How to match the batteries to a panel and charger.

[ILFE]

I hope I can explain myself clearly enough, here. I'm not always very good at doing so. Anyway, I just read the following quote by Sunking:

Good question that is asked a lot. No definitive answer exist. But here is some good rules of thumb:

500 watt panels and less 12 volt
501 to 1500 24 volts
1501 and up 48 volts.

12 volt systems use inexpensive PWM controllers. MPPT for all others.

My system will be 12vdc. So, I am under the impression the following will work fine:

A. In order to charge the battery bank from a 500watt array, I should use a 50 amp rated PWM controller.
B. In order to charge the battery bank from the grid, I assume that I should have at least a 50 amp rated charger.

With this in mind, I have three questions, please.

1. If the above hypothetical statements are true (amp rating for the chargers), how many 6vdc, 220 AH batteries should I be able to reasonably keep charged using either option, above?

2. Is there a specific formula I can use to determine this in the future?

3. Lastly, in your opinion, am I correct in that a 50 ampere controller and/or battery charger would be sufficient for this setup?

Moderators: This is not really a grid tie post, but I did not realize it until the post was made. [mod - moved]

[Sunking]

Paul battery capacity is determined by the daily watt hour use. Battery capacity formula is AH = [WH x 5] / Battery voltage.

Panel wattage is determined by daily Watt Hour use and location.

Lastly charge controller size is determined by panel wattage and controller type.

[ILFE]

I understand there are specific formulas to figure out specifics.

But, considering the parameters vary so widely, could the parameters I have shown above just be assumed?

What I am trying to do here is, to get an estimated requirement for batteries, so I can order them prior to building the solar array.

[Sunking]

What I am trying to do here is, to get an estimated requirement for batteries, so I can order them prior to building the solar array.

Paul I guess I do not understand what you asking. Finding the battery size required is very simple and straight forward. Determine your daily watt hour usage, multiply it by 5, then divide by the battery voltage. [Daily wh x 5] / Battery voltage. so if you need 1000 wh per day and want to use a 12 volt battery then [1000 x 5] / 12 volts = 416 Amp Hours.

As for AC powered battery chargers ideal size is C/10 where C = Battery Capacity Amp Hours @ the 20 hour rating. So if it is a 100 Amp Hour battery then you want a 10 amp charger

[ILFE]

Paul I guess I do not understand what you asking. Finding the battery size required is very simple and straight forward. Determine your daily watt hour usage, multiply it by 5, then divide by the battery voltage. [Daily wh x 5] / Battery voltage. so if you need 1000 wh per day and want to use a 12 volt battery then [1000 x 5] / 12 volts = 416 Amp Hours.

As for AC powered battery chargers ideal size is C/10 where C = Battery Capacity Amp Hours @ the 20 hour rating. So if it is a 100 Amp Hour battery then you want a 10 amp charger

Sorry about that. Yes, that is what I was looking for.

[Sunking]

Depending on the battery type Lead Acid batteries can do as high as C/8, and AGM's as high as C/4. But always refer to the owners manual for recommended charge rates. C/10 is just the default safe rate. Note none of this applies for Gel batteries

[Mike90250]

...
As for AC powered battery chargers ideal size is C/10 where C = Battery Capacity Amp Hours @ the 20 hour rating. So if it is a 100 Amp Hour battery then you want a 10 amp charger

If you are solar charging the batteries, you have to tweak this to allow the batteries to recharge and have enough solar to power your daytime loads, in the 4-6 solar hours in a day.