Gas Tank Sending Unit Reisitance

[Alan F]

Hi,

I am looking for what the resistance range is for a Series I gas tank sending unit. When I measure it, I get 0 -90 ohms. I recall reading on the forum that they are supposed to be over 200 ohms.

Any help would be appreciated. I am buying an aftermarket gauge and want to make sure I order the right one.

Thanks,

Alan

 

[puff4]

Alan, it should be around 40 ohms at the top of the stroke (full), and 233 ohms at the bottom of the stroke.

 

[Tom H]

Kevin, those values are pretty close to what I calculate for SV gauges. But I assume you have some data for the SI? I have always assumed the earlier Series I and II (those without the Voltage stabilizer) are different, but I've never had any snsors or gauges in hand to actually test, so I'm not sure. I am trying to collect as much actual info about Alpine gauges and senders as possible. Could you confirm where you got this data from?

Thanks ,

Tom H

 

[puff4]

Ahh.. yes, Tom.. sorry.. that data is *only* for the SIII-SV cars with stabilizer. I missed that in Alan's posting. I'm not sure, exactly, what sender was used in the SI/SII cars, but having said that, 0-270, 0-90 ohms & 0-70 ohms sending units were all used on other Smith's/Jaeger gauge installations in various LBC's... so his 0-90 ohms does not sound to out of line.

Here are a few useful references on the subject:

http://mgaguru.com/mgtech/electric/fg_01.htm

http://home.mindspring.com/~purlawson/files/Fuel Sending Unit Resistance Matching.pdf

http://home.mindspring.com/~purlawson/files/FuelSenderRangeAdjustment.pdf

http://home.mindspring.com/~purlawson/files/OldFuelGauge.pdf

http://home.mindspring.com/~purlawson/files/ElectricalBasics-Instruments.pdf

On Stabilizers:
http://home.mindspring.com/~purlawson/files/SmithsVoltageStabilizer.pdf

Tachometers:
And in the process I came across this, Tom, and thought it may be of interest to you, if you've not seen it before:

http://home.mindspring.com/~purlawson/files/Smiths Tachometer Conversion-R1.pdf

 

[Tom H]

Kevin,

Neat stuff. Most of it not specifically Alpine , but pretty useful, thanks.

For anyone else reading this and interested in the article on the Voltage Stabilizers, there is one point that has been missed by this and every other article I have read about these. It is the fact that the output voltage of the stabilizer is closer to 10.8 volts than 10 volts. That's only an 8% error and is not very significant in terms of fuel gauge, but can be a factor in temp gauge readings.

Lastly, where did you get the values you quoted, even though it is for a SIII-SV? As I said, I have calculated values based on my careful measurements of actual gauges, but I have not found any reference material that says what the sender should be. Todd Nordby recently posted 25C and 100C values he obtained from the Temp sender mfr. But I would love to see similar for the Fuel sender.

Tom

 

[Barry]

Tom,

I have measured the fuel gauge sender in my S-V and it is within a couple of ohms of 233 empty / 40 full.

FWIW, the sender mechanism consists of a "wiper" and a wire wound resistor. A good cleaning can do wonders.

 

[puff4]

Tom,

I have measured the fuel gauge sender in my S-V and it is within a couple of ohms of 233 empty / 40 full.

FWIW, the sender mechanism consists of a "wiper" and a wire wound resistor. A good cleaning can do wonders.

Barry, could it be possible that you have that backwards?

 

[Tom H]

Barry, assuming you have the numbers reversed, it matches my expectations and Kevin's numbers too. Note there are tiny dots at full and zero on the dials . (mid scale also). These are cal points. The dots above 11 gal requires a resistance of 27 Ohms to achive at 10.8 V supply. This relates pretty well to 40 ohms at "Full", not quite to the dots. And I find it takes 248 Ohms to hit the bottom dots, pretty close to the 233 ohms you see from your sensor at empty.

But Kevin, where did you get your numbers? Some spec somewhere? Or is this based on measurment of an actual sender, like Barry found? Either way It's good to know. In fact if we have two independent measurements that agree exactly, like you two, it sounds like a good number to me.

Tom

 

[Alan F]

Thanks for all of the responses and some good discussion. So, is a Series I, II sender different?

Alan

 

[puff4]

Tom, I had the numbers in my Sunbeam 'notes' file (a notebook I keep with random notes on the 'beams), but I think they originally came from an old Nissonger publication... they are in with a bunch of other notes that I'm pretty certain came from there as well. (You cannot imagine the *reams* of papers and notes I have on LBC's... sometimes I worry about myself.)

