Injector Question

[ian.stewart]

This should be a simple question to the Electronics Buffs out there,
At the moment I am just in the process of getting my injector test rig rebuilt, I know I cant run a single injector without a resistor bridged accross the circuit to protect the windings in the injector, Can somebody please tell me what I need for both High and Low impedence injectors
Ian

[jwriyadh]

Never done it but if I did I would drive a high impedance injector direct. The low impedance injector I would build out the total resistance to about 16 ohms.

jw

[kiwicar]

Hello Ian
My understanding is that with with low impedence injectors you need to limit holding current to about an amp to avoid frying the windings. So you need an over all impedence of about 12 ohms, (assuming you are using a 12v car battery) if your injectors 2 ohms then you need a 10 ohm resistor in series, if the injector is 3 ohms it will be 9 ohms. However the resistor will have to be rated at atleast 10 watts with a heat sink.
The high impedence injectors should be OK without.
The injector spec sheet should have the holding current on it (do a search on the bosch or delfie web sites) should have this info there.
Have you had a read of the injectors section of the Megasquirt website? worth it if not.
If I can help further please post
Best of luck
Mike

[ramon alban]

This should be a simple question to the Electronics Buffs out there,
At the moment I am just in the process of getting my injector test rig rebuilt, I know I cant run a single injector without a resistor bridged accross the circuit to protect the windings in the injector, Can somebody please tell me what I need for both High and Low impedence injectors
Ian

Ian,

Using the words "Across" and "Bridged" implies the resistor is in parallel with the injector.

Just to clarify, the resistor must be in series with the injector, not across it.

Whilst this provides protection for the injector much more importantly it protects the output transistors inside the ECU if the injector or the injector circuit were to become shorted out.

If you are using standard Rover SD1 injectors, which I believe would be classified as Low Impedance, the injector resistance should be 2.4 ohms + or - 0.5 ohm at 20 deg c and the series resistor should be 6 ohms + or - 1 ohm.

If you were to measure the injector and resistor together (in series, the resistances are added) the permissable range would be approx 2 + 5 = 7 ohms up to 3 + 7 = 10 ohms.

At the optimum of 2.4 + 6 = 8.4 ohm using a nominal 12.6 volt battery the injector current should be approx 12.6volts/8.4ohms = 1.5 amps.

At the limits the maximum current would be 12.6volts/7ohms = 1.8 amps and the minimum current would be 12.6volts/10ohms = 1.3 amps

I dont have any info on what might be required for High Impedance injectors.

If more clarification is needed I can PM you a page from my manual on the subject.