TheSamba.com :: View topic - Lithium Battery Build - LIFEPO4

Wed Mar 06, 2024 10:23 am

Lithium LIFEPO4 Leisure Battery Build

I've been intrigued by Lithium leisure batteries for a while now, they are not something new but not something I really knew much about.

This post is just about replacing a lead Acid / AGM leisure battery with a Lithium LIFEPO4 one and the steps involved. Its not a recommendation or anything, just what I've done and sharing the experiences I've had.

Why did I want to do this, build a lithium battery ? I was having problems with my leisure battery on roadtrips, after a few days the 'fade' of lead acid (like a torch getting dimmer) was giving me problems mainly around getting my heater started, my heater needs a load of energy to start up then happily runs with a lower draw. Anything less than a fully charged tip top LB wasn't cutting it.
Its the discharge curve that attracted me to lithium.

Lithium-ion and Life Phosphate (LifePo4) give everything for 80% of the time. After appx 30% my lead acid battery isn't giving the volts I needed, and as they age they get weaker.

So I decided in order to find out more to build a Leisure battery from scratch and this post lays it out so if anyone else wanted to have a go.
Some false information bamboozled me at the start. I understand some people posting probably weren't so familiar with whats what and just jumped in.

Got to say a big thanks to Geoff @77 Westy for giving me answers and explaining a lot of this as I was fumbling around in the dark.

So Lithium batteries, a fact of life now and will probably replace lead acid/agm batteries as leisure ones but they can be hellishly expensive. Building one.. its like riding a bike, difficult until you've actually done it, then you could do it without too much thought.

So a couple of rumours to dispel.
"You can't mix lead acid and lithium batteries in your van"
Well not as far as physically joining them together you can't but as far as 2 different types in your bus, lead acid starter and a lithium leisure battery, absolutely fine, no problem at all.
Because you never actually connect the batteries together, you go through something called a DC to DC charger they remain isolated from each other.

DC to DC charger.
So as that's the first thing I have mentioned I'll explain a DC to DC charger. Also known as a battery to battery charger. A loose cousin of a split charge but its very different. What you are doing is connecting the batteries together via a special DC to DC charger, also called a battery to battery charger.

It is NOT split charge. You can reuse the wiring but the lithium battery does not connect to the alternator and there's no relay.
What happens is you connect both batteries (which run DC current not like AC in your house hence DC to DC) into the DC to DC charger.

Your alternator (white wire above) provides a trigger to tell the charger to start working when engine running. Similar to split charge once your starter battery is full then the LB, via the DC to DC charger, draws its charge from the starter battery (all controlled carefully by the DC to DC charger) and the DC charger keeps your batteries happy.

Charging.
Back in the day I had to undo the top of my batteries to stop them exploding. The old method was to leave your charger on overnight connected to your battery. They put out 2 amps, maybe 5 if its a special one. Modern chargers you can just leave, trickle ones.

Lithium batteries charge using a different rating, its called a C rating and it blew my mind a bit to be honest.

The battery I got which I'll go though in a bit has a C rating of 1 (one). It is really important to know what your C rating is as you don't want to over cook it.

What does that C rating mean?.
Lithium has really low internal resistance, almost none, so if you have a 100ah battery with a C rating of one it means you can charge at 100amps and in 1 hour the 100ah battery will be fully charged ... from flat !.

Your old 2 amp or 5 amp charger is not much good.

So in 1 hour you could in theory charge your leisure battery full from empty if you had a 100amp charger.

But the reality is you won't buy a 100ah charger as they are expensive and your BMS will shut off at 80% discharge. I bought a 36 amp charger so in theory I could charge my lithium LB to full in about 2.5 hours.

The DC to DC charger also happens to be 40 amps so if I drive for an hour I put 40 amps back into my LB.

I haven't run long enough to know if this is true but on paper that's what it does. I do know at the end of a day my battery is totally full again, somehting I never got with my old lead acid leisure battery. Some of this is nice numbers becuase in reality (see discharge curve above) you don't take your lithium battery below 20%.
Lead acid is a dead damaged battery below 50%, 70% is as low as you would want to go.

Lithium batteries can also take more cycles (charges), they are sold with marketing in terms of number of cycles in the 1000's whereas AGM or lead acid is in the low hundreds so again in theory my lithium battery will last 10 times longer at least. 5000 cycles as oppose to 500 (optimistic I know) on my old lead acid battery.

But as I said the thing I really liked about lithium was the discharge graph.
Lead acid when it goes a bit weak fades. You can't take a lead acid battery much below 60% before it starts to damage it but a Lithium battery delivers full whack for 80% of the time then falls off a cliff. But you have a thing called a battery management system (BMS) that protects it so you won't damage it.

