Building a pair of battery generators

I have a couple of final details to add.

First off, the solar panel is on its way.  It’s not a lot—just a 28 watt unit to keep the battery topped of and maybe change on a summer day.

Secondly, I am working on an AC charger for charging on nights and cloudy days.

These two details should round out the system and leave it complete.

Eric

Update,

My solar panel arrived.  It took about 1/2 hour to wire up some connectors to hook it to the battery unit (I was moving slow).  

I have lots of great things to say about the Wago connectors.  They made hooking up a piece of cake.  Also, when the panel is not in use, I stick a connector on the end to prevent an accidental short.

After hooking up the panel to the battery through the charge controller, the battery was reading 13 volts, up from the 12.8 volts earlier (I have used the battery a little bit just to test things).  So there is no doubt that the battery can charge via sunlight.

The panel is rated an a nominal 22 volts at 1.55 amps I thought that this was perfect for charging a battery and the panel is only about 12”x18” so it is not obtrusive.  More interesting, I tested the panel on our floor in a bright sunny patch.  The light passed through glass in the window made of e-glass, so some light was knowingly blocked.  But not too much as the panel read about 21.5 volts just laying on the floor.  I even took a blanket and tossed it, all crumpled up to intentionally shade, and the volt meter still read about 14 volts, so it looks like I should be able to charge on a cloudy day.

I had planned on making a little ac charger but I am wondering if this is still necessary or even desirable.  I should be able to change in daylight at pretty much anytime.

Eric

Hello all,

It’s been a while since I last posted, but I thought I would comment on a couple of points.  First, much as in the previous post, I have to say that the solar panel is very handy to have.  Basically, as long as I have daylight (even through cloudy skies) I can get electricity and charge the unit.  Just make certain that when the solar panel is not in use that the power leads remain electrically separated and insulated from each other.  The panel can generate a surprising amount of electricity even without trying.  I will try to get some pictures of the attached solar panel soon.

The second point relates to a separate section of Permies.  If you are reading this and find it interesting, consider the PEP section HERE:

https://permies.com/f/412/pep-electricity

There are a number of projects detailed here that could be interesting to read, but especially might be interesting to try.  The list of projects is growing and it would be nice if we could get more people to document their projects and especially get the associated BB.  I linked this post to the electrical section but there are a number of other PEP areas as well.

Thanks to everyone who has followed this project and made commentary, it is sincerely appreciated.

Eric

Great build and mini portable prewired energy system! I want to try those Wago connectors soon too.

Anyone want to critique this set HERE:

https://www.amazon.com/Mighty-Max-Battery-Inverter-Outlets/dp/B01MQGXPFW

I have dropped my inverter to 1000 watts to save money and I really just don't think I will need a full 2000 watts.  I am new to both the inverter and the battery game but this looked like a good combination for the price.

Thoughts?

Eric

Well,  I had my first major malfunction on my battery generator.  I believe that my charge controller failed.  Normally when I plug in the solar panel the charge controller shows a little icon of a solar panel with an arrow pointing to the battery.

I tried hooking up a power supply into the charge controller and the solar power icon would not appear and the battery would not charge.  The battery was reading 11.8 volts and 11.5 volts is considered to be reaching a danger point.  After a couple of hours of attempted charging, the battery showed no improvement in its charge and the charge icon never appeared.  I went ahead and ordered a new charge controller for about $20.

One bit to add.  I initially attempted to charge with an old printer power supply that provided a little over 12 volts at about 1 amp.  Oddly, the online directions stated to only use a solar panel and not use a “dc power supply for charging.”  I find this curious as the solar panel provides over 20 volts at a couple of amps while the modified printer power supply provided barely over 12 volts and only at about 1 amp.  I would think this would be plenty safe for charging—underpowered if anything.  I actually had to run down the battery to below 12 volts (I stopped at about 12.9 volts) just to see if the printer power supply would work.  So far it has not and the directions suggest it might be harmful but for the life of me I can’t understand why.

I am open to any and all suggestions or input.  I can believe that the charge controller was cheap and failed on its own.  But if my meager ac to dc power supply caused it harm, I would like to know how/why.  It does not make sense to me but maybe someone else better versed can provide some illumination for me.

Thanks in advance,

Eric

I solved my own problem and I am embarrassed.  I bought a new charge controller for about $20.  Not terribly expensive.  I hooked it up, connected it to the solar panels and—no solar panel icon and no charging.

I thought I had some major problems till I turned the main panel upside down where I saw a disconnected wire—problem solved.

Like I said, embarrassing.

Eric

Can anyone explain this?

