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Old 07-26-2016, 11:22 PM   #1
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Default Lifeline (or others) charging times

This amount of time it takes to get batteries all the way charged comes up quite a bit, and without some measurement system is very hard to predict. I thought I would start this so folks who have monitoring could list some typical times for various batteries (we have 440ah of Lifeline AGM). That will, at least, give some basic idea of what everyone should expect to see with a system.

We just got back from a spur of the moment two day outing, where we were in one place for two days, only a couple hours of good sun per day for the solar, and our typical use. We pulled out today down only 35 amp hours (8% of our 440ah), which we were very OK with because of the lack of sun and compressor frig at 85 degrees outside.

We decided to see what the alternator would do at that high a state of charge, as we had 3+ hours of drive home. We can see the battery amps and voltage from the cab, so we just watched it as we drove. Voltage held steady at 14.5 volts the entire time.

At alternator connection we flashed about 50 amps and then it started down almost immediately. If we are at 50% down, we would be over 150 amps, so much slower at the higher SOC. It was under 15 amps in just over 1/2 hour, and then slowly tapered to 2 amps at just about 3 hours. When we shut off the alternator, the solar confirmed that the batteries were full, as it was already in float ( it also meters battery amps). 2 amps is at the Lifeline .5% recommendation for 100% full.

We have seen in the past, on the shore charger (100 amp max), that it takes about 8+ hours to get to the 2 amps from 50% down, so the last bits do take a lot longer to get into the battery. 42% in 5 hours and 8% in 3 hours to finish.

With the shore charger, we also see that the amps start to drop from the 100 max of the charger when the batteries are getting to about 70-75% full, so the tapering starts pretty early. From 150 amps, it would likely be even sooner. I think this points out that if you are using AGM batteries and a big alternator or engine generator, it shows that you can't just take the output and multiply hours to calculate how much you recover, unless the batteries are really low so the batteries will accept all the amps.

I need to test more, but I would guess we will get full amps to the batteries of 150-180 amps until we are something like 60-65% full and then it will start to taper. That would put us faster than the shore charger of 8+ hours (at 50%), but not by a huge amount, so maybe 7+ hours to full. Deeper than that would be at full output and give an extra hour if we went to 80% down. This shows that a long drive day of 8+ hours would usually be able to get us full or very close to full, which is good to know, but will rarely be done based on how we travel. It will give us a better understanding of what it will take to make sure we get full every 7-10 charge cycles, though.
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Old 07-27-2016, 12:44 AM   #2
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Here are some data from our setup. This is 440Ah of AGM battery (NAPA, which I believe is made by Deka) being charged with our 270 amp Nations' Alternator/Balmar setup. Started at around 35% SOC, driving at highway speed.

charge data.jpg

The bounciness in the early amps readings is, I believe, due to the alternator throttling back due to high temperature (it was a hot day).
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Old 07-27-2016, 01:12 AM   #3
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Excellent information!

It looks like your batteries are behaving very similarly to what we are seeing.

You gained about 150+ah in the first hour, to get to about 70% SOC, and then the amps started tapering. You got to what our starting point was in about 140+ minutes (92%), so you probably wound up at about 96/97% and maybe 7-8 amps? Our test would indicate you would be full in another 2+ hours, so total time between 5-6 hours or so.

You data would certainly point out that if you started at the 35%, with 4 hours of early driving (7am-11:00am) the solar would have time to top off the batteries if you had good sun.

With good timing and sun, needing shore power would be a rare occurrence.

It will be interesting to see how well they match when we get a chance to get a deeper discharge start point.
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Old 07-27-2016, 03:02 AM   #4
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I realize Lifeline has not updated their technical manual in awhile and it does not match their latest charge instructions in some cases. There is a guideline in the charging section of the technical manual for estimating the time it takes to get to full charge which basically says take the amp hours depleted divided by the charger amps and add two hours. Anyone know of an updated guideline from Lifeline that is closer to the real world times seen in the examples outlined here?
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Old 07-27-2016, 11:00 AM   #5
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Quote:
Originally Posted by gregmchugh View Post
I realize Lifeline has not updated their technical manual in awhile and it does not match their latest charge instructions in some cases. There is a guideline in the charging section of the technical manual for estimating the time it takes to get to full charge which basically says take the amp hours depleted divided by the charger amps and add two hours. Anyone know of an updated guideline from Lifeline that is closer to the real world times seen in the examples outlined here?
Not that I have seen. They do stress that the charge time is an estimate and you should go be the battery amps to check for fully charged, though, in several places. Unfortunately, even the amps will change within the (now expanded) range of charging voltage. From the charging times we have seen here and other places, the estimate is going to leave you undercharged almost all the time, as the fill doesn't use full charger amps the whole time, and the two hour hold at voltage isn't even enough. IMO, the estimate is too conservative to the undercharge side.

Adding to the question is if the .5% of capacity is really full, or not. Ours will continue to charge until they are closer to .2% of capacity, although to get there takes many more hours at absorption voltage. I think there is a real question whether or not it would be good to go that far on a regular basis. Basically a balance of getting more full to prevent walk down vs oxidation in the battery from longer on high voltage. The good news is that about 48 hours on float also seems to fill that last little bit, if you have the time to be on float that long (normally we don't when traveling, but do at home).
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Old 07-28-2016, 12:56 PM   #6
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Two great systems profiled in this topic and great info.

AGM Etrek owners will benefit from reading and understanding this topic. It will give them an idea of how many hours it would take to get 8 AGMs actually full - I think both Booster and Avanti have 4 AGMs.
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Old 07-28-2016, 01:27 PM   #7
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Originally Posted by markopolo View Post
Two great systems profiled in this topic and great info.

