Choice of converter for AGM batteries

ISTR the Parallax has a fairly low charging voltage low 14s. IMO it is as important to use the right charging voltage as it is to avoid overcharging.

You might be able to use a Charge Wizard PD to keep the thing at 14.whatever it has (they vary--check specs before buying)for its high voltage stage by keep hitting the "boost button" whenever it drops out of boost until your amps are down to zip. Don't know.

The 80amp PD needs a 20a input circuit while the 70 is good at 15a input

Mr Wizard on here has a bank of AGMs and uses a PD 70 amper for daily charging, but he got an adjustable voltage PowerMax 75 amper so he could do the necessary every so often to keep them up to speed. He knew he needed to do that somehow.

IMO might as well just get the PowerMax adjustable 75 amper in the first place and use it all the time.. Not much diff in price from a non-adj PD either.

Repetitive thankfully is not a do or die expression. It will not hurt the Lifeline one bit to do fast and dirty (voltage strictly limited) charges, for say a week then with near religious fervor do a top-up charge just as Concorde suggests, at 14.4 volts until amperage drops to one half ampere for each 100 ampere hour battery. Then the one half ampere charge rate is reached using 14.4 volts, then the charge rate can be defaulted to temperature corrected float voltage.

At 50% SOC my Lifeline Deep Throats in excess of 100 amps and all without going near the max absorbsion limit of 14.4 volts.

Even a tiny adjustable manual charger can help do the 14.4 volts finish charge rate.

Look! There Goes One Now...



https://www.ebay.com/itm/33-Amp-13-8-Volt-DC-Filtered-Power-Supply-12V-Adjustable-Voltage-MegaWatt-01/152804919927?epid=0&hash=item2393e20a77:g:CxAAAOSwzsFaHDt6

To the left of the terminal strip is a vertical green LED. See it? Just to the right is a small square plastic block. Facing straight down is a cross screwdriver slot cap. That's the adjustment. You'd only need to do this once. Once a power cord has been attacked...



https://www.ebay.com/itm/QUALITY-BesMelody-2-Pack-Power-Cord-with-on-off-Button-Switch-Replacemen-6-Feet/302515535753?epid=2130473608&hash=item466f54bf89:g:47gAAOSwPDBZ~1wX

switch the critter on and set voltage to 14.4

Then connect battery + and - to battery terminals. Turn power supply back on. Voltage will rise to near 14.4 volts with a NEAR FULL Lifeline. Tweak the little pot to get voltage in the 14.4 range.
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This is a simple fix for the AGM Finish Amperage Blues, and the fix is excellent. Get the batteries reasonably full then switch this little critter on. Try to remember to switch it off within a few days. :) I'm not joking. A precised timed shutdown is not needed at all. Shut the power supply off and let your new temp regulated converter float the batteries.

This will maintain the Lifeline at the ability to hold and dispense every last ampere of its capacity. If you fail to observe the fully charged before float rule, then you can expect the battery capacity to degrade to 80% or less. It cannot be charger fuller than 80%.

Several forum members have done this with the Megawatt. Because you would be using it during that last 8% or so of battery fill there isn't any danger at all of harming the Megawatt. It can charge your batteries from scratch but its amp capacity is puny.

Batteries need a full charge at 4:00PM? Start the Megawatt set at 14.4 volts (one time setting), go out to dinner, return, forget about the power supply running, wake up the next morning, run out to the batteries find them perfectly charged and one bored power supply.
How much easier can it get?

Concentrate on getting a temperature compensated converter for high amperage and for correct float voltage.

I have six? Seven? Megawatts sitting around. They keep batteries healthy and my wallet where it belongs.

MrWizard wrote:
1000w at 24v is not 100 amps

If you have a 100 amp controller? That's great, you are way within margin
Enjoy

I like large converters for fast generator recharge , and prefer solar for top off and carrying the daytime load

My preference would be the Power Max, adjustable converter
Set at 14.8v

Any reason to pick the PM4 series over the PM3?

Temperature compensated charging is not wrong. It is important to wire the new bank in a balanced manner.

phemens wrote:

MrWizard wrote:
1000w at 24v is not 100 amps

If you have a 100 amp controller? That's great, you are way within margin
Enjoy

I like large converters for fast generator recharge , and prefer solar for top off and carrying the daytime load

My preference would be the Power Max, adjustable converter
Set at 14.8v

Any reason to pick the PM4 series over the PM3?

You do not want either. They are not right for doing 50-90s from a generator off grid.( don't work for fast charging all the way to 90 --might drop to 13.8 at 75% eg) their charging profile is not right for that- either one.

