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Gauge & Sending Unit Questions

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ave42

New member
Ok guys, quick questions for you:

Trim gauge has an ohm rating of 0-90

Trim sending unit has an ohm rating of 10-160

Questions:

1. Will these two components be compatible with each other and work properly?

2. If these two components were connected to one another, how might the needle pointer on the trim gauge react?
 
nope. gage will read high. There are gadgets available that can compensate for incompatibility but they usually cost more than the proper gauge or sender.
 
o2batsea said:
nope. gage will read high. There are gadgets available that can compensate for incompatibility but they usually cost more than the proper gauge or sender.
Click to expand...
You are so right, I did try it once and with the outdrive trimmed up all the way; the needle pegged itself beyond the scale. It did take awhile for the needle to get there though.

Question for you, being that the two have these different ohm values in the ranges that they are; could this also cause the needle pointer to move at a snail’s pace? Seriously, the needle reaction time is so slow that you have to wait for it to catch-up with the actual position of the outdrive.

Just so you know, this is a brand new gauge. I’m only replacing it to upgrade my dash panel; I’m replacing all gauges with new ones.

Also, the old gauge works perfectly, so I’m sure the boat wiring is in good shape.
 
I did a quick GOOGLE search,

Based on what I found I would say you have the WRONG trim gauge.

There are differences between OEM specifications so some gauges have different ohm ranges.

It appears the sender has the right range of 0-160 ohm
The Gauge should match

The attachment is from early 2000's but it demonstrates my point.

See if the gauge manufacturer sells a single helm Mercruiser compatible gauge You may have gotten a dual helm gauge. The dual helm gauge is 0-80 ohms as there is two used in that set up




View attachment Manual_for_13707.pdf
 
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typically gauges are gauges and don't care about the station count (on a given hull)....now sender units come in single and dual station versions....pretty certain trim senders are no exception.....
 
makomark said:
typically gauges are gauges and don't care about the station count (on a given hull)....now sender units come in single and dual station versions....pretty certain trim senders are no exception.....
Click to expand...

I agree,
Sender is 0-160 ohms,
What i read, dual helm/station gauges are 0-80 ohm each...

I did not look to see why.

E=IR
 
I called Mercury Marine headquarters to find out about my trim sending unit. I had a nice 30 min chat with Bill regarding my issue and he gave me some good information. I gave him my engine/drive serial number and with that he was able to confirm the Mercruiser sending unit specifications/ohm range is correct.

He said the gauge I want to use with 0-90 ohm will not read correctly. The needle will overshoot the parameter of the markings on the gauge face and
possibly the reason for the slow reacting time. He also said I would need to use a gauge that matches the Mercruiser ohm values.

What upsets me is that this gauge is supposed to be "for Mercury/ Mercruiser" and is marketed as such.

I am currently waiting for a response back from the gauge manufacturer regarding this.
 
it is most likely for mercruiser but as i said,.dual helm/staion
They run two trim gauges for that so the combined ohms is

Wait for it...........

80+80=160
 
kghost said:
it is most likely for mercruiser but as i said,.dual helm/staion
They run two trim gauges for that so the combined ohms is

Wait for it...........

80+80=160
Click to expand...

Lol… So it’s two gauges wired in series then. Well, I guess that’s how they keep both gauges reading exactly the same.

I was told they only make the one gauge (0-90), but I’ll find out what’s going on when I hear back from them.

You all have been very informative, thank you very much!

I’ll keep you posted with how this turns out.
 
If you add a resistor, wont the gauge always read 80 ohms? It wont be variable any more from 0-80 ohms?
 
...Cough... Solution is easy and cheap... search up online the formula for parallel resistors. Resistors in series ADD resistance. so if you add one in series you're gonna get readings from 80 to 240 ohms! you need a 160 ohm resistor in parallel to LOWER the resistance. 1/Rt = 1/R1 + 1/R2. We have R1 is 160, so if we need Rt to be 80, R2 has to be 160 as well! Edit: it is not going to be as perfect as with a 0-80 ohm gauge. very close, but not quite, because of the resistor you are not going to get an ideally linear needle movement vs linear sender movement. if you want a graphical representation graph the final resistance vs the resistance of the sender. IMHO just adding the resistor is good enough for me, you know at what needle position the boat planes best, that is all i need to know at least.
 
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Ok guys, as shown in the attached image, these are basically the readings between the two gauges. Keep in mind, no matter how you try to adjust the sending unit, the Autometer gauge will always overshoot the “up” mark and peg the needle when the outdrive is raised fully up. The Faria gauge is fully adjustable with the sending unit. It allows you to adjust the needle so it corresponds to the outdrive position.

With the Faria gauge, the needle pointer moves in real time, it follows the outdrive position exactly.

The Autometer gauge however, has a slow response time, it lags behind, in other words, it does not read in real time. The gauge always has to play catch-up with the actual position of the outdrive, as if it has a 5-6 second time delay built in the circuit.

I think the Mercriser tech I spoke with is spot on that the slow needle movement is caused by the mismatch in ohm values between the sender and gauge.

vroomZoom and others, do you still think a simple resistor installed will solve this problem?

Wouldn’t adding a resister cause the gauge to have even more lag/delay time?


