Lead acid charging voltages

[booster]

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.

[hbn7hj]

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.

[Bruceper]

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.

[BBQ]

.

Lol

[hbn7hj]

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.

[booster]

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.

[booster]

I have had a bit of time between snow and cold adventures here in the frozen north, so I went to the Trojan site to see what they are currently saying about charging their deep cycle batteries, in relation to Handybob's statements. There have been a few small changes since the last time I looked a couple of years ago.

Trojan specializes in deep cycle wet cells, and does a very good job of it, IMO. The pair of 260ah six volt GC batteries we had tested as new after 5 years when did the switch to AGM. I will show the parameters they recommend for AGM, but they are very normal middle of the road, and likely haven't been tweaked to the extent of their wet cell recommendations. Lifeline has their AGM recommendations more refined, and IMO are more detailed for how to use in the real world.

Handybob's big complaint was about the "new" higher charge voltage profiles being recommended by various, particularly wet cell, manufacturers. AFAIK, Trojan was among the first of GC type suppliers to go to higher voltages a number of years ago. Forklift charging profiles have been at higher voltages for as long as I remember, though, for most all of them.

Handybob says that he thinks the higher voltage is in response to the chronic undercharge that most deep cycle batteries get with nearly all of the "smart" multistage chargers, and for the most part I agree with him, especially in RV and boat applications. Most of us with mobile battery systems in our vans don't have the luxury of big, expensive, very high power and accurate control, chargers every night like golf courses do for their carts. Most of us don't need a charge every day, either, like a cart does, so the application is different besides. Throw in the variability and low output of solar (which is 100% of Handybob's charging most times) and everything is messed up even more.

Here is what Trojan says about charging their deep cycle wet cells.



It shows the now very common 14.7v absorption stage, which they have for several years now. The used to also show a 14.3v for absorption if the charging was not a "daily" charge (in their terminology). This likely would indicate a golf cart charged every day would use the 14.7v and a battery charged less frequently, and that had enough time available for a longer charge cycle would use the 14.3v. I know from personal testing, confirmed by specific gravity and end of charge amps that both of those voltages will get the batteries full. The 14.7v charge will be considerably faster, though, and surprisingly they will use about the same amount of water, as long as the charges are ended at the right time. I think it is important to point out that the end of charge amps usually will be significantly higher for the 14.7v than at 14.3v so if you have your Trimetric set for 1.5%C ending amps at 14.3v, you will almost certainly overcharge the batteries at 14.7v getting to the same ending amp reading. You need to watch the amps at the end of charge to determine what appears to be the best balance of water use and charge times at each voltage to get the best results.

The Trojan description also shows a stage after the absorption stage. Essentially all of us don't have a separate stage available for that, and Handybob didn't mention how he was doing it, or I missed it. The first instinct is to just increase the absorption voltage to the higher (16+v) voltage called out for the new stage. THIS IS NOT THE THING TO DO, IMO. The absorption stage is constant voltage and ramps up to that voltage based on the battery acceptance until it levels off at setpoint. The new stage that Trojan call out is Constant Current, which is a totally different thing. The constant current will limit the amount of energy going into the battery, and thus the heat and gassing, compared to using the constant voltage, likely much higher current. Equalizing is also supposed to be constant current, but many chargers don't let you set it. This stage terminates off of voltage not current, so very different than most of us are used to seeing. This may well be at least part of what helped kill of Handybob's batteries.

Here is what the recommended Trojan wet cell profile looks like in graph form.

[booster]

So, with all of this "stuff" going on, what could possibly go wrong that would hurt your batteries?

Here is the profile for the wet cells again, with some zones marked.



The bottom of the blue zone is 13.2v and is where Trojan wants to float a full battery. In theory, you don't want to be above 13.2v with a full battery for any significant amount of time. This is why a 13.8v fixed charger will "cook" you battery over time. I think it can also show how various conditions and system differences can hard on batteries.

If you had a charger that was capable of doing the Trojan profile, you would start charging at a fairly low voltage, constant current of 10-13%C. As the battery charged, the voltage would climb with the current staying the same until it got to the 14.7v (depending on how big the charger capacity is, current might be lower by then). The charger would then go into fixed voltage of 14.7v and continue charging, and the current would start to drop until it got to the 1-3%C stage transition point. The charger would then switch back to supplying constant current at the 1-3%C amps and the voltage would start to climb above the 14.7v until it got the 16.2v setpoint (if it is set to the high end of the spec) with the same 1-3%C current. The charger would then go to float if it were to be in longer term storage, or just shut off if the battery will be used the next day.

