Rules changing for battery charging?

[booster]

I am starting to wonder if the battery charging rules are starting to drift in a different direction from where they have been for a while. A guy on the Yahoo board has a couple of good sized Trojan wet cells and a couple of hundred watts of solar. He also runs a compressor frig. He had been testing the solar's ability to keep the batteries up by itself, without being plugged into shore power, to see what to expect in actual travel and use. One of the Trojans went belly up much more quickly than would be expected, and he went to the Trojan folks and got an interesting theory. They thought that the solar did not have adequate amperage available to do a good job of charging the batteries, no matter how long they were being charged. Without adequate current available, the voltage would be lower you would normally see in a 3 step charger, if the batteries hold current is higher than the output of the solar panels. Without getting the higher voltage, you are back to a low voltage trickle charge, in effect, so you never get to high enough voltage to gas the batteries, and mix the electrolyte. They said, I think, that the battery had stratified and sulphated in the low specific gravity areas, shorting the plates. They would prefer a full 3 step charge cycle with gassing voltage every time you charge, to keep them mixed, and completely full. I found this pretty interesting as Trojan has always been very conservative on equalizing batteries, saying only once or twice a year, and only if you see a cell to cell specific gravity difference, so making sure you gas and mix was not an issue of worry in the past. We all have heard that not getting totally full can cost capacity, but I have never heard of complete failure because of it, so the gassing may be the defining part of it.

We also have Trojans, and as it turns out, one is in the van, and one on the bench (it was replaced by the two 6 volt batteries). They are identical SCS200 12 volts that were bought and run as a pair until last year. Their condition was nearly identical going into the winter last year. They did see different charging cycles over the winter, though. The one in the van was on the shore power charger almost all the time, the one on the bench charged up about every 4-6 weeks. Thus the one in the van was sitting at 13.5 float nearly all the time, while the one on the bench cycled through full charges and discharges to about 85%. I just checked them this weekend to see how their conditions were. The one on the bench, after charging, was right at 1275/1280 specific gravity on all cells. The one in the van was at 1260/1265 on five cells and 1250 on the other, right off the the charger in the van. I took it out and ran a few "recondition" cycles with the Ctek charger, which is only 8 amps but claims a desulphate step. It also does an "equalize" also but it does not really boil the battery much more than a standard charge. The specific gravity came up about 5 points across the board. I then put it on the Xantrex 40 amp charger, which is really a marine 3step converter with cables added, and did a real equalization. After two equalizing runs, it was at 1270/1275 on 5 cells and 1265 on the other. It did need the equalizing, even though it had been on the charger nearly all the time. The battery that was charged less often did not need equalizing. I found it kind of disconcerting, as we have been told that long term trickle charging is a good thing, but at least based on this, a standard 3 step charge once a month might be better.

Perhaps this is just starting to be looked at because of the increases in the use of Battery Tenders and solar, rather than periodic charging. The change to 3 step chargers could also be a big factor, as you never would have left a battery on charge all winter with the old style chargers, which were fixed voltage of somewhere in the 14.5 volt range and gassed the batteries very well, but would also empty them of water pretty quickly.

Trojan's main market is golf cart batteries and other industrial equipment applications, so the batteries get used pretty hard, and often. On a 3 step charger, they would always see full voltage charging so they wouldn't have any of the problems from too low a charging rate and voltage. This is probably new ground for them, as in the past, homeowners and RVers would have single stage chargers that would gas the batteries no matter if they were full or not. I would bet 98%+ of all battery charging testing is done on high use, high buck, applications like golf carts and forklifts, not little RVs, and the results might not translate well.

I will be very interested to see if there is any other information coming out from the battery makers in regards to storage/charging in wet cells. I think this winter, I will rig up a timer to turn on the shore power once a month for 24 hours and see how the batteries react. It will also be interesting to see if anything like this happens with AGMs that are not regularly cycled.

The other thing that seems to bee gaining traction is the recommendation to equalize AGM batteries, which was always a huge no-no. I first saw some small references to it a few years ago about Lifeline batteries. Since then, it has been more front and center in the Lifeline literature. When I looked today it said to equalize at 15.5 volts for 8 hours, but only if the batteries are starting to show signs of losing capacity. That is a pretty long equalize (way longer than I see with Xantrex on wet cells). I don't know what it does to an AGM, as with a wet cell it is to stir the electrolyte (which is not liquid in AGM), bust loose and settle crystallized sulphate (which can't get away in AGM), and maybe redesolve some newer, softer sulphate (might happen in AGM). Whatever the reasoning, it is a big change from what we used to be told to do, or not do, to AGMs.