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since we are adding a resistor in parallel, we are creating another path for the current flow, thereby decreasing the resistance. it is not an ideal solution, best would be to get the proper gauge, but if it's good enough for you, give it a try. at least it will tell you if the gauge doesn't work because of ohm mismatch or because its it's messed up. Some gauges are a slow, but i never so far encountered a slow trim gauge. My dad's honda, when you filled the tank from empty the needle would take maybe 10 seconds to slowly rise to full. Did you use this type of gauge for all the other gauges (i.e temp, oil pressure etc.)? they are all pretty much the same design.
 
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the resistance has nothing to do with the perceived lag in the meter's display......that is more likely to be caused by the filtering used within the meter itself.
 
+1. The fact that the resistance is too high might cause slow movement, but if you think about it it shouldn't. operating the sender halfway should make it 0-90 ohms, right? Does it move faster when it is in this range? If not, then adding a resistor will not help with the slow needle movement. AFAIK the trim sender goes between ground and the post on the back of the trim gauge. If you take a jumper wire (Be careful not to touch any other wires) between ground and the sender wire, the needle should move quickly to the up position. if it moves slowly as before, then that is the way the gauge is, nothing is going to make it go faster, it might be faulty. sorry also forgot to mention, check the voltage on the back of the gauge, maybe a corroded wire is causing it to lag.
 
vroomZOOM said:
+1. The fact that the resistance is too high might cause slow movement, but if you think about it it shouldn't. operating the sender halfway should make it 0-90 ohms, right? Does it move faster when it is in this range? If not, then adding a resistor will not help with the slow needle movement. AFAIK the trim sender goes between ground and the post on the back of the trim gauge. If you take a jumper wire (Be careful not to touch any other wires) between ground and the sender wire, the needle should move quickly to the up position. if it moves slowly as before, then that is the way the gauge is, nothing is going to make it go faster, it might be faulty. sorry also forgot to mention, check the voltage on the back of the gauge, maybe a corroded wire is causing it to lag.
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vroomZoom,

Yes, the needle moves much much faster when a jumper is placed across the sender terminal and ground. Doing this, the needle definitely is much quicker and would easily outrun the speed at which the outdrive moves up and down.

So, by doing this test, I would then assume the reason for the slow reaction time is due to the mismatch in ohm values?
 
I wouldn't jump to any conclusions based on the test you did....

There is no "time constant" associated with just resistors; your test made the resistive value ZERO.
 
ave42 said:
vroomZoom,

Yes, the needle moves much much faster when a jumper is placed across the sender terminal and ground. Doing this, the needle definitely is much quicker and would easily outrun the speed at which the outdrive moves up and down.

So, by doing this test, I would then assume the reason for the slow reaction time is due to the mismatch in ohm values?
Click to expand...

What this test shows is that there is no filtering inside the gauge slowing the movement of the needle, so it seems like the gauge is ok. The only thing i can think of is that this gauge works differently than the faria gauge you had. During your test, did the needle move slower on the new gauge than it would have on the faria gauge? if so, the gauge mechanism is to blame, and adding a resistor might speed it up enough to match the speed of the outdrive. I'd give it a try. The faria gauge utilizes two electromagnets, and a needle. when the voltage from the sender changes, so does the magnetic force of the two electromagnets, and the needle moves. Some gauges (not 100% sure that your autometer gauge works this way) utilize a pin that heats up and bends with more voltage, and because the trim sender cannot supply a ton of current, it takes a little while to heat the pin and move the needle. This is the only thing I can think of that is causing your problem, it MAY be causing your problem but it may be not. adding the resistor would add another path for more current to flow and make the needle move faster. $0.50 resistor is worth a try IMO.
 
vroomZOOM said:
What this test shows is that there is no filtering inside the gauge slowing the movement of the needle, so it seems like the gauge is ok. The only thing i can think of is that this gauge works differently than the faria gauge you had. During your test, did the needle move slower on the new gauge than it would have on the faria gauge? if so, the gauge mechanism is to blame, and adding a resistor might speed it up enough to match the speed of the outdrive. I'd give it a try. The faria gauge utilizes two electromagnets, and a needle. when the voltage from the sender changes, so does the magnetic force of the two electromagnets, and the needle moves. Some gauges (not 100% sure that your autometer gauge works this way) utilize a pin that heats up and bends with more voltage, and because the trim sender cannot supply a ton of current, it takes a little while to heat the pin and move the needle. This is the only thing I can think of that is causing your problem, it MAY be causing your problem but it may be not. adding the resistor would add another path for more current to flow and make the needle move faster. $0.50 resistor is worth a try IMO.
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You continue to advise adding a resistor.

This is wrong.

He needs to get the right Ohm gauge to match the sender.

Mercruiser senders, at least 99% of them that I am aware of are 0-160 ohms full travel.
Therefor he needs a Gauge that must also 0-160 ohms as 99% are. New gauges are not different unless designed for a different ohm sender.

As I said, based on what I found looking up gauge differences, if he received a gauge for a duel helm/station then it would be 0-80 ohms.
I did not make this up. This is what was specified in the installation procedure I read.

He obviously acquired the wrong gauge so sending it back and ordering the correct one is the correct answer here.

(R total = R1 + R2 ) When connected in series, not parallel.



 
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I will also add that Faria gauges are the best. Don't use those auto meter ones, they suck. My opinion. And NEVER use Teleflex. Absolute garbage.
 
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