6 volt shunt regulator

[David HK]

I have been given a batch of 6 volt (open circuit around 9 volts) photo-electric panels and have reflected on the need for a shunt regulator for inclusion in some of the circuits. They have come from Shenzhen (China) and I believe thay were intended for stand alone garden light fixtures. I don't want to connect them up for 12 volt series use and would prefer to keep them at 6 volts.

Currently I am using the Chris Greacen design shunt regulator for 12 volt systems.

Can anyone offer ideas for a simple circuit?

No doubt ghurd will be clever enough to come up with something and such an item may be a useful complemenmt to his existing designs.

David HK

[ghurd]

Hi David,

No problem.  Simple tweak of the circuit.

Need to know the regulation voltage, the intended assembly output or Isc current.

What type of battery?  AA / D nicd or nimh?  Just curious.

ghurd1 at yahoo dot comm... that is ghurd(one)

G-

[David HK]

Thanks for the quick reply ghurd.

What I have for you in an instant is:-

Open circuit voltage 9.35 volts

Battery Sealed Lead Acid 6 volts 4Ah.

No idea of isc.

I propose to use the batteries for decorative lights or to operate a FET (IRF Z44 or IRF 530)to switch larger loads - no idea what at the moment. Am just trying tp plan for the future.

regards,

David HK

[David HK]

ghurd,

The photgraph gives an idea of the hotch potch of panels avaialable. The square/rectangular ones are for 12 volts, the round ones  - centre two panels - for nominal 6 volts.

regards,

David HK

[ghurd]

A 6V SLA is easier for me than 4 nicds.

Regulation at 6.9V?

Isc really does not matter if 4AH is suitable.

IRFZ44 and IRF530 are not the best choices.

I have logic level TO-220s here that would be better suited to a 6V system.

G-

[ghurd]

Quite an assortment!

Isc is low enough for my idea.

G-

[David HK]

ghurd,

You're much more expert than I am at this.

I would, as a matter or course, follow more expert advice as you have illustrated above. I have no idea what you have in mind for the TO 220's

David HK

[ghurd]

Hi David,

If you use my standard circuit,

Change...

ZD1 to a jumper wire.

R4 68 or 82 ohm resistor.

RX and R3 to something around 25K~30K. (Not a critical value for your purpose)

Power On Indicator Green LED will barely glow, but it is a waste of a ma.  You could leave it out, or put a little switch on it, if you are concerned with the wasted ~1.5 ma.

The Yellow "dumping" indicator LED will barely glow.  But it is only On when dumping.

May want to change it's resistor (R2) to 1K so the LED is brighter.

I can not imagine wanting to use the tiny bit of extra power to heat water!

I suggest using a circuit with no dump load.  Simply short the panel output before the blocking diode.

I would use a logic level FDP7045L TO-220 power mosfet to short the panels, mostly because they are nice and I have a whole bunch here.

I would use a Schottky blocking diode.  I feel the panels are on the edge of working voltage for best output, and a Schottky may help (a little) as the battery gets near full charge. And I have a whole bunch of those here too.

All the panels can be paralleled.  Then to the power fet. Then to the blocking diode.

Here is a generic sketch.  It shows 3 paralleled panels.

You will only need 1 power fet and 1 diode.

http://www.otherpower.com/images/scimages/2050/NoLoadSlrKit.gif

The controller can be very small with no dump load solar, because there are no power resistors, and very little heat anywhere in the electronics.

Higher amp solar will get a bit of heat in the shorting fet.

Two examples of solar with no dump load.

http://www.fieldlines.com/story/2008/5/4/41311/92374

http://www.fieldlines.com/story/2008/6/22/21540/7547

I can supply better sketches via email.

G-

[David HK]

ghurd,

Thank you for taking the time to respond. I have just discovered a box that came with the panels and inside are several scores of 25 x 25mm printed circuit boards which contain what I would call a switching circuit.

Solar power, which is either 6 or 12 volts, goes in one side and it connects via a diode to a 6 or 12 volt battery for daylight charging on the other.

At night when darkness prevails the circuit automatically creates an output voltage and I currently have this wired to an LED. It works well so I feel rather guilty for trouibling you about a shunt load circuit.

If you would like a couple of these populated circuit boards to examine and play with, please drop me an e-mail to strltdATnetvigator.com with your postal address. Change AT for the obvious.

David HK

[independent]

This whole thing of 6v regulation is interesting alright, especially for standalone lighting situations.

Glen, why are 4x nicads difficult? Because of the lower regulation voltage? Under 6v? I noticed that the open circuit voltage of a stock 12v "ghurd" controller (with no battery connected) is something like 11 point something (from memory)

[ghurd]

Yes.  I still regulate solar & wind charged AAs, etc, to 1.4V each.  The max available voltage for 4 AAs is 5.6V and it drops from there.  Almost not enough left to work with using simple common cheap parts.  

Works fine in real life. The parts tend to be very over-sized for the power they deal with. Some of the data sheets for parts at hand make the simplest designs look not so great, but I never had any problem.  Hard to over heat something rated for 1 or 10A when the peak output may be 50 or 100ma.  

And if the batteries reached regulation voltage very often, I would add more batteries.

I would regulate a 6V SLA to 6.9V, which leaves plenty of voltage to work with.

G-

[ghurd]

Thanks David, but no thanks.  Too many things like that here now.

Be aware most of those circuits only switch the LED On at dusk.

They do not regulate the battery voltage because they assume the battery will never reach a worrisome voltage with the small charging current.

It looks like you will have some decent charging amps.  Keep an eye on the battery voltage if you run the system without any regulation.

G-

[independent]

This is a valuable thread. Thanks so much Ghurd for your explanations. Really useful information here