I guess what we really need is for them to get the fuel cells working, so we don't have to worry about batteries, or charging

[mlts22]

Truma, an European company that makes RV furnaces, A/Cs, and other items makes a propane fuel cell, called the VeGA. It does up to 6000 watt-hours a day, or 250 watts. This won't replace a solar array, but will keep batteries charged when not using the "B", and will offset the amps used for the furnace.

[markopolo]

20 amp output from the Truma VeGA - not bad.

[booster]

Originally Posted by markopolo

20 amp output from the Truma VeGA - not bad.

100 grams of propane per hour, so it would run like 5 days on a 30# tank, if I did the numbers correctly. Of course that would give you something like 500AH of power a day. They list run time in weeks at 40 and 70AH per day usage.

Anybody heard a price yet?

[booster]

I have been rooting around on the Trojan site to see what they are saying these days. There are a lot of different areas you can go on the site to see lots of different documents, and now they also have some training videos on there.

It does appear that they are in the process of changing their recommendations, as there is contradictory information depending on where you look. Briefly, some of what I found.

They used to recommend equalization once a year, or if the specific gravity was low or cell to cell variation was over .030. On the new training video they are saying once a month. This is a big change for them. They also spend a lot of time, in many places, explaining why equalization is necessary. All of this bucks a trend that has been going on for a few years of eliminating equalizations (probably for liability reasons do to explosions). I don't think you can even buy a home charger with equalization anymore. When my old one died, I had to buy a marine converter and wire on a plug and clamps to get a charger that would equalize. They even explain how to do a seudo-equalize with a normal multistep charger by doing a full charge, unplugging it, and then plugging it back in so you get to the bulk charge voltage (not quite equalization voltage) on a full battery to gas it some.

They have increased the "daily" (as they call it) charge voltage to 14.8 volts, from 14.4 IIRC. This is probably also in an attempt to mini-equalize the batteries at each charge cycle.

They now have the float voltage at 13.2 volts, and I think it used to be 13.5 like everybody else, and how our Tripplite does it. Don't know why they would reduce it.

When batteries are stored, they are recommending checking once an month and recharging when they hit 70% charge. I could not find anywhere that they said to leave stored batteries on a float charge, or tender, which is what almost everybody had been recommending for quite a while. No mention either about charging if higher than 70%. They also have added that they want you to equalize whenever a battery is coming out of a stored time, before use.

Trojan must have been getting a lot of stratification and sulphation failures lately, as these are pretty big changes, and very different from what we have heard in the past. They also all seem to relate to equalization type charging practices. If used, these changes would surely make is so you would need to be right on top of your watering program, I would think, as there is going to be a lot more gassing (and corrosion, too).

I need to check the available settings on the Tripplite, and the Xantrex to see if I could even get the recommended profiles.

Edit-our Tripplite does 14.4 and 13.5, so no way we can do the new specs on our RT.

[markopolo]

HandyBob has a blog post on 14.8v charging dated 2007. http://handybobsolar.wordpress.com

It depends on how you charge the batteries.

Originally Posted by HandyBob

Oh, you can charge at 14.4 volts if you are plugged into shore power for days, but running the generator for a few hours or having your solar controller shut off as soon as it reaches the set point does not work.

That's a key point.

The charger in my van only goes up to 14.4 volts. The van is plugged in when home and mostly I see 13.2v float.

My charger:

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.

[booster]

Originally Posted by markopolo

HandyBob has a blog post on 14.8v charging dated 2007. http://handybobsolar.wordpress.com

It depends on how you charge the batteries.

That's a key point.

The charger in my van only goes up to 14.4 volts. The van is plugged in when home and mostly I see 13.2v float.

My charger:

Don't you wish Handybob would just say what he thinks sometime, and not be so subtle

I have been looking at Trojan spec sheets to see what the say. The 14.8v is what they say, and have for a while on most sheets, for a "daily charge". Unfortunately, they don't define what a "daily charge" is. Some of the pdf sheets on the Trojan site list 14.8 volts for "daily" charge, but show 14.1-14.7 volts for RE applications (renewable energy). I found quite few Trojan pdf sheets on other sites for their commercial batteries that only listed the 14.1-14.7 voltage. Perhaps the "daily charge" is like at a golf course where the batteries have to get full in 10-12 hours, which wouldn't happen with a standard multistep profile, and will never see the float voltage to finish off getting them full, so they hit them hard to get them full. As Handybob says, that shouldn't do any damage, and is probably good, as long as you get it shut off once you get full. I wonder if Trojan would consider our solar charging as "daily" or "RE"? The 14.4 volts that I have always heard and seen on Trojan stuff is obviously the 14.1/14.7 midpoint. It sure makes me wonder if the old single output chargers, and folks that paid attention, weren't all that bad, and some of the new stuff may not be all that good.

