Interesting battery analysis
Printed From: R-pod Owners Forum
Category: R-pod Discussion Forums
Forum Name: Reviews and General Information
Forum Discription: Find r-pod reviews and new product announcements here
URL: http://www.rpod-owners.com/forum_posts.asp?TID=15057
Printed Date: 04 May 2024 at 9:59pm
Software Version: Web Wiz Forums 9.64 - http://www.webwizforums.com
Topic: Interesting battery analysis
Posted By: StephenH
Subject: Interesting battery analysis
Date Posted: 20 Nov 2021 at 8:17pm
|
I came across this video about comparisons of different types of batteries. It would be something good to view if one is needing to get a new battery. The bottom line is that over the lifecycle of the batteries, LiFePO4 batteries are cost effective.
https://www.youtube.com/watch?v=iy3hga_P5YY - https://www.youtube.com/watch?v=iy3hga_P5YY
-------------
StephenH
Happy is the man that findeth wisdom,...
http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS
|
Replies:
Posted By: offgrid
Date Posted: 21 Nov 2021 at 8:47am
I just watched that video. I like Morton's videos in general because he is well grounded in his electrical engineering. And I agree with the overall conclusion, which is that Li batteries are more cost effective than PbA's one a life cycle basis, and also that expensive AGM's are not cost effective relative to deep cycle flooded golf cart batteries. Finally, I agree that self heating Li batteries are a waste of energy, much better to keep them in a space that is already heated anyway, or at the very least to insulate them well.
So, here are the areas where I disagree.
First, saying that PbA's can't be used for energy storage systems because if their temperature sensitivity is silly Of course they can, what does the think has been used for off grid energy storage for a century now?
Second, he is shilling for Battle Born which is probably the most expensive Li battery alternative available. There is no test alternative with a more cost effective Li battery presented, the implication being that Battle Born is representative of all Li batteries. It is not and Morton is well aware of that. In fact, his first Li RV installation used salvage Tesla Li batteries, which are far less expensive than Battleborne is. At some point he picked up Battle Born as a sponsor and the bias shows.
Third, proposing to use energy production rather than amp hours as the metric for battery comparisons is really only valid for inverter loads. For direct DC loads (like fans, lights, furnace fans, and water pumps IOW most of our DC amconsumption) amp hours is a better metric. Why? Because they either run or they don't. No one cares if the fan runs a little slower because the voltage is lower, it's doing its job, and in fact using less amp hours at the lower voltage provided by the PbA battery, thereby saving energy. It's annoying when someone proposes using a metric simply because that makes one technology look better than another.
4th, measuring capacity to 12.2V under cold or high discharage conditions is unfair to the PbA battery. I loved it when the Battle Born guy said that they were just using the PbA manufacturers' one specs against them. Dead giveaway that someone is playing soecsmanship games.
In reality the Peukert effect and temp dependence while valid is not taking into account that both PbA and Li batteries have a coulombic efficiency of nearly 100% (not counting losses durung float or equalization after the battery reaches full charge).. Meaning that you can get all the amp hours out that you put in. You just need to take them out slower or set a lower ending voltage if it's cold and/or you have a higher discharge rate.
You can model a battery (either type) as a voltage source in series with a resistor, the resistance of which gets higher at with lower temps. So if you run at a high discharge rate and then go to a low discharge rate you will get the essentially the same capacity in amp hours out of the battery as if you ran at the low discharge rate the whole time. Ditto with discharging at a cold temp and then warming the battery up, the capacity is still there. It's not like the coulombs of charge stored in the battery plates magically disappear when it gets cold and/or the discharge rate increases, it's just that it's harder to get out and you have to set the end voltage lower to get it. That doesn't harm the battery plates because you are not changing how many coulombs you are removing.
Solar charge controller designers, myself included, have know this for decades, the good ones can be set to change their end voltage (and float voltage) based on battery temp and discharge (and charge) rates.
5th. Morton does not mention the cost of changing out charging electronics when looking at the economics if converting to Li batteries. That significantly changes the decision making process, as new shore power chargers, DC to DC converters of alternator charging, and potentially new solar charge controllers, can easily cost more than the batteries themselves do.
6th. PbA batteries are generally acknowledged to require initial formatting in order to reach full capacity while Li batteries are not. It's not clear from what I saw that this was done with the PbA's in the experiment Morton did but it could explain at least part of the low capacities measured in the test.
