Rules changing for battery charging?

[booster]

Just went back out. Batteries were ready 12.7v with .3amp draw (detectors running and solar controller). Trimetric showed at 99% state of charge.

Turned on 4.1 amps of load and it went to 12.6 volts, increased it to 7.6 volts and it went to 12.5. Fairly similar to the chart given earlier by Solar John. I think that the bigger better batteries help hold it up compared to what I saw before, but also that the Trimetric takes it voltage right at the battery, and I was at the control panel then.

I think this would be a good, and pretty accurate, way to keep track of your state of charge, once you got the chart built to match your batteries. I am sure it would also change over time a bit as the batteries aged.

Setting it up would be easy if you have wet cells and a Trimetric. At various points you would just check the amps through you load, be it normal stuff or a light bulb, read the volts and specific gravity. Specific gravity would tell you the state of charge at that voltage, with the standard load, very easy.

Same when charging look at the amps, volts, specific gravity and chart.

With AGM batteries, you would probably have to take a longer time, as you would have to determine the state of charge by the no load, rested voltage, I think. Then load it with your standard or normal stuff load and read voltage. Would take more time, and probably not as accurate as specific gravity, but I don't know how else you would do it. It would still be way more accurate than a plain voltmeter reading or idiot light, and plenty good for what we are looking at.

I really like all the versions of how to do this, Campskunks relatively constant load method (less accurate, but real time and easy), the fixed load method (more accuracy, more work, waste a bit of capacity on the test), or even making a grid of different amperages vs voltage vs state of charge.

With any of the methods, the Trimetric makes doing it easy, and also has it's own reading of state of charge to compare to.

Very good info, Marko!

[markopolo]

I just had to do some testing as well. My AGM batteries seem to be fully charged at 12.8 or even 12.9 volts.

My battery bank: 180ah
Unplugged van from utility power, removed fuse from solar panels
Fresh off 13.2 volt float charge, so fully charged batteries.
I used a 60w incandescent bulb on the inverter for the test.

At 0 minute 13.2v applied 5.7 amp load
At 3 minute 12.5v
At 7 minute 12.5v
At 10 minute 12.5v
At 40 minute 12.5v
At 60 minute 12.5v

Turned off the inverter at that point and unplugged the 60w bulb.
The battery voltage immediately recovered
at 1hr 5 minute 12.8v (used another meter then and it showed 12.82v)
at 1hr 30 minute 12.8v
at 2 hr 12.9v (used another meter then and it showed 12.85v)

My watt meter showed:
5.77ah
74 watts peak
5.92 amps peak
72.3 watt hours

My results confirm that I started with a fully charged battery bank according to John's chart and that a 6 amp load for an hour had little impact.

A State of Charge (SOC) Chart for my 180ah AGM battery bank with a 6 amp draw (or so) might look something like this:
(just a guess, but useful to give an idea of what is going on)
% of Charge - - - - At Rest - - - Discharging
100 - - - - - - - - - - 12.80 - - - - - - 12.50
90 - - - - - - - - - - - 12.70 - - - - - - 12.40
80 - - - - - - - - - - - 12.60 - - - - - - 12.30
70 - - - - - - - - - - - 12.50 - - - - - - 12.25
60 - - - - - - - - - - - 12.35 - - - - - - 12.15
50 - - - - - - - - - - - 12.20 - - - - - - 12.00

It tells me when to start charging if I don't want to drop below 50% state of charge.

It is easy for me to start with batteries at 100% at home. It is harder to get to 100% when you are away from home and off grid. I think getting to 90% state of charge daily should at least be the goal when you are away from home and off grid for long periods of time.

[booster]

Your test looks pretty similar to what I am seeing, but you have less capacity, so more voltage drop. Our wet cells don't come back immediately, though, so I have to wait to see where they are at after turning off the load.

John's chart shows more voltage drop as the state of charge decreases, which makes sense from what I have seen about current delivery at lower states of charge, so the lower ends of your chart may have more drop than you show, but we won't know without testing it to be sure.

This test is easily something that many folks could use, as the indicator lights are useless, and a plain voltmeter is dependent on what load is on, and where it is connected (usually by a lighter plug meter). I would bet most folks really have no idea what their batteries are doing, even with indicators and a voltmeter.

