AGM charge rates

[booster]

All the talk about Davyyd's new van and lithium batteries got me back to trying to find out how many amps our system (375AH) would accept off of our 250 amp alternator, if we ever decided to go to AGM batteries. There just seems to be a lack of information published except for Lifeline saying they can handle 5 times the 20 hour capacity as "inrush". I finally gave up and called Lifeline to see what they would say.

To say I was surprised at the answer may be an understatement. I explained what we had (375 AH wet cells) and what they pulled for amps when at 80% discharge (a bit over 100 amps at about 13.2 volts under load). I was told that was too high for the wet cells and would damage them, which surprised me. Then he said that the 250 amp alternator would also be capable of damaging their agm batteries, unless it was run with a smart regulator, which was an even bigger surprise, since 5 times the 20 hour rate is well over 1500 amps. When I asked about this, he said that the 5X is after the initial starting of the charge cycle, which has to be at a much lower rate (didn't say how low), and only with temp monitoring (after that slow start), which I had heard before. The claim is that the smart regulators will start off slower and not damage the batteries like just hitting them with 14.4 200+ amps from the alternator. The big question is why the Lifeline site doesn't say anything about it, that I could find. I did look at the Full River site and managed to find an initial charge rate spec, which I think is what we are talking about, and it said 20% of the the 20 hour AH rating for the batteries. That would be only 75 amps in our case, and less that the wet cells are taking. Our shore charger starts slowly, but it is not a very long time, maybe 3-5 minutes to full output, but it isn't big enough to do any damage if it is too fast.

I have seen, in lots of places, that engine generators of big capacity are great directly to AGMs, because they can take the high currents, but that seems to be contrary to what I heard today.

If we were to do the change, it looks like the smart regulator would be needed, assuming it would do the profile that they want to not damage the batteries.

Has anyone heard anything related to this situation? Perhaps I am not understanding what I was told.

I assume this would also apply to lots of systems with fairly low battery capacity, and normal sized alternators. There are lots of folks that have put in AGMs in place of wet cells.

In an unrelated topic that was mentioned by Lifeline, I was told that OTR truckers who are using Lifeline batteries without a smart regulator (14.4 volts for many hours when full) ever day see a battery life of 3 years, instead of 5 years, which makes sense.

[gerrym51]

since you have a roadtrek roadtrek has been using AGMs since june 2010. they must be using a smart regulator of some kind. especially now with thie e-trek packagaes and their hi-amp alternator.

[booster]

Originally Posted by gerrym51

since you have a roadtrek roadtrek has been using AGMs since june 2010. they must be using a smart regulator of some kind. especially now with thie e-trek packagaes and their hi-amp alternator.

As far as I know, they just switched to AGM like many others have done. I have never heard of any mfg that has used a smart regulator, and that is why the information I got today was such a surprise.

It also appears that Roadtrek continued with the 80 amp breakers in the house battery charge line, so they would have to be cycling, I would think, as the 145 GM alternator can easily put that much to the coach while driving. We have had a couple of discussions here as to if Roadtrek used a smart regulator on the engine generator, and it is still unknown I think. But they have changed the system a few times since it first came out.

The big question is why all the systems out there with AGMs and alternators aren't failing the batteries, if it is a problem like I was told. Perhaps sacrificing breakers and saving batteries?

[gerrym51]

is this the kind of thing your talking about?


http://www.amplepower.com/products/sarv3/

[booster]

That is one of the brands. As I look at a lot of the regulators, I seem to find them interested in boosting charging speed, using the full output of the alternator. This would not help the situation that a 250 amp alternator would have on 400AH of batteries, if you wanted to stay within the C/4 that appears to be the most common AGM recommendation that I am finding. The exception appears to be the Sterling battery to battery charger, which will multistep and limit output to its rated size.

http://sterling-power-usa.com/BBW121...r12vto12v.aspx

[gerrym51]

How do you know Roadtrek isn't using this-at least in the E=trek and partial e-trek combinations. the use of one of these devices could be the reason i've read that some people who have just added batteries to existing systems are not getting good results.

the e-trek system may actually use this or similiar device

advanced rv may well also

I read the manual for this-it still needs appropriate wiring

[booster]

Originally Posted by gerrym51

How do you know Roadtrek isn't using this-at least in the E=trek and partial e-trek combinations. the use of one of these devices could be the reason i've read that some people who have just added batteries to existing systems are not getting good results.

the e-trek system may actually use this or similiar device

advanced rv may well also

I read the manual for this-it still needs appropriate wiring

As I said earlier, we don't know if Roadtrek uses something like this in the e-trek systems. As far as I know or have read, they are not using them in the other models though, BUT Roadtrek doesn't have wiring diagrams in their manuals anymore so it can't be confirmed. The 2500 watt engine generator would be putting 200 amps to the 400 AH of batteries that they usually use with that generator. Add another 100 amps from the Chevy alternator, and you are well over C/2.