What charger do you have that drops to the 13.2v, but then boosts every day? That sounds like a very good answer to many of these questions. I think that many of the maintainers and multisteps use higher voltage pulses that average out to the lower voltage seen, to help desulfation, but they would do nothing for stratification. I still didn't see anything from Trojan about using maintainers instead of letting them go down to 70% and then doing a standard charge. It may be there somewhere, but I haven't found it yet, so I don't know if it is recommended or not.

Handybob's statements on MPPT controllers I found very interesting. As he says, watts are watts, and you don't want to waste them on electronics. I am not familiar with the controllers he talks about, but I have to assume they are matched to having the solar panels in series to get higher voltage and reduced wiring losses. One of the good things of an MPPT like we have is that it will do 12-36 volt input right out of the box.

My favorite of all I have seen lately is the above mentioned 14.4 bulk, 13.2 float, 14.4 boost every day, charger. It absolutely makes the most sense of all of this stuff.

[markopolo]

I installed a Progressive Dynamics PD4045 converter/charger in April 2012.

If someone buys a brand name battery they should be able to get the charging recommendations for that specific battery and should follow those recommendations if they can. Different brands will have different charging recommendations.

I have four batteries in the van. All different. 100ah and 70ah AGM for house batteries, about a year difference in age. Starting batteries consist of one AGM inside the van and a sealed wet cell under the hood, again about a year difference in age.

Note: I don't recommend that. Batteries in a battery bank should be the same type, brand, capacity and age. I couldn't spend the money needed for two more AGM's at the time to make each bank at least have matching pairs so I figured I'd take care of them as best I could and see how long it all lasts. An experiment. I think it works because I gently use them. We tour around, plus I have 120 watts solar, LED lights, LED TV. Fridge runs on propane etc. etc. etc. You get the idea, lots of charging and no big loads, no prolonged loads like a compressor fridge.

So I did some testing today to check the state of charge. The oldest batteries in the mix are probably 2 1/2 years old. The newest probably 1 1/2 years old.

You need to remove the surface charge to get an idea of the state of charge for AGM and sealed batteries.

Interstate says:

To remove battery surface charge, apply a load to the battery for a period of time. For example, apply 10–15 amps for two to three minutes, then allow the battery to sit for one minute before retesting.

I figured a 100 watt incandescent bulb plugged into my inverter would be approximately a 10 amp load. It was close; 9.5 amps was the actual load.

I unplugged the van. Also, the van is in my garage but I removed the solar panel fuse to make sure there was no voltage from it.

Two house batteries only
9.5 amp load for 3 minutes
12.4 volts on the meter during the load
Turned off inverter
Voltage on meter was 12.74 after 1 minute rest (12.7 showing on inverter)

At 20 minutes the voltage of the house batteries had climbed to 12.77 volts even though I ran my LED lights while waiting.

At 24 minutes I combined the house and chassis banks and turned on the van headlights for a minute to remove surface charge. Then I let the diesel engine glow plugs heat up (larger current draw). Then:

Two house plus two engine batteries
9.5 amp load for 3 minutes
12.6 volts on the meter during the load
Turned off inverter

30 minutes had passed at this point. Voltage was 12.82 on the combined house and chassis banks after 1 minute rest.

At 35 minutes house battery bank was showing 12.86 volts.

I combined both house and chassis banks again, ran some lights and the fantastic fan on high for 10 seconds. I shut everything off and the voltage was 12.87v at 40 minutes.

12.9 volts at 45 minutes.

12.92 volts at 50 minutes. So I ran the microwave oven on the inverter for 15 seconds on high. Voltage dipped to 12.2v while microwave oven running. That's a 90 amp draw.

At the 1 hour point voltage had recovered to 12.89V on the meter and 12.9 on the inverter.

At approx 2 1/2 hours voltage was still 12.89v.

I then isolated the banks again, pulled the propane detector fuse and will check the voltage tomorrow.

I would think that 6 minutes of 10 amp draw + occasional lights, + chassis lights, + glow plugs and microwave oven on for 15 seconds would have removed the surface charge from all 4 batteries but I'll know for sure tomorrow. With the battery banks separated the two banks should have different voltages tomorrow.

