Ready-made lithium powerboxes

My new project is a "lithium powerbox", see most recent post here: https://bkhome.org/news/202004/top-plate-of-lithium-powerbox.html

It is interesting to see what is out there, ready-made. There are many powerboxes, of varying capacities and features. Most of them are designed to be portable and readily removed from the vehicle. One of the biggest of these highly-portable types, that I know of, is a 60AH unit made by iTechWorld:

https://itechworld.com.au/collections/lithium-batteries/products/lithium-portable-power-station-1000-watt-itech1000

...which is a very nice all-in-one solution, at an excellent price. It has compromises, such as only charging via the cigarette light socket, so probably limited to 10A charging. The documentation states that it cannot be used when charging.

The more "hard core" solution is a powerbox that is intended as an alternative to a permanently wired-in system. Many 4wd owners go the latter route, with a custom permanently wired-in installation -- which often looks very messy and may be space-inefficient.

The semi-permanent "hard-core" powerbox may be left permanently in the vehicle, or taken out, perhaps if you are not going camping for awhile and need the space for something else, or change to another vehicle. These powerboxes are designed to charge directly from the car battery, at 20A or more.

I did a quick survey of what is available in Australia, in this "hard-core" category. One that I knew of from before is "The Lithium Box":

http://rvlithiumsystems.com.au/Portable-Power/portable-power.html

...the smallest has a 100AH battery and weighs 21kg -- too heavy for me! I can't see prices anywhere.

A Perth company has put together the "National Luna" box:

https://perthpro.com.au/product/customised-national-luna-redarc-portable-battery-box-dual-battery-system-with-25a-dc-dc-charger/


...with Amptron 100AH lithium battery, price is AU$1,990. Weight is 18kg.

Here is another, the "JTS Power Easy" box:

https://jts12volt.com.au/product/lithium-dual-battery-power-easy-pack/

...price is AU$2,795, with 100AH battery. Weight is given as 55kg ...gulp!

But wait, there's more! If you would like a battery box with DC-DC charger but without the battery, so that you can add your battery-of-choice later (AGM or lithium), there is the "Kickass Premium Battery Box", at AU$689:

https://www.australiandirect.com.au/buy/kickass-12v-battery-box-with-dcdc-mppt-solar-charg/KABB-G-KADC

...though, not yet available. ETA is August 2020. It is their DC-DC charger that is holding things up -- it has been on pre-sale for a few months. No doubt it is coming from China, and will do once the factories start up again, and shipping improves. 

Tags: nomad

Top-plate of lithium powerbox

The plywood floor is 235x225x9mm, with 12x20x1.5mm angle assembled around it, see previous blog post:

https://bkhome.org/news/202004/base-of-lithium-powerbox.html

The top of the powerbox will be a flat surface. This is plywood measuring 238x228mm (3mm longer on both sides than the base plate). In this case I have used 6mm ply, which will also be used for the sides. It is just that I have 6mm marine ply in my garage, and want to make use of it.

I also have some 12x12x1.5mm angle in the garage, so have used that around the edges:

...that is upside-down. Here it is the right-way-up:

The screws are 6G 9mm dome-head, for metal and wood, which meant the tips stick out the other side of the plywood. However, it was easy to file the metal tips flat to the surface.

This gives me a completely flat surface on top, on which the DC-DC charger will be mounted, plus two grab-handles.

A practical detail for anyone in the future who might follow these plans to build their own powerbox: if you cut the pieces of aluminium angle too short, no problem as they will be hidden by external plywood cladding.
On the other hand, if a tad too long, a simple way to grind the end is like this:

I used coarse sandpaper, 40-grit. The sandpaper is intended for sanding wood, but worked OK grinding aluminium -- the grains did not come off. The trick to doing it is press firmly with the finger closest to the end, and drag towards you -- pushing away from you does not work so well.

The top and bottom plates require corner posts. These are angle pieces riveted on the inside corners. I used 12x12x1.5mm angle, 30mm long. The rivets are aluminium 3.2x3.2mm (requiring a 3.2mm, or 1/8 inch, drill bit). Here they are installed in all corners:

Another practical detail: I used two "clamping pliers" to hold the corner posts while drilling. Otherwise, you could use a small block of wood and g-clamps.

