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SU fuel pump upgrade.
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Wed Jan 22, 2020 11:25 pm    Post subject: SU fuel pump upgrade. Reply with quote

I have been advised that I should fit a 'Transil' across the coil of my 12 volt SU fuel pump.

I assume this is what Wiki describes as a "transient voltage suppression diode".

I have very little understanding of electrical matters so I would appreciate a simple explanation if that is possible.
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Wed Jan 22, 2020 11:48 pm    Post subject: Reply with quote

The diodes main function is to stop electrical noise that would interfere with radio's and could damage other electronics. It will slightly reduce points wear.

They cost pence so no harm in fitting, although I doubt you will really benefit unless you have fitted a radio, electronic ignition or an alternator all of which could potentially suffer damage from transient voltage spikes generated in the pumps coil.

Dave
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Jan 23, 2020 12:09 am    Post subject: Reply with quote

ukdave2002 wrote:
The diodes main function is to stop electrical noise that would interfere with radio's and could damage other electronics. It will slightly reduce points wear.

They cost pence so no harm in fitting, although I doubt you will really benefit unless you have fitted a radio, electronic ignition or an alternator all of which could potentially suffer damage from transient voltage spikes generated in the pumps coil.

Dave


Ahh,,, so as I AM fitting an alternator (a dynamater) and an electronic distributor, I would indeed benefit from the protection it affords. It sounds like a necessity.

It is good to know about this stuff as the upgrades have cost a considerable amount and the last thing I want is to suffer is avoidable damage.

Is it easy to fit this thing?

...and what other devices will I need to protect my new and expensive electronics.??
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Thu Jan 23, 2020 10:05 am    Post subject: Reply with quote

Hi Ray

You require a 1N4007 diode; http://tiny.cc/26y2iz

The bad news is that they are only sold in a minimum quantity of 10, the good news; they are only 10p each! if you purchase 100 the price drops to 2p each!

They simply fit in parallel to the pump points, with the cathode end of the diode (marked on the diode by a clear band) connected to the +ve side of the points. Its worth adding some insulation to the diodes leads, you can use the insulation from some stripped cable.

As you are fitting an alternator, you won't have noisy (electrical noise) mechanical voltage control to worry about, so no other protection required.

Dave
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Jan 23, 2020 11:05 am    Post subject: Reply with quote

Many thanks for that Dave.

Just think how much damage a 2p diode might save!!!!

A quid well spent I should think.!
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Thu Jan 23, 2020 1:11 pm    Post subject: Reply with quote

This is a pic with the diode installed on a vehicle with +ve earth (note "cathode end" band on the diode), flip it round if the car is -ve earth



Dave
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Thu Jan 23, 2020 1:20 pm    Post subject: Reply with quote

Thanks Dave. That is clear. I have ordered some and made a note of your instructions.

I have recently bought a positive earth flasher unit recommended for LED indicators. Will this diode protect it too?
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Tue May 19, 2020 4:55 pm    Post subject: Reply with quote

Dave. I have rebuilt the old pump as you suggested. I also bought some 1N4007 silicon rectifier diodes to fit to the points but I am uncertain what I should do.

The rebuild kit came with something called a "varistor" which I have fitted.




I am somewhat out of my depth here. Are these things the same ? Will they save my valuable electronics?

According to SU the varistor they supply is polarity neutral which I seem to remember you saying is the same as the diode called a "transil".

Which should I fit?

Should they both be fitted?

(Sorry for all the questions... but if a little knowledge is a dangerous thing - then ..... )
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Tue May 19, 2020 5:30 pm    Post subject: Reply with quote

Fit the varistor on its own, its not polarity sensitive so no chance of fitting the wrong way round!

Dave
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Tue May 19, 2020 6:03 pm    Post subject: Reply with quote

ukdave2002 wrote:
Fit the varistor on its own, its not polarity sensitive so no chance of fitting the wrong way round!

Dave


Thanks Dave. How does this look?

The varistor clears the points blade O.K.
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Ray White



Joined: 02 Dec 2014
Posts: 6283
Location: Derby

PostPosted: Sat May 23, 2020 8:38 pm    Post subject: Reply with quote

I have done a bit of "surfing" and came across someone who has done the same thing with their S.U. pump and asked the same question as me... are transils and Varistors the same or, more importantly, do they do the same thing... It would seem the answer is both "yes" and "no". It all depends etc, etc, etc,.

The funny thing is that the Varistor supplied by S.U. in their kits is really a diode. Fitting it will supposedly protect my valuable electronics from "noise".

I hope it does. Rolling Eyes
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