The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: bikerbob on 09.08. 2020 16:34
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I have a 1956 A7 with 6volt positive earth and DVR2 regultor. I have been away for a week and on return found the battery completely flat showing less than 1 volt on the multimeter everything was OK before I went away, have recharged the battery showing 6.4volts prior to fitting I let the battery stand for an hour before testing. 3 hours later the battery is completely flat showing under 1 volt no indication of dischrge on the ammeter. I did notice that when I was connecting the earth wire there was a couple of sparks which indicates to me that there is possibly a short circuit somewhere as everything is switched off. I now have the battery on charge again so using a multimeter how do I trace the possible short circuit where do I start, it does have a fuse fitted 10Amp also the battery is a 3 year old Cyclon battery.
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To start, after disconnecting the battery, set your meter to ohms*, (resistance) clip one side to the bikes negative connector and the other to the positive lead. The meter will show you if there is continuity, (a leak) across the battery output. Try working around the bike operating switches, disconnecting the dynamo etc. to see if anything stops that leak. Try swinging the handlebars from lock to lock to see if wires in the loom, next to the headstock are shorting.
What type of voltage regulator do you have on the bike?
*Test the meter by clipping its leads together. You should see a full deflection, (or close to zero reading on a digital meter).
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Thanks for that reply I have connected the multimeter as advised and the meter stays at 1 if you connect the 2 leads on the multimeter together it goes down to zero. so looks like I have a short somewhere tried switching on the lights etc but nothing happened also same twisting the handlebars. I tried connecting the multimeter to the leads on my A65 which is 12v as you advise and got a reading of 1114 whatever that is,so it confirms that I have a problem on the A7, I have a DVR2 regulator fitted and with the engine running it is showing a good charge with or without the headlights on but with engine not running and battery connected it does not show any discharge on the ammeter. Will have a look at the problem on Tuesday have to go out tomorrow will let you know if I find anything thanks again.
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So you do not have a full short circuit. If you did, the fuse should have blown.
Would the meter reading of 1 correspond to 1 Ohm, do you think? Your meter can probably be set to read Ohms and multiples of Ohms, right up to Megohms
The DVR2 is very trustworthy but one of the functions of the regulator on these bikes is to disconnect the dynamo windings from the battery when the engine is not running. Did you test with the dynamo connections unplugged?
Anyone else got suggestions?
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Here's one - some years ago we had a power cut down our road the the electricity co couldn't figure. I pointed out that they were looking in the wrong place with their meters, as the road had been re-aligned some 50+ years ago. But during the conversation the guy in charge told me how he found faults - go to the substation and put a 400A fuse in. He reckoned that usually showed up where the problem was.
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Too right RD. In that case it's the house that catches fire.
BB Charge up the battery, note the voltage, leave it by itself 'til tomorrow, see if it holds charge. If it's gone flat, simple replacement is the answer. Sparks on connection indicates a circuit somewhere, not necessarily a short circuit, but something drawing current. A parasitic drain can be measured by your meter put between either the supply terminal of the battery and loom connection or earth terminal of the battery and the frame. Current drain is then a case of disconnecting and isolating sections of the loom until you find the culprit. Switches and cut outs that don't, chafed or burnt insulation for example. GB's suggestion of a drain through the dynamo is an easy check.
RD's check will work, but you will need a new loom........
Swarfy.
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It's not a full short so I suspect the dynamo windings might be live.
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Which would point to a reg fault, and easily verified by disconnecting the dynamo connections. Do DVR2's fail in this mode?
RD, have you considered that the electricity board bloke was pulling your p*sser?
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Rex - no, the electricity bloke was an old school 'get it done' type of bloke. After most of a day trying to find a cable fault in the road seemed like a good idea anyway.
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I get the thinking about forcing a fault to happen; an intermittent fault can be very hard to identify.
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Just a quick update, got back a bit early today so went into the garage to start checkingfor faults. First thing I did was remove the horn,and was surprised to find that with the horn off the bike I was able to get a continuity reading on the multimeter across the battery terminals replace the horn and no reading so it looks like the horn is the problem. The horn is the original Lucas Alette horn fitted to the bike back in 1956 was still working even with the suspected fault. I have recharged the battery and fitted it back on the bike and will see if it discharges overnight without the horn on, the battery has been on now for about 4 hours and shows no sign of discharging whereas before it would dischagre in about 3hours. Have downloaded a Lucas workshop manual for the horn it explains how to dismantle and check the horn and reassemble. So that is my job for tomorrow if it cannot be fixed I will refit it to the bike but not wire it up and buy a cheap small 6 volt horn and fit it somewhere out of sight. hope this solves my problem thanks for the replies.
