jagnut66 Posted February 11 Report Share Posted February 11 (edited) Hi, Well, one thing has remained consistent during my Heralds hiatus, that is an ongoing power drain issue. I have disconnected various items today in order to eliminate them but one thing has made me do a double take. To start at the beginning, the first thing I did today, having had the battery on charge overnight, was start her up and allow the engine to run for half an hour. During which I put my meter across the battery, it read about 14.5 volts, I switched off and it dropped to about 13.5, then carried on dropping whilst I watched......... I disconnected the alternator (to rule out backflow), no effect. The coil, no effect. The radio, no effect. The starter motor, no effect. Then I disconnected the positive lead from the starter solenoid. with just the earth lead connected to the battery the volt reading started to go back up!? I walked away and left it a while to make sure it wasn't my imagination. It had dropped to a reading of 13.19 volts. It now read 13.27 volts. So what is going on? I'm hoping someone on here can offer some clues or point me in the right direction. Best wishes, Mike. Edited February 11 by jagnut66 Link to comment Share on other sites More sharing options...
JohnD Posted February 11 Report Share Posted February 11 You have a short from the starter solenoid. But that doesn't tell you much, as the power supply to the rest of the car comes via that. See: Your analytical method is excellent, it may be easier to use your meter, if it can measure currents, but beware - most cheap multimeters can only tolerate less than 10A, and your short drops bettery volts so quickly it may be more. Good luck! John Link to comment Share on other sites More sharing options...
jagnut66 Posted February 11 Author Report Share Posted February 11 (edited) 14 minutes ago, JohnD said: You have a short from the starter solenoid. But that doesn't tell you much, as the power supply to the rest of the car comes via that. Thanks John. I take it there are no 'common causes' to check out first? Best wishes, Mike. PS: The link to the colour circuit diagram is really helpful, I have copied onto my PC, so I can print it off -- at some point Hetty may well get a new wiring loom. 👍 Edited February 11 by jagnut66 Link to comment Share on other sites More sharing options...
johny Posted February 11 Report Share Posted February 11 You could try pulling fuses one by one to narrow down the search.... Link to comment Share on other sites More sharing options...
jagnut66 Posted February 11 Author Report Share Posted February 11 The only fuses my Herald has are the inline ones that I've added...... I was under the impression that the Herald's creators didn't believe in them...... 😉 One thought that occurred to me as I wandered back to her was that, as she is still draining the battery with the ignition off and key removed, then it must be one of the permanent live circuits at fault. Or is my reasoning in error here? Best wishes, Mike. Link to comment Share on other sites More sharing options...
foshi Posted February 11 Report Share Posted February 11 you dont have anything like a aftermarket boot light switch , or faulty brake light switch you would notice if the brake lights where on though . Link to comment Share on other sites More sharing options...
johny Posted February 11 Report Share Posted February 11 Unfortunately I think your alternator is a later addition so your wiring isnt standard however, yes, most likely to be something in the permanently live system which is basically horns and lights.... Link to comment Share on other sites More sharing options...
jagnut66 Posted February 11 Author Report Share Posted February 11 30 minutes ago, foshi said: you dont have anything like a aftermarket boot light switch No, nothing like that. I do have ancillaries though, high level brake light, reversing light, gauges etc. But nothing that isn't dependant on the ignition being on, with the exception of the radio's memory circuit and I've already checked that. However, you have reminded me to include the door courtesy light switches in my 'things to check' list. 👍 Best wishes, Mike. Link to comment Share on other sites More sharing options...
jagnut66 Posted February 11 Author Report Share Posted February 11 3 minutes ago, johny said: Unfortunately I think your alternator is a later addition so your wiring isnt standard however, yes, most likely to be something in the permanently live system which is basically horns and lights.... Thanks Johny. Would my (1970) car have been positive earth originally? Best wishes, Mike. Link to comment Share on other sites More sharing options...
johny Posted February 11 Report Share Posted February 11 Sorry missed that, wouldnt have thought dynamo and +ve earth so late but its possible.... Link to comment Share on other sites More sharing options...
Wagger Posted February 11 Report Share Posted February 11 You can have a dynamo with +ve or -ve earth. Just depends on what mods have been done. I did a complete electrical conversion on two 1950's Morris Minors, one with a dynamo and fitted an alternator to the other. The dyno version just required polarising everything in the opposite direction. Buy decent current clamp for tracing current drain. It will pay dividends. No risk of burning out a meter and nothing needs disconnection. If nothing is obvious suspect bakelite bits in any old component. If it has become wet in the past, it can start tracking and produce a carbon path that will become a conductor. As carbon heats, the resistance drops too and bits become hot. That can be a give away. Left too long it can burn. Unless something has been connected wrongly, these cars do not have permanent loads. Any interior lighting would be the first thing that I would check. 1 Link to comment Share on other sites More sharing options...
JohnD Posted February 11 Report Share Posted February 11 Wagger absolutely right! A "clamp meter" has a 'claw' that is closed - loosely! - around the wire to be tested. It reads the current without even touching it! Incredible! I don't have one, so I looked to see and they come at all prices, £10-60! So affordable to mmmmmmmmmm-Could do - but! What price for a 'decent' one, Wagger? John Link to comment Share on other sites More sharing options...