I don't know of any charger that we could use in a van that would do even most of that cycle, unless you eliminate the final stage.

If the cycle shown, or one shortened by not using the last stage, is followed, I don't think there is much chance for battery damage at all because high voltage is never applied to a less than full battery.

What you really don't want to happen is to get the charge cycle "stuck" in one of the 3 outlined areas when the battery is full, as that will put high voltage on a full battery and could cause damage, which will get worse, I think the further up you go in the voltage.

We use the shortened, normal type, charge cycle in our system, which is all controlled by monitoring amps to the batteries, so if all works right we won't ever be putting the higher voltage on full batteries.

* Shore charger will go to float as soon as the battery amps is low no matter what the time, so won't overcharge. Very few shore chargers work this way, however.

* We monitor the battery amps with a meter on the dash when driving, so we can shut off the alternator charging when the batteries are full, so no overcharging. We had to make this capability ourselves.

* Then there is the solar which has the capability to mess it all up, and is likely why Handybob has issues with the higher charge voltage recommendations.

Our solar controller, and many others, runs off a shunt like the shore charger, so you would think that you could not have an over or under charge situation. True for under charge if you get enough sun, but certainly not true for over charge.

The questions are what can cause the over charge situation and what you can do about it.

* If you solar controller is a timer only version, it will put a full voltage, full length, charge cycle on a full battery like you would have coming off of shore power. I think this is quite common.

* If you solar controller runs of a shunt (good), but doesn't let you set the minimum absorption time to under 5-10 minutes (or you don't set it properly), it will put full voltage on the batteries for as long as the timer is set for, even once the batteries are full. This is likely not very common.

* What happens to us, and I assume a lot of other people, is that the solar messes itself up no matter how you set it, even with a good shunt based system. You can quite easily get "trapped" in one of the circled higher voltage zones for very long periods of time, putting high voltage on full battery.

It all comes down to if the solar is putting out enough power to run whatever loads are on in the van and supply enough power to the batteries to trigger the transition to float. If the solar is low on output compared to those conditions, the output voltage of the controller will never get high enough to trigger the transition to float. We have seen our system sit at .1-.2v under absorption voltage for essentially all day, in sun conditions and use amounts that are being used. It can run there until the maximum adsorption timer is triggered, which is usually a long time on solar systems because the are slow.

If we start out with full batteries, the solar will go right to float when the sun comes up, which is good, but if sun is poor and the frig comes on, the solar will go back into bulk. This is built into the unit and can not be disable, eg lock into float once it is triggered once in a day. Our solar will go back into bulk any time the battery voltage drops below the float setting of the solar, which normally would be 13.2v for us. So we can be in float, cloud comes over and frig turns on, voltage drops to about 12.9 before the batteries start to pick up the load, and suddenly we are back in absorption stage. Frig turns off and the voltage goes up from reduced load to 14.0 volts, but never gets to 14.3v to trigger going back into float. Our "solution" sucks at best, and is to turn down the float voltage to 12.6-12.7v to keep it from going back into bulk. It does work to prevent the rebulking, but it also makes it so the batteries are not held at 100% full with the solar running the power requirements.

We have a Blue Sky controller, and I have talked to them about this, and was told the the new engineering mgr had just recently told them that all new products or major upgrades would make the rebulk happen at 12.8v, which would help, but I do wish it could be set to only do one full cycle per day unless you disable that feature. If you ran a big load and used up some battery on a decent sun day, you would want to do a recharge cycle.

If anyone has any details of how other brands handle this situation, it would be interesting to hear how they do it.

I think this is what bit Handybob in the batteries . If he had setup to run with his top voltage of 16+v, there would be lots more instances when the system would get "stuck" and applying too much voltage to his batteries. From his descriptions, it also sounds like he is not using amps to change changing stages, so he could easily be overcharging by using the "calculated" absorb times that most timed controllers use, and at increased voltages, bad things happen faster. I think.

