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Old 11-06-2018, 09:37 PM   #1
Mini-Skoolie
 
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Do I need a charge controller?

This might be a dumb question from a newbie, but bear with me.
I am in the planning stages of an electrical system for a skoolie. I plan on using 8 (maybe just 6) 24 volt, 300 watt solar panels. I plan on keeping the system 24v and use a step down for 12 volt operations.
I like the look of the OUTBACK POWER FX2524MT 2500W 24V MOBILE/MARINE INVERTER/CHARGER to charge my group of 24v batteries and to invert to AC for AC operations.
Here is the dumb question. Do I need to add Charge controllers? The way I understand it, the controllers are used for battery charging. Could I just run from the panel combiner to the Inverter/Charger?
Thanks
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Old 11-06-2018, 10:56 PM   #2
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Yes.

The battery and loads (incl inverter) are in the same circuit with charge sources (incl the SC output.)
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Old 11-06-2018, 11:03 PM   #3
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Originally Posted by john61ct View Post
Yes.

The battery and loads (incl inverter) are in the same circuit with charge sources (incl the SC output.)
Thanks for the reply. I'm a little confused though. Yes I should use controllers? or yes I can run straight? Not sure what you mean by the same circuit
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Old 11-07-2018, 06:36 AM   #4
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Yes you need a charge controller.
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Old 11-07-2018, 07:55 AM   #5
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The only context where no controller is OK:

Storage, start with 100% Full batt
Tiny panel, used only to counteract self-discharge and vampire loads, amps under maybe .05C, compared to batt
Cheap Starter batt you don't care about
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Old 11-07-2018, 08:40 AM   #6
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Old 11-07-2018, 09:37 AM   #7
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Thanks, I think I'm starting to understand. I think I read somewhere on this site that I would need a separate controller for each panel. Is this true or could I get by with one (or two) big one(s)?
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Old 11-07-2018, 01:08 PM   #8
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Most people buy one big SC for all their panels.

But all the panels on one SC should match each other.

Some try to get best optimization of partial shade handling by using a 1:1 ratio.

Victron MPPT's pricing model allows for that without costing much more, 75/15 model only $125 supports 220-260W. Best to buy higher Voc rated panels to maximize MPPTs advantage, say 40+V
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Old 11-07-2018, 02:20 PM   #9
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WOW! That's the model I was looking at! The panels I was looking at are the Renogy 300 Watt Monocrystalline Solar Panel which have a VOC of 39.82 Volts, so I guess that would be good enough. I'd be using 8 Trojan J200-RE 12V 200AH (20HR) Premium Line Flooded Batteries, paired in series to effectively create four 24 volt batteries. Could I use one of the previously mention controllers for two panels running to a pair of batteries, or would something beefier be better?
While I'm at it, when running from the inverter/charger (charger side) to the batteries, could that connection be made through a buss bar? Inverter side?
BTW, thank you again for being so informative and patient. I'll try to come up with a diagram for approval.
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Old 11-07-2018, 04:34 PM   #10
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Originally Posted by erniejt View Post
That's the model I was looking at!
Need to go up a step if 12V bank, the 15A max output would cut off IMO too much power at peak times. Fine for a 24V House circuit though, but why?

Yes that panel voltage would let the MPPT algorithm optimize well.

> Trojan J200-RE 12V 200AH (20HR) Premium Line Flooded Batteries, paired in series to effectively create four 24 volt batteries

RE line is pricey, but yes should last longer **if** you coddle them well.

Put all those batts into one big House bank, much better for many reasons, including greater total capacity (Peukert's Law) thus less V drop, shallower cycling and greater longevity.

Then all your charge sources get connected via the same busses.

I like separating Loads from Charge busses, but that's really dictated by my BMS design for LFP usage, not usual for lead banks, unless it makes sense to you for other reasons.
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