Help with BB dash instrument removal

You need to start at the bottom air con diffusor out, radio out, to allow you to get access into the back of the gauges, they have a rear bracket with a knurled nut on them, you should be able to see the 5 0r 6 M6 studs that hold the dash on.
The driver side little pocket in the dash also has to come out.

Un-rivet the side covers on the A pillar, top and bottom, the windscreen and headlight boss that holds the stalks has a M6 bolt at the base that holds it on. The dash is a tight fiddly to remove.
I would imagine you are getting it recovered?
Like everything on these cars nothing takes 5 minutes!

Take your time!

 

I wonder why he got out the large gauges and not the small ones?

 

They have a rear bracket with a knurled alloy nut on them. its just easier if you take more stuff out to gain access.
are you putting LED ones in??

 

I was just in there. If it seems impossible, you're on the right track. When you're done, you'll have some stories to tell.

Sorry - just be super patient as it's more fun to reassemble.



Also....Congrats on the new beautiful Boxer!

 

Yes....... I have a saying
Time plus tragedy equals humour.
The LED bulbs I put in are terrific.

 

Good day,

Just a heads up... LEDs are controlled (dimming) by current and not by voltage. The rheostat is effectively a voltage divider/reducer and so what you will find is that the LED will not dim linearly... but simply dim a bit and then stop all together. These days LED dimming is done via a slightly more complicated circuit that uses what is called pulse width modulation (PWM). Here the dimming is achieved by changing the PWM frequency.

Cheers,

Sam

 

Makes perfect sense. Now the next trick is find LED makers that incorporate this tech into the bulbs. I think I just use them at full brightness, or a tick below, so I'm fine with this level of resolution.

Kind of like have 22 gear ratios on my bike. I probably only use 6 or 7 gears for 99% of my rides.

 

Soo, I presume you got it done? Pretty crazy task. Not impossible, but pretty darn close. There's no special tool I know of other than patience. Maybe wine selection (or something stronger).

A parts source once told me about replacing the rubber filler neck coupling on 308:
"You gotta be a Cirque du Soleil performer to put those on!"

 

Nope,...... no wine!
Head straight to the Bourbon!!!

 

Good day 2dinos,

You will not find LEDs that have built-in PWM dimming, as there are far too many factors and design considerations to include within this additional circuitry. As you mentioned, in most cases people set the dim level and rarely change it and so having the adjust-ability is not really a big deal.

So... if you are happy with a set LED output level, you can create a very basic current source by adding a resistor in series to the LED. The resistor is sized based upon the Voltage drop across the LED and the nominal battery voltage and the LED current. The formula is:

series resistance (ohms) = (Vbattery - VLed)/ Desired_LED_Current (amps)

- Ensure your resistor is sized appropriately to dissipate the heat that it will generate as the current flow through it.

The more current the brighter the LED. However, too much current will cause the LED to prematurely fail. LEDs are very sensitive to heat and voltage. If you over voltage a LED it will burn out. The same with heat... which is generated by the current flowing through the LED x the Voltage across the LED. LEDs are semiconductors and statistically their lifetimes are greatly influenced by heat. Lowering a semiconductor by 10C will increase its life by 10x.

Many off the shelf LED replacement auto bulbs already have a series resistor (and at times a diode bridge) installed internally. However, some LED bulb manufacturers use lower output LEDs and over drive them using a lower series resistor in order to bump up the output light levels. The result is that these LEDs bulb fail much faster... so be aware. Complicating this is that there is no way to tell what LED bulbs are good from the outside. Even examining the internals would be challenging. Then there are LED bulb counterfeiters that make almost identical products, but are crap. Even buying LED bulbs from a supplier that had a solid product previously, may have changed their manufacturer, etc and you might get a sub standard product. So... if you find a product that suits your needs, ensure to buy some extras at the same time.

It is truly a shame that LEDs get a bad wrap, as the tech works excellent and can last a very, very long time provided that LED based light is designed appropriately. I have designed numerous LED lights and all have been working 24/7 for over 10 years with zero failures. Even my very high brightness LED assemblies (20000 lumen output) are still working 2.5x the rated LED lifetimes because of special attention I paid to heat dissipation/removal and input voltage anomolies. As I said, LED tech is great... but the focus on making things cheap and/or to maximize profit are the real issues.

Cheers,

Sam

 

Hi Sam,

Thank you for taking the time to dive into this EE project. I really appreciate it. Your insights reminded me of a Boxer project I resolved a few years ago. While that issue is behind me, I still welcome feedback on an EE concept:

My headlight challenge involved all of my headlights suddenly going out without warning. Initially, I went down the usual rabbit hole, blaming the switch and other common culprits. Eventually, I discovered that one of the relays had been replaced with a 40-amp Audi/VW relay, one of the many 'joys' of buying used cars and their hidden surprises.

After some forensic work, I traced the issue to the relay coil (likely overheating or going open). I confirmed this after spending enough time testing to catch the relay clicking open despite proper voltage being applied. I resolved the issue by replacing it with a certified Tyco Electronics relay I sourced from Mouser. Not taking any chances on unreliable components!


So, here's the question for seasoned EEs regarding relay ratings:

Light filaments draw a significantly higher current due to the resistance change as they heat up. When specifying relay requirements, should the rating be based on the surge current or the operating current?

