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Post Info TOPIC: Solar Panel for trickle charging - sizing to match AGM capacity
UPO


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Solar Panel for trickle charging - sizing to match AGM capacity
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Afternoon - the subject pretty much says it all - what size solar panel ( in Watts ) is appropriate to maintain AGM battery charge ?

Just putting a shelter over the van so will place a smaller solar panel on the garage roof - battery capacity is 2 x 120Ah AGM with  balanced wiring rather than having the second battery piggy backed off the first.

Using a Ctek D250S controller for the fixed 2 x 140W panels and will connect to the Ctek solar inputs with 6mm twin core ( 4.59mmsq cable core running about 15 meters from smaller new panel to controller ). Will have a permanent connection from the Ctek to an Anderson plug so easy connect / disconnect.

In Brisbane bayside and have clear Northern aspect for most of the day - so what size panel ? Thinking of 30W monocrystaline.

Thanks for any input

 

UPO - Richard

 



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Plendo


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Richard, are you leaving anything running in the van, or is it just to maintain the batteries in a dormant state?



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Discovery 4, 

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Ondabeach


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UPO, a 30w panel will be plenty to maintain your batts with no/negligible load.



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Cheers, Steve.

 

"Any day above ground is a good day... unless you're a spelunker  :)"
Peter_n_Margaret


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30W is far too big unless it is regulated. Over charging could result.
A major feature of AGMs is their low self discharge rate. This is even more significant in cold conditions.
AGMs are typically fine for at least 6 months standing without attention provided all loads are disconnected.
To keep them topped up, an unregulated 5W solar panel will be fine.

Cheers,
Peter

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OKA196, 4x4 'C' Class, DIY, self contained motorhome. 960W of solar, 400Ah of AGMs, 310L water, 280L fuel. https://www.oka4wd.com/forum/members-vehicles-public/569-oka196-xt-motorhome
 

 
Ondabeach


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The rate of charge isn't up to the solar panel Peter, it's controlled by the charger. Richard could put a 250 watt panel up there if he wanted to waste the money, and he wouldn't be at any risk of over charging. You may have assumed he's going to connect his 'stand-by' solar panel directly to his batteries, but a careful read of Richard's original post shows that isn't the case.



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Cheers, Steve.

 

"Any day above ground is a good day... unless you're a spelunker  :)"
UPO


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Thanks for responses -

Plendo - I have asked about leaving a 1W LED light on all the time ( when van stored ) so there is activity on the battery and there responses have been form totally opposite poles...  A Battery World techie told me of a client who found that the self discharge rate was below the "trigger" rate for the controller to activate so the battery NEVER received any charge - result = failed battery.

Others have said that the Ctek D250S will detect ANY discharge and as such will allow the solar input to maintain full charge.

As the van has been stored in the open, often during the day, I leave the stero on to tickle the batteries - the fact that the van's roof solar is putting in, does this mean that the stero is, in fact, being run by the panels and any battery input is effectively nothing ? Should I just leave the stero on 24/7 ? or a 5050 LED ceiling light panel on 24/7 ?

Peter, the new small panel will be fed to the solar inputs of the Ctek D250S - I am assuming that the blocking diodes of the van roof panels will stop any reverse current flow and any input from the new panel will in fact go where I am thinking it will.......

Many years ago, I had a small cruising yacht - no battery, kero lantern, kero stove, 5HP Seagull outboard - Oh so simple but IT ALL WORKED !! - well the outboard most of the time furious especially when not really needed......................

 

Thanks - UPO - Richard



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Plendo


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Thanks for the response Richard.

Given you are running AGM, the discharge rate is so small, I would be tempted to just let it be, just make sure everything is turned off. And plug the van in at least once every six months.

If however you do decide to set up a trickle charger, then a small panel would be enough, as Peter indicated 5W would almost be overkill.

 

 



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Retreat Brampton

 
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