Pump is a LCS with 2.375 coil.
I am getting a resistance reading of 2.4 across the coil leads. One internet source says 6 ohms another says 3 ohms. SU literature does not give a coil resistance spec that I could find. Does anyone know of information regarding the coil resistance spec?
Thanks, Alan
Hi Alan,
I could not find a spec in SU literature: Fuel Pumps.
I measured two long coil two pumps I have. One was 5 Ohm, the other 7.
Regards,
Clive.
Alan,
I did the longer 3" LCS pump recently and measured a resistance (from memory) of about 3 Ohms. But as long as the coil has enough power to pull the armature, it seems OK to me.
Bob K.
OK, I measured two short coils I have (not used in LCS pumps) and they were both 3 Ohm.
Regards,
Clive.
Clive,
The armature and membrane of the earlier and later LCS pumps were identical. I assume the force required to pull the membrane up, is therefore also identical. So most likely the coils (although different in length) should therefore create the same power. The only thing that I cannot remember (too long ago since I studied Mechanical Engineering) is what the relation is between coil winding and magnetic field force, and thus the relation with the coil resistance. I only remember there was a guy with the name Henry involved …
Bob K.
Hi Bob,
The wire gauge used in the short and long coils may have been different which would factor into current draw and hence force.
I will remeasure my long coils as I measured from the terminal, and there maybe some resistance across the points.
Ultimately, as long as the coils force can overcome the diaphragm spring, it is that that determines pumping pressure.
Regards,
Clive.
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I contacted Burlen regarding the resistance specification and awaiting their response.
The pump I’m rebuilding does tick over and I will rebuild as a spare unless I find the coil windings are bad.
Alan
I took the pump covers off so I could more accurately measure the coils resistance. Both long coils came in at shade under 4 Ohm.
Regards,
Clive.
I measured 3 long coils and 2 short coils, and they were all about 6 Ohms.
BTW there is more resistance if you measure through the points.
Joseph Henry discovered magnetic self-inductance, which is how our SU pumps work. He was an early experimenter with elecro-magnets, and is credited with inventing the electric door bell, the electric motor and some work towards the telegraph key.
In about 1830 he rigged up an electro-magnet that would ring a bell in his wife’s kitchen from a control in his workshop, and when he was getting hungry he would ring the bell. So he was the first one to send a message by electric wire, the message being “Honey, I’m coming home for lunch.”
With a 2.4-5 reading (not through the points) I assuming that I have a small short in the windings.
Is the consensus that the coil is not reusable??
Alan
I may have misunderstood. I measured between the two wires of the coil, not to ground.
The coil winding package is a press fit inside the cast iron housing.
If you think there is a short to ground, i.e. the cast iron housing, you can press out the coil windings and have a look at the insulation.
Hi Alan,
I would simply try it out. How accurate are our meters in the the single digit ohm range anyway?
It may be more instructive to compare the current they consume.
Regards,
Clive.
Alan,
I re-checked the resistance of my January 1955 LCS pump SU AUA 57 and it is 4.2 Ohms.
A friend of mine went a bit further and made new coils himself. I also read somewhere that the early pumps had some extra windings to suppress sparking at the points. These were discarded later on and replaced by a capacitor. Don’t know exactly when this change was made, but it might be with the introduction of the shorter AUA 152 versions with the “stepped cap”.
My friend described the coils he made as follows:
720 windings with 3 Amp wire
80 windings with 0.1 Amp wire
May be the above also explains the differences in resistance we find.
Bob K.