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Old 01-24-2018, 11:12 PM   #11
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Thank you. Your new post shows your helpful annotated diagram. The prior post's images appear fine.
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Old 01-25-2018, 02:26 PM   #12
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Originally Posted by booster View Post
If you had a charger that was capable of doing the Trojan profile, you would start charging at a fairly low voltage, constant current of 10-13%C.
There's a lot to absorb in your analysis, but one thing I noticed was the low seeming bulk stage constant 10-13%C current Trojan recommends. I find people recommending 20%C as a minimum current in bulk, and that more is better. Is this lower recommendation new, or have I been getting opinions rather than good information? Or is this because the Trojan info is for FLA and not AGM?

Would this dissuade you from fast charging, say, with an alternator? The low level might be complementary to solar.
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Old 01-25-2018, 03:42 PM   #13
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Originally Posted by Saldar View Post
There's a lot to absorb in your analysis, but one thing I noticed was the low seeming bulk stage constant 10-13%C current Trojan recommends. I find people recommending 20%C as a minimum current in bulk, and that more is better. Is this lower recommendation new, or have I been getting opinions rather than good information? Or is this because the Trojan info is for FLA and not AGM?

Would this dissuade you from fast charging, say, with an alternator? The low level might be complementary to solar.
The 10-13% is for Trojan deep cycle wet cells, and has been around for a long as I have looked at their specs, so about 10 years. They used to list it as 11% most of the time, but no use the slightly larger range. I have looked around several times in the past, when we had Trojans in our van, for some firm numbers for maximum and it is not particularly easy to find. Even Trojan was squishy on it, but the tech there at the time said 20% max. Wet cells don't fast charge well, especially deep cycle versions, it appears, and what they will even accept from a big charger isn't all that high. IIRC, ours maxed out at about 40%C with a big charger and 14.7v, but they got hot quickly and gassed a lot. My guess is that Trojan has found out that they can put more watts into a battery faster, without too much heat being generated by keeping the lower amperage, but raising the voltage, as shown in the newer specs. Watts are what the battery stores, so it makes some sense. The batteries that Handybob failed where Crown, not Trojan, but I think they have similar specs (need to look for sure). I don't recall his solar and battery capacity, but he may have been able to get too high on current.

The fast charging from an alternator is an issue with wet cells, as most class b vans have 50-80 amp breakers to the batteries and can give them more than ideal. 20% of a 220ah bank is only 44 amps. AGMs double that amount so can be charged faster, if the alternator is OK for that much continuous output. The big problem, IMO, is that the alternator charging is nearly always uncontrolled for voltage or amperage or time. Depending on the state of charge of your batteries when you start a drive, you could be overcharging your batteries for the entire drive (if the batteries were full from shore power), or need the all day drive to get full (if they were near empty). Without some controls this can be a hazard to the batteries. IMO, having a Trimetric, or other monitor that shows a fully charged indicator, within sight of the cab, and a disconnect switch style separator is one of the best things you can do to preserve you batteries, especially if you drive long hours regularly.

AGMs do accept and recommend much higher charge amps. Most seem to spec in the 20-25% as normal, no minimum usually, but with allowances to go substantially higher as long as the charging is temp controlled to prevent overheating the batteries. We have found our Lifelines to be able to take about 40%C without getting too hot, although we do have to watch a bit because they are under the van and see underbody heat while driving, too.

I haven't seen it or other manufacturers, but in the last few years Lifeline has added a recommendation to charge at a minimum of 20%C if you are discharging more than 50%. This is likely the spec you have seen. They also say to set the normal amperage to "as high as practical", which is pretty vague. When I called them and asked about the amperage best choices, Lifeline said they would prefer 40%C for the deep discharge recoveries, with a minimum of 20%. They would probably like more than the 40% but heat would be an issue in many cases, I think. 40% on big battery banks is more than most single chargers can do. We can only get a bit past 20% with our 100 amp Magnum. Engine generators can easily get high enough, or more.

Of particular interest in this discussion of higher voltages is that Lifeline now also has a deep discharge recharge recommendation that says if you can't provide at least 20%C charging amps.



