facet boost pump started blowing fuse

[uk_figs]

Pump has worked fine for 130 hours but now is blowing fuses, replaced the fuse once and the pump worked fine for about 10 operations (touch and go's) and then quit again, I assume the fuse has blown and am reluctant to change until I figure out what the problem is. Fuse is 5 amp.The pump is wired to an idiot light on the output of the switch and that is also out suggesting the fuse has blown.

I have ordered a new pump but wanted to check to see if there is something I am missing before I crawl under the panel.

[airtractor8]

Originally Posted by uk_figs

Pump has worked fine for 130 hours but now is blowing fuses, replaced the fuse once and the pump worked fine for about 10 operations (touch and go's) and then quit again, I assume the fuse has blown and am reluctant to change until I figure out what the problem is. Fuse is 5 amp.The pump is wired to an idiot light on the output of the switch and that is also out suggesting the fuse has blown.

I have ordered a new pump but wanted to check to see if there is something I am missing before I crawl under the panel.

That fuse size sounds a little small to me. I put mine on a 10amp breaker switch and it seems to be fine. You should be able to find out what the pump draws on the web somewhere.

Good luck

[uk_figs]

Documentation that came with the pump says 3 to 5 amp fuse and another thread here suggested 5 amps as the correct value (the 3 amp fuse kept blowing). As the pump has worked fine on the 5 amp fuse for 130 hours I am assuming that something has changed to cause the problem, do they get sticky or gummed up after time?

I could try a 7.5 amp and see what happens but I think I will pull the pump anyway and see what I can find.

[uk_figs]

Thinking the problem must be the pump, I swapped the facet pump with a new one yesterday and checked operation which was fine. This morning the pump did not work and the fuse had blown again. I now suspected some kind of short had occurred but could not see any obvious problems in the wiring so I removed the switch (2-50) to see if there was a switch problem as the system had been working fine for over a year.
As I figured the problem now was not the pump, just for grins I disconnected the idiot light that tells me the pump is on, put in a new fuse to check voltages, and the lo and behold the pump worked like a champ and has done so on a number of flights all day
The idiot light is a radio shack red LED 12 volts and is wired from the switch output to the pump (both ganged together) through the lamp and to ground and in yesterdays test the lamp lit when the pump ran. It would appear that the lamp is causing high current draw and blowing the fuse but I do not understand why (not an electrical engineer) or what could change to cause this?
Appreciate any ideas as I put the light in because I keep forgetting to switch the boost pump off.

[agirard7a]

Ok. Here is a question. Can you run the power
direct from the switch to the pump, then run a seperate
wire to the light? Maybe tied in at the pump so the current draw
through the power wire is not interupted by the light. Just a thought.

[uk_figs]

The power out of the switch has a double blade connector with one wire to the power side of the pump and the second wire to the power side of the LED. The LED is grounded to the airframe (did not run a ground wire to the firewall grounding block)

[Walt]

A typical LED has a resister in series with it that limits the current to around 20ma (0.020 amps). So unless the lamp is shorted somehow (it radio shack so that would not surprise me) then the current draw to an LED would normally be insignificant.