Mx-3 Dimmer To Speedhut Inverter Project

Nd4SpdSe · Post by **Nd4SpdSe** » April 14th, 2006, 1:58 am

Can anyone give me the resistance of the potentiometer for the brightness. I ahve the upgraded inverter and I can't easilly test the resistance without taking it apart. The standard inverter looks like the connections on the pot is easilly accessable.

If anyone could check, maybe it had the resistance marked on it, but if the connections are easilly visible, it should be easilly testable with a multimeter.

reprobation · Post by **reprobation** » April 16th, 2006, 12:12 pm

Actually.. If im correct.. a potentiometer should be variable resistance, basically you can change the resistance of the piece by moving a nob (usually..).. so.. to ask the resistance of it is kind of difficult because your selecting the resistance... This is why you can get different voltage value's, and thus different settings from a single piece.

-Chris

Bochek · Post by **Bochek** » April 16th, 2006, 1:18 pm

i beleive he is asking for the range of the potentiometer. witch is PROBABLY 0-5k ohms.

just a guess tho, but that is the most comon range,

you could just take a ohm meter and backprobe the plug and then turn the knob to get the reading.

Bochek

Nd4SpdSe · Post by **Nd4SpdSe** » April 16th, 2006, 2:33 pm

Bochek wrote:i beleive he is asking for the range of the potentiometer

Exactly. I can't on mine cause I need to open her up, potentially breaking it. The standard inverter is open, so the connection should be easilly accessed for a resitance test. I just need to know the max resistance that the standard one does. It could even be marked on the pot itself.

BTW, the stock dimer is 100k, i'm hoping it's the same, or relitively close

DJsMX-3 · Post by **DJsMX-3** » April 18th, 2006, 3:53 am

Its easy to take apart without damaging it...
And you cant be sure its the same pot. on both standard and upgraded inverter.

Just peel the doublesided stickyrubber of "if you do it carefully, you can reuse it afterwards" then theres 2 or 3 little phillipsscrews, when you have taken them out you can open it and see the resistance on the pot.

I think i know what your plan is, but if youre just going to connect the speedhut inverter to the dimmerpot in the car your allmost certain going to ruin one or both circuits.....

Cant do it like that because its two diffrent circuits, having diffrent voltages and the "total resistance" of each circuit will alter eachother making everything work slightly or much diffrent from standard.

If you want to control the speedhut dimmer with the incar dimmer, you have to build a interface between the two circuits.

Nd4SpdSe · Post by **Nd4SpdSe** » April 18th, 2006, 10:55 am

DJsMX-3 wrote:I think i know what your plan is, but if youre just going to connect the speedhut inverter to the dimmerpot in the car your allmost certain going to ruin one or both circuits.....

Cant do it like that because its two diffrent circuits, having diffrent voltages and the "total resistance" of each circuit will alter eachother making everything work slightly or much diffrent from standard.

Not if there's nothing else connected to the dimmer switch, so the "different voltages" scenario won't exist. I'm trying to keep the circuit as simple as possible, but I need to research on the stock and the Speedhut switches beforehand.

As well, you may be right, the Standard and Upgraded inverters may be different...I have time today, I guess I'll risk it and see if i can find out what the pot is...and still have a working inverter at the end of the day. But it would be nice to have the value of the standard inverter, that way, if is it different, maybe it's difference in a good way.

ovendenk · Post by **ovendenk** » April 18th, 2006, 11:59 am

hey mike, let me know what you find out because i'm getting my gauges soon and want to integrate the dimmer switch as well. thanks.

Nd4SpdSe · Post by **Nd4SpdSe** » April 18th, 2006, 2:26 pm

DJsMX-3 wrote:Just peel the doublesided stickyrubber of "if you do it carefully, you can reuse it afterwards" then theres 2 or 3 little phillipsscrews, when you have taken them out you can open it and see the resistance on the pot.

Perfect, thanks

FYI, the resistance I tested is 1.5K Ohms

So I need to figure out how to get a 100K Ohm pot to control a circuit that maxes out at 1.5K Ohm...

More Info:
I hope there are some people familiar with this, but I'm reading something called Potentiometer Range Limiting, which they describe putting a resistor in parallel to diminish it by half. The example they used is that is a potentiometer maxes out at 10K, and you put a 10K resistor in parallel, the pot will function as 5K Ohms.

http://www.vias.org/feee/exp_dc_10.html

But I need to bring down the stock pot down almost 100 times.

A post I made on [H]ard|OCP
http://hardforum.com/showthread.php?t=1045228

Edit:
I found it. Putting the resistor of the value I needed (1.5K Ohm - Brown|Green|Red). I put it in parallel to the pot, and it works to the resistance that I need. I tested it with a multi-meter OK. Now I'm going to splice into the Speedhut harness. I don't know if I'm going to get to that today, hopefully tomorrow.

Edit:
I decided to go back and re-check the connections. Believe I tested at the wrong spot. I rechecked at the terminals of the pot instead (I did the connection of the incomming wires instead) and got a range of 4.5k max, and 1.5k min. So what I believe I have to do is put a 1.5k resistor in series, with a 3.5k resistor in parallel to the pot. I'll do this after supper.

