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AC/DC oddities.

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AC/DC oddities.
Started at 07:02pm on the 28th July, 2018 by another Allan
another Allan Subject: AC/DC oddities.
My bike is a 2003 iron barrel (originally a 350) with AC/DC electrics. Separate regulator and rectifier.
I've had various issues with it, mainly sorting out what the first two owners did to it. Finally, it seems to be running quite well, apart from the electrics.
Basically, the engine will cut-out or misfire at low revs when slowing down for junctions. I ride with the lights on and the bike is fine until I use the indicators and brake, when it will misfire/backfire and ultimately cut out until I turn off the indicators.
Using indicators and braking without the lights on does not cause any problems.
It is as if the alternator/battery cannot cope at low revs with the electrical load posed by everything on at once!

Anyway, I have done some checks:
Battery nearly new and shows 12.9 V and does not drop when left unused.
AC output from alternator checked and is an easy 30 Vac.
Voltage (ac) at lights checked with ac regulator in place and all ok.
DC output from regulator (measured at connector) 13.5 V at fast tickover, rising to 14.5 V at high (sic!) revs, BUT voltage across battery terminals does not rise above 12.8 V.

From this, I deduce that the alternator and rec/reg units are doing their job, but the battery is not receiving the voltage put out by the rec/reg.

The battery is well-earthed, and does not go flat in use.

Another oddity is the headlamp flasher. Although the lighting is AC in theory, the sidelights, rear light and headlamp flasher work when the engine is not running, so must be DC.
However, using the headlamp flasher (engine off) produces a yellow gleam. If the engine is ticking-over, using the flasher makes the engine stop!

Also, switching on the sidelights (engine off) and measuring the voltage at the bulbs only records about 5V.....Volts are disappearing somewhere!

Could someone please point me in the right direction?
Posted: 07:02pm 28th July, 2018
Aethelric Subject: AC/DC oddities.
The DC regulator does not output DC. It regulates the AC voltage before it goes to the rectifier. This is not to be confused with the AC regulator which is completely separate and regulates the AC voltage for the headlight. Do you mean the output from the rectifier or the regulator is 13.5 - 14.5. If it is the rectifier, that is ideal.
If the battery is at 12.9V it is getting some charge, but not enough. It sounds like you have a high resistance between the battery and the rest of the circuitry. Could be in the fuse connections, or the connectors up to the ignition switch or between the ignition switch.
Get a sewing needle, attach a wire to it, and you can push it through the insulation to measure the voltages before and after connectors and switches. You should be able to find the lost volts.
Posted: 07:28pm 28th July, 2018
Jamesy Subject: AC/DC oddities.
Listen up Aetheric.The AC voltage from the alternator goes to the rectifier where it outputs the converted DC voltage to the regulator.The regulator controls a steady dc voltage to recharge the battery.The headlights take an AC voltage directly from the alternator.
Posted: 09:13pm 28th July, 2018
Jamesy Subject: AC/DC oddities.
Stick with your multimeter for checking voltages,resistance etc.I had a weird electrical fault a while back and it was all down to a faulty HT lead.Check you have a nice blue spark then take it from there.
Posted: 09:39pm 28th July, 2018
Gwilly Subject: AC/DC oddities.
Check the rear wiring harness where it runs from the frame to the rear mudguard and around. There is a plug, also check for chaffing from the tyre..
Posted: 10:32pm 28th July, 2018
Aethelric Subject: AC/DC oddities.
The standard regulator consist of two thyristors connected in parallel in opposite directions directly across two wires from the alternator. The regulator is also connected across the same connections to the alternator and provides a rectified DC output which charges the battery and powers the DC electrics. There is also a voltage sensing circuit in the rectifier which feeds back to the regulator. When the voltage reaches around 14.4V the voltage sensing circuit feeds back to the regulator and the thyristors are switched on, short circuiting the alternator coils.
This means that the regulator does not dissipate much power as it is only ever short circuit or open circuit. The rectifier only sees the power used by the battery charging and the lights and not the full power of the alternator.
Most bikes have both circuits in the same unit, (they work the same way) but not post 1995 Bullets.
This means if you disconnect the Bullet regulator, or it goes open circuit the rectifier will still work and charge the battery - but it will overcharge it if used for a long time.
As you say, the headlights take an AC voltage direct from the alternator - there is a separate AC regulator fitted across these windings too so that lights are bright at medium revs but not blowing bulbs ar high revs.
Of course these bikes get modified all the time and yours may be non-standard.
The advice I offered was my best GUESS. I'm sure another Allan will get it sorted and the solution will be another useful piece of data for is all.
Cheers, A.
Posted: 11:44pm 28th July, 2018
Aethelric Subject: AC/DC oddities.
Jamesy, I apologise for my long winded reply. I have been commenting on two threads and I mistakingly though your comment was on the other one.
Using a needle probe though is a well established method of tracking down dodgy connectors without having to prise take them apart.
Posted: 12:13am 29th July, 2018
Jamesy Subject: AC/DC oddities.
Aetheiric you stated in your post quote " The DCregulator does not output DC.It regulates the AC voltage before it goes to the rectifier".Sorry mate that's utter tosh.In my 48 years of electrical fault finding on motorcycles and in the work place I have never had to stick a needle in a cable to diagnose a fault.
Posted: 07:51am 29th July, 2018
another Allan Subject: AC/DC oddities.
Thanks for the replies, chaps.

