How much converter/charger is really needed?

[Bobbo]

I have a pair of NAPA 9824M Marine/RV batteries with a 20 hr rating of 79AH each, wired in parallel.

Is there, really, any advantage in going from a 45 amp (PD4645V) converter/charger to a 55 amp (PD4655V) converter/charger?

I know that bigger is ALWAYS better, and the cost is not much more, but, really, is there a real advantage?

If not, how many AH do you need to make the jump from 45 amps to 55 amps useful?

[MEXICOWANDERER]

At what voltage sir? Starting with maximum absorbsion voltage of 14.8 and continuing?

[BFL13]

My ugly graph says that on a 220AH bank starting at 50%, the time difference is about 18 minutes from 50-75% and it is the same times after 75%

So you will save about 18 minutes of gen time doing a 50-80 or 50-90 (75-100 same times, so no advantage past 75% SOC.) by choosing a 60 over a 45 on 220AH.

Whether there is any point in saving that 18 minutes of gen time each time you do a 50-90 depends on how often you do it in a year, how much gasoline costs, what the gen hours are at the campground, how hard is it to get more gas, etc.

Not answered by the OP is the post in another thread where he said he can't get through one night with his current battery bank with the furnace running at a decent temperature, so they freeze under many blankets. the usual rule is one night per battery and he has two.

So that must mean his batteries are already shot, and need replacing now unless he is not going off grid for a while.

[Bobbo]

MEXICOWANDERER wrote:
If you went from 45 amps to the point of saturation charging of GC 220 batteries you may find they accept almost 100 amperes when starting out at a 50% depth of discharge.

The advice I give about saturation charging must remain in context. It is designed to reduce generator run time to a minimum. There is a heck of a difference between runtime of a Harbor Freight 2-cycle 800 watt generator charging a single group 24 RV battery and a 6,500 watt generator running to charge the same battery. A 45 ampere converter will max absorbsion voltages but the battery calls the shots. X number of minutes to go from 50% SOC to 90% SOC.

500 amperes at 28.9 volts is a lot of va. But the balance of horsepower versus saturated absorbsion charge of the batteries is entirely valid.

Lbs of fuel per hour vs kWh is not linear at low draws. It short a 6.5 generator is a FUEL HOG when powering a 500 watt load. It is just plain nuts to try charging a 400 ampere hour bank with a 45 ampere converter and six thousand watt generator.

On public power the 45 amp makes perfect sense. Off grid the 45 amp charger is a fuel spendthrift.

Mex, I know you mean well and think you are completely understandable. However, I can't translate what you just wrote into currently having a pair of Marine/RV batteries with a 158 a-h rating and a 45 amp converter on a 2000 watt Honda generator. Then upgrading the batteries, later, to a pair of 225 a-h batteries still keeping the 2000 watt Honda. Do I need to keep the 45 amp charger, or go to the 55 amp charger?

[MEXICOWANDERER]

If you went from 45 amps to the point of saturation charging of GC 220 batteries you may find they accept almost 100 amperes when starting out at a 50% depth of discharge.

The advice I give about saturation charging must remain in context. It is designed to reduce generator run time to a minimum. There is a heck of a difference between runtime of a Harbor Freight 2-cycle 800 watt generator charging a single group 24 RV battery and a 6,500 watt generator running to charge the same battery. A 45 ampere converter will max absorbsion voltages but the battery calls the shots. X number of minutes to go from 50% SOC to 90% SOC.

500 amperes at 28.9 volts is a lot of va. But the balance of horsepower versus saturated absorbsion charge of the batteries is entirely valid.

Lbs of fuel per hour vs kWh is not linear at low draws. It short a 6.5 generator is a FUEL HOG when powering a 500 watt load. It is just plain nuts to try charging a 400 ampere hour bank with a 45 ampere converter and six thousand watt generator.

On public power the 45 amp makes perfect sense. Off grid the 45 amp charger is a fuel spendthrift.

