Electric fuel pump interfering with LED bulbs

[monza29]

I have a Facet solid state fuel pump which is fitted at the back of my Elan near the fuel tank. The pump ticks continuously when the ignition is on. I decided to fit some LED bulbs and started with the reversing lights and discovered that the LED bulbs flicker in tune with the pump. The 'normal' bulbs are fine, if they are affected in any way you cannot see it.

The power to the pump is from the input side of the standard fuse box. The cable runs independently under the carpet along the backbone, enters the boot, passes through an impact switch to an in-line fuse and then to the pump. The earth from the pump goes to a battery cut-out switch.

Connecting an earth from the battery directly to the pump, the LEDs still flicker.
Connecting an earth from the battery directly to the rear lamp units, again the LEDs continue to flicker.
Connecting a power cable from the battery directly to the pump, thus by-passing the ignition circuit, the LEDs no longer flicker.

Has anyone with an electric fuel pump and LED bulbs come across this problem?

[john.p.clegg]

" Connecting a power cable from the battery directly to the pump, thus by-passing the ignition circuit, the LEDs no longer flicker. "

There's your problem, high resistance in the circuit you " patched out".

You will probably not be able to find it with a voltmeter as it's a current problem.

Disconnect the battery feed and measure the resistance of the circuit you " patched out" , moving logically along it till you find the high resistance point.
Probabaly a dodgy bullet connector , give them all a good clean.

John

[Craven]

Something like this connected closely across the pump may be worth a try.
https://www.google.com/search?client=fi ... or+2+farad

[monza29]

Thanks John, I'll give that a try. The wiring hasn't been touched for 40 years so very likely a dodgy bullet connection.

Thanks for your idea Craven. The capacitors for audio don't look like they will be suitable, my pump is mounted 'outside' above the diff. so they will be subjected to the elements. I'll follow John's suggestion initially.

[slowsprinter]

I wonder if you can tell me how you solved this issue? I have the same problem with LED lamps flickering in sympathy with my electric fuel pump which is fitted in the boot. All my wiring is new so I do not think it is caused by poor electrical connections. Could a capacitor fitted across the fuel pump live to ground cure it?

Regards
Ian

[Andy8421]

LED lights respond instantly to a change in voltage with a change in brightness, incandescent bulbs tend to 'average' the voltage because of the thermal mass of the filament - it takes time to warm up and cool down.

This is very noticeable with modern car LED indicators in comparison to older car incandescent indicators. The incandescent bulbs seem to fade in and fade out, rather than the snap on/off of the LED bulbs.

This 'flickering LED' problem is common across the old car forums, not just with Facet Pumps, but also SU and any other impulse type pump. These type of pumps have a high current draw when the piston is being pulled into the pump, and depending on the design, possibly a voltage spike when the piston is released.

If the pump and the lighting circuits share a common conductor (as they do on the Elan), then depending on the resistance of the conductor, the LED lights will flicker to a greater or lesser extent.

One fix is to feed the pump separately to the lights. A fused feed from the battery via a relay driven by a feed from the ignition switch would do the trick, and would also allow the addition of an impact disconnect, which isn't a bad idea.

[slowsprinter]

Andy

Many thanks for your detailed reply. That all makes sense to me and I may well take up your idea of feeding the fuel pump straight from the battery on an ignition switched relay. The pump is in the boot very near to the battery so this would make cable run to the pump very short which will be an advantage.

It occurred to me that it might be a voltage issue. I am currently sorting out dash wiring and am powering my car electrics from a 10Amp 12 volt power supply whilst I test circuits. When I switched the ignition on the fuel pump starts and this interferes with the LED lamps. If I pull the fuse for the pump the lights are flicker free. I measured my power supply at about 11.8V and when the pump is running I imagine it draws a fair proportion of the 10 Amp supply and may drop the voltage on load. I need to try with the battery connected I suppose firstly. I could always go back to bulbs rather than LED's. However I love the brightness of LED lights and the satisfying click of the LED flasher units for the indicators and hazard lights(which I have added). I need to resolve one way or another before I commit to final installation of the dash, which has been a difficult job!

Thank you again,
Ian

[monza29]

Having started this thread I've not checked back to the forum since 9th August, so apologies. I have resolved the problem and maybe would have done it sooner if I had read the later comments.

I have fitted a relay powered from the positive battery terminal and activated by the ignition circuit through a lead from the fuse box. An impact switch and in-line fuse are in the circuit from the relay to the pump. So simple I should have thought of it sooner

Thanks to all who responded to this thread.

[slowsprinter]

Thanks for that Monza.

I too have now done something similar to you and fitted a relay near the fuel pump in the boot so that there is a very short higher current live from the battery positive to the fuel pump which is switched by a feed routed down the passenger side of the car to the relay from the ignition circuit protected by a fuse.

Not really had chance to test it yet as my dashboard is sat on my workbench! Hopefully this will resolve the issue. I'll try and remember to report back, so that others may benefit from these findings.

Likewise thanks to all on this thread.
Ian