DIY Solar Setup - AGM vs Li Battery

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Brandoo

5 posts

Wannabe Geek

#280751 7-Jan-2021 21:18

Hey there.

I've been interested in trying a DIY solar setup, mainly just mucking around but keen to see test while eg. camping (inflating air bed with build in pump and charging various devices as well as lighting at night).

I grabbed a 180W panel from Banggood (expect it's 100 to 120 W) as well as Renogy PWM 30A PWM controller.

What I'm interested in, is power storage. I've found an Sealed AGM 45 Ah battery for around $250 and Jaycar has LiFePO4 25 Ah for around $340.

How comparable are these batteries? Is it better to go with the lower rated Li - or stick with the Sealed AGM?

FYI looking at setting up something like https://www.youtube.com/watch?v=IRRKHYwB3Uo (either 600W or 1000W inverter).

timmmay

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#2632218 8-Jan-2021 08:42

I would be concerned that a cheap charger can't charge the LiFePO4 battery properly and ruins it. Do some searching, and read this (found on Google). AGM (lead acid basically) is fairly tolerant so I'd probably do that.

I have a 120W panel and a few 30AH AGM batteries, with a cheap PWM controller. I got them so if we have a disaster I can run the router, charge phones, charge AA batteries, run USB lights, etc, with appropriate adapters. They're about 6 years old, on the PWM all the time in parallel, and my estimate is the capacity has dropped by about half. I think when I refresh the batteries I'll not leave them on charge all the time, I'll just charge them once a month with a good quality battery charger and test the solar occasionally.

A 45AH battery will weigh about 15kg, 50% more than a car battery, it's not something you want to carry around too much. You might be ok with a 15 - 30AH battery. You can discharge them to about 40% I think, much lower damages them.

Brandoo

5 posts

Wannabe Geek

#2632283 8-Jan-2021 11:00

Thanks!

The charge controller I purchased has a setting for Lithium batteries.

What I'm wondering is how comparable these batteries? I understand the AGM
should stay above > 40% so roughly is equivalent to approx 25Ah(?) where as the lithium should stay above 20% which would be around 20Ah(?)

Is this how it all works - or do the Ah ratings already take in to consideration the recommended max discharge ratings?

Jase2985

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#2632384 8-Jan-2021 11:43

no the AH raiting is a full discharge normally, you take your DoD off that. so its cheaper to get AGM and you get more capacity

timmmay

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#2632409 8-Jan-2021 13:16

For maximum longevity I keep Li batteries between 40% and 80%, but down to 25% is not too harmful. The rule of thumb is less depth of discharge is better. Reference.

For your experiments I'd probably get a medium sized AGM, if it's useful you can buy a larger one or switch to Li.

neb

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#2632503 8-Jan-2021 15:53

Brandoo: The charge controller I purchased has a setting for Lithium batteries.

Is that specifically LiFePO4? Generic "lithium" refers to LiIon, not LiFePO4, you can't charge them the same way.

Brandoo

5 posts

Wannabe Geek

#2632583 8-Jan-2021 20:16

Thanks... Lithium sounds too complicated for me right now!

Will stick with the AGM I found.

I guess another question would be re: inverter. I've read that the cheaper
modified inverters should be fine for my use case.

Are PSW inverters important for charging electronic devices and an air pump?

rp1790

738 posts

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#2633362 11-Jan-2021 07:31

Brandoo: Thanks... Lithium sounds too complicated for me right now!

Will stick with the AGM I found.

I guess another question would be re: inverter. I've read that the cheaper
modified inverters should be fine for my use case.

Are PSW inverters important for charging electronic devices and an air pump?

Whereabouts are you? I have a whole lot of solar gear, good stuff, and 2 x LifePO4 batteries if you are in the Wellington region?

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Brandoo

5 posts

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#2633592 11-Jan-2021 13:15

I'm in Wellington :)

What were you thinking?

rp1790

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#2633608 11-Jan-2021 13:31

Brandoo: I'm in Wellington :)

What were you thinking?

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