changing polarity on petrol pump

Post by **cliff** » Sat Nov 04, 2006 8:19 pm

i'm going to change my polarity to neg earth and was wondering if i needed to change polarity on the petrol pump?
i only ask because i see esm sell pumps for both polarities

Post by **alex_holden** » Sat Nov 04, 2006 8:28 pm

As far as I'm aware, the standard pump with points in it works either way round. ESM also sell a refurbished pump that's had the points replaced with an electronic controller, and that's the one that comes in two different types for positive and negative earth.

Post by **cliff** » Sat Nov 04, 2006 8:38 pm

thanx alex, i wondered why no mention was made of this potential problem on the tech tips pages.

Post by **Kevin** » Sun Nov 05, 2006 9:05 am

Yes Alex is spot on.

Post by **Alec** » Sun Nov 05, 2006 10:12 am

Hello Cliff,

there are points type S.U. electric pumps that are polarity conscious, they are the ones that use diode suppression as against capacitor supression. They are not normally fitted to Minors but over the years and various owners you can't be certain unless you check.

Alec

Post by **bmcecosse** » Sun Nov 05, 2006 11:08 am

However - the points will have developed a pit and a lump - with the reversed polarity this too reverses - so it would be a good idea to clean up the points to avoid problems down the road.

Post by **cliff** » Sun Nov 05, 2006 7:16 pm

Alec wrote: there are points type S.U. electric pumps that are polarity conscious, they are the ones that use diode suppression as against capacitor supression. They are not normally fitted to Minors but over the years and various owners you can't be certain unless you check.

how can i tell the difference between a diode and a capacitor.

i know the pump was changed back in the spring with a pump with a blue end if that's any clue.

Post by **Alec** » Sun Nov 05, 2006 9:04 pm

Hello Cliff,

the diode is smaller in diameter than the capacitor, and if memory serves me correctly, there is a small coloured band near one end, (similar to resistor marking but only one band.)

Alec

Post by **RogerRust** » Mon Nov 06, 2006 6:39 am

I'm a bit worried about the pump having a blue end.

All the mechanical ones I have seen have a black so it's best to take the cover off and see if it has points or electronics. If its an electronic one you'll need a new pump, I dont think you can change them round.

Post by **Alec** » Mon Nov 06, 2006 7:07 am

Hello all,

I've seen a replacement for the S.U. pump (German make I think) which has a blue cover. One option is to isolate it from the car and swap polarity that way but unless it is totally covered you run a real risk of shorting from the pump to the body which could be nasty. Not really recommended.

Alec

Post by **alex_holden** » Mon Nov 06, 2006 9:03 am

I would be surprised if you can't dismantle it and reverse the polarity of the controller, but I'd have to see it in person to say for sure. I don't think isolating it from the body will be easy because the fuel supply pipe is metal. Even if you replace a section of the pipe with a rubber hose, are you sure petrol isn't conductive under any circumstances? I wouldn't risk it myself.

Post by **cliff** » Mon Nov 06, 2006 9:21 am

RogerRust wrote: All the mechanical ones I have seen have a black so it's best to take the cover off and see if it has points or electronics. If its an electronic one you'll need a new pump, I dont think you can change them round.

the pump clicks when you turn on the ignition so i'm guessing this means it has points?

Post by **alex_holden** » Mon Nov 06, 2006 9:26 am

No, that's just the pump operating. Could you take the end-cap off and post a close-up picture of what's underneath?

Post by **cliff** » Mon Nov 06, 2006 9:47 am

alex_holden wrote:No, that's just the pump operating. Could you take the end-cap off and post a close-up picture of what's underneath?

i'll do it now, i've got five minutes

Post by **cliff** » Mon Nov 06, 2006 10:13 am

external shot

internal shot

something strange though, when i removed the cover i noticed a +/- marked underneath where i couldn't see and it's been connected up for negative earth, even though i'm currently positive earth.

Post by **alex_holden** » Mon Nov 06, 2006 10:22 am

That's definitely an electronic one and if it's working now it's presumably wired up for positive earth. I suspect you can probably reverse the polarity but I wouldn't be able to tell you how without examining it.

Post by **cliff** » Mon Nov 06, 2006 1:04 pm

alex_holden wrote:That's definitely an electronic one and if it's working now it's presumably wired up for positive earth. I suspect you can probably reverse the polarity but I wouldn't be able to tell you how without examining it.

i don't think the previous owner has touched the polarity of the unit - it's just working with the negative wire going to ground - so presumably it'll still work when i change polarity?

Post by **alex_holden** » Mon Nov 06, 2006 1:38 pm

Personally I wouldn't risk swapping the polarity without knowing whether the electronic controller is polarity sensitive. If it is then reversing the polarity will destroy it. You say it has + and - labels on it somewhere but it is working on a positive earth car with the - terminal connected to the body: that indicates to me that the circuit probably is polarity sensitive, and it has been reconfigured so that the terminal marked - is actually the positive connection.

Post by **cliff** » Mon Nov 06, 2006 1:46 pm

alex_holden wrote:Personally I wouldn't risk swapping the polarity without knowing whether the electronic controller is polarity sensitive. If it is then reversing the polarity will destroy it. You say it has + and - labels on it somewhere but it is working on a positive earth car with the - terminal connected to the body: that indicates to me that the circuit probably is polarity sensitive, and it has been reconfigured so that the terminal marked - is actually the positive connection.

i'll email the previous owner and ask if he did any reconfiguring - perhaps i can swop it back.

Post by **alex_holden** » Mon Nov 06, 2006 1:54 pm

He may have bought it already configured as positive earth. As discussed earlier, ESM sell an electronic pump in both positive and negative earth versions. It probably is possible to reconfigure it - perhaps take it off and show it to a local electronics engineer (eg. an old style TV repair shop where they still do board-level repairs).