[Bobbo]

OP here. My take on this, as a practical matter, is stay with the 45 amp unit and don't go over 225 a-h if and when I replace the batteries.

[doughere]

I have 2 6V-GC's, I went from a PD9245 to PD9260; I doubt I saw over 45A charging more than 10 hours in many years of use. I doubt it was worth the upgrade. Since you have the PD4645 now, I'd just be happy with it; if you were buying new, I'd get the 60.

[2oldman]

shelbyfv wrote:
Why are batteries sometimes called "jars?"

The same reason gasoline is called unleaded. Either that or jars is just a shorter word.

[MEXICOWANDERER]

because people on this forum like to feel special, because a million years ago, battery's were made in jars.

While others exhibit inferiority complex's. Maybe a million years ago Lucy got goosed by a zot from heaven? That may have been a jarring experience.

[pianotuna]

They still are made in jars--just the material has changed from glass. It is too bad they are not clear as it would make selecting thick plates for deep cycling a lot easier.

[LittleBill]

shelbyfv wrote:
Why are batteries sometimes called "jars?"

because people on this forum like to feel special, because a million years ago, battery's were made in jars.

[shelbyfv]

Why are batteries sometimes called "jars?"

[BFL13]

pianotuna wrote:
BFL13,

Bank bigger than the possible 20% charging rate is one of many reasons I went to dual banks. I can charge one while using the other. Use both, or charge both, depending on the source.

My OEM PD would not "do" 14.4 when the batteries were hungry. The Magnum does do that well, but I don't enjoy "dancing on the needles" any more.

Since I'm no longer full time, I'm back to low and slow maintenance charging on solar for most of the year.

In short, I no longer care much about treating the battery banks properly as the most they need to do is a couple of days use.

Low and slow with AGMs is what LY warns about that every so often you need to deep cycle them and do the high amps recharge. Same with Wets really.

Good to learn you will not have to sneak around this winter looking for an outdoor Xmas tree plug-in spot to run your shore cord over to. 🙂

[pianotuna]

BFL13,

Bank bigger than the possible 20% charging rate is one of many reasons I went to dual banks. I can charge one while using the other. Use both, or charge both, depending on the source.

My OEM PD would not "do" 14.4 when the batteries were hungry. The Magnum does do that well, but I don't enjoy "dancing on the needles" any more.

Since I'm no longer full time, I'm back to low and slow maintenance charging on solar for most of the year.

In short, I no longer care much about treating the battery banks properly as the most they need to do is a couple of days use.

[MEXICOWANDERER]

Except if you want to meet the 20% minimum charging rate on AGMs that Mex insists upon. A 45 amper is 20% of 225 AH. What if your bank is bigger than that?


That's like driving a KIA on the autobahn. Have good mirrors and good reflexes and make sure your life insurance is up to date.

The AGM minimum rate is there to assure against significant premature death. The maximum -recommended- charge rate is there to make the manufacturer look as good as possible. These knotheads get into ******ing contests at trade shows comparing -their- battery against say 5 competitors. "WE GET 1,190 CYCLES IF LIFE VERSUS 1,042 FOR THE COMPETITION!

Telecom has reps that attend trade shows and while the reps are suspicious of everything they do note cycle longevity.

When public power is available for my Rolls 2-volt cells, guess what? The Trace inverter does all the recharging at 120 amperes. When the Kubota is used the charge rate approaches 500 amperes. If I screw up and a hurricane is coming I throw the Lombardini online, kill the TRACE and jam almost 700 amps into the 22 cells. This is a plate-eater rate but it's the least of all evils. There is usually five thousand dollars worth of lobster at stake.

BFL the 20% rule works this way but idiot battery manufacturers do not explain it well.

If you apply recommended charging VOLTAGE to a depleted AGM battery it MUST deliver at least 20% of amp hour capacity. Maintaining the recommended voltage when the absorbsion rate forces amperage below 20% and the VOLTAGE is maintained at the recommended absorbsion rate it is perfectly fine all the way down to .5% of amp hour capacity.

