Tom,

Thanks for the info. A little noodling and a suggestion for users:

Whatever method we use to do it, lowering the peak pressure in the convertible top system has as its goal reducing the risk of hose falure while still assuring that all the mechanisms will work. This is true when selecting a pressure limit for a relief valve, or a resistor value to lower pump voltage.

But it seems the target, the ideal pressure, varies from car to car, and maybe over time in a given car. Several current cases reported here highlight this. So, what to do? There is a section in the relief valve instructions on adjusting the valve's pressure limit if it turns out to be set too low for a particular car (I don't know if this has ever been needed). The analog to this with voltage reduction is to increase the pump voltage.

Near as I can tell, there are now about 40 users of the voltage reduction system. The really good news is there have been no "green showers" reported. I believed, still do, that the "nominal" operating point (engine-off, 0.20 ohms) will work fine in just about all cases. But now we have Tom's case of a failure to latch that (maybe) isn't tracable to another cause. If this repeats, I think it calls for raising the voltage for his car. The easiest way to do this is to change from engine-off to engine-on operation, which will create ~ 100 PSI more peak pressure.

So I'm thinking we should add a "day-to-day operation" blurb to the PDF saying something like "engine-off is the preferred way to operate, but if the latch ever fails to close on the first attempt, and it can't be traced to another cause, then change to engine-on and stay with that." This should do the trick, albeit with somewhat less protection against hose failure. (If someone decided to run engine-on from the get-go, for whatever reason, I wouldn't try to talk him out of it.)

Comments? Suggestions? Brickbats?


A note on battery load when raising the top "engine-off": To get a feel for this, there's a useful coincidence. That button on the remote that turns the headlights on for thirty seconds ... it turns out that this draws roughly the same current, for roughly the same length of time, as raising the convertible top (with 0.2 ohm resistor in place). So: if use of that remote button seems like an OK thing to do, then it's also OK to raise the top engine-off. The battery can't distinguish between the two activities. This goes into the PDF too.

 

This is what I was after when I asked about loading the battery in a previous post. As a know-nothing when it comes to electrical (but an expert in earthquake response of structures) it still seems counter-intuitive to me that having headlights on for 30 seconds draws the same current as the pump motor which is basically working against a considerable pressure load for the 20 seconds or so that it takes to open or close the top.

But if that is really the case and the battery is right at the threshold where there is just enough power to start the car, it would be better to get the car started and then worry about opening or closing the top.

Doug

 

It makes me sad to post this, but I don't see that I have a choice. I've been alerted that Gus's web pages on the relief valve link to the vendor's site, which contains this:

"Do not confuse this with cheap fixes that starve the motor by inserting resistors in the motor circuit. This causes the motor to run excessively slow, does not eliminate the dead head problem, and will ultimatelly (sic) damage the motor. The kit sold here allows the motor to run at its full design speed and only acts to reduce pressure at the critical point when the work has been done. "

Please see www.scorekeeper.com/jaguar/jaguar01.htm for a response.

I have scrupulously avoided criticizing the relief valve work, though all such work has pros and cons. If things like the above are to be part of the discussion (I shudder to call it that), the gloves come off.

And if Gus or another moderator has in mind to wave their badge at me and say "give it a rest", please save the keystrokes. Pull the plug if you wish; this kind of thing is beyond the pale.

(Thanks to the fair-minded folks here for the heads-up.)

 

I've read this thread back n forth so many times. I have to keep coming back to it time and time again.....unbelievable

I'm not going into a long winded post here but will say this in response to your post Dennis.
As far as I can see the statements you mention are made by the manufacturer NOT Gus. He may have a link to their website but is not in control of their content as far as I'm aware.

Dennis, you seemt to be very knowledgable in many areas and very helpful which is fantastic. We also have many other members here who also strive to help others on the site.
In my view, we ALL need to get along as we are all here for the same reason, I assume?

The camaraderie ( mutual trust and friendship among people who spend a lot of time together ) here is outstanding, and without doubt, the best I have seen in any forum.

With that said, from time to time heated debates, fueds even, flare up between individual members and sometimes, there may even be two camps as it were, as it seems in this instance.
This may be a one off scenario?
I'd like to think it isn't a carry over from another site?

To sum up - ANY member, senior / veteran or moderator for that matter should never indulge in this type of behaviour as it upsets the harmony and balance of the forum. Whether it be a new member, or one with 1000 post count, moderator or technical guru, I could care less, they will be removed from the site should they continue in this vein....period!

Please remember, we ALL have different opinions and feel free to voice them, BUT we need to use caution in what we say and temper that to the reader.
Personally, I type once and read / re read a few times to try to ensure that I do not make that mistake.

I will leave the thread open as it is a very popular topic, and I look forward to continued discussion on this issue. Please use caution in any further posts about any other solution and or member.

