Charging a phone from a 12V SLA battery

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timmmay

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#1352165 26-Jul-2015 21:11

linw: Hope the cell towers keep going so the phones you are charging work! You've got to hope the people you are ringing have UPSs as well

We have three different cell carriers (not deliberately), plus UFB which generally works during a power outage. Hey I'm not a paranoid nut, I just figure being prepared is cheap and it's an interesting little thing to do so I figure "why not?". Everyone should have food, water, heat, communications, and first aid in case of a disaster. Any maybe we just want to be able to play games on our phones if there's a massive earthquake ;)

1eStar

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#1352211 26-Jul-2015 23:15

Pretty inefficient having power banks charging the 12v battery. Find a separate solar charger for your 12v battery, boat/caravan people use them.

Aredwood

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#1352215 27-Jul-2015 01:38

timmmay: My cheap ebay car charger arrived and works well - it charges my phone at 1200mah. Success!

Next question. How can I charge a 12V SLA battery from a 5V USB source (a solar panel)?

5V is an unusual output voltage for a solar panel. Is there some sort of regulator circuit inside it? (to allow you to connect USB devices to it maybe?) Otherwise buy another 2 of them if they are cheap and wire them in series.

timmmay

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#1352239 27-Jul-2015 07:43

1eStar: Pretty inefficient having power banks charging the 12v battery. Find a separate solar charger for your 12v battery, boat/caravan people use them.

Aredwood: 5V is an unusual output voltage for a solar panel. Is there some sort of regulator circuit inside it? (to allow you to connect USB devices to it maybe?) Otherwise buy another 2 of them if they are cheap and wire them in series.

It's made to charge USB devices directly. I guess the better option now it's pointed out is to charge the 12V directly from solar then charge the USB devices from that. The disadvantage there is I can't directly charge USB, which could be handy say on holiday sometimes, though I have a 12V to USB converter with crocodile clips on the end the adapter. For the same wattage the 12V panels are almost twice the price of the USB panels though - at least the ones that ship to NZ.

richms

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#1352247 27-Jul-2015 07:48

If you are looking at panels online the power ratings are complete fabrications on most of the small ones for charging small devices.

I have a couple of "2.5" w ones that are about 1 watt.

Richard rich.ms

timmmay

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#1352252 27-Jul-2015 08:00

richms: If you are looking at panels online the power ratings are complete fabrications on most of the small ones for charging small devices.

I have a couple of "2.5" w ones that are about 1 watt.

Interesting. Maybe a 12V panel (which actually seem to go up to 18V) would be best. Get a regulator of some kind to charge the SLA when required, otherwise I might use it to power fans out in the greenhouse in summer - oscillating and extraction.

timmmay

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#1352545 27-Jul-2015 13:54

Do I need some kind of a charge controller between the solar panel and the SLA battery?

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richms

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#1352602 27-Jul-2015 14:57

Depends if its a long term thing and the current of the panel vs the trickle current that the SLA takes.

There are basic charge controllers on ebay and aliexpress for not much, they will turn off when full, but no MPPT so wont get the most out of the panel. But at the sizes for a SLA, its a bit of a who cares type thing, MPPT would cost more than a few extra watts of panels.

Richard rich.ms

timmmay

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#1352704 27-Jul-2015 17:07

richms: Depends if its a long term thing and the current of the panel vs the trickle current that the SLA takes.

There are basic charge controllers on ebay and aliexpress for not much, they will turn off when full, but no MPPT so wont get the most out of the panel. But at the sizes for a SLA, its a bit of a who cares type thing, MPPT would cost more than a few extra watts of panels.

It's a long term thing, I expect the system to work for years with very few cycles. Amazon has charge controllers for $10, what's the downside? What's MPPT? Do they consume power so less gets into the cell? I can live with that, this is for emergency use so I can always take it out if required.

richms

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#1352716 27-Jul-2015 17:28

Maximum power point tracking. It means it will pull the max watts from the panel and use a DC to DC to step it up or down to put the most into the battery. Other ones will overload the panel when the battery is low making the wattage they pull from them drop, and when its getting near high it may not be getting the best. Its basically something that trys to automatically match the load to what is available from the panel.

PWM ones will just throttle the charge rate to stop the battery being overcharged, but do nothing to help max the rate when the battery is way low.

Richard rich.ms

timmmay

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#1352743 27-Jul-2015 18:00

Ok, thanks. This page explains it for people who can't quite keep up with you ;) I guess a cheap charge controller will help prolong battery life and costs $15 or so, so I might as well do it. Maybe something like this one? It's PWM, but comes with cables, which is handy - they sell a bundle with their panels too, like this - but reviews are average. Otherwise this one, which reviews better but not sure it comes with cables - which is just a PITA.

jimbob79

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#1352774 27-Jul-2015 18:31

Build your own solar charge controller:

https://www.youtube.com/watch?v=RAHxeNlRUZc
http://256.uk/?page_id=68

timmmay

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#1352839 27-Jul-2015 19:35

Nah, too lazy, plus I like well made stuff. My home made stuff is often ugly and less robust than commercial.

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