| Author | Message | ||
     Geoff Wootton Grand Master Username: dounraey Post Number: 693 Registered: 5-2012 |
Hi Folks I am reconditioning my SU fuel pump.  The problem I am having is whether to replace the capacitor, shown in the photo with the supplied varistor or whether to reuse the capacitor. The instructions sent with the kit state: "Where capacitors are fitted they are connected to the terminal stud at the one end and to the rocker blade securing screw at the other. Where varistors are used they are connected the same way. All kits made by Burlen are now supplied with varisters." It's the wording that's confusing me. Do they mean replace the original capacitor with the supplied varistor? To say "where capacitors are fitted" implies the capacitor should be re-fitted. I have checked out the Burlen website and although the comprehensive instructions are repeated, there are no FAQ's to clarify this situation. The photo below of the two components certainly implies I should fit the varistor - the connectors are the same.  What do your reckon - any suggestions will be gratefully received Geoff | ||
| Bob Reynolds Prolific User Username: bobreynolds Post Number: 253 Registered: 8-2012 |
I agree, very confusing. I think what they mean is: "Where capacitors were fitted they were connected to the terminal stud at the one end and to the rocker blade securing screw at the other." In other words, they are explaining how the capacitor was fitted originally, not how it should be fitted now. I would use the varistor. | ||
| David Lacey Experienced User Username: dlacey Post Number: 42 Registered: 11-2010 |
Hi Geoff, I can't read the number on the 'varistor' but it looks more like a diode...in any case, fit it as Burlen instructed to save the points from the backEMF spikes. The capacitor should go to the parts museum. | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 1297 Registered: 6-2009 |
Geoff, I can send you details, but search the forums first. The general consensus is to toss the varistor that comes with the kit and the original bit and replace it with a diode. This has been much discussed on these forums and the other we both participate in. From an electrical perspective a diode is the best possible replacement as it performs the intended function much better than a varistor. Here's a picture of a diode connected to a negative ground SU fuel pump with the correct orientation of the polarity. If reversed it just blows out and it's as though there's nothing there.  If memory serves I used a 1N4001 diode, but I can double check that. Brian | ||
| Brian Vogel Grand Master Username: guyslp Post Number: 1298 Registered: 6-2009 |
David, I thought that was a diode too, at first, but it doesn't seem to have the stripe on either end, and I've not seen any rectifier diode that doesn't have a stripe on the case for the cathode end. Brian | ||
| Martin Taylor New User Username: martin_taylor Post Number: 10 Registered: 7-2013 |
The diode will slow down the pumps (may not be enough to matter) as the collapsing magnetic field will continue to circulate through the diode until dissipated. This is why you don't use a diode on an ign coil or an elevator brake. It will probably still work with a diode however. | ||
| Geoff Wootton Grand Master Username: dounraey Post Number: 694 Registered: 5-2012 |
As always, many thanks for the help. One things for sure - the capacitor can go in the bin. The number on the supplied varistor is 1.5KE18CA. I did check it out and it is also listed as a bi-directional diode. I've not had time to read up this component. I'm inclined to take the diode route as specified by Brian, but I am interested in Martin's comments. I will do some further searches over the weekend and try figure out why Burlen supply varistors rather than diodes. If there is not much in it then it will be easier to use the supplied parts. Thanks again to everyone who's posted - it has certainly clarified the situation. Geoff | ||
| Jim Walters Experienced User Username: jim_walters Post Number: 35 Registered: 1-2014 |
Geoff, a 1.5KE15CA is a diode, not a varistor. I don't know why they are calling it that. It is a special type called a TVS diode and bidirectional. TVS diodes are Transient Voltage Suppressors. I've been using these in the SU pumps I rebuild for a few years now although I use a 1.5KE24CA which has a higher voltage limit. (24 volts vs. 15 volts) I have not had any issues using them. I think they are a better choice than a 1N4001 as they are not polarity sensitive so you can't install it incorrectly. There are other technical reasons I think they are better than a straight diode, do some research and decide for yourself. I would just use the TVS diode supplied and definitely throw out the capacitor. SRE22493 NAC-05370 www.bristolmotors.com | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 3198 Registered: 4-2003 |
Yes, the 1.5KE15CA is a TVS and should have the cathode stripe. A 1N4007 would do the job just as well. RT. | ||
| Bob UK Unregistered guest Posted From: 188.29.164.55 |
Why can't a capacitor be used as normal. After all they do work and last for years. (Message approved by david_gore) | ||
| Simon Bell Unregistered guest Posted From: 5.83.8.154 |
The capacitor could be replaced. Which is best? Tricky to say. The suppressor is a more modern component. The capacitor is better than nothing. (Message approved by david_gore) |