However, you do want the Adjustable voltage model, which is usually a modified PM3, but that doesn't matter. It works for keeping your AGMs (or wets) proper. It is not hard to turn the knob to the correct voltage once in a while. :(

http://www.bestconverter.com/Boondocker-BPCM-75-75-Amp-Adjustable-Power-ConverterCharger_p_587.html#.Wh9oAFKWxLM

My solar controller does do temp compensation, so do I need it in both?

MexicoWanderer, if I went with a separate charger like you have, I imagine I could keep it hooked up to the battery bank permanently and just flip it on when I want to do the full charge? Any downside to keeping it permanently attached?

PianoTuna - Bulk charging would likely mostly be done in the driveway. I have a 2000w Genny, but it won’t provide the needed amps to power off grid. I may go to a Champion 3400 at some point, but not in short term plans.

You can get away with a too-small generator for doing the amps--it just takes longer to do the 50-90. You can't get away with too low a charging voltage with Wets. They need to gas at say 14.2 or above. AGMs have a charging spec --whatever its voltage is.

I discovered that doing 50-90s at 35-40F needs temp comp where 14.8 spec voltage is for 77F, while at 35-40F it is 15.2 to get the same result. I used my PowerMax adjustable and did it at 15.2 at 35F and it was perfect.

Some say you can get away with a lower than spec charging voltage with AGMs--it just takes longer to charge them due to the lower amps you then get. I am not convinced, but don't know for sure. I like to stick to the specs.

The big trouble with solar as a top- off to get to AGM true full, is it gets dark. You cannot control whether it gets dark before your batteries get full. You can always get it done if you have 120v and an adjustable voltage charger.

Mex's idea of using the low amp adjustable charger in a sequence among other chargers would work if you already have the other chargers and are stuck with them all paid for.

Starting from scratch, you can just do it right the first time as mentioned before.

Sounds good, the Boondocker adjustable sounds like a good choice.
As per the specs though, it seems like the AGMs want .27c, which with a 645 AH bank realistically means I can’t achieve that with even the highest amperage charger.
My original plan for the batteries was 3x 12v 215, so i’d need to set up a switching system to charge them individually (one by one), or change up the choice of batteries (to something that would balance to 2 banks, and charge them separately)?
What do you do to manage the switching? Cut-off switches on + from distribution post back to each battery or battery bank?
What are the pros/cons of going with more but smaller amperage batteries?

To repeat, AFAIK you can get away with fewer amps doing the recharge--it just takes longer. That is not the same thing at all as not having enough voltage.

ISTR there are some batts that specify a MINIMUM charge rate, but I can't remember details on that. Your AGM spec sheet will tell you if you have that as in issue.

If they do, come back with that and a work-around can be found.

What is this .27 c?

Download and read the Lifeline manual and guaranteed nothing will be taken out of context.

PROLONGED low amperage charging, Intermittent charging, for weeks then months will cause the glass mat to become mottled.

Reminds me of SCURVY. Vitamin C prevents it. If you don't take it every day you risk scurvy? If you take too little every day then scurvy looms in your imminent future?

Red and believe the Lifeline manual. They make batteries for aerospace and the military. They are a little overly strict in some maintenance protocols but are in a universe apart from some of the stuff recommended it this thread, which looks alarming similar to some nutrition supplement advertising.

No offense people but my side is with Concorde on this stuff. The Lifeline will live as long if not longer if charged at 25 amperes per 100 ampere hours. Fifty amps per 200 ampere hours is FINE. It like to charge faster because I've done the economic workups, gen run time deterioration, fuel costs, maintenance versus maximization of SAFE charge acceptance.

During the summer power flicker, when the lights come back for a belated encore, I stuff 100 amperes into my 31. Sure enough, a half hour later they go out again. This is specialized maintenance behavior tailor made for my particular environment. Otherwise - I would be recharging at 25-amperes. Anything else would be silly when constant power is available.

Got an email from a cruising sailboat (catamaran). "We are trying to minimize generator run time" - back and forth went the emails. Turns out one engine has to run six hours a day to R/O enough water for their family. A hydraulic driven system. I told him to order up a 240-ampere alternator. Individual XBoxes or whatever his kids have in their staterooms or not, if that 240 amp alternator can't replenish daily extractions, in 8 hours, they need counseling. Running a Yanmar generator to power a battery charger is nuts if another engine has to run to power the R/O

So relax and charge the 31's at 25 amps per battery minimum.