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Open Roads Forum  >  Tech Issues

 > Starting out in solar

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Almot

Vancouver BC

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Posted: 06/11/12 01:20pm Link  |  Print  |  Notify Moderator

BFL13 wrote:

But if you have 6s of course you need to jump to four from two.

I recall now there were GC 6V batts as big as 260 AH each. Huge and heavy, though. A pair of those will make 260 AH bank @12V. The OP mentioned that he was prepared to limit the use of microwave for short-term boondocking, this would resolve the problem.

BFL13

Victoria, BC

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Posted: 06/11/12 01:33pm Link  |  Print  |  Notify Moderator

You also have 100amp draws from the kettle or the toaster. You can boil water on the stove, but never again will we use that nasty stove-top bread burner rack, lame so called toaster instead of a proper electic pop-up toaster. Next, the poor OP will be advised to go back to striking a flint to make his fire instead of flicking his Bic.


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Almot

Vancouver BC

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Posted: 06/11/12 02:01pm Link  |  Print  |  Notify Moderator

BFL13 wrote:

You also have 100amp draws from the kettle or the toaster.

The OP was willing to forgo 120V coffee maker and toaster too, for short-term boondocking.

IMO, this doesn't do any harm to nutrition. Toaster and bread itself isn't much useful if you eat other grains like pasta or buckwheat. The gourmet value of coffee maker VS stove-top or instant coffee can be debatable, but for boiling a kettle I don't see a difference between propane stove and electric hotplate, water will taste the same. Some people drink tea and hot chocolate, you know...

Bic lighter? You're living in the past, man. Even hikers don't carry them anymore, except as a backup. Their portable LP stoves are equipped with piezo igniter.

westend

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Posted: 06/11/12 05:26pm Link  |  Print  |  Notify Moderator

Some great stuff, guys, thanks so much for continuing to help me narrow my choices.
I've been scouting around for deals on batteries but will do a little more homework on what I can get. I know Trojan is a good product and the GC batteries will definitely be robust. FWIW, I have some experience with GC's, one of the more interesting ones was a gentlemen that came to visit me one day with one of the first electronic "pulsing" chargers. He held a patent on the device and I don't know if he sold that to some of the newer battery tenders or if they developed the technology simultaneously. If claims were to be believed it really improved longevity.
Anyway, the battery bank will be sized by what has been posted in this thread and current space conditions. At the end of the day, I'll have two banks of batteries with a total of 300 AH.
Would it behoove me to step up over just a battery charging system, using higher voltage panels and an MPPT controller versus 12v. panels and a PWM controller? I can see the efficiency of power delivered by the higher voltage system but is it going to be a small increment in usage instead of the lower voltage system?


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BFL13

Victoria, BC

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Posted: 06/11/12 06:03pm Link  |  Print  |  Notify Moderator

I don't know the solar situation down south in winter but ASSuming it is similar to summer "up here" I can comment based on that.

For our camping we only use solar in summer and don't bother with it for winter camping. This might be similar to OP's idea of only using solar down south in winter or maybe up north in summer too.

We use about 140AH day in winter with furnace thrown in and about 70AH in summer with little or no furnace but includes 2000w inverter running the MW, toaster, kettle as required maybe 30 minutes big inverter total per day. Add some hours of movie time on the small inverter--peanuts for AH.

A 130w panel (8.2 amps max--except in cloud effect can hit 11 and sometimes sits at 9.6 for good lengths of time) and a $60 16a simple controller keeps us mostly ok in summer where we can tilt it and point it too. Tests show that the same panel, lying flat will do 56AH on a good day. Two of those lying flat would do as well or better than this one does following the sun.

So if your AH use is under 100 per day and you have say 200 or so watts lyijng flat and a simple controller you should be in good shape down south in winter or up north in summer.

Those guys with 400-900watts on their roofs are set for winter up north I guess. No idea what they do with all the AHs in summer. ?

