Richardtr3a Posted March 2, 2021 Report Share Posted March 2, 2021 After reading Mike Jennings article, I have ordered a new earth connector for my Positive battery terminal. I am planning to use s/s fixings. Is this OK ? Is it useful to add a second connection between the body and the lifting eye on the engine as well as the existing connection from the chassis to the coil mounting on the engine. Thanks Quote Link to post Share on other sites
RobH Posted March 2, 2021 Report Share Posted March 2, 2021 Stainless fasteners should be fine Richard. A second earth link is not strictly necessary but is a useful addition as belt-and-braces. (not quite sure what you have now - the braid is usually to the engine front plate above the engine mount) Quote Link to post Share on other sites
foster461 Posted March 3, 2021 Report Share Posted March 3, 2021 On advice from council (Stuart) I added a second ground braid between the rear of the engine and the bulkhead. I did that just for insurance and because it was easy. Stan Quote Link to post Share on other sites
BlueTR3A-5EKT Posted March 3, 2021 Report Share Posted March 3, 2021 This is a mystery area for me. I have a memory of college 50 years ago that resistors in parallel have the same voltage across them. Is a bad connection at one end of an earth cable described as a resistor? What about parallel resistors? https://www.electronics-tutorials.ws/resistor/res_4.html If you have a cable connection with a resistance and you add another in parallel with less resistance what happens? I have checked for a voltage drop as described in the TR Action article and found an excessive one. (earth) Cleaning and scraping the cable connection to the bulkhead got the drop to an acceptable figure. I also checked the drop through the starter solenoid and thankfully that was at an acceptable level without any cleaning. (line) Peter W Quote Link to post Share on other sites
RobH Posted March 3, 2021 Report Share Posted March 3, 2021 28 minutes ago, BlueTR3A-5EKT said: What about parallel resistors? Simple Peter. Like water, electricity always takes the easiest route. If you have two equal value resistors the current will be shared equally between them. If one is lower value than the other, more current will flow through it. The current is shared out in inverse proportion to the resistance values. To paraphrase George Orwell - All cables and connections are resistive, but some are more resistive than others. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted March 3, 2021 Report Share Posted March 3, 2021 21 minutes ago, RobH said: Simple Peter. Like water, electricity always takes the easiest route. If you have two equal value resistors the current will be shared equally between them. If one is lower value than the other, more current will flow through it. The current is shared out in inverse proportion to the resistance values. To paraphrase George Orwell - All cables and connections are resistive, but some are more resistive than others. Thank you. Quote Link to post Share on other sites
ianc Posted March 3, 2021 Report Share Posted March 3, 2021 The advantage of a second route is that if one should fail completely, then the other - even if of slightly higher resistance - should afford a path for the little electrons! Belt and braces, really. Ian Cornish Quote Link to post Share on other sites
Richardtr3a Posted March 3, 2021 Author Report Share Posted March 3, 2021 Thanks Ian, That will be two earth straps and belt and braces twice as well. Richard & B Quote Link to post Share on other sites
john.r.davies Posted March 3, 2021 Report Share Posted March 3, 2021 And if I may, the way I was taught was not to rely on the thread of a fixing bolt to make a good connection. Use the largest ring terminal thr cable will take, abrade its surface, and the surface it wull bear on, removing all paint. Abrade that surface too. Clamp together with the fastener, protect with grease or vaseline. Quote Link to post Share on other sites
RogerH Posted March 3, 2021 Report Share Posted March 3, 2021 Has anybody tried an electrically conductive grease under an earth tag. Grease When the paint is scrapped away there is the possibility (probably very small) of rust taking hold. Roger Quote Link to post Share on other sites
Lebro Posted March 3, 2021 Report Share Posted March 3, 2021 Vaseline is good, is does not have to be conductive, it just has to keep oxygen away from the bare metal. Bob Quote Link to post Share on other sites
Ian Vincent Posted March 3, 2021 Report Share Posted March 3, 2021 That's why I put a lead washer between the earth tag and the bare metal of the body. Stops corrosion and provides a good connection. But my supplementary earth is a length of left over battery cable that goes directly from a gearbox bolt to the negative terminal on the battery, since it is really there to make sure the starter motor and alternator have a good earth. Rgds Ian Quote Link to post Share on other sites
Lebro Posted March 3, 2021 Report Share Posted March 3, 2021 I'm about to add an isolation switch to my TR3, I'm going to fit it on the blanking plate which covers where the brake / clutch MC box would be for LHD cars. It will be accessible from inside under the glove box, & it has a removable key. I will be wiring it into the live battery feed, not the earth, because I need one item to be permanently powered, & get it's earth return through the body. As this involves some changes to the battery wiring, I will probably add a direct link from Batt -ve to the bell housing while I am at it. The type of switch I have chosen has additional contacts which can be used to isolate the ignition circuit when the battery is isolated, this prevents the engine running purely from the alternator / dynamo output. Will post photos when done. Bob. Quote Link to post Share on other sites