I also have heard of folks with issues after changing or adding batteries, usually to agm and added capacity. On Roadtreks, it seems to show up as separator or circuit breaker issues first, which makes sense if the batteries are pulling big amps. Battery life issues would not show up for a period of time, as it wouldn't cause immediate failure. I would certainly think that a 50-80% discharged pair of agm's in a stock Roadtrek would pull all the capacity of the 145 amp Chevy alternator (about 120 amps to the coach), which is more than C/2 or double what is being recommended by the battery folks. You can imagine how much extra amps you would have on a single 100AH battery.

I just wonder where the C/2 to 2C charging speeds we have been hearing about came from. Have the battery folks been getting to many failures and are now backing off on their specs?

[gerrym51]

Roadtreks website says the engine generator puts out 3500 watts a t idle and up to 5500 when driving over 40. I have no idea if any of that is true.

[booster]

Originally Posted by gerrym51

Roadtreks website says the engine generator puts out 3500 watts a t idle and up to 5500 when driving over 40. I have no idea if any of that is true.

I think they may have dropped the 2500 watt engine generator, which, IIRC was the one they offered on the 2 extra battery option. The 3500 was with the full etrek 8 battery setup. They still show an engine generator without the etrek package on the CS, but don't say how big it is. If they are using the 3500 watt generator on the 440AH battery setup, they are about C/1.5, so they are hitting the batteries very hard, unless they have a current limiter. At driving speed they would be at nearly 1C. Even the etrek would be C/2.

There is so much variation in the recommendations and use, I have no idea who is right or wrong.

[gerrym51]

to the best of my knowledge there has only been 1 engine generator-the current 3500-5500 watt high amp alternator. the 4 battery pack gets a 2500 watt
inverter/charger(they actually use 3000 watt at this time) but it's the same high amp alternator.

[booster]

Originally Posted by gerrym51

to the best of my knowledge there has only been 1 engine generator-the current 3500-5500 high amp alternator. the 4 battery pack gets a 2500 watt
inverter/charger(they actually use 3000 watt at this time) but it's the same high amp alternator.

I think you are correct on the smaller generator, I misremembered the 2500 watt inverter as also being the generator size when thy went to the 4 battery setup. I did find an early reference to a 6000 watt generator, though.

That setup would be way high current, according to Lifeline, who would want the 440AH charged at about 1320 watts, or 110 amps, at C/4

[gerrym51]

Originally Posted by booster

I think you are correct on the smaller generator, I misremembered the 2500 watt inverter as also being the generator size when thy went to the 4 battery setup. I did find an early reference to a 6000 watt generator, though.

That setup would be way high current, according to Lifeline, who would want the 440AH charged at about 1320 watts, or 110 amps, at C/4

although they state minimum of 2500 watt inverter for 4 batteries and minimum 5000 for 8 batteries Roadtrek has been using 3000 and 6000 respectively inverter/chargers.

i suspect that occasionally someone doing their blurbs puts it the actual 3000 or 6000 figure. also they use watts everywhere now and not amps .

[markopolo]

pattonsr posted this link some time ago: http://sprinter-source.com/forum/showthread.php?t=25621

It's interesting to read. The debate on high amp fast charging vs low amp slow charging has been going on for a long time. Real data is not readily available. The "right" answer really depends on what you (the RV owner) are trying to accomplish.

The guy who says high amp charging is ok gets 4 years out of the battery bank.
The guy who says keep the charge rate at c/20 or lower gets 10 years out of the battery bank.

(yes, simplified and I caught the bits about AGM & Wet cells - I'm keeping it very general here)

This is where we (individually) choose what we think is best for our needs. All electric rigs don't really have the luxury of charging at a slow rate. The rig needs to be ready again for use as soon as possible. The trade-off for convenience will be replacing the lead-acid battery bank more often.

I think Booster is trying to figure out if we can do both specifically for AGM batteries; fast charging and battery longevity

As booster mentioned, the inline breaker method offers a solution (he's not suggesting that solution btw) - it's not refined and could lead to breaker failure necessitating on-the-road repairs.

