Fast charging AGM batteries

[markopolo]

Interesting book here: http://www.etf.unssa.rs.ba/~slubura/...%20Edition.pdf

A 4th edition has been released also.

Page 24.29 is the section I was reading.

Basically, a higher than expected charging voltage appears to be needed for fast charging. 2.5V to 2.55V per cell is 15 volts to 15.3 volts. The question then become can other components of the RV handle those voltages or do you need to take the batteries offline?

Charging at a low voltage, 13.5V looks to have impaired the battery if I'm reading the data correctly. I've suspected for a long time that undercharging RV batteries is probably the biggest cause of premature failure.

We've talked about some AGM's needing higher than "normal" charging voltages for optimal care. Booster shared this PDF a while back: http://www.energy1batteries.com/Tech...+Batteries.pdf - 14.7 volts was recommended on page 3 of that doc.

I think you need to make sure your batteries get a high enough voltage on a regular basis to keep them in the best condition possible. On some seasonal use batteries that I maintain, I've observed that constant float charging is not enough for optimal care.

[gerrym51]

Originally Posted by markopolo

Interesting book here: http://www.etf.unssa.rs.ba/~slubura/...%20Edition.pdf

A 4th edition has been released also.

Page 24.29 is the section I was reading.

Basically, a higher than expected charging voltage appears to be needed for fast charging. 2.5V to 2.55V per cell is 15 volts to 15.3 volts. The question then become can other components of the RV handle those voltages or do you need to take the batteries offline?

Charging at a low voltage, 13.5V looks to have impaired the battery if I'm reading the data correctly. I've suspected for a long time that undercharging RV batteries is probably the biggest cause of premature failure.

We've talked about some AGM's needing higher than "normal" charging voltages for optimal care. Booster shared this PDF a while back: http://www.energy1batteries.com/Tech...+Batteries.pdf - 14.7 volts was recommended on page 3 of that doc.

I think you need to make sure your batteries get a high enough voltage on a regular basis to keep them in the best condition possible. On some seasonal use batteries that I maintain, I've observed that constant float charging is not enough for optimal care.

i'm confused Mark. are you installing tppl =thin plate pur lead batteries? enersys is a tppl battery

[markopolo]

What has you confused Gerry? Which document?

[booster]

I find this a very interesting topic, from a whole lot of directions. As I have been looking at our future single bank AGM system, one of the things that didn't make sense in what I was reading and hearing, was what actual charge rates folks were getting on their AGMs. Most don't even get to C/2 charge rate and nowhere near the 4C and 5C that the manufacturers talk about. Needing the higher voltages certainly makes sense in being needed to get the higher charge rates, plus high wiring voltage drop surely contributes. Some of the AGM manufacturers have gone up to 14.6+ level volts for normal charge now, so they may be addressing that issue a bit. I do think above 15v could be hard on some of the van parts over time as it is right on the edge of allowable, but beyond that, I think if they made the chargers to that voltage they would have to contain a "go to float on current" type profile. Even a little time at that voltage on full batteries would probably be very bad for them.

I also have thought that undercharging is the biggest problem with batteries. Oddly, it probably became the bigger problem with the introduction of the "improved" chargers, eg multistep smart chargers. We found on our Tripplite, when we had it, there was no way to make it totally fill the batteries. It always left them somewhere between 80-90% or so. Since most of the chargers use timers to control the charge times and voltages, unless you just happen to hit the right size and type battery, you will be either under or over charging. Banks are getting bigger, so under charging is getting more and more exaggerated.

Getting higher voltage to the batteries, either during charging (if it is controlled well enough), or as an equalize (or conditioning as they want to call it now because they always said you can't equalize an AGM), is probably a very good idea. The problem, I think, is that the current charging systems, with a few exceptions, aren't good enough to do it reliably, safely, and with good results. I will pick on the Roadtrek recommendation to "condition" AGMs in their units, with a Tripplite charger. The Tripplite has non settable voltage and current for its equalize setting that you use, but voltage and current should be able to be set to match the battery being conditioned, especially for AGM. Current is especially important from what I have read, but wrong voltage can also make it ineffective, or damaging.

When we go to AGMs, I will probably run the higher voltages for charging, probably something in the 14.7v range. Our solar, and the shore charger we will use, both will be totally setable and end high voltage charging based on current to the batteries, so it should be good for the batteries without risking overcharge damage. Engine charging will be able to be manually watched while driving and end it based on current to the batteries. The engine voltage is in the 14.3-14.5 range most of the time.