Time to build, and sell , a meter with a built in load resistor, so the test could be done directly without adding a load. Kind of like a battery load tester, but lower current.

[markopolo]

Originally Posted by booster

.............Time to build, and sell , a meter with a built in load resistor, so the test could be done directly without adding a load. Kind of like a battery load tester, but lower current.

Something simple and not to costly would be nice.

Re: charging the batteries

The most useful thing you can have to tell you when to stop bulk charging the batteries is an ammeter showing incoming amps to monitor battery charging.

Take a 200 amp hr battery bank for example. Charge rates are expressed as a percentage of capacity. The Trojan battery chart posted previously in this topic showed a C/10 rate. That would be a charger that outputs 20 amps for a 200 ah battery bank.

You'll also see some battery manufacturers using charts with a C/20 charge rate. I have a 45 amp charger in my van with a 170 ah battery bank. At peak, that would be a C/26 charge rate. The amps in tapers off as the battery charges.

When the amps in flow to a relative trickle you know the bulk of your charging is done and you can shut off your generator. You'll have to decide what is a "relative trickle" for your battery bank. I've seen it expressed as C/100 or 1% of you battery bank capacity. So that would be 2ah flowing into a 200ah battery bank. Your battery bank is not "fully" charged at that point but it is mostly charged. If you have solar then it would take over at this point.

Monitoring amps flowing in is really useful if you are "off-grid". The goal is to minimize generator or engine idling run time to save fuel and motor wear and tear and still adequately maintain your batteries. It is also useful to monitor amps flowing in if you are plugged in.

There are numerous single function digital ammeters including a shunt on eBay starting at around $15 or so or you can install a full function unit like a TriMetric by Bogart Engineering. http://www.bogartengineering.com/products/TriMetric

If you don't want to install a shunt for an ammeter and only want to monitor amps and volts then consider one that uses a hall effect sensor like this one found on eBay:

http://www.ebay.ca/itm/DC-Power-Volt...-/390531224237

The battery cable goes through the hole in the hall effect sensor. This particular sensor is the split type - the sensor opens to go over the cable so you don't even have to remove the cable. Check to make sure it can measure amps coming into the battery.

[Mike]

fwiw, I checked my batteries yesterday evening with that little Equus style tester that booster suggested eons ago to me. The van has been sitting in the driveway, hasn't been started in over a week, I ran the generator for a while last weekend, while I was cleaning the van inside, after our recent week long trip, so that would be the most recent charge to the coach batteries. Maybe half an hour of generator charging. I still have a Centurion charger, which is the original factory installed converter/charger. As far as eliminating surface charge after charging, I think I had the coach lights on mid week while I was searching for something in it after dark, so I would have put a smallish draw in the batteries.
My coach batteries, according to the little plug in tester, are still at 12.7V.
What am I doing wrong?

[booster]

Originally Posted by markopolo

Something simple and not to costly would be nice.

Re: charging the batteries

The most useful thing you can have to tell you when to stop bulk charging the batteries is an ammeter showing incoming amps to monitor battery charging.

Take a 200 amp hr battery bank for example. Charge rates are expressed as a percentage of capacity. The Trojan battery chart posted previously in this topic showed a C/10 rate. That would be a charger that outputs 20 amps for a 200 ah battery bank.

You'll also see some battery manufacturers using charts with a C/20 charge rate. I have a 45 amp charger in my van with a 170 ah battery bank. At peak, that would be a C/26 charge rate. The amps in tapers off as the battery charges.

When the amps in flow to a relative trickle you know the bulk of your charging is done and you can shut off your generator. You'll have to decide what is a "relative trickle" for your battery bank. I've seen it expressed as C/100 or 1% of you battery bank capacity. So that would be 2ah flowing into a 200ah battery bank. Your battery bank is not "fully" charged at that point but it is mostly charged. If you have solar then it would take over at this point.

Monitoring amps flowing in is really useful if you are "off-grid". The goal is to minimize generator or engine idling run time to save fuel and motor wear and tear and still adequately maintain your batteries. It is also useful to monitor amps flowing in if you are plugged in.

