Dick0 wrote:

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The solar system is 4x12v/200w fixed rooftop solar panels in parallel array feeding 2x150ah AGM batteries. I am also able to connect a portable 12v/200w folding panel into this array if I wish.

Now looking at replacing the PWM controller with a brand name "true" MPPT charge controller which will also be suitable for Lithium batteries later on. Have looked at various brands like Victron, Epever etc. and am trying to ascertain the suitable Amps requirement of the charger.

The formula seems to be total Watts divided by Volts to give you Amps. However, some formulas use 12Volts or 14.4Volts in the calculation which can be confusing. I also wonder how true the 200w specs are of the panels.

I am reaching out to those who have a "true" MPPT controller and I would like to know how you determined the correct charger for your solar array. Opinions would also be appreciated.

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 Hi DickO

Yes some easy things get complicated quickly.  The max current  rating of a MPPT reg is set by the output current when the battery voltage is lowest and the sun is highest. So it is reasonable to use around 12V (flat battery) rather than 14.4V(fully charged), because the current will fall as the voltage rises under constant solar power from the panels. The max power is at mid day in full sun. 

BUT my next answer is do not run so close to the max rating that it is important. Go to the next size reg so it is not so stressed and it will reward you with a long happy life IMHO. Relying on the unit to regularly throttle the output to self protect is just a silly idea and asking for early failure IMHO. In the middle of summer everything is hot hot hot !  

I suggest you check your panels to see what they do put out. You can just measure the current now with the PWM reg and then when it reaches full battery, measure the max Voltage of each panel. Do you have a multimeter yet. Get a reasonable quality one with a DC current clamp and learn how to use it. Never have an unknown electrical question again.

Jaahn 

Dick0 wrote:

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Thank you "whenarewethere" and "jaahn" for your input.

 I suppose I wanted to know, as a free camper with my solar array, should I need a 80amp charger or would a 20amp charger suffice.

My load requirements being a 12v car radio, a 12v 24" TV, a 45lt 12v fridge freezer and several USB charging devices and evening caravan led lighting.

What would be the best solar charger amp output for 2 x 150ah batteries to supply my requirements?

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Hi Dicko 

Note the controller/regulator current rating is set by the panels size and not the batteries size. Having good solar panel watts is important and you cannot have too much IMHO.   

Looking at your system your loads are not big and should be easily accommodated by your two batteries. The fridge freezer is the biggest user as it runs 24/7 but still should be good. The rest are not so big or constant. (I run that with one battery). You have plenty of solar if they are genuine outputs but still good even if they are a bit short. You should do well even with a bit of poor weather. 

Soo what size charger ? I might think this would be reasonable(despite my previous statement about oversizing). If you find a 60A MPPT that would be OK IMHO. It might occasionally need to self regulate but that is OK. Normally your batteries should not get to low charge. So look at what are available in the various brands you are interested in and the ratings and the cost.

I hate to say this but if your panels are connected in parallel then you would be just as well off with a quality three stage PWM controller.   Save quite a bit.

Jaahn  

 

-- Edited by Jaahn on Thursday 6th of May 2021 07:15:45 PM

-- Edited by Jaahn on Thursday 6th of May 2021 07:18:39 PM

Dick0 wrote:

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Thanks Jaahn,

I need to be sure that I have the correct solar charger in place for when I upgrade to LifeP04 batteries.

So at this point of time it looks like I will steer towards an MPPT solar charger.

Also, I may be fortunate in acquiring in the near future an 80amp near new Epever charger at less than half cost (an unwanted item).

These 80amp chargers, however, are rather large in dimensions.

But with 5 x 200w total solar panels, this may be the way to go.

I am surprised Jaahn that so few on this forum have been prepared to share their knowledgeable solar wisdom.

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 Hi Dick

Some more comments to get the details right. The type of battery is not important as far as the regulator is concerned except in so far as being able to set the correct voltages of the stages to what the battery manufacturer recommends. The EPever may not be as easy to set exactly to the suitable voltage. Look up the manual for the model you are interested in. Yes they are large as they have big heat sinks to stay cool when working hard. Better quality, more expensive regulators are able to have each stage set individually to a voltage and possibly time. Note lithiums do not need or want an extra equalise voltage etc and a shorter boost charge stage may be best.   

It is not as important to have MPPT with Lithiums as the discharged battery voltages do not go so low so the extra charge overall is not so great. The advantage of using MPPT reg is best when you use the panels in series. I would say use the panels in two parallel strings with 2 panels in series. But you might have the extra portable panel ?? So use them all in parallel. 

The lithium batteries now available can have battery management systems (BMS) that work with a higher voltage than some older types and charging is controlled more by the BMS than the regulator. So I could not say what is the correct voltage except by looking at the manufacturers recommendation or their spec sheet. Some people also buy a remote meter of some sort to monitor their system and even a battery capacity meter. If you have a good system and it works well then possibly it does not need much monitoring. But that is more important if it is a bit marginal in poor weather etc.    

I might also say that I bought some books by Collyn Rivers on solar after looking at them in the library. An investment that might pay for itself in time !

 https://rvbooks.com.au/collyn-rivers/  available at a lot of caravan or camping shops and book shops and direct also.

Also a multimeter is important for checking things and learn how to use it. A model with a DC current clamp is excellent. Pays for itself also IMHO. I have several ?

Jaahn 

PS there have been unfortunate 'discussions' about solar and lithium in times past so some people have been discouraged from answering.     

