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post #1 of 42 Old 10-28-2013 Thread Starter
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Solar Panel Confusion

Hi Folks,

I have four panels on my Spirit 28, installed by the previous owner. Now that the boat is on the hard, it's time to take a look and see what the heck it's all about.

I have four batteries, tied together in two groups. Each group was two batteries, positive to positive, negative to negative.
one set are "car size" marine batteries marked 110ah. The other pair are "double size", with no indication of amp-hours.

The "car size" don't hold a charge, when I pulled them yesterday I discovered they are VERY low on fluid .

Anyway.....
I never looked at the panels much, and wasn't even sure if they were putting anything out. I was busy enjoying my boat when I could, and fixing the big stuff (i.e. engine, sails, etc).

Here is my confusion, the four panels are paired. Each pair is connected to a small control box. Each control box connects in turn to one set of batteries. Those two control boxes are putting out 20v with 6.5-7 amps...... that seems like a lot. And, from what I have read 20v is way more than you want to use to charge a battery.

I would like to replace the control boxes with MPPT units. Do I need an MPPT unit for EACH panel/battery combination? Can I use one MPPT to run all four panels to all four batteries?

thanks

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post #2 of 42 Old 10-28-2013
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Re: Solar Panel Confusion

I just bought a phocos pwm 8amp controller since the previous owner of my boat thought it wise to use lithium batteries and a direct link to the panels...the panel puts out around 19volts too...which is common unregulated...I dont know what size my panel is but its looks to be around 100 watts or so max.

mppt controllers are great but much more expensive they also do better with bigger banks and more loads and charge better and dont overcharge as much as shunt and basic pmw controllers...they also have a lower equalizing or floatong charge...which gives better pak charging and wont fry batteries as much.

having said this I will be doing the same as you and rewiring my panel...

there also seems to be a lot of positive ground panels and chargers these days and I would like to know what most guys do in this situation....

make sure you fuse with at least twice the amperage as the controller allows...my 8 amp charger says it needs a 20amp fuse inline to the battery...

Ill let you know what I end up doing...

good luck!
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post #3 of 42 Old 10-28-2013
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Re: Solar Panel Confusion

If you have 4-12V 6 celled batteries, two banks. Connecting them like this is no good. Will not charge evenly or discharge evenly. Unless you have a Battery Combiner. Better to use 6v batts and connect pos to neg.

Eric
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Last edited by Delta-T; 10-28-2013 at 04:31 PM.
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post #4 of 42 Old 10-28-2013 Thread Starter
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Re: Solar Panel Confusion

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Originally Posted by Delta-T View Post
If you have 4-12V 6 celled batteries, and you say pos to neg then you have 24V system? Are you sure they are not three celled 6V batts?
Sorry - that's positive to positive, negative to negative. parallel connection.

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Re: Solar Panel Confusion

From what i'm reading it is possible to run one controller (MPPT) for multiple panels. I am guessing with two sets of batteries (switchable between the two sets, to keep house batteries and starting batteries separate for example), I should have two independent charging units, so that the whole systems are separate from each other?
Or would that matter?

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Re: Solar Panel Confusion

you want to avoid dissimilar sized and amped batteries in general...I would use 2 banks with 2 controllers since you have uneven banks...

unless you go new batteries gel or better you dont "need" the mor expensive mppt chargers but with big banks and stuff youll see 10% or more charge in same conditions...

cheers
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Re: Solar Panel Confusion

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Originally Posted by christian.hess View Post
you want to avoid dissimilar sized and amped batteries in general...I would use 2 banks with 2 controllers since you have uneven banks...

unless you go new batteries gel or better you dont "need" the mor expensive mppt chargers but with big banks and stuff youll see 10% or more charge in same conditions...

cheers
thanks. Two might be the way to go.
Is it possible the two panels overcharged my smaller batteries, and dried them out?
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Re: Solar Panel Confusion

thats exactly what happened...The batteries I had were computer batteries backups or something they can be charged at a higher voltage...but the panel was direct...it lasted for a while apparently but not my cup o tee

I once left a brand new battery on those stupid westmarine solar maintainers that are only 5 watts or so for 6 months and sure enough because the voltage is unregulated it fried my battery even with such a minimal power output.

if yo are reusing your old batteries I would not pay extra for the mppt controllers YET...I would first buy a couple of basic pwm chargers at 25% over(amperage) your panels max output...then I would invest in a nice amp controller so you can see what your panels are actually putting out...you can also find parasitic losses this way if you hook it up to various sources.

then if yo want to add panels or battery banks you know exactly what you are dealing with...

I will be doing this next week or so...cables also play an important role...how much bigger than minimum spec, length, how close the charger is to the battery source, etc...all p`lay an important role
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Re: Solar Panel Confusion

Yeah, to second the above, MPPT controllers are for maximizing charge from the solar panels although they do also help the over voltage thing. You definitely need two controllers or there are controllers that connect to separate banks, such as this one

https://rvsolarstore.com/index.php?r...&product_id=73

You might be able to get those two batteries back by refilling with distilled water and running a desulphating charger. I have had really good luck bringing back batteries that would no longer hold a charge with the battery minder chargers. Regular chargers weren't doing the trick. They have them as low as about $50 or so. They also have a solar charger that looks very interesting to me if I had room for bigger panels.

Batteryminders Specials | BatteryMinders.com
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Re: Solar Panel Confusion


That unit looks quite good. I think its ideal for two banks, switching all the power to one when the other is fully charged.

there are cheap MPPT units on ebay..... should I assume you get what you pay for?
MPPT 10A Solar Regulator Charge Controller 12V 24V Autoswitch Solar Panel TSR | eBay

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Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did. So throw off your bowlines. Sail away from safe harbor. Catch the trade winds in your sails. Explore, Dream, Discover.

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