There are numerous single function digital ammeters including a shunt on eBay starting at around $15 or so or you can install a full function unit like a TriMetric by Bogart Engineering. http://www.bogartengineering.com/products/TriMetric

If you don't want to install a shunt for an ammeter and only want to monitor amps and volts then consider one that uses a hall effect sensor like this one found on eBay:

http://www.ebay.ca/itm/DC-Power-Volt...-/390531224237

The battery cable goes through the hole in the hall effect sensor. This particular sensor is the split type - the sensor opens to go over the cable so you don't even have to remove the cable. Check to make sure it can measure amps coming into the battery.

The Trimetric will tell you when you should be coming off of charge. You can set a voltage and amperage, and I think even a hold time once the criteria are met, IIRC. That is the point that the charging light starts to flash, indication fully charged. It is a useful feature, especially with the previously mentioned way the state of charge is calculated when charging (the charge efficiency setting) not being exact by any means.

[markopolo]

Mike - you're doing it right Just goes to show that even with an older Centurion charger and by running the van you can get your batteries fully charged (or very near full charge). I'm curious to know what voltage you get from your Centurion. You've been thinking of replacing it but maybe you don't need to as you don't keep your van plugged in.

[booster]

I just took a look at the Trimetric manual, and it would do the things Marko would like. To determine when the "charged" light blinks to show full charge, you have a setable voltage threshold that it has to go above, and a setable amp reading it has to go below before the it shows charged. There is also a setable hold time that you tell it how long after the charged conditions are met until the charged light blinks.

http://www.bogartengineering.com/pro...metric/manuals

[Mike]

I think that's probably why Trimetric is such a popular brand. I see people on different forums mention it as being a part of their power management systems.

[booster]

We are sitting in Jay Cooke state park near Duluth, MN after driving up yesterday. I had intentionally left the coach batteries go down to 80% before we left, and had the separator disconnected on the drive. The frig and other loads just about broke even with the solar on the very cloudy drive.

Plugged in when we got set up around 2:00pm and by 6:00pm, the Trimetric read charged (flashing light) and 98%. After overnight, it read 100% (13.5v and .2 amps into the 375AH wet cells. This looks like just what I would want it to do. The change in the charge efficiency from default of 92% up to 97% seems to have put it very near the best spot. It should be much more useful on the charging side of state of charge than it was.

We will continue to keep track of it as we travel the next couple of weeks.

[booster]

I have been trying to get a hold of Trojan since all this discussion started, and they finally called back today. Never did answer my e-mails or previous calls.

The tech guy I talked to was pretty much as confusing and contradictory as the literature and videos. I asked what voltage they like their batteries to be charged at and he said 14.7v. I asked if that was "daily" charge, or bulk, and he said they are the same thing. I asked why then are they listed a range of 14.1-14.7 (centered on 14.4) for bulk on the chart and 14.7 for daily. He then said they prefer the top of the range. I asked him where to get a charger that could be turned up to 14.7v on bulk, and he couldn't name any, and agreed they are almost all at 14.4/14.5v. I asked about the charge graph that shows the voltage going way up to somewhere in the 16+ volt range at the end of the charge, and he just kind of dodged so I asked if that was a mini-equalize at every charge cycle. He said most charger manufacturers have stopped putting manual equalizing on their chargers and have been trying to build a substitute into the charger to do the same thing. This might be that, who knows. I mentioned you couldn't do that on an RV as you would toast the electrical system, and he agreed. I asked about the video that said to equalize once a month vs the literature says once a year or when specific gravity got low or uneven. He said the once a month was for daily recharge applications like golf carts, but most of the new chargers can't do it anyway. I asked why they want 14.7 when the chargers and their older specs (and some current ones) say 14.4+/-.3v. He said they won't get totally full at less than 14.7v. I asked which is better, to let the batteries go down to 70-80% before charging as the literature says, or have them on float or trickle. He hummed and hawed on that one and said he didn't think it made a difference, and didn't know why they don't mention holding batteries on float charge anywhere.

Some observations I have seen on our batteries. Checking specific gravity after a 3 step charge and couple of day hold seems to fill them completely. Equalizing (unless it has been a long time) does not bring it up further, so they had to be full. The 14.4 volt bulk and then float hold had to be high enough. If I check them as soon as it goes into float they are not full. Can't say if the would be at 14.7v, but my guess is that they would be a lot closer. The Tripp-Lite charge we have will drop very quickly off of 14.4 volts on a full battery, causing very little gassing and stirring. If the battery is at 70-80% there is gassing for quite a while.

