Ballast Resistors

[stew205 17]

Ok, starting from the top ............

 

 

I have my car mapped on low impedance injectors, I can test them tomorrow night to find the exact impedence.

 

My ECU is a DTA 48 which does not have peak and hold injector drivers, it just uses the standard high impedence type.

 

I have been running it like this for a while, but there is a risk I will burn out either an injector or a driver.

 

Can I add a ballast resistor at this stage? What I mean is, will it just effect the current to the injectors so providing they get enough current to open I will not notice a difference? I.e. no remap.

 

Because it batch fires do I need to put a resistor in series with every injector? If it was sequential I would do this but does batch firing fire in parrellel thus affecting resistor size, and number?

 

I am really confused now

 

 

I really need to get this sorted as I am taking the car to the ring soon and don't want this to be the reason why I return on the back of the RAC truck

 

 

I searched but only found info on resistor location, which seemed to be preffered on the earth side of the injector loom.

 

 

Thanks

 

Stew

[DrSeuss 0]

The ballast resistor is to prevent too much current going through the injector driver mosfet.

 

Theoretically you can still use low impedance injectors with any ecu, but it'll increase the likelihood of catastrophic failure significantly.

 

I'm trying to think of a good reason for why you'd have the resistor on the ground line from the injector. I'm guessing its to do with the voltage drop across the resistor. i.e. if the injector doesn't get a full 12v it might affect opening, so you put the resistor in the earth line where any subsequent voltage drop is unimportant.

 

An RC network is formed by an inherent capacitance of the ecu, a capacitor takes time to charge, this time is proportional to a time constant RC (resistance x capacitance). This is why low impedance injectors are used, the lower resitance increases the speed of response (which improves idle quality with large injectors and small engines).

 

Ballast resistors are available from Farnell or RS and one should be sufficient. Be sure to get a resistor suitably rated for the wattage it will dissipate. An overheating resistor would increase its resistance, which is a bad thing.

 

I'm not sure how much of what i've posted is relevant to cars.

Edited March 16, 2006 by DrSeuss

[Sam 4]

Stew, its worth a ring to DTA, I'm sure they can assist, I rang omex regarding a similar matter and they were more than helpful.

Edited March 17, 2006 by Sam

[stew205 17]

I spoke to somebody briefy at DTA yesterday but they seemed to busy to give any details.

 

They said go for a 2.5V 25W resistor Does this sound right, Whats the relationship between Volts, walts and ohms? As I need to order the resistor in ohms?

 

 

So from what you said Drsuess, Use one resistor just in one of the lines?

[DrSeuss 0]

if they're batch fire. They should have a point where all injectors join into a single wire back into the ecu. If there are multiple wires back to the ecu. Then you need one resistor per wire.

 

25w sounds about fine, thats pretty hefty and won't overheat. You can order that via a good electronics retailer. I like Farnell, they're cheap and easier to search then RS.

 

www.farnell.co.uk

[d-9 0]

for DC the two equations that are relevant are:

 

Power (watts) = Current(amps) * Voltage (volts)

 

Voltage (volts) = Current (amps) * Resistance (ohms)

[Pierre_b 3]

Hello,

 

If you ECU doesn't have a PWM mode for inj, you have to add injector resistor AFAIK. This URL helps you to choose your's, and to wire them.

 

http://www.megasquirt.info/v22manual/minj.htm#injresist

 

Pierre

Edited March 19, 2006 by Pierre_b

[stew205 17]

Thanks for all the advice.

 

I Ordered some ballast reistor after the advice given and should arrive next week, then another solution pop up when I visting the scrap yard this morning.

 

A rover 820 turbo!

 

I bought the injectors. From testing them I found they are 16 ohms and from a search on here I found they flowed somewhere between 400-440cc. My old ones where around 335cc after cleaning.

 

 

I fiited them and as predicted it was overfuelling. I reduced the fuel map by 20% (approx the difference between injector flow rates) and it runs extremly well, no difference from low down to how the other injector felt (I haven't rev'ed it yet, don't want to damage anything if it is lean!).

 

I will book it in for this week (hopefully) to get the injectors cleaned then to be checked for how far the fuelling is out and get it adjusted accordingly.

 

 

I now have some ballast reistors on the way which are not needed, so if anybody is going down this route drop me a PM. I didn't really fancy cutting up my loom anyway

 

 

 

 

Thanks again for advice givern

 

 

Stew