I bought three 100 watt 2 ohm resistors from Ebay $5.00 each and installed the first one this afternoon and the top would not move with the engine off. after checking everything I put a cheap ohm meter on each of the three resistors and found that one I had installed read 2.3 ohms and the other two read .3 At this point I reinstalled the second resistor and the top worked fine but a little slower, so I think I'm OK, but a little confused on the ohm readings since 2 ohms is the spec on the resistors and I wonder if have enough resistance on .3 or the cheap ohm meter is not accurate or maybe I'm not using it right.

This the resistor bought http://cgi.ebay.com/100W-0-2-ohm-0R2...tu%3DUCI%252BI

Do you think I'm OK?

Charlie Pace

 

I think you are fine. The resistor is a 0.2 ohm, not a 2 ohm resistor. Your meter read 0.3 ohms. That is so close that you are well within the proposed specs. And as you said, it may just be that your meter is a little off.

 

I have been trying to operate my modified system with the engine off for a little more pressure reduction but the latch requires an additional press of the switch sometimes.

Guess I will just go with the engine on operation.

How in the world are you measuring a 0.20 ohm resister with a VOM? Neither of mine are anywhere near capable of measuring that small amount.

 

Great job. Congratulations. I had a dieferend idea, but this one is much more simple.
If for some one doesnt work 0,22 ohm than go for 0,2 or o,15 or even 0,1 ohm. All of them will reduce preassure at the end. Of course the higher resistance the tle lower preassure. Nice that you found the edge, and it looks thet for most people 0,20 works!

I have another idea, and I`ll try to develope it in the summer time. I want to make a cheep modul wich would close the rooy when it will start raining.........

 

Charlie,

0.2 ohm is where we'd like to be. 0.3 ohm worries me a bit. Even if the top works OK now, this value takes the voltage down too far to leave some "headroom", should the latch become dirty or lose lubrication (it might then need more pressure to work).

If you buy a nominal 0.2 ohm resistor with 10% or better tolerance, you can forgo measuring it. Let me know if you want help finding a source.


Tom,

The "engine off" behavior represents a change, no? You were good running that way earlier, I thought. Assuming fluid level, etc. look normal, would you agree that this maybe is an early indicator of a latch that's starting to need more pressure to work?

(I don't think we need to measure these resistors unless one seems to behave outside of its spec.)


Fishman,

Thank you, sir. The 0.2 ohm was arrived at by actual testing ... trying for the lowest pressure consistent with relieable operation of the latch (the thing that needs the most pressure to work). I prrefer to see things work OK "engine off", because then there is about 100 to 150 PSI held in reserve ... which can be called upon by going to "engine on" ... should the latch start to require more pressure to work (dirty or needing lubrication).

 

The only think wich is not correct in my opinion is: "Parallel combinations of resistors (e.g. four 1-ohm resistors in parallel = 0.25 ohm) should not be used."
Why not??!! You can youse it , just make sure that in this e.g. each of the resistors will be 25Watt.

 

Fishman,

I agree they could be used, but think it is not good practice for this reason: let's say one of the parallel resistors fails or we have a cold solder joint. Then we would be running with a higher resistance (~ 0.33 ohms) but would not know it. This could cause us to stress things, trying to make the system work with too low a voltage.

By avoiding parallel resistors, we have less chance of running with a different resistance than intended.

 

Thinking that way you can say do not put or solder any resistors.
I would suggest that if for someone 0.2 does not work, than he can try 0,15 ohm. To get this value jast put 1 resistor 0,2 ohm and one 0,1 in parallel. Now it will work!! Just remember about right power.

 

If someone wanted to use parallel resistors, I would not argue with him. But there are more failure points that way, so my own preference is to avoid it.

On use of different resistor values. A "healthy" mechanism should work with 0.2 ohms. So if it did not, there might be trouble brewing somewhere. Careful! 0.2 in parallel with 0.1 is NOT 0.15. It is below 0.1, and is too low for a good pressure reduction. Did you mean 0.2 in parallel with 1.0? That would be close, about 0.17.


In general terms, there is nothing special about the operating point of 14 volts, 1650 PSI peak pressure, which is how this pump operates in "stock" configuration, engine-on. This is just one point on a voltage-pressure curve. Another point on that curve is 12 volts, ~ 1450 PSI (corresponding to "stock", engine-off). A third point is 8 volts, ~ 1000 PSI (the target of our voltage reduction system). It is more than a coincidence that the voltage/pressure ratio stays nearly constant in all these cases.

If the motor is "happiest" at any of these points, it is surely the last one: lowest current, lowest power dissipation, lowest mechanical stress.

And thanks for your interest!

 

Charlie,

I read your post too quickly earlier; sorry. Resistors are almost always within spec, so we can usually get away without measuring. Yours were all spec'd at 0.2 ohms but read 2.0, 0.3, 0.3, correct? Yikes!

Maybe get those checked at Radio Shack or wherever, but ...
-One 0.3 ohm in parallel with one 2.0 ohm should be OK, but resistance will be a little high.
-Two 0.3s in parallel would be OK, but resistance a little low.