PeteH Posted February 11 Report Share Posted February 11 (edited) I have this one:- https://www.ebay.co.uk/itm/155503862555?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338749386&toolid=20006&customid=GB_12576_155503862555.143192034695~2063183476472-g_CjwKCAiA_aGuBhACEiwAly57Mc2zrm2LKhUM-hQRGi9NHe0oqAvsJewhiDUORFxpU3Rjx7BZwW8z_xoCiToQAvD_BwE Back when I bought it it was around £35. Originally to try and measure DC m-A currents in the solar system on the last Motorhome. But has been quite usefull since. Pete Edited February 11 by PeteH Link to comment Share on other sites More sharing options...
johny Posted February 11 Report Share Posted February 11 Yes beware not all models do DC current measurement and even the ones that do might not go down to the levels we're interested in.... 1 Link to comment Share on other sites More sharing options...
jagnut66 Posted February 11 Author Report Share Posted February 11 2 hours ago, PeteH said: I have this one Added it to my list, I will get one after payday next week. I take it that, with everything switched off, I am looking for anything flowing out, say on the headlamp wiring for example. Best wishes, Mike. Link to comment Share on other sites More sharing options...
Wagger Posted February 11 Report Share Posted February 11 4 hours ago, JohnD said: Wagger absolutely right! A "clamp meter" has a 'claw' that is closed - loosely! - around the wire to be tested. It reads the current without even touching it! Incredible! I don't have one, so I looked to see and they come at all prices, £10-60! So affordable to mmmmmmmmmm-Could do - but! What price for a 'decent' one, Wagger? John JohnD, Mine cost £100 fifteen years ago, but I needed a good one then for work. Just make sure it will measure DC and choose one with ranges from 20 to 200 amps. If you want to measure starter motor currents go for 500 amps. You don't need high accuracy if looking for leakage and drain as you really want a reading of zero. With some it is best to reverse the orientation and average the two readings. 1 Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 12 Report Share Posted February 12 why not put a bulb in series with the battery lead/post and with a leak drain it will illuminate just keep disconnecting till it goes out cheap and reliable Pete Link to comment Share on other sites More sharing options...
johny Posted February 12 Report Share Posted February 12 Difficult to know what size bulb to use and then its resistance in series would reduce the leak current flow anyway☹️ Link to comment Share on other sites More sharing options...
Casper Posted February 12 Report Share Posted February 12 (edited) Wipers, horn. radio and courtesy lights are 'earth switched' (ie have supply all the time) while the rest are (AFAIR) 'supply switched. Might be worth checking early on in your investigations C. Edited February 12 by Casper Link to comment Share on other sites More sharing options...
JohnD Posted February 12 Report Share Posted February 12 10 hours ago, Wagger said: JohnD, Mine cost £100 fifteen years ago, but I needed a good one then for work. Just make sure it will measure DC and choose one with ranges from 20 to 200 amps. If you want to measure starter motor currents go for 500 amps. You don't need high accuracy if looking for leakage and drain as you really want a reading of zero. With some it is best to reverse the orientation and average the two readings. Thanks, Wagger! Link to comment Share on other sites More sharing options...
Mark B Posted February 12 Report Share Posted February 12 (edited) Just been through this process on my van. Convinced for the last few years that I had bought a dud battery as it went flat in cold weather if unused for a few says. John D suggested a parasitic drain, which I had really dismissed. With the earth lead disconected I bridged between the earth lead and negative battery post with a 12v test screwdriver. With everything off, surprise, surprise, the 12 volt (cheap Halfords type) test screw driver illuminated. For some reason I don't understand, the light pulsed. Pulled each fuse alternator etc. One at a time. Long story short it was the radio at fault. Lesson learnt 'again' don't assume anything. Edited February 12 by Mark B Link to comment Share on other sites More sharing options...
Wagger Posted February 12 Report Share Posted February 12 53 minutes ago, johny said: Difficult to know what size bulb to use and then its resistance in series would reduce the leak current flow anyway☹️ Pete's advice is good. If you place a voltmeter in parallel with the bulb, even if it is not glowing, it should read zero unless there is current flowing. Bulb resistance varies extremely with luminosity, so use a known resistor if you have one then you can use V/R (Voltage reading divided by resistance value) to calculate the current. Link to comment Share on other sites More sharing options...
johny Posted February 12 Report Share Posted February 12 Might be easier just to put your multimeter, set to measure amps, in series? Link to comment Share on other sites More sharing options...
Pete Lewis Posted February 12 Report Share Posted February 12 radios./ alternator diodes/ the unknown cubby box or boot lamp are the most prolific contenders . Pete Link to comment Share on other sites More sharing options...
Wagger Posted February 12 Report Share Posted February 12 1 hour ago, johny said: Might be easier just to put your multimeter, set to measure amps, in series? Yes, but if you accidentally hit the starter or a big load you might destroy your meter. Been there, done that when I was 18. 1 1 Link to comment Share on other sites More sharing options...
(1).thumb.jpg.eb39d849c6ebf5edd08bacd462932af0.jpg)
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now