Someone must want to ask a question on solar and associated 12V stuff !

Jaahn · Guru

Someone must want to ask a question on solar and associated 12V stuff !

aussie_paul · Guru

Jaahn wrote:
Hi
There are lots of experts on GNF sitting at their keyboards just waiting to answer good question about these subjects.
Those newbies that have asked a few questions or old hands wanting to upgrade, or just interested people who want to learn a bit more, fire away.
Go for it now.
Jaahn

Sure are Jaahn, and definately appreciated by me.

Aussier Paul. smile

Tony Bev · Guru

Hi Jaahn

I have a question about a battery, being charged by solar or 240 volt battery charger

Not wanting to go off-topic on another thread I will copy and paste

check your batteries for the "C" rating, that will tell you the maximum charge rate

My question is, where do you find this "C" rating for a battery

Jaahn · Guru

Hi Tony :)

Good question, Perhaps the person who wrote "check your batteries for the "C" rating, that will tell you the maximum charge rate" will answer it for us !!

The C rating is commonly used for lithium batteries large and small and is thrown around by the lithium "experts". But from my experience it is only sometimes used for LA batteries for the discharge rating times where it means something else IMHO. It is a time rating for discharge So I do not know the answer !

My definitive answer on charging is ask the manufacturer or look for a spec sheet if you can find one. Here is a good one but does not call anything a C rating. EG https://www.everybattery.com.au/datasheets/FullRiver/DC120-12B.pdf Otherwise just use about 20% of AHr rating for a guide would be my idea. aww That is quite a bit lower rate than I get from my alternator and less than my solar puts out unfortunately. I do not have a 240V charger in my vehicle only a 5A float supply.

Cheers jaahn

Here is a lithium spec sheet and references to C this and that ! https://www.batteriesplus.com.au/shop/lithium-batteries/amptron-12v-100ah-lithium-batteries/

an extract for a 100AHr lithium:

Standard charge current	50A	0.5C
Charging time	Approximately 5 hours	When charging from low voltage cut-off point
Optimum charge current range	20A (0.2C5A) to 100A (1C3A)	Cell max voltage < 3.9V
Rapid charging	Max. charge current 100A (1C3A)	Temperature increase falling within 15°C is normal. Over 15°C will affect the service life of the cells.
Max continuous discharge current	100A	1C, cell min voltage> 2.0v
Peak discharge current	200A	2C (5 seconds)
Discharge performance in normal temperature	20A (0.2C3A) 100 1C3A 90

-- Edited by Jaahn on Wednesday 20th of May 2020 07:53:48 PM

Peter_n_Margaret · Guru

batteries can be charged using a controlled amperage or a controlled voltage.
If the voltage is controlled (the normal way), the amperage will take care of itself, up to the maximum that the charger can provide.
"C " rating never enters the equation. It is a rating used with the Ah rating to describe the battery capacity.
Cheers,
Peter

dorian · Guru

Just in case it wasn't clear, if you are charging a 100Ah battery at a rate of 100A, that's 1C.

Charging a 100Ah battery at 50A is 0.5C.

Charging an X Ah battery at Y amps is Y/X C.

Bagmaker · Senior Member

ya Sorry Tony, that was a bit unclear!
Best to find charge and discharge maximum rates for your particular battery from the manufacturer, as stated above.

Tony Bev · Guru

Thanks to everyone for replying, it is appreciated

As I now understand it, the "C" rating, seems to be applicable to lithium batteries only

As I am using AGM deep cycle batteries, with no known problems, then it may be a few more years, before I look at a lithium setup

Peter_n_Margaret · Guru

Tony Bev wrote:
As I now understand it, the "C" rating, seems to be applicable to lithium batteries only

No, AGMs (or any battery) can use C ratings too.

For example a battery may be described as 100Ah at C10, which means it will deliver 100Ah if discharged at a constant current over 10 hours.

The very same battery might be 110Ah at C20.

So it is important if you are comparing different batteries to ensure they are both using the same C rating to measure the capacity as it is easy for some vendors to make their batteries look better just by using a higher C number.

Cheers,

Peter

Cooch · Member

Being fairly new to a life on wheels I have a lot to learn about solar. Ideally i'd have more solar on the roof but wont be doing that until I reseal/repaint the roof. In the meantime how can I squeeze the most out of a single 150W panel? eg wire sizes, type of controller, connections.

Cooch · Member

This is probably more of a theoretical question than a practical one, but im curious all the same...

If solar panels work via sunlight falling on the panel, can you boost the output by reflecting more sunlight from a mirror or similar reflector?

and further, would the extra light also create more heat and thus lower the output of the panel and wipe out any gains (theoretical or otherwise)?