 

 

Hi In case of any future warranty claims on unit you buy it is best to use advertised ratings of the attached panels, this give you effectively nearly 1000 watts of panels, divide by your battery voltage of 12 volts give you a maximum current of just over 80 amps. This is getting to big for cable size and cable connection in my experience, In a system I did recently on a similiar panel size we used two controllers, seperate cable run down to the controllers. splitting the panels between them, made for much easier wirin, used MC4 connector for ease of use and paralleling panels. With only 150 amp hour of battery, I would not even waste money on MTTP controllers. Roger

Charging in poor conditions. 

The first poor condition will be the solar panels mounted on the roof. The lower the sun in the sky the less energy the panels get. The sun 30° above the horizon & the panels will only perform at 50%.

Then factor in clouds & there is not a lot left.

Make sure that other items on the caravan roof do not cast shadows in the morning. A small shadow will bring the panels to their knees. You are better off with a panel a bit smaller so it has a bigger gap to avoid shadows.

 

Do a scale drawing of the roof & everything on it & key points in the ceiling, it will save stuff ups & expense.

 

A 200 watt panel is a big & heavy panel. You probably would be better off with smaller panels but twice as many. Then you also have more redundancy if things go wrong.

If you had 4 panels you you could have 2 in series with a MPPT controller which works better in the morning or squeezing out a bit more in inclement weather. 

 

Now when the sun is overhead the panels will be putting out the maximum output. Under ideal conditions I get 11amps output from the controller from 120 watts of panels.

So if you have 400 watts that's 37amps. If it is a 30amp controller it stops at 30amps. I found this out the hard way with my first controller. Its limit was 10amps, running at capacity some of the time or close to it the rest of the time. Not ideal so I bought a 20amp controller & found out there was another amp I was missing out on. I could add a couple more 20 watt panels, but as is I have plenty for our needs.

 

At the end of the day if you have ordinary weather, modest input, how long are you prepared to last before you have to turn the engine on to charge up the batteries.

If you are moving camp sites every 3 or 4 days, you can get away with a smaller setup. If sitting put for a week or longer you might want a bit more capacity.

You can't have 2 panels in series with this controller. The the point of MPPT is to have 2 or 3 panels in series to get that bit more out of the system early in the morning or in inclement weather.

 

My system:

 

https://thegreynomads.activeboard.com/t65231112/custom-6x20-watts-solar-setup-with-mppt/

Hi Mate, If you running AGM batteries you need a controller that ramps them up to 14.8v, that why I run a 50amp Renogy, MPPT, the unit manages my 2x 100Ah Lithium batteries, with one 250 watt panel when parked up and the Alternator takes over when I'm driving, I run a few accessories, fridge, coffee machine, media player, led lights, Victron 600watt inverter, water pump, if I do get a lot of cloud and rain she works a bit harder but still managers to bring the batteries up to full charge.

In the end settled for an 80A Epever charger connected to the present solar array in parallel (1000W in total panels).

My 2000W rated dc inverter is happy running most of the AC short use appliances.

I have a PWM charger also connected to the array which charges the Breaksafe battery.

All my loads are happy operating as the batteries remain at charged capacity.

Cloudy environment is of no concern to maintaining full battery capacities.

One final test will be running load tests overnight to see the draw down level.

 

Thanks for your input.

Tony Bev wrote:

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Do you have a link to that 80A Epever charger please Richard

I did not previously comment, as I am not a techie, and do not know enough about lithium, for your future set up 

But this is what I had picked up about charging AGM batteries

1. Buy a solar controller larger than your solar panels output
   My 20 amp CTEK DC/DC solar battery charger, will switch off after more than 20 amps from the solar panels (to protect itself)
   Calculate what the solar panel output is, by using a DC amp clamp meter, or looking at the specs of the panels
   
   
2. Regardless of the size of the solar panels/solar controller, AGM batteries only take what they want
   If the batteries are nearly full, they will only be taking a few amps, and you may think the solar panels/controller are no good
   So when using a DC amp clamp meter, run the batteries half down, before connecting solar and measuring amps
   
   
3. Read somewhere that AGM batteries like to be charged about 10% capacity, (not sure if this is fact or fiction)

If I am wrong, then hopefully, someone will come along and correct my theory

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 Hi Tony,

One of these 30 or 40 amp chargers with monitor may be more suitable for your setup.

Epever MPPT Solar Charge Controller 20/40A Battery Regulator MT50 Remote Meter | eBay

I can only go by the research and advice that I have received regarding solar setups.

 

In regards to your first paragraph... Use the equation... total rated panel watts divided by 12 volts to give you total available amps (parallel array).

So, if you have 2 x 200W portable or fixed or mixed panels then maximum amps would be 33A. Then it is recommended to move up to the next higher rated controller being a 40A charger.

In that scenario I doubt that you would obtain 400W even in the best solar conditions, therefore, a 30A MPPT charger would be more than sufficient.

It is also important to connect a "true" MPPT charger rather than a cheap and fake Chinese PWM knockoff marketed as an mppt charger. Youtube has many reviews about this.

As long as you have a good quality brand true mppt solar charger your deep cycle AGM or LifePo4 batteries will be efficiently charged.

 

I believe you are correct in your second paragraph regarding the level of charging depending on the present state of charge of the batteries.

 

Not sure what you mean about your paragraph three. AGM batteries, as I understand, should not be run down below 50% prior to charging to maintain the integrity of the batteries.

 

If I am wrong anywhere here I am sure I will be corrected and I welcome opinions and feedback which is a good way to learn about this topic.

 

I hope to put up some pics of my setup in a few days time.