For example, if the surge current briefly exceeds 30A but stabilizes to around 15A after 0.5 to 1 second (just for discussion), would the surge current necessitate selecting a larger relay, or is it more typical to base the specification on the steady-state operating current? Many thanks!

 

Good day 2dinos,

You are most welcome. With regards to your question:

The answer is ... it depends. It truly depends on a number of factors one of which you touched on... the surge current duration. However, there are other considerations as well such as surge current magnitude, switching voltage, and downstream impact of the surge current. One could certainly use surge current rated relays, but this could be very much overkill (physical size, cost, speed, etc) depending on the application. Remember that the relay's rated current is mostly based upon the switching contact resistance with more current = more heat which it and other items contributing the lifetime of the contacts. Switching voltage also plays a role, as this impacts the electrical field that is generated between the contacts as they open and so can ionize the medium (usually air) that exists the contacts causing the current to still flow in a smaller surface area of the contact leading to contact wear/pitting.

In general and for low voltage applications where the surge current is relatively short in duration, the relay's rated current is typically larger than the steady state current. A rule of thumb would be say 50% higher or more based upon what relays are available, their size/form factor, and cost. If the surge current was longer, etc then one would need to consider the generated heat across the contacts along with the potentially greater e-field induced current as a relation to the reliability/lifetime expected of the relay. In addition to relay selection, a designer may decide to include ancillary components to minimize the effects of the surge current.

With that said, many "standard" auto relays are typically rated for 25A, 40A, etc with specialty ones for those circuits that can see much higher currents. Making things even more complicated these days are a number of poor quality, sub-standard, or counterfeit relays. As a result, the stated relay specs may or may not be accurate and so it can be a crap shoot with what you actually get. Recently a known manufacturer (not relays) was caught falsifying gov approval stamps on their products, and another manufacturer "had" the approvals before, but not currently.

Given your auto light example, I would simply use a standard 25A relay from a quality manufacturer (TE is great) and from an established and franchised distributor for these products. The 30A inrush duration on a 25A rated relay would not be overly significant for me to worry about. Now, if it was a fire, life safety, high reliability application... then my choice would be different + I would have a number of other components surrounding the relay's design to support the particular application + go through a third-party approval process pertaining to the various standards that need to be met.

Cheers,

Sam

 

Not an electrical engineer, but-
To add on to Sam's comment, relays have several different types of current ratings (definitions from this document published by TE):

• Rated current: "Current a relay can switch on and off and a relay or accessory can carry un-
  der specified conditions Unless otherwise defined the rated current covers:
  ■ contact current, switching current
  ■ limiting continuous current: For a relay the specified conditions are
  defined under contact ratings; see > contact ratings For accessories
  the rated current is specified for a duty factor of 50% at rated frequency
  of operation and at ambient temperature 23°C; the respective derating
  curves should be followed"
• Limiting continuous current: "the highest steady state load current a relay or an accessory can with-
  stand continuously while satisfying specified temperature rise requirements"
• Limiting making current, inrush current: "The limiting making current expressed as a current with a power factor of
  1 0 (resistive load) a contact is able to make under specified conditions; for
  20 ms data expressed as peak value, for 4 s data expressed as rms value
  Unless othwerwise stated the data refers to the Form A contact (NO con-
  tact), rated voltage and a current for a duration of max 20 ms for at least
  100 cycles or 4 s with duty factor of 10%
  Inrush current for some loads can be significantly higher than its specified
  steady state current For these load types the inrush current has to be within
  the limits for the limiting making current Typical examples for loads with high
  inrush currents are all type of lamps (incandescent, halogen, fluorescent,
  etc ) as well as motors, solenoids, transformers and capacitive load"
• Limiting short-time current, Overload current: "This test is done to confirm, that our relays withstand normal overload con-
  ditions, e g withstand short circuit conditions until a fuse opens"

Manufacturer datasheets should provide these ratings which can then be used to design according to your system. So in your example, the "limiting making current" rating would be what you should scrutinize when trying to determine whether a relay would handle the inrush current for a specific capacitative load like your lamp (see these application notes by TE for types of loads and how they apply to relay selection/design). This will be a higher figure than the rated current and limiting continuous current, which relate to the steady state load after the current stabilizes.

Note that "limiting making current" is defined as current over a specified duration, so you would need to know the duration of the inrush current spike as well as the maximum amperage (practically measured by using one of various ways to measure current over time with an oscilloscope).

I've never had to select a relay specifically for this kind of application, but my suspicion is if you select a relay with a rated current appropriately sized for the steady state load of the lamp, the limiting making current rating will be more than sufficient. YMMV, I am not an electrical engineer.

 

Thank you all.

I get the 'third party' review. Like getting ISO certified. I guess I was also wondering if relay specs might be better defined than even 20 years ago. On aircraft and medical components QSR requirements get onerous fast. I do have the TE spec sheets and noticed the n.o. vs n.c. spec are different. I'd gather the relay's pull-in force is higher than the return spring force.

In the case of the headlights, the original Bosch can had "30 Amps" on the case, so it gave a bit more confidence that the TE was marked 40, and that the TE was provided by Mouser with certification.