Jaahn · Guru

Cooch wrote:
This is probably more of a theoretical question than a practical one, but im curious all the same...

If solar panels work via sunlight falling on the panel, can you boost the output by reflecting more sunlight from a mirror or similar reflector?

and further, would the extra light also create more heat and thus lower the output of the panel and wipe out any gains (theoretical or otherwise)?
Hi Cooch

The short answers are Yes, Yes and NO.

To go back to you previous question re improving the 150W panel. As you suspected it can be improved by fitting larger gauge wire, and shortening the run of wire if possible, redoing the connections with improved types to reduce any resistance and using a genuine MPPT regulator fitted close at the battery with heavy wire. Just good practice really anyway. But why not just throw some more watts up there. I know, I know, you said why. If you do replace any of these items then allow for the increased wattage panels to be fitted later.

Probably the most improvement would be to be able to point the panel to be more directly facing the sun. And move it every few hours. but that is a major change. perhaps a large sheet or two of shiny white plastic is easier to do which brings us to....

It is quite possible to reflect more light onto the panel and it will output more watts. Particularly when they are flat mounted and are not getting close to their full output in winter. However as you again suspect in strong light and high summer temperatures the panel will get much hotter and the output will be reduced. But I do think they will always put more out. However the principle has been used with panel cooling sometimes by using water which is used for hot water in larger integrated outback installations.

Jaahn

-- Edited by Jaahn on Tuesday 26th of May 2020 05:43:22 PM

Cooch · Member

Thanks Jaahn, my 2nd question was more of an afterthought rather than something I would actually try - just curiosity...

Throwing more watts up there is on the cards and you've kind of pre-empted my thought of allowing for increased wattage later. The question I almost asked was if I have a piece of string this long how many watts can I add without changing anything. A quick glance tells me at least some of the wire is a bit on the light side and the controller is low end. However my power needs aren't high at the moment and it works well enough for now.

Might work better if I park in the middle of a bunch of white big rigs at the next rally

Peter_n_Margaret · Guru

16 years ago I set up our solar system with a 60A Plasmatronics unit (good quality, large capacity for expansion, but older PWM technology). It is still going. It has served us very well indeed, but it would not be my method of setting up a new system today.
Now I would use a small capacity Victron MPPT controller and use large domestic solar panels, then simply add extra small controllers for future expansion.
Using multiple controllers gives the added advantage of redundancy if one dies on the road.
These units are designed to "talk" to each other so can work together perfectly.
Cheers,
Peter

iana · Guru

Why is it some solar panels are rated "not suitable for series installation", flexible panels especially, but some standard panels as well?

Peter_n_Margaret · Guru

iana wrote:
Why is it some solar panels are rated "not suitable for series installation", flexible panels especially, but some standard panels as well?

I understand that they are not fitted with blocking diodes, but that is easily remedied.

Cheers,

Peter

iana · Guru

Blocking, or Bypass diodes ?

Peter_n_Margaret · Guru

iana wrote:
Blocking, or Bypass diodes ?

Blocking diodes between panels.

Cheers,

Peter

Jaahn · Guru

Hi Ian and Peter and all smile

The diode question is not simple but needs some reading to get an understanding. Here is one site; https://12voltblog.com.au/solar-panels-parallel-series-shading-diodes/

They say that a regulator does the function of the blocking diode. Redarc say they do not use blocking diodes on their panels; https://www.redarc.com.au/do-redarc-solar-panels-have-a-blocking-diode

Plenty more on the web about diodes and panels. https://www.electricaltechnology.org/2019/10/blocking-bypass-diode-solar-panel-junction-box.html

My take on it all; Blocking diodes give a small loss all the time, due to the approximately half a volt drop. Normal panels do not need them with a regulator and if working in parallel the diode effect of normal panel cells will restrict reverse current to a low current if one panel is shaded.

If working in series then by-pass diodes should be fitted. There is almost no loss for normal working but can bypass a shaded panel and keep the others producing current.

To answer your question on why some panels say they should not be used in series. The flexible panels and some other unusual panels are made differently to normal panels. The cells are not the same and are not as robust, particularly regarding reverse voltage. If the reverse voltage is higher than they can tolerate when hot on the roof, they will break down with the reverse current and fail. This usually means they are stuffed as I understand it. It is hard to get the full answer at they are reluctant to document any weakness for public viewing. I have no direct experience.

Jaahn

-- Edited by Jaahn on Friday 31st of July 2020 11:00:24 AM

iana · Guru

And again I am confused, "If working in series then by-pass diodes should be fitted. There is almost no loss for normal working but can bypass a shaded panel and keep the others producing current. " did you mean blocking diodes, aren't bypass diodes fitted to the panels as standard?

