Mobius battery based power pack

[hg1027]

I'm going to need a battery for a trip coming up. I'll be out for about 2 weeks, with a long drive every ~3 days. Power will be available at each campground, but not at each site.

I'm planning on using Mobius battery packs.

Primary demands will be one laptop for ~4 hours a day. I don't know how to determine the specific demand, if anyone can advise, if that's necessary. Also a Verizon hotspot, similar time, again unsure how to determine what it will actually draw. My wife will use her laptop a bit if she can, and we'll charge some flashlights and radios and cell phones. Those things will also be charged in the car between sites, so may not need much.

As far as a shopping list, I'm looking at some posts by @jonyjoe101 such as here and here and @RDinNHand AZ here.

I need a charger. I think I can just use a laptop charger through a generic cc/cv charger assuming I can find a barrel receiver to match my Dell output. And assuming the Dell charger isn't too smart to work.

I think I need to put a current and voltage display on the charging side, to make sure that's all working as intended. This guy seems to combine charger and screen.

On the output side, I think I need something like this 20A 300W Step Down Buck Boost Converter. I think I could probably use another one of these on the charging side, but not perfectly clear. I think I also want a display on this side.

After that, I would go to a fuse panel then to whatever output I want. I'm thinking 2 cigarette jacks for now, and just use car adapters for USB as needed, but I could build in a buck converter and put USB ports on whatever box I build.

I think I'll build the charge and load boxes separately, so I can have a pack charging somewhere while I'm using another pack somewhere else.

So, any suggestions? Wrong parts somewhere in there? Tell me I clearly don't know what I'm doing and I'll burn the house down?

 

[Rando]

Aren't these 3 cell lithium ion packs - with an operating voltage more like 10V? While the battery packs themselves are cheap, it is going to take a bunch of work to make these work with a 12V nominal system and you don't know what the remaining lifetime of these are. It seems like not much more money to start with new LiFePO4 cells that are compatible with 12v systems and are of a known condition and don't need DC-DC converters on both input AND output. It also seems that for the simple application you describe you could buy a cheap preconfigured lithium power pack (Jackery, Rockpals or whatever the current Amazon deal is) and have a more compact unit for the same price, but I understand if building it is half the fun.

 

[hg1027]

Thanks for the reply.

I'd be happy to buy off the shelf, but for the price, I'm not sure it's anywhere close. I think I can do this for under 200 with 3 batteries, and each one is 26ah. Jackery 240 is $200, 16ah, and not expandable.

It seems there's no shortage of jackery or whatever brand, so if I get down to the wire, I'll go for one of them. Just seems like if I can get more for less, with a little bit of effort, I may as well. And I might learn something.

 

[Rando]

Does the extra capacity matter if you don't need it? Laptop batteries are typically ~50 - 80 Wh, and a hot spot and cell phones are about ~10Wh. Recharging all your devices all the way should be somewhere around 80 - 120Wh (assuming you do no charging in the car). A Westinghouse 200Wh pack is around $120 and should be more than enough power for what you describe. Once you add up the cost of the batteries, converters, chargers, displays, USB ports, 12V sockets, wire, connectors, enclosure etc, I would guess you would be far more than $120 in and then end product will be less compact, less functional and less reliable than the Westinghouse unit.

If the goal is to have a fun DIY project, then go for it, but you would still do better to use LiFePO4 cells.

 

[plh]

I hate to put this out there, but I just bought 5 of these - might want more... hope they do not get sold out ( LiFePO4 cell packs )

60 LiFePo4 FullRiver 18650 cell in a 12v 22.5Ah pack

These are packs of 60 cells that are composed of 5 smaller packs containing 12 cells each, the configurations is 4s3p. Just like the Eve cells the wiring for these are a bit on the thin side so you will want to upgrade the wiring or limit your amps. Also please note that these packs have a BMS...

www.batteryclearinghouse.com

 

[hg1027]

Does the extra capacity matter if you don't need it? Laptop batteries are typically ~50 - 80 Wh, and a hot spot and cell phones are about ~10Wh. Recharging all your devices all the way should be somewhere around 80 - 120Wh (assuming you do no charging in the car). A Westinghouse 200Wh pack is around $120 and should be more than enough power for what you describe. Once you add up the cost of the batteries, converters, chargers, displays, USB ports, 12V sockets, wire, connectors, enclosure etc, I would guess you would be far more than $120 in and then end product will be less compact, less functional and less reliable than the Westinghouse unit.