What immediately jumps out is that this is very, very, close to what Trojan recommends to do on their overnight type charges. Constant current at 2%C extra stage. Trojan cuts off at voltage, which is a good idea I think. Lifeline says by time and isn't specific. Since Lifeline allows 15.5v for equalizing, that would likely be a good place to stop. Of course, none of our chargers will do this as part of a normal charge profile. I think our Magnum allows you to do an equalize and set the maximum current and voltage, but I will have to look at that. I know you have to run it as a separate operation.

All this brings us right around and back to what Handybob said, that he thought the higher voltages were to compensate for the chronic undercharging that most batteries see in use. Equalizing, which is what these extra constant current stages really are, is what you do to help recover capacity in batteries that have lost capacity, usually from poor charging, so it makes sense. Where Handybob and I start to diverge is in whether it is an overreaction, or not. At this point, I think it may not be as much of an overreaction and overdone correction, as it is a misapplication of the correction. If the added, high voltage, stages are not controlled exactly as recommended (constant current as specified, terminated at recommended voltage, temperature controlled) I think it would be very easy to destroy your batteries, and that may have been what happened to Handybob.
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Old 01-25-2018, 05:04 PM   #14
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Quote:
Originally Posted by booster View Post
My guess is that Trojan has found out that they can put more watts into a battery faster, without too much heat being generated by keeping the lower amperage, but raising the voltage, as shown in the newer specs. Watts are what the battery stores, so it makes some sense.
I'm assuming this refers to bulk charging. Then, I didn't know voltage was an element of bulk charging. (Tho obviously to provide power voltage is required....) I thought the charger supplies constant current and the voltage required is controlled by the battery chemistry. Voltage increases and when it reaches a threshold, or after some fixed interval, the charger decides to begin absorption by holding at its absorption voltage. So is the higher Trojan voltage at bulk the final threshold voltage? I think the charger must supply whatever voltage is required to keep the current constant in bulk---and that appears to rise, not be a fixed value. What does bulk stage voltage mean?

Your expanded discussion of recommended current levels for the two types of batteries is very clear.
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Old 01-25-2018, 07:45 PM   #15
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The section you quoted actually refers to the absorption stage of charging, as that is when the higher voltage is first seen, although it having a higher absorption setting will also keep the charger in bulk a little longer because the voltage has to rise more. This keeps the charger at full output longer and puts the SOC of the battery higher at the absorption transition.

Bulk charging is constant current, as you mention, so voltage is irrelevant as long as the current is where it should be. The chargers in our vans are not really true constant current devices in most cases, as you can't set the maximum output current on most of them. They turn into constant current devices by selecting a charger that has a maximum output about where we want the bulk charge constant current to be. It all works out to be the same thing in practice.

The whole battery acceptance thing gets really kind of odd when you apply it to the bulk charging stage. Normally, we hear that a battery will "accept" X amount of amps at a given voltage, which is usually the absorption setpoint voltage, and SOC. We are always looking at the amps as the variable as it changes with state of charge, and the voltage is constant. This train of thought only really works once you get to the constant voltage of absorption.

In bulk, the voltage is not even being tried to be controlled, it is whatever voltage that would match up with what the current and SOC on the charge profile for that particular battery. This is very similar to saying it is what the battery will accept in amps, but the charger can't supply it, so amps doesn't change. As bulk progresses, it is the voltage that changes with the SOC and based on the chemistry, following the bulk charge profile for the battery and charger. Wet cells require more voltage for the same amps, in general, compared to AGM, so the voltage will rise faster vs SOC in them, at the same amp %, and will have a shorter bulk stage with all other things equal.

Only when the voltage in bulk has risen to the setpoint for absorption does the acceptance of the battery control the amps it is getting, based on SOC and constant voltage. Once in absorption for a time, the amps will start to drop below the maximum output of the charger and at that point it is the battery that is controlling the amps by it's acceptance from there to completion of the charging.

