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Solar generator expansion batteries - how do they work ?

meetyg

Solar Addict
Joined
Jun 4, 2021
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So how do these off-the-shelf expansion batteries work in portable solar generators / power stations?

I mean if they connect directly to the battery of the main unit, the two batteries will most likely have a voltage difference and a large inrush current will flow from one to another.
How do the manufacturers mitigate this issue?

Do they have some sort of current limiting circuit?

Also, which battery is used first ? Or are they truly in parallel?

The reason I'm asking is mainly educational, for planning expansion batteries in my DIY solar generator builds.
 
I am sure the commercial brands, such as Ecoflow, have more sophisticated circuitry, but for DIY, I posted a separate thread that may be of help to you here: https://diysolarforum.com/threads/expansion-battery-hack-for-diy-solar-generator.88126/
First, I really like your DIY builds! They look professional, with tons of capacity in a small enclosure.

However, as you mentioned, your solution is either/or. I'm really curious how the big guys do this "parallel" magic with thier expansion batteries.

They might have a current limiting DC-DC converter on the output of each battery. But then those need to be some beefy converters, to handle the large loads.
Sounds inefficient and costly.
 
First, I really like your DIY builds! They look professional, with tons of capacity in a small enclosure.

However, as you mentioned, your solution is either/or. I'm really curious how the big guys do this "parallel" magic with thier expansion batteries.

They might have a current limiting DC-DC converter on the output of each battery. But then those need to be some beefy converters, to handle the large loads.
Sounds inefficient and costly.
Thank you. These builds have definitely been refined over time with tinkering and new ideas. If the Ecoflow Delta 2 extra battery offered something more in the way of independent features---USB outlets, 12v socket, grid and solar charging---it would be far more compelling and practical to add on. Yes, it would cost more than it already does, but would be so much more useful. Basically a Delta 2 without an inverter. As it is now, my smaller 160Ah system has the same capacity as the Delta 2 with the extra battery. Will be interesting to see how commercial products continue to add features.
 

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