Homemade temperature and fuel gauges?

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Mojogameplay
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Homemade temperature and fuel gauges?

#1

Post by Mojogameplay »

Hey there. I'm new to forums in general. Just bought an 81 goldwing early this summer. Mostly been stripping off poorly mounted aftermarket touring gear. Updating tires and bearings. Cleaning carbs. Installing carb kits. And riding it everywhere in between. But most recently I got too cocky on a dirt road and crashed her end over end at about 80 kmph. She flipped a couple of times, mangling the handlebars, right switch housing, right front signal light, back rack, right passenger peg torn from frame and indicator light cluster smashed. Guages all still functional and bike runs fine.

So my question is this. If I wanted to leave the bulky temp and fuel gauges off and the indicator cluster. Could I replace the gauges with simple voltage meters? My plan is to wire in the digital voltage displays in line between the 7 volt supply and the ground output for each of the old analog gauges. Basically I want to chop out the analog gauges and replace them with tiny digital displays. Has anyone tried this? Not sure if I need volt meters or ohmmeters? Not sure if I will get a variable voltage as the ground switches (sensors) open and close? Or if I will get a constant voltage and a variable resistance? The hope is that I will get a variable reading on each gauge somewhere between 0 and 7 volts. After that I can devide my fuel height and coolant temp into sevenths and go from there. A 7 on the fuel guage would be full and a 7 on the temp gauge would be too damn hot. Also if the voltage regulator ever decided to fry, the guages would go over 7 volts and warn me right away. Anyway, that's my plan.

I was hoping there might be some electrical wizards in here that would know better if this plan is doomed, on the wrong track, in need of modifications, or what. I'm hoping to rebuild my gauge cluster to make it look somewhat modern and unique. I have other ideas for the indicator lights that I think will be the the first of their kind, or at least very uncommon until others see what I've done.
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TNTbefree
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Re: Homemade temperature and fuel gauges?

#2

Post by TNTbefree »

Hey, just wanted to welcome you to the club. I am sure others with a bit more know-how will come along soon to help you with your gauge and electric issue. Sounds like a good plan to me.
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Re: Homemade temperature and fuel gauges?

#3

Post by Mojogameplay »

Oh and I'll post some pics of the graffiti spray paint job I did just before the crash.
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Mojogameplay
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Re: Homemade temperature and fuel gauges?

#4

Post by Mojogameplay »

Not sure about the upside-down picture situation?
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Re: Homemade temperature and fuel gauges?

#5

Post by TNTbefree »

A lot of people who post using a phone seem to have the upside down pic issue. Anyone out there have any advice on the guage issue Mojo asked about? Looking for some advice here... Thank you :)
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Re: Homemade temperature and fuel gauges?

#6

Post by Gowing »

I like the paint job.
Terrible crash, end over end for the bike. Yikes. Glad your ok. I bet your sore as heck?
Dave

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Re: Homemade temperature and fuel gauges?

#7

Post by Dirty Dave »

Similar sight, that I witnessed in May as my riding buddy crashed his freshly restored naked 1200. Too hot in a curve following me on my 1000. Ended up in a farmers field, end over end. Bent the frame and trashed a lot of irreplaceable Standard plastic parts. Bike tossed him into a nice rolling somersault away from danger. Very lucky.
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Re: Homemade temperature and fuel gauges?

#8

Post by Mojogameplay »

I was wearing a convertible riding jacket with armor in the arms. I think it soaked up a lot of the crash. Plus my convertible full face helmet, let me skid on my face for a bit. Little sore two days later when the adrenaline went down, but no noticeable damage. As for the gauges. I'm pretty sure I'll have an answer to my questions after the parts arrive. Won't take but a moment to test fit my plans and try them out. If the new gauges work I might just fit them to the back of the the headlight bucket. I have pretty big plans for the Gauge area, but I'd like to get one more cold ride in before snow starts flying. Critical parts are coming and I'm at the mercy of the post office now. I'll post up some good pictures from the computer if this experiment works out.
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Re: Homemade temperature and fuel gauges?

