solar recharging

Thanks for all the replies. Some really good info there. So it looks like you need to spend a bit to get the result i'm after. So it looks like it's not worth buying cheap panels that just won't do the job. I think i might have to invest in a new fridge that doen't draw as much power. the fridge i have at the moment is just a cheap one with a cooling fan and no themostat so it _Affordable_Storage_Drawers.aspx a fair bit more than your better quality units.

Cheers.

or more batteries :-)

Andrew

Andrew [Qld] or more batteries , only 1 problem with that [ I run a 6 battery system now already] you still have to have the means to recharge them , amps used = amps required to be replaced or sooner than later the batts are flat and the beer hot ,LOL.

Solar Panels ? There are a couple of other things to consider, some for, some against, apart from the cost which has already been mentioned.
1. once you have got it all set up the way you want it they are nearly maintenance free, no on going expence untill you need new batteries.
2.If you have them fixed to the roof of whatever outfit you have it probably meens you park it in the full sun for maximum effect, thus hot c/van camper etc.
3. If you have them portable so you can park in the shade and move the panels about to get most effect from the sun you then have a security issue.
4. You may have to pack them away if you are going to leave your camp unattended, so no recharging while packed away.
5. 65 w / 80 w panels are a fair size you may have a transportation problem.

One time I asked a bloke with an imported $150,000 5th wheeler camper why he had set up in the full sun . He said he needed to have the solar panels (which were on the roof) in the sun to charge the battery bank enough to run the airconditioner to keep the camper cool.
Didn`t make sense to me when there was ample places in good shade.

Good luck with which ever way you go.

Alloy c/t,

As you stated, "with a solar setup , maths is a critical component"

I believe your calcs are flawed slightly by the assumption that a 40 litre Engel will draw 1.9 amps per hour for 24 hours (=48.6 Amps)

I am of the opinion that this is excessive as the fridge would generally cycle on and off according to the thermostat setting and therefore the draw is somewhat less, especially at night.

I have exactly what you have used as an example.
A 40 litre Engel, usually set to 1 on the dial and also a versalite which I use for 3 or 4 hours in the evening, to keep the bogyman away.
This equipment is connected to a 75 A/H Thumper portable battery system and supported by a 40 watt BP Solar panel to put "something" back in.

The longest I have run this apparatus "continuously" is three days and the battery indicator lights still showed "charged" on the thumper's battery test display. (starting off with a fully charged supply)

This indicates to me that the Solar panel must be putting back in, about what is taken out and is exactly what the salesperson indicated to me when I bought the solar panel. If I need to, I can purchase another 40 watt panel and connect it to the regulator on the existing panel, but indications so far, is that I don't require it.
This was sound advice given to me by the manufacturer of the Thumper, who also retail the BP Solar panels.

So, I would say quite confidently, that a 40 watt solar panel, which outputs about 2.4 amps would be enough to maintain a battery supporting a 40 litre Engel, or Waeco and a "Versalite" given average sunlight conditions and the use of the fridge (as a fridge rather than a freezer) "indefinitely".

Of course, I have a "plan B" where I can connect the fridge to the auxiliary battery in the vehicle and also recharge the Thumper from the vehicle alternator, if necessary.

That is my personal experience anyway.

SandMan SA , my calculations were to be used as an example only ,not the be all and end all , dont know how you measure your amp hr usage but I run my fridges thru a Steca solar regulator ,tells me how many amps in and out in any given time frame of my choosing , can say that your average Engle in a 24hr period will use 1.9amps per hr which equates to 45.6 amps per 24 hrs ,,, next time you test your fridge put your multi meter or amp guage inline ,you may just be suprised to find that the Engle actually uses round 3.2 / 3.5amps while in the "on" part of the cycle ,,thats why even the Engle specs state 1.9amp draw per hr.

Calculations used as an example only! What sort of factual information is that?
Perhaps you should have better "qualified" your example so that people are not misled?

That is why I contributed my personal experience to the thread. To give the Originator some real life facts to consider.

The Engel specs state a maximum draw of 2.7 amps. (at least for the model I have)
Oh and I have no need to "test my fridge" with a multimeter every time I use it. I'm out in the bush to enjoy myself, not practice paranoia measuring "amp hour usage".
As long as the contents are cold enough and the 12 volt supply is healthy, I'm happy.

As I have stated, I have a "growth path" available for solar charging should I find I need it. I just haven't found the need.

Sandman , as I stated earlier , an AVERAGE of 1.9amps per hr which is a reasonable and feasable amp usage which equates to 45.6 amps per 24hrs ,you are the one who brought up fridge "cycling" and get your figures a about t

Not at idle it's not. It depends on the RPM the alternator puts out the rated current. That's normally in the rev range in which the vehicle is driven.

I should have written over a couple of thousand (engine) RPM.

And pigs fly , ,,, as a backup yes use your car sitting and running at a FAST idle ,long term power source ?? no way , why would you want to use a $50000.00+ vehicle in a detrimental way [to the vehicle] when a couple of thou$ gives you an unbreakable/ cheap[perkw] /clean power source that no one can complain about and you can use anywhere that the sun shines..

Even when My batteries are charged, if I start my car and put my Low beam on, the alternator doesn't put out enough charge to keep the battery isolator "on" until I increase the revs.

You would need at to run the engine at least a "fast idle" [1000rpm] if not more.

Remember that the alternator is designed to run at optimum when over 2000 RPM

a. You can't charge ANY lead-acid battery in an hour - and certainly not from an Alternator.

b. My 3.2 DiD Pajero charges at 25 amps at idle. The Alternator is rated at 125 amps.

Mike

An alternator, via the regulator supplies variable amps to the Battery system on an as required situation, to explain a bit more, a battery that is fairly flat will be charged at a far higher rate than a battery that is nearly fully charged.

