First Top Charge

Yes, I have the Turnigy 1080w. You're probably familiar with the over-current-protection issue I have with it. I have solved that by simply clamping on my cps1620 for a few minutes. So, yes, a bit of a pita, but no real biggy. I have yet to try it on very-near-full batts. The starting amperage may or may not still spike over its ~60a set point, at power on. If it does, on goes the little gophert for a few minutes.

Lately I've had my 430Ah bank split, so I've been using all 3 chargers to see how each performs. The modified pm4b-45 can be dialed up to 16v, as well as both the turnigy and gophert. So I'm covered either way. But the issue is still keeping up the amps while charge acceptance declines.

Remember, top charging borders on "over charging", as you're trying to force amps into a batt that says its quite near full... kinda like trying to put away that last hotdog in an eating contest.

EQ'ing IS overcharging, and the same issue exists... trying to force feed current into a greatly diminished load... kinda like that Monty Python skit where the waiter offers that really big guy a 'wafer thin mint', after he's already eaten way more than needed. But the gophert, being variable-adjustable, (meaning amps and volts can be adjusted) allows for the amps to decline as usual, but then when they start coming back up as the battery starts to overheat slightly, the amps are limited to my 5% setting, thus preventing thermal run away... at least that's my understanding of what's going on.

So, to answer your question, I do a half-azz top charging like everyone else. The best one can do with a constant voltage charger is bring the batts to a very low amp reading at 15-16 volts. I generally bring mine to about 2.5 amps per 2-6v's, at 14.8v. And if an EQ is in order, I will take them to about 2a at 15v before EQ'ing.

And 'til now, I have always done roughly 80-97's, while boondocking, so a lot of top charging was not needed, but if I switch to say 70-90's next season, I will have to stay up on the top charging, weekly or bi-weekly. I will let the SG readings determine that. Of course, going solar next year will change everything, as well.

The Mega is plenty big enough. I mused this for a bit and came up with an idea. Apply the Mega. 15.0 volts. This time disregard the amperage. Instead monitor the acid in all cells. When all cells are bubbling slightly note the time elapsed between start to finish. This can easily eat a couple of hours, so don't worry. Just ensure you are starting from a level of battery charge that is easily repeatable. That way you can top charge with a timer. I'm soooooo lazy I use an interval timer, but one with a battery backup (I further cheat and use a cheap 12 volt voltage regulator and timer and suck power off the 24 volt bank - not likely to run out of memory). A weatherproof timer is inexpensive and you will look for a lawn sprinkler TYPE timer, which is called an INTERVAL TIMER. While I'm doing important things like reading, snoring, or staring out across the sea the timer and charger is doing it's thing. Not important whether your timer is AC or DC, but it is important that it not lose it's mind (timing cycle) because of a power outage.

Let those batteries bubble a little. If one cell is reluctant, find out why. Usually it is a sign of sulfation. Do an equalization. Then try it again down the road. Bubbling the start of which is an incredibly underused tool in battery management. Use it to VERIFY your perception of state of charge.

APART: I would love to see - it would be my reward to see declarations here "Gee I followed this stuff, it was simple, and it apparently doubled the lifespan of my batteries". Then I will have accomplished my goal. Vamos A Ver.

The increase of sophistication of these threads puts a smile on my face - thanks guys, for the time being, that is reward enough :)

Menna661, Tell me about your batt Bank. As you may have read it took me about 11hr to get my bank to 14.8v. I realize that #4ga ,may have something to do with it but 11hr seems like a long time even with that gauge. What is your starting voltage and how long does your Mega Watt stay at a high amperage? My voltage/amperage started out at 15v/33A. Amperage dropped to the 3-5A range quickly.
So tell me jrnymn7, Is your PS a Turnigy 1080Watt? How do you Top Charge?

sjturbo,

Like with all things electrical, big amps cost big bucks. This includes buck and boost converters. It gets to a point where the buck/booster gets as expensive as another charger.

I had recommended a bucker for getting V down to 8v for EQ'ing individual 6v batts. But for top charging the full bank, you may be better off boosting that PD 9270's output? See Mex's 'Playing with dc-dc Boosters' thread.

But you'd still be into a fairly high amperage booster, so it will get costly. Notice the one Mex links to is limited to 12a max output; perfect for a 220Ah bank. This is where bank splitting comes in. It eliminates the need for such high amperages (12a vs. 24a, in your case) But, of course, it all depends on how accessible your bank is, and how much time you want to spend re'and re'ing wires.

