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Old 10-03-2014, 08:17 PM   #1
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Default AGM charge rates

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.
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Old 10-03-2014, 09:17 PM   #2
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Default Re: AGM charge rates

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.
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Old 10-03-2014, 09:38 PM   #3
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Default Re: AGM charge rates

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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?
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Old 10-03-2014, 10:28 PM   #4
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Default Re: AGM charge rates

is this the kind of thing your talking about?


http://www.amplepower.com/products/sarv3/
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Old 10-03-2014, 11:48 PM   #5
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Default Re: AGM charge rates

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
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Old 10-04-2014, 12:00 AM   #6
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Default Re: AGM charge rates

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
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Old 10-04-2014, 12:59 AM   #7
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Default Re: AGM charge rates

Quote:
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?
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Old 10-04-2014, 01:38 AM   #8
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Default Re: AGM charge rates

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.
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Old 10-04-2014, 02:11 AM   #9
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Default Re: AGM charge rates

Quote:
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.
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Old 10-04-2014, 02:22 AM   #10
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Default Re: AGM charge rates

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.
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