At this point it looks like my batteries are still in good shape. (all four being maintained together with the Progressive Dynamics PD4045)

Note: 4 voltage meters used during testing - results were consistent, at most 0.02v difference on the meters that show two numbers after the decimal point.

[booster]

Originally Posted by markopolo

If someone buys a brand name battery they should be able to get the charging recommendations for that specific battery and should follow those recommendations if they can. Different brands will have different charging recommendations.

I totally agree, but seem to have run into a couple of problems. First being what specs Trojan really wants. I had always heard 14.4 bulk, but they told the guy with the failure 14.8. Here is the chart from the user manual for Trojan, non-industrial, flooded deep cycle batteries.



The chart shows both charge voltages, but doesn't say how to determine which to use. If you go to the flat section of the graph, it is 14.1 to 14.7 volts per the note. They then show it increasing to 14.7 to16.7 volts, which is too high even for equalizing, per their own chart. They have me very confused.

The second issue is finding a charger that you can set to suggested parameters. Most seem to be setup to what the maker of the charger deem to be the correct voltages and profiles.

We also have mixed batteries without any noticeable issues from it.

[markopolo]

If you ignore the flat spot on the graph then you see that they are just taking taking a deeply discharged battery (80% discharged) all the way up to charged (100% charged).

The voltage of the battery rapidly increases as it is being charged from 20% to 90% state of charge. Then the battery voltage increase slows from 90% to 95%. The graph seems to indicate that to get the battery from 95% to 100% charged you need a charger that outputs 14.7 volts (or more).

The graph is what is happening to the battery, not what the charger is doing. The charger would output 14.7v (or more) all the way from 20% to 100%.

After all this you'd deal with storage or float charge.

I think HandyBob has been pointing out that this way is a more efficient way to reach the goal of 100% charged. If you have more time available then you can get there with 14.4 volts also.

Note the low charge amperage; 10% to 13% of the battery's capacity and how you can tell that you are at 95% SoC when the amps into the battery slows to a relative trickle (1% to 3% of capacity).

[booster]

Yep, the flat spot can be anywhere from 14.1 to 14.7 when taking it up to near full, I guess that was my point. I also don't understand the graph going to nearly 17 volts as a "typical" charge cycle. Trojan does not say that 14.8 is the right voltage to use under some, or all conditions, except for daily charge, which they don't define or show on the chart except as the very high end of the flat spot. I certainly am not saying the Handybob is incorrect, no doubt it will charge to full faster, don't know about less water use, don't know about battery life. I do know that when my alternator was charging at above 14.5 volts, the batteries used lots of water compared to the 13.9/14.0 volts they see now when driving. That is why I wish Trojan would be more specific. My guess is that they are trying to say that if you need to get them full in an overnight (or overday with solar) charge, use the 14.8. If you have the time, use the 14.4. The 14.4 won't have enough time to fill them during the charging period with solar. Trojan must know which way is the best for the batteries in varied conditions, but are kind of vague. If you don't get them full each time you charge, you will wreck them quickly, as Handybob stated, and since he, and the others he referred to are using solar, they do need to charge quickly. Thus they don't have the time to use the lower voltage. Handybob is always offgrid and without a generator, so he has to get full with the solar alone, to keep his batteries alive, all the time. He may or may not have enough output to do an equalization. Most of us also plug in pretty regularly, so the requirements might be different.

I guess the big question for me would be, if you don't have solar, and boondock a day or two, which voltage is best for the batteries when you go home and plug in? Which voltage is better for the batteries, if you have the time to charge thoroughly? If you are stored and doing the Trojan recommended charge when you hit 70%, which would be the recommended voltage? (I also still wonder what they would prefer, the go to 70% and charge, or stay on float continuously) If you don't have much time, I agree that you don't have much choice to go to the higher voltage, as the consequences are high for not getting the batteries full, and the higher voltage is the way to do that, but what about other times.

From looking at the way the videos and literature is starting to slant to the higher voltages, I wouldn't be surprised to see the lower voltages go away, except for special applications, as Trojan is probably getting more failures due to sulfation and undercharging than they are from overvoltage and boiling. I wonder if the charger manufacturers would follow and increase their voltages.

[markopolo]

I'm convinced now that Trojan's "daily charge" means the same as Interstate's "Recharge as soon as possible after one day’s use."