 

[Tom H]

Alan, Sorry about that, but I've been trying to learn about the early Series gauges and senders for several years with no success. Note that one of the links Kevin included - the one ending in "20 matching" - indicates that 0 to 90 ohms is a common sender value. That correlates to the measurements you have made, so I would have pretty high confidence that 0 to 90 is what is used in early series and in your car.

Note also that the same article includes a lot of info about converting to an aftermarket gauge.

If you or anyone would send me a Series I or II gauge on loan, either Fuel or Temp, I would make some accurate meaurements of the gauge, calculate the resistance values and publish the data for all to have.

Tom

 

[Alan F]

Tom,

No need to be sorry. I find the discussion interesting. I was trying to recall where my original gauges are and if I can locate them, I'll send them to you to play with.


Alan

 

[socorob]

i know the tanks are different on the later series cars, but is the sending unit the same size... will it bolt into an early series fuel tank?

 

[Barry]

Barry, could it be possible that you have that backwards?

Kevin (and Tom),

The 233 ohms empty / 40 ohms full resistance numbers are NOT reversed. The fuel level sender is wired in series with the fuel gauge; lower sender resistance in the full position means higher current which results in a higher gauge reading.

 

[Tom H]

Barry,

Doh! Of course! Kevin had a senior moment and I followed him. But if you look at the details I wrote, I DO understand! At full there is less resistance in the sender, so more current flows, and the meter reads higher.

Robbie, I don't know how similar the early and late senders are in construction. Obviously the arms are different. And from everything I can read on this forum I am 95% sure the actual resistance values are different. It seems that the early ones are 0-90 ohms and later ones 40-240 ohms.

I think I have read a post on this forum about swapping early and late fuel senders. I think it indicated the mechanical mounting is similar. Do an "advanced search" on "Stock" for the word Sender or try "Modified" forum.

Tom

 

[RootesRacer]

Tom,

I have some spare guages from my SII, I'll throw one on my power supply with a rheostat and see what it comes up with.

Any idea what the current will be so I can choose an appropriate wattage?

 

[puff4]

Tom, I don't have 'senior moments'... I live in a constant state of senioritis!


As to the voltage, don't SI/SII just use straight 12v? I don't think they have a stabiliser, do they?

 

[RootesRacer]

Tom, I don't have 'senior moments'... I live in a constant state of senioritis!


As to the voltage, don't SI/SII just use straight 12v? I don't think they have a stabiliser, do they?

No stabilizer and the meters are battery voltage sensitive.

I'll do my testing at 13.5v.

 

[Barry]

Jarrid,

Since the Alpine gauges are based on resistive heating elements and bi-metal strips (unlike most gauges), knowing the gauge resistance and the sender resistance would allow calculating the series current at a given voltage.

Having said that, a chart of actual current vs. gauge reading would be very interesting. Confirmation that the fuel and temperature gauges exhibit the same response would also be nice to have.

 

[Tom H]

Yes, The SI and II use raw battery voltage. My assumption is that they are set up to be accurate when "highway" running and gen is charging a full battery, so I would assume 14.0 or 14.5 volts source.

So Jarrid. It seems the early Series use a fuel sensor that goes from 0-90 ohms. I don't know about the temp sensor. I am 99% sure the early Series do not use the bimetal gauges, but rather a straight galvanometer movement- either moving coil or moving magnet. I don't know if the early Series use the identical gauge mechanism for both Temp and Fuel, like the late Series do. I am guessing that the gauges have an internal resistance of something near 100 ohms (the late Series are 61 Ohms). This would mean about 145 mA at full scale - when the Fuel sender is at 0 ohms . I can't figure out what the temp sender would do. It's a thermistor and NEVER gets to zero ohms.

So measure the ohms of the gauge, to be sure of the max current you'll have, connect it to a 14.5 volt source, through a 0 to 250 or 0 to 100 (?) ohm rheostat. Adjust the rheostat for full scale on the gauge, disconnect it and measure its ohms. Reconnect, adjust for empty on the gauge, and measure it again.

Or you could just send them to me on loan. I have access to some of the best precision Volts, Ohms, and Amps sources and measuring gear you have ever seen.

Are there any tiny dots on the dials of the early Series gauges? On the SV there are clearly little cal dots at bottom, mid, and full scale. These are obviously what the factory used to adjust the gauges to some specific milliamp value. The dots typicaly are not located at any "user" value of Temp or Fuel marked on the dial. In fact you don't even see a "hash mark" for Full , or Gal or a specific Temp. The needle just points in that area - close enough!

If you do plan to send the gauges to me, send an e-mail, not a PM. I think you have to go to my profile under "Members" to send an e-mail.

Barry , I have the exact data you ask. Based on measurements made on 3 different gauges. Temp and Fuel are identical except for dial markings. I'll post that later. And if I can get my hands on some early Series I'll post that data too

Tom