Solar question

Submitted: Monday, Apr 05, 2021 at 00:14
ThreadID: 141343 Views:893 Replies:5 FollowUps:10
Have been camping for many years in Aus. But am new to solar.Have recently bought a 300w Kickass solar panel which is to charge two 120 amp agm Fullriver batteries in my camper trailer through a Ctek dcdc charger.My question is how long should I be able to stay in one spot using only solar in good sunshine.I will be running a 32l Engel as freezer,a 40l Engel as fridge plus a couple led lights.
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Reply By: Gronk - Monday, Apr 05, 2021 at 07:49

Monday, Apr 05, 2021 at 07:49
One year......provided you get good sunshine every day.
No calcs needed.... just stick that panel out every morning.

Sorry, can't be one'll have to move to get more beer !!
AnswerID: 635886

Follow Up By: TrevorDavid - Tuesday, Apr 06, 2021 at 05:46

Tuesday, Apr 06, 2021 at 05:46
Yep, agree with Gronk, just don’t run out of the frothy stuff.

Actually I run 32 & 35 L fridges (as fridges) with a 115w of solar, no problems when it’s sunny, as you have asked.



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FollowupID: 913657

Reply By: qldcamper - Monday, Apr 05, 2021 at 08:47

Monday, Apr 05, 2021 at 08:47
As Gronk said 300 watts of panel should be plenty as long as it is a true 300.

I just attempted a camping trip in SE QLD and a realistic 240 watts (advertised as 400 watts) kept my waeco CFX35 going easily. 2 flexables in parallel fed into the redarc bcdc 25lv, and the folding 200 watt(cough cough) that arrived the day before we left so still in parallel and through its onboard reg just plugged into the rear ando plug direct to the same battery the redarc was charging into, so possibly the most inefficient overcast configuration possible and still got over 2 amps out of each system so covered my needs in the poorest conditions we are likley to be out in. It actually shocked me, was not expecting that.

A simple way for you to know whats going on is simply a volt meter on the battery, assuming you have a devoted accessory battery, and if it is still 12 volts or above first thing in the morning before first light WHEN THE FRIDGE COMPRESSOR IS RUNNING, then your system is doing ok.
AnswerID: 635888

Reply By: mike39 - Monday, Apr 05, 2021 at 10:06

Monday, Apr 05, 2021 at 10:06
Agree that the 300w. panel will be adequate for the load nominated, but a little wary about the Ctek controller.
Is this a PWM controller? If so changing to a MPPT will give you a much more efficient charge regime. (google)
It would possibly require some modification to the panel wiring plus the controller needs to be mounted as close to the battery bank as possible.
I have been using a Victron 15/75 MPPT controller for some years, a 200w. panel generating up to 14a., charging batteries connected to a Trailblaza 60l. on freeze setting and an Engel 80l. van fridge.
With full sun, usually see the controller go into float around 2.30 - 3pm. after which (winter) the charge rate begins to fall anyway.
I have the panel connected through a voltmeter plus 0-20a. ammeter so can closely monitor.
AnswerID: 635890

Follow Up By: The Rambler( W.A.) - Monday, Apr 05, 2021 at 12:00

Monday, Apr 05, 2021 at 12:00
Yes the Ctek does have an MPPT controller and I have a voltmeter installed so can monitor battery’s..
FollowupID: 913629

Follow Up By: RMD - Monday, Apr 05, 2021 at 16:24

Monday, Apr 05, 2021 at 16:24
Are there PWM DCDC units available?
FollowupID: 913636

Follow Up By: Gronk - Monday, Apr 05, 2021 at 17:17

Monday, Apr 05, 2021 at 17:17
When batteries are over 1/2 charged you don't get a huge advantage of a MPPT over a PWM charger, especially if connected in parallel.

I used to charge 3 x 100 a/h batts with a PWM and since using an Epever MPPT only see on average one extra amp going into them.
FollowupID: 913638

Follow Up By: mike39 - Monday, Apr 05, 2021 at 19:16

Monday, Apr 05, 2021 at 19:16
I have no idea, not familiar with dc/dc unit solar charging regime. My system uses a Bosch marine solenoid isolator for in vehicle aux. battery charging, by solar a portable 200w. folding panel with remote MPPT controller.
My travel mate installed a dc/dc unit on his L/C Troopy only to find it started shredding the fan belts. Think there may have been an excessive load on the alternator.
FollowupID: 913641

Follow Up By: qldcamper - Tuesday, Apr 06, 2021 at 07:59

Tuesday, Apr 06, 2021 at 07:59
Classic example why 40 amp bcdc units are a bad idea on a 12 volt system unless the alternator has been upgraded, the whole system has to be calculated, not just bang a bcdc charger in the car then another in the trailer as well cause the guy selling the hardware said it would be a good idea.

