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Christian S. Hansen
Grand Master
Username: enquiring_mind

Post Number: 496
Registered: 4-2015
Posted on Wednesday, 25 January, 2017 - 06:58 pm:   Edit PostDelete PostView Post/Check IP

Re: 1954 Silver Dawn STH53

1954 Silver Dawn STH53

The EPW Silver Dawns apparently started life with Positive (+) ground system, but were for whatever reason often later converted to Negative (-) ground. It is time to recommission STH53 but I need to determine the proper grounding since it is unknown whether it was ever converted.

Which componenet(s) can be observed to determine its current state? The obvious solution of simply observing the battery to determine which terminal is grounded has been eliminated since I took the battery out upon storage without noting the ground arrangement. While the cable that is grounded to the chassis near the battery is red, which would seem to indicate the original (+) grounding, matters are complicated and doubt is cast on this conclusion because at some prior time the symbols (+) and (-) were painted onto the floorboard adjacent to where the terminals would be located were the battery in position, but are reversed as if the polarity conversion had been effected. That is, the painted (-) is adjacent to where the red grounded cable comes to the battery and the painted (+) is where the black cable that goes to the starter comes to the battery. While the painted symbols seem to indicate that the polarity has been changed, the colors of the cables indicate the original configuration.

So...what else can be checked to verify the facts??

.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1100
Registered: 9-2004
Posted on Wednesday, 25 January, 2017 - 08:05 pm:   Edit PostDelete PostView Post/Check IP

"So...what else can be checked to verify the facts??"

HT coil.
Radio if fitted.
Amp meter if fitted.
Scope ETC.
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Christian S. Hansen
Grand Master
Username: enquiring_mind

Post Number: 497
Registered: 4-2015
Posted on Wednesday, 25 January, 2017 - 08:32 pm:   Edit PostDelete PostView Post/Check IP

Patrick...
Thanks, but please clarify as you are dealing with one of the dumber ones here.
What do I check and how do I check it? What is it I am looking for?
What would a "scope ETC" tell me and how?
What do I check on the radio? Oh, sorry. Don't have one.
Given that I don't want to start the engine until I know the polarity and hence the correct way to hook up the battery, what would the ammeter tell me?
What is it I should look at on the HT Coil? I presume that the other places + and - sides are connected to is the secret, but what is that secret?
Thanks for more details.

.
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Mark Aldridge
Grand Master
Username: mark_aldridge

Post Number: 392
Registered: 10-2008
Posted on Wednesday, 25 January, 2017 - 11:12 pm:   Edit PostDelete PostView Post/Check IP

Christian, the + and- terminals are different sizes on the battery and on the car ,unless someone has fitted "universal" clamp to size terminals. The car terminals are usually stamped + or -. Be careful however as it is not unknown for "people" to open up or squeeze up clamps to make them fit battery terminals !
Mark
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1569
Registered: 5-2012
Posted on Thursday, 26 January, 2017 - 01:02 am:   Edit PostDelete PostView Post/Check IP

Hi Christian

I would just disconnect the dynamo to prevent reverse polarizing it, connect the battery and watch which way the ammeter deflects. If the ammeter jumps into the + side you know the battery is connected the wrong way round. It may be necessary to turn the headlights on to apply some load for the ammeter.

Geoff
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Geoff Wootton
Grand Master
Username: dounraey

Post Number: 1570
Registered: 5-2012
Posted on Thursday, 26 January, 2017 - 01:06 am:   Edit PostDelete PostView Post/Check IP

I'm assuming of course you have not fitted any electronic units to the car. Reverse polarity may damage electronic ignition and I would not turn the radio on.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1101
Registered: 9-2004
Posted on Thursday, 26 January, 2017 - 03:26 am:   Edit PostDelete PostView Post/Check IP

Hi Christian, The coil check first.
The L/T lead from the distributor to coil will be + for pos earth and if its connected - it will be negitive earth for battery connections.
Unless it has been run wrong when last used.
When battery is connected the next test is to turn the ignition on watching the direction of the ampmeter [do not start engine] if it shows a negitive then the battery battery is connected ok.

The ref to the old type radio if fitted is to check the wires to the amplifier.