AGM Etrek owners will benefit from reading and understanding this topic. It will give them an idea of how many hours it would take to get 8 AGMs actually full - I think both Booster and Avanti have 4 AGMs.
Interesting question, how much difference in time to full charge is there between a 4 battery AGM discharged 200 amps vs an 8 battery AGM discharged 400 amps? Seems the minimum time for the eTrek would be 1.5-2 hours of engine generator charging and if not driving then switching to shore or solar. If on shore already can you charge from shore and engine generator in parallel to get 300 amps charging during bulk charging?
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Old 07-28-2016, 01:50 PM   #8
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A key factor would be the voltage that the setup can produce and maintain. Booster's setup maintained 14.5V. That would allow for greater current flow through the system than a setup that could only get to say 14V or less.

I might have an opportunity coming up to run the batteries in my van down by using the air conditioner on battery. If so, I will post what numbers I see on the recharge. I expect it will struggle on voltage also be limited by the stock alternator amp throughput. I guess the most interesting bit of data I can provide will be how much the old stock alternator is able to put back after 1hr & 2hrs driving etc.
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Old 07-28-2016, 03:55 PM   #9
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Quote:
Originally Posted by gregmchugh View Post
Interesting question, how much difference in time to full charge is there between a 4 battery AGM discharged 200 amps vs an 8 battery AGM discharged 400 amps? Seems the minimum time for the eTrek would be 1.5-2 hours of engine generator charging and if not driving then switching to shore or solar. If on shore already can you charge from shore and engine generator in parallel to get 300 amps charging during bulk charging?
As they say "It's complicated" But not nearly as complicated if you take the charging time total as a series of steps.

The 200ah on 4 vs 400ah on 8 in theory would take the same amount of time to charge full, but only if you were able to supply double the amps (at the same voltages) to the 8 battery bank.

If you take it in steps, assuming engine generator charging, you would start out in bulk at 50% down. By definition, bulk is at constant current, and will be at lower than absorption voltage, but climbing. We normally look at the bulk as being at the max output of the charging source, but it is obvious from Avanti's graph that for a typical engine generator, the output is anything but constant do to heat throttling. This makes predicting the time spent in the bulk stage very difficult and it will be different for nearly every setup. It will even vary day to day depending on ambient temperatures or other loads on in the coach. Avanti looked to have netted about 150-160ah the first hour, which also looked to have coincidentally been the transition to absorption. The high points of the oscillating output looked to be somewhere in the 210 amp range, so the average was quite a bit lower. I would bet nearly all of the alternator based systems do the same thing, but few people have the method of seeing or tracking it (or maybe aren't interested). Based on Avanti's numbers, he nets about 60% of the rated capacity of the alternator over the bulk stage (sample size of one, so certainly not certain). If that number is consistent with other systems, it could be the key to more accurately predicting recharge times. A system like ours that is not a standalone generator will be a bit less do to also running the van and charging the starter battery.

The next step is going into absorption, or constant voltage stage. This point is going to be controlled by the crossover point of the output of the charger and the acceptance rate of the batteries (which will vary with brand and capacity). This is the thing that Marko is referring to (I think) when he talks about being able to hold voltage. The more capacity you have in your charging system, the higher the current will be when the system goes to constant voltage absorption mode. The very interesting thing that crops up, though, is that because it transitions at higher amps on the acceptance vs SOC curve, you will actually be transitioning at a lower SOC with a high amp source than with a lower amp source, which will go into absorption later. This is also why you will see your system go into absorption at different times depending on which charging source you use. It may be at 70% SOC on the engine generator, 80% on shore charger, and at 90+% on solar because of their hugely different charging capacities. Avanti's graph is what we need to see where the different sources would transition to absorption based on source amps vs acceptance amps. I do think that once you know where you go to absorption on each source and how long it takes after that to finish the charge after that, it should stay very consistent. Once in absorption, your time to finish from any given SOC should always be the same, regardless of charging capacity of the source.

Bottom line: High amp charging will be in bulk much less time, but in absorption somewhat longer than a low amp source that will be in bulk much longer and in absorption less time.

I think this is why Lifeline wants at least 20% of capacity in charging amps for deeper discharges. They want to get into absorption as soon as possible so they have the longer hold time at absorption voltage to convert more sulphate.

All of this certainly points out, at least to me, that the simple formulas that manufacturers put out are exactly that, simplistic. I have tried lots of them, and none came even close to matching what I see in the real world. Most severely underestimate the time required.

The highly variability also shows why using the acceptance amps to the batteries is really the only reliable way of telling the SOC of the battery, especially at the float transition at fully charged.

Hopefully, we will get some more data from other systems, and further info on the one's already seen. I know we need to do some more, especially at the deeper discharges, driving recharges.

Just a side note: If the 60% of rated amps proves out to be accurate and consistent, it could very much effect the calculations of engine generator to coach wire sizes. Once you get to 1/0 and bigger, all the sizes have quite a bit of capacity and low enough voltage drop, but get bounced out of the calculators (like the Blue Sea Circuit Wizard) base on temp rise due to being in conduit or sleeving. The temp rise is going to be based on the average amps, I think, so you should be able to use that in the rating defactoring section.
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Old 07-28-2016, 03:56 PM   #10
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One of the nice things about the Balmar regulator is that it has a battery voltage sense line, so it compensates for the voltage drop between the generator and the battery--which in my case is the length of the vehicle.
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