Solar charging and mains charging question

J

joha

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Hi

Do you use the mains charger when the solar is charging? I am living aboard in the UK at the moment and have just fitted an 80 watt panel running to a blue solar 70/15 MPPT last night the mains charger was at float 13.8v and this morning the monitor (smart gauge was reading 14.4v and 100% charge I turned the mains off and went to work and on return tonight the monitor was showing 13.25v and 100% charge even though the fridge had been running all day, temprature has been 23-25 degs and weather sunny. Would it be better to keep the mains off until winter sets in?

Thanks

J
 
If both the solar panel and the mains battery charger provide regulated voltages,as one would expect, then having them both connected will do no harm.
 
Agreed, the battery charger is presumably regulated.

In a normal charging cycle, you can expect the voltage to build to 14.4 volts and be maintained at that voltage for a period, then drop away to a 'float' voltage of 13.8volts. When the mains charger is switched off, and without solar, the voltage would drop to around 12.7 volts at full charge.

If you have an 80W panel doing say 60W effective, that's around 5A, which should more than power your refrigerator during the day. Usually about 4A at 50% duty cycle is required.
 
Thanks Guys
Yes both chargers are regulated. The mains / shore power charger is a c-tech charger and the solar one is a Blue solar MPPT 70/15. Came home today and with only the solar it seems to be sitting on 13.2 volts float occasionally going to 13.5. I propose just using solar for charging while this sunny weather lasts and see how it goes.
Thank you all for your replies.

Regards

John
 
chuckr said:
sorry i am an american -- so clarify please -- when you mean mains are you talking about being hooked up to an external power source on the dock?

chuck patty and svsoulmates
in la lina spain
Click to expand...

Surely you remember Scotty in Star Trek yelling to Captain Kirk that "....I'll have to take the mains offline captain!"....? :)
 
joha said:
Thanks Guys
I propose just using solar for charging while this sunny weather lasts and see how it goes.
Thank you all for your replies.

Regards

John

That's what I do.Run the mains charger at night, and the panels alone during sunny days.
They must confuse each other!
Click to expand...
 
Not sure why you need them both on at the same time -- as someone said run the solar during the day and main at night or just the solar and let the batteries go down a bit at night and then recharge during the day -- why buy expensive electricity when you do not have to? we have 3 panels and about 400w and have not hooked up to power since december -- but then again i need a transformer that i forgot to get before we left the caribbean so i really can not hook up to shore power -- but our batteries are full by noon or so - then again we are on the south coast of spain
cheers
chuck patty and svsoulmates
in la lina spain
 
If the charger is on all the time then the batteries can suffer from being "idle" too long - they are not putting out any current. This causes stratification - the acid falls to the bottom and is too highly concentrated on the bottom of the plates causing damage. The batteries should be boost charged for an hour only - about once a week - to mix up the electrolyte. Some good chargers like Victron and Mastervolt do that. This is maybe the source of the old wives tale of "batteries need to be used". Take them down to maybe 80%, or low enough so that when the charger comes on it will stay there for an hour. Cycling them down to 50% just to be able to stir up the electrolyte is not a good idea. This will shorten their life. The life of a battery at 80% SoC maybe three times as much as at 80% SoC.

Living aboard, or leaving the boat for the winter, ideally needs the charger to be set for a winter mode so the Absorption cycle can be set for just one hour whereas the default value maybe four hours or more.

Leaving the solar on all the time in the summer WITHOUT discharging the batteries at all may boil them as the solar may come on in the morning and stay at boost for maybe 4 hours without really needing to charge the batteries. Again a programmable winter mode for the solar regulator is much better. In the winter in sunny climates this can cause over gassing problems which are bad for sealed batteries.

A compromise is to set the absorption voltage to a lower charger profile - or below the gassing voltage - this will help to stir up the electrolyte - but batteries need to gas slightly to charge a battery properly.

Batteries and charging is often a compromise which unfortunately leads to a shorter battery life.
 
My mains charger has not been turned on for several years. 125 watts of solar power is sufficient for all our needs in the summer so that even in port we have no need of mains power except for a large 230 volt fan when the heat becomes oppressive. In winter I leave the boat with a 38 watt panel powering our 350 Ah batteries through a regulator.
 
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