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Old 01-12-2018, 06:29 PM   #1
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Default Lead acid charging voltages

Harry (hbn7hj) has a discussion going about the often misunderstood 50% rule for lead acid batteries in which he has a quote from the always interesting "handybob", that many of us have spent lots of time reading his articles in the past. I hadn't checked in on him lately, so I used Harry's link to go look at some of his more current, 2018, preachings. As always, they are as entertaining as informative.

Handybob's specialty is living off of solar and batteries, so sort of, kinda, applies to how most of use our vans. No regular generator or shore power options for him.

He likes wet cells, like many off grid solar users do, and some very specific products for controllers, monitors, etc.

His recent articles described early battery failures, which kind of surprised me because of his charging pickyness. He attributes the failures to too high of charge voltage being recommended by the battery manufacutrers, particularly when they start going up over 14.6v absorption Handybob attributes the very high recommendations to an overreaction to the chronic undercharging that has happened in the past on nearly all systems, which I totally agree with.

In typical handybob form, he kind of lumped a bunch of stuff together in saying he would never, ever, put a wet cell over 14.6v or AGM over 14.4v, which isn't inherently bad, IMO, but probably isn't completely right either in a lot of cases.

I think a lot of the higher voltage things started about 10 years ago when folks like Trojan started showing 14.7v absorption voltages as being desirable. It was kind of odd to me how they presented it in their charging tables, as they used 14.7v for a "daily charge", but 14.3v for "absorption charge" in another line. I called them and got a bunch of different answers to what it was all about, and after also talking to some local golf cart shops, it seemed to make some sense.

It appears that the higher voltage was directly aimed at batteries that are cycled fairly deeply, every day, and need to be ready to go after overnight. They also need to have a reliable charging source to give that voltage for the right amount of time without overcharging. In other words, this is for golf courses because the 14.4v charging voltage couldn't get them all the way full, to give best capacity and life, in the time available. Trojan has even add a short 15+v stage after the absorption as a mini equalize for the daily charged setups like golf carts now

As everything battery seems to be, the whole thing quickly spread to pretty much all applications, regardless if it was correct or not. In particular, I think solar is one of the application where it often not a good idea to go with the higher voltages, so that would explain why handybob came to his conclusions.

We have seen first hand, in repeated tests on our 300 watt system, that there are conditions that can make the controller mess up the voltage to the batteries, to the high side, and it is worse if the absorption is set to more than 14.3v. In our case it only happens in the no man's land of charging between about 80% full and 100% full, where controller is in full absorption voltage, but if the solar input conditions vary with clouds, shade, whatever, the panels may not be able supply enough energy to hold that full absorption voltage. If the controller doesn't see absorption full voltage, the absorption timer does not run, even though it may be only .1v below setpoint. We saw ours run 14.5-14.6 for many hours on essentially full batteries because there were clouds holding down output, and the small van loads were enough to drop the voltage. It got even worse with compressor frig because on many cycles, it would drop the voltage enough to put it in bulk again. If you put 14.6v on a wet cell all for 8 hours, it is going to use a lot of water, and an AGM will start to dry out. This is what had to be happening with handybob, it think, but it may have also had some other causes contributing. He mentioned the controllers he uses having "calculated absorption times", which says no shunt, so no accurate stopping of absorption stage. With the higher voltage, solar conditions would leave him in bulk for a long time, so the calculated absorption time would also likely go long because of that. Lowering the voltage made his system react better because it could hold the 14.4v easier, and thus got more accurate absorption times, when he has enough capacity.

Hanyybob states he likes using the Trimetric % returned AH to determine full, which isn't horrible but not nearly as accurate as measuring the actual amps to the batteries. With no shunt, he has no automatic voltage reduction when the batteries are full, except for the internal timers of the controllers.

