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Low Battery Voltage Blows Fuel Pump Fuse?

 
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user9253



Joined: 28 Mar 2008
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Location: Riley TWP Michigan

PostPosted: Mon May 21, 2018 3:53 pm    Post subject: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

There is a recent thread on VansAirforce about the electric fuel pump 5 amp fuse blowing as a result of low battery voltage.
http://www.vansairforce.com/community/showthread.php?t=160595
I would have attributed the blown fuse to some other cause, except that two pilots reported the same symptoms on two different aircraft. The fuel pump is Facet part number 40105. According to Aircraft Spruce, that pump draws 1 amp. I measured the current draw on my spare pump (same make and model) at 3/4 amp with a light load. When I connected a 6 volt battery to the pump instead of 12 volts, the pump quit working and the current dropped to about 1/2 amp. I do not have a power supply with adjustable voltage output. Does the current draw for a DC pump motor actually increase as the voltage decreases? And even if it did, which I doubt, the current would have to increase by a factor of 5 in order to blow the fuse.


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user9253



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PostPosted: Mon May 21, 2018 4:22 pm    Post subject: Re: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

I called it a pump motor but, judging by the sound, the Facet 40105 is more likely to be a solenoid that operates a piston. It is advertised as solid state, which probably refers to the pulsing control circuit.

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PostPosted: Mon May 21, 2018 6:47 pm    Post subject: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Hi Joe;
Try hooking up a 9 volt lantern battery. These are very handy for trouble-shooting and represent about the lowest your starter (and fuel pump) might see while cranking the engine. So you can see what happens without actually cranking.
Cheers! Stu.

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PostPosted: Tue May 22, 2018 4:46 am    Post subject: Re: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Thanks for that suggestion Stu.

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PostPosted: Tue May 22, 2018 6:00 am    Post subject: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Ah, Joe. A Simpson 260.. now that brings back memories. The battery connectors on my have ‘given up the ghost’. I need to design a suitable battery holder replacement. Any ideas? Thanks for all your informative posts!

Quote:
On May 21, 2018, at 9:16 PM, user9253 <fransew(at)gmail.com> wrote:



Bob,
Thanks for the reply and explanation about how the pump works. I had neglected to mention that the fuel pump fuse blows during engine cranking. I do not think that makes any difference to the pump, other than causing a voltage sag. I measured the current draw of my spare pump with an analog Simpson 260. I am as mystified as you. Unfortunately the plane is located hundreds of miles away. All I have to go by is second hand information.

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user9253



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PostPosted: Tue May 22, 2018 9:20 am    Post subject: Re: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Without seeing your battery holders and exactly what is wrong, it is hard to make a suggestion. But here is a link to battery holders and parts from Mouser:
https://www.mouser.com/Power/Battery-Holders-Clips-Contacts/_/N-cicxgZ1yzvvqx?P=1z0y6wzZ1yuke34
I have even soldered wires to batteries before using a soldering gun and short contact time to minimize damage to the cell. I remember that Bob has described welding wires to dry cells, but I can not remember how he did it.


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PostPosted: Tue May 22, 2018 1:40 pm    Post subject: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Joe:
I really do not think I am going to be saying anything that you already do not know.
12 VDC (at) 1 Amp = 12 Watts
Considering the charge voltage at 14.2 VDC the Wattage becomes 14.2 Watts. 
If the Voltage drops to half 6 VDC and the pumps is still trying to work, you have
I = W/6VDC  or 14.2 / 6 = 2.37 Amps
12 / 6 = 2 Amps  The Amperage Doubles.
The only problem is the Pump is not a restive load it is both resistive and inductive.  So the current draw is not uniform.
It is very possible that the current can well spike to above the fused 5 Amp limit.
The 'solid state' part of the pump is only the opening and closing of the contacts for the coil.
Which may or may not be able to handle the increased current?
Barry


On Mon, May 21, 2018 at 7:54 PM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

