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Old 15-02-2009, 20:24   #1
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Engine Sending Units

I want to put a second Engine Instrument Panel on my boat (one in the cockpit and one in the pilothouse) and have looked at several ways to do it with each being a compromise or very expensive. The engine is a Westerbeke 46. I even talked to Westerbeke at the boat show">Annapolis boat show and they said that they had tried to produce a system that included a Y type wiring harness and never sold it as they could not get it to work. It does not make any sense that they could not help me but they didn't.
I know that the sensor work on resistance and connecting them in series will not work, having said that, I'm wondering if I can just put a T into the location where the different sending units fasten to the engine a install two sending units at each of those locations?
Any and all advice would be appreciated.

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Old 15-02-2009, 20:36   #2
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I may be way off here, but you are right. You cant wire your gauges in series. You CAN wire them in parallel though. Aren't oil and water temps and pressure sensors just variable resistors? The gauges would basically just be voltmeters with different markings. If so, no problem with parallel. The tach is just a pulse counter in most cases. The gauges are all fed positive voltage (+), and measure the resistance to ground thru the engine block. Someone correct me if I'm wrong here (like I needed to say that!).
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Old 15-02-2009, 20:57   #3
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I may be way off here, but you are right. You cant wire your gauges in series. You CAN wire them in parallel though. Aren't oil and water temps and pressure sensors just variable resistors? The gauges would basically just be voltmeters with different markings. If so, no problem with parallel. The tach is just a pulse counter in most cases. The gauges are all fed positive voltage (+), and measure the resistance to ground thru the engine block. Someone correct me if I'm wrong here (like I needed to say that!).
WHAT!, you can wire them in parallel?
You mean I just haven't been asking the right questions? That has never been offered up to me before, Thanks. To be clear when you say parallel, I can connect an additional wire (2 total) to the existing sending units and take them to different gauges and both gauges will work properly?
If that gets confirmed, I've got one of these :kissy: for you. (just kidding).

Anyone to confirm?

Thanks,
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Old 15-02-2009, 21:16   #4
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Anyone to confirm?
Makes sense to me!
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Old 15-02-2009, 21:45   #5
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Extemp...I am going to pm you on this

My First suggestion would be to put mechanical gauges on the engine for safety and reudundancy. Mechanicals don't need electricity.
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Old 16-02-2009, 03:57   #6
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My Mermaid (J444) manufacturer said it would require dual sending units for the temp and I think the oil pressure as well...the tack was no problem.
Mine are VDO and it did make a difference as to which ones I had.
I have not pursued it further.
If I had told them that was my intension they would have set it up from the Fact. that way.
I'll be looking into "Murphy gauges" next.
Any info would be appreciated.
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Old 16-02-2009, 05:02   #7
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Dual Station senders are available for all brands of engine gauges.
Dual Station Senders, operating two Gauges from one sender, will have One-Half the Resistance values of comparable Single Station senders.
The two gauges will be wired in parallel.
If one Gauge (of a Dual Station Pair) fails, or you installed two gauges on a Single Station sender; the Gauge will read much Higher than expected.

See also:
Basic Engine Gauge Theory and Testing
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Old 16-02-2009, 11:50   #8
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Identification?

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Originally Posted by GordMay View Post
Dual Station senders are available for all brands of engine gauges.
Dual Station Senders, operating two Gauges from one sender, will have One-Half the Resistance values of comparable Single Station senders.
The two gauges will be wired in parallel.
If one Gauge (of a Dual Station Pair) fails, or you installed two gauges on a Single Station sender; the Gauge will read much Higher than expected.

See also:
Basic Engine Gauge Theory and Testing
Thanks Gord.
I had read through this some time back however I didn't pickup on the dual sending units. Didn't even know they existed until recently.

So as far as identification of type goes, is that to say that if my gauges are the voltmeter type it will have 4 wires to it (if it has a light) and if it is an ammeter type it will have 3 wires to it (if it has a light)?
The actual voltage gauge accepted.

Anyone know of a good supplier of dual sending units in Canada?

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Old 16-02-2009, 13:23   #9
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Couldnt you just use a good brass switch to route the signal from the sender to either station? (on-off-on)
hmmm.... never have delved into it, but the Perkins in my little trawler does not read correctly on the gauges unless both the Flybridge and the lower unit are "plugged in". (The flybridge unit unplugs) The total resistance must be wrong unless both are active. Unfortunately I've never looked to see if they are parallel or series. Two resistances in paralell equal half of the value of one of the resistances. Two in series are double the value.
Coul
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Old 16-02-2009, 13:52   #10
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You will likely need to match the Gauges and senders by Mfg. (ie. VDO gauges with VDO senders., Teleflex with teleflex etc.) They are not all created the same.

VDO MARINE ranges for oil pressure use 10 Ohm - 180 ohm gauges (0-full pressure) and are available in 80psi (5 Bar) 150psi (10 Bar) 350 and 400 psi for trans psi also.

Most USA Mfg's use 240-33 ohm (0- Full pressure) for Oil pressure

VDO Temp gauges are scaled for 250 Deg F max (120C)

Most USA mfg. use 220F

The senders must match the gauges. If you use 2 gauges per sender you must have Dual Station Senders which will have about 1/2 of the single station Ohm range.

Most VDO senders have a single terminal on the top. If it is a dual station sender it will have a "D" stamped on one of the hex flats (Where the wrench goes)

VDO also has some senders that have 2 terminals on the top. This is usually an ungrounded sender in order to keep the engine out of the ground system or one is the switch for the Idiot light and is marked with a "W" (Warning contact)

Most US resistive senders have only one terminal and ground through the engine block. The dual station units are identified by the stamped part number

Do not use teflon tape on sending units as this may interupt grounding.
Do not use long tee fittings as they will vibrate and break

Excluding the light in the gauges there are only three wires Pos+ , Neg- and Sender. It is really simple.

Just to confuse you... Cummins uses a voltage comparrison circuit (The little black board on the back of their factory panel) and does not use dual station senders on many of their panels.
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Old 16-02-2009, 13:55   #11
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Oops, I forgot. For a good gauge supplier in Toronto area Google Forester instruments in Missasagaua I think. Nice folks and know that stuff.
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Old 16-02-2009, 14:27   #12
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Ext,

I have the W46 in my boat. I just asked my marine dealer friend and he said it is no problem with Teleflex Morse gear to do dual station instrumentation.
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Old 16-02-2009, 21:13   #13
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Spent some time today taking some of the Rocket Science Syndrome out of this. Colored up my wiring diagram and did some reading. I just might be okay.
Anyway, thought I would post it.
Now I just have to figure out if I want a second stock panel or something different. What I need is a Volt Meter, Oil Pressure, Water Temp., Tach, Pre-heat Switch, Starter Switch. I don't need an ignition switch.
Thanks all, I may be back with more questions later.

Regards,
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Old 17-02-2009, 03:05   #14
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Extemp.
Very nice drawing - wish I had learnt CAD when I had the opportunity.
I'm viewing it (with tired old eyes) on a small notebook, so will print it out this weekend and comment in detail (if required).
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Old 17-02-2009, 18:20   #15
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Extemp.
Very nice drawing - wish I had learnt CAD when I had the opportunity.
I'm viewing it (with tired old eyes) on a small notebook, so will print it out this weekend and comment in detail (if required).
Gord,
Wish I had learned it also. Can't take credit for the CAD work, I just colored it up.
I hope you don't think any the less of me.

Regards,
Extemp.

P.S. I don't know how large you are printing it but if you want I can send you a higher resolution file.
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