What will happen next, is there will be 175mm lengths of 12x20x1.5mm angle vertically on each corner. The reason for having the inside posts is that the final result will be a flush surface onto which the plywood cladding can be screwed -- except for the little bumps where the rivets are, but that can be fixed by appropriate indenting on the back sides of the cladding.

EDIT 2020-05-01: Important design change
After building the powerbox, I found a very big problem, it was very difficult to access the battery terminals. The fix is to make the top-plate removable.

Which it isn't as shown in the above photos, as the screws are underneath, inside the box. So, instead, screw from the top, through the plywood into the aluminium.

Please see this post, that shows the final box with battery inside:

https://bkhome.org/news/202004/dc-dc-charger-issues-and-powerbox-improvements.html

The box will then have removable panels on all four sides and the top. The screws used are 8G 15mm button-head timber screws:

https://www.bunnings.com.au/zenith-8g-x-15mm-galvanised-button-head-stitching-timber-screws-35-pack_p2410091

The drill bit used is 2mm. The wood screws are able to self-tap into the aluminium.

Placement of the screws needs to be thought about. I placed them 8mm in from the edges of the plywood, and they need to be placed so as not to be underneath where the DC-DC charger is proposed to be located. Also, there are two handles on the top, which will also have screws that tap into the aluminium. 

  

Tags: nomad

Confusing online voltage drop calculators

I received an email from Gerard, claiming that my voltage-drop formula is wrong, by a factor of 2. That is, where I calculated 1.11V drop, Gerard said it should be 2.22V. See this post from a couple of days ago:

https://bkhome.org/news/202004/cable-sizes-for-battery-camping-system.html

The factor of 2 difference should have been the big hint. I was confused for awhile, as some online calculators seemed to support what Gerard claimed. But then we both realised the reason for the difference...

Most of the online calculators are for AC cable, with ISO sizes, and use of twin-core. The online calculators require the length of the actual cable to be entered, not the total "round trip" through each core. So for my 15m cable from the solar panel, "15" has to be entered into the online calculator, not "30".

In other words, where it asks for "cable length" it means the length of the twin-core cable, not adding the return path.

Regarding ISO sizes, these are used for electrical building wiring in Australia and just about everywhere internationally. There is a nice table here that shows AWG versus ISO sizes:

https://topwiretraveller.com/sizing-automotive-wiring/#3---table-of-common-cable-sizes-

In fact, that page is an excellent read to understand about all of the different cable sizes -- and in particular how confusing "auto cable" is:

https://topwiretraveller.com/sizing-automotive-wiring/ 

...that page has an online calculator, that requires entry of the length of one core, so in the case of 15m twin-core, enter "30". 

Tags: nomad

Base of lithium powerbox

I have constructed the base, or floor, of what is intended to become a lithium battery power box. See previous post in this new project:

https://bkhome.org/news/202004/powerbox-fuse-redesign.html

The foundation is a good place to start, as you would build a house. Having the floor, how the rest will fit in can start to be seen. Here is the floor, with battery:

...that empty space on the side of the battery is where the electrical wiring will go, with a side-opening to enable easy access. Also in that gap, at the front there will be the front-panel sockets and coulometer LCD display.

There is about 20mm gap at the back-side of the battery, where there will be some cabling. The externally-mounted circuit-breakers will be directly behind the battery.

The DC-DC charger sits on top of the box, and grab-handles will also be screwed onto the top of the box.

Here is the detail of the floor of the box:

The floor is a piece of 9mm thick plywood, 235mm along the front, 225mm deep. I painted it, hence the off-white colour. I used marine ply, but anything will do, even a chopping board from Kmart or BigW.

Though, the chopping board would need to be 9mm thick or more. The screws are 6G 9mm dome-head metal/wood type, from Bunnings -- I couldn't find any shorter screws, hence the thickness requirement of the plywood. Well, actually, 8mm plywood/chopping-board would do, as the aluminium angle is 1.4mm thick.

The aluminium is unequal-angle, 12x20mm, 1.4mm thick. I cut each piece 3mm longer than the board, 45 degree cuts using a mitre-board and hacksaw. Three holes in each for the screws. I pre-drilled holes in the plywood, so as not to stress the plywood when screwing the screws in -- as they are close to the edge of the plywood.

