Board logo

Dropping voltage
scutter - 27/3/10 at 12:03 PM

Ok Lecky types.

I need to drop the 12v power supply coming out of the relay down to 5v for my VVC solenoid.

The simplest discriptions please

ATB Dan.

thunderace - 27/3/10 at 12:24 PM

go to maplins and buy a Resistors ,
to make it 5v
costs about 50p

MikeRJ - 27/3/10 at 12:45 PM

Are you sure your VVC solenoid is really 5v? That is pretty unusual; sensors often run at lower, regulated voltages but actuators almost always run from 12v.

Note that a resistor can not provide a fixed voltage drop unless the current load is constant V=IR. However, for a simple solenoid, a series resistor will be adequate as you simply need to limit the coil current to a sensible value. You will need to determine the resistance of the solenoid coil to calculate a suitable resistor value. It may be written on the solenoid itself, if not use a decent multimeter and measure it.

richardlee237 - 27/3/10 at 01:24 PM

Fit a 12v / 5v voltage convertor, cheap and simple, just make sure it can handle the current.

rayward - 27/3/10 at 01:25 PM

yeah as said, check it really is 5v, does sound a bit odd?

i might have something lying around will check

Ray

scutter - 27/3/10 at 03:52 PM

I got the 5V information from the end of THIS thread.

ATB Dan.

Dave Bailey - 27/3/10 at 10:47 PM

I have an ST170 Engine in my velocity and I am using a DTA ECU.... They have a config for driving the valve....... I am pretty sure it is 12V......

I haven't tested mine yet....

Dave Bailey

scutter - 28/3/10 at 08:16 AM

I'll use 12V to start with, to keep things simple. I assume the solenoid will just get hot with 12V?

ATB Dan.

splitrivet - 28/3/10 at 05:34 PM

A 7805 regulator IC is the easiest way but sounds a bit odd .
Cheers,
Bob

scutter - 28/3/10 at 07:00 PM

I've been out and checked the solenoid has 5V written on it!

ATB Dan.

Dave Bailey - 28/3/10 at 08:15 PM

You have me worried now..... I was told by DTA to use an AUx input that sinks 12V... I need to check with DTA tomorrow....it may be that they wanted me to use this input but driv eit from 5V...

Dave B

02GF74 - 28/3/10 at 09:13 PM

quote:
Originally posted by scutter
I'll use 12V to start with, to keep things simple. I assume the solenoid will just get hot with 12V?

.


car electrics run closer to 14 V.

remember power = V squared / R

so by almost tripling the voltage, you are dissipating close to 9 times the power it was designed to handle.

I doubt it will last long - I would not recommend.

depending on the current, then a 7805 on a heat sink would give best regulation;

cruder method, as ^^^^ said, is resistor or use diodes to drop the voltage.

scutter - 28/3/10 at 09:16 PM

I'll switch it down

Dave, would you be able to check your solenoid? I'm pretty sure the top line had 5V in it.

ATB Dan.

ss1turbo - 5/4/10 at 08:15 PM

It may be getting 5v via a PWM signal originally, but some engine electrics do use 5v reference signals (TPS, temp, etc). It all depends on the power/current requirements of the solenoid though - I've got 5V coming off a 12v/USB cig lighter adaptor, but only at about 1A or so.