Weight, lithium batteries are light, I guess about 1/4 of the weight for the same capacity lead acid battery.

So what do you need to build one. How much?.

Cost Breakdown March 2023 (in GBP)

Battery Cells

I got mine from AliExpress but it took 4 attempts, there's a lot of dubious sellers out there. Most never shipped or showed a shipped receipt/tracking to 'London' somewhere etc but I didn't lose any money.
The vendor who came good is a gold supplier and I found they were prompt to answer questions . Tracking was rubbish but the battery cells turned up. I used Global Power LT store.
You buy cells, each is rated 3.2v so you need 4 as 4 x 3.2 is your 12v battery.
I got 105 ah cells which you can get for appx/less than £70ea incl shipping.

BMS
You need a Battery management system, a BMS. I bought a 80A BT, LiFePO4 4S 12V BMS from hibms official store (also on AliExpress) which cost me £35.64
Note about these, it says 80A but that's its theoretical discharge amps. Input is half that, 40 amps.
A year on 2024 there's more on the market, try to get one that includes balancing now.

Indoor Charger
A variable lithium charger is the way to go which can charge from 1 or 2 volts right up to 40A. Note your old lead acid battery charger running 12v and 2 or 3 amps isn't suitable.
This is the one I got, 0-15v variable

Why the variable recommendation ?. Balancing the cells. You need to balance charge at lower volts 3.2v, but then, when built as a 12v battery in series as will be explained you charge appx 14v.

Battery Capacity Meter
A battery health meter/reader is nice to have, and cheap, was £5.12 from
ThinkingLeader Store
Battery Capacity Indicator DC 8V-100V Lead Acid Lithium LiFePO4 Car Motorcycle Voltmeter Voltage Gauge 12V 24V 48V 72V

Cabling and terminals
Load of cabling, I bought 7 meters of black and 7 of red 65amp cable and 12x 65amp terminals cost me £50 from local car store

Quick Release Plugs
Anderson plugs, these cost me about £10 for a packet of 10
*note about the terminals, a good crimper will handle these solid metal ones, I did it on the 'yellow' crimp slot and it crimped these no problem. I then squeezed them up a bit more and shrink wrap sleeved them.

I also put in another fuse box in the rear just for ease, £8 which I found in the future was a godsend when I needed external 12v supply to run off grid.
and some wood and corner brackets (to build a battery box) say £5

DC to DC charger £112
I got a Renogy 40A one. If you sign up to 'Honey' you can get discount codes etc.
You could live without this and just get a home charger (above) but then it won't charge when you are out. Me and the Mrs do off grid road trips so charging while driving is important.

So that's about £450 in total.

Some number crunching and you can see the battery cells on their own, battery, nothing else, only work out to be about 35% of the total cost. Its the other stuff around it you need that pushes the price up, and this isn't solar which needs other controllers etc but I don't need solar so can't go into that.

I did find my old wiring had a problem, back in the day in order to to share the load (amps) I'd doubled up 16a cable which had worked, but plugging in my lithium battery the volt drop was huge. I don't know why it showed up now but I do know the cause was too small gauge wiring so I used 65a to my heater and now volt drop is tiny. That's irrelevant to this post but I thought I'd share it anyway. Rely on fuses to save you, don't under spec wiring.

Next thing is getting it all connected. And when you buy your BMS make sure its got bluetooth, you set it up from your phone. Again not difficult when you know how but it threw me a bit first.

So how to build it....
Assuming you bought all the above
Batteries arrive like this

Each cells is 3.2 so they need to be connected to give 12v.

Balancing
Before you start you need to balance them.
How ?: The easiest way (I found), connect each cell in parallel, so each +ve to each +ve and each -ve to each -ve in a row.
Then set your variable charger to 3.2v
Connect variable charger to the +ve and -ve
Turn on and let it run for a few hours. What will happen is each cell will be balanced to 3.2v.
4 x 3.2 = your 12.8v battery.
You can do it to 3.6v per cell but at this stage walk then run, you'll find loads of videos online about balancing, this is about finding your feet and getting comfortable with it.

Now to connect in series.

Carefully disconnect your balanced, connected in parallel, battery cells.

This is the video I used. Click to open YouTube connect BMS video
.

This guy also does the BMS setup video later.
I followed what he did
Number the cells and connect in series.

You connect the cells in series. Bit of paper in between because someone on youtube advised it I couldn't see why not. You number the cells back to front and connect the cells and BMS.

It ends up like this

I used some tubing i had laying around to keep the BMS (on the left) away from the battery to help with heat dissipation. Nobody said to do this but I just did.