Can you imagine the extra heat the alternator would have been generating internally that its poor cooling system had to try to cope with as well.
40 amps adds 1.5 horsepower of extra load to the belt and 560 watts of extra heat generated to produce that extra 40 amps that the alternator will struggle to get rid of.

Automotive alternators are not engineered to run close to max output for more than a few minutes. To run one so hard it shreads belts is inviting trouble.
FollowupID: 913660

Follow Up By: qldcamper - Tuesday, Apr 06, 2021 at 09:36

Tuesday, Apr 06, 2021 at 09:36

See if this works.
It is advertising for victron products but it does give an accurate demonstration of the risks of pushing an alternator too hard.
Their suggested compromise is their products that there are many alternatives.
Whats the point of fitting one of their alternators if it is just going to derate itself, just use a smaller dcdc charger and be aware of not loading up the system with headlights and high speed AC fan when you know the accessory batteries are low.

And especially dont idle your engine to top up after a couple of overcast days.
FollowupID: 913662

Reply By: RMD - Monday, Apr 05, 2021 at 16:39

Monday, Apr 05, 2021 at 16:39
Having good sunshine is great but sometimes not quite like that. Rating things at their best is ok I suppose but considering some over capacity is a good idea for those days when full and constant sun isn't happening. The 300w panel you have sounds ideal, but perhaps a test of it short circuited for a second or two with an appropriate capacity ampmeter across the wires to see what it REALLY produces current wise. Actual will be a bit less than that though at it's rated working voltage. So the Amps possible and the voltage possible is what the DCDC unit sees as energy to convert to battery voltage and charge current flow over time. Is the panel to be fixed on roof or chasing the sun all day. A variation there too. You may find the 300w claim isn't real and less is available. Whatever you have, it still has to work and have an overkill factor of quite a few % if cloudy days or overcast is experienced, to keep you going. I prefer to work on an overcast ability with the knowledge that sunny days are excess power days.
AnswerID: 635895

Follow Up By: The Rambler( W.A.) - Monday, Apr 05, 2021 at 18:28

Monday, Apr 05, 2021 at 18:28
From what I understand the 300w kickass solar panel is very close to it’s rated output.It comes in 4 foldable sections with a total area of 1.9 sq.m.Working on 150w per sq.m that gives me 285w which I am happy with.The panel is not on the roof and I understand that output will drop on cloudy days but I carry a generator for such events.
FollowupID: 913640

Follow Up By: RMD - Monday, Apr 05, 2021 at 19:42

Monday, Apr 05, 2021 at 19:42
Just curious as to what generator charging backup you have/use. Is it 240v powering a decent 250v to 12v charger. I hope it isn't via the so called 8 amp output as provided in many generators.
FollowupID: 913645

Follow Up By: The Rambler( W.A.) - Monday, Apr 05, 2021 at 22:49

Monday, Apr 05, 2021 at 22:49
My generator is 1 kv Honda which supplies 240 v to a 25 amp Ctek charger which has done me well for many years.
FollowupID: 913652

Reply By: swampy - Monday, Apr 05, 2021 at 17:31

Monday, Apr 05, 2021 at 17:31
Loaded question
40lt fridge
Depends on ambient temp
20 deg cel 10AH
40degcel 40AH in 24 hr period ,, freezer

solar 200watts
5.5 hrs per day effective sun/solar summer /spring /autumn for mainland ozzy
Effective day light varies with season and location called PSH ,, peak sun hours

200watt watt = 48ah
++ mppt +++ xtra PSH sun these as extras cannot be measured reliably

300watt =72ah recharge in 24hr period

400watts is a good reliable solar source but it depends upon how much "" spare"" amps u like to allow for cloud etc

avg gain 20% amperage upto 30% if agm is around 1/3 flat or greater
Sharp and Kyocera 400 watts gives approx 28 amps with mppt ,,around 21amps without
AnswerID: 635896

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