There is a recent thread on VansAirforce about the electric fuel pump 5 amp fuse blowing as a result of low battery voltage.
http://www.vansairforce.com/community/showthread.php?t=160595
I would have attributed the blown fuse to some other cause, except that two pilots reported the same symptoms on two different aircraft.  The fuel pump is Facet part number 40105.  According to Aircraft Spruce, that pump draws 1 amp.  I measured the current draw on my spare pump (same make and model) at 3/4 amp with a light load.  When I connected a 6 volt battery to the pump instead of 12 volts, the pump quit working and the current dropped to about 1/2 amp.  I do not have a power supply with adjustable voltage output.  Does the current draw for a DC pump motor actually increase as the voltage decreases?  And even if it did, which I doubt, the current would have to increase by a factor of 5 in order to blow the fuse.

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PostPosted: Tue May 22, 2018 3:42 pm    Post subject: Re: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

The wattage for most electrical loads varies directly with the applied voltage. As the voltage goes down, so does the current and wattage go down. An exception is a switching power supply. But it is unlikely that the Facet pump has a switching power supply. Even if the pump current tripled from 1 amp to 3 amps, a 5 amp fuse should not blow. Looking at the schematic, there is an electrolytic capacitor in parallel with the pump, if that matters.
The Facet pump is used in lots of airplanes. If it blew fuses while cranking the engine with a weak battery, it seems that there would be more reports of that. My guess is that there is something unique about this one particular airplane. It will be interesting to learn if a new battery cures the fuse blowing problem.


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PostPosted: Tue May 22, 2018 4:09 pm    Post subject: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Agreed Joe;
But, as you say 'most'...  When a shunt motor gets less voltage the motor does not stop, it tries to perform the same job as if it had full voltage.  What becomes compensated is the current draw.  
Sitting behind a computer as we are; We don't know the condition of the pump, wires, wire size or connections.  And as you say: "My guess is that there is something unique about this one particular airplane."
I do have Fact pumps:  Both the very old 20+ year old and newer 8 year old styles.  I can hook then up to a heavy duty power supply and play with the voltage and see what results we get.  Won't be able to do it till next week though.
Side Note:  Many certified aircraft complete the circuit by completing the Ground.  Grounds have lots of resistance issues.
Barry


On Tue, May 22, 2018 at 7:42 PM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

The wattage for most electrical loads varies directly with the applied voltage.  As the voltage goes down, so does the current and wattage go down.  An exception is a switching power supply.  But it is unlikely that the Facet pump has a switching power supply.  Even if the pump current tripled from 1 amp to 3 amps, a 5 amp fuse should not blow.  Looking at the schematic, there is an electrolytic capacitor in parallel with the pump, if that matters.
  The Facet pump is used in lots of airplanes.  If it blew fuses while cranking the engine with a weak battery, it seems that there would be more reports of that.  My guess is that there is something unique about this one particular airplane.  It will be interesting to learn if a new battery cures the fuse blowing problem.

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Joe Gores




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PostPosted: Tue May 22, 2018 6:17 pm    Post subject: Re: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Barry, that is a great idea about using a variable voltage power supply. Wish I had one. About the pump. It does not have a motor. It is a solenoid driven piston. The owner of the aircraft intends to fly tomorrow with a new battery. I am looking forward to his report, to see if a new battery cures the fuel pump fuse blowing problem while starting the engine.

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PostPosted: Tue May 22, 2018 7:19 pm    Post subject: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Joe:
You just made me think ... I wonder...  What would happen if the boost pump was installed backwards?
Not electrically, since that part is solid-state. 
I WILL run the test next week.
Barry
On Tue, May 22, 2018 at 10:17 PM, user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:
Quote:
--> AeroElectric-List message posted by: "user9253" <fransew(at)gmail.com (fransew(at)gmail.com)>

Barry, that is a great idea about using a variable voltage power supply.  Wish I had one.  About the pump.  It does not have a motor.  It is a solenoid driven piston.  The owner of the aircraft intends to fly tomorrow with a new battery.  I am looking forward to his report, to see if a new battery cures the fuel pump fuse blowing problem while starting the engine.

