Replacing a 55 amp converter with a 45?

jrnymn7 wrote:
Thanks, Niner, but I (we) are trying to determine whether or not using a higher charge rate, i.e; using BFL's mega AMP approach, is resulting in increased sulfation/stratification. SMK has expressed his concern that such a fast replacement of Ah's does not allow for sufficient cleaning of the plates.

I, for one, think this is a very reasonable concern on smk's part, and believe it is deserving of further investigation. That said, I have yet to see any evidence to support such a notion. But then again, I read an interesting article this morning that mentions the 'Amp Hour Law' which suggests limiting Charge Current to the amount of Amp Hours needing to be replaced.

So, for example, a 200Ah bank, at 50% dod, should be charged at no more than a 100a charge current. And as Ah's are replaced, the charge current should decrease accordingly. So, by the time the bank is at 20% dod, the current should have tapered down to 40a max.

Of course, this cannot be accomplished using any power supply / smart charger that operates in a constant current mode from 50-80% soc. It would require a single stage dumb charger, with a particular max amp output, set to the appropriate voltage, to best approximate such a charge profile.

A charger with more amps to give, is designed to be scaled to the amount of amp hours you have on your complete battery pack setup. It should be a standard ratio, perhaps somewhere between C/5 and C/7. Or even C/10. It stands to reason that the slower the charge rate, or the bigger the battery pack AH in relationship to the amps of the charger, the less resistance will be measured by the charger before it shifts out of "bulk" mode, where all the "easy" charging takes place. When resistance gets high, at a given voltage, increasing voltage is the easiest way to overcome the chemical reaction resistance to force the chemical reaction of putting sulfur back into solution.

I would think that a high and fast bulk charge rate at C/5 will consistently bump into "the wall" faster and get out of bulk charging mode at a lower SOC, consistently, if done at 14.4V like on a Progressive Dynamics charger. The Iota takes it to 14.6V, with the little cheater wire loop in place. All the charge controller manufacturers are worried about liability issues caused by The Least Common Denominator that buys their product pre wired in to their new RV unit, and the propensity of FAIL and to not RTFM when they are new owners.

People drive cars their whole lives and don't understand battery charging principles, or discharging principles, or need for routine maintenance. The dumbing down of americans and the low standards of education will make this worse and worse, the need to protect stupid people from themselves. We have a whole new generation of adults that take no accountability for their actions, or inactions, in life.

In general, there is no Statute of Limitations on Stupid... it's a life sentence.

A RV is a whole bunch of systems tied together and integrated, of which it requires the skills of home ownership to maintain, though being 12V some of the skill sets are different than being hooked up full time to a utility company. Cutting off the pedestal at the RV park and going dry camping is cutting the umbilical cord. It makes you responsible and independent to have to learn all that you can to take care of yourself. That most charge controllers are engineered to be 13.6v power supplies tied to the grid all the time means that if you go off grid, time to charge and keep your batteries healthy on a daily basis requires a different approach and different requirements and different voltages from your charge controller. It requires more volts, the amps will follow, as the batteries chemistry and resistance will allow.

In summary, are you off grid or off the power pedestal?

1 = No= 14.4V bulk charge is fine, 13.6V maintinence voltage is fine, since you are plugged in 24/7, and you have the hours at low voltage continuous to top charge your batteries. Battery size, shape or electrolyte to lead plate ratio doesn't matter, you are on the grid and have charging capacity 24/7.

2 = Yes = 14.8V minimum bulk charge rate should be fine if you have good batteries that have a high electrolyte amount and level to amount of lead plates ratio... ie 6V GC-2's

3 = Yes = 15.0V or maybe up to 15.3V bulk charge rate. This is conditional... it depends on the size and shape of your battery, a poor shape, poor design due to other parameters such as space requirements, or designed for cars, or boats, or the confined space of floor sweepers, ie the Trojan T-1275, or the US Battery Screwy 31.

All of the batteries in group 3 are specialized batteries designed around other more important parameters. They require higher voltage to "stir' or bubble slightly the electrolyte to get rid of stratification of acid, or to expose and churn the electrolyte so that fresh low density acid that can take on more sulfur from the plates is exposed to the sulphated portions of the lead plated. The higher voltage creates a "churning" effect on the electrolyte, homogenizing the whole mix so that more sulfur can be taken on. A little bit of heat, in the form of amps lost during charging, is the goal. Not a lot of heat, not gross "boiling" of the electrolyte, but just a little heat, to cause the hot electrolyte to rise in the cells, and the cold electrolyte to sink.

Clear as mud, right? Hope this helps, find out which group of campers and battery requirements and chargers you are in.