A fully charged battery will at times effectively recieve none to miniscule amps from the alternator/regulator because it's fully charged and the opposite applies, a heavily discharged battery will recieve heaps of charge from the reg till it is fully charged.

The 125 amp alternator does not supply 25 amps all the time, the alternator would still supply 25 amps to the battery at 3,000 revs, because the amp output to the battery from the regulater depends on the condition of the battery, you can't put 125 amps into any battery - not without a big bang.

all the above is said without any attempt to denigrate the original poster...
but to clarify the charging situation with batteries in various states of charge.

"edit" and before I'm 'told' the regulater does not regulate amps, the referance to the regulater in the line starting, The 125 amp alternater.... should have read "alternater/regulater' as was previously refered to in the parragraph above it.

Another good example would be my own Aux battery system, I have an in-line amp guage in fridge power cable, as well as LCD display in solar reg, at night both show ~8.2 amps negative when fridge is running, however when in direct sun can show 2 to 5 amps positive, still with fridge running, due to the fact that the solar system is putting into the Aux battery system more power than the fridge is using when running, when in direct sun.

If in direct sun and the fridge stops cycling the Aux batteries can be seen to be charged at ~12 amp and shortly after as the Aux batteries are reaching fully charged the 'solar' regulater is only putting O.2 amps into the charged Aux batteries.

"My 3.2 DiD Pajero charges at 25 amps at idle. The Alternator is rated at 125 amps.
"

To clarify -
1. Some charging systems are capable of putting out useful current when the engine is at idle.
2. In my vehicle at idle, it can put out 20% of the Alternator's peak current capability into the battery.
3. Diesel engines are more likely to have higher output current at idle because their peak engine revs are around 4000 whereas petrol engine peak revs will be closer to 6000.

Nice rig you have there Grungle very nice setup. Some really good ideas from everyone, but it looks like the duel battery setup will have to do for a while unless the tax man wants to give me a large tax return.

Cheers TAS PAJ. Whatever you do, it is step in the right direction and you can build on it from there. Good luck with everything.

Regards
David

Would you like to tell all and sundry what "decent" fridge uses 30amps per day ,,factory specs from the two major fridge compressors used in 12v all state figures way more than 30amps per day [24hrs].

It would be my pleasure to tell all and sundry, Alloy.

The engle fridges use between, 0.5 to 2.5 AMPS Maximum

look here:
Site Link

they do not run 24 hours a day (it depends how often you open the door and ambient temperature)

So we have a maximum range of between: 12Ah (0.5A x 24h) and 60Ah (2.5A x 24h), assuming the fridges are running 24 hours a day.

If it makes you happy Alloy, we both can be right.

Max
Information Manager
Energy Matters
1300 727 151

No way ,real world use shows that a 40lt Engle _Affordable_Storage_Drawers.aspx over 3amps on kick in and settles to 2.7amp with an average of 1.9amps total draw per hr ,used as fridge ,setting 1.5 / 2 on the dial temp internal 2c / 4c ambient average over 24hr = 27c. fridge full /opened 6times.

Hi Alloy,

I'll have to admit I have never used the fridge, i was just working off the specs I read. I guess it would depend on system voltage. If it works at 24V (as opposed to 12V) it would probably use half the amps, but you would need twice as many batteries.

If you're only going away for a few days, then you could get away with the 80W panel and 100+Ah of batteries. A popular configuration that we sell is 2 x 6V Trojan T105 Batteries (250Ah) and an 80W panel. The panel puts in between 20-30 Ah a day under optimal conditions, so the batteries won't get discharged more than 50% (which you do not want to do for deep cycle batteries) over a few days out in the bush.

Regards,

Max

Mainey ,where have you been hiding for the last couple of months ,"they" finaly let you out of goal eh ?? lol.

"4.8 amps x 6 hours = 28.8 Amps "
- you can't multiply amps by hours and get amps. Cumulative current is amphours (not amp/hours).

This should read
"4.8 amps x 6 hours = 28.8 Amphours "

Alloy, been away up north for a while, back in Perth only for a week then returing back to the far North West for the rest of winter.

Mike, what I did is multiply the number of amps produced by a 80watt solar panel (~4.8 amps is specified on most 80watt panels) by the number of hours (full sun hours per day) to get an answer which is relative to the total number of amps produced in the day, nothing more nothing less!! the answer is 28.8 amps (total) remember the original statement was the number of amps available in a day!!!
There is 28.8 amps (total) produced by the solar panel in a 24 hour day using this equasion.

If you draw fuel from a tank at 2 litres per hour for 24 hours, then you will have drained a total of 48 litres, the total is NOT 48 litres per hour. i.e you multiply litres per hour (2) by hours (24) you end up with (litres per hour) x hours = litres.

Similarly amps x hours = amphours, NOT amps.

Amps = an instantaneous rate of flow

Amphours = cumulative amps over a period of time. If measured over one hour, then the number of amphours will be the same as the AVERAGE amps over one hour, even though the amps at any one may vary e.g. 4 amps or zero amps as the thermostat cycles on and off.

If you are reading values off your Steca note that "A" indicates it is displaying Amps and "Ah" indicates it is displaying Amphours.

Panel rated at say 5 amps/hour used for 6 hours gives you 30amps.
(5amps/hrs x hrs =amps)

The output of a panel in amps, not amps/hour.

Maybe it would be easier if you thought of the instantaneous "flow" of current as "amphours per hour". This is still a technically correct unit, just a bit wordy ( since the two hours cancel each other out anyway).

Then a panel putting out 2 amphours per hour for 6 hours would put 12 amphours into your battery.

2 "amphours per hour" x 6 hours = 12 amphours.

The units used to measure electricity have not changed in the last hundred years.