changing polarity on petrol pump

[JimK]

Why would it be necessary to alter the pump?

Could cliff not simply reverse the connections? Does it matter whether the voltages are 0 and -12 or +12 and 0? That's still a 12V drop across the terminals, and isn't that all it cares about?

[tickman]

the problem it is an "electronic pump" not an electric pump and unfortunatly not as simply to reverse polarity as the curcuit will have been designed to suit positive earth. it seems that there is a circuit designed for negative earth and if compared you could identify the parts that needed changing and sorce these at maplins or rs components (rs trade only!) and sort this yourself. other options are to leave it as positive earth or are you fitting other equiptment like a stereo or an alternator?

[JimK]

the problem it is an "electronic pump" not an electric pump and unfortunatly not as simply to reverse polarity as the curcuit will have been designed to suit positive earth.

I don't know if you were answering me, but in case you were:

Change the wiring to negative earth and switch the connections at the pump. By changing both the wiring polarity and the pump connections the polarity the pump sees is unchanged.[/u]

[alex_holden]

Change the wiring to negative earth and switch the connections at the pump. By changing both the wiring polarity and the pump connections the polarity the pump sees is unchanged.

It depends if one of the terminals is electrically connected to the body of the pump. It's unlikely to require components altering but it might need some wires changing around inside. If it was as simple as swapping the connections on the outside of the pump, why would the suppliers sell two different versions?

[JimK]

It depends if one of the terminals is electrically connected to the body of the pump.

Good point, I hadn't thought of that. I deal in 1s and 0s, not actual voltages...

If it was as simple as swapping the connections on the outside of the pump, why would the suppliers sell two different versions?

It would be possible to be cynical about that...

[cliff]

other options are to leave it as positive earth or are you fitting other equipment like a stereo or an alternator?

this is getting heavy .... no i want to fit some gauges, one of which is a temp gauge - i believe for that to work it needs to be neg earth?

i am puzzled though that it is currently connected neg to earth - surely if it was going to burn out it would have done it already!

[bigginger]

Topic moved here, 'cos it seems to be 'electrical' rather than 'mechanical'

[alex_holden]

this is getting heavy .... no i want to fit some gauges, one of which is a temp gauge - i believe for that to work it needs to be neg earth?

I'm not sure, but I suspect an electrical temperature gauge will work either way. If it's the capillary type then it definitely doesn't matter.

i am puzzled though that it is currently connected neg to earth - surely if it was going to burn out it would have done it already!

It may be that it's a negative earth design which was rewired in the factory to be positive earth, but they didn't change the labels round.

[RogerRust]

I'm convinced if you don't replace the pump it will wreck it if you connect it the wrong way round.

But as Alex says I think the temp gauge should work either way round.

[bigginger]

Same here, on both counts

[cliff]

But as Alex says I think the temp gauge should work either way round.

i thought i'd read somewhere that to work properly the temperature gauge needed a neg earth car.

if it will work ok in a car with pos earth then i won't need to change the polarity