240 General: New (to me) 1980 Volvo 244

[Stephen Edwin]

It is good that your newly acquired whels have turned out good for you. I hope your diligent paint work survived the violence of fitting the tyres.

There's a lot to be said for having winter tyres and summer tyres. I think that you will not regret that decision.

I think your choice of which wheels to use with which tyres will perhaps settle in your mind ... in a little while from now.

Comrade Stephen Edwin




.

[Othen]

The RB's instrument lights have always been a little bit disappointing - even with the rheostat turned right up.

Some readers may recall I returned the instruments back to their original fitment (three BA7s bulbs instead of an awful LED array) some months ago. That time I fitted normal incandescent bulbs; I'd been meaning to try some LED bulbs to see if they improved the lighting, had ordered some (as cheap as chips - a fiver for a bag of 5) and the packet had been sitting on the kitchen counter for a couple of weeks:

https://www.ebay.co.uk/itm/BA7S-281-...53.m2749.l2649

Today I got round to pulling out the instrument pod, not that difficult (half a dozen screws and two spring clips) but very fiddly. I suppose it only took 10 minutes or so to get apart. The BA7s LED's were a straight swap of course and the whole thing was buttoned up in another 10 minutes.

I've just had to wait for darkness to see how the LED bulbs work, and I'm delighted to report there is a really good improvement:



Unfortunately I forgot to take a photo with the incandescent lighting previously, but I can say the lights are brighter and the instruments are much clearer.

One mistake on my part was that I forgot to order dimmable LED bulbs, so the rheostat either has them off or on - in practice this matters not as the lighting is now just about right.

Another little job ticked off my list.

Alan

[Laird Scooby]

That's a vast improvement Alan, as for dimmable LED bulbs i've not seen any for DC and certainly not in a package as small as the BA7s as the usual method is PWM - Pulse Width Modulation.

In short the LED is switched on and off many times a second and in any given on/off cycle, the on time is varied, usually between 10-90% of the total time. For example, one cycle is 10mS and for 90% brightness, the on time is 9mS with off time of 1mS. Conversely for 10%, the on time is 1mS and the off time is 9mS and the pattern is followed for other various brightness levels, 30% brightness is on for 3mS, off for 7mS, 60% is on for 6mS and off for 4mS - you get the idea.

It would probably be fairly easy to knock something up from a 555 timer IC and a few discrete components but that would only give about 50% duty cycle at the most (if memory serves it's possible to get to about 45% without resorting to lots of silly tricks) so you'd have either 10-45% or 55-90%, depending how you wired it.

However that might be more annoying than having very little adjustment at all. Do the heater controls dim with the rheostat as well?

[Othen]

Originally Posted by Laird Scooby

That's a vast improvement Alan, as for dimmable LED bulbs i've not seen any for DC and certainly not in a package as small as the BA7s as the usual method is PWM - Pulse Width Modulation.

In short the LED is switched on and off many times a second and in any given on/off cycle, the on time is varied, usually between 10-90% of the total time. For example, one cycle is 10mS and for 90% brightness, the on time is 9mS with off time of 1mS. Conversely for 10%, the on time is 1mS and the off time is 9mS and the pattern is followed for other various brightness levels, 30% brightness is on for 3mS, off for 7mS, 60% is on for 6mS and off for 4mS - you get the idea.

It would probably be fairly easy to knock something up from a 555 timer IC and a few discrete components but that would only give about 50% duty cycle at the most (if memory serves it's possible to get to about 45% without resorting to lots of silly tricks) so you'd have either 10-45% or 55-90%, depending how you wired it.

However that might be more annoying than having very little adjustment at all. Do the heater controls dim with the rheostat as well?

That is interesting Dave, I had not particularly looked for dimmable LEDs in BA7s size. To be candid that facility is no great loss, it didn't work very well with the incandescent bulbs anyway as the rheostat had to be turned right up to get even a modicum of light on the instruments. The current (sorry about the pun) arrangement works fine - I think the heater controls do dip (I may change them to LED the next time I have the console apart). The LEDs will probably last a lot longer than incandescent ones as well, which is a bonus (getting to them is more than a little bit fiddly if one has very large hands).

I'm not surprised that DC LEDs don't dim with a rheostat when I think about it - domestic 230v AC ones don't either (trailing edge dimmer switches work like you say and chop up the supply).