IMO the OP should concentrate on getting enough AH battery bank for inverter use -300 or more (prefer at least four 6s)- and don't bother with the MPPT big panels for huge money. Just get 200w or so of 12v (17v) panels and a cheapo PWM controller --30amps would be good to handle cloud effect etc. (210w will get you about 13 amps at noon so a 30amper will have lots of margin and not cost much more than a 20 amper)

But it is key to get at least a 1000w Honda gen with all the money you saved by not going so overboard on the solar.

Now you have some "balance" so you can camp in all conditions, charging with solar or gen as required when required and enough battery bank so you can do it all without any nail-biting.

full_mosey

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Posted: 06/11/12 06:32pm Link  |  Print  |  Notify Moderator

With 300AH of battery you will have no problem with the three day trips.

I would hold off on the solar decisions. You could extend a day if you manage your usage. There is always the option of using jumper cables to the tow vehicle(TV) if you need to freshen the bank or want to use your inverter for short runs.

It is hard to get solar right the first time and can be expensive when you figure out what you really need.

I ended up with 300W solar and 189AH total battery. That puts me at PT's fully-recharge-daily(150+) end of the range. My longest dry-camping trip is 30 consecutive days.

HTH;
John

Almot

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Posted: 06/11/12 06:46pm Link  |  Print  |  Notify Moderator

West, you need to narrow your scenario down again, now that you have all the numbers. This thread is becoming so long that I don't know what we are talking about now.

3 days boondocking? In summer? With 80 AH fridge and microwave? Then you draw at least 150 AH a day, and you need at least 400W panel if mounted flat. Better yet, 2*235W, because there are bad weather days and because panels will lose 10% efficiency in 10 years. 2*235W will be 24V panels because panels larger than 200W are always 24V. For 24V panels you need MPPT controller.

Modified solution for the above scenario: 2*140W panels @12V, cheaper PWM controller, and batteries won't be fully charged but will have more than 50% SOC by the day 3, and without a generator you won't be able to extend your stay or will run into trouble if it will rain 2 out of 3 days. With 150 AH drawn daily, you will need a generator after 2 days of bad weather, with any imaginable battery bank.

Another scenario: 3 days with a proper 12V fridge and microwave.

Yet another scenario: 3 days with an LP fridge, sans microwave, toaster and other unnecessary (IMNSHO) gadgets, but leaving "peanuts" like laptop and TV on.

Alternative solution offered by Mosey - no solar, but 300 AH bank. Doable for 3 days on one condition: you have to get rid of 80 AH fridge.

Take your pick. In any of these scenarios you can go without a generator, if your system is sized properly (this includes sizing on the consuming end).

full_mosey

Oklahoma

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Posted: 06/11/12 07:09pm Link  |  Print  |  Notify Moderator

I thought the dorm fridge was off the table and that is the basis of the postpone the solar suggestion. For three day trips it is 5-day ice chests and block ice.

HTH;
John

pianotuna

Regina, SK, Canada

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Posted: 06/11/12 08:17pm Link  |  Print  |  Notify Moderator

Hi,

Cheapo pwm doesn't do temperature compensation nor three stage charging. You have to think solar not generator based charging.


Regards, Don
Full Time in a Kustom Koach Class C 28'5", 256 watts Unisolar, 875 amp hours in two battery banks 12 volt batteries, 2500 MSW watt inverter.

BFL13

Victoria, BC

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Posted: 06/11/12 08:35pm Link  |  Print  |  Notify Moderator

For a solar assist set-up, why do you need such accuracy in voltage that temp comp is required so not to exceed/go below some set point?

It will charge the batts whether it goes between 13.5 -14.3 or between 14.1-14.9 who cares? The OP is doing this down south so he doesn't have to worry about cold temps making the set voltage too low. It is just to make sure he gets his three or four days in before the batts get below 50%.

My cheapo controller has temp comp but it's not doing anything useful the way I use solar. In fact it is a nuisance because if I want to limit the high point to 14.9v so it won't do over 15 and make the inverter quit, then I can't just set it to 14.9 and it will stay there. Phooey on temp comp!

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