So I was testing/using my battery box which drained the battery down to 11.8 volts.  I made a couple of DC chargers from old printer power supplies and those got me to about 12.3 volts.  Today was relatively warm and sunny so I took my battery pack and 20 volt, 28 watt solar panel outside to sit flat on the ground and soak up some sunlight.  After about 1ish hours, the voltage surged to 13 volts!  I let the system set longer, admittedly though some thin clouds and checked after a couple of hours and the voltage was 12.9 volts.  I just considered this a fluke, moved the battery to avoid some approaching shadows from a tree and placed on a slight southern incline just as the clouds broke into clear air.  I let the unit sit for a couple more hours when the wind picked up, clouds moved in and I decided to bring things inside.  This time when I checked the voltage was at 12.6 volts.  I brought everything in, disconnected everything and checked again and the voltage was 12.5 volts.

Can anyone explain to me why the voltage would spike from 12.3 volts to 13 volts only to drop back to 12.6 volts, all while attached to a 20v 28 watt solar panel in sunlight?  I hypothesized that maybe the battery had cooled off sitting on cold ground and was just not as capable of putting out the voltage like a warm one would.  But that is just my idea.

I am going to try again tomorrow if the weather is sunny and see what happens.

But if anyone has a better explanation of why a battery would discharge while under charge, I would love to hear.

Thanks in advance,

Eric

Update here:

It is 12/3/2021 and I am updating my experience with my new battery box.  The little box had sat around for several months and I finally decided to give it a little torture test.  I wanted to see how many phone charges I could get from the battery.

It actually worked fairly well but I do need to make an adjustment.  I started with the battery at 12.5 volts, not bad for sitting around.  I charged my phone 50% and barely touched the voltage.  I then charged 4 devices (including one iPad) all at once.  By this point the battery dropped to around 11.9 volts.  I then charged my phone 4 more times and used the phone while connected for some time.  The voltage dropped to 11.5v.

Turns out that I should not discharge below about 12.1 volts for max battery life.  I doubt I had a real 12.5 volts to start with so my figures are probably off.  

At the moment the battery is outside and being charged by a 20 watt solar panel.  I expect to get around 13 volts by this afternoon.

I will keep updating.

Eric

Your next project prompted me to catch up on this thread. Great documentation.  Even though I have solar and a generator, I will probably dive into a similar project. The idea of a portable power source makes sense.

Thanks John.

If I were to make one more portable power unit after this one it would be based on a 5.56mm magazine ammo can which is about 50% larger than my .50 cal ammo can.  I would use the 20ah LiFePo4 battery I use now instead of SLA. I would go ahead and perforate the case for easy external power access and have at least 1 outside light.

I know this is probably premature but I still like to concoct new ideas.  If this helps you, so much the better.

Eric

Solar ammo can update (12/28/2022):

It’s been a while since I have posted.  I have been working on and off (mostly off, such is life) on my larger build HERE:

https://permies.com/t/174618/Building-battery-generator

I am at a point on my larger build where I need to install a coulomb meter or charge meter.  This is different from a regular volt meter on a lead-acid battery because the discharge profile of lithium batteries is so flat that measuring voltage alone does not really give a very good indication of total charge in a LiFePo4 battery.  The charge meter also gives all sorts of good information like amperage and such.

Unfortunately I have had 3 such meters that have failed to some degree.  These were cheap Amazon specials so I guess I get what I pay for, but I have a 4th(!) coming and I want to test it out by giving it power before I hook it up and install it.  I plan to use my ammo can battery box as the power supply as it is very convenient for these purposes and I thought I would update it as it has been sitting around unused for 10 months.

The battery may have been a bit over discharged.  I once discharged it to about 11.9 volts and apparently 12.1 is the lowest I should go.  Yesterday I wired up an old laptop power supply (19v, 6 amps) and let it charge the battery box for a couple of hours.  The charge went right up to 13 volts but quickly came back down to 12.6 volts, barely .2 volts above where it had been at after sitting for 10 months unused.

Right now I have sunny skies so I am letting it charge outside in the sun on a solar panel.  I am curious to see if the solar panel charges any better than the laptop brick.  I don’t know why it would, but I will report my findings.

Eric

I forgot to add,

While I expect that my battery box will work fine for today’s project, if it will not fully charge or hold a charge, I have two options and I may do both.

Option #1.  I might buy a new SLA battery and replace the existing one, keeping in mind that 12.1 volts is the new minimum voltage (might even install a low-voltage cutoff switch).  A new battery costs $30-$35, so not a terribly expensive fix.

Option #2.  I could take the battery out and stick it on a charger I have that has a battery restoration setting.  Apparently it can go through a desulfurization process.  If this is true then the cost is nothing.

And I may do both.  Having an extra battery around is not such a bad idea.

Eric