[Laird Scooby]

Originally Posted by Othen

I'm not surprised that DC LEDs don't dim with a rheostat when I think about it - domestic 230v AC ones don't either (trailing edge dimmer switches work like you say and chop up the supply).

You can get dimmable ac LED bulbs Alan, they respond to the chopped ac signal by varying the pulse width on the LEDs but the trailing edge dimmer switches chop the signal by altering the turn on/off threshold voltage of the triac to give part or all of the waveform to the bulb.
From what i understand of the dimmable LEDs, they average out the ac voltage into a DC level and use that as the control voltage for a PWM drive module.

https://www.ebay.co.uk/itm/2-4-LED-D...W/324368423003

With the DC LEDs, they simply use a current limiting resistor. Most have typical ratings of Vf = 2V, Imax = 30mA but maximum brightness is usually achieved at ~20mA and 4mA is normally the minimum usable brightness current.

With the rheostat in your RB, it's simply that, a rheostat as far as i'm aware. Because it was originally designed to run say a dozen bulbs of ~100mA each, that would make maximum current of ~1.2A but let's call it 1A to make the maths easy. That makes a total resistance of 12 Ohms for the lighting that's controlled by the rheostat, to drop the brightness a maximum of a 12 Ohm potentiometer would be likely. This would drop 6V to the original bulbs in the system but with the LEDs only taking ~20mA each, assuming all incandescent bulbs were changed, that would be 240mA or 2.88V drop across the rheostat.

Further calculations can be made using Ohms Law to work out a value that would give a reasonable amount of dimming but because you don't know what current limiting resistor is in the bulbs, it would be "experimental design" to start with.

However, if your rheostat is wired simply as a variable resistor i would suggest as a starting point adding a 10 Ohm resistor in series with the rheostat which would probably just take the edge off the brightness at maximum but actually give a useful dimmable range. That said you may find a 22 Ohm resistor works better, it all depends how near the edge of the LED limits they've gone with the built-in current limiting resistors. A lot of the cheap Chinese "12V LEDs" work on maximum supply voltage of 12V and maximum current through the LEDs at that voltage. Considering alternators charge at 14V, there is immediately a problem as the LEDs will be running at ~35mA which is over their Imax level.
This will be somwhat mitigated by blue or white LEDs as generally their Vf is ~3.6V (handy putting 4 in series to get 14.4V) and as you have white LEDs you should be a little safer.

Once you've got past this point, LEDs will be more reliable with a longer lifespan (typically 30-50k hours or 1.2m to 1.5m miles!) so it's worth spending a bit of time sorting it out.

[Othen]

Originally Posted by Laird Scooby

You can get dimmable ac LED bulbs Alan, they respond to the chopped ac signal by varying the pulse width on the LEDs but the trailing edge dimmer switches chop the signal by altering the turn on/off threshold voltage of the triac to give part or all of the waveform to the bulb.
From what i understand of the dimmable LEDs, they average out the ac voltage into a DC level and use that as the control voltage for a PWM drive module.

https://www.ebay.co.uk/itm/2-4-LED-D...W/324368423003

With the DC LEDs, they simply use a current limiting resistor. Most have typical ratings of Vf = 2V, Imax = 30mA but maximum brightness is usually achieved at ~20mA and 4mA is normally the minimum usable brightness current.

With the rheostat in your RB, it's simply that, a rheostat as far as i'm aware. Because it was originally designed to run say a dozen bulbs of ~100mA each, that would make maximum current of ~1.2A but let's call it 1A to make the maths easy. That makes a total resistance of 12 Ohms for the lighting that's controlled by the rheostat, to drop the brightness a maximum of a 12 Ohm potentiometer would be likely. This would drop 6V to the original bulbs in the system but with the LEDs only taking ~20mA each, assuming all incandescent bulbs were changed, that would be 240mA or 2.88V drop across the rheostat.

Further calculations can be made using Ohms Law to work out a value that would give a reasonable amount of dimming but because you don't know what current limiting resistor is in the bulbs, it would be "experimental design" to start with.