I bought 20x12x1.4mm angle, 3m length:

https://www.bunnings.com.au/metal-mate-20-x-12-x-1-4mm-3m-aluminium-unequal-angle_p1079496

Also, for later in the project, 3m of 10x10x1.5mm channel:

https://www.bunnings.com.au/metal-mate-10-x-10-x-1-5mm-3m-aluminium-channel_p1079640

Only simple hand tools have been used, which I anticipate will be the case for the entire powerbox. 

Tags: nomad

Powerbox fuse redesign

Previous post for new camping powerbox:

https://bkhome.org/news/202004/cable-sizes-for-battery-camping-system.html

A couple of days ago, created a preliminary circuit diagram, with quasi-physical layout:

https://bkhome.org/news/202004/portable-lithium-power-for-camping.html

After more study of other circuits, I have redesigned with two more fuses:

Previously, if the bottom-right circuit breaker was switched to open-circuit, while still charging from the car's alternator, it may have an odd effect on the +bus. Now, that circuit-breaker disconnects from the +bus, and another fuse has been added to the "DC out" (black Anderson plug).

It may be overkill, but I also added one to the grey plug, going out to the solar panel.

I also made a note for the red Anderson plug. Modern cars have "smart" alternators, where there is a shunt between the battery negative terminal and chassis-earth, just like I have done with the lithium battery in above diagram.

For the electronic control system of the car to recognise the existence of the DC-DC charger, the negative lead from the red plug must go to chassis-earth, preferably close to the car battery.

EDIT 2020-05-03:
A "protected +bus" has been added -- the "+bus" is connected directly to the lithium battery, whereas the "protected +bus" is on the other side of a 30A circuit breaker. Also, binding posts have been added. Both of these changes are discussed in a later blog post:

https://bkhome.org/news/202004/dc-dc-charger-issues-and-powerbox-improvements.html

Consequently, the circuit diagram has been updated:

 

This was created by Dia (a Linux GUI application, available in EasyOS, Quirky, Puppy Linux, and most other Linux distributions). Here is the Dia file:

https://bkhome.org/news/202004/files/powerbox-wiring-diagram3.dia.gz

Here is the file exported to SVG:

https://bkhome.org/news/202004/files/powerbox-wiring-diagram3.svg.gz 

Tags: nomad

Cable sizes for battery camping system

This is a continuation of the new project, a portable lithium-battery power system for camping, see the first post here:

https://bkhome.org/news/202004/portable-lithium-power-for-camping.html

It doesn't have to be a lithium battery -- my project can easily be used with a deep-cycle AGM/GEL battery. The Amptron DC-DC charger that I am using can handle all types of batteries.

In previous camping trips, I used somewhat undersized electrical cables. I used a "6mm" automotive twin-core cable, 15m long, from solar panel to the MPPT battery regulator. From the battery to my tent I used a Narva "heavy duty" 5m cigarette-lighter extension cable (purchased from Autobarn).

Thinking about the cable run from solar panel to MPPT regulator. You need to be careful what the vendor is selling you when they claim "6mm". 6mm automotive cable is slightly less diameter than 10AWG. AWG is the same as B&S -- these are American wire standards, widely used internationally, including Australia.

I found a nice table of wire sizes, from here:

https://offroadliving.com.au/blogs/articles/q-a-series-3-what-is-b-s-and-why-is-it-so-important-to-the-output-of-your-solar-panels

The table doesn't have it, but the wire diameter of "6mm" auto cable is 2.42mm. Those diameters are actual copper wire diameter, not including the insulation.

The big question is, how much power was I losing in that fairly thin cable? There is a formula:

		Length (m) x Current (A) x 0.017
Voltage drop	=
		Area (mm2)

...that constant 0.017 is for copper wire.

My 15m cable is 30m round-trip. My "250W" panel was at best only giving about 10A. Plug the values into the formula:

Voltage drop = (30 x 10 x 0.017) / 4.59
             = 1.11V

Let's say that the panel is putting out a voltage of 16V, so the power output of the panel is:

Panel power out = 16 x 10
                = 160W

And the loss in the cable:

Power loss = 10 x 1.11
           = 11.1W

...that is a power loss of 7%

Do I want to throw away that much power? No...

Firstly, I decided on a shorter cable. I used 15m before, as there was one site where I had to place the panel a long way from my car and tent. However, can make-do with just 10m.