How all this refers to the quote is a bit of an apples and oranges. I based it on the assumption that the battery manufacturer wants to increase the charging speed of their batteries. Since batteries really store watts (amps times volts) you can increase the charging speed by putting in either, or both, amps and volts faster. It appears that they chose to leave the constant amps in bulk the same so no speed gain there, but they increased the voltage in the absorption stage which will put watts in faster in that stage. The increased voltage will increase both volts and amps at that point because the charger will no longer be maxed out like in bulk. It is likely that if the increased the amperage in the bulk stage, they feel they would get excessive heat or some other issue, but that the increases in absorption would not give those issues, and having the higher voltage might even help some the chemical conversions of charging which get slower and harder to do as the SOC nears 100%.

I did look at the Crown charging profile recommendations, and they do very similar to Trojan with a constant current final stage to a maximum voltage cutoff. One thing they do differently is recommend a higher charging current % than Trojan at 15-18% instead of 10-13% which would be close the 20% max that Trojan had told me.

I went back and looked at my notes from speaking with Lifeline on charging amps as %C. For discharges of over 50% SOC, 20%C minimum, 40% recommended. I had also asked how much a 20% SOC Lifeline AGM bank will accept if you have it available and could hold the voltage up to 11v or more. Inrush could be quite high and hard to tell for sure because of components and wiring, but would likely be 80-100%C. After a few minutes it would likely settle at 70-80%C for about 30 minutes and then start down. Those kinds of amps would overheat our batteries in about 15 minutes. For that reason, we are setup with two turndown settings on our engine generator setup. One runs at 280 amps and the other at 180 amps. If we even need a very quick recovery of a couple of days use, we can get it with very short engine run at 280 amps, otherwise we would use the 180 amps which will not overheat the batteries and can run to full. To this point we have never needed to use the 280 amp output.
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Old 02-10-2018, 05:53 PM   #16
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Thanks to all of you for these discussions, I am back into RV ownership after some years of taking a break while teenage kids lost interest. With my previous TT I replaced the batteries once in the eight years, so maybe I got five years out of the first set without any real care or understanding of them. This van has middle of the road capacity using inexpensive components, with two Interstate gc2 6v batteries, a 55a wfco converter/charger, 95w solar panel with a 25a go-power controller, 600w inverter, and a 2.5kw Onan. So lots of scope for upgrades. The batteries appear to be original and three years old now, so experiments won't be expensive for now.

Both of the charge controllers are a little improved over the old TT's, boasting 3 or 4 states but are voltage triggered and timed. The voltages for the solar controller are modestly programmable, but all choices have higher float and absorption voltages than the wfco. A quick glance around shows many inexpensive pwm solar controllers with a 13.7v float listed, although to be fair the night or shaded float voltage will effectively be zero. I wonder if the solar controller having higher voltages keeps the two feedback control loops from interacting? And if the expectation is that while boondocking the batteries will draw down every night so that a small panel like ours will always want as many watts as possible, thus high voltages, morning boost, etc?

Another thought is that since I'm still a working stiff, like the TT, this van will sit in covered storage many more days than it will be used. So a main concern will be how to keep the batteries happy in storage. The van has a nice battery disconnect switch, but the solar appears to be wired around it. So you have a choice of overcharging if stored outdoors or a 6ma draw from the controller if sheltered. Maybe that's only an amp-hour a week if I do my math right, but it doesn't make much sense to me and makes me wonder what else is wired around the switch. The wfco's 13.2v float may be ok in storage, I'll watch the water levels and if it is boiling of water I'll go back to the disconnect switch. And there is now a starter battery to think of too, for convenience I'm going to try the Battery Tender Jr and see how that goes.

I could be wrong, but when I look at I the Trojan charge profile, I imagine that they are initially limited by thermal considerations, so that the I^2*R power is controlled until the current acceptance drops. In the absorption phase the battery's thermals are self limiting by it's current acceptance. My solar panel is so weak that there won't be a problem overdriving the bulk/boost phases, but the wfco might overheat the 225 ah batteries if it can really deliver 55a in bulk, so I might watch the water level for a while.

And a thought about alternator overcharging, I have a 3 way refrigerator, so in theory I could switch that on DC when I'm plugged in overnight and traveling the next day with full batteries. We shall see if I remember to try it, and then remember to switch it to propane when we stop, LOL.
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Old 02-10-2018, 06:58 PM   #17
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Welcome to the forum!