My Rolls batteries are wet. I set an ambiguous voltage when starting out fresh. Ambient air temperature around 30c 86F.

I applied 15.00 volts to the terminals. 540 or so amps dependent on the state of charge.

When the cell gravity ramped up and the electrolyte began to bubble vigorously, I took at "hot" dip on all the cells. Compensated, I came up with a gravity result too low for the circumstances. I was over amping the batteries. I reduced constant voltage charge rate to 14.8. It cut almost 60 amps off the total charge rate. The temperature gain on the cells was also reduced.

The 4 cylinder Kubota engine was modified to operate at 1,200 RPM for the six pole KATO generator. Simply put it's a ten thousand dollar engine. Along with fuel cost, engine wearout is factored into generator cost per kWh. Balance that with battery longevity and fuel cost and a complete cost reality was made apparent despite the contrasting dichotomy. This is exactly why I specified .300" plate thickness batteries. It all is designed to produce rational kWh at minimum total cost. Every four dollar per gallon diesel that gets sucked through that engine gets squeezed for every cent it costs. Every charge cycle timewise is at a bare minimum to reduce generator -wearout- and squeeze every Aztec fart out of every centavo of fuel.

Generators do three things

Annoy
Produce electrical power
Eat money like it's going out of style.

Does anyone out there desire generator noise to nature?
Smile a wider smile as more twenty dollar bills are extracted from wallet or purse?

Whistle zippidty-do-dah as they push the front door open on a generator rebuiding shop?

When I am hauling five freshly filled drums of diesel back from a 56 mile fuel run I am not the happiest of campers. My wallet is light. The truck gets 12 mpg. Kiss 20 dollars down the drain. Wear and tear and it screwed up my Saturday.

So, "Let's let the generator run to save 4% (thick plate batteries)" is not high up on my top-20-tunes

[BFL13]

pianotuna wrote:
Bobbo,


What Mex is saying is that if you have shore power for charging, converter size doesn't matter much. If, on the other hand, a generator is being run, a device capable of high amperage charging is of benefit, and worth an upgrade.

Bobbo wrote:

OP here. When I am able to understand Mex's posts, I learn a lot. When, like this one, I don't have a clue what he is saying, I just go on and don't worry about it.

Except if you want to meet the 20% minimum charging rate on AGMs that Mex insists upon. A 45 amper is 20% of 225 AH. What if your bank is bigger than that?

I do my recharge on shore power when I get home, but I still have to meet the 20% minimum. (on 450 AH) The voltage is no problem with my adjustable voltage chargers.

I have to split the bank to get the parts down to where my converter is at least 20% of the larger part, a 250AH 8D AGM. So I need at least 50 amps for that. (spec max is 100 amps for that battery but Mex says ignore that spec. Doesn't matter, I can't run a 100 amper with my 2200 gen or on shore power at the house-pops breaker--so I use a 75 amper for that one.

The other part is two 100s in parallel so I need at least 40 amps to do the pair. Rated max is 27 each or 54, but Mex says to ignore that. If I do go with that spec, I am boxed in between 40 and 54 amps to do them. I use a 55 amper as it happens. Mex is saying I could use the 75 on them too.

( The problem is when driving home and the batts get some recharge from alternator charging and solar. Easy to get home with the batts high enough in SOC that they will not accept 20% amps. So now you can't meet the 20% rule. Now what?---discharge them till they will and now recharge them? Before leaving for home, disconnect alternator charging and solar? BTDT.---I find that 20% rule to be a real PITA, but I do follow it grudgingly.

Anyway, if the OP stays with Wets, he can do the low amp but proper voltage thing on shore power, but not with AGMs and a 45 amper unless he has 225AH or less of a bank. I think he could do that with a pair of those Trojan T-105-AGMs at 217AH.

https://www.trojanbattery.com/product/t105-agm/?_vsrefdom=adwords&gclid=EAIaIQobChMIk7aswufM3gIVD8pk...