All of these things also apply to AGM batteries, too, I think, just not as radically, as the highest voltage most recommend is in the 14.3-14.6v range.

Overcharging or undercharging in our vans is very, very, common, I think. based on the shore, solar chargers and uncontrolled alternator charging we almost all deal with. Which you get (or when you get either) will come down to what equipment you have, and your use patterns. It is not particularly cheap or easy to get rid of the issues, but they can be reduced with some less extreme measures.

[Saldar]

Originally Posted by booster

Here is the profile for the wet cells again, with some zones marked.

As usual, I'm hanging on your every word. Did you intend to include a diagram? I don't see it for this last post, and I'm sure it would be helpful.

[booster]

Originally Posted by Saldar

As usual, I'm hanging on your every word. Did you intend to include a diagram? I don't see it for this last post, and I'm sure it would be helpful.

Interesting, the diagram shows on my computer right after the line you quote. Did the two in the previous quote show up? None of them are showing as attachments at the bottom of the page, but are showing in the post itself, which is odd. I will put the diagram in here, again, to see if it makes it.

[Saldar]

Thank you. Your new post shows your helpful annotated diagram. The prior post's images appear fine.

[Saldar]

Originally Posted by booster

If you had a charger that was capable of doing the Trojan profile, you would start charging at a fairly low voltage, constant current of 10-13%C.

There's a lot to absorb in your analysis, but one thing I noticed was the low seeming bulk stage constant 10-13%C current Trojan recommends. I find people recommending 20%C as a minimum current in bulk, and that more is better. Is this lower recommendation new, or have I been getting opinions rather than good information? Or is this because the Trojan info is for FLA and not AGM?

Would this dissuade you from fast charging, say, with an alternator? The low level might be complementary to solar.

[booster]

Originally Posted by Saldar

There's a lot to absorb in your analysis, but one thing I noticed was the low seeming bulk stage constant 10-13%C current Trojan recommends. I find people recommending 20%C as a minimum current in bulk, and that more is better. Is this lower recommendation new, or have I been getting opinions rather than good information? Or is this because the Trojan info is for FLA and not AGM?

Would this dissuade you from fast charging, say, with an alternator? The low level might be complementary to solar.

The 10-13% is for Trojan deep cycle wet cells, and has been around for a long as I have looked at their specs, so about 10 years. They used to list it as 11% most of the time, but no use the slightly larger range. I have looked around several times in the past, when we had Trojans in our van, for some firm numbers for maximum and it is not particularly easy to find. Even Trojan was squishy on it, but the tech there at the time said 20% max. Wet cells don't fast charge well, especially deep cycle versions, it appears, and what they will even accept from a big charger isn't all that high. IIRC, ours maxed out at about 40%C with a big charger and 14.7v, but they got hot quickly and gassed a lot. My guess is that Trojan has found out that they can put more watts into a battery faster, without too much heat being generated by keeping the lower amperage, but raising the voltage, as shown in the newer specs. Watts are what the battery stores, so it makes some sense. The batteries that Handybob failed where Crown, not Trojan, but I think they have similar specs (need to look for sure). I don't recall his solar and battery capacity, but he may have been able to get too high on current.

The fast charging from an alternator is an issue with wet cells, as most class b vans have 50-80 amp breakers to the batteries and can give them more than ideal. 20% of a 220ah bank is only 44 amps. AGMs double that amount so can be charged faster, if the alternator is OK for that much continuous output. The big problem, IMO, is that the alternator charging is nearly always uncontrolled for voltage or amperage or time. Depending on the state of charge of your batteries when you start a drive, you could be overcharging your batteries for the entire drive (if the batteries were full from shore power), or need the all day drive to get full (if they were near empty). Without some controls this can be a hazard to the batteries. IMO, having a Trimetric, or other monitor that shows a fully charged indicator, within sight of the cab, and a disconnect switch style separator is one of the best things you can do to preserve you batteries, especially if you drive long hours regularly.

AGMs do accept and recommend much higher charge amps. Most seem to spec in the 20-25% as normal, no minimum usually, but with allowances to go substantially higher as long as the charging is temp controlled to prevent overheating the batteries. We have found our Lifelines to be able to take about 40%C without getting too hot, although we do have to watch a bit because they are under the van and see underbody heat while driving, too.

