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  1. #21
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    Quote Originally Posted by SolarPoweredRV View Post
    It is important to understand that when you parallel Lithium batteries, the output might be limited by the internal BMS (Battery Management System), i.e.: stringing 4, 100 amp (current draw, not amp hour rating), batteries may be limited to only 100 amps of current draw because, all the power is going through a single battery that is attached to the load and the BMS is limiting the amount of power that can be drawn to 100 amps (you would still get 400amp hours of energy storage, only be limited to drawing 100 amps).

    The way to get around this limitation is to use Buss Bars. Attach each cable from the battery to the Buss Bars (one positive and one negative) and then attach the load to the Buss Bar. This way, each battery can contribute their entire 100 amps to the load instead of being limited by the Internal BMS of the first battery.

    Here is an example of the type of Buss Bar I am talking about. Additionally, I have attached a research paper that explains the advantage of using Buss Bars in detail (I also included a Wire Gauge Chart):
    So what you are saying is to run each positive cable from each battery to a buss and each negative cable from each battery to a buss. So the only connection between the batteries would be through the buss bar and that would keep the BMS from limiting the output?
    I was going to use a buss but was only going to have one positive and one negative coming into the buss which in fact might limit the output from what you are saying.
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  2. #22
    Site Sponsor SolarPoweredRV's Avatar
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    Quote Originally Posted by Chad74 View Post
    So what you are saying is to run each positive cable from each battery to a buss and each negative cable from each battery to a buss. So the only connection between the batteries would be through the buss bar and that would keep the BMS from limiting the output?
    I was going to use a buss but was only going to have one positive and one negative coming into the buss which in fact might limit the output from what you are saying.
    Yes, Exactly. If you look at the research paper it is labeled as "Method 3":
    Attached Thumbnails Attached Thumbnails Method 3.png  
    David and Peggy
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  3. #23
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    Quote Originally Posted by SolarPoweredRV View Post
    Yes, Exactly. If you look at the research paper it is labeled as "Method 3":

    Before I add to this, I think I need to share a little bit about myself. I am not trying to be argumentative (I know I come across that way sometimes). I truly value the expertise that can be found here and enjoy reading through all of the posts.

    I spent a lot of years as a credentialed vocational instructor in a couple of different state prisons. A key strategy for me was to constantly challenge my self, my students and the “industry”. Always ask why - always see if you can improve upon...

    David, in my opinion, is absolutely correct as this method offers the most balanced circuit (total resistance between each battery and load). Tying each battery directly to a buss bar also allows you to use smaller conductors (battery to buss bar) as each circuit’s current will be limited by the BMS. From the buss bar to the various loads, conductor size would have to be appropriate for each load.

    There are other things to consider as well. Takes up more real estate unless you opt for a single terminal as opposed to an actual buss bar. Placement of a battery disconnect switch and fuse(s) would have to be on the load side of the buss bar (unless you opted to use one for each of the batteries -even more real estate). One could take any battery out of service by simply disconnecting it - cabling to the other batteries would remain in tact.

    Lots to consider...
    Last edited by Jomani; 03-16-2023 at 04:05 PM.
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  4. #24
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    We replaced our 2 lead Acid batteries with 4 Lithium 100 AH batteries and a 2000W Inverter - and it is FANTASTIC. Batteries are way lighter, last way longer and all our 120V items operate just like at home! We have never run out of power.

  5. #25
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    Lots of good info about the battery configuration, so I'll just share my poor man's/limited use experience:

    On both my old 5th, and the current TT, I went with 2 6v (lithium was a VERY expensive dream at that point). Gives me a useable 100Ah, 200Ah total.
    The inverter in both was a sine-wave 600watt. Not very big, but good enough for smaller loads, like a TV.
    Important to install the inverter as close to the batteries as possible, to reduce line loss on the wires to it.
    On the fifth, I ran a heavy duty extension cord through an existing opening to an interior cabinet. If I needed to watch TV, or run my CPAP at night, I would uncoil the cord and just plug in to that. Inverters pull power even when not in use, so installed a remote on/off switch for it, so I didn't have to go out at night to the compartment it was installed in. Could get about 2 days off the batteries, if I was careful as to power use.
    Now with the TT, I plug directly into the main outside power plug. This nominally could power the whole thing, but with 600w, there's not much that I can really run. An oops like running the microwave or coffee pot, and the inverter shuts down due to overload! One MUST make sure to turn off the converter with this scheme, as otherwise your 120v feed will try to charge the batteries. Not a good idea.
    It works, but now with 2 CPAPS and some TV watching, I only get about 8-9 hrs out of the batteries, if very lucky. Inverter alarms when input volts get too low, and currently I now have to go outside at 4 am to shut it off. Plus have no 12v....
    The lesson - having more battery and more inverter is better.
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  6. #26
    Site Sponsor SolarPoweredRV's Avatar
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    Quote Originally Posted by sande005 View Post
    Lots of good info about the battery configuration, so I'll just share my poor man's/limited use experience:

    On both my old 5th, and the current TT, I went with 2 6v (lithium was a VERY expensive dream at that point). Gives me a useable 100Ah, 200Ah total.
    The inverter in both was a sine-wave 600watt. Not very big, but good enough for smaller loads, like a TV.
    Important to install the inverter as close to the batteries as possible, to reduce line loss on the wires to it.
    On the fifth, I ran a heavy duty extension cord through an existing opening to an interior cabinet. If I needed to watch TV, or run my CPAP at night, I would uncoil the cord and just plug in to that. Inverters pull power even when not in use, so installed a remote on/off switch for it, so I didn't have to go out at night to the compartment it was installed in. Could get about 2 days off the batteries, if I was careful as to power use.
    Now with the TT, I plug directly into the main outside power plug. This nominally could power the whole thing, but with 600w, there's not much that I can really run. An oops like running the microwave or coffee pot, and the inverter shuts down due to overload! One MUST make sure to turn off the converter with this scheme, as otherwise your 120v feed will try to charge the batteries. Not a good idea.
    It works, but now with 2 CPAPS and some TV watching, I only get about 8-9 hrs out of the batteries, if very lucky. Inverter alarms when input volts get too low, and currently I now have to go outside at 4 am to shut it off. Plus have no 12v....
    The lesson - having more battery and more inverter is better.
    Simply switching to a pair of Lithium batteries and replacing the Converter with a Lithium ready Converter would double your run time and literally let you sleep better at night .

    Here is a thread comparing Lithium batteries to Lead Acid batteries:

    Lithium-over-Lead-Acid-Batteries

    Also ,you might find this thread interesting, it shows many actual experiences with using the more value priced Lithium batteries:

    Cheap-Lithium-Batteries-Do-You-Have-Them-Do-You-Like-Them
    Last edited by SolarPoweredRV; 03-19-2023 at 09:24 AM.
    David and Peggy
    2019 Ford F350 Lariat, 6.7L Diesel, Dually, Long Bed
    Running with 20k Reese Goosebox (Love It) and Ford Factory "Puck" system.
    Stopping with 8,000 lb Disc Brakes and Titan Hydraulic over Electric Brakes system.
    Powering all this fun with 1200 Watts of Solar, two Tesla, Model S, battery modules, 24 volt Victron Inverter.
    2018 Solitude 310 GK

  7. #27
    Site Sponsor sande005's Avatar
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    Quote Originally Posted by SolarPoweredRV View Post
    Simply switching to a pair of Lithium batteries and replacing the Converter with a Lithium ready Converter would double your run time and literally let you sleep better at night .