I purchased 10 metres of 6AWG from Big Al's on eBay. I like Big Al's, delivery has always been remarkably fast. Though, my purchases were pre-Covid-19, so I don't know about the current situation.

This is the cable I bought:

https://www.ebay.com.au/itm/124137673594

That is heavy cable! Expensive, but much cheaper than buying it locally. Plugging it into the formula:

Voltage drop = (20 x 10 x 0.017) / 13.30
             = 0.255V

So the power loss is 2.55W, which is 1.6% ...ah, much better!

Then there is the 5m cable running from the battery (in the car) into my tent, to run light, computer, fan ...and maybe even a TV. I have a fridge, but that stays in the car.

I have not done quantitative measurements yet, but did have a problem on the last camping trip. I took two laptops, my old power-hungry one, and a modern baby one. I powered them (one at a time) through a 150W inverter, and it would cutout when tried to run the old laptop -- this was because the voltage into the inverter dropped to 11.5V, which causes the inverter to turn off.

On that occasion, I was also running an LED lamp, and was charging my phone. Sometimes plugged a USB 1TB HDD into the laptop.

So the plan is to upgrade to 8AWG cable, and probably keep the length of 5m, or maybe a tad longer, say 6m. Will need to do some calculation of power load and voltage drop first. 

Tags: nomad

Portable lithium power for camping

Unable to go camping, but putting home-isolation to good use -- starting a new project, a portable lithium battery box for camping.

My solar water distiller project isn't finished -- I had hoped that it would be, however, the last prototype did not perform as well as I expected. Sometime, I intend to modify the last prototype, to see if the efficiency can be improved. for now though, starting a brand new project...

I own a Dometic 45AH battery box, with deep-cycle AGM battery. This is lead-acid technology, and has various limitations:

EDIT 2020-05-09: Added item-7 to comparison list 

1. Should only be discharged to 50%, any more will dramatically shorten the life of the battery.
2. The battery must not be left in a partially-discharged state, it must be charged promptly.
3. The number of discharge-recharge cycles is about 600-1000 (when discharged to 50%).
4. Self-discharge about 2%/month at 20degC, 4%/month at 40degC.
   
5. Lead-acid batteries are very heavy -- a 12V, 100AH AGM battery weighs about 29kg.
6. Voltage drops considerably at lower state-of-charge.
7. Discharge/recharge cycle 70-85% efficient (15-30% lost as heat). 
   

...they are just the ones that I can think if right now!

If the battery can only be discharged to 50%, that means my 45AH battery is effectively only 22.5AH. As I go camping infrequently, I need to be mindful of the self-discharge, and attach a battery charger every now and again.

Comparing the above items with a LiFePO4 lithium battery:

1. Should be discharged no lower than 20%, otherwise life will be shortened.
2. OK to leave indefinitely in a partially-charged state.
3. The number of discharge-recharge cycles is about 2500 (when discharged to 20% capacity, 80% DoD), and about 5000 cycles when discharged to 50% capacity.
4. Self-discharge is about 1-5%/month (I don't have any accurate figures for this).
   
5. A 12V 100AH battery weighs about 11.5kg.
6. Voltage stays fairly constant right down to nearly 0% capacity.
7. Discharge/recharge cycle 90-92% efficient. 
   

Several years ago I bought a 110AH AGM deep cycle battery, but at over 30kg I could not lift it. Well, I could, at great risk of putting my back out. Sometime after that I bought the Dometic 45AH box --mostly because I could lift it!

So, finally have decided to go over to a lithium system for camping. I purchased an Amptron 12V 50AH battery -- oh joy, it weigh only 7kg! The company claims that even if discharged 100% (DoD), that is, down to 0% capacity, it will still give 2000 cycles -- hmmm. If I discharge it by 80% DoD (down to 20% capacity), that gives me 40AH, almost twice that of my Dometic battery box.

Here is the company web page for this battery:

https://www.amptron.com.au/12v-50ah-lithium-lifepo4-battery.html

...and immediately you will see a problem: the price. yes, AU$545, plus postage. For 100AH, you would be looking at around AU$800 - 900. You can find cheaper on eBay, but beware, they are cheap for a reason.

