Building a new battery generator

Howdy everyone!

About 2 years ago I built a little 12 volt battery box based on a 15ah SLA battery housed in a .50 cal. Ammo can.  It was designed mainly to power mostly USB devices and the occasional 12 volt DC device.  And while it has given me good service it was also designed as practice for building a much larger unit based on a 100 ah unit with a dc inverter.

So I recently acquired most of the components I have started to build the unit.  I did make a fundamental change though.  I changed the battery type from a 100 ah SLA battery to a 20 ah LiFePo4 battery.  I did some research and found that in terms of actual power output the LiFePo4 battery has twice to 3 times the output compared to an SLA battery with the same AH rating.  I went with a 20 ah version because it was affordable and I left room for expansion so this could be a 40, 60 or maybe 80 ah system set in parallel in the future.

At any rate the device will eventually have the following outputs:

8 USB fast charging ports

2 USB type C charging ports

2 car type 12 volt power outlets

A collection of Anderson Power Pole jacks for genetic 12v power. (Probably 2-4 jacks)

1500 watt 120 volt inverter for AC power


I will send another post showing pictures of my build step-by-step in another post


I have a link to my original build here:

https://permies.com/t/135729/permaculture-projects/Building-pair-battery-generators

Eric

Here are some pictures so far

Hi Eric.  I like having little mobile power units around too.  I have been playing with a 223 can.  I put a 5 farad super capacitor with 2 x 5 ah batteries to charge phones and run lights.  It worked well until I was charging it on a snowy sunny day.  The darn thing hit 17v and the capacitors went poof.  I am going to put a charge plug in it separately now that is made to hook straight to a 10w solar panel.  I found some small voltage regulators cheap to experiment with.  

Hi Christopher and thanks for sharing your project.  

I didn’t mention this in my earlier post but my build will have no perforations in the case.  To use I will have to open the lid and everything will be accessed from a large panel that covers the inside of the case.  This is not necessary, but rather an idiosyncrasy of mine.  I want the case to remain completely waterproof while closed.  Again, not necessary, just my personal preference.

If this goes well I might at some point build a third unit from a .223 magazine case (larger than a regular.50 cal. Case.  This would have a 20 ah LiFePo4 battery and perforations for external power and at least one light.  But I am getting carried away with ideas and should probably stick to the project at hand.

Eric

Bear in mind that your 20Ah battery is going to have a limited output. I searched on amazon, and the one I pulled up specified 30Amps as the max continuous current draw. So your 1500 watt inverter is going to trip the battery BMS (if it has one) at just over 360 Watts. If it doesnt have one, the battery will likely be damaged by too large a load.

Lifepo batteries are much better than lead, but they do have limitations. You should reasonably expect 80% DOD on lithiums, so 20ah X 12V X .8 = 192 Wh

That 100Ah SLA could probably only reliably give you 50% DOD, so you would have more like 100 Ah X 12V X .5 = 600Wh. This also assumes a slow discharge, you will lose a lot more to the peukert effect if you discharge your lead batteries quickly. Lithium does not really suffer from that.

Carl,

Thanks for the math!

Actually I don’t really expect this battery by itself to do much in the way of powering ac power.  For ac I was thinking about expanding with another battery (or two, or three if necessary).  I would connect these in parallel.  I actually am setting up the internal placement of the battery for future expansion.

By the way, how many batteries do you think I would need to power the inverter?

Thanks in advance,

Eric

Just did the math myself.  Looks like with 4 batteries I will top out at just under the 1500 watt max.  I can live with that.

I will be watching this thread with great interest. Thanks!

Well, thanks to incoming weather, I will be getting out of school early and school is out for the rest of the week.  Hopefully I can get some work done.

BTW, if you or anyone has a good idea about securing the battery(ies) I am all ears.  The battery will go in a corner along the side and leaves space for up to 3 more batteries.  I don’t want to perforate the side and interior room is going to be tight with a total of 4 batteries.

For the moment I was thinking about attaching/securing with some high quality Velcro glued to the sides, but I am still open to suggestions.