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Hi Bob
It is possible to fit a modern horn inside the old Altette but I think you may need to machine a little off the inside of the Altette body on a lathe. Can't remember where I read it but if may have been on "Taff the Horn's" site. Be prepared for some weird results when you Google it *whistle*
Jim
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I don't know if we are dealing with semantics or misreading the multimeter but measuring into the bike wiring, (battery disconnected) there should be no continuity; meaning, we do not want to see a circuit. A circuit when nothing is turned on will drain the battery.
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Quite correct GB. With the battery disconnected and everything turned off there should be no continuity into the loom. If there is, something is conducting when it shouldn't. The multimeter is reading a circuit through the loom, via a faulty component, to earth.
B B With the horn disconnected, continuity across the battery terminals is not what you are measuring. You are measuring battery voltage. If reconnecting the horn drops this reading then the horn is taking power when it should not and you have found your problem.
Swarfy.
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Now more baffled than ever. Last night took the horn off left the bttery on the bike overnight, at 10pm last night battery showing 6.12 volts 9am this morning showing 6.10 volts. With the horn connected to the bike there is no continuity across battery terminals ( battery disconected) disconnect the horn then there is continuity acroos the terminals. So thinking that the problem is the horn I started to dismantle the horn, basically there is very little you can do without major surgery as the internal parts of the horn are riveted in place so you are only removing the chrome rim and the diaphragm. Either side of the diaphragm according to Lucas you have a fibre shims these on my horn were completely finished. I checked as best I could the wiring inside the horn everything looked OK and tested for continuity. I rebuilt the horn and used thin Gasket paper instead for the fibre shims. The orignal shims just looked like very thin hard gasket paoer not fibre. Fitted the horn back on the bike,then before fitting the battery I did a continuity test across the battery terminals and got a reading which I did not have with the battery fitted before dismantling. So I thought job done. On fitting tthe battery I noticed that when fitting the positive earth lead there were tiny spaks not good but everything was working. Checked the battery voltage it has dropped from 6.12 to 5.84 in 20 minutes. Disconnected the battery and getting a continuity reading across the terminals with the horn still connected. Disconnected the horn wiring and am still getting tiny sparks when connecting the earth leadso have removed the battery and put back on charge. Will have another go at this problem tomorrow fed up athe moment will do as you say Greybeard and check Dynamo terminals should I get a reading doing a continuity check a croos the green and yellow wires after removing from the dynamo and should the battery be connected or not. Thanks
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There's always going to be continuity across the horn terminals as it's the horn button which makes the circuit to earth and which makes the horn sound. I suggest you either put the DVM on Amps or a small lamp and connect it in series with the bike's wiring with the battery in-circuit and see when the lamp goes out/DVM returns to zero as you disconnect components.
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BB The wiring diagram shows the horn to be a "one in/one out" design. In other words one terminal takes current in, through the guts and out from the other terminal. What you should be able to do is find continuity between the terminals, but no connection from either terminal to the horn body and from there to earth. No reading across the horn terminals means an break in the internal wiring. A reading from either terminal to the horn body represents the source of the parasitic drain. Having read your posts again I don't think the horn unit is the problem, but you have not said that it actually works.
Rex has a good plan there, a visual indication of current flow. Digital meters are sometimes too clever for their own good and old fashioned lumens from your low wattage test bulb may save the day. Other suspects are the dynamo, due to the cutout not working, as mentioned, and the brake light switch sticking and continuing to pass a small current, but insufficient to light the brake light bulb.
Swarfy.
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With the battery disconnected, set your meter to Single Ohms. Clip the meter leads to the wires that normally connect to the battery, so, you are looking 'in' to the bikes wiring. If the meter shows a reading it indicates a circuit is being made through the machine's electrics. If all switches are turned off there should be no circuit. The horn, light switch and brake switch if operated will show a circuit.
If the voltage regulator is faulty it may be allowing the dynamo windings to be making a circuit. Undo that screw on the end cap of the dynamo and (gently) pull out the two wires that are held in place by metal pluggy things. Has that made a difference?