Although it is a different discussion, I do think overcharging will become more of an issue going forward, as basically uncontrolled engine generator and big alternator systems get more common.

I think all this points out that pretty much every RV should have a good battery monitor in it, and folks should learn how to use it effectively.

[avanti]

One important aspect of this discussion is the voltage drops commonly seen in the chassis alternator-to-house battery wiring. Upfitters have a robust tendency to under-size this often-very-long wire run, generally ending up with a system that has enough voltage drop so as to make it impossible to fully-charge the house-battery from driving alone. This is maybe not so bad a thing, since, as Booster says, this represents "dumb" charging which few people pay any attention to. But it is important to understand that solar and/or shore-powered intelligent charging is important to finish the job that the chassis alternator starts..

[gerrym51]

Originally Posted by markopolo

What has you confused Gerry? Which document?

mark the energy1 battery document -the lower one-those are TPPL agm batteries

[markopolo]

Overcharging on long drives could be problem. It all might turn out to be somewhat self regulating as heat build up in the alternator decreases the voltage output.

I don't think we'll see 15 volts out of alternators to see the fast charging discussed in the book though. All the amps in the world won't charge a battery if the voltage isn't sufficient.

Are we babying these AGM's even the off brand ones? I'm kinda liking the periodic conditioning charge idea. None of us want to risk wrecking an expensive AGM though. You often see "consult your battery manual for charging voltage" but some batteries don't come with that info.

I have one charger that can get to 15V and I'm thinking about hitting all the batteries with that periodically. I have to think about it some more hence all the research.

[booster]

X2 on what Avanti says, I think it is impossible to overemphasize the importance of having a good finishing charge, especially if you don't have the capability of monitoring the engine charging. IMO you don't need the finishing charge on every cycle, but I would think the once in every 5 would be a good place to be. As has been discussed here several other times, getting mostly full on the engine quickly, and then letting the solar finish off the charge with engine generator disconnected, is an excellent way to do it easily, and no shore power needed.

It is interesting that the undersized wiring can cause undercharging for sure, as the reduced voltage do to wiring drop really slows the charge rate. What it also doesn't do is prevent overcharging if you start out the drive with full, or near full, batteries. With full batteries, the current drops low enough that the batteries see full alternator voltage, so you can still overcharge them for the entire drive. Thus the need to be able to shut off the separator when needed.

[avanti]

Originally Posted by booster

With full batteries, the current drops low enough that the batteries see full alternator voltage, so you can still overcharge them for the entire drive. Thus the need to be able to shut off the separator when needed.

I've actually been wondering about this. Doesn't the regulator in the alternator see the combined demand from the house and chassis batteries (which, being in parallel, should balance each other out), and simply dial the current down to safe levels when the demand isn't there?

[markopolo]

I was typing while everyone else was posting and I'm kind of a slow typist ....

[markopolo]

You need voltage to go along with current to force charging.
For example: If I hit my already charged batteries with 14v right now amps would flow in. However, more amps would flow in at 14.4v and even more amps would flow in at 15v.

[booster]

Originally Posted by avanti

I've actually been wondering about this. Doesn't the regulator in the alternator see the combined demand from the house and chassis batteries (which, being in parallel, should balance each other out), and simply dial the current down to safe levels when the demand isn't there?

I don't have that totally figured out at this point, and I think it has to do with type of alternator and regulator. Our GM alternator did what I always had seen in our other vehicles. It would start out high at maybe 14.8 volts for a couple of minutes and then start to drop down to running voltage, which was quite stable at about 14.4 volts with moderate loads on it. The only time it seemed to vary was with temperature changes. Either hot engine air on it, or hot from extra load would reduce voltage to as low as 14.0 volts, and really cold temps would move it up to 14.6 or higher. It actually would run lower voltage when the batteries were empty, than full, because it ran hotter.

The DC Power Engineering alternator we have now has a Denso regulator in it, that was touted to be "smarter" than the other brands, in that it did more monitoring and adjusting. It seems to sample the output every ? minutes, and adjust the voltage, so it tends to jump around a lot on voltage. It is pretty stable on a going down the road at constant speed drive, but if you have up and down speed, sitting still, loads on and off, it changes the voltage a lot. In moderate weather we see 13.9-14.5 volts within minutes of each other. The change isn't continuous, it appears, as it will all of sudden jump, stabilize for a while and jump again. Since I want to control the separator based on amps going to the coach batteries, it is a bit irritating because the full amps drawn changes with voltage, as we have been talking about. I wait until the voltage is 14.4 to check amps and shut off the separator.

