Replacing a 55 amp converter with a 45?

Great article, thanks!

So, I guess the answer to my question is, lower V & A charging could possibly accommodate the time required for the SG to max out, during the charging process, before the batteries are put back into service, and thus (re-)discharged.

But how long does it take the SG to catch up? If not long, then even at a higher V & A charge, the time it takes to do that final 90-100% may just provide enough time. And if the SG requires more than that amount of time, letting the batteries rest for X amount of time, following a higher V & A charge, may possibly work just as well.

This, then would become a matter of convenience. If one could realistically remove all loads from the bank once charging had ended, perhaps one could minimize Gen run time, and still accomplish the same "quality" of charge.

But only by doing similar charge cycles, using both methods, could one make such comparisons.

So probably 150 amps would be the absolute max on a healthy 430Ah bank. And with a (-)215Ah, 50% soc, that means:

1) the 1:1 ratio is not obtainable, using realistic voltages, and

2) charging a 430Ah bank with a 150a charger is well within the guidelines of this proposed "Amp Hour Law".

jrnymn7 wrote:
Understood, Niner. And I guess I should have prefaced that the idyllic 1:1 ratio is a max charge rate, not necessarily an obtainable one.

BTW, does anyone know how many amps can realistically be accepted, on say a 430Ah bank, at 50% dod?

My ugly graph shows 70 amps on 220 with some constant amps time to it. That means you get the same time and curve with 140amps on 440AH. (which I do)

You can go higher but it means you will have a very short time before hitting that acceptance rate curve where it goes vertical on the left so there is no point going higher. The taper then is a vertical dive at that end of the curve. Diminishing returns.

The battery acceptance rate curve is its "natural acceptance rate" If you try to use more amps than that it just goes off as heat. If you use less than that, you are just wasting generator time. the amps get real low and the time long for that 90-100 part and that gives time for the "quality" of the recharge to settle in. That is also when the SG catches up right at the end too. See the SG lag drawing here for the recharge side:

http://www.engineersedge.com/battery/specific_gravity_battery.htm

Niner said;

"It takes tremendous energy and losses to get a battery back to 100% SOC. Which is why it's best done on the grid, at low voltage and low amps."

This is essentially what we are trying to determine...

... Overall charge times aside, is it really necessary to use low voltage and low amps to get the job done effectively ??? In other words, are there any known significant benefits, strictly regarding battery health and longevity, of charging at lower V & A than at higher V & A ???

Understood, Niner. And I guess I should have prefaced that the idyllic 1:1 ratio is a max charge rate, not necessarily an obtainable one.

BTW, does anyone know how many amps can realistically be accepted, on say a 430Ah bank, at 50% dod?

jrnymn7 wrote:
Let's see if I understand this correctly.

V3 is higher than. V1. Subsequently, A3 is lower than A1...

??? is this a result of more pressure (v) pushing more Ah's (a) into the bank faster, and thus causing amps to taper faster? (to clarify, both start off at about the same amps, but the one tapers much more quickly).

And yes, I see that even at ~ 118 amps charge current, per the 180 Ah's needing to be replaced, amps did indeed begin to taper immediately. So yes, it stands to reason a 180 Amp charge current would taper amps well before 50% soc.

And it's finally dawning on me that I have never done a C/2 charge on my bank. The most I've ever done is about a C/5. So I wasn't even considering the effects of such a high charge rate on the time it would take for amps to taper. I mean, I knew there was some effect, but I hadn't seriously considered it within these parameters.

The next thing to consider, I guess, is whether or not amps taper fast enough to stay within that 1:1 ratio of Amps/Ah's discharged.

1/1 amps ratio is hypothetical... ask yourself, at what bulk recharge voltage is the amps used to amps replaced ratio 1/1? There will always be losses in restoring chemical reactions and returning the potential energy in the battery chemistry. There are always some loses due to resistance, although battery resistance is lowest from probably a 35% to 85 or 90% SOC. Lower than 35%, electrolyte is closer to water and makes a poor conductor, about 85%, there's not much element left in the form of sulfur, to be absorbed back into ionic state as Sulfuric acid, it takes tremendous energy and losses to get a battery back to 100% SOC. Which is why it's best done on the grid, at low voltage and low amps, something that is not a luxury for the most part, daily, while off the grid. Hence the once every 10 to 14 day EQ charge session after top off, at a full 16.0V

Thanks Niner,

Yes, I've been saying for years... "If you dummy proof a society, you end up with a society full of dummies" !!!

It all seems pretty clear to me. And I'm not saying I have my situation all worked out, but I believe I'm on a much straighter path than many folks who have been rv'ing for way longer than I have. And as an acquaintance of mine would often say, "please don't confuse my confidence with arrogance" :)

BFL13 wrote:

westend wrote:

Yeah, she's holed up in a coral reef somewhere last I heard.

Recent sighting---

Looks like she just got back from the beauty parlour there. Here is what she looks like first thing in the morning

I keep telling her there's lotion for those scales but what do I know. And, BTW, that's parLOR. :B


Ah crap. I messed up my numbers from earlier. When I said C/7, I meant 7% of C. Same for C/5. I messed that up. Sorry guys. I wanted to give a data point on low amp charging and how in my case it doesn't raise SG any higher than BFL's fast charging.

Let's see if I understand this correctly.

V3 is higher than. V1. Subsequently, A3 is lower than A1...

??? is this a result of more pressure (v) pushing more Ah's (a) into the bank faster, and thus causing amps to taper faster? (to clarify, both start off at about the same amps, but the one tapers much more quickly).

And yes, I see that even at ~ 118 amps charge current, per the 180 Ah's needing to be replaced, amps did indeed begin to taper immediately. So yes, it stands to reason a 180 Amp charge current would taper amps well before 50% soc.

And it's finally dawning on me that I have never done a C/2 charge on my bank. The most I've ever done is about a C/5. So I wasn't even considering the effects of such a high charge rate on the time it would take for amps to taper. I mean, I knew there was some effect, but I hadn't seriously considered it within these parameters.

The next thing to consider, I guess, is whether or not amps taper fast enough to stay within that 1:1 ratio of Amps/Ah's discharged.

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.