Ammeter ? for Doc Watson (ANDY)

Steve C · 02-07-08, 01:12 AM

Andy,

Does your CAV 60A Ammeter have or use an external shunt or is it directly connected?

Thanks, Steve

Doc Watson · 02-07-08, 11:05 AM

Will have to wait until I get home from work... will let you know then.

Andy

Doc Watson · 02-07-08, 01:19 PM

To be honest I dont know, how will I find out????

Andy

G Gear · 02-07-08, 01:34 PM

Hi Doc

The big bit of metel across the back of the meter is the shunt (not the fixing bracket) hope it helps

Geoff

Doc Watson · 02-07-08, 02:00 PM

Thanks Geoff just been reading up on shunts and wiring of ammeters

My part number is... 5539/233T and is a 60-0-60 ammeter.

Andy

Steve C · 02-07-08, 07:35 PM

Andy,

Thanks for the pic (just what I wanted to see) and thanks Geoff for the ID of the "shunt".

Andy...is the gauge illuminated?

Anyone....I'm considering purchase of a used CAV meter and wonder if I should be concerned about "shunt aging"...Anyone have any ideas on this?

Steve P2125

John W · 02-08-08, 05:42 PM

shunt aging ?

I wouldn't even consider this to be a problem.
If the shunt were a thin piece of wire then just maybe it may age harden, but the shunt shown is a plate, so unlikely to be a problem.
What may change is the spring tension for need damping, but this can be adjusted if required - its normally only a problem if the meter registers a high current reading for prolonged periods of time.

Steve C · 02-08-08, 09:37 PM

John,

Thought so..just looking for confirmation.

Andy..Hopeing you can advise if the CAV gauge is illuminated..I think it is but, don't see any socket on rear...Is the bulb internal and internally wired off the main terminals?

Tx, Steve

Steve C · 02-10-08, 09:09 AM

Andy,

Please advise if your CAV Ammeter has internal illumination ( I don't see any socket in pic you posted of the meter backside).

Thanks, Steve

Gary Kadrmas · 02-10-08, 09:59 AM

Steve,

Some gauges have elongated oval holes that are around the outside of the guage shoulder that meets the dash surface. Their is a bracket that either clips to the gauge, or it is fastened to the gauge by another means, and the bulb socket is fit into that bracket. The light from the bulb then shines into the oval holes. It also throws alot of light under the dash everywhere.

Not as effective as the type that has a hole in the back of the gauge. If you do not have that bracket, I have been successful in fabricating them out of thin sheet metal.

Good luck, and Cheers!!!!!!!!!!

Doc Watson · 02-10-08, 12:31 PM

No there is no light but I will be putting one in myself. I'm taking the assembly apart to paint the inside of the gauge red as per originals and while doing that sorting out the drilling of a hole in the rear for a bulb and holder. Also the gauges (apart from the ammeter) all need a 'Chinese hat' added to the needle holder which is a 6-7mm plastic cover (see the rev counter photo, the needle centre has a disc on it which looks like a chinese hat) which prevents light shining through the needle assembly on 'normal gauges' although looking at the ammeter there is loads of empty space where a back light could shine through.... might need to rethink the ammeter lighting. Picture of my oil pressure gauge with back lit bulb and holder, ammeter will have similar bulb and holder. Also pic of 'chinese hat' in original rev gauge, and original cav ammeter which just shows the red internals.

Andy

Doc Watson · 02-10-08, 12:44 PM

Steve, all gauge bulbs are wired seperate to the gauges and have a small knob which is used to increase/decrease the intensity of the bulb lights so are wired together as a group. The circuit is wired to a switch (see photo, middle knob) which turns on and changes the gauge bulbs intensity.

Discussed bulb for ammeter in the other thread, sorry had a wedding reception friday, and work saturday.... if your gunna have a hangover at least get paid for it.... so late replying hope this helps.

Photo of dimmer knob shown.