Scope the car and it will show the trace etc the wrong way if connected wrong and much more.
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gordon le feuvre
Prolific User
Username: triumph

Post Number: 154
Registered: 7-2012
Posted on Thursday, 26 January, 2017 - 07:40 am:   Edit PostDelete PostView Post/Check IP

I understood that all R-R cars were always negative earth,even from the very early years. Royce preferred it that way. Lots of British stuff had positive earth, cars and motor cycles, but Henry Royce believed that there was less corrosion build up (or something) using negative earth. Your not labouring under the misapprehension that because it was UK early post war that it was positive earth, as lots of things were. I cannot believe a coachbuilder would have changed the earth? or am I about to be re-educated!
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Norman Geeson
Unregistered guest
Posted From: 81.97.73.87
Posted on Thursday, 26 January, 2017 - 03:54 am:   Edit PostDelete PostView Post/Check IP

Christian

I would isolate/disconnect the radio, electric clock, fuel pumps and any electronic additions before trying to connect the battery.

It may even be prudent to pull out all the fuses except for the roof light, which I think is N0 3 fuse, that will provide an ammeter load

(Message approved by david_gore)
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Christian S. Hansen
Grand Master
Username: enquiring_mind

Post Number: 498
Registered: 4-2015
Posted on Thursday, 26 January, 2017 - 12:16 pm:   Edit PostDelete PostView Post/Check IP

My head spins. I had assumed that the car was converted to (-) ground as indicated by the painted symbols adjacent to the battery box, but that the cables were not replaced which is why the red cable (originally the positive lead to ground) is now attached to the negative terminal of the battery, but that the COLOR of the cable was not changed. I also assume that the post size difference was accomodated by simply opening up or pinching down the connector diameters to suit.

The problem is that red usually means positive and black usually means negative, rather than black meaning ground and red meaning live (hot). Therefore, with positive ground, the red cable goes to ground but with negative ground, the black cable goes to ground. Because the cable colors were not changed when the grounding polarity was changed, and the only hint being the painted marks on the floorboard, the current confusion is precipitated. I suppose I will first observe the coil connetions and then take Norman's suggestion and disconnect everything other than one load, connect a battery with negative terminal grounded, and see which way the ammeter points.

P.S. Gordon...yes, apparently the first EPW cars were positive ground. Go figure!! With his practical experience from the era, I wonder if Norman can regale us with what the thought process was?

.
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Patrick Lockyer.
Grand Master
Username: pat_lockyer

Post Number: 1103
Registered: 9-2004
Posted on Thursday, 26 January, 2017 - 03:03 pm:   Edit PostDelete PostView Post/Check IP

And to put a higher load through the ammmeter just turn on the side lights.
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Martin Webster
Unregistered guest
Posted From: 109.151.66.155
Posted on Friday, 27 January, 2017 - 12:45 pm:   Edit PostDelete PostView Post/Check IP

Christian, If you have a glance at the SW service manual available on this forum in technical documents, it mentions that the electrical system is earthed via the positive side of the battery. My Mk VI is totally original and is positively earthed. Have a look at the manuals.
All the best,
Martin B88HR

(Message approved by david_gore)
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Christian S. Hansen
Grand Master
Username: enquiring_mind

Post Number: 499
Registered: 4-2015
Posted on Friday, 27 January, 2017 - 02:26 pm:   Edit PostDelete PostView Post/Check IP

Martin...
Thanks, but while I have no doubt that the chassis was originally positive earthed, the question is whether it has been converted which suspicion is based on the clue given by the painted +/- symbols on the floorboard adjacent to the battery, but which being reversed, indicate that it was converted, but that conclusion questioned by the red cable going to the chassis earth...which color typically indicates that it is the positive cable. The manual says positive earth. The color of the cable indicates positive earth, unless it was not converted and thus contributing to the confusion rather than clarifying the conversion, and while the painted "clues" certainly indicate conversion to negative earth, the absence of a clarifying "yes, converted to negative ground on ...(date)" leaves one wondering without finality. The conflicting evidence is thus what led me to inquire of a way to verify the actual, rather than original, but perhaps obsolete, earthing. Unfortunately the manual only confirms what was, rather than what is. Thanks anyway.

.
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Christian S. Hansen
Grand Master
Username: enquiring_mind

Post Number: 502
Registered: 4-2015
Posted on Tuesday, 31 January, 2017 - 05:48 pm:   Edit PostDelete PostView Post/Check IP

The recommended observations confirmed the conversion had been accomplished as was hinted by the floorboard markings and with battery terminals simply resized to fit. Installed battery and engine fired right up.
Thanks to all for their advice.
I now have a new toy!

Freestone & Webb Silver Dawn

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