However, if your rheostat is wired simply as a variable resistor i would suggest as a starting point adding a 10 Ohm resistor in series with the rheostat which would probably just take the edge off the brightness at maximum but actually give a useful dimmable range. That said you may find a 22 Ohm resistor works better, it all depends how near the edge of the LED limits they've gone with the built-in current limiting resistors. A lot of the cheap Chinese "12V LEDs" work on maximum supply voltage of 12V and maximum current through the LEDs at that voltage. Considering alternators charge at 14V, there is immediately a problem as the LEDs will be running at ~35mA which is over their Imax level.
This will be somwhat mitigated by blue or white LEDs as generally their Vf is ~3.6V (handy putting 4 in series to get 14.4V) and as you have white LEDs you should be a little safer.

Once you've got past this point, LEDs will be more reliable with a longer lifespan (typically 30-50k hours or 1.2m to 1.5m miles!) so it's worth spending a bit of time sorting it out.

Many thanks for that Dave. I see your points, but I don't think it is worth trying to fix something that isn't particularly broken. The set up works fine and I'm just happy that the previously almost invisible (at night) instruments are well lit now :-)

[Othen]

I've been running the 195/65R15 (both summer and winter) tyres on the RB at 27 PSI, that being the recommendation for the closest size I can find for the RB (185/70R14) It occurs to me that the tyre I'm using is 5% wider than the 185, so perhaps I should be reducing the pressure by 5% - so say 25 PSI?

There must be plenty of other 244 or 240 saloon owners out there with 15" wheels, what pressure do you use?

Alan

[Laird Scooby]

Originally Posted by Othen

I've been running the 195/65R15 (both summer and winter) tyres on the RB at 27 PSI, that being the recommendation for the closest size I can find for the RB (185/70R14) It occurs to me that the tyre I'm using is 5% wider than the 185, so perhaps I should be reducing the pressure by 5% - so say 25 PSI?

There must be plenty of other 244 or 240 saloon owners out there with 15" wheels, what pressure do you use?

Alan

I use a little more based on experience of the tyres, car, ride and handling Alan. The "official" pressures for mine are 28 front, 31 rear but i've been using 32 front and 34 rear and it seems to work very well for the tyres/car in question.

The standard pressures had the outer edges of the tyres feathering a little so increased the pressures, decreasing would have made it worse, not to mention makng the steering heavy!

While i know my car is different, the same tyre sizes are recommened including the 195/65/15 and all pressures the same. That's why i suggested a little experimentation to find what works best for you.

As for the lighting, i agree - if it ain't broke, don't fix it!

[Othen]

Originally Posted by Laird Scooby

I use a little more based on experience of the tyres, car, ride and handling Alan. The "official" pressures for mine are 28 front, 31 rear but i've been using 32 front and 34 rear and it seems to work very well for the tyres/car in question.

The standard pressures had the outer edges of the tyres feathering a little so increased the pressures, decreasing would have made it worse, not to mention makng the steering heavy!

While i know my car is different, the same tyre sizes are recommened including the 195/65/15 and all pressures the same. That's why i suggested a little experimentation to find what works best for you.

As for the lighting, i agree - if it ain't broke, don't fix it!

My feeling (having done only about 20 miles on the new wheels and tyres) is that there is a tiny bit of understeer, which is why I thought the pressures might be just a tad higher than they needed to be. I doubt that I'll do 1,000 miles on the winter tyres between now and Easter, so I probably won't notice any uneven wear, which is why I asked whether anyone else with a 244 had any experience.

What I might do is reduce from 27 to 25 PSI one day next week and try that. Overall I'm happy with the winter tyres, and I just can't get over how good the RB looks with the Pholus wheels.

Re: the instrument lights, agreed, if it ain't broke...

:-)

[Laird Scooby]

Originally Posted by Othen

My feeling (having done only about 20 miles on the new wheels and tyres) is that there is a tiny bit of understeer, which is why I thought the pressures might be just a tad higher than they needed to be. I doubt that I'll do 1,000 miles on the winter tyres between now and Easter, so I probably won't notice any uneven wear, which is why I asked whether anyone else with a 244 had any experience.

What I might do is reduce from 27 to 25 PSI one day next week and try that. Overall I'm happy with the winter tyres, and I just can't get over how good the RB looks with the Pholus wheels.

Re: the instrument lights, agreed, if it ain't broke...

:-)

Have you checked the pressures in them Alan? If you're going on the tyre place inflating them to 27 psi, they could have put more in for any number of reasons.