I think its awesome that Powermax has the adjustable voltage units available. Too bad they don't use an external 10 turn potentiometer for precision voltage dialing and include a 2 decimal place calibratable voltmeter.
I Use a Meanwell rsp-500-15 adjustable voltage power supply as a converter,charger/portable floater, which is capable of delivering 40 amps at any voltage betwen 13.12 ans 19.23v, but it came with one of those itty bitty voltage trim pots rated for 25 cycles or something.
I disassembled it and removed that tiny trim pit, installed wires in its place and ran it to a 10 turn bourns 2k OHm potentiometer, as well as added heatsinking and more ventilation, and have gotten tons of use out of it over the last 5 years.
I've been doing a lot of removing trimpots installing wires in their place which then run to real potentiometers, on smaller voltage boosters or buckers or buck boosters, to use as LED dimmers or fan speed controllers.
If you've done the power plug on laptop multilayer motherboards, then you will have no issue removing trimpots and doing what I have done to all my power supplies. Very few of my power supplies require a tool to change voltage anymore.
When my Meanwell goes portable, I use the 45 amp anderson powerpole connectors to attach some 8 awg alligator clamps, but one can get into issues with alligator clamps, when they cant dig into a nice soft lead automotive battery post. I'd recommend bypassing any alligator clamp or parrot clamp when possible, in favor of a 75 amp or larger winch style connector, it depends on what wire size you are using . This can also remove any potential spark well away from the battery terminals. I have 45 amp anderson powerpoles everywhere, it is my universal connector and I can use to charge or power loads.
I've run my 180 amp starter motor current through a pair of 45 amp anderson powerpoles in parallel, and 8mm2 wire which is really close to 8awg and a tiny 18Ah AGM battery that dropped to high 8 volt range without being able to notice any heating of the powerpole connectors.
Wire thicker than 10awg needs to be destranded to 10awg gauge at the 45 amp anderson powerpole contact for crimping/soldering. The 45 amp contacts are a bit hard to crimp well without their special crimpers, but it can be done.
Meanwell RPS series power supplies are power factor corrected and come in 500 750 1000 and 1500 watt versions. My 500 watt version will do 600 all day long. I've no experience with the higher rated wattage versions. MIA, Mexico wanderer does though. The larger wattage versions have voltage sense wires, both + and - and some features the 500 watt version does not.
I've paralleled my meanwell with a 25 amp schumacher 'intelli' charger about 100 times now when I want 65 amps instead of 40 to achieve 14.7v ASAP, then remove the bipolar schumacher once the 40 amps of the meanwell is enough to maintain 14.7v by itself.
I am not as rigorous in following manufacturer voltage recommendations as some, and I will gladly and without worry exceed their 'recommended maximum amperage'. Those 65 amps of my combined charging sources, are going into a single 90Ah AGM battery, and it is now 1 month shy of 6 years old, and about 1300 deep cycles, thousands of shallow cycles and engine starts on it, but it is nearly done. I credit the meanwell's ability to actually reach full charge, for these rather incredible figures of Lead acid battery longevity.
Don't fear exceeding that 10-13% trojan recommendation. In my opinion.
With an adjustable voltage charger, when you have more than enough time to plug in and reach full charge, you can lower charge rate by setting voltage lower initially and then boost it in stages to maintain a lower overall amperage. If you want.
I use an OTC4619 hydrometer, but my meanwell also has a wattmeter installed on the output leads, which counts amp hours and watt hours and a few other figures, so i can determine full buy amperage accepted at absorption voltage, and on flooded batteries then verify with the hydrometer, and when the hydrometer reads full, see how many amps the battery is accepting at absorption voltage, then the next recharge just shoot for that amperage at the same absorption voltage, and skip dipping the hydrometer for a few dozen deep cycles.
I love spinning a Potentiometer dial and being able to change the current flow, but 270 degree potentiometers are hard to dial in precisely, but a 10 turn/3600 degree bourns pot with a turns counter makes it easy to dial in voltage to 0.01v.
When one has a voltmeter and an Ammeter, and one can see just how many amps the battery(s) is/are accepting at voltage X then changing that voltage by a finger twist, then Almost all the mystery about battery charging quickly dissolves into a 'Why did I not do this sooner?'
How much voltage the battery maintains powering X amount of load( especially with X AH removed from the battery) is a great way to gauge battery performance and health, and see just when an EQ charge would be beneficial
That feeling is then soon followed by a sneering contempt for anything which claims to do it 'automatically', and the faith some people put in their charger's green light. Especially when the hydrometer and/or ammeter reveal just how far from fully charged the battery still is when automatic has declared 'good enough' and refuses to be tricked into reseeking and holding absorption voltage for the extra time needed to actually achieve full charge.
Regarding storing the batteries with no charging source. If the temps are cold, then self discharge slows, so disconnect them when not in use to eliminate any parasitic draw. Their self discharge will increase with age( and higher ambient temperatures), but if you make sure to use distilled water and not allow any contaminants in the cells when watering then, it self discharge does not get hugely worse with age, compared to less pure water, or inadvertently washing detritus into the cells when watering which can be difficult to achieve on 12v batteries whose cell caps are recessed and ganged 3.
Since you have soldering skills, and wanted to modify the tiny trimpot on a powermax, I thought you should know about the Meanwell power supply option. While you have to provide your own AC input, and DC output wiring to it, you can likely save money, even over the reasonably priced powermax option.
As i said the 750 watt and higher version of the Meanwell rsp power supply might have other considerations to getting them functioning as a battery charger. I know of One guy who bought a 750 watt version could not get it to work properly and returned it for a 500 watt version which he claimed was outputting 50 amps, where mine maxes at 40.
What the issue was with the meanwell rsp- 750-15, I could not discern through the internet . If MExwanderer checks in you can ask him, or shoot him a PM.
Make sure to get the -15 version, not the -12, as the -12 might not go into the 15's or higher, and you want 16.2v for EQing flooded Trojan's
