Club 80-90 Forums

I appreciate that I may have to test each component separately but they're all soldered together. I'm am reluctant to separate them as I am a complete amateur at soldering - I only started the art a week ago and haven't used it for disassembly.

I think you may be measuring "raw" DC, ie unsmoothed. You could try connecting a big capacitor across the output & seeing what voltage you get then?
E D I T; ghost beat me to it!

Ok,just got 24.2volts ac and 14,5volts dc on my 50 year old battery charger.
I think that the digital meter is reading the unsmoothed ac pulses,i didn't try with an Avo8 as its a bit cold in the garage.

OK I'll have a go at the 240v problem - mains plug wired wrongly?

Earleir ^^^ :-

Bubble Meister wrote:I measured from the rectifier output to the chassis. I got 9.51dcv AND 240acv

(bold by me)

Bubble Meister wrote:Measuring across the dc terminals of the rectifier with the cigarette lighter on I have 22.7acv!

Ummmm

So the difference between those two measurements is just that in one case you are going +ve off bridge to earth, and in the next you are going +ve from bridge to -ve on bridge, so the only difference is a path through a turned on SCR (which should show a DC voltage drop of ~ .7 of a Volt.

Though I think "we" should be forgetting measuring AC after the rectifier, as I mentioned above, because of the way a digital meter works on AC, the pulsed DC present will give meaningless readings.

So, two things to now consider:-
A) - Why is there 240V AC present on the DC side (that is not simply a misreading due to meter function on AC I suspect, as it is actually 240V AC mains obviously present). This could be an important safety issue.
B) - Do you still have issues with the actual output voltage (and importantly current) from the circuit to the battery? (as in with a good condition battery connected, what DC voltage is present on the battery terminals?

240? not 24volts?
I think the scr/zenner is to stop the battery pushing a voltage back into the mains charger.

Bubble Meister wrote:I measured from the rectifier output to the chassis. I got 9.51dcv AND 240acv

In view of Dave's test, are you sure it's 240V AC and not 24 V AC (aprox)?

E D I T, now Dave beet me to it

I've been told to get off the computer and do summat outside because it's really quite a nice day here today

Bolloc%s!
Autocorrect got in the way! The thread should have read:
I've just been out to the garage. I put the cigarette lighter on and measured some readings. I measured from the rectifier output to the chassis. I got 9.51dcv AND 20.1acv I could have sworn that I'd checked for ac power! The comment about the battery acting as the capacitor may make sense now.

I fear I may have miss led you all.
If I'm right, the RMS (dc equivalent) of 20.1acv (x 0.707) is 14.21.
The two voltages would be enough to charge a battery?
I'm sorry that this revelation has come so late on.


So its 20.1acv NOT 240acv as my autocorrect would have you believe!!

Bubble Meister wrote:Bolloc%s!
So its 20.1acv NOT 240acv as my autocorrect would have you believe!!

ghost123uk wrote: So, two things to now consider:-
A) Now defunct
B) - Do you still have issues with the actual output voltage (and importantly current) from the circuit to the battery? (as in with a good condition battery connected, what DC voltage is present on the battery terminals?

dave friday wrote: I think the scr/zenner is to stop the battery pushing a voltage back into the mains charger.

Would the bridge on it's own not perform that function?

ghost123uk wrote: B) - Do you still have issues with the actual output voltage (and importantly current) from the circuit to the battery? (as in with a good condition battery connected, what DC voltage is present on the battery terminals?

And if you answer "13.summat Volts" we are all going to kill you

if youd used a analogue meter!...
Im off to sit in the sun!

An oscilloscope is your friend.

dave friday wrote:if you’d used a analogue meter!...

Totally agree. I have an AVO8 too (and a cheap Maplins analogue I keep in the van).
I do own a very decent (yellow of course ) digi one, and a Thandar bench one too, but I use the analogue ones much more often.

dave friday wrote:Im off to sit in the sun!

I'm told to wash the van and do some gardening by her who must be obeyed. Good for my health apparently

To answer some aspects:
Yes I'm using a digital meter - it's a reasonable one too (around £40 when new).

Thanks Dave, is your charger a CF8 too?

Marlin Owner - The plug is wired up correctly, I think the type error of 240acv has led you to ask that?

Ghost - Question A can be, to some degree, due to the type error - and I can see how a digital meter would pick up pulsed dc with the meter set to ac
Question B - It still only gives out indicated 9dcv. However - this is on my bench and not connected to any battery. Im starting to think I should have made that clear right at the beginning.

I've purposefully being comparing the voltage at the dc terminals of the rectifier to the voltage from the +ve terminal of the rectifier to the chassis as this appears to highlight that the dc voltage drop is somewhere across the SCR / Zener arrangement.

I noticed that the cigarette lighter appeared to work well -if only 9dcv were powering it then it would be slow to heat up - the acv (pulsed dcv) must be having an effect!

Ive now resized some a couple of images: