Newbie electrical woes

[morris]

Just a thought, but something similar (voltmeter bouncing all over the place) once happened to me. It appeared to be a bad earth between dynamo body and engine case. To be sure, try an earth wire from the dynamo cover screw to the frame. I run mine permanently like that now.
The blowing fuse could be nothing more than voltage dropping to low. As a rule of thumb you can say that when the voltage is dropping by let's say 20% (corresponding to 1.2V on a 6V system) amps will go up by 20% as the item in use at that time will draw more current (amps) to compensate for the loss in tension. A 15 amp fuse which normally would be fine will then blow. That's also the reason why wires on a 6V system have to be thicker than on a 12V system

[duTch]

...a bad earth between dynamo body and engine case. To be sure, try an earth wire from the dynamo cover screw to the frame. 

I ran a wire from the brush/field earth screw straight to the battery, the alloy end cover doesn't quite work the same

[Sam C]

Confession time (and this is very embarrassing):

I have a cheap multimeter. I was resting the multimeter on the frame by the battery when I took my previous readings. I'm an idiot.

Having moved the multimeter as far away from the bike as I can, I don't get that 'bouncing around' - move it closer to the bike and it returns. What an idiot I am. I guess the electronic ignition or something else is messing around with the multimeter.

So sorry for the wasted time and thoughts I've inflicted on you. What a tw*t I am (or for our American cousins: a d*ck).

I'll post another post in a second starting again - self flagellation has been done, I assure you.

[Sam C]

So, moving on!:

In case people of forgotten: original issue here is my battery drained flat mid journey. And weirdly, my indicators (that I put on) keep blowing their 10amp fuse mid journey (but not in garage), but a 15amp fuse is fine. I've taken a wrong turn with the 'readings moving around' (very embarrassing).... but I now have a better set of readings (taken at the battery terminals - with a new battery) that are shown below:

7.9v > 10 v at low tickover (higher end of this range when all electrical items are turned off, decreasing down with each item that is turned on i.e. the lowest reading is when lights, indicator and footbreak all turned on: 7.9v)

8.2v > 8.45v at high tickover (this time higher voltage being when all electrical items are turned on(!)).

8.8v > 9.2v at high revs (higher voltage when electrical items turned on - but couldn't work out how to do this with the footbreak too - not enough hands / good enough balance!)

So the question is: is that normal or, as it instinctively feels to me, a bit too high (as an average). Similarly, should there be this amount of variation - since I expected the regulator to just 'regulate' everything at about 7.8v all the time (unless the dynamo couldn't deliver enough to match the pull of electricity - perhaps when 'everything' is turned on, or revs drop below a certain range - in which case it would drop suddenly to something less than 6.25v).

Given this, an observation that seems very odd to me is that from the moment the bike is running the voltage jumps markedly from the 6.25v resting to something around the 9v - 10v mark) i.e. if I'm reading it right the dynamo is 'always on' and 'always delivering (a lot of) charge to the battery'. But surely that's just impossible?!

So... very.... confused.

Cheers all and apologies once again for wasting people's time with earlier post!

Sam

[muskrat]

G'day Sam. I'm not the best with electrickery but that sounds way too high. If the F & D wires from the dynamo are joined and run through a multimeter to earth and motor started it won't take long (a few seconds) for the reading to climb to 20v. Once connected to the reg it shouldn't exceed 7.5 - 8 volts even with nothing turned on. So your original problem would be the reg has cooked your battery.
I'll now duck for cover as more knowledgeable sparkies shoot me down. 
Cheers

[duTch]

 yeah Sam, what muskie said- should have no more than 8ish(?) for 6v.... I tried to add a Lucas reg page I have but file is too big..What reg and other specs (not the things on face for visualizing) do you have...?

[Sam C]

Thanks both.

Regulator is a modern job - I wonder if I've frazzled it when I was messing around fitting the indicators. Another is in the post - only £30.

I'll try fitting that to see if that helps.

I appreciate the quick response - cheers!

Sam

[muskrat]

Is the reg polarity sensitive? Make sure and flash the dynamo to be the same.
Cheers

[duTch]

Regulator is a modern job

 Whadda yea mean...'modern'..?  you mean non-mechanical...??

 When I say

should have no more than 8ish(?) for 6v

. that is subject to criticism from those who know..

[Johnny J]

Actually for a normal lead acid it should be max 7.2-7.5V, higher than that and the lead starts to boil away...the higher voltage the quicker.

[Sam C]

Yes the battery is a normal lead acid battery - not even a sealed one, I had to put the acid in separately.

The regulator is non-mechanical. It was swapped, I think when the previous owner (my step-father in law) fitted electronic ignition. It's one of these:

http://www.ebay.co.uk/itm/271947548026?ru=http%3A%2F%2Fwww.ebay.co.uk%2Fsch%2Fi.html%3F_from%3DR40%26_sacat%3D0%26_nkw%3D271947548026%26_rdc%3D1

I actually still have the old mechanical one, which is tempting to fit, but probably easier just to wait until the replacement arrives.

I think this is sounding very much like the right explanation for my woes - at least in terms of killing the battery.

Thanks all - responses have been amazing. Very much appreciated.

[Sam C]

And I'm going with the knackered battery as an explanation for the indicators' fuse getting blown too... unless there's any view that contradicts this?

Cheers all

Sam

[Greybeard]

There is a forum member that manufactures a really good voltage regulator. Don't buy a cheapie until you have researched the...can't remember the name at the mo. I'll go and do a search and come back here. Don't go anywhere.

It's the DVR2. It is dual voltage, virtually bomb proof and a very nice chap sells them.
www.dynamoregulators.com

[Sam C]

Thank you Graybeard.

I have a regulator ordered now. With the benefit of hindsight I should have waited and shopped around - I'll definitely give your man a go if there are any issues once new regulator fitted.

Cheers all - been a massive help so far.

Cheers

Sam

[trevinoz]

I don't think a knackered battery will cause a fuse to blow unless it has developed a short circuit which could cause a high generator current to flow.

Morris, if the voltage drops the current cannot increase to compensate if the resistance stays constant. Current is calculated by dividing the voltage by the resistance.