I'd sleep better if you went to a single 0.2 somewhere down the road.

 

Great group. I love this car.

charlie pace

 

I was fiddling with my car today (it was a bright, sunny, 70 degrees here today) and when I tried to close the top it wouldn't close. It wouldn't even move! I went back to the back where I had installed the resistor and discovered that one of my crimp connections had come apart. I recrimped it, then I dropped a drop of superglue into the crimp connections just to be sure. (Superglue is a conductor and when I was in the Marines we used to use it to hold the pins on the wires that went into the cannon plugs on airplane connectors. )

Anyway, after fixing the connection the top worked fine. I went back and felt the resistor and it was pretty hot. I pulled out my IR thermometer and it said the resistor was 135 degrees. I cycled the top again and this time it went up to 157 degrees. I doubt I'll ever be cycling the top more than once every few minutes, but I decided to screw the resistor to the metal rack that holds the pump, CD and nav system. The metal should do a much better job of dissipating the heat.

 

The Weather here in St. Louis is much improved too. So I had my car out too. But instead of just crimping the wire with the connector I soldered them together. I don't think those temps are anything to worry about. In the guitar amps we work on every day here(mostly old Marshalls and Fenders) things can get much hotter and they are on for hours.

 

Hi, sorry for my mistake. Of course I was thinking about 1 ohm parael with 0.2 ohm.
THe best think is what you did found out take one resistor 0.2 ohm 100W or more + radiator (safer).
But is this not work for some one, becouse his set up has weak points he can definitly try to go for pararel set up and try a little lower resistance. I just mention about it becouse I`m almost sure that they will be some people with such a problem.
I had a problem first with actuators so now I`m having custom ones. Then leaking from the top pipe. I Need to reduce preassure!! And first move will be you sugestion 0,2 ohm but if it fails than I will play with dieferend recistance becouse I know that it is fine to do it!

Any way thanks for advice, becouse it is your great idea. Great idea.


[
quote=Dennis07;305723]If someone wanted to use parallel resistors, I would not argue with him. But there are more failure points that way, so my own preference is to avoid it.

On use of different resistor values. A "healthy" mechanism should work with 0.2 ohms. So if it did not, there might be trouble brewing somewhere. Careful! 0.2 in parallel with 0.1 is NOT 0.15. It is below 0.1, and is too low for a good pressure reduction. Did you mean 0.2 in parallel with 1.0? That would be close, about 0.17.


In general terms, there is nothing special about the operating point of 14 volts, 1650 PSI peak pressure, which is how this pump operates in "stock" configuration, engine-on. This is just one point on a voltage-pressure curve. Another point on that curve is 12 volts, ~ 1450 PSI (corresponding to "stock", engine-off). A third point is 8 volts, ~ 1000 PSI (the target of our voltage reduction system). It is more than a coincidence that the voltage/pressure ratio stays nearly constant in all these cases.

If the motor is "happiest" at any of these points, it is surely the last one: lowest current, lowest power dissipation, lowest mechanical stress.

And thanks for your interest![/quote]

 

Sam,

Heat: one of the solenoids on top of the pump gets pretty hot too with up/down cycles in rapid succession. Probably best to avoid such with or without (shudder) pressure reduction.

Super glue conducts?! Who knew?

(I was at the dentist yesterday, and it the midst of asking the gal for this tool and that part he says "guerrilla glue". He swears he was not just messing with me, that they really have a product for dentists, but I'm still not sure.


Fishman,

Yes, I'm OK with your idea of adding parallel resistors as a way to fine tune things. It just requires that we be especially careful making a good, durable connection.

(This whole project is trivial compared to what you accomplished with the supercharger. Congrat's on that.)

 

Someone else PMed me about the super glue. I DO have the ability to solder, LOL, however the spade connectors I was using have plastic covers on them. They are meant to be crimped, and soldering them would melt the plastic. The super glue is just a little assurance that the crimp will hold.

I installed the resistor by soldering a short lead onto each end of it, then crimping the spade connectors to the leads. That way if I need to remove it I can easily unplug it and reconnect the wires.

 

This is why I used solder connections instead of crimp connections and insulated with shrink tubing. Be liberal with the flux and use a hi-temp solder gun when soldering and it will all but alleviate a cold solder joint.

 

Lew, I think this is a great suggestion. Seems like there have been at least a few cases where a connector or cold joint issue has caused headaches.

After all, we're working in an environment where a few 100ths of an ohm can make a difference.

Nice catch!

 

Mine had the spade connectors too. I first pulled the plastic covers back over the wire then I tipped the wire then tipped the crimps with solder then crimped them. Heated it back up added a little solder let it cool and pulled the plastic cover back over the spade. Looks great. Nice and neat.

 

I just order the resister today. I plan on installing it before I need to "drop the top" here in Chicago. I think I have a few months. Just a note on installing a spade lug. You can buy an uninsulated lug and solder them and use some "heat shrink" tube which comes in many colors. This can make a very nice looking job.