Lithium battery fully charged! (1 Viewer)

[berni109]

Here is my planned solution to be implemented when all the bits arrive.
Attach a trailing lead fused 2 pin socket directly to the battery.
Butcher a metal box (knew it would come in useful one day) to have a plug that will attach to the trailing lead.
Inside the box will be a low voltage cutoff device that monitors when to switch off the load.
On top of the box will be:
A) H4 headlamp bulb connector. The headlight bulb will be the load to suck the juice out of the battery.
B) voltage display to easily monitor battery voltage.

When the van is parked up unused and I plug this in the solar panels and controller can be left to do what they are intended to do and I will have a very brightly lit van interior until the battery is depleted to 60% state of charge.

So what am I missing? Fire hazard? Fading furnishings?

Ps. Why dont all you pi enthusiasts start a new thread and share the information to a wider audience where it wont get lost in a thread that few will bother reading through in detail. Just a thought not a criticism

 

[cmcardle75]

Here is my planned solution to be implemented when all the bits arrive.
Attach a trailing lead fused 2 pin socket directly to the battery.
Butcher a metal box (knew it would come in useful one day) to have a plug that will attach to the trailing lead.
Inside the box will be a low voltage cutoff device that monitors when to switch off the load.
On top of the box will be:
A) H4 headlamp bulb connector. The headlight bulb will be the load to suck the juice out of the battery.
B) voltage display to easily monitor battery voltage.

When the van is parked up unused and I plug this in the solar panels and controller can be left to do what they are intended to do and I will have a very brightly lit van interior until the battery is depleted to 60% state of charge.

So what am I missing? Fire hazard? Fading furnishings?

Ps. Why dont all you pi enthusiasts start a new thread and share the information to a wider audience where it wont get lost in a thread that few will bother reading through in detail. Just a thought not a criticism

You won't be able to do it by voltage as state of charge can't be determined reliably by voltage on a LiFePO4.

The on-load timing should be calcualted to give around 60-70% from a known 100% charge. It isn't very critical, though.

For storage, you'd disconnect the solar. Indeed, it is best to literally disconnect the battery entirely to remove parasitic load and it'll last years from a 70% charge. Just check your BMS isn't greedy.

 

[steveh57]

Ps. Why dont all you pi enthusiasts start a new thread and share the information to a wider audience where it wont get lost in a thread that few will bother reading through in detail. Just a thought not a criticism

I’ll attempt to write a walkthrough when I get round to it,but my Linux skills are somewhat limited, which I guess is not a bad thing because if I can manage it so will many others.

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[berni109]

cmcardle75 said "You won't be able to do it by voltage as state of charge can't be determined reliably by voltage"
From the research I have done it looks like the discharge curve on lifepo4 is relatively consistent and with a slight downward gradient until it falls off a cliff at low state of charge.
13.1v looks to be the spot that I should be aiming for when the van is in storage. (Raul ?)
Ideally I want to leave all the electrics exactly as they are for normal use and just plug my gizmo in when I am not using the van for a few weeks.
Perhaps I am overthinking the whole scenario with lithium battery and should just except the suppliers contention that it's a drop in replacement and rely on the 7 year guarantee.

 

[cmcardle75]

cmcardle75 said "You won't be able to do it by voltage as state of charge can't be determined reliably by voltage"
From the research I have done it looks like the discharge curve on lifepo4 is relatively consistent and with a slight downward gradient until it falls off a cliff at low state of charge.

I wouldn't be so sure. It is hard enough determining SOC of a lead acid from its voltage/capacity graph and that has a much steeper curve (although admitedly its high internal resistance doesn't help). If you get your voltage set point even a fraction of a volt out, or any discharge affects the voltage at the terminals you might be burning energy until you hit the cliff edge, which won't be fun.

 

[Hoovie]

It's hard to get out of the lead-acid mindset, where 100% full is the target, which must be reached at least every few days to avoid degradation. The equivalent with a lithium battery is the 50% level. For long-term storage, that's the best. If not using the MH for weeks, best to discharge it to 50%, provided you have the time and the means to charge it to nearly full just before you need it again. I don't know of any automatic charger that will do that, but no doubt someone is working on it as we speak.

I do . (I am )

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[Pausim]

Avoiding long term storage of LiFePO4 batteries at 100% is best avoided but I think we are talking about months rather than days and weeks. The real killer is temperature, anything above 45C is very bad for them. Perhaps not a big issue for us in the UK but there could be a few in W Canada and NW USA that are now having to think about this.