I haven't seen it or other manufacturers, but in the last few years Lifeline has added a recommendation to charge at a minimum of 20%C if you are discharging more than 50%. This is likely the spec you have seen. They also say to set the normal amperage to "as high as practical", which is pretty vague. When I called them and asked about the amperage best choices, Lifeline said they would prefer 40%C for the deep discharge recoveries, with a minimum of 20%. They would probably like more than the 40% but heat would be an issue in many cases, I think. 40% on big battery banks is more than most single chargers can do. We can only get a bit past 20% with our 100 amp Magnum. Engine generators can easily get high enough, or more.

Of particular interest in this discussion of higher voltages is that Lifeline now also has a deep discharge recharge recommendation that says if you can't provide at least 20%C charging amps.



What immediately jumps out is that this is very, very, close to what Trojan recommends to do on their overnight type charges. Constant current at 2%C extra stage. Trojan cuts off at voltage, which is a good idea I think. Lifeline says by time and isn't specific. Since Lifeline allows 15.5v for equalizing, that would likely be a good place to stop. Of course, none of our chargers will do this as part of a normal charge profile. I think our Magnum allows you to do an equalize and set the maximum current and voltage, but I will have to look at that. I know you have to run it as a separate operation.

All this brings us right around and back to what Handybob said, that he thought the higher voltages were to compensate for the chronic undercharging that most batteries see in use. Equalizing, which is what these extra constant current stages really are, is what you do to help recover capacity in batteries that have lost capacity, usually from poor charging, so it makes sense. Where Handybob and I start to diverge is in whether it is an overreaction, or not. At this point, I think it may not be as much of an overreaction and overdone correction, as it is a misapplication of the correction. If the added, high voltage, stages are not controlled exactly as recommended (constant current as specified, terminated at recommended voltage, temperature controlled) I think it would be very easy to destroy your batteries, and that may have been what happened to Handybob.

[Saldar]

Originally Posted by booster

My guess is that Trojan has found out that they can put more watts into a battery faster, without too much heat being generated by keeping the lower amperage, but raising the voltage, as shown in the newer specs. Watts are what the battery stores, so it makes some sense.

I'm assuming this refers to bulk charging. Then, I didn't know voltage was an element of bulk charging. (Tho obviously to provide power voltage is required....) I thought the charger supplies constant current and the voltage required is controlled by the battery chemistry. Voltage increases and when it reaches a threshold, or after some fixed interval, the charger decides to begin absorption by holding at its absorption voltage. So is the higher Trojan voltage at bulk the final threshold voltage? I think the charger must supply whatever voltage is required to keep the current constant in bulk---and that appears to rise, not be a fixed value. What does bulk stage voltage mean?

Your expanded discussion of recommended current levels for the two types of batteries is very clear.

[booster]

The section you quoted actually refers to the absorption stage of charging, as that is when the higher voltage is first seen, although it having a higher absorption setting will also keep the charger in bulk a little longer because the voltage has to rise more. This keeps the charger at full output longer and puts the SOC of the battery higher at the absorption transition.

Bulk charging is constant current, as you mention, so voltage is irrelevant as long as the current is where it should be. The chargers in our vans are not really true constant current devices in most cases, as you can't set the maximum output current on most of them. They turn into constant current devices by selecting a charger that has a maximum output about where we want the bulk charge constant current to be. It all works out to be the same thing in practice.

The whole battery acceptance thing gets really kind of odd when you apply it to the bulk charging stage. Normally, we hear that a battery will "accept" X amount of amps at a given voltage, which is usually the absorption setpoint voltage, and SOC. We are always looking at the amps as the variable as it changes with state of charge, and the voltage is constant. This train of thought only really works once you get to the constant voltage of absorption.

In bulk, the voltage is not even being tried to be controlled, it is whatever voltage that would match up with what the current and SOC on the charge profile for that particular battery. This is very similar to saying it is what the battery will accept in amps, but the charger can't supply it, so amps doesn't change. As bulk progresses, it is the voltage that changes with the SOC and based on the chemistry, following the bulk charge profile for the battery and charger. Wet cells require more voltage for the same amps, in general, compared to AGM, so the voltage will rise faster vs SOC in them, at the same amp %, and will have a shorter bulk stage with all other things equal.

