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Charging Batteries Through Solar Controller?


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#1 CoreyTrevor

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Posted 23 July 2020 - 07:39 PM

I came up with a weird idea. Or maybe everyone does it and I haven't noticed.

 

I want to use a plug-in battery charger, not sure which one yet, connected to the PV inputs on my Victron MPPT 100/30. The reason for this is to be able to use the charging profile of the Victron to control charging of my Dakota Lithium batteries. I want to charge them to only 80-90%, as I have learned that this should increase their lifespan. I believe most LiFePO4 chargers will not stop charging until +/- 100%.

 

I could try to find an adjustable LiFePO4 charger, but the Victron is already there and designed to do what I want to do. I would switch off the breaker between the panels and controller when using the shore power charger. I know the charger will also have to be able to put out high enough voltage to get the batteries to the desired SOC.

 

I found a couple people online talking about doing this and saying it's a good idea and will work, but there is some really good solar knowledge here, so I was hoping for some input on this.

 

So what say the (obviously) more solar-savvy members about this?

 

Thanks!   :ph34r:  :)


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#2 Jack

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Posted 24 July 2020 - 08:24 PM

Checkout the Victron Forums: community.victronenergy.com

A quick search yielded two posts that may help. More/better searching should bring up more.

 

https://community.vi...ut-to-a-sm.html

https://community.vi...-instead-p.html

 

 


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#3 rando

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Posted 24 July 2020 - 08:24 PM

While not exactly standard practice, this is a great way to charge your batteries, and it works well.  

 

What you want for this is not a battery charger, but a DC power supply.   The power supply voltage needs to be about 5V over your battery voltage, and ideally close to what your solar panels put out. 

 

Something like this 600W 24v at 25A power supply would work well:

https://www.meanwell...spx?prod=SE-600

https://smile.amazon.../dp/B00DEDB2U2/

  

The key thing is that the power supply must be able to support the maximum power (as in Watts) that you will be charging the battery at.   If you want to run your MPPT 100/30 at 30A, then the power supply must be rated for at least 30A * 14.5V = 435W.  Figure some losses in the system, and you should probably go for at least a 500W power supply.   You can just plug this straight into the portable panel SAE connector on the side of your camper, or wire it internally off the 120V shore power plug inside the camper.    No need to switch off the solar panels, it is fine to put the power supply in parallel with the panels. 

 

You can use a smaller power supply, but you will need to reduce the charge current in the MPPT100/30 settings to make sure you stay under the power rating of your power supply.   If you dial back the charge current to 20A (~300W), then something like this would be fine:

https://smile.amazon...l/dp/B07VRK86SP


Edited by rando, 25 July 2020 - 03:00 PM.

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#4 CoreyTrevor

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Posted 26 July 2020 - 08:07 PM

Hey, thanks for the replies. Sorry to take so long to get back here. Every time I looked at my post on the main page, it said zero views and no replies, so I never opened it back up. It's still stuck on zero and never moved to the top either. No idea why.

 

Edit: I just noticed that my post was moved to the electrical forum.  I finally noticed at the top of the page that I was in a different forum. I tried clicking on the arrow by my post, but it doesn't give the message unless you hover on it and don't click.

 

I did search around, like I always do before asking a question, but I knew I would get some good info directly related to my situation from the knowledgeable people here. And look, I did!  And since I didn't find anything on WTW about this, it seemed like having some info here could be helpful to others, now or in the future. Maybe someone will just happen on it and have it work well for them.

 

rando, is there a reason I couldn't use a charger like this one, set to 10A, which I already have?

 

99d0b2d762edbbaa7e81b6afb1d4e985.jpg?_ve

 

I don't need a high charge rate, 5-10 amps will be plenty. Would it hurt to try it set on 10A? I think you are saying that with a power supply, if I have the Victron set at 30A max charge, it will draw too many amps from a lower amp 12V power supply. I don't really want to have to change the settings just to top off the battery, but I have no need to charge at 30A either. Is there some kind of power supply that can limit itself to 5 or 10 amps? I've never played with AC to DC power supplies before, so I don't have a clue.

 

I have my 3 panels in series with no blocking diodes. Will the panels act as diodes with power coming at them from the opposite direction?

 

Thanks again for the help!


Edited by CoreyTrevor, 26 July 2020 - 08:15 PM.

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#5 rando

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Posted 26 July 2020 - 08:20 PM

That charger probably won't work.   The Victron MPPT won't switch on until it sees the battery voltage +5V on the solar panel input.   Unless the charger is putting out > 18V, the MPPT won't turn on.    If you are OK with lower charge currents, you can use the much cheaper 15A/24V power supply and set the max charge current to ~15A on the MPPT. 

 

With 3 panels in series, you would want to be a little careful not to have your power supply plugged in AND the panels in the sun as the higher voltage from the panels could damage the power supply.  However, I assume you are parking indoors if you want a shore charger.  You could also use a 48V power supply if there is a chance your panels are illuminated. 

 

Think of the power supply just as another panel in parallel with your existing panels.   If one of your panels is shaded, you still get the power from the others, and it doesn't damage the unshaded panel. 


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#6 CoreyTrevor

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Posted 26 July 2020 - 08:47 PM

You're right. The charger only puts out around 11V open circuit. Oh well.

 

I think I understand now what I need to do to make this work.

 

I think I will look at higher voltage power supplies around 30A, so I don't have to constantly mess with the settings, or forget and then fry something.

 

Thanks again for the help, and the reply in 13 minutes!


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