PV 444 switch and wire question

[blueosprey90]

On the PV wiring diagram, wires are indicated by color and size, e.g., 1.5 red; 2.5 green; 6 black. What specifically does the size refer to and how to relate to modern America Wire Gauge (AMG)?

My car still uses the 6 volt system. A Bosch ignition switch that I am considering as a replacement is rated 16 amp @ 12 volts and 8 amp @ 24 volts. Does this suggest that I might consider it for use in the 6 volt system - as in being strong enough - 32 amp @ 6 volts????

I'm having a devil of a time finding an ignition switch specifically rated for a 6 volt system.

Thanks

[Ron Kwas]

bo90;

Number preceding Color Code on Volvo wire diagrams gives the cross section area of wire in mm(squared)...a quick search will give charts which relate that to AWG.

...and interpretation of switch or other component ratings is probably difficult for an un electrically-qualified individual, as it takes some insight and understanding of the finer points... i.e. voltage/current rating(s) on any switch are maximum rating (and they don't come into play at the same time)...that is, ANY switch is suitable for 6V, because it makes and breaks the current (the voltage rating refers to the "voltage withstand" capabilities of the insulation and contact spacing when the switch is OPEN...and this is less taxes the lower the voltage applied...[Exception: Very low voltages <5 where welding arcs must be quenched, by the opening contact.])...

...but since typically at the lower automotive voltages (6V), higher currents flow (presuming an equal load, and since work is typically measured in Watts, these are kept equal, strictly for purpose of discussion), the current rating of a switch (which is also a maximum recommended) should be higher than the actual current expected in the particular application.

Your interpolation of 32A @ 6V is reasonable, BUT such interpolations presume linearity of the characteristics, which is not always the case, so IF you were to really use the switch at those parameter magnitudes (which I seriously doubt is the case), tests would have to be done to make sure a decent lifespan could be expected of the component.

So now that all this electrical mumbo-jumbo has confused all but seasoned electrical engineers, your switch rated 12V/16A will work just fine at 6V and I doubt your 6V sys will draw more than 16A, so it will be alright from a current handling capability standpoint also. My recommendation is: Go ahead and use!

Cheers

[142 Guy]

Switch current ratings take into consideration at least two factors, continuous and interrupting rating. The continuous rating is a function of the contact size and contact material of the switch and is limited by heating or actual contact material transfer on the contact. Within reason the continuous ratings are not influenced by the operating voltage. The interrupting rating of the switch reflects how quickly the voltage withstand across the open contacts increases as the switch opens. Typically current interrupting rating drops as the operating voltage increases. However, I am a bit mystified that the current rating on that switch drops so quickly between 12 and 24 volts. We don't know whether the 12volt/16A rating of the switch is established by its continuous rating or its interrupting rating. The safer assumption is that it is established by the continuous rating and therefor will not increase at lower operating voltages. 16 amps at 6 volts should be a safe assumption. I would not attempt 32 amps.

[blueosprey90]

Thank you both for the information, although I must admit that I must have been goofing off in physics class - or alternatively, just a bit too stupid to understand the material.

There are several fuses that are 25 amp fuses, although I'm not sure they are powered through the switch. Others are a mere 8 amps.

I'll order the switch and then see if I can make it work. Stay tuned in about a month.

[Army]

Originally Posted by blueosprey90

Thank you both for the information, although I must admit that I must have been goofing off in physics class - or alternatively, just a bit too stupid to understand the material.

There are several fuses that are 25 amp fuses, although I'm not sure they are powered through the switch. Others are a mere 8 amps.

I'll order the switch and then see if I can make it work. Stay tuned in about a month.

In a month?

Wow that would be considered to be grease lightning round 'ere!

[blueosprey90]

First, I have to order the part. Then, I have to figure out how to take my old switch off of the armored cable. Then I have to figure out how to mount in the dash. Then I have to figure out how to connect the wiring. Then I need to figure out how to charge the battery.

What with all that head scratching, I'll probably be bald in a month.

[Derek UK]

Which brings us to the question "What is wrong with the original switch"? If it still turns with the key you should be able to depress the small plunger that holds the lock into the cable socket. That might take patience but if that fails drilling it out and using a new one should sort it. The actual switch is part of the cable. The coil and the switch works fine without the armoured sleeve. There is just one red wire in it. You just lose the anti theft protection. Not something that's is too important now. You can fit a hidden switch in that line to do the same job.
Tell us the full story or have I missed that bit?

[blueosprey90]

"Tell us the full story or have I missed that bit?"

The "full story" is that I am ham fisted. If I turn the switch all the way to the right (momentary start position), it get locked in that position. Although I can turn the car off, I need to immediately disconnect the battery. I can remove two studs and push the ignition switch back through the dash to get access the the button on the tumbler, remove the tumbler and with a screwdriver inserted deep into the switch force the switch back to the run and then off positions.

I do have the secret button under the dash to bypass the need for the momentary start position, but I'm fed up with having to be so dainty with the key and switch. It's always just a problem waiting to happen, so I'm going to try to install a new switch and eliminate it once and for all. Time will tell.

[Derek UK]

Getting an intact coil/cable/switch is not impossible but depending where you get it, can be expensive. There will be more switches that have been severed from the cables and that would be a cheaper option. The armoured cable can be chopped off where you like and as I said just contains a single red wire to the bottom of the coil housing under the dash. New lock tumbler complete with a couple of keys readily available and not too expensive. Being USA you will have the short cable. 1800 has a different number of mounting holes and maybe the PV one is the same as one or the other. 2 or 3 screw mount. Talk to the usual suspects.

[Laird Scooby]

Nothing i can add on the switch characteristics, all been said very eloquently but have you considered stripping your existing switch down and refurbishing it? Won't necessarlily be easy to find the parts but would keep the car original and be more satisfying in the long run.

Different era i knnow but the ignition switch on my 760 was playing up, fairly cheap from Volvo (~£45 inc discounts) so i decided i had very little to lose by dismantling it and refurbing it. As it happened it was successful, eventually i'll need a new one but it's given it a new lease of life and more reliable starting/running meanwhile.

Might be worth a try seeing as it seems you're likley to replace the switch with something newer, if you can successfully refurb it then it gives you more funds to do other things as well as the satisfaction of fixing it yourself.