 

Thanks, Jim, for your even-handed comments.

I have tried scrupulously to avoid saying anything critical about the relief valve approach to this problem. If you (or anyone) know of a case where I have failed in that, please let me know about it. Seriously.

Of couse I would try to hold to the same standard in the future too.

Best,

 

 

Speaking of this, I have done the resistor retrofit and am having problems. One problem that occurred was that the top did not latch fully. Releasing the switch and pressing again completed the latch closure. Another problem was that the rear windows did not completely close, but everything else completed closure. A re-engagement of the switch completed the closure of the rear windows. I thought procedures like the closing of the rear windows had to complete before the top latched. This is strange and I may reconsider the resistor retrofit. Any ideas on what is happening?

 

In this case, there will always be two 'camps', and we've talked about it here and the other 'relief valve' thread. Dennis, if you feel confident in your approach, and I think you are based on your knowledge of electrical components (including motors), try not to let other comments hinder that. No matter what topic we are talking about, whether it be cars, life, politics, religion...there is ALWAYS someone (or more than one) that will believe exactly the opposite. When sales of a product are involved, truth is often stretched or facts omitted, and the marketing can be very negative, especially towards a competitive item.

In this situation, on this topic of the hydraulics, due to the complexity of the different approaches, not everyone will understand 100% the theory or principle behind the two. I support your method, and its continued option for the hydraulic pressure solution on this forum, though due to my confidence and understanding in a mechanical resolution over the electricity magic, I would select the former. It doesn't, and shouldn't matter, however, on this forum.

 

Matt:

You and I are OK. Yes, for sure there will be camps favoring this approach or that, and I have no quarrel with anyone picking one or the other. But there's no excuse for just making stuff up about a competing idea, whatever one's commercial interests. Stretching the truth is one thing; saying "black is white" is quite another. (Many lawyers would go hungry if there were less of this, huh.)

It's amazing to me how people will sometimes pound the table about what will or won't work before they have asked their first question about something which may be new to them. Anyway, I have no interest in brickbats back and forth. But as somebody once said: "I am not vindictive, but I can be provoked."


Lew:

I did not know you were having trouble. Please give a yell if you want help going forward.

The only cases (I know of) where there has been a "failure to latch" while using voltage reduction so far were traced to a cold solder joint, or low fluid level, or a leaking ram. These were all resolved.

But remember too that even in cars with no pressure reduction, failures to latch have been reported when the latch mechanism gets gummed up or dirty. With any form of pressure reduction, such cases can be expected to show up more frequently.

Questions:
- value of the resistor ?
- was your engine on or off ?

The rear windows raise after the latch closes, so I don't think you have a problem there, based on what you described. They won't try to close until the latch is fully closed and you hear the "bong".

 

Lew,

Under normal conditions the windows will not operate closed until the rear right ram is in the fully closed position first. If for any reason that the ram is not fully closed the windows will not operate. An obvious synchronizing problem. This system is dependent on the electrical, hyd, body processor and security systems working in sync. Reading you situation I would ask that you check the mechanical operation at the roof header and I put a little information together for you to see http://www.gusglikas.com/images/Auto...atchRepair.pdf Have you checked the fluid level at the tank? It could be a little low. The other could be that your pump went into a deadhead condition and when you released the switch and attempted to close again it cleared itself. This deadheading will cause and unusual motor noise. Did you hear the motor? I would recommend check your battery as well. I hope this helps!

 

Lew,

Just so we don't over-think this ... From what you described, there is no reason to suspect anything is wrong with the rear windows. They can close only after the latch is closed ("bong"), and we must hold the button down until they do (~ 3 seconds). Given the situation, we would expect them to behave exactly as you saw.

I forgot to ask ... please check fluid level.

The reason that releasing and re-pressing the switch can get the latch to cooperate is that the motor makes max torque at zero RPM, which gives us, briefly, a little extra hydraulic pressure (proportional to torque).

If everything we can check looks good, this may just be one of those cases where the latch mechanism wants lubrication / cleaning.

 

Received an email telling me that the Moser power resistor spec'd in the PDF file is no longer available. Here's a replacement:
Digikey.com
850FR10E-ND 0.1 ohm, 50 watt, 2 required, @ $7.84

Some folks have used a single 0.2 ohm resistor, various sources. I don't know about availability of these.

Revised part number will be included in the next edition of the paper describing the system.
Most current version always found at ... www.scorekeeper.com/jaguar/jaguar02.htm

 

Dennis 07 - "Received an email telling me that the Moser power resistor spec'd in the PDF file is no longer available. Here's a replacement:
Digikey.com
850FR10E-ND 0.1 ohm, 50 watt, 2 required, @ $7.84
Some folks have used a single 0.2 ohm resistor, various sources. I don't know about availability of these.
Revised part number will be posted with the PDF file (URL above)."