Morton did his first Li conversion to have much more capacity without increasing weight, and in my opinion that remains the most compelling reason to stop using PbA batteries. If you don't need high capacity and are ok with the weight of PbA batteries, then inexpensive flooded golf cart batteries remain the best option for most folks. And if you want to make the switch then there are much cheaper alternative than Battle Born.
-------------
1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
|
Posted By: StephenH
Date Posted: 21 Nov 2021 at 5:19pm
|
I agree. I don't have a Battle Born battery because I did investigate the alternatives and opted for a much lower cost battery both times, the 100 AH and the 200 AH ones. I agree also that the costs of changing converter and installing a DC to DC charger can be significant, having done so.
Weight was a big factor in my decision to change. Also, the ability to have more usable power from the LiFePO4 battery is significant since I can draw it down lower than 50% without risk of shortening its lifespan.
I figured you would provide a good analysis of the video. I am keeping my batteries in spaces where I don't have to worry about low temperatures. The 200AH battery does state that it has a heater that activates at temperatures of under 0C (32F) and will heat to 10C (50F). It will also has low ambient temperature cut-off for charging and discharging. Since I keep it in a space which is protected, I should not have issues with cold temperatures.
I'm also looking forward to the much longer life of the LiFePO4 battery. Our 6V batteries lasted about 5 years before I noticed that the cases were starting to swell. I had always tried to keep them well maintained, but even so, the maintenance free aspect of the LiFePO4 battery is attractive also.
-------------
StephenH
Happy is the man that findeth wisdom,...
http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS
|
Posted By: offgrid
Date Posted: 22 Nov 2021 at 4:52am
Agreed, you were an ideal candidate for the Li conversion.
I would also mention that an expectation of keeping your rpod long term is key as well. If you don't plan to keep it at least another few years then it's not a great idea to invest in Li batteries, the average buyer wont understand and/or need the benefits so won't be willing to pay you extra for them. That's why I didn't convert, I was not planning to keep the rpod long enough. Also my objective would have been to be able to run an a/c overnight during campground quiet hours, which would have required at least 5 kwh capacity and a change to 24Vdc and a a minisplit for efficiency. A high
time and cost conversion for sure.
Some higher end trailers are now offered with Li battery systems from the factory. As that becomes more common the economics will change, if you don't have to change out all the charging systems there isn't a good reason not to go with Li from the beginning. The ev manufacturers are now sourcing Li batteries for around $100 per kWh so they will soon be on par with all but the cheapest PbA's in initial cost.
-------------
1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
|
Posted By: StephenH
Date Posted: 22 Nov 2021 at 1:21pm
I tried to make my conversion so that if and when we change trailers, I can revert the RPod to lead-acid and move the LiFePO4 equipment to a new trailer. I still have the WF-8955MBA and the rest can be removed and the connections switched to support the battery on the tongue again.
-------------
StephenH
Happy is the man that findeth wisdom,...
http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS
|
Posted By: offgrid
Date Posted: 22 Nov 2021 at 7:41pm
Good idea, your electrical system is likely to outlive the trailer itself.
-------------
1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
|
Posted By: Old Man Running
Date Posted: 09 Dec 2021 at 11:15pm
|
I am considering replacing my current Lead Acid 12V battery to the LiFePO4 and have two basic questions. I currently have a 2021 RPod-196 and was wondering if I need to replace the Charge Controller currently installed in the RPod. Second question is whether the LiFePO4 can be charged with a solar panel, and if yes, do I need a solar panel with any special requirements?
|
Posted By: StephenH
Date Posted: 10 Dec 2021 at 9:49am
Okay. A lot depends on what model converter is installed. Check your manual to see whether there is a switch to enable you to set it for proper charging of the LiFePO4 battery. Since it is 2021, it is more likely than it was with our 2016. As for solar panels, the charge controller is the key there. The panel just produces electricity. The charge controller applies it. I chose a Renogy system that was negative ground to match the negative ground of the RPod. I saw that some panels were available with positive ground. Offgrid would need to answer but as for me, I avoided the positive ground models.