Eric

I should point out one shortcoming in obtaining components, namely the case.

I have a medium sized rolling tool case/job box that I use to haul tools from place to place.  I really wanted to buy duplicate of that case.  If memory serves, it was a 35 gallon case.  While big, this would be easy for mounting and modifying if necessary.  Also, the interior was basically 4 flat sided with a flat floor—perfectly normal.

When I went to buy the case I could not find any (the brand was Blue Hawk).  The alternatives at Home Depot was either a broad but very shallow tool case or a gigantic 50 gallon rolling case (also $100, more than I wanted to spend).

I eventually found a Craftsman 24 gallon case with appropriate dimensions.  Unfortunately the interior is not as flat as I would like and the bottom has two levels—a small, higher one to accommodate the axle for the wheels and a larger, lower one.  If you look at the pictures, you can probably see two bottom pieces, and high one and a low one.  I am planning on mounting the battery on the lower one (unfortunately, near the handle, but I don’t plan on moving it too much.  

The inverter is long—it takes up a large portion of the internal length and will be mounted on one side.  If you look closely, you can see mounting blocks I glued in place.  I put in those mounting blocks because that was where the side of the case was flat.  They were attached with JB Weld plastic version.  I plan to mount a wooden plate to those blocks and mount the inverter to those blocks.  As this is plastic I am crossing my fingers that the JB Weld holds.  Finally, I plan on attaching the internal components (fuse block, etc. on the high floor.  

Though not visible—because I have not made it yet—the power outputs will be mounted to a top plate nearly flush with the top edge.it will rest by its own weight and be able to tip in the same orientation as the lid so as to make access to interior components straightforward.

So there is my plan so far.  I know that is a lot to explain with only a few pictures.  Hopefully I will have updates soon.

Eric

I included a picture to show the approximate location of the internal components.  I would like to run the inverter in a perpendicular direction opposite the battery but I want to leave room for airflow.  Another benefit of not squeezing all the components together is to allow air movement and better cooling.

Brief update:

School is canceled for the rest of the week so I thought I would make some progress on my battery generator.

I glued my side plate for mounting the inverter to the spacer blocks about an hour ago.  Prior to glueing I fit the inverter in place and attached it with screws.  I then removed the screws and the inverter, tipped the box on its side and glued the plate it with Gorilla Glue.  I have found GG to be a cheap but very powerful glue for wooden projects, especially where a little bit of squeezed out glue doesn’t really matter.

At any rate, here is a picture of the inverter briefly mounted to the side plate—though out of the actual box.

I made good use of the snow day today.

I got my side plate glued in place and the inverter is in place.  I think my next step is to include some actual wiring plans.

I will basically have two parallel circuits (unless anyone can suggest a better option).  One circuit will power the inverter and the other will power the dc plugs like USB and car 12v power.

I have one fuse block and one shunt for the battery multimeter (necessary with a LiFePo4 battery.  A simple voltmeter just won’t do).  I also have two roughly 10” pieces of 8 gage wire.  I would like to avoid needing two more pieces of 8 gage wire.

I am attaching a picture of the wiring instructions that came with the multimeter.  If anyone out there reads electrical diagrams and had any suggestions, please do fire away.

And a picture of the mounted inverter.

A picture with approximate location of internal components.  Nothing is fixed in place yet.

You are going to need some more wire, and either crimp-on lugs for making the connections or some of the aluminum blocks with set screws. Also, I do not see a fuse, and you always need a fuse anytime you connect something to a battery. A 50A fuse would be fine to protect 8ga wiring, and then use that all the way to the fuse block and to the inverter. You can connect multiple wires to the studs coming off of a a fuse or shunt. If you need more wire, home depot sells it by the foot in a variety of sizes, and they would also have the lugs you need. The shunt should go in the negative line, and then the meter can be connected to it with tiny little wires. 18 or 20 ga would be fine. Get a little inline fuse holder, and put a 1A fuse on the voltage supply to the meter. Wire your DC stuff from the fuse block back to the upstream side of the shunt so that the meter reads the current going to those loads. Use an appropriate sized fuse for whatever wiring you end up using for that. 14 ga would would probably be fine - that would let you pull 15A or 180W, which is all a 12v socket is generally rated for anyway.