[gerrym51]

the zion has no seperator because it only charges house battery from the extra alternator. the vans actual alternator just works on the van. none of the chassis original systems are touched. the zions extra alternator also uses it's own separate pulley and belt.

[markopolo]

Originally Posted by gerrym51

mark the energy1 battery document -the lower one-those are TPPL agm batteries

That's a good one for you to read Gerry. If you see higher than common charging voltages occasionally when plugged in then that most likely means Roadtrek followed the published Northstar recommendations when setting up the inverter/charger parameters.

The other PDF file also notes thin plate technology and how it accommodates faster charging.

[booster]

Originally Posted by gerrym51

the zion has no seperator because it only charges house battery from the extra alternator. the vans actual alternator just works on the van. none of the chassis original systems are touched. the zions extra alternator also uses it's own separate pulley and belt.

IMO, that is not the way they should do it, but I think it is pretty common in other models also.

If it were mine, I would add a cutoff to help save the batteries. You may want to look at this discussion, where it is about how we are going to upgrade our separator setup. Our parts are do today.

[markopolo]

Originally Posted by markopolo

............................

Are we babying these AGM's even the off brand ones? I'm kinda liking the periodic conditioning charge idea. None of us want to risk wrecking an expensive AGM though. You often see "consult your battery manual for charging voltage" but some batteries don't come with that info.

I have one charger that can get to 15V and I'm thinking about hitting all the batteries with that periodically. I have to think about it some more hence all the research.............

I'm quoting this to get some discussion or comments on it.

[markopolo]

Originally Posted by gerrym51

the zion has no seperator because it only charges house battery from the extra alternator. the vans actual alternator just works on the van. none of the chassis original systems are touched. the zions extra alternator also uses it's own separate pulley and belt.

I guess they decided to change things sometime after you asked about if the rooftop solar would maintain the starter battery. I don't see how it can now without the separator. If you find out differently let us know.

[avanti]

If I went to all the trouble and expense of installing a separate belt-driven alternator/generator, I would certainly also want to connect it via a proper 3-stage charger! DC-DC chargers aren't cheap, but as a percentage of the whole system...

[booster]

Originally Posted by markopolo

I'm quoting this to get some discussion or comments on it.

I would put that in the very valid question category

There is no doubt in my mind that you can make the batteries last longer and give more usable power when you get good full charges regularly. I have seen many articles that state you can be easily in the mid 100s of cycles with abused batteries that claim 1000 cycles if treated well. That doesn't make it a good idea for everyone, though, IMO. If 150 cycles will be 20 years, for instance.

If you have a "decent" system, currently, and if you hire it done, I doubt you could justify upgrading to what it takes to do a stellar job of charging and maximizing battery life. It is a bunch of spendy hardware, and probably more batteries to limit depth of discharge. You would probably be better of just buying batteries on a regular basis, monetarily.

If you want to be able to have more capacity, with the same batteries, and have not them degrade as fast over charge cycles, you would have weigh that against the previously mentioned cost. You can get more usable capacity if you get them totally full. If you are only getting to 85% full, and you discharge only to 50% you will gain 43% usable capacity by getting the batteries to 100%.

If you go crazy over things not working as well as they should-cost is no objectDon't ask about how I know that.

If you enjoy the tinker part of it and seeing your changes work and make your life easier-call it a hobby and do it.

So to answer Marko's question--yep we are babying--yep it will help--is it the right thing to do, maybe--is it necessary or for everyone, nope.

[booster]

Originally Posted by avanti

If I went to all the trouble and expense of installing a separate belt-driven alternator/generator, I would certainly also want to connect it via a proper 3-stage charger! DC-DC chargers aren't cheap, but as a percentage of the whole system...

I had planned to do just that in our upgrade, but now I don't think I will, for a couple of reasons.

None of the 12v to 12v chargers do the return amp charging, so they are on timers and will likely over or undercharge the batteries under varying conditions.

The alternator voltage may not be perfect for the AGM batteries, but most are well within the absorption range recommended, except for those now recommending the higher volts. You will still get very very nearly full at 14.4 volts and the solar can finish off the higher voltage at the end.

The biggest 12v to 12v charger I know of is 120 amps (they list a 180, but it is not available).

Cost and extra wiring, connection points, complexity.

For others, this may not be true. If you don't monitor your engine charging and manually turn it off, when driving, the 12v to 12v will do better than not having anything. IMO, it won't do as well as the manual watching of amps, unless you do the same manual shutoff of the charger.