On Thu, 19 Jan 2017 16:03:23 -0800, etpm wrote:

On Thu, 19 Jan 2017 16:25:20 -0600, Tim Wescott
wrote:

On Thu, 19 Jan 2017 11:44:40 -0800, etpm wrote:

I figure Clare will know the answer but maybe others will too. I got
my hands on an old Acura fuel injector last night. It is apparently
the high impedence type because it measures 14 ohms resistance and
draws only .7 amps @ 12 volts. This means I don't need a fancy chip,
just a 555 timer circuit. So I put one together using a relay (because
that's what I have on hand) instead of a mosfet to apply power to the
injector.
I put a snubber diode across the injector just like I did for the
relay coil. All the injector circuits I have seen online use either a
pretty high voltage zener, 75 volts, or a resistor across the
injector. From what I have read the 75 volt zener seems to be the
most common and it lets the injector close slower to prevent damage to
the injector from slamming closed. I guess the circuits with a
resistor in parallel with the injector do the same thing. I don't have
any 75 volt zeners in my kit but do have lots of resistors in many
different values and watt ratings. Does using just a resistor make
sense? Maybe I misread the circuit.
Thanks,
Eric

The higher the voltage at the injector, the faster the magnetic field
will collapse and the faster it'll close.

75V means that they're using transistors rated for 100V or so, which
means spendy. It also means that the magnetic field is collapsing way
faster than it was generated. So they're at least tuning the turn-off
time.
So can I just use a regular diode like I would with a relay but with a
resistor in series with the diode if I want to have the injector close
slower?
Eric

If you're talking about a circuit like this, then the HIGHER you make the
resistor value, the FASTER the current in the coil will decay, and the
FASTER the injector will close.

If you have a website or some other easy-to-access reference that says
differently, that was written by someone who actually knows their physics
(i.e., not just some columnist for a car magazine), then I'd like to see
it.


+12V o ----------------o-----.
| |
| |
.-. |
resistor | | |
| | |
'-' C| injector
| C| coil
| C|
| |
- |
diode ^ |
| |
| |
o-----'
|
|
|
||-+
||-
o---------------||-+
|
|
===
GND
(created by AACircuit v1.28.7 beta 02/28/13 www.tech-chat.de)

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

I'm looking for work -- see my website!