Dash Voltage Regulator

[TexasGeneral]

Decided I didnt want to pay $60 for one so I spent $4 at radio shack.... 7805 chip and 100uf cap.. done!

[Pete in NH]

Congratulations on being willing to try something in the electronics area!  A suggestion you might want to try to make sure your new regulator works properly and continues to work. As your photo shows the 7805 regulator there is no heatsink to help keep it cool. The 7805 in this circuit has to get rid of several watts of power in the form of heat. If you have three gauges in the car rather than two and an oil light it has to deal with even more watts of heat. So, you need to attach the metal tab of the 7805 to a piece of metal called a heatsink to help it get rid of the heat into the surrounding air. If you do a search on this regulator upgrade for Mopars you will see photos of the 7805 on heatsinks. I have done some bench testing of this circuit and found a 1-1/2 x 4 inch piece of 1/8" aluminum will give you a good heat sink.

The 7805 has some internal circuitry that will try to protect it if it gets too hot. What will happen if the circuit kicks in is that the output voltage will shut off and the gauges will go to zero.  Good luck, you're on the right track and almost there- add that heat sink!

[A383Wing]

I have done the same...I put the chip on the outside of the can to use as a heatsink..those chips will get hot and burn up if you don't cool them properly.

I burned up 2 of them until I figured it out

[Sixtyeight]

Hi,

Also made a new limiter using the 7805, a capacitor and a good heat sink. It works great, but after a few miles and/or minutes of driving the voltage of the 7805 drops from 5 to 3.5 volts. With the voltage drop, also the reading of the gauges drops a bit.

I don't understand why this happens because the input voltage only gets higher when driving.

When measured colt with the engine not runnig it measures a steady 4.96 volts.

Who nows?

Jeroen.

[Pete in NH]

Hi,

See my posting above on adding a heat sink to keep the 7805 regulator from over heating. What you are describing is typical of the 7805 over heating and protecting its self by lowing its output voltage.

[Sixtyeight]

Please look at my posting also, it´s in a good heat sink, and it insnt getting so hot at all...

Jeroen.

[Pete in NH]

When you say the heat sink is not getting to hot does that mean you can still keep you finger on it? The fact that it supplies 5 volts for a period of time and then goes to 3.5 volts and then goes back to 5 volts after you turn it off a while still points to a thermal issue. A photo of what you have built would be helpful. Another possibility is that you need another capacitor like you have on the 5volt output placed on the 12 volt input to the regulator to keep it stable. But, lets make sure its not a themal issue first.

[Sixtyeight]

Yes i can put my finger on it easily. No burning sensation...

I suspect it has something to do with the amounts of amperes it can deliver. Maybe less then the 3 gauges require?

Jeroen.

[Pete in NH]

The 7805 can deliver up to 1 Amp. Each gauge requires a maximum of .166 Amp. The gauge is about 20 ohms and the sending unit at full scale reading is 10 ohms. So, that's 30 ohms and 5 volts applied or .166 Amp. So, all three gauges would require .5 Amp Maximum well below the 7805's current ability.

At this point i would try that input capacitor. Try a 10MF/ 50Volt capacitor between the input pin on the 7805 and the ground pin. Plus side of the capacitor on the input pin.

[Sixtyeight]

The capacitor is already present as I wrote in my post...only its a 100 uf 16v. I was told this should be the one...
Is that the mistake?

Jeroen.

[Pete in NH]

That present capacitor should be on the regulator output and 100MF/16volts is fine. I'm asking you to put a second capacitor on the input pin of the 7805 to ground to see if that helps stabilize the 7805. It should be a 50volt rated capacitor to deal with the voltage spikes in an automobile electrical system. If you look at the manufacturer's application notes for the 7805 they recommend this input capacitor if the 7805 is too far from its power source which in this case it is.

[Sixtyeight]

Thanks for the advice, I ordered the 10MF/ 50Volt capacitor ...

Jeroen

[Sixtyeight]

Hi,

Installed the 10MF/ 50Volt capacitor as described, but the voltage drop remains the same.

When I drive hard with high rpm, the voltage drops more then when I drive in the cruising mode...

Jeroen

[Sixtyeight]

Hi,

Since the former solution didn't work I tried a 7809 in serie with a 7805 to make the voltage limiting in steps from 12 to 9 to 5 volts...

Suprisingly the voltage drop now became even bigger and the combination got really hot... so made everything worse...

Running out of ideas now...+ I don't understand why it drops?

Anyone any idea?

Tnx

Jeroen.