Low Cost Lithium Battery Motorhome Conversion

Raj174 · December 2014

Re: Low Cost Lithium Battery Motorhome Conversion

Hi DoubleDD,
I have read a good bit about the Stark Power batteries. Built in BMS is a plus and the batteries also shut down at 20% capacity, which is very desirable in the event of improper low voltage disconnect settings on the inverter. Series connections are always preferred, but I would say especially for LiFePO4. The Stark Power 12 V batteries are actually a series/parallel battery pack with management. I think that it would be better if all the cells in the system were under the same management, i.e. 100 AH battery instead of two 50 AH batteries (less headache checking battery voltage differences), but that's just me.
If you do set up 2 in parallel make sure your cable lengths are the same and monitor the voltage of the batteries to make sure they don't drift apart. The only other thing is charging voltage. Although Stark Power says it is a drop in replacement for a lead acid battery and has over charge protection, I would not use lead acid charging parameters on these batteries. I would charge at 14.1 volts and set float to a little lower than that. I would not discharge to lower than 12.4 volts, even though the management will shut the battery off at 20% capacity. Just my opinion.
Good luck
Rick

DoubleDD · December 2014

Re: Low Cost Lithium Battery Motorhome Conversion

Raj174 wrote: »

Hi DoubleDD,
I have read a good bit about the Stark Power batteries. Built in BMS is a plus and the batteries also shut down at 20% capacity, which is very desirable in the event of improper low voltage disconnect settings on the inverter. Series connections are always preferred, but I would say especially for LiFePO4. The Stark Power 12 V batteries are actually a series/parallel battery pack with management. I think that it would be better if all the cells in the system were under the same management, i.e. 100 AH battery instead of two 50 AH batteries (less headache checking battery voltage differences), but that's just me.
If you do set up 2 in parallel make sure your cable lengths are the same and monitor the voltage of the batteries to make sure they don't drift apart. The only other thing is charging voltage. Although Stark Power says it is a drop in replacement for a lead acid battery and has over charge protection, I would not use lead acid charging parameters on these batteries. I would charge at 14.1 volts and set float to a little lower than that. I would not discharge to lower than 12.4 volts, even though the management will shut the battery off at 20% capacity. Just my opinion.
Good luck
Rick

Thanks for your thoughts.
I was planning on wiring the batteries as outline in the pic below so I could add additional batteries easily. All wires would be 2/0 welding cables (18") from battery to post. I'm still trying to find the best MPPT solar charger for this application. Any suggestions?
Wouldn't the individual BMS keep each battery in sync? By setting the cutoff for discharge at 12.4 volts, what would that work out in % of used AH in a 50AH battery.

Would you recommend going down the path of LifePo4 GBS/Winston cells with a central programable BMS instead?

Attachment not found.

DoubleDD

Raj174 · December 2014

Re: Low Cost Lithium Battery Motorhome Conversion

DoubleDD wrote: »

Thanks for your thoughts.
I was planning on wiring the batteries as outline in the pic below so I could add additional batteries easily. All wires would be 2/0 welding cables (18") from battery to post. I'm still trying to find the best MPPT solar charger for this application. Any suggestions?
Wouldn't the individual BMS keep each battery in sync? By setting the cutoff for discharge at 12.4 volts, what would that work out in % of used AH in a 50AH battery.

Would you recommend going down the path of LifePo4 GBS/Winston cells with a central programable BMS instead?

Attachment not found.

DoubleDD

Hi DoubleDD,
I wish I could recommend a charge controller but I am not familiar with 12 V equipment. I would look for one that can be configured to charge your LFP battery. As far as an inverter goes I would want one that I could configure a low voltage disconnect setting. I believe the bigger ones have this. I don't know about those under about 2000 watts.
The battery management for each battery is separate and distinct and not in sync, and the voltage in a parallel connection is likely to drift and become unequal. If you do it you need to monitor it. It seems like, as much as you use the RV it shouldn't be a problem. Just check it before you take off for your trip.
Also, you spoke of charging the batteries from the panels between RV use. I don't think you need to. I would just leave them at about 80% capacity and they would be good for about a year, dropping to about 50% capacity. Another good thing about lithium batteries, they do not need to be charged once a week or even once a month. They are happy at middle capacity. Another reason for this is that component failure could cause expensive equipment and/or battery loss. I would call Stark Power and ask them about length of time between charging and also about the automatic shutoff at 10.5 volts. That is 2.63 volts per each cell and is dangerously low in my opinion. However they do warranty the battery for a year.
I would not recommend using individual 3.2 volt prismatic cells if you are not willing to put in the time and effort to get a really good understanding LiFePO4 technology and chemistry. That means spend a month or two reading many threads, watching videos and synthesizing all that information into an understanding that you can use to determine what you want, put it together and diagnose issues. If you do not want to do that then I recommend a preconfigured battery pack with BMS under warranty.

Rick

westbranch · December 2014

Re: Low Cost Lithium Battery Motorhome Conversion

There are 8 pages of threads on this forum if you search for LITHIUM or LIFEPO4.. Lots of information to digest..... hth

CraziFuzzy · December 2014

Re: Low Cost Lithium Battery Motorhome Conversion

You know, I still love Lead Acid cells. That does not equate to a love of lead acid batteries though. Even the OP's 'Lead Acid Nightmare' was not really the result of the chemsitry, but much more a result of configuration. Having a single cell in a 3 cell battery fail is costly, because you end up having to replace 3 times what failed. Having any cell fail in a battery bank with a parallel configuration is even worse, as it can easily kill the other good string.

