Lithium battery size?

[patrickgreen]

With prices coming down and people starting to experiment with Lithium batteries I was wondering if there has been a consensus on what amp hour is proving to be the sweet spot.

I am looking for a 82 Diesel westy with an Engel MT45f fridge and an Espar D2 heater using most of the energy.
I will be charging with a 100-watt solar panel and a 1000 watt honda generator.

Any and all help/experiences would be greatly appreciated.

I should mention that my main goal is to be able to run the furnace for at least a few days. This never seemed possible with my lead acid batteries.

[Sodo]

I have 150Ah LiFePO4 and 100W Solar and can run a Truckfridge fridge for something like 10 days in the summer.
I have a 60A DC-DC charger and a 130A alternator.
The 60A charger is kinda huge unit to find a place for in a little Vanagon.
I was traumatized by under-performing lead batteries that won't take a charge etc, then only put out half of their rated Ah. If that.
Consequently I was researching a 2nd flexible panel for 200w etc, following the Solar custom of Go big or go home.
Anyway we went on some trips and found that with the 60Ah DC-DC charger I can charge my 150Ah from zero to full driving 2.5 hours (every 10 days).
This is handy I suppose.....
Now I don't have to find a 2nd 100w panel not a stash spot for it, or setup the wiring outlets, extension cables etc.
Which I was dearly looking forward to, harnessing every bit of Sunlight afforded my way etc.
But then reality stepped in.

What I would change now is ditch the 60A charger, and get appx 40A DC-DC charger + Solar controller + shore charger all in one.
Skipping the shore charger if it adds too much cost or whatever.

I think 100Ah of LiFePO4 and 100 Watts Solar and 30A DC-DC charger is a sweet spot for 3-5 days.
I would not carry a generator, you already have a gas generator (your alternator).
Apply that $$ and synapses to a 30A (or 40?) DC-DC charger so your alternator can charge the LiFePO4.
_________________


'90 Westy EJ25, 2Peloquins, 3knobs, pressure-oiled GT mainshaft, filtered, cooled gearbox
'87 Tintop w 47k 53k, '12 SmallCar EJ25, cooled filtered gearbox
....KTMs, GasGas, SPOT mtb

[dobryan]

Agreed on no generator. Your alternator will charge a LiFePO4 quickly.

If you are going with the battery under the rear bench or in the cabinets somewhere just spend a small amount more and go with one of the DIY 280ah LiFePO4 setups. That is the ticket!
_________________
Dave O
'87 Westy w/ 2002 Subaru EJ25 and Peloquin TBD

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[patrickgreen]

Thanks for the advice "Sodo" and "dobryan". I was thinking that charging from the alternator would put a lot of drag on an already pretty weak diesel engine(1.6TD with a Giles pump) I like the thought of a 3 in one charger. Was there a brand name that you preferred?

[Sodo]

[Howesight]

I have installed a 280A/h LiFePo4 DIY battery as Dobryan and a number of others have done. We talk about "fully charging the battery in 2 or 3 or 4 hours" or somewhat more, etc. I have become so used to lead acid batteries over the last many years that my thinking is still stuck on their needs, but should not be.

Lead Acid batteries MUST be fully charged every chance you get and especially when they are not used for any length of time. By contrast, LiFePo4 batteries live quite comfortably in the middle -range (say, 40% to 60%) of their state-of-charge (SOC) and should never be stored fully charged as it shortens their lives. The great thing about using a large capacity LiFePo4 battery is that the middle-range is huge. So, if you have a 280 A/h battery, even if your DC-DC charging system will not fill it up after driving for 3 hours, you still will have added the same amount of energy to the battery as if you had only a 100A/h battery. The difference will be that the 100 A/h battery went from 10% (10 amp hours) to 100% (100 amp hours), while the 280 A/h battery will have gone from, say, 10% (28 amp hours) to only 42%, but that is still 118 amp hours. If, after setting up, you have to scoot to the park store or the fishing hole, the DC-DC charger will add a bit more energy to the 280 A/h unit, while the 100 A/h battery is full and you add nothing.

I found that the footprint of the 280 DIY LiFePo4 battery is only slightly larger than the 100 or 150 A/h DIY units. Note that the "off-the-shelf" LiFePo4 batteries, like the Battleborn, Renogy, and SOK do waste some space by adding a rugged enclosure with padding, etc , but in a Westfalia, there are several well-protected spaces available for the less-protected DIY batteries. I put mine in the cabinet next to the water-tank:

In the heatwave/heat dome we had this past summer (115F at one point in Kamloops, BC), I needed the whole 280 amp hours for my TF-65 fridge. At those temps, the fridge ran pretty much non-stop and, because I modified my fridge controller, it ran at high speed too. I kept up with demand by deploying my solar panels which I only brought along because the original plan on that trip (before the heat dome changed everything), was to run both my TF-65 and a Whynter 65-litre compressor fridge from my LiFePo4 battery (for a crowd of beer-drinkers)

We also have unreliable sun here in coastal BC and have a lot of shady camp sites, unlike the US southwest, for example. So, we have to have the capacity to get through a few cloudy or rainy days. In winter, the fridge draw is less, but the diesel heater is a constant draw. The daylight hours are short, meaning, again, that excess capacity is a godsend.

As you know, these batteries should never be kept at a full charge for any length of time, so when I get home, if the battery is well over 60% full, I leave the fridge on for a few days to knock down the SOC a bit. So far, I have never had to use a shore charger with this setup. My DC-DC charger is the Redarc BCDC1240D, which charges at 40 to 43 amps. From, say, 10% SOC (28 amp hours), it takes 5.2 hours of engine running to fully (90% SOC) charge my 280 A/h battery. But we rarely get to discharge all that power, so I don't stress over being at only, say, 70% SOC. My batteries could easily have taken the 50 Amp Redarc, but I wanted to be kind to my alternator and selected the 40-amp (nominal) unit. It's a small package and gives off a lot of heat, so I put the Redarc here:

The key thing with charging your LiFePo4 battery from the alternator is that you must use a DC-DC charger to ensure that the voltage output is high enough, but does not exceed 14.6 volts, to prevent over-charge battery damage. Charging directly from the alternator output (which is moderated somewhat by the starter battery and loads), is a very bad idea. LiFePo4 batteries are very sensitive to charging and over-discharge and can be ruined by either or both. Lead-acid batteries just take a hit on longevity when run down too low or charged too quickly, but for LiFePo4, death can occur.

Like Dave O'Bryan, I encourage all to go big on LiFePo4 battery sizing - - you won't regret it.
_________________
'86 Syncro Westy SVX

[Italjohn]

Here are my Lithium setup. managed to fit it under the front seat as well.


Link

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[Vanuber]

[dobryan]

[patrickgreen]

Thank you all for the amazing information. As if working on the Westy wasn't enough it looks like I will try to build a battery as well. I have the space so I will start looking for 280 AH cells. I understand what the BMS does but have no clue the difference between a good one and a bad one. Also, has anyone installed a heat pad with theres. If I am building I might as well incorporate one from the beginning.

[Vanuber]

[Butcher]

Doesn't the DC/DC charger paired up with the BMS prevent any charging issues?

Although an alternator would be the item that charges the battery, there should be enough safeguards built in, that would prevent an over charge situation.

[Vanuber]

[dobryan]

[DeLvxe]