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riah's avatar
riah
Explorer
Dec 18, 2020

2003AF990 battery conversion from lead acid to LiFePO4

Hi,

I'm still trying to figure out electrical systems, so bear with me as I'm really green with the dual use solar and batteries in RVs.

Has anyone tried to fit a Big Battery 24V LiFePO4 battery block into the battery box location on their (2003) AF 990? [We are trying to figure out if that is even an option (vs ordering 2 Big Battery 12V LiFePO4 battery blocks.]

Although I'm confused if we would be better off with 2 12V battery blocks, as that would give us 340 Amp hours vs 170 Amp hours, correct? Or is it the 24V equivalent to the (2) 12V batteries together.

Also, what modifications would one need to do to get it to work? - as right now I believe it is set up as 12V system, not 24V.

Our solar battery controller is an EPEVER MMPT 30 AMP 12V/24V auto solar charger and right now we have 200 Watts of solar currently installed (with 200 Watts additionally available to add this current setup, for a total of 400 watts.)

[Also, I presume I would need to reprogram the solar charger as well? If so, I'll also need to get the adapter to be able to make programmatic changes, as well as the temperature sensor too.]

So, that said, what would y'all do? Just order 2 12V battery blocks? or a 24V battery? Please advise! TY!

29 Replies

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  • phemens's avatar
    phemens
    Explorer
    Dec 19, 2020
    The one variable you didn't include in the SiO2 batteries is weight. They weigh as much as lead acid batteries, if that is part of your consideration. OP didn't mention that as a factor, but should be aware of the difference. Weight is the primary reason I went with LiFePO4.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Dec 19, 2020
    riah wrote:
    PS - Where does one find SiO2 batteries? (I looked on Amazon but they didn't seem to have any available there for purchase.)


    There is a link in to the Cdn dealer in the freecampsites series. They do sell to USA. Iirc price is about $477 usd.

    https://freecampsites.net/adding-solar/
  • riah's avatar
    riah
    Explorer
    Dec 18, 2020
    PS - Where does one find SiO2 batteries? (I looked on Amazon but they didn't seem to have any available there for purchase.)

    *PS2 - I'm in the US unfortunately not CA - although I want to be back there as soon as this pandemic is under control here!

    pianotuna wrote:
    There is little advantage to 24 volts, especially since the existing controller can easily accommodate 400 watts.

    If at a later date, you wish to move to 24 volts and add more panels that option is open.

    I would go with 2 SiO2 100 amp-hour batteries wired in parallel, for these reasons.

    1. no special chargers are required
    2. they can be taken to 0 volts without damage, after 620 times 80% of oem capacity is still there.
    3. they can be used in extreme cold.
    4. they are 1/2 the price of Li.

    For 24 volts if you place two 12 volt batteries in series the number of amp-hours remains the same--but the number of watt-hours of capacity doubles.

    For 12 volts if you place two 12 volt batteries in parallel the number of amp-hours doubles--and the number of watt hours of capacity doubles.

    If you move to 24 volts, the sensible solution would be to get a DC to dc converter that is capable of running all the 12 volt loads in the RV.

    This series of articles may help you understand solar better: https://freecampsites.net/adding-solar/

    In your case my personal choice would be to stay with 12 volts.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Dec 18, 2020
    riah wrote:

    We are limited on battery space and had hoped for more amp hours available, which is what LiFePO4 seems to allow.


    SiO2 will give you more amp-hours than the LI. Li is 20% to 100%. Preferred is 40% to 90%

    SiO2 is 0% to 100% (620 cycles) and longest life is 50% to 100% (2800 cycles).
  • Lwiddis's avatar
    Lwiddis
    Explorer II
    Dec 18, 2020
    Volts is a pressure measurement. To try to pump 24 volts through your camper would be a disaster! I respectfully suggest you replace your batteries with help from someone knowledgeable.
  • riah's avatar
    riah
    Explorer
    Dec 18, 2020
    jeglenn wrote:
    24v sounds like a bad idea. Why not two 12v batteries in parralel instead?


    I was thinking that it would be less expensive to wire as well as the LiFEPO4 battery is less than 2 12V LiFePO4 batteries - but it sounds like we should just stick to the 12 V setup as that's what the system is designed for originally and it would be the most straightforward seeing we are only looking at 400 Watts of solar currently. Thanks for the reply!
  • riah's avatar
    riah
    Explorer
    Dec 18, 2020
    Thanks! It appears that we will need to stick with the 12 V setup and max of 400 watts of solar for now!

    I wasn't realizing that I would need to "step down"/convert it again to use the 12 V system and to be able to still charge using the existing system setup.

    We are limited on battery space and had hoped for more amp hours available, which is what LiFePO4 seems to allow.

    I can see that the consensus is to stick with 12 V now!

    Thanks so much!

    pianotuna wrote:
    There is little advantage to 24 volts, especially since the existing controller can easily accommodate 400 watts.

    If at a later date, you wish to move to 24 volts and add more panels that option is open.

    I would go with 2 SiO2 100 amp-hour batteries wired in parallel, for these reasons.

    1. no special chargers are required
    2. they can be taken to 0 volts without damage, after 620 times 80% of oem capacity is still there.
    3. they can be used in extreme cold.
    4. they are 1/2 the price of Li.

    For 24 volts if you place two 12 volt batteries in series the number of amp-hours remains the same--but the number of watt-hours of capacity doubles.

    For 12 volts if you place two 12 volt batteries in parallel the number of amp-hours doubles--and the number of watt hours of capacity doubles.

    If you move to 24 volts, the sensible solution would be to get a DC to dc converter that is capable of running all the 12 volt loads in the RV.

    This series of articles may help you understand solar better: https://freecampsites.net/adding-solar/

    In your case my personal choice would be to stay with 12 volts.
  • pianotuna's avatar
    pianotuna
    Nomad III
    Dec 18, 2020
    There is little advantage to 24 volts, especially since the existing controller can easily accommodate 400 watts.

    If at a later date, you wish to move to 24 volts and add more panels that option is open.

    I would go with 2 SiO2 100 amp-hour batteries wired in parallel, for these reasons.

    1. no special chargers are required
    2. they can be taken to 0 volts without damage, after 620 times 80% of oem capacity is still there.
    3. they can be used in extreme cold.
    4. they are 1/2 the price of Li.

    For 24 volts if you place two 12 volt batteries in series the number of amp-hours remains the same--but the number of watt-hours of capacity doubles.

    For 12 volts if you place two 12 volt batteries in parallel the number of amp-hours doubles--and the number of watt hours of capacity doubles.

    If you move to 24 volts, the sensible solution would be to get a DC to dc converter that is capable of running all the 12 volt loads in the RV.

    This series of articles may help you understand solar better: https://freecampsites.net/adding-solar/

    In your case my personal choice would be to stay with 12 volts.
  • jeglenn's avatar
    jeglenn
    Explorer
    Dec 18, 2020
    24v sounds like a bad idea. Why not two 12v batteries in parralel instead?

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