There you go, you have made a 12v (12.8v) LIFEPO4 battery. #4 above will be your +ve and from the BMS that black wire is your negative. This was how it looks on paper. B+ (from #4 +ve on your cells is +ve and P- is -ve

You can see here, I connected the charger to what in my mind is still +ve and negative post

What you will do is have a lead (65A red cable) from #4 +ve and your -ve is the BMS P- cable.

I have these 2 cables, with ring terminal on the end, poking outside my box to which I connect a 3 tail leads, one to the DC to DC charger, one to the fuse box in the rear and one to my amplifier. My wire is over spec but remember fuses save you and bigger wire = less resistance so its not a bad thing.

Use the chassis as your earth to connect P-

I made a box with some carpet underlay inside to protect it. The great thing about lithium is no fluid, its solid state so I laid mine on its side in the rear opposite side of the starter battery in a crude box.

Whatever you do when you run the lead from your main battery to the DC charger (you run one from Lithium and one from starter) label up the main battery leads (or DC if you want) so you know what what when they come out the other side.

The DC to DC charger I placed underneath the armrest inside the van, it was a perfect fit.

I drilled cable holes through my spare wheel well and into the engine bay. I connect all leads using Anderson connectors and bought an earth terminal block from screwfix (local DIY store) to attach earth connections.

That looks really messy but its working ok for now.

Once its in you need to configure your BMS. Same bloke as above (and thanks again to 77 Westy for finding this)
Click this

you can shut the whole system down and tweak it (avoid shorts etc)

If your DC to DC charger is working correctly it'll give you a green light when ign is on. I totally forgot to connect the -ve to my main batt -ve which threw me for half an hour but I eventually realised what I had done.

I've since added a temp controlled relay to my coolbox.

In real life
Some 2 week off grid road trips (so moving every couple of days or so) I haven't run out of battery power to my heater, it/everything works a treat.

My next adventure we will be static for a little while and I'm not going down solar route so I have decided to build a bigger 310ah one (I have got kids so 2 fridges etc) this time I only need the cells, not the rest of the bits.

Long thread but concise, hope it helps.

PG

Wed Mar 06, 2024 10:36 am

Thanks for putting this together. Lots to think about and digest. What's the approximate cost all in if you don't mind sharing?

Wed Mar 06, 2024 12:09 pm

Shonandb wrote: Thanks for putting this together. Lots to think about and digest. What's the approximate cost all in if you don't mind sharing?

under the cost breakdown :thumbsup:

Wed Mar 06, 2024 1:22 pm

pgtips wrote: Shonandb wrote: Thanks for putting this together. Lots to think about and digest. What's the approximate cost all in if you don't mind sharing?

under the cost breakdown :thumbsup:

Sorry, I was on the train/commuting and trying to skim through on my phone and missed it. Thanks.

Thu Mar 07, 2024 9:05 pm

On a related note, to those thinking of switching to lithium for their main battery: if you have an alternator, be careful! The Battery management System (BMS) module protects the battery from overcharge by disconnecting it from the electrical system if needed. This can cause the alternator to run electrically unclamped, and to emit a sizable momentary overvoltage, cooking anything electronic (FI stereo, etc.), as well as the alternator itself. I understand that some newer BMS units issue a signal before disconnecting, which can be used to disable the alternator, but have not researched this... FWIW

Thu Mar 07, 2024 11:21 pm

I use an Optima BlueTop battery for my leisure battery, and only have anecdotal evidence based on my own experiences, but one huge advantage I have found with the Optima BlueTop is recovery after using.

By that I mean that I use the battery during the day, and it discharges and when left overnight it gains back most of its voltage and is good for the next day.

I'm not a scientist, and obviously over time it will slowly decline as it discharges, but your graph of discharge is a bit simplistic.

My graph would show discharge, bounce back and discharge in cycles.

The Optima is a great deep cycle battery that I can use for several days without charging.

Granted that my use is that I am only asking for significant voltage during the day - and at night just charging a phone or two, so no constant load over 24 hours. (I use an icebox, so no demand for a fridge for example)

Just throwing out there, as different folks have different needs.

I'm also super leery about the safety of lithium batteries which can be a big problem in some cases when charging.

Fri Mar 08, 2024 5:54 am

It's always been a work in progress on my RV for me when it comes to my overall goal. Mostly because the cost of the batteries were over the top for a long time. Now they are more mainstream and going down in price. Now this is for an RV and it's a bit over the top.

I used a Sungold all in one unit and literally wired it up to run all of the 110V AC if it needed (it has an automatic switch). Then added 800W of solar. After that put in three 100Ah Lithium batteries with a DC-DC charger.

At this point it works fine but there are limitations but you just got to have what your expectations are and go from there. I can run my fridge on electric, run the electric furnace, watch TV and a number of other things.

One thing people can do (which I see various setups when I camp) is you can mount various smaller Lithium batteries in various places as with a bus, you have limited space. Running a couple of wires from one to another is no big deal.