Originally Posted by Interstate

Charging Tip: Do not delay charging your batteries after use. Recharge as soon as possible after one day’s use. Allowing the battery to sit discharged for several days may hamper its recharge acceptance and ultimately its performance.

The flat spot matches the rapid decline in amps being absorbed by the battery.

The Trojan info does not look to be meant for typical RV use. You'd have to isolate the battery bank from the RV coach systems if you hit it with almost 17 volts when charging.

Good point re: solar not charging long enough. Solar charging is limited to the number of daylight hours on a given day.

Your batteries using water at 14.5v is probably due to the fact that your batteries are fully charged or near full charge when you start the trip.

An RVer without solar or who parks in a garage after a trip (with batteries charged from driving) should do ok using 13.6v initially then floating at 13.2 volts for storage.

I subscribe to the "a charged battery is a happy battery" theory so mine are stored on a float charge.

It does look like charging voltages are higher now. RV chargers are made to suit a wide variety of batteries and have to accommodate for battery age so we might not see those higher voltages in general purpose RV chargers.

------------------------------------------
An update on my batteries:

After 17 hours at rest my house batteries were at 12.88v and chassis batteries at 12.86v using my "best meter". I suspect a bit of surface charge is still there but it looks like my batteries are still in great shape so I'll continue doing what I've been doing - plug the van in at home. I'll check them again next year.

[markopolo]

I think the advice re: depth of discharge has changed or has gotten much more specific according to battery type.

In the past, I've referenced this chart for deep cycle battery state of charge %:



Interstate published a very easy to read and understand booklet on Marine/RV "deep-cycle" battery maintenance. Many RV's have these hybrid or all-purpose batteries. They are not true deep cycle batteries and should not be used and maintained as such.

Look at the differences between the chart above and this chart:



I think the second chart is a better reference for typical RV use.

You really shorten your Marine / RV battery's life with deep discharges:



You can download a copy of the RV / Marine battery booklet here: Interstate RV / Marine battery booklet

[booster]

I thought all wet cells generated the same voltage at the same state of charge, so that is a surprise. I wonder if they also have changed the specific gravity chart for them.

Also, I think all of these voltages are the ones that say the battery should "rest" with no load on it for an hour, which makes them very difficult to use in the real world.

Campskunk made himself a chart that listed his state of charge, which he got from hydrometer readings, vs voltage, but with his typical load running. IIRC the voltages were considerably lower, which would be expected. I would think a chart of that type would be much more useful in the real world, once you determined what your typical load was, and could repeat it easily.

[markopolo]

You can get a reasonable idea of the state of charge for AGM and sealed batteries from the voltage after you stop charging them and remove the surface charge.

Interstate says:

To remove battery surface charge, apply a load to the battery for a period of time. For example, apply 10–15 amps for two to three minutes, then allow the battery to sit for one minute before retesting.

That won't be perfect but it will tell you if you need charge the batteries if, for example, after removing the surface charge and waiting a few minutes your battery voltage is below 12.7 volts.

Note: a larger battery bank would require a larger load to remove the surface charge prior to checking the voltage.

While charging or while under load the state of charge won't be static. It's either going to be increasing or decreasing. It should be pretty easy to stop all loads and all charging for 10 minutes or so to remove the surface charge to check the state of charge of your AGM and other sealed batteries. Other websites recommend a 20 amp load for a few minutes to remove the surface charge for this quick test. I think that might be better than the 10–15 amp load recommended by Interstate because that was likely for only one battery and many RV's now have more than one house battery.

Creating the 10, 15 or 20 amp load will require that you turn on a combination of items for the few minutes to remove the surface charge.

Item_____________________________Amps

Lighting (1156 Single bulb)___________1.3
Lighting (Led 1156 Replacement)______0.1
Lighting (Fluorescent)_______________1.4
Furnace__________________________2.8
Fantastic Fan Low__________________1.86
Fantastic Fan Medium_______________2.29
Fantastic Fan High__________________3
Stove Hood Fan____________________2.2
Microwave on inverter_______________90
CO Detector_______________________0.06
LP Detector________________________0.086
Water Pump_______________________3.8
Water Heater______________________0.75
TV_______________________________4
DVD_____________________________2

[booster]

The sealed batteries do complicate things a bit

I assume Marko is removing surface charge from freshly charged batteries, or batteries that are being charged, so they have a surface charge on them. I don't want to speak for Campskunk, but I think what he was trying to have was a chart that he could reference as he was discharging with "normal" stuff running over his day, so he knew what he had left without shutting everything down or doing specific gravity readings. My understanding is that the batteries should sit at least 20-60 minutes with no load if you want a good reading of state of charge based on voltage.

