In the other thread we were discussing how the AGS works, and what the battery voltage should be to set the AGS for start.
My question is, how do you determine exactly what voltage to set the AGS trigger to start? 12.18VDC was shown to be the 50% mark for my batteries. Last night I left the coach unplugged to let it run down and this morning it's still at 12.3V. If I turn on some loads (AH heating 2 zones, microwave fan, some lights), I can get it to drop to 12.0V under load. Then I turned the loads off and the battery voltage recovered to 12.3V again. If the AGS was set for 12.18V, then it would have started while under load.
So is the best course of action to use the 50% voltage (12.18V) as my trigger point, which will likely fire the generator anytime there are decent loads applied, or pick a lower number that corresponds to the loaded voltage?
I would do a lower number UNLESS the "monitor period" is 5+ minutes. Yes, if voltage below 12.18 for more than 5 minutes, you want the generator.
But, I don't know the "monitor period" that triggers generator start.
That WILL influence the trigger voltage.
However, while our last coach had an AGS, I disabled it. That is MY job.
We do not use the AGS anymore. But I think it needs to start when the resting voltage gets below the 50% level. That said the voltage could be at 12.2v and drop to 11.8v if you start the microwave or turn on a toaster. That may stay there or recover a bit once startup loads are relieved. The smarter AGS systems will start when the voltage gets below a set voltage for a set time duration. This reduces unwanted starts due to startup loads. A coffee maker or a toaster are just big loads. And then set a minimum run time for 2-4 hours. If run time is set to shut off when a certain voltage is reached the generator may only run for 15 minutes. Some of the smarter AGS systems will start the generator at a specified SOC and run until a higher specified SOC is reached. This takes voltage swings out of the process.
If your resting voltage (no big loads) for AGM or GEL or wet batteries gets below the 50% SOC level, whatever voltage that is for your batteries, you should be recharging. And that should go back to 100% SOC especially for AGM and GEL batteries to preserve maximum life cycles and charge capacity. If you have 3 8D batteries a couple hours on the generator will not do that.
I'm purposely putting load on the batteries today to figure out how long it takes for the batts to recharge to floating, while under some load. The kinds of things I'd be using while boondocking, as a worst case scenario. I can set the delay start time from 0-7 minutes with the BCM-12. I believe it's set for 3 minutes currently.
Lifeline gives you more technical stuff than most battery manufacturers. From the Lifeline technical manual:
5.4 Charging
Charging Lifeline® AGM batteries is a matter of replacing the ampere-hours removed during discharge plus a little extra to make up for charging inefficiency. The ampere-hour input necessary for a full recharge depends on the depth of discharge, rate of recharge, and temperature. Typically, between 102% and 110% of the discharged ampere-hours must be returned for full recharge. If the recharge is insufficient, the battery's state of charge will gradually "walk down" as it is cycled, resulting in sulfation and premature failure.
The recommended method of charging Lifeline® AGM batteries is to use a 3-stage charging profile. In the first stage, a constant current is applied until the voltage reaches a pre-set limit. The first stage is often called the Bulk charging stage.
In the second stage, the voltage is held constant at the same pre-set limit until the charging current tapers to a very low value, at which point the battery is fully charged. The second stage is often called the Absorption charging stage. A voltage setting of 14.3 volts ± 0.1 volts (7.15 ± 0.05 volt for a 6-volt battery) should be used when the battery temperature is 77°F (25°C). The battery is considered to be fully charged when the current drops below 0.5% of the battery's rated capacity (0.5A for a 100Ah battery). The absorption stage will typically last 2 – 4 hours before the current reaches this level.
In the third stage, the charging voltage is reduced to a lower value that minimizes the amount of overcharge, while maintaining the battery at 100% state of charge. This third stage is often called the Float charging stage. A float voltage of 13.3 ± 0.1 volts (6.65 ± 0.05 volts for a 6-volt battery) should be used when the battery temperature is 77°F (25°C).
The following table provides recommended absorption times for Lifeline® Batteries: Table 5-2 Recommended Absorption Times
Average Depth of Discharge (DOD) Absorption Time
Less than 30%. 2 hours
30 – 50%. 3 hours
More than 50%. 4 hours
The absorption time may need to be fine-tuned from these values to assure the batteries consistently reach full charge per the criteria given above (charging current is less than 0.5% of battery's rated capacity).
The charging current during the Bulk stage should be set as high as practical; higher current levels mean faster recharge time and less time for the plates to become sulfated. Due to the low impedance design, Lifeline® batteries can tolerate in-rush current levels as high as 5C (500A for a 100Ah battery). The time to reach full charge at temperatures in the range of 20- 30°C (68 to 86°F) can be estimated from the following equation:
Charge Time = [(DOD/100) x Rated Capacity (Ah) ÷ Output of Charger (Amps)] + Absorb Time.