PDF File attached -

 

I ordered the resistor from eBay and installed it a few weeks ago. I've only cycled the top a couple of times, but it appears to work fine. I can definitely tell that the motor/pump sound a little different, but the cycle doesn't seem to take any longer. Of course, I didn't time it. If it's taking longer then it's not really noticeable to me. Next time I open it up I'm going to put a little grease on the latch just as a preventative measure. I can see how the reduced pressure would make it a little harder for the latch to "latch". Of course, that's a sign that the resistor is doing what we want it to, right?

 

Right!

Based on Walt's published pressure charts the 1600 psi spike only occurs at the latch operation. The point is to be able to reliably operate the latch at a much lower pressure level. Walt found that to be at around 1000 psi. Dennis found that to be at somewhere around 9 volts. Results are the same.

After 9 months and the resolution of a cold solder joint on the resistor my top operation has been perfect.

 

Sam,

Glad to hear.

Yeah, the cycle time is a little longer, but it's at latch-closure that things pay off. Both this system and the relief valve are trying to hit a sort of pressure sweet spot ... enough pressure to reliably close the latch, not so much as to blow out a hose or a fitting.

0.2 ohms, right? Then you should be developing about 950 PSI or 1050 PSI depending on whether your engine is running (alternator voltage makes more motor torque, more pressure than battery voltage). Those numbers from memory, but it's close. By way of comparison, the relief valve is set to 950 PSI (I think).

Which brings me to ... with any pressure reduction system, we're giving ourselves less margin for error in getting the latch to close, compared to a stock system. Say, for example that a clean, well lubricated latch needs 850 PSI to close. Then it starts to get dirty or the lube dries out and next thing you know it needs 875 or 900 or whatever. With a stock system, we have plenty of pressure in reserve (~ 1600 PSI) assuming nothing breaks, but here not so much. For this reason, I think we will be seeing more "failure to latch" cases than in a stock system, calling for some attention to the latch. But this is a small price to pay compared to the green shower.

If we were to see a lot of "failure to latch" cases", we could do a trade-off ... run a lower resistor value to get more pressure, but give up some hose protection. Some more time with systems in use will tell us if this would be wise.

Sorry, went off on a tangent there ...

Keep us posted on how things perform, OK?

 

I have been diligent at keeping the latch lubricated. The rear window closed to about 1/2in left. Pushing the button again completed the closure. The window power doesn't go through the resistor?? Maybe I just didn't hold it long enough. I'll address this again when warm weather returns and I start using it again.

 

Lew,

Right, the window power is separate. Resistor only limits power to pump. Again, the windows won't go up until the latch is closed, tagged by the "bong" sound. It's possible there's an issue with the windows, but seems like too much of a coincidence. A test would be "bong" + 3 seconds or so with the button held down, and they should be up.

If your latch didn't want to close last time we know either the pressure needed to do so has gone up, or the pressure made by the pump has gone down.

Everything I can think of to check (much of this old news):
- fliud level in pump reservoir normal
- manual valve on pump body fully closed
- resistor circuit integrity; connectors fully closed, inspect for cold joints
- try "engine on" operation if failed attempt had happened "engine off"
- check for leaking ram or pump connection
- latch cleanliness and lubrication

(Please use me as a resource on this if you see trouble again. It's the only system out there with problems that I know of, and will bug me until I know it's sorted out.)

Best,

 

This might help! You can read the entire thing or just go to page 7 http://www.gusglikas.com/images/Auto...s/501-11am.pdf and if you look at page 9 at the top it references a low battery. I hope this helps!

 

There is nothing new under the sun. I did not know this, but a common practice in the auto industry for some time has been to insert a resistor in series with the fuel pump to lower its voltage. This is, of course, exactly what we're doing here for the convertible top hydraulic pump.

In the fuel pump application, the resistor is automatically switched in and out as needed. When needed, it is switched in so the pump will not create too much pressure(!) and also to lessen power dissipation in the pump. It is switched out when high flow from the pump is needed. Resistor values are typically chosen so as to lower the pump voltage to 8-10 volts. In our convertible top system, the target is about 8 volts.

(This practice is now giving way to PWM (pulse width modulation) as a means of fuel pump voltage control. PWM is more energy-efficient and can provide variable pump voltage. But PWM would not be a good choice for our purposes because of cost and complexity, and because energy efficiency is unimportant with the convertible top pump running so infrequently.)

Here's a thread selected almost at random that discusses this practice ...
http://www.rx7club.com/showthread.php?t=786591
The resistors shown are heftier than the ones we use, but this is so because they have to work full-time.

So the "resistor method" is not such a peculiar idea after all. Sometimes the problem picks its own solution. It's deja vu all over again.