Diode Setup for 24 volt

[acapulco]

hey,

i have 4 x 60w Solarex panels(oldish) that have been all set at 12

volt and run paralell.  I have recently aquired a 24volt inverter and i am trying to

figure out how best to set up the panels to run 24 volt. I've searched here and google for frickin hours but can't seem to find the info i need. i was intending on setting the 4 panels to 6 volt output and run them in series to make 24 volt but have been told that's not the go.(solarex www).

  At this point i assume the setup will be to set all 4 panels to 12 volt output and

run 2 series strings(12v + 12v) and paralell the 2 strings.

What I don't know is the setup for the blocking and bypass diodes

Any help/advice appreciated

Ian.

[AbyssUnderground]

Go with the series-parallel option, it will probably be most efficient.

+12v-+12v-

|             |

+12v-+12v-

|             |

+             -

[wpowokal]

Most if not all panels have blocking diodes built into the junction box, if so then no need for any more just fuse the output of each two seriesed panels with an apropriate size fuse say 10 amp.

allan down under

[acapulco]

ok,

I probably didn't give enough detail.

Panels are SOLAREX SX-60 and i have 4 of them.

The previous 12 volt setup / panels / inverter came with property and were not set up

by me.

 As they are now(still set up for 12 volt) the first and second panels(first being the panel where the output wires come from) have blocking diodes installed, the third and fourth panels have bypass diodes installed(all 4 panels are connected in paralell)

What i want to know is, If i change the setup to 24 volt(12+12x2) what is the diode setup?

I'm guessing each string of 2 panels should have a blocking diode and a bypass diode()

If so should the blocking diode be on the + end of string or - ?

Same question with bypass diode?

Or am I completely off track alltogether?

Other info:

I have no regulater, these panels have always been connected directly to battery bank

(8 x Trojan T-105's - 6v/225amp/hours)

I know ideally i should have some sort of Regulater inbetween and that most if not all regulaters have blocking diodes built in, but what about the bypass diodes?

I'm not entirely sure i even need bypass diodes seeming where the panels are is completely clear of tree and or other obstructions(ie: nothing can block or partialy block any panels, they either get sun on all or none)

Hopefully this makes sense.

(sigh)

thanks,

Ian Acapulco.

Sunshine Coast,

Australia

BTW: I have no grid power at all, this is my power source entirely(backup 240 volt genset and charger)

[Flux]

I am not the solar expert here but as I see it they are 12v panels so you need two in series to make 24v and two strings in parallel. Don't use 4 in series, they don't become 6v panels.

With only 2 panels in series I doubt that bypass diodes would be much use. With one panel shaded the other wouldn't charge 24v anyway. If you have no shading then there is even less use for them.

Ideally you need a blocking diode in each 24v string. It seems almost certain that each panel has one and it would be easier to leave it with 2 in each string rather than short one out.

Even the blocking diodes are not that essential but are worth including ( and they are likely there already).

For large series strings used with mppt controllers the bypass diode across each panel will keep it running if one panel gets shaded, but the remaining ones in series must be able to exceed battery volts for it to work.

Just reconnect series parallel instead of parallel. If you sure there are no diodes in the panels just add one series diode per pair of panels.

Flux

[independent]

Also, there is a method whereby you test the panels for output matching those in series (I think) and then paralleling the two matched panels. (please correct if I've got this wrong)

[Flux]

Panels from the same batch are usually similar but if you have odd ones then remember they are current sources so it would make sense to use those with similar short circuit currents in the same series circuit if possible. The lowest current one in the string will set the current. If two gave a high current and two a lower one then you will do better with the two high current ones in one string and the others in parallel with them. If they are all different you can't have the best results.

I presume this is what you mean.

Flux

[acapulco]

Ok,

  The panels have sequential serial #'s but i tested the open circuit voltage and

current and all 4 were virtually identical.

As far as the blocking/bypass diode setup, I set a blocking diode in all 4 panels and pissed off the bypass diodes alltogether.

I re-wired the boxes on back to the same gauge as i am using to get back to batteries

(about 8-10m). I wired one string directly to the other string via the connection boxes on back of panels seeming they have nice flexible conduits linking all four, this keeps everything neat with just the + and - wires coming out of one panel and down to batteries.

Someone mentioned fusing each string with 10amp each.

seeming ive joined the two strings via the boxes on back I was thinking of just putting an inline auto type fuse of 20 amp on the + wire somewhere down near the batteries.

(mind you, looking at some of the pics here of other people's setups mine seems to need a little work ;p)

As is now there is no fusing on the DC side, only an inline 20 amp on the batteries to inverter + wire. The AC system(all lights and powerpoints) ends in a plug to plug straight in to either inverter or generator and has 40amp breakers on the light string and the powerpoint string.

Is it needed to have fuses/breakers on the DC side

Inverter is 1500watt cont. but rarely if ever gets near that. I also have a little 300watt inverter that i leave on 24/7 so lights etc can be used in middle of night/coming home at night etc.

I currently run an LP-gas powered refridgerater but am considering a DC powered if my system will allow.

Anyone Know approx amp/hour per 24hours consumption of average dc fridge?

In the short term I am considering getting a solar regulater of some type, with cool things like amp/hours in and out, charging current, battery voltage and capacity etc. Also I was thinking maybe to run a couple of fat cables from the battery bank up to a board or something and run all connections from there rather than directly from bank. Some pics of other setups like that look good, i have a mess of wires and cable now.

Thanks to those who offered advice, I now have the panels up and running at 24volt and so far all looks good.

It's about middle of day here and still winter.

I had already charged batteries up to about 85-90% yesterday and hooked up the panels to the batteries this morning. when there is no cloud i can here the batteries bubbling a bit and voltage goes upto about 27-28 volts measured straight off batteries with multi meter.  If a bit of cloud comes past you can see the voltage start to come down a bit!

This is starting to get fun ;p

[independent]

Starting to see the end of Winter with the birds behaviour changing, going into Spring.

How many amps does a DC fridge use, is a very difficult question to answer--too many variables ("how long is a piece of string?", comes to mind). I know the small portable fridges like the waeco 40ltr ones can average around 2a per hour, but that rate is virtually meaningless as I don't know if that's Winter use as opposed to Summer (it was to -2C). The exploroz site has alot of real-usage information on it from people who use those smaller fridges. Anything bigger is going to use more..  unless it has very thick insulation and not opened very often

[ghurd]

It would be a bit better to use only 1 blocking diode per series string.

If power can't go back through one, then it can't go back through the other in that string.

So only 2 diodes.

If they can't be blocked or shaded at all, then there is no need for blocking diodes after the controller is installed.

The 24/7 300W inverter is taking a good portion of your power.

Might have a look at Speo's remote controlled inverter...

http://www.fieldlines.com/story/2008/4/11/5115/12104

G-

[acapulco]

So the blocking diode should be in the + end(panel) of each string?

[ghurd]

That's the most common place.

http://www.windsun.com/General/tech_tips.htm

G-

[acapulco]

actually these panels (solarex SX-60) can be configured as 6volt or 12 volt...

!