If the goal is to have a fun DIY project, then go for it, but you would still do better to use LiFePO4 cells.

Interesting, I had not looked at any other brands since I assumed they were all similar price. I think I'll order that, at least as a backup, and think about a diy later.

 

[hg1027]

I hate to put this out there, but I just bought 5 of these - might want more... hope they do not get sold out ( LiFePO4 cell packs )

60 LiFePo4 FullRiver 18650 cell in a 12v 22.5Ah pack

These are packs of 60 cells that are composed of 5 smaller packs containing 12 cells each, the configurations is 4s3p. Just like the Eve cells the wiring for these are a bit on the thin side so you will want to upgrade the wiring or limit your amps. Also please note that these packs have a BMS...

www.batteryclearinghouse.com

I guess I'd have similar questions on setting this up, except that the wattbox noted above also used lifepo4, so I could copy most of the accessories.

 

[plh]

I guess I'd have similar questions on setting this up, except that the wattbox noted above also used lifepo4, so I could copy most of the accessories.

yes, but being LiFePO4 cells are 3.2V (20% SOC) it make a "good" 12.8V nominal / 14.4V full charge in 4S arrangement instead of Li ion which is 3.6V per cell or 10.8V nominal / 12.6V full charge in 3S arrangement or 14.4V nominal / 16.8V full charge in 4S arrangement.

You wouldn't need the 20A step down buck with a 4S LiFePO4 setup.

I built a 4S Li Ion pack last summer and am reconfiguring it to 4S LiFePO4 cells.

 

[jonyjoe101]

If you already have the mobius, they should work for you, I been using mine since last november. All you need is a boost/buck converter to charge them (dc to dc) and also for the output (regulated output). If you plan to charge the mobius with AC power (laptop adapter) then all you need is a buck converter to reduce dc output to 12.6 volts.

The mobius will power most devices as is, for fridges or devices that are sensitive to low voltage you will need a boost/buck converter. With a boost/buck converter set to 13.2 volts output, the mobius will power my fridge even when the mobius voltage reaches 10 volts.

If you use a laptop 3 to 4 hours a day, 1x mobius will power it for about 5 days. You can use the mobius as a single unit or you can connect in parallel to increase the AH. I got these results using a small 200 watt inverter powering my 12.5 inch screen I5 laptop.

No need for lifepo4, my 220ah lifepo4 had problems powering my fridge because everytime the conpresser came on the voltage sag caused problems. The mobius is ready to go, the only DIY is the connectors and the charging system. Doesnt get any easier then that, and its as safe as any other powerpack with its "industrial" grade BMS. You can gauge the battery status by voltage: 12.6 is full, 10 volts is near empty, 9 volts is when the bms shutsoff.

boost buck converter (this is used for dc to dc) for instance charging from the car 12 volt system, boost converter raises the voltage to 18 volts then the buck lowers it to 12.6 volts, doing it this way lets you get max amps to the mobius. Also this can be used as a regulated output. The buck converter has two small screws that let you set the output voltage. Just make sure you use a fan to keep it cool. This is simple to build 2 input wires to the boost, then 2 wires output of boost to input of buck, then 2 wires output of buck to accessorys. The other wires are for the toggle switch and led meter. With this boost/buck I charge the mobius at 6 amps, these converters are overrated and if you try to run them at the advertised amps they overheat and short out. I lost about 3 boost converter, I havent lost any of the buck converters.


These are the LED volt/amp meters I'm using. The 10 amp model (no shunt required) cost around 6 dollars, the 50 amp model (shunt required) cost around 8 dollars. On these just pay close attention on how to wire up the shunt/amp wires. The amp input to the meter has a red and black wire, but the wires should both be black.

 

[hg1027]

Gave up on the diy for now and ordered a jackery 240. Might go crazy and put together a solar panel.

I will be taking a little piece of this research and ordered a fuse box and new crimpers for my 69 beetle. So not all lost.