Fuel gauge current consumption - SailNet Community
Reply
 
LinkBack Thread Tools
post #1 of 11 Old 10-07-2019 Thread Starter
Senior Member
 
Join Date: Jul 2008
Posts: 1,189
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 12
 
Fuel gauge current consumption

I'm trying to figure out how much current a fuel gauge consumes. Typically, a sending unit is 33 to 240 ohms, so in a 12V system that would mean a maximum current draw of 364ma, which I suspect is not true. I'm guessing there is some electronics inside the gauge to account for voltage changes and such and that this changes the consumption.

Since we can pretty much replace brand x gauge with brand y gauge (the analog ones) I assume there is a standard. Can anyone explain? Thank you.
jarcher is offline  
Sponsored Links
Advertisement
 
post #2 of 11 Old 10-07-2019
Senior Member
 
JimsCAL's Avatar
 
Join Date: May 2007
Location: Glen Cove, NY
Posts: 4,523
Thanks: 5
Thanked 205 Times in 197 Posts
Rep Power: 13
 
Re: Fuel gauge current consumption

Actually I think that's not that far off. The gauge is just a voltmeter, and I suspect it has a fixed resistor in it and is measuring the voltage drop across it. So current would depend on the sum of the sender and gauge resistances.

S/V First Tracks
1985 Cal 33-2
JimsCAL is online now  
post #3 of 11 Old 10-07-2019 Thread Starter
Senior Member
 
Join Date: Jul 2008
Posts: 1,189
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 12
 
Re: Fuel gauge current consumption

Quote:
Originally Posted by JimsCAL View Post
Actually I think that's not that far off. The gauge is just a voltmeter, and I suspect it has a fixed resistor in it and is measuring the voltage drop across it. So current would depend on the sum of the sender and gauge resistances.
I would be surprised if it's that simple. If it were, then the gauge reading would be very dependant on the battery voltage. Fuel gauges probably are mostly turned on when the engine is running, but water and waste tank gauges tend to be on quite bit. If each gauge used 300+ ma that would be an amp burned up and the readings dependant on the battery state.
jarcher is offline  
 
post #4 of 11 Old 10-07-2019
Senior Member
 
Join Date: Jan 2007
Location: The house is in Kingsport, TN. Boats are on Watauga Lake and in New Bern, NC
Posts: 619
Thanks: 18
Thanked 90 Times in 79 Posts
Rep Power: 13
 
Re: Fuel gauge current consumption

The gauge is not a simple voltmeter or ammeter. There are two coils in the instrument and their resistance and the circuit configuration must be included in your calculation of the amount of current that the gauge circuit draws. The gauge is also damped.



Google around a little bit or measure the resistance of your particular gauge.

Bill
wsmurdoch is offline  
post #5 of 11 Old 10-07-2019
Senior Member
 
JimsCAL's Avatar
 
Join Date: May 2007
Location: Glen Cove, NY
Posts: 4,523
Thanks: 5
Thanked 205 Times in 197 Posts
Rep Power: 13
 
Re: Fuel gauge current consumption

I do know the gauge and sender are just connected in series across the 12 volt supply. I have no idea what the resistance of the gauge is, but if it is similar to that of the sender, you are looking at maybe 300 ohms at half level, which would be 40ma. Again, all dependent on the resistance of the gauge,

S/V First Tracks
1985 Cal 33-2
JimsCAL is online now  
post #6 of 11 Old 10-07-2019
Senior Member
 
Join Date: Jan 2007
Location: The house is in Kingsport, TN. Boats are on Watauga Lake and in New Bern, NC
Posts: 619
Thanks: 18
Thanked 90 Times in 79 Posts
Rep Power: 13
 
Re: Fuel gauge current consumption

The gauge has two coils. One in series with the sender and one in parallel. The magnet on the armature is balanced between them. This eliminates battery voltage from influencing the reading. The resistances of two individual coils in the gauge can be measured by the resistances between the three connections on the gauge. Google may also answer the question for your gauge.

Bill
wsmurdoch is offline  
post #7 of 11 Old 10-08-2019
bell ringer
 
Don L's Avatar
 
Join Date: Aug 2008
Location: Marathon Fl
Posts: 4,239
Thanks: 10
Thanked 119 Times in 106 Posts
Rep Power: 12
 
Re: Fuel gauge current consumption

Quote:
Originally Posted by jarcher View Post
I'm trying to figure out how much current a fuel gauge consumes.
a gnats fart worth

Why do you really what to know? (fusing or wire size maybe)

Don't blow air up my rear, be useful and blow it at the sails!
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.
Don L is online now  
post #8 of 11 Old 10-11-2019 Thread Starter
Senior Member
 
Join Date: Jul 2008
Posts: 1,189
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 12
 
Re: Fuel gauge current consumption

Quote:
Originally Posted by Don0190 View Post
a gnats fart worth

Why do you really what to know? (fusing or wire size maybe)
I want to know exactly what I asked.
jarcher is offline  
post #9 of 11 Old 10-11-2019 Thread Starter
Senior Member
 
Join Date: Jul 2008
Posts: 1,189
Thanks: 0
Thanked 3 Times in 3 Posts
Rep Power: 12
 
Re: Fuel gauge current consumption

I bought an inexpensive one on Amazon and played with it. It's hooked up between 12VDC on one side, and on another side it goes to 12VDC with the tank sensor in line. This makes sense if you think about the system with two coils as posted earlier.

Measuring the current, the side with the sensor varies roughly between 5ma and 35ma while the other side seems to want 30ma. Not a lot of current, especially when the engine is running, which is when you want the fuel gauge anyhow. But that's the fuel gauge. Water and waste tanks have the same type of sensors and are typically turned on under battery power. Of course, other brands gauges will probably be different but probably not dramatically so. Maybe older bimetal ones will use more power.

I want to simulate a tank sensor. I was able to simulate the variable resistor based sensor with resistors of course, but also with a constant current power supply. I suspect that if I can have a constant current supply I can vary from 0ma to 50ma I'll be able to control most gauges.

Thanks to everyone who replied, your suggestions were very helpful.
jarcher is offline  
post #10 of 11 Old 10-11-2019
Senior Member
 
bristol299bob's Avatar
 
Join Date: Apr 2011
Location: Oriental NC
Posts: 471
Thanks: 124
Thanked 34 Times in 27 Posts
Rep Power: 9
 
Re: Fuel gauge current consumption

Quote:
Originally Posted by jarcher View Post
But that's the fuel gauge. Water and waste tanks have the same type of sensors and are typically turned on under battery power.
For the record there is no need to have any tank reading it's level all of the time. A momentary switch to check the level anytime curiosity strikes is what I would do.

1977 Bristol 29.9
Surprise
Hull #5
Oriental NC
bristol299bob is online now  
Reply

Quick Reply
Message:
Options

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now



In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.


User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.

Password:


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:
OR

Log-in











Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page



Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are On
Pingbacks are On
Refbacks are On

 
For the best viewing experience please update your browser to Google Chrome