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DIY 12v 35Ah (420Wh) Portable Power Box


GotAU?

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I made this 12v 35Ah (420Wh) portable power battery with left over parts, but you can do it for $100 to $150 (or more) depending on options you want, such as solar charging, vehicle charging vs. 120v charging, adding a 120v power inverter, etc.

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The battery is based on a low cost 12v 35Ah deep cycle gel cell made for mobility scooters and trolling motors like these:

Mighty Max Battery ML35-12 - 12V 35AH U1 Deep Cycle AGM Solar Battery Replaces 33Ah, 34Ah, 36Ah Brand Product 

 
 
 
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Mighty Max Battery ML35-12 - 12V 35AH U1 Deep Cycle AGM Solar Battery Replaces 33Ah, 34Ah, 36Ah Brand Product https://www.amazon.com/dp/B00K8E0WAG/ref=cm_sw_r_cp_api_i_k-tQEbXSZ1ZA0

The case is a HF plastic ammo box with a built-in handy cover storage area for cables, connectors, etc.:

https://www.harborfreight.com/tactical-ammoutility-box-64113.html

And I added a switch, voltage meter, USB power pluss and a cigarette lighter plug port like this to it:
 

 
 
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Linkstyle 4 in 1 Charger Socket Panel, 12V 4.2A Dual USB Charger Socket Power Outlet & LED Voltmeter & Cigarette Lighter Socket & LED Lighted ON Off Rocker Toggle Switch for Car Marine Boat RV Truck
 
https://www.amazon.com/dp/B07JHH5YP4/ref=cm_sw_r_cp_api_i_.buQEb57XPGAE

Also adding a 13.8v step up transformer to run my refrigerator and drone charger as they are designed for slightly higher voltage than the 12v a automotive battery provides after the engine turns off:
 
 
 
 
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DC-DC Boost Module 9-14V to 13.8V 10A 138Wmax Power Supply Converter
 


Stay tuned, this project is in progress still (adding fuses and additional plugs) so I will add more info to the build here shortly, including how to make just the basic version with the parts listed above and just a few more.
Edited by GotAU?
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That is an excellent project with very apparent good workmanship . I have had 2 accidents  ( both of which could have been fatal) attempting to use  power directly  from my vehicle with the hood up. More fuses are a plus. 

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1 hour ago, Gilaoro said:

That is an excellent project with very apparent good workmanship . I have had 2 accidents  ( both of which could have been fatal) attempting to use  power directly  from my vehicle with the hood up. More fuses are a plus. 

I am glad you’re safe! I always (now) try to wear goggles whenever I am messing around with my batteries under the hood, yes due to other accidents I’ve also had, like the time I hooked up a 12v charger set on fast charge to a 6v tractor battery... ever see a mini acid geyser?  Doh!!

I totally agree about fuses and circuit breakers, I went so far as to putting a circuit breaker on my spare truck battery under the hood and ran cables from that to the back of my pickup where I have an fuse protected outlet that recharges this battery.  In the photo I took here, there’s a fuse not seen in the battery wiring underneath the box’s auxiliary panel.  Since then, I also installed a circuit breaker to the hot battery terminal. I have to swap out the photo above with the new updated one soon.

Edited by GotAU?
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M y first close call  (well (both) (ALL) of them were utter stupidity). I had a Geo Tracker  and was parked behind my Baja Campo close to the wall about 2 feet away to be in the shade while was wiring it for an alarm system  that I did not have a schematic for. The ignition was off, the hood was folded back over the windshield , it was in 4 WD because it was beach sand , the drivers door was open. I was sitting on a milk crate  on the sand  at the doorpost facing the Geo  and had passed a wire  through the firewall to the on/off switch of the alarm system  which  was laying loose in the drivers side floor board.  I was reaching a little too far in behind the open drivers and it shorted on a bare spot on the door frame. Instantly the engine started, the Geo  took off slamming in too the  back wall of the camp dragging me off the milk crate leaving me about inline with the back of the seat with my right leg under the Geo.  I could not reach anything in the Geo and it was just sitting there digging in ,  I knew it would not stall and would keep digging until the tires lowered it to the frame sat on the ground. Luckily my wife came out to see  what had knocked all the shelves  off the bathroom wall ! My neighbor had me soon  dug out with no injury's.

