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Old 11-29-2013, 11:37 PM   #1
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Default How "smart" are smart chargers

Marko may want to move this to one of the other charging system discussions, but it may be get some extra feedback here, too.

I have been testing and trying to figure out why we don't get a full charge off of our Tripp-lite 750 on our Trojan wet cells. I have found that the Tripp-lite stops the absorption charge very early, leaving the batteries at 80-90% charged, and at float,so they don't ever really get full. If I unplug/replug in the shore power it will go into absorption for a while again, but not very long. I can make it stay in longer by using over 10 amps of other power to trick it, but it still won't fill the batteries.

I use a Xantrex2 20 amp charger as a bench charger, and if I put that on the same Trojan batteries, it also stops early, and it will not go back into absorption on an unplug/replug, it just shows that the batteries are charged and goes to float. The surface charge on the batteries can easily give 13+ volts, even at 80% state of charge, so it that is what the charger looks at, it will not charge the rest of the way.

We also have a little 8 amp CTEK charger, which is supposedly very sophisticated technology, and rated for much larger battery banks than its 8 amps would indicate. If I put it onto the same 80% state of charge, 13+volts battery, it goes to bulk for a couple minutes, then to absorption until it times out in a couple of hours. On big batteries, it can't get them full with such low output, but you can repeat the cycle as many times as needed, and it will get them full.

The way the CTEK works makes sense. Turn it on, it checks not just for voltage but also if the battery will accept current high enough to indicate it isn't fully charged, and then decides whether or not to go into absorption for the set time. The other chargers just bail out of charging a battery that needs topping off if the voltage is good.

It certainly makes it possible that you could get stuck with less than full batteries, when you thought you were full. If you ran your batteries down 50% boondocking, and then drove a few hours to another campsite, you would put some state of charge back in, and put on the surface charge (alternator at 13.9-14.4 volts doing the work). You get to the next site where you have shore power, so you can top off the batteries, and plug in. The charger sees the surface charge of 13 volts and decides to go right into float at 13.5 volts. You merrily camp a day or two, figuring you are going to be leaving fully charged for the next boondock stop, but you are only at 80% because the charger never charged the batteries, and you don't even know it.

I only have access to the 3 chargers mentioned, so I don't know how others do it. Has anybody noticed this happening to them? I think I will contact a few of the charger companies and see what they say about it, especially since we are considering an upgrade to the charging/inverting systems.
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Old 11-30-2013, 02:52 AM   #2
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Default Re: How "smart" are smart chargers

You almost have to experiment with them. I've had a three stage external charger which, once the batteries were in float mode, would stay in float mode until the charger was reset, even if the batteries started having a large amp draw. The exact thing mentioned above cost me a good deep-cycle battery because it was supposed to be at 100% SOC, and the charger was still floating it... but when that charger was removed, the voltage was in the 11 volt range.
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Old 11-30-2013, 03:30 AM   #3
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Default Re: How "smart" are smart chargers

Quote:
Originally Posted by mlts22
You almost have to experiment with them. I've had a three stage external charger which, once the batteries were in float mode, would stay in float mode until the charger was reset, even if the batteries started having a large amp draw. The exact thing mentioned above cost me a good deep-cycle battery because it was supposed to be at 100% SOC, and the charger was still floating it... but when that charger was removed, the voltage was in the 11 volt range.
The more I read and experiment, the more I think this could be a major issue with way the chargers function. The CTEK seems to be the only one I have seen, or heard of, that will go into charge mode if the voltage is at full charge, regardless of the actual state of charge. What really started to worry me was that when the solar is running during the day, it holds the voltage up, obviously because it is charging. But--it is not charging anywhere near what the batteries could be taking, and maybe even at a lower voltage than ideal based on charging amps and sunlight. If we plug in under those conditions, the charger would do absolutely nothing, just go into float. Once in float, it would stay there, even after dark, leaving the batteries uncharged.

Today, as I continued testing, particularly with the CTEK, it really started to soak in that I needed to find out what was going on, and if anyone had a solution. I did a bunch (hours) of Google searching, most of it fruitless, but one of them led me back to the Handybob blog, and his very, very, long discussion of solar and batteries, living off grid. Aside from the information, it is entertaining besides. Handybob doesn't have a lot of time for the off the shelf products, or their designs, and in his "discussion" about converters and chargers, he actually had a very brief mention of exactly what we are talking about here, even down to the fact that the solar will prevent the charger from charging. Unfortunately, all he had for a solution was to plug into shore power after dark.

As of right now, the only way I know of to get the batteries to fully charge, when the charger won't kick in for the above reasons, is to use the equalize function. On every charger I have seen, the equalize is designed to be used on full batteries, so it will always come on if you tell it too. The little bit I have played with it on our Roadtrek shows the equalize will bring the SCS200 Trojan 12v (115AH) from 90% to 98% in one hour of equalizing. The two T145 Trojan 6v (260AH) take about 3 hours to go from 80% to 98%. The 90% and 80% starting points are about where the batteries are after a "full" charge off of the Tripp-lite when they start at 50-60% state of charge. Trojan's charging chart actually shows that they would like you to take the voltage up over 15 volts at the end of the charge cycle, so I am sure that is why it works so well.

