So I was working on replacing a Facet cube type rattle pump. What surprised me was it had a diode on the main power wire going to ground that was attached to the +12V wire connector. I didnt think that it needed it but when I went to the wiring diagram, it was shown there. So I am wondering why it would need it. Tim
Electric fuel pump discovery...
- Thread starter astjp2
- Start date
BC12D-4-85
SPONSOR
Fairbanks, AK.
Post the diagram and maybe someone will know?
Edit: Apparently they can be used with pos or neg ground. Maybe something to do with that? Reverse polarity protection?
Gary
Edit: Apparently they can be used with pos or neg ground. Maybe something to do with that? Reverse polarity protection?
Gary
Last edited:
skywagon8a
MEMBER
SE Mass MA6
These pumps are not serviceable other than the filter screen. Where is this diode mounted? Was is for your particular aircraft's installation?
http://www.facet-purolator.com/wp-content/uploads/pdfs/GOLD-FLO Flyer 2017.pdf?
http://www.facet-purolator.com/wp-content/uploads/pdfs/GOLD-FLO Flyer 2017.pdf?Attachments
wireweinie
FOUNDER
Palmer, AK
Every time the current flow stops in a coil (like the one in the pump) a voltage spike is generated. This spike can be as much as two to three times the original voltage and is ALWAYS reverse polarity. A spike diode is placed across the leads of the coil, backwards. I.e., the positive lead from the diode is connected to the ground lead of the coil and the negative lead from the diode is connected to the positive lead of the coil. The means that under normal circumstances the diode will not conduct and will have no effect on the pump circuit. But the moment a reverse polarity spike is generated in the coil, the diode conducts and literally short circuits the spike. Preventing this spike from moving up the wire harness protects all items with diodes/chips in their circuits.
Web
Web
BC12D-4-85
SPONSOR
Fairbanks, AK.
wireweinie
FOUNDER
Palmer, AK
Any of the 1N4000 series will work well.
Web
Web
cubflier
MEMBER
Palmer, AK
I assume the diagram is not from the pump manufacturer? It is a solid state pump so the control of the coil is from a transistor internal to the pump. Flyback concerns would have to be addressed internally to protect switching transistor that turns the coil on and off at a frequency. The diode in the diagram is on the wrong side of the transistor. I would think if flyback were happening the first casualty would be the pump transistor. I did ask Facet support if there were external flyback concerns and they said there were none and that diode was not needed. I have two transfer pumps in my plane and no external diodes that I can find.
I'm not trying to make any point, just trying to better understand things. I'm sure there is something I'm missing here.
Jerry
wireweinie
FOUNDER
Palmer, AK
I think you're referring to a different model pump. There are newer ones that have circuit controls but the majority of the ones in use are going to be the style in post #3.
If they have a circuit card for control, I agree that the most likely do not need a spike diode. But the old style can make some noise and may benefit from a diode.
Web
cubflier
MEMBER
Palmer, AK
Web, as I understood the original post it was a reference to a Facet Cube style which as I understand it is a solid state circuit activated coil.
I have two of the Facet Pumps in post#3 and no diode protection external to the pump that I can see. I will look further. This on the Maule so who knows what design concerns are addressed. I have another plumbing project with a version of the Cube and was just curious if the external diode in question was actually a TVS diode possibly, hence my asking for the part description.
Thanks - Jerry
I have two of the Facet Pumps in post#3 and no diode protection external to the pump that I can see. I will look further. This on the Maule so who knows what design concerns are addressed. I have another plumbing project with a version of the Cube and was just curious if the external diode in question was actually a TVS diode possibly, hence my asking for the part description.
Thanks - Jerry
wireweinie
FOUNDER
Palmer, AK
Well a Maule is a whole different argument, lol.
The drawing in #11 is an airframe diagram. The spike diode might just be a leftover from earlier installations. I pulled up random drawings for some of the Cubes, from Facet, and didn't find a reference to anything other than power and ground connections.
Web
The drawing in #11 is an airframe diagram. The spike diode might just be a leftover from earlier installations. I pulled up random drawings for some of the Cubes, from Facet, and didn't find a reference to anything other than power and ground connections.
Web
cubflier
MEMBER
Palmer, AK
And the pumps in the Maule clearly state "For Automotive Use Only".
But then again I don't think Facet touts any of their pumps as "Aircraft" rated.;-)
As far as tossing any jelly bean diode where it is not needed, I have a belief that the less connections the better.
Jerry
BC12D-4-85
SPONSOR
Fairbanks, AK.
Maybe it was audible on the radio>
"Some energy is also lost from the system as a whole and from the arc as a broad spectrum of electromagnetic radiation, in the form of radio waves and light. These radio waves can cause undesirable clicks and pops on nearby radio receivers.To minimise the antenna-like radiation of this electromagnetic energy from wires connected to the inductor, the flyback diode should be connected as physically close to the inductor as practicable. This approach also minimises those parts of the circuit that are subject to an unwanted high-voltage — a good engineering practice"
"Some energy is also lost from the system as a whole and from the arc as a broad spectrum of electromagnetic radiation, in the form of radio waves and light. These radio waves can cause undesirable clicks and pops on nearby radio receivers.To minimise the antenna-like radiation of this electromagnetic energy from wires connected to the inductor, the flyback diode should be connected as physically close to the inductor as practicable. This approach also minimises those parts of the circuit that are subject to an unwanted high-voltage — a good engineering practice"
