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nuckolls.bob(at)aeroelect
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 Posted: Wed Dec 14, 2011 10:18 am Post subject: Auto Aux Fuel Pump Circuit Idea |
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Fred,
During the review of design goals on your idea
you mentioned the possibility of using a PIC
micro-controller to accomplish the task. I mentioned
a "do lots" board and enclosure that could
be useful to your efforts. The schematic for
the board is . . .
http://aeroelectric.com/Pictures/Schematics/Do-Much_Board_Schematic.pdf
If you want to massage it in a cad program . . .
http://aeroelectric.com/Pictures/Schematics/Do-Much_Board.dwg
Obviously, if you put ALL the parts on the board, there
would be some conflicts of functionality. However,
depending on what parts are put on, what are left
off, values of parts and nature of software installed
in the 8DIP PIC, you can "Do Lots" . . .
[img]cid:.0[/img]
The board is being re-configured to accept surface mount
power FETs as opposed to the 4DIP parts shown.
The whole thing fits into this enclosure
http://www.aeroelectric.com/Catalog/AEC/9011/A15_Package.jpg
I think there's room under the board to let you jeep
a TO247 power FET into the enclosure . . . depending
on a refinement of design goals and preliminary design
review, this combination of parts might save you a lot
of time and offer a good finished product.
Use as it suits your needs.
Bob . . .
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Fred Stucklen
Joined: 10 Jan 2006
Posts: 10
Location: East Windsor, CT
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| Posted: Thu Dec 15, 2011 7:59 pm Post subject: Re: Auto Aux Fuel Pump Circuit Idea |
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I've given some more thought and testing on the Auto Aux Fuel Pump idea that I originally posted. I've attached a schematic of a circuit I've bread boarded and tested. Seems to to work.
The idea/implementation is to automatically turn the pump ON for as long as the fuel pressure is below a set limit, and don't turn it off until the pressure has been above that limit for at least 10 seconds. If the pressure go low again, the process is repeated.
I'm planning on making up a hardwired proto board and actually testing in my RV-7A, but probably not until after the new year.....
Fred Stucklen
RV-7A N924RV 650 Hrs
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| Description: |
| Auto Aux Fuel Pump Control |
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Auto_Aux_Fuel_Pump.pdf |
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nuckolls.bob(at)aeroelect
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| Posted: Fri Dec 16, 2011 9:22 am Post subject: Auto Aux Fuel Pump Circuit Idea |
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At 09:59 PM 12/15/2011, you wrote:
| Quote: |
<fred.stucklen(at)utcfuelcells.com>
I've given some more thought and testing on the Auto Aux Fuel Pump
idea that I originally posted. I've attached a schematic of a
circuit I've bread boarded and tested. Seems to to work.
The idea/implementation is to automatically turn the pump ON for
as long as the fuel pressure is below a set limit, and don't turn
it off until the pressure has been above that limit for at least 10
seconds. If the pressure go low again, the process is repeated.
I'm planning on making up a hardwired proto board and actually
testing in my RV-7A, but probably not until after the new year.....
|
The circuit yields well to critical review but it took
me a bit of feather-sorting to understand application
of the power FET as drawn. You your schematic has the
bulk connection tied to the drain terminal and the
thing that jumped off the page at me was an N-channel
FET. But after sorting out the S-G-D labels and
application in the circuit, the real P-channel
device emerged.
Another approach worth considering is use of an N-Channel
device as a pull-down switch. You'd need to do some re-wiring
to make the pump's manual ops be pull-to-ground too.
The N-channel offers potentially 1/10th the on-resistance
of a P-channel. Heat sinking of the device becomes much
easier and performance goes up with the reduced voltage
drop.
Bob . . .
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Fred Stucklen
Joined: 10 Jan 2006
Posts: 10
Location: East Windsor, CT
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| Posted: Fri Dec 16, 2011 1:37 pm Post subject: Re: Auto Aux Fuel Pump Circuit Idea |
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| nuckolls.bob(at)aeroelect wrote: | At 09:59 PM 12/15/2011, you wrote:
Bob,
Yep, I guess I drew the MOSFET incorrectly. It is a "P" channel device. Power dissipation on this .02 ohm ON device should be minimal. So far testing has show that it can draw 10 amps with no heatsink.... I will heatsink it in the prototype.
I'd rather test the concept in a way that involves little change to the existing wiring in the plane. I currently have the circuit wired to switch the positive side, so the "P" Channel device works better for me. Very easy to change it to a pull down circuit if some one else wanted that method.
I think the next step is to prototype it, bench check it using an actual pump (instead of the halogen bulb I'm currently using for a load)and then begin actual flight testing of the timed concept. If this works out OK, it might be lower cost to implement the design using the PIC processor.
By the way, thanks for the proto board idea. I might use that in the future...
Fred Stucklen
RV-7A N924RV 650 Hrs
|
The circuit yields well to critical review but it took
me a bit of feather-sorting to understand application
of the power FET as drawn. You your schematic has the
bulk connection tied to the drain terminal and the
thing that jumped off the page at me was an N-channel
FET. But after sorting out the S-G-D labels and
application in the circuit, the real P-channel
device emerged.
Another approach worth considering is use of an N-Channel
device as a pull-down switch. You'd need to do some re-wiring
to make the pump's manual ops be pull-to-ground too.
The N-channel offers potentially 1/10th the on-resistance
of a P-channel. Heat sinking of the device becomes much
easier and performance goes up with the reduced voltage
drop.
Bob . . .[/quote]
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