It sounds like you have a good grasp on most of what is going on.

First off charge voltages for wet cells, and particularly GC2 golf cart batteries which are usually some of the best true deep cycle types. (I will put a disclaimer here that there is unproven chatter that the newest versions of the Interstate GC2 batteries are made with combo battery construction and not true deep cycle. Time will tell if that is true, as it should be able to tell pretty easy from the water use). IMO, the latest and best voltages for GC2 wet cells would be 14.7v absorption and 13.2v float, but I will say this is really only exactly right if the charging system is very good at getting the batteries truly full regularly and not doing any major amounts of overcharge.

The 55 amp charger is a bit too big but not bad for your wet cells. Interstates are probably around 220ah, and we have found that charging at 20% on deep cycle wet cells works OK, but you really should have temperature correction. If you were way down on charge, the 55 amp would likely get the batteries pretty warm, especially if it is not temp controlled.

The solar is an interesting situation, especially with your storage situation. You didn't say if you have shore power there, but if you are testing a tender, you likely do. With shore power, the solar could be totally disconnected without issue as the shore power will take care of it fine. The solar is probably wired so the controller does not shut off if the main disconnect is shut off? They do that so to protect the electrical systems because if you were sitting in the sun the panel would generating a higher voltage than the controller would if it was on. Turn the batteries on without the controller already regulating the voltage, and a big spike can come through from the panel. The solution we use is to have an easy to pull fuse for the controller so you can disconnect the batteries completely from everything except the charger, just remember to put it back in with the panel in the dark.

When camping, I think you are probably very close when you say the solar is so small you won't likely overcharge. The panel will give about 30ah per day maximum and usually less than that. Most class b's with a gas frig, furnace, and hot water will use about 20ah per day +/-. The only time it would overcharge would be if the batteries were full when the day started, and it ran a full charge cycle all day. Better controllers look at the voltage when they come on in the morning and decide whether to charge or not. There would be no benefit, I think, in running DC at night on shore power as the AC is more efficient in the gas frigs and does a better job. The batteries will get charge either way, so no reason to use DC. unless you wanted to do it to reduce the current to the batteries due to the big charger.

The van alternator is likely your largest chance to overcharge, especially if you normally have shore power overnight so you are starting with full coach batteries. Isolators will run lower voltage to the batteries, which is good if they are full, but bad if you are trying to charge them. Separators will charge better but will put full alternator voltage on the batteries when you drive regardless of if they are full or not. Disconnects for the alternator charging can be done pretty readily if that becomes an issue.

Good luck with your reindoctrination to camping.
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Old 02-10-2018, 07:35 PM   #18
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Thanks Booster. Regarding the Interstates, they are a cheap brand, not what I would use for replacement, and it wouldn't surprise me if a cost savings measure is thinner plates ala a marine combo battery. I'll use them until they wear out, then get something better. A battery monitor, trimetric or victron, is on my list. Regarding shore power in storage, yes I have access to 15a which should be enough with them already essentially full. The 30a to 15a adapter just arrived and I'll take it out to the lot later today or tomorrow. Great point about using a fuse to disconnect solar, and thanks for the heads up about a spike if the panels are lit up when the fuse is replaced. If the voltage drop over the past 10 days seems consistent with my 1 ah/week estimate, or if I decide to trust the wfco, I may not worry about it. Also, I'll double check the wfco, I thought I recalled the model being 8955, but even an 8935 would be enough for these batteries so maybe I misremember the model no. Finally, I was only thinking of having the refrigerator on 12vdc while driving to offset the alternator, my TT didn't get enough cooling off of 12v to use it if propane or 120v is avail, and it kills the battery, but I don't like driving with propane on.

But you make me want to sit down and map out some common combinations to think through, shore power vs none overnight followed by a day of driving vs camping, with or without good solar or shore power. Several permutations, but that's what spreadsheets are for...
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Old 02-10-2018, 07:55 PM   #19
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Just a suggestion but use a permanently installed Trik-L-Start or Xantrex echo charger for the chassis battery. Don't have to think about it again.
Harry
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