First Top Charge

You are right to do an overcharge right after getting the new batts
home, and then take your "baseline SG" from that as your target for future overcharge sessions.

Meanwhile the battery will have a spec for what the SG should be when truly full. Try and have your own baseline SG resemble the spec for that battery.

If you are at that SG in the morning (adjusted for temperature) quit!

sjturbo,

Are you checking voltage at the battery terminals, with a hand held multi-meter, or just at the charger outputs? It's at the batteries that matters.

You said the batteries were at 13.2v when you started. Was this shortly after a near full charge? How did the batts end up at 13.2v exactly?

Thanks.

And as Mex pointed out, that's a rather large bank for that charger, but it still shouldn't take so long to top charge. Personally, I would split that bank in two, if it's not in heavy service, and use one bank while topping off the other.

Well I have monitored it but not every 15 min. After the first hour of 15 minute intervals I started monitoring it hourly. We are at about the 10hr point. Regarding measuring the voltage with the charger in operation it always reads what the MW is set at, 15v. Unfortunately I did not understand that readings were to be taken with the charger in operation. It does not change with the charger on! The amperage at initial start up was 33a. At 15 min intervals the voltage was taken with the Mega Watt off, (just the batteries).
Within 5 min or so the amperage had dropped to 5.5a. Within an hour the amperage had dropped to 3a. In three hours when I stopped charge for paint run the amperage was at 2.5a. This afternoon voltage remained at 15 (charger on) and amperage was 2.1a. At approx. 8hrs I decided to raise MW voltage to 15.3v which changed the amperage to 5.6a. I plan to terminate charging before I go to bed! I have had moderate bubbling throughout the process, with a size in the "tiny range" likely 1mm. Some have been larger. When I increased the voltage to 15.3 the bubbling increased. So can I resume this tomorrow if I don't reach 15v by bed time or should I wait a week? By the way thanks for all the inputs.

Voltages are read with the charger in operation. Because of the larger size bank of the OP his power supply is striking a "more reasonable" intensity of charge because of the large bank capacity. If power supply operation slows way down at say 14.7 volts, let's give it a 3.0 charge rate for fun - then that's too slow. The power supply should do better than that. Offering a "feel" for how many amperes are flowing at different levels of voltage here is vital. Otherwise advice is being given while being blindfolded. Not worth spit.

AMPS WHILE TOP CHARGING. HOW MANY AMPS? This means the Megawatt is running...

At

13.50 volts?

13.75 volts?

14.00 volts?

14.25 volts?

14.50 volts?

14.75 volts?

14.85 volts?

14.95 volts?

15.00 volts?

How LONG in minutes did it take to go from start to 15.00 volts? Can the Mega stay charging at 15.00 volts and maintain an inflow of more than 10 amperes? Or does the amperage drop like a stone?

Note: This is where a "smart charger" would need a good dose of thorazine. It simply does not have the computing power to figure 1% of the above information, out, never mind deal with it...

The OP needs to understand that this is not a 'set it and forget it" battery charger. You do need to be observant, it is a manual charger, it requires you to monitor it from time to time, from start to finish charging or top charging. As you do more recharging with it, you will know what to expect and how long it takes, time wise.

It is quite normal for the V to drop very quickly, immediately after removing the charge. It will level out at some point, and then dissipate very slowly from there.

You would require a "constant current" power supply to maintain the 5a / 100Ah rate. Your mega watt does operate in cc mode while its amps are maxed out in "boost", when the batteries are at or below about 80% soc, generally speaking, but switches to "constant voltage" during abs/top charging, during which time amps taper. The only way to maintain amps during cv mode is to raise the voltage, but you don't want to go over 16v, so...

To clarify, your power supply will operate in constant current mode while battery V is catching up to the power supply's V setting (which you set at 14.8v, or whatever). Once the batteries reach close to that setting, the V setting will be held steady. This is constant voltage mode, during which time amps will taper as amp acceptance decreases with ever increasing charge state. With a so-called smart charger, these two modes are called Boost and Absorption. 3 stage smart chargers are basically just switching power supply units (like your mega watt), but with factory presets, and an additional float mode.

Thanks jrnymn7. I actually had to shut down the charge for almost 2hrs to run to Paint store. At shutdown voltage measured at 14.1 Measure at return was 13.2v? I would have expected the voltage to be higher. I am only at about 2+amps and I know I should be at about 23a (5% of 470) this could take a while.

sjturbo,

I believe what they are saying is check the V readings while charging.

Because of V drop across the cables, the charger could be putting out 15v, but the batteries may read only 14.85v, or whatever. But the battery V will come up, eventually. So you need to take each reading at the charger's outputs, as well as at the battery terminals.

Another thing to watch for is equal V readings across individual batteries, during charging, as well as while resting. So, for example, if a pair of 6v batts in series are getting 14.8v, at the battery terminals, then both 6v should read 7.4v, not 7.3 and 7.5. Likewise, if they are resting (leveled out) at 12.7v, they should both be equal at 6.35v.

As for 'waiting' to take V readings, that is for getting the resting V. And after a good top charge, that could take several days of resting, with no loads, for the "surface charge" to self discharge. For example, yesterday evening, I brought my two 215Ah banks to 2.25a/14.89v and 2.4a/14.88v . 12 hours later, they still read 12.93v and 12.91v, but they usually settle at about 12.78v.

The important thing to measure is SG. After several charge cycles, each followed by a good top up, the SG will likely improve. This will then be your "baseline" SG, as these guys have taught me. You can take SG readings after each 15 minute interval, but there may be some lag. Take readings throughout, and then an hour or two after, and compare.

I generally wait until (at least) the next day to check SG after an actual EQ, but that can't happen if the batts need to be put back into to service right away.

Ok, The batteries are four CR235 in series/parallel. 470 amp hours. I understand that I am looking for 15v at the batteries but if I am checking that every 15 minutes I need to know when to take a voltage reading between those increments. Some say wait an hour to measure, others indicate that surface voltage dissipates quickly? That is the one thing I need an answer to. These batteries are basically new. I am doing this as an initial Top Charge.

Let voltage rise to 15 then watch the clock. Fifteen minutes later shut it down.

Top charging is not done to a sulfated battery. it is done to a battery to mix electrolyte, chop off dendrite sulfation trees and is considered a health tonic treatment not intensive care, like equalization.

I would rather strike that, much rather see batteries charged at 5% amp hour rating to reach 15 volts, but anything is better than nothing.