#9

Post by RB »

PICS
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98 1500 SE..
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Re: Homemade temperature and fuel gauges?

#10

Post by Toehead »

Mojo,

You should be able to wire them up as a voltage divider. See as follows:
divider.png
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This requires that you add another resistor inline. As the resistance of the fuel sender changes, you will get a varying voltage on the other side of the resistor.

You need to choose the value of the resistor to accomplish a few things:

1) It must be large enough in value give you enough voltage drop: Use V=I*R
2) It must be rated for enough power to avoid burning up.
3) It must be small enough in value that it doesn't become the dominant factor. For instance, if the sender only varies by 100 ohms, don't put a 200 K-ohm resistor.

fIrst start by determining what the resistance value of the sender is at empty and full. I think we should be able to size the resistor appropriately then.
2012 Golf TDI, fast and frugal oil burner
1980 CX500C, All around road warrior (Sold)
1975 TS125 (Sold), old smoker
1977 naked GL1000, Highway cruiser
'81 GL1100 14,000 (reconditioned and sold)
'81 GL1100 50,000 miles (under construction)
2X 1981 CM400 beginner bike (sold)
1980 CB750C (sold)
1994 Virago 750 (Wifey's bike)
'76 GL1000 Sulphur Yellow (Megasquirted efi build) http://www.ngwclub.com/forum/viewtopic.php?f=47&t=59774
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Re: Homemade temperature and fuel gauges?

#11

Post by Mojogameplay »

Toehead,

I'm quite dumb on electronics so excuse me if I need a longer lesson on everything you just said. Also thank you for your response. Firstly I could look all these things up but your terms might make more sense and save me time. These questions may be frustrating, but it wasn't that long ago that I learnt what a resistor was. I hope you have the time to clear up some of this confusion.
1. What is voltage drop?
2. Is the v in the picture the voltage meter?
3. Is the squiggly line with an arrow pointed at it a reostat (dimmer switch) and the fuel sensor?
4. If v is a voltmeter why does it have its own ground? Would I not be able to wire it in series between the 7 volt supply and the fuel sender(this is how I assumed the old gauge was wired)?
5. I think I'm starting to figure out how this circuit works. Correct me if I'm wrong? As the fuel sender opens all the way up, power travels through it bypassing the the voltmeter, showing a low voltage on the voltmeter? When the fuel sender closes off, power bypasses through the voltmeter showing a higher voltage reading?
6. If the voltmeter has a lower resistance than the fuel sender, won't the voltage always tend to travel through the the voltmeter and show a higher voltage? If the resistor prevents the voltage from bypassing through the voltmeter constantly, why wouldn't it just be applied to the voltmeter circuit, instead of the voltmeter and fuel sender at the same time?

Thank you in advance for any questions that you can clear up.
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Re: Homemade temperature and fuel gauges?

#12

Post by Mojogameplay »

So I tried it on a circuit simulator. And it works. I just don't understand any of it. Math is why I dropped out of physics. :-?
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Re: Homemade temperature and fuel gauges?

#13

Post by Mojogameplay »

You can use a digital ohm meter to make sure that your sending unit is within the following factory specifications: 1975-1979 GL1000 — 65-75 ohms empty, 10-15 ohms full 1980-1983 GL 1100 — 75-80 ohms empty, 6-10 ohms full 1984-1987 GL1200 — 101-110 ohms empty, 43-52 ohms full.

Found this on randakks site.

So I guess around 80 ohms for the resistors.
I'm thinking that the analog guages acted as the resistors for the sending units. The gauges needles are moved back and forth as a bimetalic strip is heated and cooled. I would assumed the coils around the strip would be matched as resistors to the sending units? So the old gauges should show a resistance value across the terminals matching to the sending units they correspond to?

I'll have to check that out later.

