The Powermax is a Switching Power Supply, which allows the high amperage DC output in a small physical size casing.
I have not yet heard anything about the 75 Maximum amps from the model with a 100 amp sticker on it. It was my friend's purchase, on my recommendation, and I forgot to ask him about their response if any, yet, but I do feel they put a 75 amp model in a 100 amp casing, and until they make this right I cannot recommend them. Feel free to contact them and ask what is up. I doubt they want any bad press, and I want them to make this right. I Spoke with Errin:
http://www.powermaxconverters.com/contact.html
The regular powermax models sold on Amazon have a 14.4v Absorption threshold, which, with this algorithm, after the powermax gets the batteries upto 14.4 volts, it triggers their 13.8v absorption mode, which is not conductive to quickly completing the charge. Most converters will hold absorption voltage for a period of time before reverting to lower voltages.
The PowerMax models sold through bestconverter.com will goto 14.6v, but then still revert to 13.8v once the batteries get to 14.6v. Better, but not what I'd want personally.
There are also other RV converters that have slightly different approaches in their charge algorithms, and some can be forced via a 'pendant' to stay at higher voltage for longer. Progressive Dynamics and Iota are two well known RV converters, and come in different amperage flavors, but if going over 55 amps Iota, or 60 Amps PD, then these require a 20amp AC receptacle, whereas the Powerfactor corrected powermax can be plugged into a standard 15 amp receptacle on the 100 amp model.
When the cabling between battery and powermax is not very fat, then the reversion to 13.8v happens when the actual battery voltage is lower than 14.4 or 14.6v, due to voltage drop along the cabling.
Neither of these charge algorithms is good for generator charging. They will waste fuel and make you listen to and smell the generator while not doing much charging at the 80% or more state of charge range. Getting to a true 100% takes many hours even at high absorption voltages, but many many times longer when voltages drop prematurely. Most who do generator recharging stop at ~80% charged, doing 50% to 80%, Some spend another hour or two and do 50 to 90%. These types eventually go home and plug in, but van dwellers need to get the batteries to 100% every 14 cycles or so, minimum or the batteries really walk down in capacity. Getting to a true 100% is not easy. It takes a lot of time, and once again, linking green lights do not indicate a true 100%, only that the charger source/controller has stopped applying absorption voltage.
Solar is great, but in most cases it is slow. Those with flooded batteries and believe the full charge indicator will be surprised to see the low specific gravity after cycling nightly for a week. A charge controller with adjustable voltage setpoints will pay for itself in extended battery life. Temperature compensation is also a big bonus, especially for those who deal with temperature extremes.
Powermax has an Adjustable voltage charger/converter, which has no 'stages' One sets a voltage, and the unit applies maximum current until battery voltage climbs to the preset voltage( constant current phase) and once this absorption voltage (ABSV oe Vabs) is reached, it stays there( Constant voltage), and the amperage required to hold the battery at this voltage begins to taper. It actually begins to taper once it closes in on the ABSV.
http://www.bestconverter.com/Boondo...ower-ConverterCharger_p_587.html#.VPFW3HzF_cw
This is a much better option for generator charging as it is feeding the battery not only at the manufacturer specified ABSV, but holding it there while the battery absorbs the last ~ 20% of the charge, and completes it faster. Generally 4 hours at ABSV is needed
before the battery is fully charged, but this depends on the level of depletion, the battery, its health, and the initial amp rate applied.
BUT, these adjustable voltage powermaxes are not automatic. Overcharging is possible if the Absorption voltage is held too long. Not much of an issue if one is listening to and paying for fuel to power a generator, but the person who plugs into the grid, sets 14.8v, and comes back 24 hours later will have overcharged the battery that has suffered excessive water loss and positive plate shedding. If an AGM battery, the vents will have popped, electrolyte lost and can't be replaced, and thermal runaway is also a possibility.
I bring up the powermax Adjustable voltage model as it specifically addresses the issue of premature voltage dropping during the Absorption stage. it has a voltmeter, and a dial to adjust Voltage, and is among the best products available for someone trying to recharge as much as possible during the least amount of generator run time but it requires a human with a brain to control it. A frontal lobe charger, if you will.
I personally went with a MeanWell RSP-500-15 power supply, and I use no generator. While rated for 500 watts, it will do 600 watts, and pump 41 amps maximum into either of my depleted batteries at voltages upto 19.23V. Which of course I never let it do, the 19.23 part. I allow 41 amps often.
This Meanwell is also Power factor corrected, meaning it is more efficient, turning less AC power into heat.