OK so a flexible panel is not suitable for our set up, is that correct ? Pity one thought was to mount it on our partially open awning, which would set it at about 40 degrees angle for the morning sun.

iana · Guru

The basic question is, with the panels (3) wired in series, apparently if one has shade, all are taken out. The panels are 36 cell fitted with two bypass diodes during manufacture. I had fitted blocking diodes between panels but removed the diodes off two panels, in order to change from parallel to series. So one question is should they be put back into position, will require a new junction box etc.

The next question is harnessing the morning sun. I have installed an Anderson plug set as a jumper into the circuit, so one I can pull out the jumper and disconnect the panels prior to any work on the batteries, but also, so I can connect into the system another portable panel still being in series. From 66v (3 x 22v) plus one at 22 volts takes it to 88v max for the regulator to handle.

Or should I look at being able to disconnect the roof mounted panels completely, and connect into the system portable panels (2x) angled to capture the morning sun, and also avoiding shadows.

Jaahn · Guru

iana wrote:
The basic question is, with the panels (3) wired in series, apparently if one has shade, all are taken out. The panels are 36 cell fitted with two bypass diodes during manufacture. I had fitted blocking diodes between panels but removed the diodes off two panels, in order to change from parallel to series. So one question is should they be put back into position, will require a new junction box etc.

The next question is harnessing the morning sun. I have installed an Anderson plug set as a jumper into the circuit, so one I can pull out the jumper and disconnect the panels prior to any work on the batteries, but also, so I can connect into the system another portable panel still being in series. From 66v (3 x 22v) plus one at 22 volts takes it to 88v max for the regulator to handle.

Or should I look at being able to disconnect the roof mounted panels completely, and connect into the system portable panels (2x) angled to capture the morning sun, and also avoiding shadows.

Hi Ian smile

Looks like no one else wants to comment, this is my considered opinion. wink any other discussion is welcomed.

Firstly; if your panels have 2 bypass diodes, one for each half panel, then some limited shading will mean that the bypass diodes will bypass the main current past the low output sections, and the full sun sections will continue to produce. The total output will be reduced by increments of half a panel that are partly shaded. The usual arrangement is the panel is divided into two "sides". The minimum loss is 1/6th of the three panels output for a small shading, and increasing by a x/6 as the shading spreads. I would not worry about the blocking diodes in series connection except as said below. aww

I would put the two different lots of panels into two parallel connected strings of two new and three old panels. I would fit blocking diodes in each string so the weaker string will not allow back flow current. In the morning or afternoon the portable panels will produce more voltage than the flat mounted panels anyway, but when the sun is up high the flat panels will be better voltage (depending on the location). The MPPT in the controller will look for the best outcome throughout the day as the string outputs shifts around and the panel string adjust to the different voltages to produce current, automatically, by their very nature as shown on a graph of current V voltage. smile

Thirdly; avoid shadows no matter what ! furious

Cheers Jaahn

-- Edited by Jaahn on Wednesday 12th of August 2020 07:29:41 PM

-- Edited by Jaahn on Wednesday 12th of August 2020 07:33:20 PM

iana · Guru

After doing more reading, I decided blocking diodes will stop the panels working, except for one at the end of the series. I read also more about flexible panels, and after what I read came to the conclusion, these are not made to be portable. And looking at the sun as late as 8:30 in the morning, saw it is still very low, and long shadows, meaning one cannot really get away from shadows in the winter. Conclusion do nothing and plug into 240, the just wait for longer days with the sun higher and the problem will go away.

Jaahn · Guru

Hi Ian smile

Well that's the easiest way out. Time will tell aww

i am puzzled by your statement " blocking diodes will stop the panels working ". If you put blocking diodes one each panel you will get around 1.2-1.5 V drop for the three in the series string. If you only have one in a string it will be 0.4-0.5 depending on the type, note that is using Schotteky diodes. Is this loss what you consider will stop the panels working ? Silicon diodes give a higher drop of 0.6-0.7V each. Note also using over sized diodes also can reduce the voltage loss a bit by running lower on the curve. hmm

If the panels put out a bit more power than required, that is a voltage a bit more than the minimum required to charge then some current will flow. But you would probably be better off with a PWM controller in these circumstances as the losses are lower.(who said that ?) The MPPT controller has losses at low panel power and no advantage until the panel voltage gets up quite a bit above the minimum. aww

I guess we try to select our campsite to allow for a clear sun path if possible if we need the power. hmm Or run the engine.

Jaahn

-- Edited by Jaahn on Saturday 15th of August 2020 06:10:47 PM