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This guy thinks outside the box adding lead to a LiFePO bank...

Hi I'm Clark. I'm the guy in the video.
You are all right to be concerned with the charging and reconnect issues. I agree that a dc-dc charger is not the right solution for this problem for the reasons listed above. The lead would prefer a longer time cooking under the solar panels. I made another video describing the other side of this (from my point of view)

And I will be making one video about something that you guys might find interesting.
I've developed a circuit that disconnects the lithium batteries when they are charged fully and only reconnects when both banks meet at the same voltage so there is no problem with inrush current.
This circuit diagram will be made available for anyone who is handy with a soldering iron and I might do a production run for resale if there is interest.
This might be the answer to my system. I am converting from Lead Acid to LiFePo4 and have a PMA wind generator designed for Lead Acid. This would take care of the problem I was facing when the LiFePO4 are completely charged and the wind kicks up and needs a place to absorb the winds power and activate the dump load control.
 
The PMA wind generator on my system works very well especially at night and during winter. The relatively young lead acid I have should remain for that, and for added capacity when I install the lifepo4. So I ordered the BBMS to run them in parallel. Might be a few months before it's set up, but I am optimistic.
 
This might be the answer to my system. I am converting from Lead Acid to LiFePo4 and have a PMA wind generator designed for Lead Acid. This would take care of the problem I was facing when the LiFePO4 are completely charged and the wind kicks up and needs a place to absorb the winds power and activate the dump load control.
The issue I see with this configuration is if you have a shorted cell and multiple parallel strings, you are in for a bad time. Think about the internal resistance of a LiFePO4 string feeding into a shorted cell Lead Acid string. Could cause a big mess and lots of heat.

If you go this route, use OCPD on each parallel string, no exceptions. Size it correctly for your application.

In my opinion, I would avoid this configuration. Make a larger LiFePO4 battery instead. They are cheap these days.
 
The issue I see with this configuration is if you have a shorted cell and multiple parallel strings, you are in for a bad time. Think about the internal resistance of a LiFePO4 string feeding into a shorted cell Lead Acid string. Could cause a big mess and lots of heat.

If you go this route, use OCPD on each parallel string, no exceptions. Size it correctly for your application.

In my opinion, I would avoid this configuration. Make a larger LiFePO4 battery instead. They are cheap these days.
Appreciate the reminder, and I absolutely agree with using OCPD, no exceptions! What about the EG4 24v with overcurrent protection built in, would that suffice? I am looking at that build, and would still be inclined to fuse on top of that, agree?
 
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When I saw this it struck me as the right answer for people who live in places where temps stay below freezing over long periods.

Given a stinky two-week run in the weather (happens a lot in northern flyover country), a reasonable-sized lifepo bank could get depleted so it no longer had enough energy to keep itself warm and therefore couldn't take any charging at all -- a total fail. For this reason, in those areas, lifepo-only systems just aren't a viable answer.

AGM systems aren't that great, but you can always keep them operating at some level of power. Series-connected panels trickle-charging unheated AGMs in the freezing temps is better than no power at all. Worst case; you can at least get them going again with the next sunshine if they really run low and you have to shut all the power down.

Then came this answer of using a two bank AGM and lifepo system. Set it up like this:

Have the batteries in separate enclosures and have the AGM bank set up so it can also provide power for the Lifepo-bank battery warming pads. Normal operating mode is when enough solar is available to charge the AGMs and to warm and charge the lifepo bank, with the load power being provided by the lifepos. In bad weather, once there isn't enough sun-power for both banks, favor the AGM bank charging and use what you can of the lifepos. When heating the lifepo bank becomes impractical, use only the AGMs; i.e.: Just charge and use the AGMs when temps and sun preclude charging the lifepos because there isn't enough power to heat the lifepo battery bank. When conditions become better, warm up the lifepos and start again.

This approach gives a controlled-failure-with-backup set to the problem of weather becoming too cold and too bad for too long for you to bet your life on a lifepo-only system.

Why isn't that a better way to set up for those conditions? What would you suggest instead, besides massively more panels and batteries?
 
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