DIY: Mini Solar 'generator'

[tx2sturgis]

What charge controller will be good enough?

You are going to need a controller that is designed to charge the LFP4 batteries. 

Here are a some that might work well:

https://www.bioennopower.com/collections/solar-controllers

https://genasun.com/products-store/mppt-solar-charge-controllers/mppt-for-lithium-batteries/

 

[jonyjoe303]

Does one really need an mppt controller for this? Thanks for any info.
For a 50 watt panel, you don't need mppt controller. Most panels under 120 watts are 21 volt panels A cheap 20 dollar pwm controller will work. You only need mppt for the larger 36 volt panels. Mppt uses the higher voltage to extract more amps from the panel.

 

[John61CT]

No charger I've come across as labeled "for LFP" has ever actually delivered a charge profile I consider suitable for longevity.

Any charger, or power supply, that is user custom setpoint **adjustable** will do a better job.

Good overcurrent protection is also important.

 

[RVTravel]

Hi John. I did read the thread on charging lithium where y'all mentioned a lower charge voltage being better.

 

[RowanFae]

That's awesome!

A couple questions from a completely ignorant of solar/electronics person so please forgive any stupid questions.

About how much does it weigh?

Can you use a higher watt solar panel with what you put together and if so, how much higher?

How much of the battery power is usable without risk of over draining or is that not as much of an issue with the type of battery you used. Like, if I used it in my tent overnight to run a fan and keep my phone charged or to watch a couple hours of video on my laptop?

 

[tx2sturgis]

I just weighed it with a handly little fish scale I have, and the pack weighs about 7 pounds, and the 20 watt panel weighs about 3 pounds.

The controller I used is rated at 4.5 amps, so with this controller, you would be limited to about 75 watts of solar with very little safety margin.  50 watts would give more safety margin for controller heat tolerance, very sunny days, etc. 

It works quite well for charging phones, laptops, etc. I have even used it to power a small 12v tire inflator to add air to my trailer tires.

I will be adding a simple, inexpensive, voltage monitor to it, just havent gotten around to that yet. I use this thing a LOT when I'm out and about..

I often set it up on a picnic table and run my laptop (using a 'car charger') and charge my phone for an hour or two, with or without the solar panel attached. Of course, the battery needs to be charged when possible, usually the next day.

I also wired up a charging cable that plugs into my dash and charges the pack's battery while I drive. I unplug the solar panel, and plug the cord in, and the pack is recharged as I drive.

It's been working well and I dont leave home without it!

 

[RowanFae]

I think that's really cool, and I might try to put one together. Not any time soon, maybe after winter. Sure would come in handy.

 

[tx2sturgis]

I added a small, simple voltage monitor light to the lid of this portable pack...its made by GammaTronix. They are made for motorcycles so the form factor is small, simple, waterproof, and easy to install just about anywhere.

Standby current is very low, as low as .5 ma when not charging. 

It is steady green during charging, and flashing green when not charging but battery voltage is OK. 

Blinking yellow if battery voltage drops below 12.5 volts.



I also installed one on the exterior of my trailer, so I can check the voltage of the trailer battery from outside, when the trailer is stored and I dont even have to unlock the door, plus, I can easily monitor the battery voltage in the trailer while traveling. A bonus: at night when the solar panels aren't charging the battery, the LED blinks and looks kinda like an alarm system light.



GammaTronix voltage monitor:

https://www.ebay.com/itm/Motorcycle...e=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

 

[Seminole Wind]

Maybe 20-60AH? True deep cycle, flooded unless you really need sealed.

do you have a source or link recommendation for true deep cycle batteries in this amp hour range?

 

[John61CT]

No, but can list mfg I trust to check with.

You really **need** small and light? FLA or AGM?

Note they will be pricey enough it may be cheaper to just get standard once replaced more often.

Especially if won't be cared for properly.


A $200 pair of Deka FLA GCs is usually the cheapest true deep cycle batt, and shallow-cyvling 200+AH will just make them last (much) longer if otherwise well coddled.