 The next time was years later  and I had an old Jeep. I was dry washing on my claim.  I would drive right to the edge of the wash , it was about 2 feet deep and I just threw the hood back and hooked the leads from the battery to the dry washer . I don't know  what happened  but he engine started  and  down into the wash it came with me on the opposite end of the dry washer with my back to a high bank.  As soon as the front wheels  broke over the bank  I shoved the dry washer under it and got clear.  It bent my dry washer  bad  and I had to do some shoveling to get it out and got a longer cord for the dry washer . I have drove on and off the road 100's of thousands  of miles in most of the US, Mexico  and Canada mining in places that many of them had never saw a four wheel drive Geo Tracker  and had some pretty bad break downs some requiring welding but it always brought me back but that old jeep would break down every time I took it in to the Monarch Wash  and I would have to walk out or get to where I had cell phone service and get someone to come and tow it back  to Morristown. If I was  physically fit I would still own one and a Toyota  Pick up!  Tow the Geo behind the Toyota , the Toyota behind the a motor Home , when the  motor home gets stuck , camp and tow the Geo behind the Toyota , when the Toyota gets stuck take the Geo to wherever you want to go  then reverse  that till you get everything back to good road. Some walking and digging required!!

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  • 2 weeks later...

I’d like to know the wattage and cubic feet of the fridge.  I’m getting a solar system together, and running a fridge off solar is a little much and goes back to running it off propane.  A 70 watt fan can run for three hours off a 420 AH battery before it takes the battery to 50%, and beyond that the battery could die pretty quick and not be able to be charged again.  Tough thing is figuring out how long the fridge is using juice to cool it down compared to when it shuts off.

I also like the idea of putting a circuit breaker in there.  THe manufacturers website will mention a discharge rate, and from there you can figure out the fuse size to put in.  My guess would be 15 amps based off a 20 hour discharge rate, but  could be wrong.  That is at the battery not whatever system you step the voltage up through.

I’m finding the cost for solar energy is many times the price of gridded energy from the power company.

Edited by chrisski
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Here is a solar generator I put together with a battery and inverter I had around the house, a 100 watt solar panel purchased new off of a nextdoor.com deal, and a cheap charge converter from amazon.

The battery may be 96 amp hours.  It can safely charge a couple of USB ports at 10 watts each, and perhaps make 60 Watts of. Power through the 120V inverter when sunny, so 80 watts total, and then provide the same power for 5 hours after sundown, and then the battery would be dead, and its off to Interstate to buy a new $120 battery.  I did the math in my head, and its kind of on the conservative side, but may get a little more time and may draw a little more power.  The most I had hooked up to it was 19 watts.

4FD50938-070D-48C3-93B6-8D3A0EED6F4B.jpeg

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  • 1 month later...
On 5/13/2020 at 5:40 AM, chrisski said:

I’d like to know the wattage and cubic feet of the fridge.  I’m getting a solar system together, and running a fridge off solar is a little much and goes back to running it off propane.  A 70 watt fan can run for three hours off a 420 AH battery before it takes the battery to 50%, and beyond that the battery could die pretty quick and not be able to be charged again.  Tough thing is figuring out how long the fridge is using juice to cool it down compared to when it shuts off.

I also like the idea of putting a circuit breaker in there.  THe manufacturers website will mention a discharge rate, and from there you can figure out the fuse size to put in.  My guess would be 15 amps based off a 20 hour discharge rate, but  could be wrong.  That is at the battery not whatever system you step the voltage up through.

I’m finding the cost for solar energy is many times the price of gridded energy from the power company.

Sorry didn’t get back to you sooner, I didn’t select notify me of replies. My fridge is 45w 52 qt.  I run it off the portable battery at night, but it’s in my truck and also running on a spare truck battery that charges the portable system as well.

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Updated photo:

That 30amp circuit breaker I’m pointing to allows me to turn the battery off when I’m not using it.AF20F15A-4A86-43A5-87AE-27AC29C3D0EE.jpeg

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