Only when the voltage in bulk has risen to the setpoint for absorption does the acceptance of the battery control the amps it is getting, based on SOC and constant voltage. Once in absorption for a time, the amps will start to drop below the maximum output of the charger and at that point it is the battery that is controlling the amps by it's acceptance from there to completion of the charging.

How all this refers to the quote is a bit of an apples and oranges. I based it on the assumption that the battery manufacturer wants to increase the charging speed of their batteries. Since batteries really store watts (amps times volts) you can increase the charging speed by putting in either, or both, amps and volts faster. It appears that they chose to leave the constant amps in bulk the same so no speed gain there, but they increased the voltage in the absorption stage which will put watts in faster in that stage. The increased voltage will increase both volts and amps at that point because the charger will no longer be maxed out like in bulk. It is likely that if the increased the amperage in the bulk stage, they feel they would get excessive heat or some other issue, but that the increases in absorption would not give those issues, and having the higher voltage might even help some the chemical conversions of charging which get slower and harder to do as the SOC nears 100%.

I did look at the Crown charging profile recommendations, and they do very similar to Trojan with a constant current final stage to a maximum voltage cutoff. One thing they do differently is recommend a higher charging current % than Trojan at 15-18% instead of 10-13% which would be close the 20% max that Trojan had told me.

I went back and looked at my notes from speaking with Lifeline on charging amps as %C. For discharges of over 50% SOC, 20%C minimum, 40% recommended. I had also asked how much a 20% SOC Lifeline AGM bank will accept if you have it available and could hold the voltage up to 11v or more. Inrush could be quite high and hard to tell for sure because of components and wiring, but would likely be 80-100%C. After a few minutes it would likely settle at 70-80%C for about 30 minutes and then start down. Those kinds of amps would overheat our batteries in about 15 minutes. For that reason, we are setup with two turndown settings on our engine generator setup. One runs at 280 amps and the other at 180 amps. If we even need a very quick recovery of a couple of days use, we can get it with very short engine run at 280 amps, otherwise we would use the 180 amps which will not overheat the batteries and can run to full. To this point we have never needed to use the 280 amp output.

[Mfturner]

Thanks to all of you for these discussions, I am back into RV ownership after some years of taking a break while teenage kids lost interest. With my previous TT I replaced the batteries once in the eight years, so maybe I got five years out of the first set without any real care or understanding of them. This van has middle of the road capacity using inexpensive components, with two Interstate gc2 6v batteries, a 55a wfco converter/charger, 95w solar panel with a 25a go-power controller, 600w inverter, and a 2.5kw Onan. So lots of scope for upgrades. The batteries appear to be original and three years old now, so experiments won't be expensive for now.

Both of the charge controllers are a little improved over the old TT's, boasting 3 or 4 states but are voltage triggered and timed. The voltages for the solar controller are modestly programmable, but all choices have higher float and absorption voltages than the wfco. A quick glance around shows many inexpensive pwm solar controllers with a 13.7v float listed, although to be fair the night or shaded float voltage will effectively be zero. I wonder if the solar controller having higher voltages keeps the two feedback control loops from interacting? And if the expectation is that while boondocking the batteries will draw down every night so that a small panel like ours will always want as many watts as possible, thus high voltages, morning boost, etc?

Another thought is that since I'm still a working stiff, like the TT, this van will sit in covered storage many more days than it will be used. So a main concern will be how to keep the batteries happy in storage. The van has a nice battery disconnect switch, but the solar appears to be wired around it. So you have a choice of overcharging if stored outdoors or a 6ma draw from the controller if sheltered. Maybe that's only an amp-hour a week if I do my math right, but it doesn't make much sense to me and makes me wonder what else is wired around the switch. The wfco's 13.2v float may be ok in storage, I'll watch the water levels and if it is boiling of water I'll go back to the disconnect switch. And there is now a starter battery to think of too, for convenience I'm going to try the Battery Tender Jr and see how that goes.

I could be wrong, but when I look at I the Trojan charge profile, I imagine that they are initially limited by thermal considerations, so that the I^2*R power is controlled until the current acceptance drops. In the absorption phase the battery's thermals are self limiting by it's current acceptance. My solar panel is so weak that there won't be a problem overdriving the bulk/boost phases, but the wfco might overheat the 225 ah batteries if it can really deliver 55a in bulk, so I might watch the water level for a while.