Handybob said he doesn't think any RV that is in a park, or using shore power with a little driving, is ever anywhere near fully charged, and I think there is a very good chance he right on for this. I think he said they would be about 75% charged.

It would be so so so easy to fix, though. If all chargers worked like the CTEK, that would do it. If the charger had a manual button to push to have it start in the bulk charge instead of going straight to float, that would do it. Not all that tough, I would think.
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Old 11-30-2013, 12:02 PM   #4
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Default Re: How "smart" are smart chargers

The converter charger in my van is mostly controlled by timer functions I think.

Quote:
BOOST MODE: If the converter senses that the battery voltage has dropped below a preset level the output voltage is increased to
approximately 14.4 volts DC to rapidly recharge the battery.

NORMAL MODE: Output voltage set at approximately 13.6 volts DC.

STORAGE MODE: When the converter senses that there has been no significant battery usage for 30 hours the output voltage is
reduced to 13.2 volts DC for minimal water usage. When in storage mode the microprocessor automatically increases the output voltage
to 14.4 volts DC for 15 minutes every 21 hours to help reduce sulfation of the battery plates.
I think the 13.6V normal (absorption) mode is a charging voltage for most batteries - meaning enough voltage to overcome a battery's internal resistance - but it would be slower hence the 30 hours at that voltage.

I have been wondering how all other add-on charging sources like solar affect the primary charger. For example, if the batteries are not fully charged and the solar output at the batteries is 12.9 volts and you plug in what will the main charger do? Will the main charger "see" a fully charged battery bank (more than 12.7 or 12.8 volts) and go into normal or storage mode instead of bulk or boost mode?

My van's charger sometimes gets tricked into boost mode. That tells me it isn't testing the state-of-charge. I've noticed if I bring the van out of the garage to wash it then put it back in the garage and plug it in it will sometimes go into boost mode. I added a switch to force it into the 'gel' charging profile which is a simple reduction of .4 volts if I don't think 14.4v boost is required. I have to remember to put it back into wet cell mode later though.

3 stage charging:
Bulk - Absorption - Float
aka Boost - Normal - Storage

Shouldn't Bulk Mode get your batteries to 90%?
Is your Tripp Lite set to full 45 amp output (fast) or limited 11 amp output (slow)?
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Old 11-30-2013, 01:14 PM   #5
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Default Re: How "smart" are smart chargers

Quote:
Originally Posted by markopolo
The converter charger in my van is mostly controlled by timer functions I think.

Quote:
BOOST MODE: If the converter senses that the battery voltage has dropped below a preset level the output voltage is increased to
approximately 14.4 volts DC to rapidly recharge the battery.

This is what most of the battery folks are now calling "bulk charging"

NORMAL MODE: Output voltage set at approximately 13.6 volts DC.

This is what they call "absorption charging"

STORAGE MODE: When the converter senses that there has been no significant battery usage for 30 hours the output voltage is
reduced to 13.2 volts DC for minimal water usage. When in storage mode the microprocessor automatically increases the output voltage
to 14.4 volts DC for 15 minutes every 21 hours to help reduce sulfation of the battery plates.
This is the "float charging"

Your voltages are pretty low compared to most chargers. The "typical" is now a constant current current bulk charge that has the voltage increasing until it gets to the absorption voltage of about 14.4 volts, then an absorption charge held at that voltage for a fixed amount of time and/or until minimum time and maximum current are reached. It then goes into float charge for long term storage which is usually about 13.5 volts.


I think the 13.6V normal (absorption) mode is a charging voltage for most batteries - meaning enough voltage to overcome a battery's internal resistance - but it would be slower hence the 30 hours at that voltage.

I have been wondering how all other add-on charging sources like solar affect the primary charger. For example, if the batteries are not fully charged and the solar output at the batteries is 12.9 volts and you plug in what will the main charger do? Will the main charger "see" a fully charged battery bank (more than 12.7 or 12.8 volts) and go into normal or storage mode instead of bulk or boost mode?

That does seem to be what happens, and also what Handybob stated that he sees. I see it on the Tripp-lite and on the Xantrex Truecharge. The solar is a problem, but surface charge is also. Yesterday I had the T145 Trojans just off of charge on the Tripp-lite, but they were only at 83% per specific gravity. They did check at 13.2 volts, though, because of surface charge. If I put the Tripp-lite back on, it would go to absorption, but only stay there for about 5 minutes and then go to float, so there was no way to get more charge in the batteries. The Xantrex didn't do anything but go straight to float. The CTEK did great and went through the whole cycle, but it was tiny and took 3 charge cycles to get them full. I would think if you have just driven the van a ways, you would often have enough surface charge on the batteries to keep the charger from kicking in when you plug in. And once it is sitting there in float, it will never go back to absorption so you don't get any battery charging, except the pittance you get at float

My van's charger sometimes gets tricked into boost mode. That tells me it isn't testing the state-of-charge. I've noticed if I bring the van out of the garage to wash it then put it back in the garage and plug it in it will sometimes go into boost mode. It may actually have done the right thing in this case. It is very possible you were sitting in float charge with less than full batteries for the reasons stated above. Two engine starts (especially with a diesel) probably does a very good job of taking the surface charge from the 13.2/13.6 volt float off, so the charger sees the actual battery voltage which is low enough to start a charge cycle. I added a switch to force it into the 'gel' charging profile which is a simple reduction of .4 volts if I don't think 14.4v boost is required. I have to remember to put it back into wet cell mode later though.

