Charging different Ah batteries

[fivewin]

Suppose you have an array of 300Wp panels and you aleady use a 180Ah battery. You want to add a smaller 45Ah battery to your system.

What is the best option to charge the extra smaller battery with the existing solar array?

[Wy_White_Wolf]

The best and only real option would be to something like Morningstar's DUO charge controller that has the capabilities of charging 2 separate battery banks.

WWW

[fivewin]

Ok thanks. Suppose it is not available in the country where I am. I was thinking of charging the second battery with an ac battery charger via the inverter, only during peakhours. Is this a good idea or not?

[Suprasoup]

You want a dc to dc charger. Tecmate makes a charger that will charge a smaller battery from a larger one:

https://www.amazon.com/OptiMATE-TM-500-Battery-supply-Charger/dp/B011J76CFE

Personally I use a RC hobbyist charger like a Hyperion EOS or Tenergy. Almost all of them have settings to charge Lead acid batteries. Bonus you can use it to charge pretty much anything else as well. They come in both AC and DC models.

https://www.amazon.com/gp/product/B01E5KB6T4/ref=s9_dcacsd_dcoop_bw_c_x_3_w

[Sunking]

Suppose you have an array of 300Wp panels and you aleady use a 180Ah battery. You want to add a smaller 45Ah battery to your system.

What is the best option to charge the extra smaller battery with the existing solar array?

300 watts / 12 volts = 25 Amps. Way too much for such a small battery unless it is an AGM. Whatever you do, DO NOT connect i tin parallel with the other battery. If you did the larger battery can supply enough current to give a Bad Hair Day by soaking you with battery acid spewing out.

[Gerard Fivewin]

Thanks for the replies, Sunking that is what I mean. Is it a good idea to charge the smaller one with an ac charger via the inverter only during peak hours. The smaller battery will be used for some low wattage leds only and sometimes a dc fan. The 180Ah AGM battery is already being used for some time. They up till discharge the bigger battery for 30% only and now they want to load more and want to use therefor a smaller battery.

[Sunking]

Thanks for the replies, Sunking that is what I mean.

You are welcome.

Is it a good idea to charge the smaller one with an ac charger via the inverter only during peak hours.

Lot of ways to skin this cat. Just keep charge current to C/6 or less. 45 AH / 6 Hours = roughly 8 amps or less. If using MPPT controller a 100 watt panel.