Just my opinion, but it appears Trojan may have had an increase in battery failures due to stratification and sulfation. With the equalizing options going away on chargers, and not many single stage chargers around any more, many folks don't get have the opportunity to equalize, or gas the battery, and wind up with earlier failures than if they did. The fact that they are recommending high voltage at the end of normal charge, in one of the videos they even suggested getting a seudo-equalize by charging you batteries full on the 3 step and then unplugging and replugging it in to get the higher voltage for a while on the full battery, and the higher bulk charge voltage would all seem to tie together. Back in the days of single stage, poorly regulated chargers, batteries saw lots of gassing, and it may actually have been better for them

All this would point out that, especially for daily charging where you don't get a good hold time at float, that the higher voltage recommended is probably a very good idea, if you can do it. Most chargers won't go there, and you would have to have enough solar panels to generate enough current to hold that higher voltage, so it isn't an easy thing for most of use. My guess is that if you have the time to hold the batteries on float for a day or two, you will get them full, as long as they aren't stratified. If they are, you need to equalize, if you can. Don't know what you would do if you can't equalize. It also MAY be better to let them run down a bit before recharging, rather than months of float, but I don't know how you would prove anything.

When I was trying to find a charger that equalizes a few years ago, several techs at manufacturers said they were going away from equalizing because too many folks were blowing up batteries and building from gas buildup. Too much liability. I suspect the chargers will try to continue to come up with ways to get the benefits of equalizing without the hazards. I think Trojan is kind of doing the same thing with higher charge voltage. Ctek claims all kinds of advanced technology to preserve and even renovate batteries, but don't really tell you what they do. We used our 8 amp Ctek on a 12+ year old Optima yellow that was in very poor shape, and after a few charge cycles, it did bring it back, so there may be something to it. I haven't seen that is does as well as a good equalize on the deep cycle wet cells, though.

I think we will know more about all this in a couple of years, when more of this sorts out, especially with all the solar going on things, which is probably one of the biggest chances of lower voltage, less than full, charging. We will continue to as we are, but be more aware of getting it onto the charger as soon as we can after being on solar for a while. I will also monitor the specific gravity while we are on solar more closely to see if we are losing capacity compared to other charging methods.

I can imagine that even a 5-10% reduction in life would be a huge expense for golf courses, and they would know it because they can keep good track of their batteries.

[Mike]

"Batteries and chargers are like a box of chocolates, you never know what you're gonna get"
I'm thinking I'm glad I didn't go to a 3 stage charger after all?
If my batteries don't explode, I think my head might.

[booster]

Originally Posted by Mike

"Batteries and chargers are like a box of chocolates, you never know what you're gonna get"
I'm thinking I'm glad I didn't go to a 3 stage charger after all?
If my batteries don't explode, I think my head might.

The three step charger question is totally speculation on my part. I think that when they came up with the multistep charging, and all the claims that it was better for batteries, they assumed that everyone would be able to have the 24-48 hours needed to get a full charge, every time. Back then, the multisteps often had equalization on them too. if you have the time to charge fully, they work very well and don't ruin the battery if you forget to shut them off on when the batteries are charged, so they do as they were intended. An occasional equalization and you had it covered. Now we have low charge amp and voltage solar, lots of boondocking with batteries not having the long charge cycles to bring them full, chargers without equalization, etc, so they may not work as well, or need to be run at the higher voltage that Trojan is suggesting.

I don't think it is limited to wet cells, either. A few years ago, Lifeline started to recommend equalization for their AGM batteries. Equalizing AGMs had always been an no-no because it would dry out the electrolyte and you can't remoisten it. They say to do it if the batteries start to lose capacity. Short charge cycles and low voltage probably causes similar issues in their AGMs as it does in wet cells.

[Mike]

All joking aside, maybe that's part of why I've never noticed that much degradation in charge capacity and recovery in my AGMs over the last few years. As Mark has said, I have single stage charging with an antiquated converter/charger, at higher amps/volts probably (I still haven't checked to see what's actually hitting the + terminals at the batteries), as a result of our style of travel which includes more touring. That said, I haven't ever run short of power, even when running furnaces, and TV, and lighting, and water pump, and so on in some pretty cold temperatures, to boot. I know they aren't indestructible, and they do appear to be slowly aging, as expected, based on the rates of discharge under our usual loads that I see when I remember to check with that simple charge level gauge, but they always seem to do what I need them to do, and that's what matters most to me.
This thread has discussed some ideas on what to look for in power maintenance systems and battery choices, including their care and feeding. It's all good.