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I have set the meter to 1ohm and connected the probes to the battery wires and the meter goes down to zero. Disconnected the green and yellow wires from the dynamo and with meter set to 1ohm probes connected to leads meter reads 1ohm. Set the meter to read amps then disconnected the earth wire from battery and placed the probes on the earth lead and the earth battery lead and it is showing 3.4 amps no wonder the battery is dischraging. Disconnected all the leads from the DVR2 regulator still showing 3.4 amps dischage, so I reckon this rules out any problem with the regulator. Strangely this discharge is not showing up on the ammeter but if I connect the battery up as normal and switch the lights on the ammeter shows the normal discharge for pilot and head light. So I think over the next few days I will have to start disconnecting each electrical component and do an amp test each time until I find the component that is causing the problem.
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The DVM showing a 3.4A discharge will be a lot more accurate than the bike's ammeter showing a normal discharge, so possibly the discharge is still present even with the lights switched. Have you tried the lights etc with the DVM in circuit?
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Measuring the discharge in amps on your multimeter is more accurate than measuring low resistances in ohm.
Also, if you are looking for leakage through solid state components, the multimeter’s applied voltage may be too low to disclose the problem.
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If the brake light is wired directly from the battery (not via the ammeter) I think I would disconnect that as your first next move and see if the discharge disappears when you repeat your last 'amps' test.
It or the horn are the most likely suspects, and you've checked out the horn. You know it's not the cut-out in the regulator, having disconnected all those wires but not eliminated the problem. The brake light has to be a strong possibility I reckon . . . . and at least is easy to check.
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Been out all day just got back read your post Groily so went into the garage pulled the 2 wires one that goes from the rear light to the stop lamp switch and the other wire from the stop lamp switch, done an amp test and no amp discharge so I thought problem located I replaced the wires and done a test again expecting to find a discharge again but no all OK. At the moment I do not seem to have a problem everything is working as it should no amp discharge. Now I rewired the bike about 4 years ago and all wiring is new except for the 2 short wires that come out of back of the rear stop tail unit as at the time it meant I would have to remove the rear number plate unit and to be honest the wires looked OK and at sometime in the past had been replaced whereas the rest of the wiring was original from 1956. So it looks now I will have to replace those wires as maybe they are causing the problem.Looking at the original wiring diagram there are only 2 wires but on a later diagram that I downloaded some years ago there is a sperate earth wire attached one of the light unit mounting bolts. But this still does not explain why at the moment there is not a problem when all I have done is disconnect those 2 wires and replaced them.
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You've moved them? That's often enough to remove a chafed short. Third (earth) wire to the rear light is a sensible mod.
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BB Now you've found a suspect circuit, the brake light switch is the likely cause, as the power goes to the switch first, then the lampholder, bulb, and earth return. A wiring fault between the switch and bulb would mean no brake light. Test the switch for operation, sticking on and a drain to earth before examining the lampholder wiring.
If you thought this is a hard one to solve, keep away from trailer lighting boards....they defy all known laws of physics.
Swarfy.
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Update, Spent the better part of yesterday removing the rear light bracket would have been easier if I had taken off the back wheel but managed to get at the 4 bolts only problem that I found was some previous owner had somehow snapped or cut the wire going to the stop light had had just twisted the wires together and covered with shrink tubing but it was not bared at all. Anyway renewed both tail wires and refitted. Removed the stop light switch it is an original switch and to dismantle you bend back 4 tabs and prise apart, inside it was a bit grotty but could not see anything basically wrong so cleaned it up and refitted. Everything is now back to as it should be no discharge showing and when engine running ammeter shows correct readings for lights on or off. But am still a bit uneasy as I feel that I have not actually found anything that I could say there is the fault and I have fixed it, will have to wait and see but if it happens again I will go straight to the stop light switch to test first. Thanks again to all those who have contributed to this post.
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That twisted connection with shrink-wrap sound like a possible source of a partial short if there was dampness in there. I can't recall if one of those wires are permanently live. I think the stoplight may be live to the bulb and get earthed at the brake switch.
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No, the brake light switch has a live feed, and when it makes it sends the juice to the rear lamp, the other side of which is earthed.
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Getting continuity with the horn disconnected and no continuity with horn connected is unexpected but not impossible. Could you take a photo of the meter while getting continuity (meter leads shorted together and with the meter at the battery terminals with batt. disconnected) showing both the meter display and it's control knob/buttons?
Meter readings and terminology can be confusing but photos tell a better story. Small sparks at 6V probably mean at least 1 amp of current but 6 watts would not produce enough heat to detect.