I still think that inverter is WAY too big for what you are building. Bear in mind that if you wire it with 8 ga wire you will be limited to about 55Amps - and that is only 660 Watts. If you want to make it possible to use the full output down the road, you would want to beef up the wiring substantially (along with the batteries, of course).

Carl, thanks for your input.  I really appreciate the experience of others.  

I have a preliminary setup and I can send you a picture.

You may well be right about the inverter.  Originally this was going to be based on a SLA 100 amp hour battery but I switched to LiFePo4.  I only started with 20 AH thinking that I could add additional batteries in parallel later on.  If I need to replace my inverter with a smaller version,  then so be it.

I will send you a picture soon.  I have a migraine Headache I need to tackle right now.

Eric

This is a picture of a rough wiring layout.  It is not finished and I know some of the connections may not look right but I thought I would show how the overall layout is going to look.  

I just ordered a 30 amp in-line circuit breaker to shut down the inverter loop.  I know this will limit me to about 360 watts, but that’s about all I can run with this battery anyways.

The attached fuse block will run my DC side, meaning everything aside from the inverter such as USB, 12 car power sockets and the like.  I was thinking about protecting all the 12 gauge wiring on the DC side with 15 or 20 amp fuses, though I am open to suggestions.  If a 10 or even a 5 amp fuse is appropriate, please let me know.

At any rate, here is a VERY preliminary and imperfect layout picture.

12 ga wire can handle 20 Amps, so a 20A fuse would protect the wiring just fine. Some of the things you mention, like the USB sockets, are likely not going to need or be able to handle that much power, so you should try and fuse them accordingly. If you have a single USB port for example, that can put out 2 Amps at 5V, then you would only need to supply 10W of power. Convert that back to amps on the 12v side and you get 10/12 = .83 A So in that case, you could put a 1A fuse in your fuseblock and use very fine wires, like 16 or 18 ga. Trying to connect small electronics to beefy wire does not really work very well anyway.

Same goes for a standard automotive 12v socket - make the fuse match whatever it is rated to supply. The contact area in the plug is pretty small, and it will overheat if too much current is pulled through it. I seem to recall they are usually fused at 15A, but I cant really remember.

Its looking good so far!

I made a Block Diagram here.  This should clear things up more.  I know that my fuse block needs to be wired after the shunt so the whole thing will be in a series.

The R1 and R2 refer to two different routes by which I can wire in the fuse block (it can also stand for Red).  I am leaning towards the R2 line in order to keep everything in a series.  I guess series is going to be important as the battery multi-meter will need to measure the total draw of power across the shunt.  Also, I just purchased a 30A inline circuit breaker which I can also use as an on/off switch.

Carl, I do have much finer wire (16 gauge?) for the USB side of things.  I do know how even 14 gauge wire can get hard to move around in tight confines.  Also, thanks for narrowing down the size of fuse I will need for the USB side of things.

Any other thoughts?

Eric

I see one issue - you are switching from 8 ga from to 12 ga to run to the fuse block - this means that this section of wire is not really protected as well it should be. Since you are using a smaller breaker (30A) it would likely not be a safety issue, as 12 ga would probably handle that load briefly. 10ga or 8ga wire would be better. Larger wire has less voltage drop, so is a good idea for large loads - but with how small the loads coming off the fuse block will likely be it is not too much of a concern here.

R1 and R2 are both in parallel, and electrically equivalent. Series would mean that you wired the fuse block into the negative line of the inverter - which would not make any sense. You do need to make sure all the return paths to the battery (the negative wires) go through the shunt; which it seems you understand.

Breakers are nice to have. 12v is not dangerous to work on hot, but a battery can easily produce enough current to cause problems. I welded a wrench to the posts of a 12v car battery once by brushing it into the other pole. Thankfully I had another tool at hand and quickly smacked it free, but left to its own devices it would probably have melted. There are plenty of videos on youtube to inspire a mindset of safety when it comes to batteries.