The solar overvoltaging thing is very hard to address completely, I think. I know we have not come up with a foolproof way to this point. If we are getting good sun nearly every day and not doing any driving, I will set the solar absorption to 14.4v, and it will get there and go to float well. We do have a problem that the Blue Sky controller will go back into absorption if the voltage drops below float voltage, so in the later afternoon a cloud can go over and the frig turn on and it rebulks and holds up the voltage above float when the cloud goes away or the frig goes off. I normally set the float voltage low, a bit below where the full batteries run, at about 12.7v so that is will not rebulk once full and in float so easily. Blue Sky says they will addressing the rebulk in future controllers by lowering the rebulk threshold to 12.8v.

On days where we know that there isn't going to be enough sun to have solar run a full charge cycle because it won't hold voltage, I often will turn the absorption voltage down to under the gassing point of the AGM batteries, usually 13.9v.

I wish we didn't need to do this, but without more sophisticated control, the variable input is difficult to address.

For the shore charger, it is a lot easier because there is always enough power to hold the voltages up where they are set. The "daily charge" thing can apply here though, if you chose to do it, and it may help especially if you have a smallish charger. If we are doing longer offgrid times and aren't able to get full on solar regularly because of conditions, I will use 14.5v for absorption to give bit of a boost to the charging to recover better from mid state of charge cycling. If we anticipate longer shore power stays, storage, or are getting full with driving and solar, the absorption is at 14.2-14.3v. It is really very rare that we would turn up to the 14.5v because the solar and even tiny amounts of driving get us full most of the time.

I think all of this also is a good reminder that for many of us it is important to know when the coach batteries are full when driving, so they can be shut off to prevent them from seeing high voltage all day.

The handybob articles are the first that I remember seeing about being careful about the new higher recommendation, but I think we will be seeing more if it in the future, as the higher voltages will likely tilt the battery damage ratio of undercharge to overcharge toward overcharging.
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Old 01-12-2018, 07:11 PM   #2
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Booster, thanks for the summary! I couldn't make sense of what he was saying and was going to try again this evening. I will still read it again now that you have explained some things.
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Old 01-15-2018, 03:26 AM   #3
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I watched one "handybob" video and concluded he is an idiot who will likely die in a van fire. But that's just like, my opinion man.
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Old 01-15-2018, 03:51 AM   #4
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.

Lol

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Old 01-15-2018, 08:55 AM   #5
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If it wasn't for Handybob's rant I'd still be trying to get by on 3/4 charged batteries so he has made all the difference for me and I do appreciate it. I wouldn't have figured it out on my own.

The higher voltages work fine for me so I think I'll stick with them. I seldom see full charge and full sun for hours on end so that may be the difference. I have one manual charger set for 15.4 volts on a group 27 battery so I'll pay attention to that one. I may cut it down to 14.8 volts. Anyhow, I owe him one.

Now if I could only figure out the 1.2 volt drop between my batteries and TV. It isn't resistive because it doesn't vary with current nor did it change when I parallel it with 6 gauge. Thinking it had to be in the ground path I put six gauge in for that but it is still there. The TV cuts off at 11.4. I quit trying to figure it out and put in a voltage stabilizer but one of these days I may reopen that research project. It can't be that difficult.

Most of the people I meet dry camping don't have a clue. They run the generator to watch evening TV and charge the battery with a 13.7 volt converter. One of the camp hosts couldn't figure out why he had to run the truck engine or generator to open a slide out after a day's driving. Handybob's rant would tell him.

Between Booster and Handybob I get all the info I need!

Harry 2006RB LazyDaze and 2003 C190P Roadtrek.
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Old 01-15-2018, 04:52 PM   #6
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Any discussion of Handybob always has a wide variety of opinions, that is for certain.

I certainly do think that his personality and presentation get in the way both his own ability to expand his knowledge and to explain his ideas to others, which is unfortunate, but the way he is.

I would be the last one to say to take Handybob's ideas as gospel facts, as I do think he misapplies some things and misses others, but he does understand, and preach, some things that many of us also support (50% rule for instance). Most of his stuff is derived from offgrid stationary solar applications like his, and I do think he tends to apply it to other applications where it might not be as applicable.

A read of Handybob's writings can be very entertaining as long as you keep in mind that no matter how he presents things as facts, they are really opinions and just another piece of the puzzle we all are working on all the time.
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