Zig CF8 poor output

[dave friday]

I had an oscilloscope once but I had to move away and we lost contact!

[Bubble Meister]

I do appreciate everyone's help and appreciate that everyone has more important things to do! I'm off for breakfast before work (late start). Hopefully its all starting to make sense. I've certainly learnt something - that the acv setting on a digital meter can pick up pulsed dcv!

From the photos you will see that its been tweaked: the current protection device is now wired straight after the rectifier: the reason is that I wanted to b@stardise the Zig to run my leisure DC power system when 240acv was available. This would be achieved by a relay that changed the power source from the battery to the Zig. This now presents a problem with smoothing as I never intended for the Zig to power the battery!

I have a Ring Smart Charger that I was going to use to maintain the battery (whether camping or at home). It defaults to 2Amps so I don't think its sufficient to power the DC power system.

This may be one of my less fruitful concepts!

[Oldiebut goodie]

I have a couple of Ring chargers - if you have a heater (Eberspächer or Webasto) be aware that the chargers can push the voltage over the voltage limit for these so you are left puzzling why the heater is cutting out when you have plenty of power! I have seen this numerous times as I use these chargers to keep my spare batteries topped up that I use for testing heaters in the workshop. An old style non-smart charger may be preferable for this scenario. (Acting more as a power supply)
That defaulting to 2 amps is the same on one of mine and is a pain and not very smart! It is my smaller one - a 16 Amp one.

[ghost123uk]

Just popped in for a cuppa and wish to add:-

The fag lighter you used to test it likely pulls more current than the transformer is designed for (as it a modest battery charge unit) so the measured DC voltage will be significantly less than when the unit is connected to a battery. This is the normal nature of a non regulated current limited power supply / charger.

[dave friday]

Perhaps the scr/zenner is a "soft start circuit"

[ghost123uk]

Soft start circuit would require a capacitor in it

How are "we" getting on with this now

[dave friday]

I thought that perhaps that the resistor would provide a bit of a delay?

[ghost123uk]

No Dave, actually, thinking about it, it wouldn't work as a soft start even with a cap because an SCR is an "avalanche" device, not a linear one, as soon as the gate voltage reaches the threshold (usually .7 of a volt) it turns on like a switch, not gradually like a transistor. It also stays on even if the gate voltage disappears, it turns off when the current drops below a certain (usually pretty low, i'e. milliamps) level.

So I / we still don't understand what that bit of the circuit is doing

[dave friday]

Hi John,i talked to a very helpful guy at Zig who said its a safety bit/feature to stop the transformer burning out...in case of spikes on the mains etc!
He didn't explain the circuit action!
So a bit closer,but no cigar!

[Bubble Meister]

Hi Gents, Sorry I went quiet - had a bit of a rush on at work.

Thanks for all the suggestions. I think the SCR and Zener are probably a safety feature but I haven't a clue how. I understand that the ac measurement is actually a peak dc so RMS is around 14dcv - this would be smoothed by the battery, acting as a capacitor. I think its safe to say that the unit is actually working: a combination of 9dcv and 14dcv pulsed. Its a shame that the function of the SCR and Zener are still elusive.
Anyway, I've just gone and done some measurements. I used the Zig to operate a 30A relay (a lighter load than the cig lighter)(note: the 15A over current device never tripped when the lighter placed a load on the system)

With the negative probe of my meter kept on the chassis, I made the following measurements - referenced to the schematic and selecting both ac and dc on my multimeter:

Rectifier DC +ve terminal 11.17dcv 24.1acv (actually pulsed dc)
Rectifier DC -ve terminal -0.77dcv 0acv
SCR cathode / resistor terminal -0.72dcv 0acv
SCR Gate / resistor / zener terminal -0.05dcv 0acv
SCR anode / zener / chasssis terminal 0.02dcv 0acv

To fit a capacitor for smoothing I would first need to be assured of the function of the SCR and Zener - I don't want to affect their function.

[Oldiebut goodie]

Nothing wrong with pulsed dc for charging a battery, in fact it is recommended by some people.

[ghost123uk]

Yes, I agree, leave it as standard. Adding a cap might / would increase the DC voltage at the output to a level that might be too high. (peak to peak voltages being stored by the capacitor).

[windy]

He stated that he was intending to run leisure equipment from the Zig unit whilst it was being powered by 240v AC, (Not the leisure battery) so he would need the addition of a capacitor to smooth the DC for this,

But....

if he was using it to charge a battery, adding a capacitor would make very little difference, as the battery is itself a huge capacitor.

PS. Personally I don't think its a good idea to run anything from the Zig unit in the way he was proposing.

[Bubble Meister]

The only problem is is that it doesn't suit my application- to directly power the leisure system. I'll have to rethink my plan!

[Oldiebut goodie]

You can get 18/20 amps @ 12v from computer power supplies easy enough, you just need to trick them into starting up. Plenty of info for this on the interweb thingy. I've got a load of new power supplies in my shed that would be suitable but a lower output I think. You then have the benefit of a 5v and 3.3v source also. (also -12v also, usually only 1/2 amp though but useful if you want a low current 24v source utilizing a spare +12v which is normally present)