I think my comment about the dc voltage measured at the regulator was a bit imprecise.

I meant at the 4-way connector between the loom and the rectifier. Sorry if I caused confusion.

Anyway, my measurements show that the alternator and rec/reg are working correctly, both ac and dc.

I'll take the advice given and work through all the connections and switches.
My multimeter will be my friend!

As a slight aside, I have never come across such thin wiring as that within the casquette. Most of the leads between switches, lights etc are very thin. Even the connections to the ammeter seem very thin considering the relatively high currents they can pass.
Posted: 09:53am 29th July, 2018
Aethelric Subject: AC/DC oddities.
Jamesy, have it your own way. The workshop manual must be wrong then. Maybe if you invested in some Needle Probes you could speed up your fault finding. I have used them for more years than I care to remember.
Allan the wires are thin, but there is not much current. You can make up a probe using a needle some wire, and insulating tape. Start at sidelight where you only have 5V and check each side of the connectors back to the battery until you find where you ar losing the other 7V. If it takes a while you may need to connect the battery charger.
Or you could take each connector apart until you find the corrosion which is the probably cause. You may be lucky first time. Either approach will work.
Posted: 10:41am 29th July, 2018
another Allan Subject: AC/DC oddities.
Thanks Aethelric.
I've heard of needle probes used with a meter, so I'll give it a try.
Posted: 10:54am 29th July, 2018
Jamesy Subject: AC/DC oddities.
What workshop manual is that? A needle,wire and insulating tape? totally unnecessary.There are plenty of connectors on an Enfield to check voltage and continuity.Sorry I would rather do it my way than start piercing insulation on any electrical cables.
Posted: 11:56am 29th July, 2018
Aethelric Subject: AC/DC oddities.
This manual Jamesy.
Each to his own on the needle probes.
Cheers, A
Posted: 12:33pm 29th July, 2018
Jamesy Subject: AC/DC oddities.
Image and video hosting by TinyPic And on the previous page this very brief explanation.
Posted: 12:38pm 29th July, 2018
Jamesy Subject: AC/DC oddities.
As you can see from your diagram the AC voltage in the first instance is fed to the bridge rectifier then smoothed and zener regulated for delivery to the battery.All really basic stuff.
Posted: 01:00pm 29th July, 2018
Aethelric Subject: AC/DC oddities.
Well Jamesy you can either believe the explanation on page 61, or believe the schematic on page 62 which is pretty unambiguous. Also it states "the regulator can be disconnected from the circuit and charging will take place without any regulation of current." It could not do that if the regulator was after the rectifier.
The manual IS a bit flakey, I don't think it mentions the regulator for the AC lighting at all and the diagram is for DC only system.
However that is the regulator method that most fairly low power motorcycle regulators work nowadays although the rectifier and regulator are usually mounted together in the same package.
Posted: 01:07pm 29th July, 2018
Aethelric Subject: AC/DC oddities.
Jamesy, that zener is not regulating by itself. It is feeding a signal back to the thyristors SCR1 and SCR2. R1 and R2 will be chosen to compensate for variations in the zener, They are usually only +/-5%.
Posted: 01:10pm 29th July, 2018
Jamesy Subject: AC/DC oddities.
I know the zener is not regulating by itself.You can run the bike on the rectifier as stated but it would only be for an emergency short period of time before cooking the battery.I learned all this basic electronics back in 74 on power supply units which I had to build.I am thinking you are looking at that diagram and coming up with your own analysis/explanation.Which is wrong.
Posted: 01:32pm 29th July, 2018
Aethelric Subject: AC/DC oddities.
I'm sure I'm interpreting right Jamesy. I was an electronic engineer for most of my working life (retired now), mostly in design, but also in test and maintenance. There is not really another way to interpret the diagram correctly.
You are thinking of the older power zener diode regulators where it IS just a zener across the output of the rectifier. That was used on british bike for a while. The Bullet does not use that system.
Posted: 02:50pm 29th July, 2018
Jamesy Subject: AC/DC oddities.
Are you kidding me on.An electronic design engineer without a basic knowledge of an AC to DC power supply.
Posted: 11:48pm 29th July, 2018

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