-------------
StephenH
Happy is the man that findeth wisdom,...
http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS
|
Posted By: Old Man Running
Date Posted: 10 Dec 2021 at 1:24pm
|
Thanks Stephen for your timely reply. I am wondering where the charge controller is located. I have located the Power Converter with Panel, which basically contains the circuit breakers for the 120 volt AC power and fuses for the 12 volt DC power. I assume that the charge controller is a smaller box, but not sure where it could be installed. Any thoughts?
|
Posted By: StephenH
Date Posted: 10 Dec 2021 at 3:06pm
Is your RPod equipped with solar or just solar ready? If it is the second one, then the wiring is in place, but things like solar panels and charge controllers are not. Since I have no idea about 2021 models, I really can't help you much.
-------------
StephenH
Happy is the man that findeth wisdom,...
http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS
|
Posted By: Old Man Running
Date Posted: 10 Dec 2021 at 3:42pm
|
After contacting the WFCO tech services, I learned that to install a Lithium ion battery I must replace the existing converter, which consists of the 120 volt AC circuit breakers and the 12 volt DC fuses. He further indicated that the term Control Charger and Converter were really the same thing. He indicated that I must replace the existing model WF-8735P with model WF-8735-PB-LIS. The newer model provides the option to switch from Lead-Acid to Lithium to AGM. The only problem is that the sources of supply are out of stock, so my project may be put on hold until the parts become available.
Also, my RV is pre-wired for solar, but from what I understand you will probably want to connect the solar panel directly to the battery. I do not intend to make the solar panel(s) a permanent installation, but prefer a mobile arrangement.
I hope that the information I have provided above will be of use to other Forum members.
Thanks for your help, it was most appreciated.
|
Posted By: StephenH
Date Posted: 10 Dec 2021 at 4:28pm
|
One correction: You do NOT want to connect the solar panel directly to the battery. It needs to go through a charge controller. The WFCO information is okay as concerning when you are connected to shore power. However, the WFCO converter does not act as a charge controller for a solar panel.
There are two types of charge controllers you can use. PWM and MPPT. See this article for an explanation of what those letters mean: https://www.generationsolar.com/charge-controllers/solar-charge-controller-types-shunt-pwm-mppt/ - https://www.generationsolar.com/charge-controllers/solar-charge-controller-types-shunt-pwm-mppt/
-------------
StephenH
Happy is the man that findeth wisdom,...
http://www.rpod-owners.com/forum_posts.asp?TID=7712 - ouR escaPOD mods
Former RPod 179
Current Cherokee Grey Wolf 24 JS
|
Posted By: offgrid
Date Posted: 10 Dec 2021 at 10:00pm
Re positive vs. negative grounding, that refers to which polarity in the system wiring is connected to the trailer and tow vehicle chassis. That is the negative buss in all but some now antique cars. So yes you need a solar charge controller that can be negative grounded, meaning the negative conductors in the circuit are connected together and never opened, so that the charge controllers battery voltage regulation action is done on the positive side of the circuit.
There is sometimes confusion about positive vs negative grounding effects on the solar modules themselves. Some solar modules operating at high voltages (as in a big residential or commercial grid tie system) need to be positive grounded to protect them from potential induced degradatiin (PID) which occurs via leakage of ions through the glass and plastic encapsulation of the solar cells. While PID can be a big deal with some solar module types operating at high voltages under some conditions it's really a non issue for our little 12V power systems.
Re connecting a solar module directly to a battery +1 on not doing that. First and foremost, there has to be an appropriate fuse or circuit breaker protecting the wiring from the battery to the solar module. That fuse should be placed in the positive conductor (to maintaing negative chassis grounding as discussed above) as close as possible to the battery because the battery is effectively an unlimited source of current if you short it out. The solar module can only produce as much current as it has sunlight shining on it so it doesn't need a fuse (unless you have more than 2 parallel connected solar modules which we don't usually need to get into discussing here).
The other reason not to direct connect is that you can overcharge your battery which especially in the case of Li batteries can cause a really nasty thermal runaway effect resulting in a fire.
-------------
1994 Chinook Concourse
1995 RV6A Experimental Aircraft
2015 Rpod 179 - sold
|
Posted By: Old Man Running
Date Posted: 11 Dec 2021 at 12:19am
|
Thanks Stephen for keeping me straight on connecting the solar panel directly to the battery. I misspoke on this issue. I do know that there needs to be an interfacing charge controller between the solar panel and the battery. When I said that I intended to connect the solar panel directly to the battery, I meant that I did not intend to use the RV's prewire connection. Thanks for the link to the solar panel article and thanks to Offgrid for his detail explanation.
|
|