Also, when I was out camping on BLM land and since I have an onboard generator (4000W Onan), A guy in a mid 90's Ford Van who had some solar and a nice Lithium setup, asked me if he could plug in and top off. We are in this all together and I agreed. That's all I was doing because I was out in the boonies for a while and since solar is not perfect, I wanted to top off for an hour of running. That's another option. I found that offering a beer in payment, really works well. So, keep in mind, beer is a good currency (especially if it's something odd).

If a bus showed up and wanted the same service, I'd give them a beer. Keep that in mind.

Fri Mar 15, 2024 1:32 pm

Great post and nicely informative :vw:

I went the easier route and got my bits from Renogy, and all on sale cuz it ain't cheap :shock:

Sat Mar 16, 2024 8:44 am

it's awesome to see bus people playing with this kind of stuff

is that BMS a JBD / Xiaoxiang? (easy way to check, try one of the various "xiaoxiang" bluetooth apps on your phone...)

here are some links that might be interesting

https://www.jag35.com
https://www.youtube.com/@WillProwse

it would be cool to see what capacities custom batteries super 'form fit' for specific spots in the bus could hold ..

Sun Apr 14, 2024 12:13 am

telford dorr wrote: On a related note, to those thinking of switching to lithium for their main battery: if you have an alternator, be careful! The Battery management System (BMS) module protects the battery from overcharge by disconnecting it from the electrical system if needed. This can cause the alternator to run electrically unclamped, and to emit a sizable momentary overvoltage, cooking anything electronic (FI stereo, etc.), as well as the alternator itself. I understand that some newer BMS units issue a signal before disconnecting, which can be used to disable the alternator, but have not researched this... FWIW

I am in that camp, about to make the switch as my Yellow Top has apparently Yee'd its last Haw.

Today I serviced a $300k Sprinter camper with only a few hundred miles on it. Two alternators, 22Kw/h of DEAD 24v house batteries, 600w of solar, a microwave, air conditioner, and water heater. It was the perfect storm of electrical diagnosis, and I think you and metahacker might appreciate it. My generator has never had such silly issues…

After two days of running the AC in the desert, the house system went completely dead in the middle of the night. The next day, some things worked but most devices gave errors. I found all the lithium battery modules had alarm LED's flashing, and were at their intended cutoff voltage. I reset the BMS and got nothing but a rapid clicking sound, even though the solar charge should have kicked the lithium BMS back to life. (Solar is great for letting lithium batteries sit unused, they need to be "woken up" by the BMS or most self-disconnect after 30 days, as these all had.) Climbing up the titanium roof ladder, I found the panels covered in mud and dirt…

I grabbed my Eco Flow power pack, and plugged the van's shore power in to wake up the batteries. Great! One at a time, each lithium module took 5 amps waking up and 30 amps beginning their charge sequence. I think a common lithium charge profile is to ease into charging before going full gas, which can then charge much faster than lead acid batteries.

I fired up the van and tested the alternator output. No change in voltage regardless of RPM after several minutes with the now~20% batteries back online.

BUT! We "full field" tested the 24v aux alternator, and heard an immediate drop in engine RPM and a whistle from the alternator! Deep inside the engine compartment, there is a programmable voltage regulator. Sitting there in "setup" mode with a flashing LED. Never once asked to charge a battery. But what do you expect for $300k?

Now he's sitting pretty with a smart voltage regulator that communicates with the lithium BMS for a safe shutdown. The technology is here! And it's frickin' cool if you install/program it properly.

My takeaways from this…
- Know how to reset your BMS.
- All of this work was done on iPhones, with the only tool being a paper clip to test the alternator. The house system had a "smart shunt" that read voltage, current, and trends of the auxiliary battery system straight to our phones. No tools or drty hands required.
- Clean your solar panels
- Know how to program your voltage regulator, I guess?

Robbie

Sun Apr 14, 2024 8:29 am

This is why I like running two batteries. One so you can start and run the vehicle on battery A and then run the rest on battery B. I suggest people spend time with a notepad, pencil and a tape measure. Go out and find in your bus, what can you fit in somewhere. Then look at cost then look at what you need for capacity.

Solar can be done and if you look at some more of the recent offerings, you can get flexible panels and put them on the roof where they don't look like big huge square blocks on your roof. For today, solar is an affordable option as it can help you out for long trips out in the boonies. It ends up becoming free power. Don;t expect miracles.

Then when looking at what you need for capacity there are things like:
12V fridge/freezers
coffee makers
music (speakers and whatnot)
fans
lights

I suggest looking into what truckers use as there is a whole world out there that many never access and they have lots of products for them which are for small areas and can run off of 12V.

Spending time navigating this complex world full of opinions is not easy but it can be done.