[markopolo]

Re: The Centurion converter in Mike's RT, from a Centurion manual:

Your converter is designed to output a constant voltage of 13.5~13.6 volts

You wouldn't necessarily expect Mike's batteries to do well but they do and that is probably because they are AGM batteries.

AGM batteries have low internal resistance so they recharge faster than wet cell batteries. (up to 5 times faster)
AGM batteries have a very low self-discharge rate so they don't need to be recharged as often when in storage.
AGM batteries tolerate a higher float voltage than wet cell batteries.

I doubt the wet cell batteries would do as well on the Centurion.

The 12.7v at rest on his AGM's is probably not 100% charged (more like 95%). My AGM's will measure over 12.8v at rest fully charged.

-----------------------------------------------

Looks like the info we were looking at on the Trojan batteries is optimal (almost theoretical) maintenance but not easy to do in an RV with typically available equipment. If your equipment can't produce the 14.7v then hopefully you can compensate for that by charging longer. I'd do that with a float voltage I think. The battery should charge if the voltage applied is more than the battery's internal resistance.

Trojan SCS200 Data Sheet (wet cell)
Daily Charge 14.8 v
Float 13.2 v
Equalize 15.5 v

Contrast that to the Trojan 27-AGM data sheet:
Absorption Charge 14.1 – 14.7
Float Charge 13.5

No equalizing mentioned for the AGM.

I'm still a fan of keeping the batteries plugged in (on a smart charger) all the time when at home. I figure that keeping them charged or charging should prevent sulfation and preventing sulfation is probably easier than reversing it.

In lead-acid cells, the electrolyte (sulfuric acid) participates in the cell’s normal charge/discharge reactions. As the cells are discharged, the sulfate ions are bonded to the plates — sulfuric acid leaves the electrolyte. The process is reversed when the cell is recharged.

[Mike]

OK, OK, I'm going with what you said.
I always knew my crappy charger was ideal for AGMs.
And you're probably right about 95% charged.
Based on our usage and states of charge/discharge noted when I remember to actually check.

[booster]

Earlier, it had been mentioned that Interstate had some different voltages, also. I just found a chart for their recommendations, and they are also recommending a very high voltage at the end of the charge, before the float voltage. They are at over 15 volts, similar to Trojan, and within .1 volt of what the say for equalization.

It certainly does look like some variation of equalization substitute is going to be in most charge profiles in the future, if they can keep from frying our electronicss

http://www.batteries-faq.com/activek...p?questionid=1

[booster]

Getting back to battery charging

I finally got the e-mail answer from Trojan, with a very polite explanation it must have gotten lost in cyberspace, as the survey doesn't go out until after the message is sent. Good to know.

Here is the e-mail

The 14.8V "daily" charge is the same as the "bulk" charge. This value is the "ideal" charge voltage that Trojan would like for their batteries to be charged at. The bulk or daily charge step is where the majority of the charge is put back into the battery. During this step or stage of the charge, the charger's maximum output capability should be from 10-13% of the total capacity of the battery bank (amps) to allow the batteries to be recharged in a period of time greater than 10 hours. When the recharge period of 8-10 hours is needed, then 20% can be used. The range (14.1V - 14.7V) which is listed for renewable energy application "absorption" charging is listed as a range for reasons such as having a controller that doesn't allow adjusting set-points. The lower the voltage setting means longer charge times. All will depend on where the specific gravity of the battery is at the end of charge. The gravity tells you if you need to adjust the voltage settings or time settings. As for storing batteries, batteries can be float charged, but we recommend 13.2Vm, which is a safe voltage where there is very little to no gassing taking place in the battery which leads to low water usage. The higher the float voltage, means the possibility of more water usage, therefore water additions may be more frequent. 13.5V can be used, but you will have to frequently check batteries for water usage. This is part of maintaining your batteries. Remember, that these batteries are not maintenance-free batteries.