mpbarrett Posted October 31, 2023 Share Posted October 31, 2023 (edited) I took the Herald great Yarmouth on Sunday (LOWMEX exhibition). I have a volt meter on the car and noticed on the way home (very wet afternoon) that the battery voltage was reading 13.8V at around 1000 rpm which is the normal charging voltage, at >1500 rpm the voltage was dropping to 12.4V (headlights and wipers on ) that suggest it not charging. Once the engine speed dropped the voltage went back up to 13.8V. Not sure what's going on I would have thought the alternator regulator would control the voltage regardless of engine rpm, if its an alternator fault not sure whats happening. Any ideas very welcome! mike Edited October 31, 2023 by mpbarrett Link to comment Share on other sites More sharing options...
DeTRacted Posted October 31, 2023 Share Posted October 31, 2023 Fan belt slipping at higher revs perhaps - maybe the belt was wet ? If it's not that and definitely the alternator, might be worn brushes or slip-ring, not making good contact at faster speeds. 1 Link to comment Share on other sites More sharing options...
Nick Jones Posted October 31, 2023 Share Posted October 31, 2023 Odd. Belt tight? Pulley tight on the shaft? Connections all good? Next check the brushes. Is it a Lucas ACR or something more modern? Link to comment Share on other sites More sharing options...
Nick Jones Posted October 31, 2023 Share Posted October 31, 2023 Hah… Rob is thinking along the same lines and beat me to it Link to comment Share on other sites More sharing options...
mpbarrett Posted November 1, 2023 Author Share Posted November 1, 2023 (edited) Just a standard Lucas ACR, will have a look at the belt. Stupidly I was tying to work out what strange fault in the alternator would cause this instead of considering the obvious solution! I expect the belt was wet, everything in Suffolk was very wet! BTW how do you stop water coming thru at the top right corner where the hood fixes to the windscreen frame.... mike Edited November 1, 2023 by mpbarrett Link to comment Share on other sites More sharing options...
Nick Jones Posted November 1, 2023 Share Posted November 1, 2023 1 hour ago, mpbarrett said: BTW how do you stop water coming thru at the top right corner where the hood fixes to the windscreen frame.... Umm….. if you find out, let us know. I have a feeling it’s a “feature” rather than a “fault”. Though to be fair mine doesn’t leak much there and more on the passenger side. 1 Link to comment Share on other sites More sharing options...
JohnD Posted November 1, 2023 Share Posted November 1, 2023 (edited) Would this be another use for WD40? It works to diagnose/treat 'water pump squeak' when it's the fan belt on the pulley that's noisy. That might be due to some lubrication qualities of the product, but it doesn't seem to cause belt slip. If rain water were causing belt slip then WD's original property as "Water Dispersant No.40" might help! John Edited November 1, 2023 by JohnD 1 Link to comment Share on other sites More sharing options...
Nick Jones Posted November 1, 2023 Share Posted November 1, 2023 Something to look for on vee belt drives is the bottom of the pulley grooves getting polished. The drive is transmitted by the sides (the belt is supposed to “wedge”) so if the belt has reached the bottom either it is worn out or the wrong size (width) for the pulley. Link to comment Share on other sites More sharing options...
Sprint95m Posted November 1, 2023 Share Posted November 1, 2023 In the 90s when I returned a Dolomite Sprint to the road I had the same thing happen (in fact putting dipped headlamps on caused it to drop even further to less than 12V). On inspection of the belt, I thought it was sitting lower in the crankshaft pulley so I concluded it had worn taking surface rust from the pulley with it. A new belt did the ttrick. Ian Link to comment Share on other sites More sharing options...
rogerguzzi Posted November 1, 2023 Share Posted November 1, 2023 Hello All I always buy my belts from a bearing/Tranmision shop there you can get belts of allsorts of sizes and grades usually cheaper than the Big Boys Poor offerings! Even Gates make belts or at least under their name so probably better if the petrol pipe is anything to go by? Roger Link to comment Share on other sites More sharing options...
mpbarrett Posted November 6, 2023 Author Share Posted November 6, 2023 New Gates belt ordered (type 10A 1150). I am sure I had a new spare that I took on the 10CR last year but cant find it and I know it wont turn up until the new belt arrives... I did find a couple of new belts in the garage but they are a bit short and bring the alternator far too close to the front spark plug. Old one very shiny and lots of small cracks between the V teeth. All the pulleys are shiny so I guess it been slipping for a while.... No more adjustment on the bracket holding the alternator (could be stretch in the old belt) so will modify it slightly so that I can get a decent tension on the new belt. To be honest since last summer (2023), when I got it ready for the 10CR, I have done nothing to the Herald apart from just using it, and enjoying it, in all weathers. I think she really needs a long weekend of TLC, new fluids and tweaking..... The plan this year was to pull the engine and gearbox, change the clutch, change the gear ratios and stops some leaks from the engine. Its now November and it hasn't happened. But she is having some body work done in December, new door panel repair sections to repair the very bubbly new door skins fitted 10 years ago, and some other bits that have started to bubbly... I am afraid this might escalate to a full body respray. I have found a very good body shop who are happy to work on old cars and were looking for a Christmas project to work on. mike Link to comment Share on other sites More sharing options...
spitfire6 Posted December 7, 2023 Share Posted December 7, 2023 Hi. For £15 or less, you can fit a matchbox-sized module to your battery. View real-time voltage on your smartphone or export the data from it to view historic data. Example attached. Cheers, Iain. 50547B24188D_Dec 2023_Report.xls Link to comment Share on other sites More sharing options...
mpbarrett Posted December 8, 2023 Author Share Posted December 8, 2023 interesting, whats the module called and where did you get it from? I am Interested in putting one in our campervan. mike Link to comment Share on other sites More sharing options...
JohnD Posted December 8, 2023 Share Posted December 8, 2023 Teeth of the gods! That's interconnection overkill! If you have a accessory socket (fag lighter) then there are many USB sockets that will plug in, let you charge your phone etc, AND show the voltage on your loom. A cheap, multipurpose voltmeter! Link to comment Share on other sites More sharing options...
spitfire6 Posted December 8, 2023 Share Posted December 8, 2023 Hi Mike, Mine was from eBay: ANCEL BM200 Bluetooth 12V Battery Monitor Battery Tester For Android & IOS Be careful as prices vary a lot. Many other types could potentially be "better". Cheers, Iain. Link to comment Share on other sites More sharing options...
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