RMP NC Posted October 13, 2020 Report Share Posted October 13, 2020 I recall reading but can't find a post where it was explained how to use a coil of wire connected across the ammeter contacts in parallel with the meter to act a shunt and allow higher amperage alternators to be used with a stock TR4 ammeter. Thought it was on this forum. Maybe I'm wrong. If I'm off base let me know but otherwise can someone recall that post and how to find or give me that info again, please? I've look for a couple hours and not finding. thanks all. Quote Link to post Share on other sites
RobH Posted October 13, 2020 Report Share Posted October 13, 2020 No point. The only time there could be an over-range of the meter is just after starting the car as the battery re-charges and that peak lasts seconds. An alternator only supplies whatever current is demanded by the load so a bigger alternator does not necessarily imply any higher currents through the ammeter. The ammeter should only show current flowing into or out of the battery so changing the range is really not necessary. Quote Link to post Share on other sites
trchris Posted October 13, 2020 Report Share Posted October 13, 2020 As Rob above however also consider your wiring unless you've uprated it the main output from dynamo and subsequent ammeter wiring is rated at 30amps Chris Quote Link to post Share on other sites
RMP NC Posted October 13, 2020 Author Report Share Posted October 13, 2020 (edited) Given the original response, which thank you Rob for providing, it would sound like I'd not see over 30 amps unless I had a near dead battery. Right? But in that scenario I guess if the alternator was rated above 30 amps I'd be pegging out the ammeter and exceeding the 30 amp wire rating by however much the alternator was capable. So I would absolutely improve the wiring to handle whatever amperage the alternator could muster in that scenario. I'm rebuilding from ground up so have a new harness to put in and I will increase the amperage handling for all the wiring between alternator and battery. In anther non-Triumph car rebuild I bypassed the ammeter entirely and put in a very large alternator to battery wire, bypassing all connections to avoid a fire, which had happened before due to dirty connections which get hot and make a fire. Again in a low battery scenario would the however long pegging of the ammeter above the rating of 30 amps burn it out or mechanically harm it? I am not bothered if it doesn't hurt it. I had considered getting a voltmeter and eliminating the ammeter altogether. Edited October 13, 2020 by RMP NC typo Quote Link to post Share on other sites
RobH Posted October 13, 2020 Report Share Posted October 13, 2020 (edited) The ammeter is a pretty crude and robust device. Being a moving-iron device it is unlikely to be damaged mechanically by pegging the needle at full-scale for a few seconds. The weakness seems to be in the soldered joints internally, which connect the terminals to the single loop of thick wire which forms the magnetic coil; but those have been known to fail with the standard dynamo set-up anyway, perhaps with age through vibration. (see the photo in Roger's post on this thread:) Many would do as you suggest and fit a voltmeter instead, but then you lose the diagnostics that only an ammeter can provide. FWIW my 3A has a 38-amp alternator and the standard ammeter which seems to work fine. It would be easy to fit a shunt externally across the terminals but since the internal coil is so short, a couple of inches of heavy gauge wire is all that is necessary. You could see the effect by turning on the headlights with the engine off. The current discharge should be about 10 amps so you could use that to arrive at a suitable length to reduce the reading. Edited October 13, 2020 by RobH Quote Link to post Share on other sites
Z320 Posted October 13, 2020 Report Share Posted October 13, 2020 (edited) 1 hour ago, RobH said: No point. The only time there could be an over-range of the meter is just after starting the car as the battery re-charges and that peak lasts seconds. An alternator only supplies whatever current is demanded by the load so a bigger alternator does not necessarily imply any higher currents through the ammeter. The ammeter should only show current flowing into or out of the battery so changing the range is really not necessary. Hi Rob, the "shunt-story" sadly is very popular and I'm very pleased you explain what I'm also convinced about the simple facts. Ciao, Marco Edited October 13, 2020 by Z320 Quote Link to post Share on other sites
RMP NC Posted October 13, 2020 Author Report Share Posted October 13, 2020 By the way I found an explanation to my original question about how to do the shunt in a post on this site: "to go from 30 to 60A.....the shunt resistor will be an extremely low value, roughly equal to the resistance of the ammeter it's self. To go 30 to 60A full scale it would be the same resistance, from 30 to 50 it would be ammeter resistance * 1.67. It of course has to be able to carry the extra 20 amps, so in effect it will be a short length of stout copper wire, trimmed to get the resistance you need." There was another longer discussion somewhere in this forum with pictures and such but that above is the gist of what I was seeking. The information about how the ammeter only sees what is going to battery vs what is being consumed in total by the car was new info to me. I think in some US cars (Chrysler products) in the 50s up to the early 70s the ammeter carried the WHOLE load of the car and that's why some old ones burn up now and again due to the time based corrosion on the contacts at the firewall terminal block. They didn't do wires through the firewall but had a connecting terminal block. Likewise the reminder about wire amp rating was spot on. When I have a running car I'll experiment a bit and make a choice. Not yet sure if my religion is ammeter with no changes, ammeter with shunt, or voltmeter. I did buy an alternator so I've made at least an investment in that direction. I like the usefulness of the ammeter but fear the amps, especially the extra ones. Decisions to make. Thanks guys. Quote Link to post Share on other sites