I went with a 60a adjustable 13.6-18v power supply, so that I can do regular top charging without overtaxing it's duty cycle. But it still doesn't compare to the versatility of the cps1620.

But it still doesn't deal with the constant current issue. It's one thing to supply power to a constant load, such as a string of led lights, it's a whole other thing when dealing with an ever decreasing load, such as a battery that's being charged. I'm still trying to figure what would best solve this issue. How does one maintain that 5% rate throughout, without continually raising the voltage?

sjturbo wrote:
Morning MW. Thanks for the kudo's! Since it appears that for Top Charging the Mega Watt is somewhat inadequate for my bank, (recommended 5A/100ah, constant for 470ah ~ 24A), is there a "bucker" up to the job or should I look at an alternative? I'll be ordering the Freas today. Thanks again!

The MegaWatts come in 30 and 36A. Plenty for your bank. I use the 30A on mine and it's larger than your bank. The smaller chargers just take longer to get things accomplished but when you're on shore power, that doesn't matter much. If you're boondocking then you need the bigger chargers.

jrnymn7 wrote:
Thanks, Mex,

I was wondering if the resting V could hold strong while SG drops.

Most definitely! I've seen 12.8V on my batts with a 1.265 SG. Voltage doesn't tell me squat! I get more info looking at amps draw. If I see anything more than 0 amps on my Victron on float (technically this would be net amps), either I just came back from a boondock trip and the batts are not 100.000000000000000% full (after charging, batts on float I'll still get some NET charging amps for a day or two even if SG says they're full) OR I have a problem (had to fix TWO different wiring issues). I ONLY use voltage to see if the charger is running properly.

Morning MW. Thanks for the kudo's! Since it appears that for Top Charging the Mega Watt is somewhat inadequate for my bank, (recommended 5A/100ah, constant for 470ah ~ 24A), is there a "bucker" up to the job or should I look at an alternative? I'll be ordering the Freas today. Thanks again!

And again, I'll point out that battery management is like learning to use a computer - confusing and frustrating at first, then a laugh-a-minute later. One a person "knows their battery bank" it's more effort to go out and fetch the paper from the driveway than to manage batteries. My son-in-law has a 6th grade education from rural Mexico. His intelligence is plenty high. He has learned how to manage batteries correctly and he loves it. The community now refers to him as a "Battery Guru".

I remember the look of horror on the face of the battery store owner when Jesus hauled in a 500-amp carbon-pile and Freas hydrometer to check group 27 batteries before he purchased one for his "lancha". Out of a stack of 7 batteries, Jesus, culled six, and cherry-picked the best of the breed.

Once-per-month top charging: Recommended constant 5 amp per 100 amp hours input for one-half hour via a trusted (battery backup for memory) interval timer, is plenty. That will free a lot of your time.

Storage temps of less than 0 C need a full forty minutes of 5% amperage. Pianotuna could use almost an hour a month. And a hot water bottle :)

Thanks, Mex,

I was wondering if the resting V could hold strong while SG drops. I will keep a better eye on SG's this winter, while the batts are "hybernating", and if necessary, hit them with a good stirring.

Good Looking Setup SJ!

Depending on how fast and -why- specific gravity is slumping on float standby you may or may not need to bump the float voltage up a tenth.

If you've not moved your rig for months and the batteries are floated seemingly at correct voltage for the temperature, chances are it's a matter of stratification. If you suddenly apply bulk charging voltage, the amperage starts out seemingly high but then drops rapidly, trends and tendencies tells me the problem is most likely stratified acid. Time for a top charge. If the bulk charging voltage does not slump right back down then perhaps the batteries are not being floated at a high enough voltage. Sometimes I will zap a battery bank with 16.0 volts (takes a lot of amperage to do this) and watch the cells. They should start bubbling almost immediately. Continue for 15-minuted then cease. If the density of the acid rose appreciably it means the acid had stratified. When you get talented with a good hydrometer you will learn and recognize the behavior of your own bank. Slumping density (at rest, disconnected, no charge) but not a great change is resting voltage is another excellent clue to start looking for stratified acid.

The ultimate goal which is not easy to achieve is to absolutely minimize float AMPERAGE while not allowing the voltage to sag, meaning allowing the battery to drop from full charge to 99, then 98 and on to 97% charge. This is done with voltage control. Try it and see. Full, absolutely full batteries, zero load, how many milliamperes does it take to maintain the batteries? This changes over time, and if the batteries are becoming sulfated. The trifecta: Voltage, milliamperes and the hydrometer. You'll get to be an expert in no time.