For example, charging a 100Ah battery at 40% DOD with a 25A charger would take: [(40/100) x 100 ÷ 25] + 3 = 4.6 hours to reach full charge.
If a 10A charger is used, it would take:
[(40/100) x 100 ÷ 10] + 3 = 7 hours to reach full charge.
Note that this formula is approximate and the full charge state should be verified using the criteria given above (current drops below 0.5% of rated capacity). If the recharge does not return 102 to 110% of the discharged capacity, the battery's state of charge will gradually "walk down" as it is cycled leading to premature failure. Therefore, it is important to verify that the battery is not being undercharged.
For a 50% DOD on 3 8D 255 amp hr batteries the recharge time with a 100 amp charger is about
50/100 x 765 ÷ 100 + 4 = 7.8 hours.
With a 120 amp charger it is 7.2 hrs.
Other battery brands might be different but this is a good reference.
I just got done going through the process. With the loads removed from the batteries when the generator came online, they were reading 12.3V. They had been at 12.1 with loads applied previous to the generator starting, which is the 50% DOD value. It took 3hrs and 15 minutes for the generator to charge the batteries to the float portion of the Xantrex charging cycle. The Freedom SW3000 will charge at 150A max. I had also turned off the solar charger, so that this is only based on what the generator/charger would do.
I've now set my run time to 3hrs and 15 minutes. If it's daytime and the solar is producing, the batteries should be charged sooner, but always before the time expires.
Based on the numbers above, it sounds like I'm not actually getting to the 50% DOD in the first place. Next weekend Offthegrid solar is installing a Victron BMV-712, so I'll be able to monitor this directly based on Ah in and out very soon.
If your batteries are older and have not been regularly fully recharged then they are likely suffering from loss of capacity as discussed in the Lifeline article above. Do the math backwards in the equations above to get a better estimate of actual capacity as they are now.
I would like to reset the generator run time and voltage shut down but I have no
idea and I can't find any information on how to do it. Anyone got any information
on how to do it.
What AGS do you have (make and model)?
BCM12 is this it
The adjustment procedure starts on page 11 of the manual.
BCM-12 manual (http://www.foreforums.com/index.php?action=dlattach;topic=24398.0;attach=30951)
Keith I can't seem to open it. It could be I have a really slow Wifi
How about these?
Thanks Keith those look great.
Thanks Keith I reset the high voltage shutdown higher and tried it out tonight and that
is working and I turned down the length of time it runs and I will play with it until I get
it where I want.
Revisiting this after having the Victron BMV-712 installed. I believe you have one of these too Roger, so perhaps you have some input here.
I fully charged the coach from shore power, then unplugged yesterday morning and let it sit idle. The solar was putting some power into it to help maintain, but slowly drops in voltage. Overnight, it has dropped to 12.22V, but the BMV is showing 71% capacity left. It has measured the consumed Ah as 285Ah. My 3 x 8D's are supposed to be 765Ah total. Since the Lifeline documentation shows the batteries are 50% at 12.18V, does that indicate that the batteries no longer have 765Ah available, and this value should be adjusted so that when the batteries reach 12.18V, the BMV is showing 50% SOC?
Keith,
Look through the book that comes with the BMV-712. There are a lot of settings.
Lifelines when new have a rated 20hr capacity of 255 amp hrs each. So for three that is 765 amp hrs. If the BMV has measured a net outflow of 285 amp hrs you should have (765-285)/765 = 63% left. So something is not quite right. It can take as many 24 hrs to fully charge a lifeline, maybe more with three. Be sure they are fully charged before resetting the 100% SOC level. See the Lifeline tech manual for more charging info.
If 285 amp hrs consumed is 71% SOC, that implies a 100% SOC capacity of about 982 amp hrs. Something is not quite right here either. A Lifeline battery is considered fully charged when the charge rate falls below 5% of the rated 20 hr capacity. That is about 37 amps for 3 Lifelines in parallel. As commonly wired in FTs, the battery in the middle will get 15% less charge and discharge than the end batteries due to internal resistance of the batteries.
It is common for any AGM battery to lose capacity over time. The only way to prevent this or minimize this is to very methodically return to a 100% SOC every charge cycle.
12.18v at a SOC of 50% is a resting voltage at little or no load, something the batteries in your coach rarely see.
Had a Buddy set my run time for me today so it is all set up. The math was too
complicated for me. I set it for just over an hour and that should work for my
batteries. The only time I will leave it on automatic is if I am leaving the coach.
When I broke down a 3 weeks ago, I was going to leave it all night so I tried it
and found it would only run a few minutes so that's why I got into it. Now it's
set .