And a thought about alternator overcharging, I have a 3 way refrigerator, so in theory I could switch that on DC when I'm plugged in overnight and traveling the next day with full batteries. We shall see if I remember to try it, and then remember to switch it to propane when we stop, LOL.

[booster]

Welcome to the forum!

It sounds like you have a good grasp on most of what is going on.

First off charge voltages for wet cells, and particularly GC2 golf cart batteries which are usually some of the best true deep cycle types. (I will put a disclaimer here that there is unproven chatter that the newest versions of the Interstate GC2 batteries are made with combo battery construction and not true deep cycle. Time will tell if that is true, as it should be able to tell pretty easy from the water use). IMO, the latest and best voltages for GC2 wet cells would be 14.7v absorption and 13.2v float, but I will say this is really only exactly right if the charging system is very good at getting the batteries truly full regularly and not doing any major amounts of overcharge.

The 55 amp charger is a bit too big but not bad for your wet cells. Interstates are probably around 220ah, and we have found that charging at 20% on deep cycle wet cells works OK, but you really should have temperature correction. If you were way down on charge, the 55 amp would likely get the batteries pretty warm, especially if it is not temp controlled.

The solar is an interesting situation, especially with your storage situation. You didn't say if you have shore power there, but if you are testing a tender, you likely do. With shore power, the solar could be totally disconnected without issue as the shore power will take care of it fine. The solar is probably wired so the controller does not shut off if the main disconnect is shut off? They do that so to protect the electrical systems because if you were sitting in the sun the panel would generating a higher voltage than the controller would if it was on. Turn the batteries on without the controller already regulating the voltage, and a big spike can come through from the panel. The solution we use is to have an easy to pull fuse for the controller so you can disconnect the batteries completely from everything except the charger, just remember to put it back in with the panel in the dark.

When camping, I think you are probably very close when you say the solar is so small you won't likely overcharge. The panel will give about 30ah per day maximum and usually less than that. Most class b's with a gas frig, furnace, and hot water will use about 20ah per day +/-. The only time it would overcharge would be if the batteries were full when the day started, and it ran a full charge cycle all day. Better controllers look at the voltage when they come on in the morning and decide whether to charge or not. There would be no benefit, I think, in running DC at night on shore power as the AC is more efficient in the gas frigs and does a better job. The batteries will get charge either way, so no reason to use DC. unless you wanted to do it to reduce the current to the batteries due to the big charger.

The van alternator is likely your largest chance to overcharge, especially if you normally have shore power overnight so you are starting with full coach batteries. Isolators will run lower voltage to the batteries, which is good if they are full, but bad if you are trying to charge them. Separators will charge better but will put full alternator voltage on the batteries when you drive regardless of if they are full or not. Disconnects for the alternator charging can be done pretty readily if that becomes an issue.

Good luck with your reindoctrination to camping.

[Mfturner]

Thanks Booster. Regarding the Interstates, they are a cheap brand, not what I would use for replacement, and it wouldn't surprise me if a cost savings measure is thinner plates ala a marine combo battery. I'll use them until they wear out, then get something better. A battery monitor, trimetric or victron, is on my list. Regarding shore power in storage, yes I have access to 15a which should be enough with them already essentially full. The 30a to 15a adapter just arrived and I'll take it out to the lot later today or tomorrow. Great point about using a fuse to disconnect solar, and thanks for the heads up about a spike if the panels are lit up when the fuse is replaced. If the voltage drop over the past 10 days seems consistent with my 1 ah/week estimate, or if I decide to trust the wfco, I may not worry about it. Also, I'll double check the wfco, I thought I recalled the model being 8955, but even an 8935 would be enough for these batteries so maybe I misremember the model no. Finally, I was only thinking of having the refrigerator on 12vdc while driving to offset the alternator, my TT didn't get enough cooling off of 12v to use it if propane or 120v is avail, and it kills the battery, but I don't like driving with propane on.

But you make me want to sit down and map out some common combinations to think through, shore power vs none overnight followed by a day of driving vs camping, with or without good solar or shore power. Several permutations, but that's what spreadsheets are for...

[hbn7hj]

Just a suggestion but use a permanently installed Trik-L-Start or Xantrex echo charger for the chassis battery. Don't have to think about it again.
Harry