Friday, November 4, 2011

It's An Imperfect World, Screws Fall Out

One of the frustrating things that occurred during this summer's work on the car was that stuff seems to have broken all on it's own.  Through no intervention on my part, at least two items on the car stopped working.  Trust me when I tell you I've been responsible for breaking a number of things related to the car, but I think I'm innocent here.

After I hooked the batteries back up and turned on the new TBS Link-Pro meter, I had to run through a series of menus to set it up properly.  When it came to the prescaler menu, I selected the 1/10 prescaler because that's what I was using for the older Xantrex Link-10.  To my surprise the meter read that my pack voltage was 68.9 volts.  Well that's a bit off as my pack voltage is 160V.  I double checked the meter looking through all the settings and found everything was correct.  Eventually I pulled the meter out and measured the leads coming from the prescaler itself only to find that the leads which should have read 16V, instead read 6.89V.  Well that put the blame solidly on the prescaler, the meter itself is fine.

I checked and the prescaler was hooked up correctly, after all I hadn't changed any of that.  But there was no doubt about it, the prescaler was spitting out the wrong voltage.  I have no idea why it broke, how it broke or when it broke.  All I know is that when I unhooked the batteries in May, it worked, and when I put them back together in September it didn't. 

Not being an expert in electronic circuits, I have no idea how to fix the prescaler.  As far as I'm concerned, I put 160V on two wires that lead to a little box in which some magic happens, and then on the two wires coming out the other side, there's 16V.  Besides, the unit is sealed.  I was left with one option and that is to replace it. 

I got the replacement 1/10 prescaler and thought I'd measure it before I disassembled the dashboard to put it in.  I carefully hooked it up to the positive and negative leads to the 160V system, and to my amazement the other end read 48.3V.  What the hell!?  Now I had two different prescalers, each of which should be working fine, but both spit out completely different and incorrect voltages.  I sent the new one back at which point they evaluated it and said it was fine.  What!?

I'd ordered the part from Evolve Electrics and was working with Justin Dunn.  It turned out that both of us learned something about this prescaler and the TBS meters.  Both the 1/5 and the 1/10 prescalers will read 48V when hooked up to the pack.  It's only after you hook it to the meter does it somehow adjust the voltage and display it properly.  Like I said before, magic.  Neither of us expected that.  By the way, Justin was great to work with.  I feel quite comfortable recommending Evolve Electrics. 

The second thing that seems to have broken while the car was sitting still was the tachometer.  I drove the car around for a couple days after putting it back on the road, and all was well.  But one evening I left my destination to head home, turned on the lights and found that the tachometer's dial didn't light up.  A few moments later I realized it wasn't working at all!   It had been working when I arrived earlier when the lights weren't on.  When I came to a stop light, I turned off the lights and revved the motor.  Sure enough the tach sprang to life and worked perfectly.  It was hovering at about 2000 RPM and I turned the lights back on and the needle froze where it was. 

I have no idea what would cause such strange behavior, but I do know that I didn't touch any of those systems or their wires when I was performing the work this summer.  But then it just got worse.  A couple weeks ago I was accelerating from a light in second gear.  At about 35 MPH I went to shift to fourth and I noticed that the tach read 5000 RPM.  I thought that was odd because 35 MPH in second gear is about 4000 RPM.  I dropped it into fourth and watched the needle come down to about 3000 RPM, which I know is too high for that speed.  Suddenly the needle jerked up to 5000 RPM, then 6500 RPM.  By the time I finished my trip, the tach's needle had moved well beyond the 8000 RPM top of the dial, and was approaching a full lap coming around to 0 again.  Now the tach just jumps around all over the place providing no useful data.  It's just become a distraction.  I believe I'll be unhooking it.

So what the heck happened to these two pieces of equipment while they were sitting still and not being powered over the summer?  I really wish I knew.  The tach I can live without.  I'll probably replace it at some point, but for now, it stays.  Justin sent the prescaler back to me and I popped it in yesterday.  It works just fine and the meter is behaving like I expected.  If you ever end up with the TBS meter and prescaler combo, don't bother taking a voltage measurement from the prescaler itself, it won't be what you expect it should be.  It has to be hooked up to the meter. 


Gam0ra said...

I believe that is a phenomenon related to the fact that you can't demonstrate a fault when an expert is there to watch. That being that gremlins have infested your car, probably while it was being transported to the con.

Tim Catellier said...

Where is Phoebe Cates when you need her?!

achims E-Umbau said...

I am sorry to hear that, hope you can fix the tachometer.
But i am as well concerned about the 1/10 prescaler, because i bought last week one for my TBS e-xpert pro from Justin. Hope this one will work better than yours.

Tim Catellier said...

Achims, It should be fine. When you first attach the 1/10 prescaler to the your battery pack it will likely read 48V. But once you connect the prescaler to the meter, the meter will display the proper voltage as long as you choose the 1/10 option in settings.

vehikelfranz said...

The prescaler is normally
nothing more than two resistors
in series....
10 : 1 means for example
9k + 1k in series so, you will have
1/10 of the whole voltage at
the 1k resistor.
I am quite sure that Your
voltage-meter (TBS e-xpert) has
a certain resistor at its input.
so, the prescaler must be
adjusted so that the lower resistor of the prescaler
in parallel with the resistor inside the voltmeter is 1/9
of the larger resistor of the
prescaler. so, if the internal
resistor is missing the voltage
of the precaler is too high.
I think, thats all....
(that does not explain the failure,
but it explains the function
and the 48V when not connected)

Tim Catellier said...

Thanks for the input. Slowly I'm becoming more familiar with electronics.

To be clear, the only failure was with the old 1/10 prescaler I was using with the Xantrex Link-10. I'm not sure if I was clear about that. None of the components for the newer TBS Link-Pro were faulty.

vehikelfranz said...

Oh! That means, You had used a
prescaler that was intended to work with the Xantrex, and not with the TBS..... and if both instruments have different input resistors, this cant work.... and the old prescaler is not defect, it is only the wrong one.

Tim Catellier said...

That was my thought too, but there's one problem with that. The output voltage of the old prescaler (the one used with the Xantrex) was 6.83 volts. If it was working properly, that would mean that the Xantrex took a 6.83 volt input and displayed it as 160 volts. That seems strange. On the other hand, that may be exactly how it worked, I can't say for sure.

My mistake was in thinking that a 1/10 prescaler actually put out 1/10 of the input voltage, and that one 1/10 prescaler was just like any other 1/10 prescaler. Clearly that's not the case.

vehikelfranz said...

I cant test it, but i am very sure that the xantrex prescaler will have an output of 16V on 160V when it is connected to the xantrex, as the xantrex seems to have a higher resistor at the input than the TBS has.
When open, the output should be
a little bit lower than 48V at 160V
maybe around 30V.But, maybe You should simply be glad, that it works now ;-)

Tim Catellier said...

That, I am!