size of lithium battery bank - 3.2v cells

Discussion in 'Electrical Systems' started by jdory, Oct 4, 2018.

  1. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Junior Member

    I'm building a 30' catamaran and so far don't have a windlass planned, nor refrigeration.. but could see that in the future. So basically I'll have radio, LED lights for nav and cabin, and some instrumentation which I haven't priced out yet. On a strict budget since I'm retired.

    I'm searching for a place for batteries and, wanting to keep weight down, hoping I can afford lithium. I was thinking of a DIY system based on the marinehowto website, using 4 - 3.2V cells. Thinking for now perhaps 200 amp or up to 360 possibly.. 400 max but don't see the need yet.

    My question would be how to fit these. I have a bench midship with space that is 10" wide or a touch more.. but see some packages come in something like 11" x 11" (w x l). Curious if these cells can be configured to fit - I've got a space 10" plus wide by 30" long. I'm having a hard time finding where to source these kinds of batteries in the U.S.A or wherever providing shipping is not too un-affordable. China is an option but not sure how the market is there with the trade war waging. I'm just too unaware of possibilities of fitting and getting. I do have an 11 x 11 plus area but is getting close to stern and want to keep weight out of those areas.

    thanks, JD
     
  2. Ike
    Joined: Apr 2006
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    Ike Senior Member

    You need to do more research on lithium batteries for marine use. Marine lithium batteries are usually 12v, and very expensive. I read the article you refer to and one paragraph stood out.
    "DIY Builds:
    This is a real cost saver but is not for the faint of heart or the limited skill DIY’er. In a DIY build you source the cells, confirm the cells are well matched for Ah capacity, choose all the components, choose the BMS, design the system schematic, choose the high voltage cut and low voltage cut relays, main contactor, wire and assemble everything, balance the pack and chose chargers, solar or alternator regulators that can be programmed to suit LFP. A DIY build is a very time consuming project but one that can save over 50% of the cost of a factory made bank."

    LiFePO4 Batteries On Boats https://marinehowto.com/lifepo4-batteries-on-boats/

    In other words if you don't know what you are doing, don't!

    Lithium batteries are very sensitive to overcharging and heat. They require a Battery Management System. Some have a BMS built in, some don't. The charger for a Lithium battery bank must be made specifically for lithium batteries. In other words the system must be designed from the ground up for Lithium. They cannot be a drop in replacement for a Lead Acid battery.
     
  3. JamesG123
    Joined: Mar 2015
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    JamesG123 Senior Member

    Also, always go bigger in Ah than you think you need because you will always need more.
     
  4. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Junior Member

    Thanks Ike for the warning in case someone else stumbles across my post. Of course I've read the quoted warning (since I mentioned the article in my first post there) probably more than once. My question wasn't so much as how to do it but on dimensions of battery packs. I've since contacted a vendor and am working with them on sizing.

    Also thanks JamesG123.. advice I would love to take but am on such a budget that I'm still trying to figure out how to afford needed hardware to get the boat in the water, let alone putting more money into possible future needs.
     
  5. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    I have recently outfitted a small racing sailboat with a 125 AH battery.
    AGM was >5 times cheaper than LiFePo4 and 2.2 times heavier.
    It was a tough decision but the AGM won out despite it's weight penalty.
    Considerations were: weight, shock resistance, fire hazard, longevity,
    complexity, reliability, cost, etc.
     
  6. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Junior Member

    Thanks for the reply BlueBell. Good to have data points. As for the expense of batteries themselves, I am seeing near parity in price. This is under the assumption you need nearly 400 ah of AGM to equal 200 ah of LifPo4 (over simplification perhaps). Also, lithium drop-in systems definitely are still rather expensive compared to AGM. As an example, I just looked at first battery offered by FisheriesSupply, a vendor I deal with regularly. Their Lifeline GPL4DL 200 ah AGM is nearly $700 and 130 lbs.. or $1400 and 260 lbs for two. Maybe the tech is changing there too so one doesn't need quite 400 ah to meet 200 ah lithium? I don't know. The lithium pack I was looking at was a GBS 200Ah for $1345 and 57 lbs. Shipping more than makes up BMS and other stuff. I said "was" because the vendor said that they now have an even better battery than that one they will quote me. Shopping around will no doubt turn up cheaper AGM batteries but I didn't put in the time.

    The marinehowto site author is on the facebook page "Lithium on a boat".. so is ready to nay say any bad ideas. (I would be loathe to send anyone to facebook who is not already entrenched there..)

    Technology is changing rapidly in this field as well.. I have some time yet before I jump.
     
  7. BlueBell
    Joined: May 2017
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    Location: Victoria BC Canada

    BlueBell Ahhhhh...

    I agree, 2:1 ratio for AGM capacity versus LiFePo4 capacity.

    My 125AH AGM is 63 pounds vs 28 pounds for a 65 AH LiFePo4
    but the fire and shock prevention measures would have nearly equalled the weight difference...
     
  8. Ike
    Joined: Apr 2006
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    Location: Washington

    Ike Senior Member


  9. jdory
    Joined: Aug 2015
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    Location: Nome, Alaska

    jdory Junior Member

    Thanks Ike.. lots in that thread.
     
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