It may come down to how much you are willing to spend for how much you gain (longevity increase). Some of these solutions are expensive. They might be cost efficient for very large battery banks if you gain enough years. If you just have a few batteries then replacing them more often might be an easy way to go. BCI indicated that 98% of battery lead is recycled.

Another simple solution might be to not discharge too deeply and charge more frequently. It would be interesting to know the difference in the current flow to the batteries at 20% SOC and 50% SOC for example.

[booster]

That was a very good read in the link, and covered a lot of what I had heard in the past, particularly the statements about Lifeline stating that their batteries could handle very high charge rates in bulk, as long as you were temp monitored. That is why I was so surprised that Lifeline took so much issue when I asked about putting 200 amps into a 400+AH bank. I was told that was worse for the batteries than driving all day at 14.4 volts.

The part that now has me really wondering is that Lifeline guy said the cure for the high amps problem could be cured with a smart alternator regulator, but I have not been able to find one that limits the amperage from the alternator, and many claim to boost it to higher amps. I don't see how that would solve anything as the voltage and amperage in bulk would stay the same, with the benefits coming later in absorption and float.

All this starts to put us in a catch 22 situation because we need about 110 amps at idle to run the microwave and inverter. This put us into the 250 amp alternator, which was the only one I could find that would give that much at idle. But it also gives 200+ amps available going down the road, which is claimed to be too high now. The mentioned smart regulators won't fix anything, so I have to question if the information I got was misunderstood, or wrong from Lifeline. The Sterling battery to battery chargers would take care of it since they limit alternator output, but I do wonder if they are really necessary as long as the wire sizes are good and temp monitored.

My sense is that some of Lifelines past statements may be coming back to haunt them, like the unlimited amps in bulk, and now they have swung (overswung?) back to the safe side of claims. I also seem to remember that Trojan used to say C/5 was OK if you temp monitored. I think it was what the gulf courses needed to do to get the batteries full overnight. If we are at 70% discharge our 375 AH pull over 90 amps, so we are over that, even, and would assume everyone else with wet cells is similar. I think that going C/3 or C/2 with AGMs, temp monitored, probably is not as big an issue as I was led to believe by Lifeline, but the unlimited thing would be a problem, and that is what they are really addressing.

[markopolo]

C/20 to me is 20% of capacity
C*2 would be 2 times the capacity

I don't know if either is right but we should come up with common way to express the charge rate.

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State of charge is a big factor in this. I could make a 1000 amps available to a fully charged battery and it wouldn't take it because it is already fully charged is my understanding of it. You could force some current in by upping the voltage but just having the amps available doesn't mean the battery will take it.

[booster]

Originally Posted by markopolo

C/20 to me is 20% of capacity
C*2 would be 2 times the capacity

I don't know if either is right but we should come up with common way to express the charge rate.

-------------

State of charge is a big factor in this. I could make a 1000 amps available to a fully charged battery and it wouldn't take it because it is already fully charged is my understanding of it. You could force some current in by upping the voltage but just having the amps available doesn't mean the battery will take it.

I like those rate designations. I had been using 2C to differentiate from C/2 for your example, but the * makes it very clear.

As you say, how much current you have is only relevant if the batteries will take it. What does seem to be consistent is that most any battery or bank will take a higher current than recommended if it is more than about 50% (?) discharged (if the current is available), which makes for a tough situation if you need an engine generator to run high watt things, unless they have a way to current limit the charge to the batteries, or run a charger off the inverter to charge the batteries.

[gerrym51]

since i have neither the ability or knowledge to do this myself i'll have to trust Roadtrek to do it-Just as Davydd is trusting Advance to do it for him

[markopolo]

It looks like keeping the state-of-charge up above 50% might really be the way to go. #1 the shallower cycles are easier on the battery & #2 less chance actually causing damage.

[booster]

Originally Posted by markopolo

It looks like keeping the state-of-charge up above 50% might really be the way to go. #1 the shallower cycles are easier on the battery & #2 less chance actually causing damage.

That certainly would help the situation. I wonder how much current an AGM at 50% would actually take at 14.4 volts? The other question would be what do you do if you do wind up at 30% state of charge? Maybe on 5 minutes, off 5 minute until you get the amps down a bit. Or just buck up and take what is likely a very small hit on battery life by letting it take full amps, up to maybe C/2.