Rod1883 Posted March 3, 2021 Report Share Posted March 3, 2021 I've been considering doing similar in the same location for a little while now. Will be interested to see your progress Bob. Rod Quote Link to post Share on other sites
Lebro Posted March 4, 2021 Report Share Posted March 4, 2021 (edited) On 3/3/2021 at 12:22 PM, Lebro said: I'm about to add an isolation switch to my TR3, I'm going to fit it on the blanking plate which covers where the brake / clutch MC box would be for LHD cars. It will be accessible from inside under the glove box, & it has a removable key. I will be wiring it into the live battery feed, not the earth, because I need one item to be permanently powered, & get it's earth return through the body. As this involves some changes to the battery wiring, I will probably add a direct link from Batt -ve to the bell housing while I am at it. The type of switch I have chosen has additional contacts which can be used to isolate the ignition circuit when the battery is isolated, this prevents the engine running purely from the alternator / dynamo output. Will post photos when done. Bob. Ok, well I have now fitted it, I know it's fairly usual to isolate the earth end as the wiring is easier, but as I wanted to keep volts on one particular item, in the end I decided to switch the live (+ve in my case) side. In order to make my life a bit easier, I swapped batteries with another one I had which has the terminals the other way round. I removed the brake / clutch M/C blanking plate, & drilled it to take the new switch, then refitted, then spent all this afternoon wiring it all up. The white wire normally going to the coil, was rerouted to the extra switch contacts on the new switch, then a new white wire was run from the switch down to the coil. this disconnects the coil when the main switch is off, thus stopping the engine straight away. A new heavy cable was run from the starter solenoid along in front of the battery to the switch, and the existing +ve battery cable (now on the nearside) also connected to the switch. Cable runs were held down with some plastic "P" clips, & job done. The switch is accessible from inside, just under the glove box, & is pretty easy to reach, the red key can be left in place when off, or can be removed completely. This is the switch I used: https://www.ebay.co.uk/itm/FIA-Type-Battery-Ignition-Master-Isolator-Cut-Off-Kill-Switch-Road-Race-Rally/323093252092?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649 Bob. Edited March 4, 2021 by Lebro Quote Link to post Share on other sites
RogerH Posted March 4, 2021 Report Share Posted March 4, 2021 Hi Bob, I'm sure you are aware but just in case - your spare coil does not have a cap on the HT orifice. Roger Quote Link to post Share on other sites
Lebro Posted March 4, 2021 Report Share Posted March 4, 2021 Should it ? Bob Quote Link to post Share on other sites
Hamish Posted March 4, 2021 Report Share Posted March 4, 2021 I just used the finger tip off some latex gloves I used to use when working on the car. Just to keep random crud out. Quote Link to post Share on other sites
ianc Posted March 5, 2021 Report Share Posted March 5, 2021 I agree with Hamish - not just dirt, but moisture, too. Some 50 years ago I found a piece of small diameter rubber tube with a sealed end, and that's been sitting atop my spare coil ever since. No idea where I found it. Ian Cornish Quote Link to post Share on other sites
Lebro Posted March 5, 2021 Report Share Posted March 5, 2021 OK, I will see to it today. Bob Quote Link to post Share on other sites
Hamish Posted March 5, 2021 Report Share Posted March 5, 2021 (edited) 1 hour ago, Lebro said: OK, I will see to it today. Bob Don’t feel pressured into it Bob risk is prob minimal. Edited March 5, 2021 by Hamish Quote Link to post Share on other sites
Rod1883 Posted June 1, 2021 Report Share Posted June 1, 2021 I'm about to fit an isolator switch in a similar fashion to that done by Bob above. The main difference is that the '2' is still Positive earth and so I'll be sourcing new insulated cables to run from the positive battery post to the switch, and from the switch to the body connection where the existing braid is currently attached. Looking on line there appears to be a wide range of cable amp rating to choose from. What would the rating need to be? Quote Link to post Share on other sites
RobH Posted June 1, 2021 Report Share Posted June 1, 2021 It's only a very short run so 25mm^2 will be fine. That is called '170 Amp' but is fine for a good bit more in a short run for short bursts. Current rating of cable is based on how hot it will get from the voltage drop, which depends on length and how it is enclosed. Quote Link to post Share on other sites
Rod1883 Posted June 1, 2021 Report Share Posted June 1, 2021 Thanks Rob. Quote Link to post Share on other sites
Rod1883 Posted June 5, 2021 Report Share Posted June 5, 2021 Not as complex as Bob's set up, but a pretty neat result, I think... Quote Link to post Share on other sites
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