Topic: Left ignition on o/n, NOW problems....#$%* (no longer: DANG)!

[Harry]

Hi

Well, Mr Potato Head here left the ignition on overnight, charged battery next day, but after 12 hours trickle charging the voltage was just 10V so I chucked the battery and bought a new, which now reads 12,8V. But, when I connect battery minus to frame, and connect my multimeter between the battery positive terminal and the positive cable on the bike....I get a reading of 7V with the bike switched off!!!! So, the bike is drawing current event though it is switched off! Switch on the ignition - 12V - switch off ignition - 7V again. Soooo, my massive powers of deduction drive me to conclude that I have a short somewhere...but where? Before I start searching, I remember reading that there is a good chance that you will blow some component if you leave the ignition switched on for an extended time - does anyone know what this component is and if it could cause a short which would give the symptoms described above?

[SteveD CB500F]

Hello Harry.

First.  Whats this "dang" stuff.  If you want to say #$%*, say it!

Second.  My son's Fiesta (I know it's a car but it still has engine, electrics etc - just 4 wheels) had a similar problem which was eventually traced to the starter.  The commutator was all clagged up with road dirt and drew enough current when off to drop  a new battery to 5V!!

Seriously, it shouldn't be too difficult to trace. Disconnect stuff until you find the culprit.

[Mikeshonda750F]

What sort of ignition you have on this beast? You could have welded the points together causing the coils to energize like crazy. Its entirely possible it burnt the contacts in your ignition switch up. Unlike modern machines which are ran by relays, most of the power consumed comes through the switch... try unplugging it and see if your draw goes away. Though it would be highly uncommon and unlikely that it would cause a voltage drop that bad... if one of your points was welded together, it would certainly chew up voltage... also feel for wires that are warm.. not many wires on your machine will be able to withstand that much of a current ramp without eventually burning up.

[Raul CB750K1]

With ignition off there is no way that any consuming devices are connected. You could have fried the coils, but they are not connected with ignition off.

Furthermore, you are not measuring correctly. Voltage is measured in parallel, current is measured in series. If you have only connected the negative lead, if you want to check battery voltage you have to measure between the battery terminals, with both leads connected. Your measurement is completely normal. If the bike resistance should have been 0 ohms, voltage should be battery - voltage dropped. 0 ohm drops 0 volts, so you should have read 12 V. As there are a lot of wires on the wire loom, and also the rectifiers and regulator, even with the high impedance of the voltimeter that measurement could happen.

If you want to check if there is something sinking current, make sure that the ignition is off, connect only negative battery lead and connect the current meter between battery and positive lead. Reading should be 0 amps. If you connect the ignition, headlight and coils will be connected and reading should jump to several amps, so make sure that your scale in the current meter is high enough.

Raul

[Mikeshonda750F]

The way i read what he is saying is he is measuring the voltage at the positive battery cable and at the frame... but i could be wrong.

[jesse]

i agree with raul on the voltage and current measurements.check for current draw as the bike is now then unplug the wires from your ignition switch then check again.you should not draw any current with the switch off.also ,what type and year is the bike?

[Harry]

Thanks for all your input! The bike is a late model 500K. Bike just clicked when pressing starter, but now suddenly fires up and runs just fine - suggesting points and coils are ok?

Voltage is measured in parallel, current is measured in series. If you have only connected the negative lead, if you want to check battery voltage you have to measure between the battery terminals, with both leads connected. Your measurement is completely normal. If the bike resistance should have been 0 ohms, voltage should be battery - voltage dropped. 0 ohm drops 0 volts, so you should have read 12 V. As there are a lot of wires on the wire loom, and also the rectifiers and regulator, even with the high impedance of the voltimeter that measurement could happen.

I cleaned my connectors, and now when I  connect the volt meter between battery and positive lead the reading is 11V with ignition off (up from 7V, 12.8V with ignition on.

If you want to check if there is something sinking current, make sure that the ignition is off, connect only negative battery lead and connect the current meter between battery and positive lead. Reading should be 0 amps. If you connect the ignition, headlight and coils will be connected and reading should jump to several amps, so make sure that your scale in the current meter is high enough.

If I connect the current meter between battery and positive lead with ignition switched off I draw a current of 0,23mA (if I am reading the meter correctly). With the ignition on the current "jumps" to only 0,27mA. I dunno, perhaps there is no current draw after all?? I would just hate to connect the battery only to have it drain overnight and be damaged like the previous battery ($$$).

[Ibsen]

If I'm not mistaken, when you turn on the ignition, you also turn on the power to the voltage regulator?

http://oldmanhonda.com/MC/wiring500.html

[Harry]

Furthermore, you are not measuring correctly. Voltage is measured in parallel, current is measured in series. If you have only connected the negative lead, if you want to check battery voltage you have to measure between the battery terminals, with both leads connected. Your measurement is completely normal. If the bike resistance should have been 0 ohms, voltage should be battery - voltage dropped. 0 ohm drops 0 volts, so you should have read 12 V. As there are a lot of wires on the wire loom, and also the rectifiers and regulator, even with the high impedance of the voltimeter that measurement could happen.

Sorry, still dont understand: if I connect the volt meter between battery and positive lead, and the ignition is off, why do I get a reading (now) of 11V instead of 0V?

[Harry]

If you want to check if there is something sinking current, make sure that the ignition is off, connect only negative battery lead and connect the current meter between battery and positive lead. Reading should be 0 amps. If you connect the ignition, headlight and coils will be connected and reading should jump to several amps, so make sure that your scale in the current meter is high enough.

Raul

Hmmm....I checked with a cheap multimeter with a scale up to 2000mA - is this high enough or did I fry the multimeter?

[Ibsen]

Try to disconnect the rectifier. That is the only unit that still gets power when the ignition is off.

[bryanj]

2000ma is only 2Amp so you probably fried the meter. are you doing all the voltage checks accross the two battery terminals? or +ve to frame. Email me direct Harry as I am terrible at going back to posts. I used to do all the electrical work in the dealers i was at so i ought to be able to get the brain working!!

[Harry]

Try to disconnect the rectifier. That is the only unit that still gets power when the ignition is off.

Oooh, yes, rectifier: 3 yellow, 1 green, 1 black cable. Took off the green cable and volts fell from 11 to 0.25! According to oldmanhonda this cable goes to the alternator. Anybody able to diagnose this? Perhaps I should start the motor and run the revs up to 5k for a few minutes and see if this "unsticks" the alternator?

[bryanj]

Harry green on the RECTIFIER is a ground wire its the green on the REGULATOR that goes to the alternator. You relly need to peruse the manual carefully to understand the charging system. It took me several readings to "get" it.

[Harry]

Harry green on the RECTIFIER is a ground wire its the green on the REGULATOR that goes to the alternator. You relly need to peruse the manual carefully to understand the charging system. It took me several readings to "get" it.

Really? Thanks, the diagram is a bit confusing on this point. But clearly, the rectifier is the only component connected to the battery BEFORE the ignition switch (thanks Ibsen), so somehow there is a flow through the rectifier to earth, right? So the rectifier may be shot, I will try the resistance test described by Mr. Clymer later this evening.

Watch this space....

[Harry]

Well now, I have been monitoring the battery and it has held a steady 12.70 volts now for three days so it seems all is (was?) well. I havent got wiser as to where the electrons are/arent dribbling around, but as they dont seem to be going anywhere far away, I will leave well enough alone!

[bryanj]

If there is a current flow with ignition off it could be the rectifier. The starter solenoid is also before the switch--in fact both the loom +ve and the rectifier +ve are connected at the solenoid (also the fuse+ve from memory)