Carl,

R1 and R2 are two wiring options I am considering.  I am not going to use both but you have a good eye for details.

The 12 gauge wire tapping from the shunt should be protected by the fuses in the fuse block.  I am assuming that the 10A or smaller fuses in the fuse block would protect it just fine or is there something I should know?

Also, the in-line circuit breaker would be physically more convenient if it were located on the negative side just out from the negative terminal level although I know it is customary for it to be located on the positive side.  Is there a reason for this?  Seems to me that a broken circuit is a broken circuit no matter where it is on the line.  Thoughts?

And again, thanks in advance, you have been very helpful.

Eric

I am sending an update.

There are two main differences.  

The first, not-so-obvious is the fuse box is wired to tap power directly from the red/positive lead from the inverter.  I needed to go and get a 1/4” ring terminal to make that work.

The second, obvious difference is that I have connected the inverter to the battery by a line with an in-line circuit breaker.  I had to buy a special, 30 amp breaker for this and I needed to drastically shorten the red wire that came with the inverter and the final installation just barely fit, but it is in place and I am satisfied with it’s location and the security of connection.

If I ever want to expand to a second or third battery I will need some serious rework but it will be fine for now.

Later today I should be getting a 20 amp in-line circuit breaker to protect the 12 gauge wire.  When that arrives I will work that in.

After that point I will need to start cutting the top panel and working it into place so I can start actually mounting outlets.

Thoughts?

Eric

Ok, I should have sent the picture!  Well, there it is.

It sounds like you are getting it figured out. Your system is not bonded to a ground, I think it is called "floating" but I do not exactly recall. That means that a fuse on either lead would interrupt the current just the same. In a car, the negative side of the 12v battery is connected to the frame of the vehicle. Since all the metal surfaces therefore return to the battery, you need to put the fuse on the positive side so that a ground fault (fault between positive wire and chassis) does not burn up the wiring. Also, DC breakers are polarity sensitive - if you use them in the negative lead, you would need to flip them around. There are some good responses on this forum about the question including some diagrams that might explain it better.

https://electronics.stackexchange.com/questions/445740/does-it-matter-if-a-fuse-is-connected-to-the-negative-or-positive-terminal-of-a

The 12ga black wire coming from your fuse block is going to the wrong end of the shunt - the meter will not be able to measure the current flowing through those loads. Think of the shunt as a bridge that all the electrons have to cross over on the way back to the battery to get counted - the ones from the fuseblock will go straight back to the battery without crossing it.

Carl,

So thanks again for your help.  I always thought that in the system like I have, a circuit breaker would work anywhere on the line, but I stuck with convention anyways.

Regarding the shunt, I was thinking that the 12 gauge line simply had to tap into power on either side of the shunt.  In my case, the black lead is tapping right AT the shunt because that’s the easiest place to do so while the red line taps at the inverter (other side of the shunt), again, for ease.  Is this not correct?

Thanks again,

Eric

Yes, a breaker anywhere in the system will work on a floating system. But, if the breaker has polarity, then it needs to face a certain direction to work properly. Putting it in the opposite leg would reverse that direction - so you would in effect need to be installing it backwards.

With the shunt, I feel like you are missing something about the nature of a circuit. Power is trying to make a loop from the two posts of the battery. It will take the most direct route back. As you have it wired, the power to the fuse block will not cross the shunt.



it needs to look like this:

So for the moment I am in a drying phase.  I can’t really make any more wiring changes until I have the top panel in place as the wires all now need to start running up.  More specifically, the wiring will need to run to the back by the lid hinge so the panel can be lifted up by the front edge so the internal components accessed.  At any rate, here is a picture of what the panel will look like prior to any holes being drilled or cut or any components mounted.

Eric

Ok, some progress today.

I have attached a couple of pictures.  The first one shows the top panel with the circuit breaker/master power switch at the top.  When I bought my in-line circuit breaker, they came in pairs so I thought I would make use of the second one by using it as a power switch.

