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Question Scalextric powerbase information needed - Printable Version

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Scalextric powerbase information needed - CMOTD - 2nd-Jun-20

This is the innards of an obsolete Scalextric Powerbase C8217:
[attachment=6924][attachment=6923]

Could somebody who knows more about electronics than I do please explain the purpose of the various resistor doodahs?

Also, this one had the option of using two power supplies but the current versions will only accept one. Anybody know why this was changed?

RE: Scalextric powerbase information needed - woodcote - 2nd-Jun-20

I don't know how much more I know about electronics than you, but that is a reasonably clear old-school circuit board - so I'll have a go...

The brown striped resistor is there for the LED, essentially to drop the voltage so the red LED lights up and does not blow. There's a diode in that circuit too to rectify the input current to the LED...

There are four pairs of diodes (black cylinders with silver tops), most likely in the power circuit to each lane - maybe two in each, depending on what that blue switch is doing... The diodes 'rectify' Alternating Current (which the power packs deliver) into Direct Current, which a slot car's motor needs to work. Each diode also drops the voltage about 0.6 of a volt - so a circuit with two diodes will drop the 15 volt AC input to around 13.8 volts DC at the track.

The green things either end... I presume they are resettable fuses. But I could be wrong.

Why change the excellent two-input set-up? I guess it was to simplify the operation. From browsing UK slot car Facebook groups, these powerbases are the #1 reason for the question "why is only one lane working on my Scalextric set?". In my opinion, it is the best analogue powerbase Scalextric have produced, precisely because it had separate power for the two lanes and avoided the dreaded power surge when your opponent crashed.

RE: Scalextric powerbase information needed - Scuderia_Turini - 2nd-Jun-20

Picking up from where Andy left off...

There are four diodes for each lane. These provide "full-wave" rectification to channel the AC into DC. That is that two diodes pass the current when the AC is one way around and the other two pass when the AC is the other way around (Alternating Current). 

The other two diodes pass current from each power supply circuit to the LED (feeding via the single dropper resistor). That way the LED lights up if any one of the poweer sockets is being fed and also if both are.

The green components are simply capacitors to provide a little smoothing of the DC current going to the lanes/cars, acting as suppressors. 

The switch connects/disconnects the two power lines. This is after the rectification stages so that the power-packs are effectively isolated from each other by the diodes. 

The introduction of these power-bases and the accompanying three-wire controllers was a step up for Hornby/Scalextric but it has all been undone in the more recent power-bases and controllers. 

Perhaps Hornby were inundated with service calls concerning operator error with the switch and therefore they decided to dumb-down back to the simple arrangement.

The carbon-fibre look was very trendy! Below is how mine looks nowadays.

Leo

PS - A Nerdy bit - these power-bases are constructed using "discrete components" where each item has its own single function. Pretty old-fashioned technology in the age of "chips" which combine several functions into one component.

[attachment=6925]

RE: Scalextric powerbase information needed - CMOTD - 3rd-Jun-20

Thanks Leo and Andy.
Supplementary question if you can help - why does their power supply produce 16v AC with the powerbase converting to approx 12v DC when it is easy enough to produce one that supplies the correct voltage in the first place? Something to do with Digital?

RE: Scalextric powerbase information needed - BAracer - 3rd-Jun-20

So what components deal with the situation when I come off, and presumably short between the two rails,a it drops into safe mode, and I have to unplug and switch it on again after counting to 10?

RE: Scalextric powerbase information needed - Scuderia_Turini - 3rd-Jun-20

@CMOTD - OK... Alternating Current is by definition not a fixed voltage, the voltage varies between (say)  +15 volts through to zero volts and to -15 volts and so on.  A Direct Current voltage remains at a fixed voltage (although that can be varied!). The DC equivalent of an AC voltage is known as the Root Mean Square voltage (RMS).  RMS may ring a bell as it is used in rating the power output of sound systems (Watts RMS). 

Its all about working out the average/mean voltage of a sine wave to end up with a voltage that will result from rectiifiying the AC. 

Rectification is the technique of channelling alternating current into uni-directional current so as to produce direct current. 

Pictures tell a thousand words so here is a sine-wave diagram from Wikipedia page - Wiki RMS
You can see the AC voltage swing from positive to negative, with the RMS indicated.

Hope this helps,  Leo

[attachment=6934]

RE: Scalextric powerbase information needed - Scuderia_Turini - 3rd-Jun-20

(3rd-Jun-20, 09:16 AM)BourneAgainRacer Wrote:  So what components deal with the situation when I come off, and presumably short between the two rails,a it drops into safe mode, and I have to unplug and switch it on again after counting to 10?

Hello Jeremy,
That is because the electronics in the Power-base or power supply cuts-out or "clamps" the supply voltage when it detects an overload (short-circuit).  That can either be reset automatically after a delay or by powering down and up again.  In powering down and up again it is best practice to wait a few seconds rather than simply flicking the switch off and on again. The delayed restart will ensure that all current flow is fully dissipated.
Which power base are you using?

Leo

RE: Scalextric powerbase information needed - BAracer - 3rd-Jun-20

The type above, but carbon fibre, not rosso!

RE: Scalextric powerbase information needed - CMOTD - 3rd-Jun-20

Got that Leo but a transformer/rectifier (240v AC - 12 v DC) in one unit is a common thing, indeed the older Scalextric power supplies were exactly that, so why do they now feel the need to split the two functions between transformer and powerbase?

RE: Scalextric powerbase information needed - Scuderia_Turini - 3rd-Jun-20

Hello Jeremy,
The short-circuit detection must be in the power-supply that you are using. 

I just tried the only Hornby AC plug-pack that I have (C912) and with that plugged in the power-base a short-cut simply shorts out the power and it restored again when the the short-circuit was removed (screwdriver across the rails).
The green components that Andy mentioned are marked as 2A224J  and a quick Google shows them as 220 Nano Farad capacitors.  

I thought I had a more recent Hornby plug-pack but cannot find it. I think I saved the cable and re-cycled the actual unit.

Leo