| My experience with LiFePO4 batteries so far [message #365337] |
Sat, 10 July 2021 14:12  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
Karma: 3
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Senior Member |
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Richard Waters asked me in another thread about changing to LiFePO4 (LFP) from lead-acid (LA) batteries. So I thought I would start a new thread on this subject.
Richard,
I found a Vendor here in Canada selling selling LiFePO4 batteries for $450Cdn (~$350USD) for 12 volt 100Ahr so I purchased 2 batteries. The batteries are of course made in China and private labeled for them. At that price they are close to the same cost as as lead-acid... or less for the same usable capacity.
They also now have a heated version for charging at under 0C.
https://www.ablithium.ca/
LFP batteries are happy being connected in parallel and these batteries are rated for charging at 0.5C rate so that is 50Amps, so you could charge them from discharged to full in 2 hours. But they will live a long life at 20Amps, so I have my charger set to 40Amps. I have a 150 watt solar panel mounted to the roof pod with at MPPT charge controller.
For charging from the chassis I have a Renogy 20 amp DC-DC charger. This limits the charge from the engine alternator to 20Amps Max and properly controls the charge voltages even as the chassis voltages changes. After I purchased it I noticed the Renogy 40 and 60 Amp units have a 1/2 power mode which would limit the current to 20 and 30Amps respectively. If I had known that I would have purchased the 40Amp unit and had the option to limit the current to 20 Amps or 40.
I have a Samlex EVO-1212 Inverter/Charger Transfer switch unit that has multiple charging profiles and about 3 of them usable with Lithium batteries. It also has an external charger input for up to 50Amps to wire the solar and DC-DC charger through.
To charge a LFP battery you can use 2 or 3 stages. First stage is Bulk where you limit the current to a programmed value by controlling the voltage (mine is set to 40 amps, 20 amps for each battery). Once the Bulk voltage hits the Absorb voltage value, it transitions to second stage Absorb. In Absorb, the voltage is constant (mine is set to 14.2V) so the current slowly tapers off. Absorb stage can be either for a set time, or until the charge current drops below a set value (this depends on the charging profile you have picked). If you picked 2 stage, then the charger switches OFF until the battery voltage drops below a set value and the charge cycle starts again. Since we have a 'Loaded Battery' lights etc run off the battery, I have the profile set to 3 stage. The third stage is Float where the charger backs off the voltage and just supplies current for the lights etc as needed.
Unlike LA batteries where you must recharge them fully immediately after use, LFP batteries don't really care about their current state of charge, just don't leave them completely discharged. When you store them for extended periods, they are happier if they are at about 50% charge. Their self-discharge rate is only about 3% per month so after 6 months of storage they would still have about 30% charge left.
I have an all-electric fridge, hence the 200Ahrs of capacity. I ran the fridge and Fantastic fan for 36hrs and consumed 150Ahrs of charge, so I could get 2 days out of it... and more if it was sunny. I fully recharged in about 4 hours... with LA it would take about 10 hrs to properly recharge them.
LFP batteries can have a longer life if you don't fully charge or discharge them. I plan on running them between the 20-90% range. Again unlike LA, LPF batteries do not need to be fully recharged and that last 5% or so of recharge takes the longest. Also LFP batteries are much more efficient at taking a charge. A LA battery will waste about 15% to heat, while a LFP battery only 1% (~99% efficient).
At 20% charge left, under load the batteries were still delivering 12.9 volts.
The LPF batteries weigh less than 30lbs each
Costs:
-Again I paid $450Cdn each for the batteries. A 100Ahr LFP battery is about equal to two LA 6V golf cart batteries taking into account the higher usable charge capacity of LFP. I would think you can find LFP batteries in the USA for the same price. Google "Will Prowse" for lots of info on solar and LFP battery sources.
-So you will likely need to replace your charger. LFP rated chargers are not much more than LA chargers, only the voltages are different so likely about $250USD. Mine is an Inverter/Charger/Transfer switch. Samlex EVO-1212, I see them from US vendors on-line for about $700USD
-The DC-DC charger is available for about $120-150USD depending on the current rating.
-I replaced my PWM solar charge controller with a Victron MPPT for higher efficiency for about $150USD.
-I would also suggest a Battery Monitor like the Victron BMV700 series. It tells you the voltage at the battery, charge or discharge current, state of charge in Ahrs and watt/hrs. Very handy. they are about $200USD
One thing I wish my Samlex charger had was remote battery voltage sense. Mine is installed in the electrical cupboard. At 40 Amp charge rate I lose about 400mv in the wiring to the battery. About 75mV is lost across the 60 Amps battery breaker alone. If it had a remote sense wire, the charger would make up for this just like our OEM 3 wire alternators. Charging a LFP battery is very voltage sensitive.
So that is my experience so far... and I like it!
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
[Updated on: Sat, 10 July 2021 14:36] Report message to a moderator |
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| Re: My experience with LiFePO4 batteries so far [message #365351 is a reply to message #365337] |
Sun, 11 July 2021 08:00  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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Bruce,
As I was replacing my GC2s with new T105 about two years ago, I looked long and hard at LFPs, but I could not locate some of the hardware that you have and did not even know where to look. It looks like you have answered all the questions except where to put the additional hardware. Battleborn were off the budget and the Renogy things I found left questions that they did not answer. As the Trojans are now three years old, I will probably be looking to you for a supplier list in about another three years.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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