BTW the 'Pull' knob is for activating the martin baker passenger seat ;-)

Andy

Steve C · 02-10-08, 03:32 PM

Andy,

Thanks for reply, sounds like you had a good time at the reception.

More questions, a few comments and some ideas from here.

What is case material ? Looks to be a high quality plastic that will easily be able to handle the 60A shunt current. I also really like the robust shunt the CAV gauge incorporates. (I don't think they make gauges as well now days).

Looking at rear of case I guess you plan to mount the light socket in middle of case and UNDER the shunt? If so probably best to use a plastic socket as a metal socket will require a case ground and if comes loose could bridge the shunt and short out the gauge light ckt but, you probably already figured this out.

What type of paint (compatible with plastic) and colour will you use?

I understand need for the "Chinese Hat" to direct back the light coming from behind the gauge face but, as you said the CAV gauge has lots of open space around the gauge face for light scattering so I agree the hat won't be the fix. How about either coloring the bulb ( I have used a red dye in the past) or more recently I have used a plastic "condom like" red boot made for this purpose sold in AUTOZONE stores here in the States?

Your pic in post of 5:31PM shows a CAV gauge with what looks to be an adjusting slotted screw head at bottom of gauge glass (is it glass or plastic...I'm still waiting for my gauge so don't have it in hand)...Is this for "zeroing adjust?..Wonder why ones now available don't have this feature or is it for something else?

Look foreworrd to your reply.

Steve P2125

Doc Watson · 02-10-08, 06:32 PM

Back in the day when I had to run around in the dark with a gun and a map we used to buy cheap torches and 'pen in' the lens with permenent red pen, I agree that it would be prudent to do this to the bulb in the ammeter. Also with regard to placements of the bulb, I havent taken the thing apart yet to paint the interior but the bulb would be either on the lower back or possibly mounted on the side at the top...time will tell. The plastic is of good quality and I dont see any problems with painting the interior or drilling for the bulb holder, will just need to wash the plastic in soapy water, lightly sand, wash again, dry and paint.

Residue of mould release agent for plastic components can linger for many years. I'm in the process of building a 1967 Tamiya kit of a HONDA RA273 and thought that the residue would be gone after 40 years..... the rest of this sentance writes itself.

I did ask on this forum about the colour of the internal dials and nobody could help so I'm going for ferrari red.... so every time I look at the gauges it will remind me why the GT40 came into existance.

The photo of the original does have an extension on the zeroing screw, I will probably keep mine as is but check its zeroed before I refit the glass after painting.

Andy

HILLY · 02-11-08, 01:32 AM

Hi Andy,
I am at a similar stage with my gauges as you are and I would be interested in what you are planning to do with the 'Chinese hats'. They would be fiddly little things to machine so it would be good to hear of any other options.
The red colour for the gauge internals seem to be a 'flat' looking red colour. Does the Ferrari red you are using have a flat or gloss appearance??
Cheers
Peter

Jim c · 02-11-08, 05:21 AM

Ok Hilly
I have been watching you pocking around buying original bits and peices.
Are you turning that RF into an original.
Sorry for the drift Doc.

Jim

HILLY · 02-11-08, 07:05 AM

HI Jim,
PM on the way to you.
Sorry Doc. Back on track now.

Doc Watson · 02-11-08, 09:09 AM

Peter,

Hey dont mind at all....we all like a bit of drifting...... just let us all know what your up to.... got one of these????

and I will probably make the hats from plastic, heated and then formed, although I will check some gauge restorers/suppliers first.

Andy

HILLY · 02-12-08, 05:53 AM

Hi Andy,
I am right in the middle of a heap of choices at the moment but when I decide on a direction I'll let you know.
That is a nice little piece that you have found and no I do not have one!! (along with a thousand other things!!)
I will be running the Gurney heads and the carb / linkage set-up is still to be researched and any info or photo's from the masses would be appreciated especially good photo's of the Gulf engine bay.
I will try the machining approach on the gauge hats but getting them off the shelf somewhere would be the way to go. Let me know how you go.
Cheers
Peter