Correct sized charge controller?

mightiestmouse

New member
I've been running my dual battery setup for almost a year at this point. The setup includes

(2) 100 amp hour deep cycle group 31 batteries
Blue sea ACR
Blue sea fuse block with 100amp breaker

Currently running my ARB50 fridge 24/7 and the setup hasn't skipped a beat. If I leave town for a week or so I simply unplug the fridge and move the perishables inside the house. I want to add solar to my setup so that I can remain parked for numerous days and also help keep the house battery charged during the dog days of summer.

My solar panel is a 100W renogy that a lot of people use: https://www.renogy.com/renogy-100-watt-12-volt-monocrystalline-solar-panel/

I know the charge controller I want is the morningstar sunsaver: https://www.morningstarcorp.com/products/productssunsaver-gen-3/

My question is... will the 10 amp version be ok to run with this panel or should I bump up to the 20 amp? Price is about half so just trying to save a little bit of money. Also, could I mount the charge controller in the engine bay or does it need to be inside the cab/enclosure to keep it clear of water?

Thanks in advance
 

Steve F

Adventurer
A 100W panel will put (at absolute most) 7.6A into the battery at 13V, so a 10A regulator will be fine. If I was you I would up the solar though, 100W to charge two 100AH batteries (so potentially needs to put in 100A a day) is not going to do it. Of course if you never draw the batteries down much then it won't matter, but oneday the sun wont come out and you'll need to try and get that 100A in as quick as you can.

So with all that in mind size the charge controller to the batteries you want to charge, not the panels in this case, then you can up the panel wattage in the future knowing the control will cope. The 20A controller will let you put enough charge into the batteries (with the right panels) to bring them from flat to charged in one day of sunlight (Just).

Cheers
Steve
 

sabbatical

New member
Should you decide that your system might grow and you follow Steve F's advice, give Bogart Engineering a look. Their new charge controller is awesome and would give you room to grow your solar input as funds and need grow.
For an in depth review from a well respected member of the mobile solar community, look to handybobsolar.com

Sent from my Pixel 2 using Tapatalk
 

Rando

Explorer
I would argue that you should skip the Bogart stuff - it ends up being ~$350 for a 30A PWM charge controller and an archaic battery monitor, which is totally absurd. The morningstar controllers you are looking at are a much better option, although as others have said, I would up it to a 15 or 20A controller so you have room to grow.

If you want more advanced features, Victron has an very nice 15A MPPT controller for ~$80 or with built in bluetooth interface for ~$100. Given that you can get quality MPPT controllers for only slightly more than a quality PWM controller, I would just go straight to MPPT to gain a little bit of extra efficiency, and the ability to use different battery chemistry in the future.
 

mightiestmouse

New member
All great advice. I know that a 100W panel isn't going to keep (2) 100ah batteries completely charged, but this would only be to shore up my house battery as all of my (extra) accessories currently off of that battery. I oversized my batteries when building my system so I wouldn't have to go back at a later date.

Another controller I found while browsing is by a company called Zamp https://www.zampsolar.com/charge-controllers/ . Their all weather controllers can be mounted exterior to the vehicle which would make my installation that much more simple. Figured I would mount it to the underside of my panel and can view the screen through my sunroof. Cable runs would be extremely simple too.
 

Rando

Explorer
The charge controller should be mounted as close to your battery as possible, not the solar panel. This is for two reasons:
1. If the controller has temperature compensation for the battery (most good ones do) it needs to be at or near the same temperature as the battery. Mounted outside, it is likely to be at a very different temperature than the battery and therefore have a completely incorrect temperature compensation.
2. Losses on the cables between the solar panel and the charge controller don't really matter (particularly with a PWM controller), but loses between the controller and the battery do matter as it means the controller is sensing a higher voltage than the battery is seeing, and with charging voltages a fraction of a volt does matter. So it is fine to have long runs of reasonable size wire between the panel and controller, but you don't want long runs between the controller and the battery.
 
Last edited:

john61ct

Adventurer
The size of the bank does not dictate how much charge input you need each day.

You just need to put more in than you took out since last time it was Full.

A bigger bank just gives a bigger buffer between sunny days (or other charge sources).

With lead batts, getting to true 100% at least couple times a week is required for good bank longevity.

As well as only rarely drawing below 50%.
 

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