BFL13 wrote:
Read it and weep. No converter will do this. Some chargers will.
http://pdf.wholesalesolar.com/battery-folder/charging_instruction_2011_2.pdf
I have been using PM converters as chargers for a few years now. We are off grid at a seasonal site from mid-April to end Sep. What lets us do that is solar plus using the gen and charger as required when it is cloudy and solar can't keep up.
I modified my 100amper so instead of dropping to 13.6 as soon as it gets the batts to 14.6, it stays at 14.6. So it now is no good as a converter, but the trailer already has a perfectly good converter for when on shore power.
I did have some trouble with the 100amper blowing its in-rush thermistor but it turned out that was due to using it as a stand alone charger. I had rigged a set of heavy jumper cable clamps to it for connecting and it turns out you need to clamp on first, then start the unit. If that conks out your gen because it is not warmed up and you restart the PM right away after the gen is restarted, the PM will blow that thermistor from not waiting long enough for it to cool--maybe half an hour.
Anyway, once that all got sorted out, I really like my modified PM100 for a fast charger followed by solar the rest of the day. The solar controller is now the key to success where it can get the batts to 15v or so, which meets the battery spec.
If all you have when off grid is that un-modified PM75 you are always going to be in trouble. I recommend you leave it un-modified and get a VEC1093DBD to use as well. After the 75amper drops to 13.6, disconnect that and clamp on your 40amper VEC and let it finish the job. It goes to 14.8 ( and that is temp comp!)and stays there. If you stay out more than a couple weeks doing 50-90s, then you absolutely need solar, since after several 50-90s in a row your bank will have lost a bunch of capacity and may not even get you through one night anymore. Then you are stuck until you can get shore power and a few days to do a "recovery episode" so you can go off-grid again.
yes, it looks like solar is an absolute necessity for me, seeing as i boondock continuously for months at a time. as i have said, i very rarely have shore power at my disposal. and i have found the high voltage portables tend to boil my batteries, and do not kick into float mode, which is supposed to be the whole point of a "smart" charger, is it not?
so i find myself right back to having to figure out when the bank is fully charged, and i know of no other way than measuring the SG every time i charge... at least until i figure out my bank's specs. for even with the VEC1093DBD, will i be able to rely on it to tell me when the bank is truly full??? i've been using a "peak performance" 40amper (among others) and it has not met my needs, and i just can't imagine any other portable doing a better job.
the whole reason i went with the pm4b was the lower voltages, thinking this would be better for my batteries, but many here say that a higher voltage is better. so in an effort to shorten charging time, i thought higher amps were the key, not higher voltage. and the fact that my batteries can sustain close to 12.8 v for weeks at a time when not in use tells me that a 13.6 v charge should suffice, provided the charge duration is ample... no pun intended :)
charging time is not a huge issue for me, as i usually have a good four hour window during which i can run the gennie. with the 75 amper, and the fact that i usually charge at or above a 12.6 battery voltage level, makes me think that should be sufficient time to bring them back up to 12.8 volts (actual charge, not surface charge).
i think what may end up being the case, is my charging time may not change all that much, overall, but will require more time in absorption mode and less time in bulk. the 40 ampers i've tried take quite a while to get to absorption mode, but do seem to top off these batteries as fast as the pm4b, initially, anyway. however, the pm4b appears to have the kahunas to take these batteries into low single digit charge amp levels quicker, even at the lower charge voltage.
so, initially i keep leaning towards giving the pm4b a chance to prove itself. and as well as keeping a good record of charging times, regular SG readings could ultimately determine the fate of the pm4b.