3 stage charging:
Bulk - Absorption - Float
aka Boost - Normal - Storage

Shouldn't Bulk Mode get your batteries to 90%? That is what the theory says, but it doesn't seem to happen that way. With the 14.4 volt transition to absorption, the 12 volt battery is in the 80% range and the 6 volts in the 70% range for us. Then the absorption time/parameters are not long enough to get them to full, so they wind up at 90% and 80% approximately when done. This has to be why Trojan, Crown, and Interstate are now wanting the higher voltages. The charger would stay in bulk longer in getting to 14.8 volts, and put in more AH because of the higher voltage also, getting you to the 90% better. Then the higher absorption voltage would be able to finish them to full in less time because they have less to go and are at higher charge rate

Is your Tripp Lite set to full 45 amp output (fast) or limited 11 amp output (slow)?
Ours is set at the 45 amp output, and runs there if the batteries start the charge at 30% state of charge. At 70% state of charge start point they run at about 40 amps.

At least I can test specific gravity to find out a bit of what is actually happening. If AGM batteries do the same thing with surface charge (we know they will have the same issue with solar) you would never know it because you can't check the specific gravity any way but voltage, which may be bogus at any given time.

The Blue Sea charger has all kinds of adjustable timers and amperage thresholds on the absorption phase, and adjustable voltages for all the phases, so I think it would be able to get all my batteries to full on "normal" charge, which is way better than what is happening now. But, I don't see anything in the literature of what they do at startup when you first plug in (I will be talking to them about it). The CTEK goes through the entire charge cycle, but it blows through ones that are not needed very quickly. If the battery voltage is up, it still starts, but then it will be in the bulk charge a minute or two and go to absorption. If the battery isn't full, it will be there for two hours (must be on a max timer), if the battery is full, it will only be there a few minutes before going to float. It does a much better job than the Tripp-lite or the Xantrex, but it is only 8 amp charge capacity.
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Old 11-30-2013, 04:09 PM   #6
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Default Re: How "smart" are smart chargers

Looks like CTEK now has a 25 amp version of their charger. If it works like the smaller one, it would be possible to use two of them, one for each bank. They have done a better job of explaining the 8 step charging they tout, it has desulphate every charge cycle, and a separate equalize at the end which is selectable.

This is very tempting, and similar cost. Just can't get remote display.

http://smartercharger.com/products/b...ulti-us-25000/
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Old 11-30-2013, 08:22 PM   #7
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Default Re: How "smart" are smart chargers

Is the CTEK bulk voltage 14.4v? Will that work well enough for Trojan batteries needing 14.7v?
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Old 11-30-2013, 08:58 PM   #8
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Default Re: How "smart" are smart chargers

Also, what do think about sizing the charger to allow for a C/20 initial rate of charging? That would be an 80 amp charger for a 400ah battery bank.
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Old 11-30-2013, 09:51 PM   #9
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Default Re: How "smart" are smart chargers

Quote:
Originally Posted by markopolo
Is the CTEK bulk voltage 14.4v? Will that work well enough for Trojan batteries needing 14.7v?
Definitely a concern. From what I have read, they will get charged but take a lot longer. Not sure if they get to 100% on 14.4v. The chargers do have an equalize, so that could be used for a top off if you were in a hurry, but it would be nice not to have to do that.
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Old 11-30-2013, 10:00 PM   #10
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Default Re: How "smart" are smart chargers

Quote:
Originally Posted by markopolo
Also, what do think about sizing the charger to allow for a C/20 initial rate of charging? That would be an 80 amp charger for a 400ah battery bank.
I have no idea where they came up with the "rules" for charger size. They say 10-13% of bank capacity, which is pretty low, compared to what I would think. A 400AH bank taken to 20% state of charge would take 32 amps average for 10 hours, to get full, without any dwell times. I don't think golf courses could get the carts all charged quick enough for the next day. 13% makes it a bit better, but not a lot. They have a lot of disclaimers on the charger size recommendation, all indicating going up as not much problem at all, and down only minor, from the 10-13%. If I had the wiring for it, I wouldn't hesitate to use an 80 amp charger for 400AH, to speed up recovery time. It does seem the more sophisticated the chargers get, the fewer large ones are available, though.

I am still hoping Blue Sea will have some insight when I can get a hold of them next week, as their charger is a very good fit, if I can get it to start with the solar and surface charge issues.
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