A lead acid bank configured in the same way the LiFePo4 are configured, single string of individual cells, would have all the advantages of lead acid (ruggedness, simplicity), with most of the the perceived advantages of LiFePo4 (bank life cycle). The only REAL advantage Lithium based chemistries have is energy density. They really are a LOT lighter and smaller than their lead acid equivalent, but that is not what the OP was looking for.

Very few things can beat a bank of 6 individual lead acid cells for reliability and lifetime. Look what kind of live submarines get out of their lead acid batteries. There is nothing inherently different between them and any other deep cycle lead acid battery, other than size, and an air agitation system (to fight stratification that the bigger size causes).

Columbo · October 2015

Just want to thank all of you for your input. I will be buying a trailer within the next year, and full timing as soon as I retire. I've been researching LiFe Po4 batteries and solar systems as I plan on doing a lot of boondocking. When I finalize the plans for my system I will run it by everyone for input. Thanks again! BTW, I am a auto repair shop owner and will be happy to help anyone with mechanical problems.

PNjunction · October 2015

Columbo - when researching, just keep your non-applicable application filter on!

Despite the massive thread depths and amount of information of nearly biblical proportion out there, OUR APPLICATION is vastly different from what you'll get from EV, or RC modeling users. For them, operating at the extremes is the norm, frequently not even using LFP but some other li-ion chemistry, and when it comes time to advising us about LFP batteries, they miss the forest for the trees.

That is, they tend to overcomplicate what is actually very very simple for us, and bring unnecessary complexity with them to our application. Either that, or the cheapskates that only think in terms of cycle life without taking into account the *other* operational characteristics that can be highly desirable.

Avoid the fighting - much of which is not about LFP at all, but merely trying to win an argument. Unfortunate, but true just about everywhere, not just here.

inMichigan · October 2015

We're coming up on 18th months since FEEDHORN made the original post. How's it charging out there?

MarkC · October 2015

feedhorn said:

Re: Low Cost Lithium Battery Motorhome Conversion

Six Month Report:

All is well with my Lithium conversion everything is working perfectly.

These long days show my DoD of only 25 Ah over the short night time.

Battery is usually fully charged by 9 AM.

With only 100 Ah capacity it more than covers what the 4 golf cart batteries did.

I would expect that I would need 1000Ah of lead acid to give the same charge/discharge performance as these lithium do.

With no maintenance on the lithium battery, its easy to forget you even have a battery just perpetual free electricity always at the proper voltage.

I would definitely do the conversion again and am now sure that I don't need any additional capacity.

FH

feedhorn;
This post is over a year old. Can you report progress? I expect many of us are in the process of convincing ourselves to give Li technology a substantial "test" at least. I'd really like to try a drop-in replacement for my 4 - 155AH Trojans in my golf cart that gets used every week or so and can be quickly hooked up via Andersons to my emergency "off-grid" system (along with a spare set of 4). I likely have sufficient 120V AC to recharge daily via my SMA SPS system (sort of solar) - eventually moving to direct solar CC. I have a Shorai (and charger) for my dirt bike that has been flawless for almost 3 years now - a major improvement over sealed lead acid for which I'd been SOL in the middle of Colorado outback several times over 3 years - think I've forgotten how to kick-start!

Reed · October 2015

There were a few folks who wondered if LFP is cost effective. We are primarily boondockers (and mootchdockers, aka, parking in our kids' backyards when we visit) and have spent perhaps one night in a commercial RV park in last year. The result of not paying $20 to $50/night adds up each year.

We are 28 months with a solar autonomous system. We can run 3.5 hours with the Dometic A/C power hog (1700 W or thereabouts) with solar and battery suite. We have not had to use generator once and hooked into line power only one day as noted above. It was 105 in the shade and so and so we hooked up. We do travel in Mexico (Yucatan and Baja) and the power can be fairly dirty (vary from 80 V to 140 V) and that can fry electronics to include micro-wave (burned out one in Baja and another in Yucatan) and A/C. Our son visited us in Yucatan and installed a battery charger. We just ran 110 V AC to battery charger and everything was fine. We tossed the 50 Amp cord and plan only to use the 15 amp cord in the future.

We spent a week on Olympic peninsula in 150' timber. Solar harvest was perhaps 300 W instead of the normal 8000 W a day for July so we turned off inverter when not in use (micro-wave and watching Mystery Theater on DVD at night) and we were only down to 55% SOC. Called Mora CG in Olympic National Park and asked for a sunny spot and explained why. I was mildly chided "sir, this is a rain forest, your solar panels will not be of much use!" Had the same thing occur when we were at Cave Creek in Arizona. A great spot at Stewart CG (Sunny Bench is always filled) but total shade. We lasted a week there and only down to 50% SOC. It was a great birding spot with Blue-throated and Magnificent Hummers. Just have to adapt power management to the situation.

The primary problem with LFP is extreme heat and cold. The folks at Technomadia are quite honest with their errors in their first four years of LFP. They had their battery suite in an enclosed chamber with the inverter, on tarmac, in Phoenix in summertime and suffered capacity degradation. The problem with heat starts somewhere around 120 F. The battery suite should have ventilation. We do have a remote thermometer (aka Walmart $15) in the battery suite compartment and it has not gotten above ambient this summer, with a max of 89F. A small 12 V fan might help mitigate if it got hotter and we have a 12 V outlet in the compartment. LFP can safely discharge at fairly low temperatures but the conventional wisdom seems to be to not charge at high C below freezing. CALB (Chinese Aviation Lithium Batteries) cells have a different physical construction and may not be as prone to degradation at low temperatures as other constructs but I cannot verify this.
Reed and Elaine

Low Cost Lithium Battery Motorhome Conversion

Comments

Categories