    Here is a thread comparing Lithium batteries to Lead Acid batteries:

    Lithium-over-Lead-Acid-Batteries

    Also ,you might find this thread interesting, it shows many actual experiences with using the more value priced Lithium batteries:

    Cheap-Lithium-Batteries-Do-You-Have-Them-Do-You-Like-Them
    The inverter alarms when the lead acid is close to completely done, so I'm burning 200Ah. While not at all good to do for the leads, in the end I'd get about the same run time with the lithium's unless I went bigger or more. Very rare that I am off grid, so not a lot of motivation to dig into it all...first move might be to invest in travel CPAPs that don't pull the power like our current versions do (they're 24v.....so I'm converting 12 to 120 and back to 24, which is terribly inefficient by itself!).
    2017 Imagine 2670MK
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  8. #28
    Site Sponsor SolarPoweredRV's Avatar
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    Quote Originally Posted by sande005 View Post
    The inverter alarms when the lead acid is close to completely done, so I'm burning 200Ah. While not at all good to do for the leads, in the end I'd get about the same run time with the lithium's unless I went bigger or more. Very rare that I am off grid, so not a lot of motivation to dig into it all...first move might be to invest in travel CPAPs that don't pull the power like our current versions do (they're 24v.....so I'm converting 12 to 120 and back to 24, which is terribly inefficient by itself!).
    The alarm rings when the voltage gets low (probably around 11.8 volts). The Inverter does not draw down your batteries to 0% State Of Charge (SOC) before it shuts itself off, so you are not actually getting the full 200ah from your Lead Acid batteries.

    You might be better served with a 12v to 24v DC-DC Converter for use with your CPAPs. This would be fairly easy to install and much cheaper than two new CPAPs. I would recommend you look into the Victron line of DC-DC Converters, they can be adjusted to give you the actual voltage your machines need. You might want to try the DC-DC Converter before you even try the Lithium batteries. Just be certain your DC-DC Converter has enough amperage to run both machines.

    To find the appropriate DC-DC Converter, I recommend pkys.com, they are a reliable Victron dealer and they could help you choose the correct Converter. Note: their website is not slick, nor easy to use, but if you search for an "up-voltage DC-DC Converter 12v - 24v" you should get to the correct page.

    PS: the staff is very knowledgeable and should be able to help you if you need it, just have the exact voltage and amperage of your CPAPs.
    Last edited by SolarPoweredRV; 03-20-2023 at 06:45 AM.
    David and Peggy
    2019 Ford F350 Lariat, 6.7L Diesel, Dually, Long Bed
    Running with 20k Reese Goosebox (Love It) and Ford Factory "Puck" system.
    Stopping with 8,000 lb Disc Brakes and Titan Hydraulic over Electric Brakes system.
    Powering all this fun with 1200 Watts of Solar, two Tesla, Model S, battery modules, 24 volt Victron Inverter.
    2018 Solitude 310 GK

  9. #29
    Site Sponsor sande005's Avatar
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    Quote Originally Posted by SolarPoweredRV View Post
    The alarm rings when the voltage gets low (probably around 11.8 volts). The Inverter does not draw down your batteries to 0% State Of Charge (SOC) before it shuts itself off, so you are not actually getting the full 200ah from your Lead Acid batteries.

    You might be better served with a 12v to 24v DC-DC Converter for use with your CPAPs. This would be fairly easy to install and much cheaper than two new CPAPs. Iwoild recommend you look into the Victron line of DC-DC Converters, they can be adjusted to Gove you the actual voltage your machines need. You might want to try the DC-DC Converter before you even try the Lithium batteries. Just be certain your DC-DC Converter has enough amperage to run both machines.

    To find the appropriate DC-DC Converter, I recommend pkys.com, they are a reliable Victron dealer and they could help you choose the correct Converter. Note: their website is not slick, nor easy to use, but if you search for an "up-voltage DC-DC Converter 12v - 24v" you should get to the correct page.

    PS: the staff is very knowledgeable and should be able to help you if you need it, just have the exact voltage and amperage of your CPAPs.
    Wow, great tips! Thank you! I will definitely give them a look.
    2017 Imagine 2670MK
    2012 F-150 SCrew, Eco, 4x4 6.5 box
    Max. Tow, HD Payload, Airbags, ProPride hitch
    (Previous: Jayco 26.5RLS Fifth, Revolution Pinbox)

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