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PostPosted: Tue May 22, 2018 7:27 pm    Post subject: Low Battery Voltage Blows Fuel Pump Fuse? Reply with quote

Gaggle:
Just had another thought...  I know this to be an issue with Grumman's.
The Boost Pump and the Strobes are on the same fuse.  
And when things are handled wrong - The fuse pops.
So, the procedure for starting is:
All lights off - Except for the rotating beacon - UNLESS you do not have a rotating beacon.
Boost Pump - ON
Wait for fuel pressure to build and clicking to slow down.
Boost Pump - OFF
Start Engine.
Bring the rest of the plane On-Line - Lights and Avionics.
Barry


On Tue, May 22, 2018 at 10:26 PM, dj_theis <djtheis58(at)gmail.com (djtheis58(at)gmail.com)> wrote:
Quote:
--> AeroElectric-List message posted by: "dj_theis" <djtheis58(at)gmail.com (djtheis58(at)gmail.com)>

user9253 wrote:
Bob,
Thanks for the reply and explanation about how the pump works.  I had neglected to mention that the fuel pump fuse blows during engine cranking.  I do not think that makes any difference to the pump, other than causing a voltage sag.  I measured the current draw of my spare pump with an analog Simpson 260.  I am as mystified as you.  Unfortunately the plane is located hundreds of miles away.  All I have to go by is second hand information.


I've read through the comments as well as the Vans forum posts Joe references and have something to add that might confuse the issue even more (or maybe not).
I'm a member of a flying club with 5 Piper Cherokees and one Mooney.  Last fall one of the members reported the same problem (fuel pump failed during cranking).  I doubted the two events were related and asked the A&P the club used, to replace the fuse and I would watch the problem.  A few days later the fuse (allegedly) blew again during the cranking cycle.  Again, I doubted the cranking had anything to do with the fuse. It did not make any sense to me.  I should note, that this plane was also having an intermittent problem with a "tired battery" during starting, particularly, now that the weather was getting colder (I should note, this was last fall in Minnesota). 

A day or so after the fuse was replaced the second time I took the plane for a flight myself.  Pre-flight went fine and I started the fuel pump and began to crank the engine.  The weather was probably 30 degrees and the battery had a hard time turning the engine.  After the flight I checked the fuel pump again and sure enough, it's fuse had blown.

I  was perplexed as to how the fuel pump fuse failure could be related to starting the engine.  Lower voltage during cranking was likely but I assumed this would also result in lower current (as noted by many in this post).  So, I assumed there might be something wrong with the fuel pump and had the A&P install a new one.

Within a few days after the new fuel pump was installed, the problem resurfaced.  Throughout all of this, the battery continued to be an issue when starting with a cold engine.  Winter was coming and the battery problem would only get worse.  The battery passed the A&P's load testing but it was at least 4 years old.  So, following the best advice from the Aeroelectric connection, I asked the A&P to replace the battery with an RG  (Recumbent Gas) battery. 

Problem solved.  Plane started all winter without fail and no more blown fuel pump fuses.

My only thought was that the low battery was resulting in a voltage spike, immediately after starting.  The high voltage spike that would catch the fuel pump with high voltage and create an over current situation.   It could be that the regulator on this plane allowed for higher than normal voltages.   I did check the JPI data on the plane and yes, there were many small events that showed up to 15.1 volts but we generally don't have avionics powered up until after starting so there was no JPI data during the start cycle.  I think the regulator could be set a little higher on this plane or it may have a tendency to overshoot.  I don't have enough details prove this out.

In any case, replacing the fuel pump did not solve the problem.  Replacing the battery did and I've not seen this issue on any other planes but their JPI records did not show the high voltage events that this Archer did.

For what its worth...

Dan Theis.

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