Dropping resistor question

[lee]

I personally prefer the shifting characteristics of the transmission without the dropping resistor in place. However, then one gives up the feature of the blinking power light's warning of impending doom.

So, I did a bit of investigation and want to solicit the opinions of the forum.

With a 1-K ohm resistor (all this is in place of the stock resistor) the power light still blinks.

With a 500-ohm load the light no longer blinks.

Since I seem to remember the forum concluding the dropping resistor was in parallel with the solenoid, I conclude the highest resistance that "fools" the TCU will most closely provide the no resistor characteristics while still providing the blinking light "alarm".

So, I tried a two-block round-trip drive with two 1-W, 1-k ohm resistors wired in parallel across the dropping resistor connector. I think that means I have 500-ohms with 2-W capability. If this is a parallel circuit that seems like enough power handling given the current flow would be reduced by a factor of 50 (20 watt power is what I think the OEM resistor is rated at). All seems well, but I'm hesitent to use this until somebody with some electrical knowledge and/or common sense wades in here (I am sadly lacking both ).

So, concensus?

[svx_commuter]

That's right, you got a 2w 500 k ohm resistor in there. I put 2 of the regular resistors in series so I got about 26 ohms. This should not cause any damage to the solenoid as it will be no different than running without the resistor. I can't answer your question about long term damage to the TCU for sure. The question is: Does more power go through the TCU circuits? This may cause higher heat loads.

[oab_au]

Hi, Lee we know the effects that we feel, when the resistor is disconnected but, What the actually purpose of it, is still a mystery to me.

The modulated voltage that operates the A solenoid ranges from 1.5 to 3.0V throttle closed.
0.5 V max throttle open.

The voltage that feeds the resistor is supplied by the
TCU and ranges from:
5V to 14V Throttle closed
0.5V, max Throttle open.

I am starting to think that the TCU varies the voltage to the resistor, to achieve pressure changes along with the modulated voltage, in the A solenoid. If this is the case, the resistor is just a dropping resistor to lower the 12V to the 5V that the solenoid runs. Otherwise the feed for the resistor would come from a 12V supply, instead of coming from the TCU.

May be some body would like to check the voltage feed to the resistor on the road, to see if the voltage to the resistor does vary with load conditions.

Harvey.

Edit .put C.instead of A.

[lee]

Harvey if you're confused, that means I'm hopelessly lost.

To all readers:

I did find one site that talks about modifying dropping resistor values for pressure control, but I don't understand enough about transmission operation to know what it implies.

I do have the value that solenoid A on the SVX should have a resistence between 1.5 and 4.5 ohms.

see this site - if it helps anyone to understand please let me know:

http://www.gearsmagazine.com/2002-05/2002-05_40.pdf

[lee]

As a follow-up to my last post and after reading the article on the site referenced, I come to the following conclusions:

The article writer offers an opinion that to maximize pressure while avoiding failure of the pressure regulator valve, the solenoid should see about 0.2A. The values for the stock resistor value and solenoid A's resistance, taken at central values put the solenoid current at around 1 amp (too much in the writer's opinion, and of lots of us here too from the number of folks running without a resistor).

Working the numbers for 0.2A, that corresponds to a total resistance value of 66 ohms (given 13.8V as max seen by the system, using 14V only changes the value to 70 ohms).

Since the solenoid has a value between 1.5 and 4.5 ohms, the dropping resistor value, to maximize pressure and still be consistent with pressure regulator protection, would be slightly over 60 ohms.

So basically I have answered my original post - 500 ohms is too much - gives a value of about 0.02A at the solenoid using the info in the article. Still standing by for competent review & my limited ability to understand.

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[svx_commuter]

Harvey,
I drove around for awhile with an anolog volt meter connected to the voltage lead for the "A" solenoid at the TCU and yes the voltage goes down when the gas peddle goes down. I had a range of .5 to 3 volts as I remember. Without the dropping resistor it's peg'd at .5 volts.

[Trevor]

Lee,

The dropping resistor has a specified resistance of 9 - 15 ohms. Fitting a second resistor in series or a substitute resistor so that the resulting resistance exceedes 15 ohms will result in the load on the TCU control circuit being reduced therefore no harm should result.

If the wattage rating of the substitute series resistor is too low it will simply overheat and burn out with no damage to the TCU. ( Given that a short circuit does not occur due to mechanical considerations.)

You mention two 1000 ohms 1 watt resistors in parallel to provide 500 ohms as operating without trouble. Taking into account the increase in resistance and therefore the reduced current flow this should be OK. On the basis of the figures we have on hand the maximum expected with 500 ohms in series would be approx. 0.4 watts.

The resistor can not properly be considered to be in parallel with the solenoid as it is supplied from a separate circuit.