Lebro Posted October 13, 2020 Report Share Posted October 13, 2020 There really is no need to do anything to the ammeter, as stated above it will cope happily with any short term high currents, & by the way I have standard loom & a 50A alternator, & I have never seen the ammeter hit the end stop. Bob. Quote Link to post Share on other sites
RMP NC Posted October 13, 2020 Author Report Share Posted October 13, 2020 Thanks Bob. That's really good to know and helps a lot. I think the quote I listed above was from you by the way. Quote Link to post Share on other sites
ctc77965o Posted October 14, 2020 Report Share Posted October 14, 2020 Beware that fitting a larger alternator may activate the occurrence of a Simple Momentary Olfactory Knowledge Event , which Triumph & Lucas developed in the 1950's and licenced to all british car manufacturers. Quote Link to post Share on other sites
Lebro Posted October 14, 2020 Report Share Posted October 14, 2020 Also bear in mind that the ammeter is monitoring current in & out of the battery, not the alternator, so if, say, you have lights on, cooling fan on (if fitted) etc, & a partially discharged battery, the alternator will be supplying more current than will be passing through the ammeter. Bob. Quote Link to post Share on other sites
RogerH Posted October 14, 2020 Report Share Posted October 14, 2020 41 minutes ago, Lebro said: Also bear in mind that the ammeter is monitoring current in & out of the battery, not the alternator, so if, say, you have lights on, cooling fan on (if fitted) etc, & a partially discharged battery, the alternator will be supplying more current than will be passing through the ammeter. Bob. +1 However, be careful when the engine is not running. If the Rad Fan (electric) headlights, radio etc is on you may draw quite a bit of current. Roger Quote Link to post Share on other sites
Lebro Posted October 14, 2020 Report Share Posted October 14, 2020 14 minutes ago, RogerH said: +1 However, be careful when the engine is not running. If the Rad Fan (electric) headlights, radio etc is on you may draw quite a bit of current. Roger Yes, but that has nothing to do with fitting an alternator !! Bob. Quote Link to post Share on other sites
Z320 Posted October 14, 2020 Report Share Posted October 14, 2020 Bob, we are two persons but have one thought! Quote Link to post Share on other sites
RogerH Posted October 14, 2020 Report Share Posted October 14, 2020 1 hour ago, Lebro said: Yes, but that has nothing to do with fitting an alternator !! Bob. Hi Bob, but the issue is the ammeter. I would leave as is but a modified car system with all the modern goodies may show a weakness in the meter. Just a thought. Roger Quote Link to post Share on other sites
Z320 Posted October 14, 2020 Report Share Posted October 14, 2020 At Germany we call this "Bauchgefühl" meens: I can't explain but my stomach tells me.... Quote Link to post Share on other sites
Kiwifrog Posted October 14, 2020 Report Share Posted October 14, 2020 22 minutes ago, Z320 said: At Germany we call this "Bauchgefühl" meens: I can't explain but my stomach tells me.... English being a germanic language we have the same "Gut feeling" phrase in our language cheers Alan Quote Link to post Share on other sites
RMP NC Posted October 14, 2020 Author Report Share Posted October 14, 2020 Plan on using a belt driven fan, will have reasonable modern audio setup (small head-unit w bluetooth), have a new SPAL fan for heater (using the setup w the motor controller that was recently covered in this forum), may use elec fuel pump w inertia switch, plan to use a elec ignition module (like the pertronix setup) and will use more or less regular headlights, otherwise stock. Think that about covers the options on the current draw areas. I have a brand new harness and will be getting new or cleaning up the contacts on my switches, fuse box, etc.. I think I'll be safe but I will be wary of engine-off potential high current events. Quote Link to post Share on other sites
Lebro Posted October 14, 2020 Report Share Posted October 14, 2020 (edited) Electric cooling fans have the highest current draw. All the stuff you mentioned is much less Bob Edited October 14, 2020 by Lebro Quote Link to post Share on other sites
BlueTR3A-5EKT Posted October 14, 2020 Report Share Posted October 14, 2020 (edited) I have NOS black bezel with flat glass Lucas part number 36438 50+ 0 -50 ammeter for sale - For sale at £50.00 plus postage. No exchange required. Now Sold I have fitted one in my TR3 which has an alternator and changed the bezel to a chrome one but kept the flat glass - see installed picture. Cheers Peter W . Edited October 14, 2020 by BlueTR3A-5EKT Quote Link to post Share on other sites
RMP NC Posted October 14, 2020 Author Report Share Posted October 14, 2020 Sent a PM to you BlueTR3A. Quote Link to post Share on other sites
BlueTR3A-5EKT Posted October 14, 2020 Report Share Posted October 14, 2020 3 minutes ago, RMP NC said: Sent a PM to you BlueTR3A. PM reply sent with details as requested. Peter W Quote Link to post Share on other sites
Z320 Posted October 15, 2020 Report Share Posted October 15, 2020 I ask myself what is a 50A gauge good for the 99% standard situations? Why not use a 100A gauge? Quote Link to post Share on other sites
RobH Posted October 15, 2020 Report Share Posted October 15, 2020 Quote Link to post Share on other sites
BlueTR3A-5EKT Posted October 15, 2020 Report Share Posted October 15, 2020 1 hour ago, Z320 said: I ask myself what is a 50A gauge good for the 99% standard situations? Why not use a 100A gauge? Does the volume control on your home hi fi amplifier go to 11? Joking aside - 50 amp ammeter was the original factory fitted option for TR4/4A with alternator. Peter W Quote Link to post Share on other sites
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