Author Topic: Possible short circuit  (Read 533 times)

Offline bikerbob

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Possible short circuit
« on: 09.08. 2020 16:34 »
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.

Online Greybeard

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Re: Possible short circuit
« Reply #1 on: 09.08. 2020 16:53 »
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).

Offline bikerbob

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Re: Possible short circuit
« Reply #2 on: 09.08. 2020 18:25 »
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.

Online Greybeard

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Re: Possible short circuit
« Reply #3 on: 09.08. 2020 18:44 »
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?

Online RDfella

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Re: Possible short circuit
« Reply #4 on: 09.08. 2020 19:49 »
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.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

Offline Swarfcut

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Re: Possible short circuit
« Reply #5 on: 09.08. 2020 20:09 »
   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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Re: Possible short circuit
« Reply #6 on: 09.08. 2020 20:12 »
It's not a full short so I suspect the dynamo windings might be live.

Online Rex

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Re: Possible short circuit
« Reply #7 on: 10.08. 2020 08:46 »
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?

Online RDfella

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Re: Possible short circuit
« Reply #8 on: 10.08. 2020 13:25 »
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.
'49 B31, '49 M21, '53 DOT, '58 Flash, '00 Firestorm, Weslake sprint bike.

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Re: Possible short circuit
« Reply #9 on: 10.08. 2020 13:58 »
I get the thinking about forcing a fault to happen; an intermittent fault can be very hard to identify.

Offline bikerbob

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Re: Possible short circuit
« Reply #10 on: 10.08. 2020 17:11 »
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.

Offline lawnmowerman

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Re: Possible short circuit
« Reply #11 on: 10.08. 2020 18:54 »
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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1938 Wolseley 14/60
1955 Ferguson TEF20 tractor
1965 Ferguson 135 tractor
1952 Matchless G80 rigid
1960 BMW R60
1954 Matchless G80S
1955 Ariel 500 VH
1951 Sunbeam S7DL
1960 Matchless G12 with Watsonian Monza
......and loads of lawnmowers

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Online Greybeard

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Re: Possible short circuit
« Reply #12 on: 10.08. 2020 19:30 »
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.


Offline Swarfcut

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Re: Possible short circuit
« Reply #13 on: 10.08. 2020 19:56 »
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.

Offline bikerbob

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Re: Possible short circuit
« Reply #14 on: 11.08. 2020 15:27 »
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