I've read posts that 3ohm 5 watt are the way to go for 160lb injectors.

Ok this is what I know.

Injector driver should never see more than 2 Amps.

Since I = E/R (Current = Voltage/Resistance)

2 Amps = 12v / 6ohm (total resistance on injector needed to keep limit)

My 160lb injectors are 2.9ohm (measured at cleaning)
My 80lb injectors are 5.5ohm (measured at cleaning)

In order to keep them under the 2amp Limit, I would need a 3.1ohm (or as close as possible to 3ohm resistor) for the 160lb, and for the 80lb injector I would need a .5ohm resistor.

Now, my question is... WHY 5 WATTS?!?

If P = I X E (Power = Current x Voltage)

And I = 2amps (injector driver max)
And E = 12v (from battery)

P would = 24 watts

So you would need a 3.1 ohm 25watt Resistor and a .5ohm 25watt resistor.

I am not understanding how a 5watt resistor would be good enough for the injector setup. Wouldn't the excess power blow out that resistor?

I may be missing something, but I was wondering why a 5watt resistor was recommended over a 25watt resistor.

Any info would be appreciated.

Thanks,
Darren

 

I haven't taken the circuit load into account which was pointed out by a good friend of mine. Anyway, any comments would be nice =P

 

I'm having the same difficulty; i.e. choosing resistors. Talked to Pineapple Racing when I was buying the dual EGT and their builders don't recommend using resistors. Told them I'm using a PFC and the 1680 secondaries and they told me flat out they do not use resistors on any of their builds. I'm going to go without until proven otherwise.

 

Injector didnt need 2amp to work thats why you need only 5 watt resistor.
The 2 amp is the max load who the injector circuit can handle.
Now if you use 5w resistor and for any reason the injectors circuit need more than 5w or 1 ampere then the resistor will be burn.
The best way to choose your resistor for your injectors is to connect ampere meter in series with 12v dc pulse 50-100hz and see how many ampere injector need ,for example if need 500ma then 5w is ok.

 

That is what I figured. I thought the injector is only going to pull the current it needs from the circuit. 2amp would be the max the circuit could handle, but the injector would only need say 500mA for example in order to operate well. I suppose if you were pushing the injectors to 100% for a long period of time that it may be needed... but typically it would use much less current to operate.

 

I think that the injector on 100% operation and with hot engine 90c the max current will be + 20% from normal operation ,not more.
But I am not sure for that.

 

I bought my resistors from keith@kgparts.com, they were cheap too. I think they're the same ones that rx7store sells but I paid less from keith.

I have zero lag at the changeover, no hesitation or stutter or anything, it's as silky smooth as it could be. If anybody is having that issue and is not running resistors, I highly recomment id.

By the way, they are 4 ohm 25 watt resistors. Don't use the cheap ones, get the ones with the heat-sink on them. I think I paid like $12 total for the pair.

RX7Store has them here for $8 /per:
http://www.rx7store.net/product_p/in...20resistor.htm