct ?
If so, when it's in the center position, the stack of 1k resistors form a voltage divider which partially turns on all mosfets,
causing a large current draw. That's a trouble spot.

You could remove the very top 1k on each side of the bridge, so when the switch is in center-off, the gates will be pulled down. You don't need resistors to pull the gates off because the switch does that in both "on" positions.