Re: Testing 22-23 series fuel gage
Posted by HH56 On 2023/7/20 18:35:54
I don't know of any way to accurately test the 48-50 gauge units without having another good sender although grounding the wire and have it do very little is suspicious.
The gauges work with a pair of heaters in series influencing each other. When the heater in the sender gets current it heats a bimetal strip which closes a contact to ground. The ground lets the heater in the gauge move the needle and when it cuts off lets the gauge heater cool. When it is heating, it's bimetal strip raises the needle. Not exactly sure how the heaters interact but suspect the heaters may be wound using a special wire that changes resistance when it changes temperature. The changing resistance on one controls current being able to flow and affects the heating on the other.
Here is a bit from an old Motors Manual. The fuel gauge works the same way except instead of pressure bending a diaphragm, the float works a cam affair and its position is what biases the bimetal strip. The oscilloscope photo is what is happening electrically as the sender heater opens and closes the contact going to ground.
Do not believe there are any reproductions and NOS Packard senders are rather scarce. IIRC, BDeB posted a few months back that some Ford senders of that era will drop right in and may still be found at some of their vendors. Maybe a search will find that post as I don't remember if he gave any years or models.
Attach file:
bimetaloil1.jpg (182.85 KB)
22-23 bimetal sender action.jpg (150.07 KB)
The gauges work with a pair of heaters in series influencing each other. When the heater in the sender gets current it heats a bimetal strip which closes a contact to ground. The ground lets the heater in the gauge move the needle and when it cuts off lets the gauge heater cool. When it is heating, it's bimetal strip raises the needle. Not exactly sure how the heaters interact but suspect the heaters may be wound using a special wire that changes resistance when it changes temperature. The changing resistance on one controls current being able to flow and affects the heating on the other.
Here is a bit from an old Motors Manual. The fuel gauge works the same way except instead of pressure bending a diaphragm, the float works a cam affair and its position is what biases the bimetal strip. The oscilloscope photo is what is happening electrically as the sender heater opens and closes the contact going to ground.
Do not believe there are any reproductions and NOS Packard senders are rather scarce. IIRC, BDeB posted a few months back that some Ford senders of that era will drop right in and may still be found at some of their vendors. Maybe a search will find that post as I don't remember if he gave any years or models.
Attach file:
bimetaloil1.jpg (182.85 KB)
22-23 bimetal sender action.jpg (150.07 KB)
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