In the past, I did a little checking to see how much difference loads make on the voltage reading, even without the resting time, and it was plenty big enough to totally mess you up if you wanted to know your state of charge. IIRC a 50% state of charge battery (approx) would give just under 11.7/11.8v or so, with only an under 2 amp load. It was at about 12.0v with no load, no rest and 12.1v after rest. I was very surprised how far the voltage dropped with small loads.

I just went to the Interstate site to see if they had a specific gravity chart, and found their charge voltage chart. They have bulk at 14.4 but the absorption is at 15.5v, at least on some of the charts. These ratings that go that high (Trojans went even higher) must only be for situations where the batteries are disconnected when they are charged. You just don't want to put that much voltage on the stuff in your RV or boat.

[markopolo]

Is that what your Trimetric monitor does? A battery "fuel gauge" of sorts. How much fuel (amp hrs) is left in the tank (battery).

[booster]

Originally Posted by markopolo

Is that what your Trimetric monitor does? A battery "fuel gauge" of sorts. How much fuel (amp hrs) is left in the tank (battery).

Yep, that is the basic premise of the Trimetric, plus you can see current in or out of the battery, to know how much you are using, and battery voltage. We haven't had a lot experience with it yet, but the way they say to set it up makes it much more useful in discharging than charging. When you are discharging, it juts totallizes the amp to amp-hours and calcs off of your programmed battery capacity. When you are charging, they have you program in a "charging efficiency". This is because not 100% of the amps going into the battery turn into stored power. Default is 92% for wet cells, and at that setting, we have seen our batteries never get above 88% state of charge no matter how long they are on charge. I currently have it at 97%, and it seems to be much better, and gets to 100% just about when the batteries are full. I talked to Bogart about it, and they said they do it like they do because folks would see the 100% and shut the charge off too early to fully top off the batteries. There is also fully charged light that comes on, and it is a bit early also.

I think once it is dialed in, the Trimetric will be a very useful tool, especially when out for longer times, with possible less than full charging cycles from the solar, but to do that, the charging amount gained has to be accurate.

[markopolo]

The author of this blog - http://solarjohn.blogspot.ca/2007/03...of-charge.html - created a chart that shows battery state-of-charge at rest and under a load. The load must be significant relative to the size of the battery bank. For a 100 to 200 amp/hour battery bank he suggests using a 50-Watt incandescent light bulb.

My battery bank is 170 amp/hour so I'll use a 60 watt incandescent light bulb for the “Discharging” procedure he describes.

link to full article: http://solarjohn.blogspot.ca/2007/03...of-charge.html that has the chart and suggested loads.

It might be interesting to compare to a Tri-metric.

[booster]

Originally Posted by markopolo

The author of this blog - http://solarjohn.blogspot.ca/2007/03...of-charge.html - created a chart that shows battery state-of-charge at rest and under a load. The load must be significant relative to the size of the battery bank. For a 100 to 200 amp/hour battery bank he suggests using a 50-Watt incandescent light bulb.

My battery bank is 170 amp/hour so I'll use a 60 watt incandescent light bulb for the “Discharging” procedure he describes.

link to full article: http://solarjohn.blogspot.ca/2007/03...of-charge.html that has the chart and suggested loads.

It might be interesting to compare to a Tri-metric.

That is a very easy test with the Trimetric, but for accuracy you would need to confirm state of charge with specific gravity.

The Trimetric makes it easy to check load vs voltage drop, as it shows battery in/out amps, and battery voltage. All you need to do is check with everything off and rested, then turn stuff on and get the new amps and volts.

We have a lot more battery than the last time I did any of this testing at 375AH instead of 180 original or 230 a bit later.

I just went out and took it off the charger, let it sit 10 minutes and it was at 13.4 volts, .3 amps. I turned on the inverter and stereo for a bit over 4 amp load and it dropped to 13.2 volts. Turned them off and it came back to 13.4.

I left them running now, to get off of fully charged, and will repeat the test later. The numbers he has on his chart seem to be a bit low on voltage drop vs state of charge, with a load, but my past history was on a smaller bank and not as quality batteries. His chart also shows the voltage drop to be bigger as the state of charge drops, essentially doubling from full to 20% state if charge, so weaker batteries probably would have a larger drop. It appears he has done similar to Campskunk, except he adds a set load for the test reading, and Campskunk is counting on a similar load all the time.

I will know a bit more in an hour or two, when the batteries have run down a bit.