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Post Info TOPIC: Questions - solar charging


Guru

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Posts: 1957
Date:
Questions - solar charging


Hello everyone,

My use for DC power in our caravan is quite low - a couple of LED lights, the TV & very occasionally the pump. I have recently added another 55w solar panel, in theory giving me 110w. Having had the gas struts regassed has certainly assisted in lifting the roof - one reason why I kept the power supplied to a minimum. Previously I've just used a PWM controller, but I bought an el-cheapio - el-nastio Kings so called MPPT unit a few months ago. Yes, I saw an increase in power into the battery, but it went back to the shop as the voltage didn't cut out - I saw the battery voltage rise to 15v+ (the spec sheet said it was set to 14.7v - still too high for my liking).

I'm about to purchase a better controller & here is where I need assistance. I could boost the solar input by 60w using my one set of my portables - which have matching output voltages to the fixed ones. Do I get a controller that has a maximum input of 15A (close to the maximum input)? Or one that slightly larger eg 20A?

Next question - I saw somewhere recently where it was suggested that keeping a battery on float for an extended period of time could be detrimental to it - fact or fiction? I thought, based on years of working on telecommunications equipment that it was false. I do cycle the battery (100AH AGM) occasionally, taking it down to 25-50% capacity & charging with a mains powered 7 stage smart charger.

Am looking forward to your replies.



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Warren

----------------

If you don't get it done today, there's always tomorrow!

2019 Isuzu D-Max dual cab, canopy, Fulcrum suspension; 2011 17' Jayco Discovery poptop Outback



Guru

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My Victron 75/10 was at its maximum output of 10 amps with 120 watts of panels under ideal conditions. The MPPT will put out more amps at a lower voltage when the battery is obviously at a lower voltage. Most of the time its output is around 9 amps so the 75/10 is ok.

But under ideal conditions the 75/10 was hitting its 10 amp limit output & I was interested to know how much more I could get. I didn't think it would be much but I was nevertheless interested. 11.3 amps at times, which it really rather academic on many levels as it was under perfect conditions, water cooled & using jump-starting leads between the solar panels & MPPT. But let's say a bit over 10 amps occasionally.

So the next dilemma, as I had already done endless research for 120 watts of solar, a 75/10 should be plenty. At that stage I didn't see myself needing more than 120 watts & still don't. So do I buy a 75/15 which would definitely be enough or to hell with it buy the Victron 100/20 which is much better made with large heatsink.

In the end I decided to buy the Victron 100/20. Very happy with it. Ok, it is overkill but if on the very remote chance I add more solar I have plenty of spare capacity. I didn't want to buy another one unnecessarily. I keep the 75/10 as a spare as it is perfectly adequate for 120 watts.

I have noticed that my Victron 75/10 was just a whisker more efficient, about 1% more than my Victron 100/20. So there is a very slight loss of efficiency. I could wire both in & switch between the two.

You will only need the additional output for when the sun is working hard! In the morning its not going to be as strong so you won't need a higher output for that. In the instruction manual it notes full rated output up to 40C, so it must derate to its maximum 60C operating temperature. So if the ambient temperature is very high & it's running at full output, a bit more headroom is probably worth considering. But this is probably more a midday or afternoon issue & by then your battery is probably charged.

75/10 from my experience is enough for your 110 watts.

75/15 provides headroom & will be more than enough if you add another solar panel in less than ideal conditions or for high ambient temperature.

100/20 is just nicely made with large heatsink, with headroom & additional solar capacity in really extreme ambient conditions.

I have gone completely overboard with adding additional heatsinks, but why not. Even thought of adding a really efficient Noctua 0.6 watt fan (I have a spare) but it's not with the 0.6 watt load.

IMG_3710_055616.jpg

100/20 with even more heatsinks, the cover got warm as well. The 75/10 on the boot floor being tested with a solar 80 watt 40 watt split using 2 controllers. 2 controllers work, but without fine adjustment the smaller controller was dictating the charging & was switching off the 100/20. So one would need to adjust the settings so the larger controller was running things.

IMG_3850_055613.jpg

I do find the Bluetooth data handy at times. You can also run your load through the Victron MPPT so you you have complete input & output data. So the 100/20 might be more handy with a 20 amp load when fridge is running & you switch on a few other things up to 20 amps maximum load.



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Senior Member

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Posts: 332
Date:

If you are not going to add anymore solar panels then a 15A controller will do just fine for you. You will be lucky to get 80% of the output with roof and portable panels.



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Guru

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Posts: 1957
Date:

Thank you TimTim & Whenarewethere,

I had a recommendation from a previous workmate who now does a bit of solar work to look at the Renogy 20A Rover & other than being a little larger, heavier than the Victron & having noise issues to AM/FM radio, it looks pretty good - the price is good too.
I found a website produced by the Clean Energy Summit (cleanenergysummit.org/best-mppt-solar-charge-controllers/ ) that compares the 10 best controllers - the Renogy 20A comes in at second, the Victron at third so there isn't much between them.

Also in my dabbles today I found an identical controller to the Kings - being marketed by a WA company who advertises a lot in various travel magazines. The only differences were the colour & price. I had suspicions that the one I bought from Kings must have had some short comings because of the low price - having a high cutout voltage was one!!

I found an error in my first post above - I have never discharged the battery beyond 50% (& that wasn't for very long either). I put in one "to" too many!

Whenarewethere - your system is spot on & I feel if there was to be a prize for the best contribution on this forum, you must surely be in the running for it.

TimTim - the bit about efficiency - I found by lying the panels down flat it certainly dropped the output (one beauty of having portable panels) as they can be set at the optimum angle to the sun - depending on the lattitude. I noted that there was quite a bit of discussion on one post here in this forum about optimum panel angles. I was always taught that it is equivalent to the lattitude degrees so having them flat (with an air gap) is fine if we were to drive around the Equator but it would get a bit wet, as well as being HOT! One has to be practical.



__________________

Warren

----------------

If you don't get it done today, there's always tomorrow!

2019 Isuzu D-Max dual cab, canopy, Fulcrum suspension; 2011 17' Jayco Discovery poptop Outback

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