The second picture is the top panel with several instruments roughly set in place.  As I have it set up, the switch is at the top, the multi meter is second, the inverter remote switch is third and the battery charger is at the bottom.  This is not a final plan.

The last picture is the battery now wired up into the switch and back down to the shunt.  It looks a little messy but I needed enough wire to connect from the floor to piercing the panel and allow for easily opening the lid from the front.

Eric

I am almost at the point where I can actually power something.  I am setting up components on my top panel now and wiring in my USB row.  I have finished for the night but with the addition of two black wires and two fuses, I should be able to power up the USB.  All-in-all I will have 8 fast charging USB 3 ports along with two USB type C ports.  I can test the USB 3 ports right away (at least for a few moments—I don’t have my battery meter hooked up yet).  I don’t have anything that charges by USB type C so I will just have to wait on that one.

But I am tired and finished for the night.  I will have a great place to start tomorrow.

As always, I appreciate any commentary.

Eric

Well, I thought I was doing well, but somehow my battery drained substantially and even hooking up my charge controller was not good enough to bring battery back up.

I ordered a LiFePo4 battery charger to bring the battery back to life but in the meantime I need to figure out how I am going to wire the unit differently.

I did, however, hook the charge controller briefly to my other battery pack just to power it up and get the parameters set—that is, set up for LiFePo4 from the standard SLA battery setting.

The charger should come tomorrow at which point I can start to figure out wiring again.

Eric

Anyone want to try to help me make sense of this wiring diagram for a 12v switch?  The color coding seems backwards to me.

Ignore the color code, and try to understand the current path instead. The black lead will be at high potential once the switch is thrown. The switch probably doesnt really care which direction the current flows through it, but it needs a certain polarity to be maintained for the LED to come on when the switch is turned to ON. I assume this is an illuminated switch? I suspect that the light would simply remain on at all times if the red and black leads were reversed, even though the switch would still function normally.

Carl,

What I have so far is that the yellow is the switched ground wire.  I can operate a USB socket using just the yellow wire and black wire attached in series with the switch performing a simple circuit-interrupt function.  During this time the switch blue light does not come on.  The little switch light would be nice but is not a total deal breaker.

I did make a simple circuit with a USB socket and switch powered by my older battery box and it worked fine aside from the tiny blue light.  When I try to get more than one socket set up, I apparently get a short and my battery box faults out.

Would any pictures help?

The intent is for it to be wired like this:


The yellow wire is not meant to be a switched ground, it is just a ground for the LED. Do you have a multimeter with a continuity test function? It is a handy thing to know how to use. Just measuring the resistance will also let you figure out how a switch is connected up inside, but in this case the diagram lays it all out for you.

Thanks Carl.  I have a volt meter with a basic continuity check.  And indeed, if I connect the probes to the yellow and black then the yellow switches.

I can also make a basic on-off switch hooking up this way.

I do appreciate the diagrams.  They are helpful.  I am questioning in part whether or not the yellow is in fact assigned correctly.

Eric

Here is a picture of the wiring setup when the socket switched properly but the little switch light did not illuminate.

The power supply is coming from off of the left side.  The switch is near the top and the socket at the right.  I know the picture is a bit confusing.

You have the switch in the negative lead of your load. The wiring diagram shows it being placed in the positive. If you want the light to work, you will need to follow the wiring diagram.

Edit: looking at the picture again, I realize that the colored wires on there just attach with spade connectors, dont they. So they could easily have been switched. Check for a resistance between the center and one of the other legs. A value in the hundreds of ohms would be your LED circuit.

On a slightly different note, is there any reason I shouldn’t use 16 gauge wire just for testing (not for permanent setup)?  I can’t find 14 gauge and the 12 gauge is taking a toll on my hands what will all the stripping for short test runs.  Also, I might be getting near the end of my run of 12 gauge and I don’t want to waste it on small test strips.

Scratch that.  It looks like I bought 25’ of whatever gauge the switches have coming out.  I think I will run with that.