VDO Engine guages -what's inside?

[Billjratt]

Insurance work being done on engine. Perkins 4108, 1978.
oil pressure and water temp guages now inoperative. Wiring and senders renewed professionally.
The temp guage goes full-scale, but does not drop even when shorted at the back. I have corrected a ground circuit error, and wonder if the unit is now ruined.
The oil pressure guage doesn't move at all. but hasn't been closely investigated yet (tomorrow!)
I know it could be anything, I just want to know what's inside the guage? a transistor maybe?
Your experience please.

Thanks in anticipation, Bill

 

[TYKE]

Some guages work on zero volts giving full deflection of the needle and some work the other way ie 12v for full deflection, I cant remember which way VDO guages work but I think its the unusual way! the new senders on my boat were for the other sort of guage so nothing worked when they were replaced with the wrong ones. If you have had new senders fitted I bet they are for the other type of guage.
There was no damage to my guages you will be pleased to hear.

 

[Billjratt]

Thanks for that, I'm off to have another look now.

 

[halcyon]

Insurance work being done on engine. Perkins 4108, 1978.
oil pressure and water temp guages now inoperative. Wiring and senders renewed professionally.
The temp guage goes full-scale, but does not drop even when shorted at the back. I have corrected a ground circuit error, and wonder if the unit is now ruined.
The oil pressure guage doesn't move at all. but hasn't been closely investigated yet (tomorrow!)
I know it could be anything, I just want to know what's inside the guage? a transistor maybe?
Your experience please.

Thanks in anticipation, Bill

Last time I looked very little, from memory it was a bi-metal strip. varying voltage caused strip to move and thus the needle.

But designs change.

Brian

 

[nigelmercier]

I just want to know what's inside the guage?

A simple voltmeter, with a bit of damping. No only are there two types: open or closed circuit for full scale, there are also different resistance requirements. As you can see on the lower face of the attached, this one is for a sensor that varies between 10 and 180 ohms.

 

[rogerthebodger]

The VDO gauge I have for water and fuel level using the twin rod capacitive sender are 4-20 mA gauges.

 

[Billjratt]

Stiil dud. Thanks Nigel - I will look closely to see if there is a hint anywhere on my units.
The measured resistances from the senders are 30ohm stopped 140ohm running for oil pressure and around 350ohm for temperature.
Neither guage responds to opencct/shortcct across the terminals and power is applied OK (although it has been wrong previously)
The temp guage goes FSD and the oil gauge stays at 0.
The oil pressure switch does transfer, although curiously it makes at pressure rather than breaking like in a car. That does fit with another poster who mentioned it could be used to excite the alternator field though.

 

[Billjratt]

I'm excited. I found this on another forum. The "G" connector is not 'ground'
it's the sender connector... so now if I wire them differently, I may have a working system. Can't wait for the warmth of tomorrow morning to have a go.

Re: Perkins 4.108 rebuild now no instruments?

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Sounds like a ground issue. Instruments are simple. 3 basic connections (forget the lights for now)

Positive
Negative
Sender (S or G)

Many of the perkins panels had VDO instruments so the Sender connection on the gauge may be marked "G" which is "Geber" or giver in German. This often confuses folks.

Check to see if the gauges are getting power. Make sure there is a ground to the engine or to a ground buss bar. The engine may not be part of trhe ground system if it is a euro boat.

The oil pressure sender will be about 1.5 inches in diameter and somewhere in the oil system near the oil filter. The temp sender is in the head (top) near the Thermoastat and will be a small brass unit Hex (Where you put the wrench)with one or two connectors. If it is a VDO temp sender it will have part numbers and max temp (Deg "C") stamped on trhe hex flats (Where you put the wernch).

If the senders have two connectors you likely have an ungrounded system where the ground does not go through the engine. Or you may have sender /warning light combo senders.

Look at the top of the oil sender. It may have a "G" (Sender) and a "WK" (Warning contact) that turns on a light at low pressure.

Etc. Etc. Etc.

 

[rogerthebodger]

Have a look here

http://www.vdo.com/generator/www/co...marine_instruments/marine_instruments_en.html

and here

http://www.sealandpower.com/Electrical Parts & Access/VDO Ocean Line(8).pdf

there are lots of docs if you google VDO Oceanline both senders and gauges.

There are also installation docs but need a little hunting for.

 

[Billjratt]

Incident closed

Thanks Roger, I didn't find my rather old units on the site but have pinned it for future reference.
My guages now work ! Whoohooo. Yer professional sparks must have failed to note the wiring positions on the rear of the units and got the negative and sender wires reversed - an easy mistake to make when you look at the units.
So be warned and draw a picture if fiddling...

Well that's the end of the saga, it's been six long months since the near-sinking, but we're ready to get the boat back to it's berth at last.

 

[nigelmercier]

I'm excited. I found this on another forum. The "G" connector is not 'ground' it's the sender connector...

Indeed, the ground looks like this:

 

[Billjratt]

Not on mine, or it was so faint I didn't see it. The negative terminal on mine is the tab insulated on a paxolin plate as opposed to plastic inserts on the other two. (visually you would think the two plastic ones would be supply and the paxolin one would be signal, but no)
Possibly vdo made isolated versions for Perkins rather than having the negative connected to the case.
Anyway they're fine now, so it looks as if they survive abuse by perverse voltages!