DJsMX-3 · Post by **DJsMX-3** » April 18th, 2006, 8:14 pm

You could do it like that but youll most likely get standoffs and possible very little adjustment..

If youre completely dropping the original car dimmer and only using the pot for controlling the speedhutinverter, just go down to your local radioshack show them the type of pot and get them to order one, just like it for you, but with the correct resistance

This only works if they know what theyre doing though

But why are you droping your original dimmer intirely?
The way to go really is to build a interface, but i can tell you in advance that its no little task.

Nd4SpdSe · Post by **Nd4SpdSe** » April 18th, 2006, 8:40 pm

I could, but the who point to this project is to use the stock dimmer switch, to have a stock look. I've had the speedhut ingraded inverter and I've been literally hanging around for over 2 years. I just can't find a good place to put it. The standard one is bigger and I'd have even worse of a place to put it. This way, I can use the stock Mx-3 dimmer for a nice clean look, and have my Speedhut guages.

I've already removed my stock dimmer when I installed my speedhut guages. But in haste, I didn't realise it controlled my HVAC panel, but that's not a problem, i got the Speedhut HVAC panel. At this point, the only "problem" is that I can't dim the dash clock (whoop-dee-doo) and because I don't have the stock dash backlight, I can't see my trip and odometer at night, but those don't bother me at all.

For future reference, if someone wanted to keep the stock dimmer, they could go to the wreckers and get a second one, do this mod, and put it in the empty space beside the stock dimmer. Always a possibility

BTW, I built the circuit on a breadboard and got it working, It's a little sensitive, the last 25% on the stock dimmer controls like 90% of the brightness, but it's not too bad, and I'll be happy with that. It's getting dark, but tomorrow I'm going to start to integrated the circuit into the stock dimmer. One thing I want to do as well is have it perma-blue. The speedhut dimmer had a switch between green and blue. All I want is blue, so to clean it up, I'm going to figure out the circuit for the color switching, and hard-wire it.

ovendenk · Post by **ovendenk** » April 19th, 2006, 11:26 am

mike, i'm confused. i thought that if you put a 1.5k (1.53k to be exact) resistor in parallel with the 0-100k pot, you'd end up with a range of 0-1.5k ohm. no? where'd the 4.5k come from?

btw, would it be possible to mount the speedhut pot into the stock pot location? are they anywhere near the same dimensions?

Post by **Custommx3** » April 19th, 2006, 11:50 am

I actually have my Speedhut gauges feeding off of my Dimmer switch in the RS. It does dim my gauges for me I believe. Id check, but the battery is dead

Im about to pull the motor in it and rebuild it.

mr1in6billion · Post by **mr1in6billion** » April 19th, 2006, 1:54 pm

Have you opened up both dimmers? I haven't had a chance to look at our dimmers, but if it's anything like my old civics dimmer....

The little black box is a current regulater. By adding this to the circuit any readings taken at the terminal (unless fully powered) will be unreliable. And the value of the real pot will also be irrelevent. The only way to truely convert one dimmer to the other is to power them, then record the resulting output, then figure out how to alter the stock dimmer to mimic it.

Nd4SpdSe · Post by **Nd4SpdSe** » April 19th, 2006, 1:55 pm

ovendenk wrote:mike, i'm confused. i thought that if you put a 1.5k (1.53k to be exact) resistor in parallel with the 0-100k pot, you'd end up with a range of 0-1.5k ohm. no? where'd the 4.5k come from?

btw, would it be possible to mount the speedhut pot into the stock pot location? are they anywhere near the same dimensions?

Actually I made a mistake when I initially measured the resistance on the Speedhut put. At first I measured the pot's range to be from 0 to 1.5K, but I double checked and the pot lat night, and it's range is from 1.5K to 4.5K

Putting the 1.5K pot in parallel with the stock Mx-3 dimmer will make it funtion similat to a 1.5K pot, yes, but 1.5K is wrong The pot needs to be set to 3k. 3k is the range between 1.5K and 4.5K that the Speedhut guages want. But putting only the 3k resitor on the pot will mean it's range will be 0 to 3K. So what needs to be done is putting a 1.5K resistor in series to the pot/resistor circuit. That add's 1.5K Ohms to the resistance of the circuit, so the range will now be 1.5k to 4.5K, as required.

I'm going to have to make this done and come to the meet for you this weekend, aren't I

I actually have my Speedhut gauges feeding off of my Dimmer switch in the RS. It does dim my gauges for me I believe. I'd check, but the battery is dead Im about to pull the motor in it and rebuild it.

Speedhut specifically says NOT to put the inverter after the stock dimmer. If it works, cool, but my stock dimmer is non-existant because I took out for the Speedhut guages. It's probably not good for the Speedhut inverter, but I'm guessing you've had it working for a while, so maybe not

ovendenk · Post by **ovendenk** » April 19th, 2006, 2:27 pm

Nd4SpdSe wrote:I'm going to have to make this done and come to the meet for you this weekend, aren't I

yes please.

btw, if it does work properly, could you bring a second set of resistors because i don't have a reliable source to get resistors from quickly. pretty please.

does this mean you're coming assuming it's not raining?