Russian 2DOF wiper motor simulator

Hi all!

We were glad to find this site, which were able to find everything you need to build my own autosimulator. I want to share our experiences with others. Construction of the simulator is not yet complete, but we have some photos and video materials. And while a small description on our site for Russian users. Check our site for more info.

[urlguest=http://infarct.nm.ru/xsim.htm]Russian X-Sim Project here (in russian)[/urlguest]

[urlguest=http://translate.google.ru/translate?u=http%3A%2F%2Finfarct.nm.ru%2Fxsim.htm&sl=ru&tl=en&hl=&ie=UTF-8]Russian X-Sim Project here. Trough google translate.[/urlguest]







Information will be added as completed.

WBR
ru.null, ru.zlokot

Problems with hbridge. IRFZ44's overheat.

http://www.youtube.com/watch?v=qGfpaMOV5AA

By screwing them all together onto a single cooler, you shortcutted them!

And that lightbulb may draw a lot of current additionally.

regards

We use insulating gaskets and bushings for mosfets. No short circuit. We double check it. On final design we will use separated coolers.

Ok, I didnt see the insulating gaskets in the video.

Do they keep cooler without the light bulb?

light bulb is used as - ballast resistance (12V 40W)

They also overheat. The lamp is not very powerful. We think gates on mosfets not opened properly. Because we lost voltage (about 2volt) on irfz44's.

Both circuits, AMC and H-bridge are approved.
You may have a shortcut somewhere on the h-bridge board, or the mosfets are damaged. So double check your solder job, and after that try to replace the mosfets.

Once I damaged the mosfets on my h-bridge by accidentially shortcutting them with an uninsulated screwdriver
Perhaps you killed them during the solder job (too much heat) or shortcutted them like I did.

If the H-Bridge works both ways and overheats bad, these might be a problem:

- Your load draws too much current.

-Your MOSFET's don't turn completely ON/OFF in the circuit.

-Your switching PWM frequency is too high, the transistors spend much time in the linear region instead of cut-off/saturation.

You said the MOSFETs drop 2V Source-Drain. Your bulb (40W) draws about 3.3A with 12V as you said, so if you have 2V across transistor, 10V across your load, you have about 3A going through the circuit. That is 6W power lost in the transistor.

Check your voltages, especially Gate-Source and check your circuit. Take some current measurmeents too if you can and compare with theoretical values.

Did you isolate the motors internal ground from the motor housing?
If not, and in case you are using both motors together yet, and the motors casings are somehow connected together, you have a shortcut there, which results in overheating the mosfets as well.

Thank you for your posts. Tell me, how much voltage is necessary for the full opening irfz44? I have datasheet .... this is Vgs(th) parameter?

Yes it is. Vgs(th) is the absolute minimum, where the transistor starts to conduct. If you look at Fig.2, you can see different Vgs and it's effect on current and Vds.

4.5Vgs will max out the current at about 16A(pulsed) with ~1.5Vds and it will only increase Vds, but not the current.
8Vgs on the other hand will max out over 100A(pulsed) with ~6Vds

You should aim for 10-12Vgs for the best saturation.

If i understand correctly, now we have 11v - 4905, 5v - z44 on gates. Why can this be?

You have to look at the circuit diagram and see what turns it on. It is the 74HC08 that drives the lower mosfets directly, and the opposite upper mosfets through a transistor. You can see the upper FETs are pulled up to the 12V to turn off, the transistor pulls them low to 0V which turns them on.

You need the opposite action on the lower mosfets, 0Vgs on the gate will shut them off, +12V will turn them on completely. Unfortunately you will have to modify the circuit and add this transistor with a pull-down resistor to the gates.

I had already thought about it. But why not work a standard scheme? What wrong?

Stop it! He needs to change anything! The circuit is approved by many people as it is already. It does not need change.

If he uses the right components, the problem has to be either a solder job shortcut, a misplaced or a damaged (overheated while soldering) piece part.

I appreciate your initiative, and I know you just want to help.
And it seems you also have a pretty solid knowledge in electronics.
But right now you are misleading them.

@ru.null
Save yourself time and ask Thanos (tronicgr) for advice. The circuit is flawless. Your solder job or the components you're using are the problem. Are you sure that all the wires you added are connected the way they should?

Wires are added by us are connected correctly. We have checked this. I follow your advice and ask Thanos. Also, we will welcome any assistance from others.

ego, I'm sure it works and I know a lot of people use it with no problems. It works for them too, the problem here is the overheating. For others the mosfets may not overheat because they don't have such high loads on them.

When you run a DC motor on the H-Bridge, you are not drawing a lot of current all the time, only when the motor is accelerating (or decelerating), so the Mosfet's have time to cool in between. It may not be noticable for everyone, but I am sure that the lower FETs don't turn on completely, wasting power which causes more heat. And this comes from the irf-z44 datasheet, 5Vgs is not enough for maximum conduction.

Let me correct my advice so I don't mislead anyone here:
In order to reduce overheating with constant high loads such as a light bulb, you will need to drive the lower mosfet's with more than 12V - hence you need to modify the original circuit.

If you use the H-Bridge with a DC motor, the circuit might just work fine the way it is and the overheating will be reduced. I don't see any problems with your voltages, and I am confident that the H-Bridge is just working the way it should.

You guys could test this manually, but be very careful not to cause shoot through:
Connect 0V Ground to one of the upper mosfet GATE, connect 12V to the OPPOSITE lower mosfet GATE. Your mosfet should be cooler.

That is done all right, but the z44 is always heated more than 4905? If so, I'm really ready to remake Hbridge to get more efficiency and less heat. You can help me with this? This would benefit not only me but the rest of the community.

Also, I find it interesting view Thanos. I sent him a PM requesting assistance.

Here is the schematic. Left is the original, Right is the modified with 12V driving the lower MOSFETs. You can compare the two, and please note the red dots are connections, crossing lines do not connect.


12V -> BC546 Collector BC546 Emitter -> IRF-Z44 Gate and 1.5K ohm pull-down resistor -> Ground
BC546 Base -> TTL input from the 74HC08

Please note:
I don't have the H-Bridge built and I have not tested the above circuit in any way. Just as you built the original circuit on your own risk, please do any modifications to it on your own risk as well.