Anyway, I have been squirrelling-away parts required for this project over the past several months. Have recently ordered a couple of final parts off eBay -- coming from the other side of Australia, so may take awhile. Just about have everything ready to go, sitting here in my loungeroom, and can now eye-ball it all and visualize how it will fit together.

What I am proposing is a portable box, that will sit in the front of my vehicle, where the passenger's legs would normally go -- I am hoping that there will be enough space for the occasional passenger to place their legs beside/behind/in-front of it -- whatever.

But it could go anywhere, for example behind the front seats -- you would just need to run longer cables from the car's battery.

To get the ball rolling for this project, I need a circuit diagram, but I want one that also indicates the physical layout. I constructed the diagram in Dia, an app in EasyOS and EasyPup. This is the result, exported to PNG:

Here is the Dia file:

portable-4wd-wiring.dia.gz

Here is the file exported to SVG:

portable-4wd-wiring.svg.gz

EDIT 2020-04-12:
The circuit diagram has been improved, see later post:

https://bkhome.org/news/202004/powerbox-fuse-redesign.html 

...more fuses, to make it safer.

A note about Dia: I found it to be adequate. I couldn't see how to create arbitrary snap-to nodes. There doesn't seem to be any object rotation. These are features that were in diagramming apps that I used 20 years ago in Windows. Anyway, managed to construct a reasonable-looking diagram.

The left side of the diagram is the "front", which would be the side facing the door, so that the readouts can be seen. The right side is the "back", furthest away from the door.

In a vehicle, you would bring a single-core cable from the ignition key. This will have 12V on it when the ignition is turned on, and tells the DC-DC charger that charging will be coming from the car's alternator.

A twin-core cable will come from the car's battery, to a red Anderson plug. Both of these can be easily unplugged if it is desired to remove the battery box from the car.

The circuit breakers are there just-in-case. but probably useful to turn off if not going camping for awhile -- the DC-DC charger does draw a small current in standby mode.

The Amptron coulometer LCD display also draws a small standby current, however I have wired that directly to the battery terminals, as it needs to be calibrated for the battery, and calibration might be lost if power is disconnected.

The black Anderson plug on the "front" is DC output, for whatever purpose required. It can also be used for charging the battery -- I have an Amptron mains-powered 15A LiFePO4 battery charger, which can plug into the black Anderson plug -- handy to recharge the battery if it is not being used for camping, maybe removed from the car. 

That's enough for this blog post. I plan to provide more details as the project progresses, such as where to buy the various components, design of the box, putting it together, and anything else required. 

Tags: nomad

Distiller basin-type proto-3 test result underwhelming

This has taken me by surprise. I have posted reports on what was intended to become DIY plans for a solar water distiller. Last post here:

https://bkhome.org/news/202002/finishing-touches-to-solar-water-distiller.html

...there have been many prototypes, and the latest is "basin-type prototype-3". Yesterday was a sunny sky, just a few wisps of cloud, predicted maximum temperature of 32 degC, so I decided to test the distiller.

I put in 1.5 litres, then used wood shims under the feet to level the basin -- very easy to do, just make sure the water is spread across the entire surface. Then added another 2.5 litres.

Here are the measurements during the day:

Time am/pm	Amb. degC	Sun W/m2	Top degC	Back degC	Comment
9.05	24.4	850	28.3	26.2	Full sun at 8.15am
10.05	25.5	940	38.9	30.2	5mm water in bottle
11.05	26.7	975	50.1	35.3
12.25	28.2	980	62.1	44.2
1.05	29.2	999	65.8	44.5
2.15	30.6	980	63.8	45.3
3.15	30.5	930	60.6	45.5
4.20	30.5	820	51.8	41.1	Stopped at 6.00pm

Total collected distilled water: 1.23 litres

That is not as much as expected. See here for comparison:

https://bkhome.org/news/201912/solar-distiller-showdown-take-2.html

And for the record, some further analysis that lead to design of the latest prototype:

https://bkhome.org/news/201912/further-analysis-of-basin-type-distiller-test.html

The current design, with 20 degrees glass slope, has very large side-walls, and the temperatures measured on the back outside are rather high. I might construct insulation on the side walls and test again. Note, those top and back temperature measurements were taken with the IR meter held about 2 inches away from the surface, about 3/4 the way up the glass and the back side. 

Tags: nomad