Does anyone know the resistance on the temperature sending unit in an 81 gl11 00?
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Re: Homemade temperature and fuel gauges?

#14

Post by Toehead »

I'll try to explain the math a bit. It's all based on Ohms law, V=I*R
You are correct that the fuel sender is basically a potentiometer and varies in resistance.
Let's call the resistance of the fuel sender R2 (R2 can vary with fuel level, but let's assume that it is fixed for now)

The inline resistor that you add is R1.

To get the total current flow through the system, you need to find the total resistance of the circuit. In this case, it is R1 + R2.

You can substitute this into the V=I*R equation
V= 7Volts from the regulator.

7= (R1 + R2)* I(current)

I= 7/(R1+R2)

This will give you the total current through the system.

Each resistor in the system, R1 and R2, will have a voltage across it. If you measure the voltage across the resistor, you will get a nonzero value. This can be calculated using ohm's law. Since we know the total current flowing (and it flows through both R1 and R2 since they are in series) we can do the following:

Voltage drop R1= I * R1
Vr1= 7/(R1+R2) * R1

Voltage drop R1= I * R1
Vr2= 7/(R1+R2) * R2

If you put the digital voltmeter leads on either side of the resistor, you will read this value.



There is also another law, Kirchhoff's law, that says that the sum of all the individual voltage drops over the resistors will equal the voltage supply.
Vr1+Vr2=7volts

We know on the ground size of the fuel sender, we are at zero volts.

If you want to know what the voltage is on the wire connecting R1 and the fuel sender, we can say that this voltage equals 0 volts + the voltage drop over R2, which is Vr2.

You can also say that it equals 7volts - Vr1. They are the same.


Regarding the voltmeter, you can't visualize a digital voltmeter as a parallel path. The input resistance of these meters is extremely high, so that almost no current flows through. This avoids changing the signal you are trying to measure.


Lastly, regarding the stock fuel sender: Yes, this is inline with the sender and is a mostly fixed resistance.
As you mentioned, the gauge works by heating a bimetallic strip, which moves the needle.

The purpose of the resistance in the gauge is to generate heat in response to current. In this way, it is responding to the current draw in the circuit.

When the fuel sender is full, the resistance is low. This means that because of V=I*R, more current flows through the fixed gauge resistance. This high current flow gets dissipated as heat, which moves the needle (power dissipated = I^2 * R)

When the tank is empty, the resistance is high and less current flows. Therefore, less heat is generated and the gauge doesn't move as far.
2012 Golf TDI, fast and frugal oil burner
1980 CX500C, All around road warrior (Sold)
1975 TS125 (Sold), old smoker
1977 naked GL1000, Highway cruiser
'81 GL1100 14,000 (reconditioned and sold)
'81 GL1100 50,000 miles (under construction)
2X 1981 CM400 beginner bike (sold)
1980 CB750C (sold)
1994 Virago 750 (Wifey's bike)
'76 GL1000 Sulphur Yellow (Megasquirted efi build) http://www.ngwclub.com/forum/viewtopic.php?f=47&t=59774
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Re: Homemade temperature and fuel gauges?

#15

Post by Toehead »

One word of caution with using the voltmeter to read the tank level with a voltage divider. If your voltmeter is powered by the input voltage (if it only has 2 wires), it will shut off if the voltage gets too low. You will likely need one that has a separate power input to allow you to read really low voltages.
2012 Golf TDI, fast and frugal oil burner
1980 CX500C, All around road warrior (Sold)
1975 TS125 (Sold), old smoker
1977 naked GL1000, Highway cruiser
'81 GL1100 14,000 (reconditioned and sold)
'81 GL1100 50,000 miles (under construction)
2X 1981 CM400 beginner bike (sold)
1980 CB750C (sold)
1994 Virago 750 (Wifey's bike)
'76 GL1000 Sulphur Yellow (Megasquirted efi build) http://www.ngwclub.com/forum/viewtopic.php?f=47&t=59774
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