They make a Meanwell rsp-750-15, which should max out at around 60 amps. These are also very compact charging sources.
http://www.meanwell.com/search/RSP-750/RSP-750-spec.pdf
It should be noted that the Meanwells have tiny voltage potentiometers to adjust the voltage with a jeweler's screwdriver, and no Built in Voltmeter. One must also provide both the AC and DC leads to the unit and to the battery.
Also note than Meanwell makes other power supplies which are cheaper, but do not do constant current limiting on overload, but shut off when overloaded, which one does not desire when battery charging. There are a few lesser wattage models which do have constant current limiting on overload but I do not remember the prefixes/ model numbers.
There is another power supply called Megawatt, which are also good as manual adjustable voltage battery chargers. They have a 30 and a 36 amp unit, and internal protections from an overload condition, and any large depleted lead acid battery can easily max out these power supplies. They use the aluminum casing as a heat sink, and ventilation is required, same as the MeanWells.
http://www.12voltpowersupplies.us/
These are also sold on Amazon, but again, these are Manual chargers which must be monitored or put on a timer.
http://www.amazon.com/MegaWatt-S-350-12-9-5-15-Adjustable-Supply/dp/B00JZBE97U
In Amazon's description they refer to Clones of these Megawatts.
These are Cheap, under 25$, and have no overvoltage or overcurrent protections built in. I'd bought one as an Experiment, and it worked well, but I had to constantly adjust the voltage to keep it just under 36.2 amps.
http://www.amazon.com/Universal-Reg.../B00D7CWSCG/ref=pd_cp_e_0/176-5692621-3716519
There are literally over a Dozen of these clones sold on Amazon. Some claim to have some protections against overload, I'd not believe them, and I do not recommend these for usage as battery chargers.
When I got tired of babysitting this clone through the bulk phase, I decided to sacrifice it to science. I turned it upto 15 volts, hooked it to a depleted battery, and let it go. Rated for 350 watts, it provided 538 watts for 17 minutes, then the Magic Smoke was released, with some sparks involved as well. I was there to unplug it. It did not trip the breaker on my power Strip, and could very well have been a fire hazard had i not unplugged it. I'll never know.
So these switching power supplies are Compact. The powermax has a large internal heatsink, and does not use the casing as a heat sink. There are reports by those who bought the 100 amp adjustable voltage model and measured 105 amps from it so I hope my 75 amps from a 100 amp model is a fluke and not the new business practice of the company.
With a pair of 00 gauge cables with alligator clamps on them, this POwermax 100 amp unit will put those old wheeled battery chargers to shame, for a fraction of the size. Those old wheeled chargers also do not limit voltage. They basically force charge any battery which was way over depleted( well under 10.5V) to get the customer out the door ASAP.
The fan on the powermax is pretty quiet. The same cannot be said about the Megawatt, the Meanwell, or the dangerous cheapoclones.
To my Meanwell rsp-500-15, I have added two more quiet fans to the casing, and I removed the tiny trim voltage potentiometer and added a 10 turn potentiometer that allows me to easily dial in voltage to the hundredth of a volt easily. Only when maxed out in ambient temps over 70F, will the loud fan kick on on my unit, but this was more often and for longer before I added the fans.
I love my MeanWell. I have a thread on it here:
I am not sure why the pics are not showing up though.
https://vanlivingforum.com/Thread-My-newest-electrical-toy?page=2
I use this adjustable voltage power supply, because No Automatic charger or 3 or 4 stage converter can actually fully charge a battery properly, unless plugged in for several days. Blinking green lights don't fool me or My hydrometer, and performing a true 16v Equalization on my flooded battery is something very few charging sources can actually do. My solar controller can, if the panels can make at least 6.2 amps when I need it to.
My Meanwell allows me to determine how much amperage I want to feed a battery, what voltage to absorb or float it at, and also allows me to perform 16V equalization charge cycles. This is not a charging source for everybody. Most don't really care about battery charging until their batteries no longer meet their overnight needs.
My Schumacher SC2500a Automatic "smart" charger is in my storage unit. I could never trust it, or leave it alone as it was just as likely to overcharge as it was to severely undercharge my batteries. While it could, on the 12 amp setting, both charge my batteries and power my cycling fridge, voltage would cycle from 13.2 to 15.7 when the fridge shut off. not good.
I very nearly bought a PD or an Iota or a powermax several different times, but saw all of them as a compromise to my desires.
The Meanwell covers all of my desires, but requires I be there to lower the voltage at some point, or turn it off. I've yet to acquire a timer for it, and letting it run too long at too high a voltage has not been an issue for me yet, but it is a concern.