Roger has made this statement before and he has posted information from the Impact Battery blog "How to Charge Lead Acid Marine and RV Batteries in Parallel" in an attempt to justify his statements. However, neither he nor Impact Battery have provided a scientific explanation nor test data to support those claims. Without actual test data using new batteries from the same manufacturer to support those claims they are quite difficult to believe. I think nearly all of us realize that simply posting claims in a blog doesn't make the information accurate.
Pretty good explanation and how to balance charging battles in parallel. Makes sense but need even number of batteries. I have three start and house batteries so would change things. Guess you could swap the position of the ground and power on your battery cable. Mine are actually long enough to do that . Interesting
Scott
https://www.solar-electric.com/lib/wind-sun/Iota_balanced_charging.pdf
Interesting claims—but no actual battery information and no test data to support those claims.
So, what is your solution?
"Method 1 for Balanced Charging" shows the same total cable length (and number of connections) when you consider the current loop from the charger positive through each battery to the charger negative.
So a couple of different articles suggest that three or four batteries connected in parallel with charging and loading coming off opposite corners as shown in Method 1 result in an imperfect charge and discharge load on the center battery or batteries. Even with exactly equal cable lengths, perfect crimps, equal connections the internal resistance of batteries causes a difference in what the center batteries see in amps available to charge into and discharge out of the center batteries. This will have a detrimental effect on the life expectancy of the center batteries compared to the outer batteries.
I am not sure what source for verifying this information will satisfy Mr. Osborn. Probably none. He hasn't presented a source in opposition. Doing as he suggests in Method 1 is not, as stated in both referenced articles, an optimal balanced solution. It works, it is just not as good as it could be.
My conclusion after reading many articles like these and talking to system designers was to wire each battery in parallel with equal length cables (as equal as practical) to common bus bars. And from them to all other charge sources and loads with the negative side going through a shunt to monitor power flow.
Each of us can consider what we read, learn what we can, and understand and choose a way forward for ourselves. It appears that some methods may be better than others. Pretty much the way it is with everything.
The way the house and start batteries were wired from the factory was adequate for production reasons but likely not ideal for battery life. It will work, maybe just not as well.
I look for actual test data to support claims that are made. Neither Roger nor the sources he has cited has provided data to support the numbers they have claimed. Where are the data to support the claimed unbalance numbers rhey have stated as facts?
David I had never really given it much thought or for that matter concern. I can't present any actual hands on information, but the equal charge amperage seems it would be beneficial to battery life. That being said with 4 OOOO cables for charging purposes I would think they would be almost identical at that low charging amperage. However since you brought this to my attention and helped force my simple mind to think about this I am now compelled to put the main cables on the inner/center battery posts to attempt to be more in balance. Who knows if it will make any difference but it makes sense to me. My cables are on 3/8 posts so swapping would be little effort. Center battery will have no cables so hope it can handle the extra charge. Output shouldn't change. I will report back with my findings in 5-8 years. Again interesting
Scott
For those actually interested in the engineering behind the issue, here is some light reading from Victron. In theory they have some idea what is going on.
https://www.victronenergy.com/upload/documents/Wiring-Unlimited-EN.pdf
It is too big to attach.
Scott, connecting your plus and minus to the center battery and then from there short links to the outer batteries will unbalance charge and discharge even more than connecting across opposite corners. Your center battery offers the least resistance to charge and discharge and will do most of the work and suffer the most wear and tear.
I'm no expert here, but was talking with a friend about this today. We were of the opinion that connecting each battery individually to a bus bar, with equal length cables, would be better than connecting the batteries themselves together. To do this, I'd use a bus bar like this:
Lynx Power In - Victron Energy (http://www.victronenergy.com/dc-distribution-systems/lynx-power-in#pd-nav-image)
Do you agree Roger?
Keith, the Victron Lynx power distribution components are quite nice. That can be used for battery connections on one end of a distribution chain and all other loads and charge sources on the other with a battery shunt and main switch and fuse in the middle.
Plus sides are modular design and expandability. They offer the opportunity to fuse each incoming battery and on each outgoing load or incoming charge connection downstream.
The downsides are cost and size. Each of these is almost 12" long. I just didn't have enough room to connect my distribution system this way but I have all of the same functionality except for individual battery fusing which would be pretty easy to add using a Bussmann MRBF Fuse and holder at each positive battery terminal.
If you look at the installation section of the user manual they show equal length cables for each plus and minus connection from the battery to the Lynx distribution box. The same is true for a bus bar connection. This picture was before cleaning up the smaller wires. I cut all of my 34" cables at the same time, maybe 1/8" variation, and then attached all the lugs. That is close enough to all being equal length.