Charging Rates

[hayton55]

Trying to understand basic electrons here; just picked my MH and it has two Full River 12v 105AH Type 27 batteries. The charge rate on the battery says it has a max charge rate of 30 amps; ok, given that, if you have two in parallel does that mean the charge rate is 60 amps looking at the battery as one big 210AH? Or does the 30 amps suffice to charge both within the same time frame....

 

[snoobler]

Two in parallel are like a 210Ah 12V battery capable of 60A charge. In practice, a lower charge closer to 21A (10% of C) improves longevity. PEAK charges below 5-8% of C should be avoided as charging them at too low of a rate encourages sulfation resulting in capacity loss.

30A for your 210Ah battery is fine.

 

[SolarQueen]

Correct. Double the Ah in parallel, double the charging rate. But that's a pretty high charge rate, when they say max, that doesn't necessarily mean recommended or optimum. 25A or lower each may extend their life.

 

[SolarQueen]

Two in parallel are like a 210Ah 12V battery capable of 60A charge. In practice, a lower charge closer to 21A (10% of C) improves longevity. PEAK charges below 5-8% of C should be avoided as charging them at too low of a rate encourages sulfation resulting in capacity loss.

30A for your 210Ah battery is fine.

Dang, he beat me again!

 

[snoobler]

It's also a function of the fact that the RV likely has something around a 50-60A AC-DC converter for the 12V system.

 

[hayton55]

okay, sounds good....soooo if I expand the batteries to 420AH, do I still stick with 30? Because I plan on getting solar sometime in the near future and was thinking I needed a 60 amp charge controller...if not, then I definitely can save a few $$$.....

 

[snoobler]

420 would need a 42A optimal charge current. 30 would be marginal but acceptable.

How do you actually intend to charge the batteries?

 

[hayton55]

For now I'm planning on using the alternator with a B2B interface of 40 amps; as well as generator/shore power, then for solar I was looking at a couple of panels that give me 620 watts @40v combined with a controller that could handle 60 amps....this is just from reading all of the forum threads and budget....

 

[snoobler]

40A via alternator
?A via genny/shore power RV AC-DC converter (55-60A assumed)
40A via solar.

Those options should be good for 210 or 420Ah capacities.

 

[hayton55]

Sweet! So ditch the 60 amp solar charge controller, go with 40 amps and save some $$$! That will work for me

 

[snoobler]

Yeah. You'd need more solar to use the 60A anyway.

 

[grizzzman]

It's also a function of the fact that the RV likely has something around a 50-60A AC-DC converter for the 12V system.

What is sad is most RV converters are choked due to wire size/length I have seen many 55 amp converters with a 30 amp breaker on the output.