A couple of battery charging questions

If you really use 30 amps per day then you would need a solar panel of at least 100 watts which is quite large.

I get away with a portable 80 Watt panel as when the vehicle is stationary then the panel supplies the Engel and when moving the vehicle supplies the fridg.

There will be efficiency issues which will slow it down the charging, and as the battery gets closer to capacity it will only accept charge at a lower rate, and the charger will switch down to a trickle feed.
The effect of drawing 30 AMPHours on the battery will depend on how quickly you draw it, and at what operating temperature it is working. Drawing 30 AMPHours really quickly might well flatten it.
How much power you get from the solar panel will, of course, depend on how much sun you get on the day, and how well you orient the panel.

>I have a 95 AMP hour battery & understand that I should not
>flatten it below about 50% of its capacity.

The more you discharge a battery the shorter its life will be.

If you can avoid discharging below (say) 20% you will get, pretty much the maximum, life from your battery. If you frequently discharge it to 50% you will get a short life span and if you discharge it below 25% capacity you may only get a handful of cycles from it.

I'm sure you appreciate these guidelines are not written in stone but they do represent the statistical norm - being familiar with the battery "experts" on this site I have no doubt there will be one who has discharged his 200Ah AGM to 0% every night for the past 10 years and "it's still going strong!" :)

As Andrew says; the Jaycar charger is a "constant voltage" device and will tail off as the battery charge approaches 100% so it may take (guessing) 4 hours to fully replace your 30Ah. You could go to a "constant current" charger but these are not recommended for lead acid batteries and may cause problems because they will drive the charging voltage up to 17V or so which is outside manufacturers spec. but you can get away with it if you're careful - I use one but I watch it closely and would not, generally, recommend one.

Solar panels: how long is a piece of string? An 80W panel ($500?) will probably provide somewhere between 3 and 6 amps of usable output for X sunshine hours per day, providing you can track the sun to some degree. In the Vic High Country in winter I suspect solar would be all but useless. However in The Alice in December it would be great.

Tell us more about where you go and what you need to run and we'll try to advise.

Mike Harding

Barry,
If you are running down the battery by a fridge, then it will be running more during the day than at night.

If you bought a 100 watt solar panel it would supply ~6 Amps during the nice sunny periods of the day, the fridge would be using less than is produced by the solar panel, so the fridge would be running and the battery would also be being charged at the same time.

Top Steca picture shows my fridge is drawing 7.8 Amps (obviously not Engel or Waeco)
The white Amp gauge shows 0.5 Amps is also charging the (13.8 Volt) battery

Total Amps supplied is only 8.3 out of ~12 Amps available, because the battery is almost always fully charged.

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This battery system is only dis-charged during the night and when no power is received at Solar system regulator.
However, when a fridge is not running during the day ALL power required is supplied to the battery system by the solar regulator, your fridge possibly runs on about a 50% duty cycle so you will maintain a fully charged battery during the day.

This system avoids the battery from being discharged to the drastic numbers talked about.

Mainey . . .

Hi Barry
#1 yes your method of calculating use is correct, watts divided by volts = amps drawn,
#2 multipy amps drawn per item by estimated hrs of use = amphrs used per item
#3 add amphrs for all items= total amp hrs used per day
.#4 charging ineffiency means you would have to put in approx 25to 50 % more in than you took out . take out 30 ahrs put back up to 45ahs
#5 as others have said rate of draw can affect available amp hrs
#6 charging at 1or 2 aps will not do much to charge, For long life of deep cycle baaterries recommended charging current is 20% of amp hr capacity ,ie 4amp for 80 amp hr battery,but higher rates can be used.
#7 a 80w solar panel will give 4 to 4.5 amps output on a bright sunny day[ sometimes up to 5amps under very high light conditions]
You can generally assume 6hrs @ 4to4.5 amps if you have panel tilted & facing the sun so that it is at 90Degrees to sun, ie 24 to 28 amphrs input.You can gain a little more if you track the sun all day

Barry,

The advice you got from Battery World was quite practical and good on them.

For occasional use, running the battery down to 30% (about 11.6 volts) is a more realistic practise. That is why fixed low voltage cutout devices are set to this voltage.

You should get at least 2 days of use, unless the fridge is very hungry.

What you then need to determine is a practical way of replenishing the energy in the battery. Some people do this via a solar panel, which can be connected permanently. The solar panel has to be big enough to put back as much and preferably more amps than you are taking out.
Alternatives to a solar panel is either a generator, (not always socially acceptable) or via the vehicle alternator, preferably taking the vehicle (and fridge) for a drive.

I have been with people who run their vehicle stationary for half an hour, but that doesn't put back anywhere near enough amperage to last that long.

You haven't stated how big your fridge is, or what the current draw is, but a solar panel of even 40 watts may be enough, without over capitalising on an investment. A 40 watt panel will put in around 2 amps continuously for several hours each day. Sometimes more, sometimes less, depending on sunlight etc.

Bill.

Barry
As you recently benefitted from one of my "dumb" questions, I have learned a lot from the response to this question.
Thanks for asking.
What worries me is that if you and I find ourselves set up in a camp remotely together, we could be in real trouble unless we can log on to the forum for advice.
Happy planning.
Cheers
jeff