Interesting sticky topic i found on solar charging

No temperature compensation for him eh?

I'm moving to Li which doesn't care if it's undercharged. Perfect for boondockers.

I got tired of the author misspelling 'manufacturers'.

His recommendations seem designed for those with a low ratio of solar W to battery Ah.

For my system, (700W solar, 440Ah batts) I would be concerned about setting the float V as high as absorb V.

We do raise our solar charger's float V when actively boondocking, but when not using much current I drop it down to 13.2V. Otherwise I'd just be boiling off water without increasing the charge.

Otherwise, yes, the batteries get hammered at least once a day with the absorb setpoint of 14.9V, temperature compensated, and absorb doesn't stop until the current drops to about 0.6% of Ah capacity. That's full as far as I can tell. And when in storage with full sun, it takes less than 5 min. The rest of the day is float.

After a stretch of solar undercharging, I equalize at 16V for 1-2hrs.

Have heard concerns elsewhere that these higher absorb voltages like 14.8-14.9V might be hard on trailer electronics. Especially as temperature compensation can raise them well into the 15's. But so far, all is working as it should ...

I don't have a long term experience to back me up, but I do agree with his idea. I started with a previous generation Morningstar Sunsaver PWM controller. It only does one voltage, which is 14.4 adjusted up or down by ambient temperature. My cheap 12v batteries seemed to do just fine with it. I did not go for long periods on solar, though.

I started a thread a year or two ago asking why float mode was needed on solar. Float mode is the end of a long charge cycle. With solar, every day is a new charge cycle, with complete rest every night. Float mode seems useless. If you get full during the regular daily cycle, the amps taper down to virtually nothing. The sun goes down, and it shuts off. What else do you need? Even the models with float mode still start every new day in the bulk cycle, and onward from there. It's not like you are sitting in float continuously like you would on a shore power converter.

The current version of the Morningstar Sunsaver PWM has float mode. I asked them why the change, and I got the feeling they didn't want to say it was for marketing reasons.

All controllers have float now. Usually after Vabs has been present for 1-4 hours, it drops to float. Why??? You might still be able to get a few more KwH out of absorption.

Most people in my thread didn't like my idea.
https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/28696964.cfm

Now I have added more wattage, and I have a Renogy controller that runs 14.8, and 13.8 float. Okay, whatever.

I've been looking for my sweet spot for years... No luck so far...

I don't have solar panels yet but about to get into it... I start my day/night run with at least 90% SOC and will only do the 50% to 90% charge cycles for a few days.

I always follow up using my generator or shore power at the house to do the full 100% charge state ops... This takes over 12 hours to do so sometimes this may be a problem depending if you are at a location where running the generator is not allowed to run that long of a time. I would think one could almost always get the initial charge state going for an hour or so using the generator and then let the solar panels complete the charge cycle when in high sun. Of course you will run out of high sun especially here on the east coast side of the US.

The most I can see happening is you should be able to get your batteries from the 50% to the 90% charge state each day for doing a week long camping trip off grid and then do the long charging period after you get back to shore power somewhere (At Home in my case)... I do this routine using my generator each day for around three hours of run time when allowed and it keeps my 255AH battery bank pretty happy... They have lasted from 2009 to just last season 2015 and just won't hold a 90% charge state very long any more...

My camping routine is I usually draw around 20-23AMPS DC current from my 12V battery bank between the 6PM to 10PM time frame each day. This is probably high for the average off-grid camper...

In the old tent camping days all one needed was bag full of D-CElls and a can of white gas... We did just fine back then haha... Now we got all of those 120VAC appliances and things to deal with.

Roy Ken

I've tried it out on my fairly small system and it seems to hold its voltage better during the night and the specific gravity is coming back up. I was quite nervous about the higher voltage but the hydrometer says i'm finally getting a better charge and the water usage still seems to be low.

I can only imagine how it could be if i did this from the start but that's why i bought cheap batteries to start with.

Edit: thanks for checking this out i was hoping the two of you would take a look along with Mex.

Obviously written by somebody who actually uses a hydrometer, and is not of the "float equals full' mentality.

The fully off grid guys don't get to give their batteries a rest and plug in for several days when their outing is over. That can make up for much battery abuse, a luxury the off grid guys do not have.

Set controller to 'maximum smoke'. I like it.

I'm also on the AGM bandwagon, so no hydrometer for my battery.

When amps taper to 0.5% of absorption voltage is how I judge 'nominally full' or acceptable full.

But the true reset to maximum potential remaining capacity requires a high amp recharge from 50% or less charged, then holding Absv until amps taper to 0.5%, or less. Then if possible, float overnight at 13.6v. Usually ammeter reads 0.0x by morning, and goosing voltage back to 14.7 usually has amps taper back to 0.0x again, and this is what I consider true bursting full, on this AGM.

I am over 500 deep cycles and my single 90 Ah battery at the moment is 22Ah from full, 12.56v under a 7.1 amp load.

In terms of voltage held for X AH removed under X load, this 90Ah battery is outperforming 230Ah worth of flooded marine battery, and has already outlived them cycle wise and time wise.

i agree
i'm already in that state of mind
i run the generator everyday and utilize a 70amp PD converter, in fact usually every morning
i have set my solar charge controller at 14.8v
and i also have a 75 amp converter with adj voltage and have it set at 14.8v

but i do have sealed AGM surplus telco batteries, 102# each , 135 ampHrs each at the 8hr rate, capable of 500w per cell
so i can't use a hydometer, even though i have one
i am forced to use tapered charge rate vers voltage vrs 'trends and tendecies"
works pretty good for me