4 ms·

This is nice idea that I watched some video about it few months ago, but will prowse (do you know him?) didn't like the idea as he prefers all lithium (he think

This is nice idea that I watched some video about it few months ago, but will prowse (do you know him?) didn't like the idea as he prefers all lithium (he thinks it's cheap enough), I'm living in 3rd world country with a LOT of power outages (basically no power), I have a solar array with tubular lead acid but I'm soon switching to LiFePo4 when my package come from China, I feel tempted to implement your idea instead of selling my acid batteries. Do you think I can use MPPT controller instead of DC-to-DC charger? Technically it works like that I think

roflyear 4y ago
Yeah he knows way more than I do - and I agree that all lithium is probably the best way to go if you can afford it and are starting from scratch. In my case, similar to yours, I had a ton of lead already - replacing all of it would have cost a lot of money, and would have been wasteful as the lead was only a few years old. > Do you think I can use MPPT controller instead of DC-to-DC charger? Only two issues I can think of, but definitely do your own research: 1) unsure if you can set up something for the MPPT to cut off charge if your source battery drops below a certain voltage, which you can do with at least some DC-DC chargers, and 2) it is common for MPPT charge controllers to lack the capability to boost voltage, just convert it lower. #2 can be mitigated by setting up your lithium bank to provide higher current, which has its own dangers, but has added benefits as well such as requiring smaller diameter wire. #1 is a serious concern and can also give you safety problems outside of maybe killing your lithium - so please make sure you're being safe and doing your research. maybe ask in diysolarforum.com ? I haven't posted there myself but have gotten great info from threads there.
- aiProgMach 4y ago
  Thanks for the advice I will consider posting a question on the forum when the package arrive. Will's opinion was a comment on this video btw, I can see now it's not totally negative though [1] For the problem #1 I think the BMS can solve the issue as I already ordered a JBD BMS so it can cut off whenever it reaches the critical voltage. For #2 you're right I think I should check, my MPPT is good one (Epever) but not sure it could lift the voltage properly from such a narrow difference, unless maybe I use higher voltage (such as 48) than my pack 's voltage (24v) so it will be guaranteed to only reduce the voltage to the lead acid levels. Thanks so much! -- 1: https://youtu.be/tAuPfgZgXec https://youtu.be/tAuPfgZgXec
  - diggernet 4y ago
    I used to have an Epever MPPT. Really nice unit. However, as I recall, the manual emphasized that you should only use solar panels for the input. This is because when the battery is full the MPPT will stop charging by shorting the input. This is fine when the input is solar. But if you are doing LiFePO4 -> MPPT -> lead, it's going to short out your LiFePO4 battery when the lead battery is full, which would be very very bad.
    - aiProgMach 4y ago
      I checked the manual and wasn't able to find this warning, but you might be correct. Thanks for heads up I didn't think of this scenario!
  - roflyear 4y ago
    Yes - I have watched this video. Emily & Clark have a different setup, as he uses a different device (or even, no device) to connect the two different banks (lithium and lead acid). I didn't see Will's comment tho, thank you for sending that, very thought provoking! The comment by him "Trickle charging lead acid all night with lithium seems very inefficient" is 100% true, but in my case I consider this effect a bonus b/c the lithium acts like a capacitor for the solar array (quickly charges, then slowly charges the lead!)
    - aiProgMach 4y ago
      You're right, I think my situation is similar to yours. My solar array is not so big (for now at least) so I have lot of power in the noon but less in other times, so it will be very helpful to have a lithium pack that absorb all that power quickly and then feed it to the lazy lead pack over the next few hours.
      - roflyear 4y ago
        yes, same - I only have 400W of solar!

roflyear 4y ago

Yeah he knows way more than I do - and I agree that all lithium is probably the best way to go if you can afford it and are starting from scratch. In my case, similar to yours, I had a ton of lead already - replacing all of it would have cost a lot of money, and would have been wasteful as the lead was only a few years old. > Do you think I can use MPPT controller instead of DC-to-DC charger? Only two issues I can think of, but definitely do your own research: 1) unsure if you can set up something for the MPPT to cut off charge if your source battery drops below a certain voltage, which you can do with at least some DC-DC chargers, and 2) it is common for MPPT charge controllers to lack the capability to boost voltage, just convert it lower. #2 can be mitigated by setting up your lithium bank to provide higher current, which has its own dangers, but has added benefits as well such as requiring smaller diameter wire. #1 is a serious concern and can also give you safety problems outside of maybe killing your lithium - so please make sure you're being safe and doing your research. maybe ask in diysolarforum.com ? I haven't posted there myself but have gotten great info from threads there.

aiProgMach 4y ago
Thanks for the advice I will consider posting a question on the forum when the package arrive. Will's opinion was a comment on this video btw, I can see now it's not totally negative though [1] For the problem #1 I think the BMS can solve the issue as I already ordered a JBD BMS so it can cut off whenever it reaches the critical voltage. For #2 you're right I think I should check, my MPPT is good one (Epever) but not sure it could lift the voltage properly from such a narrow difference, unless maybe I use higher voltage (such as 48) than my pack 's voltage (24v) so it will be guaranteed to only reduce the voltage to the lead acid levels. Thanks so much! -- 1: https://youtu.be/tAuPfgZgXec https://youtu.be/tAuPfgZgXec
- diggernet 4y ago
  I used to have an Epever MPPT. Really nice unit. However, as I recall, the manual emphasized that you should only use solar panels for the input. This is because when the battery is full the MPPT will stop charging by shorting the input. This is fine when the input is solar. But if you are doing LiFePO4 -> MPPT -> lead, it's going to short out your LiFePO4 battery when the lead battery is full, which would be very very bad.
  - aiProgMach 4y ago
    I checked the manual and wasn't able to find this warning, but you might be correct. Thanks for heads up I didn't think of this scenario!
- roflyear 4y ago
  Yes - I have watched this video. Emily & Clark have a different setup, as he uses a different device (or even, no device) to connect the two different banks (lithium and lead acid). I didn't see Will's comment tho, thank you for sending that, very thought provoking! The comment by him "Trickle charging lead acid all night with lithium seems very inefficient" is 100% true, but in my case I consider this effect a bonus b/c the lithium acts like a capacitor for the solar array (quickly charges, then slowly charges the lead!)
  - aiProgMach 4y ago
    You're right, I think my situation is similar to yours. My solar array is not so big (for now at least) so I have lot of power in the noon but less in other times, so it will be very helpful to have a lithium pack that absorb all that power quickly and then feed it to the lazy lead pack over the next few hours.
    - roflyear 4y ago
      yes, same - I only have 400W of solar!