Fuel pump polarity

Post by **samheath100** » Tue Mar 08, 2005 7:13 pm

Hi group, does anyone know if it is possible to change the cars pollarity without affecting the fuel pump. I have been told that when I change the car from positive earth to negetive earth the fuel guage will read the wrong way (until I change the connections over). Thanks sam.

Post by **bigginger** » Tue Mar 08, 2005 7:19 pm

I might be wrong, but it's the first time I've heard that - no mention of it in the technical tips either - http://www.mmoc.org.uk/technicaltips/Ne ... Earth.html
a

Post by **TerryG** » Tue Mar 08, 2005 7:27 pm

All i did with mine was turn the battery round, everything seems fine. its only been like it for 5 years now

Post by **Chris Morley** » Tue Mar 08, 2005 7:42 pm

In a word Sam - NO!

(It's an old wives tale, at least in respect of the Minor's fuel gauge). In respect of the title, the pump and fuel gauge are separate items - but neither have polarity issues....

All i did with mine was turn the battery round, everything seems fine. its only been like it for 5 years now

Four and a half years since I did mine. You're supposed to reverse the dynamo's polarity (which I did), but it seems that some dynamos will change over anyway (like Terry's).

Moved to electrical where this belongs.

Post by **Cam** » Tue Mar 08, 2005 9:53 pm

Also you have to swap the coil connections over.....

Post by **moggyminor16** » Tue Mar 08, 2005 10:42 pm

had no problems with my lot just changer a cuple of wires on the regulator box and the new cable for al;ternator or just do the dynamo cables if you keep the dynamo no change on fuel pump

Post by **Alec** » Wed Mar 09, 2005 7:43 am

Hello all,

one point regarding S.U. fuel pumps, some models have diode suppression across the points, these are polarity conscious. Shouldn't be fitted to a Minor, but you never can be sure unless you check.

Alec

Post by **Cam** » Wed Mar 09, 2005 10:37 am

Alec,

Diode supression? are you sure it's not capacitor supression? or does the diode prevent EMF from spiking the line when the coil is turned off? If so then it should be in series not parallel like a capactor.

Post by **Alec** » Wed Mar 09, 2005 11:05 am

Hello Cam,
it is in parallel with the coil and quenches the back EMF when the points open. The diode is available in either polarity, at a guess it would be easy enough to reverse anyway.

Alec

Post by **Cam** » Wed Mar 09, 2005 11:17 am

Alec, thanks for the explanation. So with those systems it's REALLY important that the polarity is observed as connecting the terminals the wrong way will blow the diode!!

Yes, diodes are only available in one polarity. It just depends on which way round you connect them so it should be easy enough to de-solder and reverse. Assuming of course that the solenoid arrangement is not polarity/direction senstive!

Post by **Alec** » Wed Mar 09, 2005 1:11 pm

Hello Cam,
the replacement diodes from Burlen, presumably because there is a terminal included, are sold in either polarity. As you say a soldering iron will suffice to swap terminals.

Alec

Post by **Cam** » Wed Mar 09, 2005 5:57 pm

Thanks for the explanation again Alec! I thought it was a bit odd for diodes to be sold for different polarities!! (it reminded me of left-handed hammers etc!

). Makes sense if the correct terminals are attached.

Post by **samheath100** » Wed Mar 09, 2005 7:22 pm

arnt the two battery conexions slighly different to stop you turning the battery round. Did you have to modify them.

Post by **Cam** » Wed Mar 09, 2005 10:14 pm

I replaced the battery connections with new ones when I turned my battery around as the old ones were past their best.