johne

I’m about to buy resistors for my Siemens injectors that I bought from racetronix. I did a quick froogle and came up with these:
http://www.newark.com/NewarkWebComme...KU=01F9896&N=0

They are 50 watts and 1.5 ohms. I read in the archives that we should use 25W resistors, I assume that using 50W resistors will just give me extra heat dissipation abilities but if I am incorrect someone PLEASE let me know. I would just buy 25W 1.5 ohm resistors as suggested but I cannot find them for sale anywhere.

Thanks in advance,
John

NZ951

I actually used 2.5ohm resistors on my Siemens 850's

David Floyd

http://www.newark.com/NewarkWebComme...KU=01F9895&N=0

what I am using

johne

Thanks for the replies guys.

NZ951,
Really, 2.5?

David Floyd,
Holy cow, that link goes to 10 ohm resistors. Are you sure your not using 1.0 ohm resistors. If so do you mind me asking why you went with 1.0 instead of 1.5? Also did you order your resistors from Newark?



Here is how I came to the 1.5 ohm resistance:
Stock injectors are ~5.5ohms(I measured) each resistor will see 2 injectors in parallel so their effective resistance is ~2.75 ohms.

My Siemens 75lb’ers are ~2.6 ohms (I measured J ) once again they will be in parallel so their effective resistance is ~1.3 ohms.

So if I add a 1.5ohm resistor in series then I will be at 2.8 ohms, which is almost perfect. If I use 2.5 then I am at 3.8 ohms, which might not give the injectors enough current (I don’t know their minimum requirement though.

Thanks in advance again,
John

David Floyd

Yes, should be 1 ohm, I went by Sam's formula and I did buy from Newark.


"Sam Lin

Stock injectors are 5.5 ohms when in series in the stock arrangement - they are 2.75 ohms each, hence the use of a 1-ohm ballast resistor when Racetronix 2.35 ohm are used. The final result is 2.35x2, 4.70+1, 5.7 ohm load for the DME, very close to stock 5.5 ohm.

Good luck.
Sam "

johne

David,
Thanks for the reply.
I figured they must be 1ohm. I’m pretty sure Sam’s math is off at the end. The value of 2.35 is the value of the 2 injectors together is parallel, so you don’t multiply it times 2. I think you should still be fine though since your resistance is 2.3 when you are shooting for 2.75 so it's pretty close. Definitely closer than the 1.3 they are at without the resistors. I especially think you should be fine since some people run ok without any resistors.

A second question is about the wattage of the resistors, do you (or anyone else) know the difference between running 25W resistors and 50W ones?

Thanks again,
John

david fracolli

Sorry but 50 watt resistors will not draw twice the load. A 1 ohm 10 watt resistor will draw the same current as a 500 watt 1 ohm resistor. The wattage is the rating of the amount of power that the resistor can dissipate not what it draws.

johne

Thanks guys, I was thinking both of you fella’s thoughts, but I couldn’t decide if the wattage rating of the resistors stood for what it would draw or what it safely could draw.

Thank you everyone for the input. This community is an invaluable resource.

Thanks again,
John

E-man930

David is right,
I think the older I get, the dumber I become!
I forget a resistor is designed to impede current flow...
In fact, look @ the resistors I bought...
I'll try and think things through next time!
E-man

Andy

I thought the general consensus was resistors were't really necessary...

E-man, good to see you're still around! I'll send you a PM.

toddk911

Anyone NOT running resistors with their non stock injectors???

toddk911

In regards to wattage, just make sure 12V times what ever current flow is not more than the wattage of the resistor.

For 50 watt resistor you are safe up to 4 amps.

David Floyd

I have, actually did about 20 dyno pulls one day, DME was HOT!!!! resistors went in the next week.

toddk911

Cool, David, thanks.

Andy

But did you either do 20 dyno runs on stock injectors or 20 runs after adding the resistors to find out if it's "less hot?"

Just asking, I need to get bigger injectors myself...