I wanted to share my experience when I've built my own power tank having 1 unregulated 11-13.5V output and 2 regulated 12V outputs.
Looking at the batteries for astro, many options are available. I was looking for big LiFePO4 batteries.
Complete solutions like BLUETTI, offering with the EB series with 2 regulated 12V 10A max.
- EB55 is a 537Wh battery (~ 45Ah at 12V) and costs 550 euros.
- EB70 is a 716Wh battery (~ 60Ah at 12V) and costs 650 euros.
There are also raw LiFePO4 batteries like the Amperetime 12V 100Ah LiFePO4 battery (1200Wh) at 600 euros with the 20A charger.
I chose this battery because of the reviews and specs:
- Has a very good SoC and can nearly maintain more than 11V until the end
- Has an integrated BMS which shutowns the battery between 9-10V
- It is at 13.5 fully charged and the recommended cut voltage is 10.8V. It can deliver more than 12V even at 10% capacity.
- This is also roughly twice the capacity for the same price...
But is it really cheaper ? Because complete solutions come with inverters, a good box, fan, integrated buck boost regulators, BMS, LCD monitors, etc.
So what is really the price of a power tank built with such battery ? Let's see...
- Have at least 2x regulated 12V 10A ports (like BLUETTI), but the advantage of an Ampere Time battery is that it won't be a total of 10A, it will 10A per socket
- Have a direct access to the battery voltage (DC 9.5-13.5V in this case)
- ON/OFF switch
- LCD battery monitor with Shunt and alternate power input so that it works if the battery is too low (small Li backup battery for that)
- Transport case with wheels
- 14 and 16 AWG at least for the cables
Why regulated output ?
A lot of people are directly connecting their 12V equipment (Mounts, Asiair, etc) to a LiFePO4 battery. If they are doing that, it doesn't mean you can! For 12V equipment, there is a tolerance range of 10%: so 12V equipment can be powered with ~ 11-13V without problem. If the LiFePO4 battery has a very good SoC and is able to maintain a voltage around this range, then it is fine. Otherwise, it isn't, and it is better to have a regulated 12V output. The Ampere Time battery for example goes from 13.5V and maintains more than 12V until less than 10%. So with such battery, we could get rid of the regulators if we wanted to.
The thing is that some devices are more sensitive to voltage compared to others so to not take any chance, I opted to add 2 regulated 12V outputs. Also, using a regulated 12V output helps determining the required capacity for one equipment in advance.
EXCEPTIONS: some devices like Asiair sometimes put the supported input voltage in their spec. Example for Asiair: 11-15V.
- 12 Volt - Maximum Wire Length vs. Current (https://www.engineer...art-d_1689.html)
This calculator gives an approximation of cable length depending on the AWG numer, maximum allowed voltage drop and amperage.
For example with 16AWG cables CC 5521 cables (see below), I can go up to 6A with a length of 3m and only a 2% voltage drop.
- 1x Ampere Time 12V 100Ah battery + 20A charger: 600 euros (https://www.ampereti...ilt-in-100a-bms)
Note: I took the 20A charger, I think it's worth it for the price difference
- 2x Buck-boost voltage regulator 8-14V to 12V 10A: 2x 20 euros (https://fr.aliexpres...2868026249.html)
Note: these at the 2 regulators to give a constant 12V (10A max). Pay attention to the efficiency level. It has to be has high as possible.
- 6x 1.5m CC 5521 16AWG cables: 6x 1 euro (https://fr.aliexpres...1561298133.html)
Note: I took more to gave spares, but the idea is this one: if you need a few amperage (around 4-5A), then you cna combine 2 wires and go up to 3 meters without any voltage drop. If you need more amp, then just use 1.5m.
- 1x Stanley FMST1-75753 Case with wheels: 75 euros (https://www.amazon.f...duct/B01N64SZN7)
Note: hard cases like Pelican or others are super expensive. So I went with hardware cases: they support a high load, are stackable and a lot less expensive. They are not waterproof though.
- 3x Foam for Stanley FMST1-75753 to protect the battery: 3x 20 euros (https://www.amazon.f...duct/B00U7G3NRE)
Note: this is to protect the battery in the case
- 1x Kit of 12V DC 5521 female connectors with rings and caps: 20 euros (https://www.amazon.f...uct/B08SM2NNLV)
- 1x Battery monitor with Shunt: 30 euros (https://www.amazon.f...duct/B09KLJXDSH)
Note: I have connected the shunt directly on the battery with a M8 bolt... This avoided me to built a case for the shunt, but you need a M8 bolt for that.
- 1x ON/OFF switch with M8 screws and battery cables: 30 euros (https://www.amazon.f...duct/B08BP11X4G)
Note: this is overkill for the need, but I didn't find any other switch with M8 bolts and 6 AWG wires with M8 connectors.
- 2x XT60 14AWG split: 2x 10 euros (https://www.amazon.f...duct/B09L7VP4FV)
Note: this is to connect in parallel the 3 DC outputs
- 1x XT60 14AWG wires: 10 euros (https://www.amazon.f...duct/B09SNNRJJ3)
Note: this is to connect to the DC 5521 female sockets and do some extensions. UN-SOLDER THE THIN CABLES FROM THE 5521 FEMALE SOCKETS: THEIR AWG IS TOO HIGH. WE ONLY NEED THE DC DOCKET.
- 1x XT60 14AWG connectors: 10 euros (https://www.amazon.f...duct/B07N1N2C94)
Note: this is to wire the regulators
- 1x 14AWG XT60 extension (https://www.amazon.f...duct/B08LV8YPRT)
Note: you'll probably need some cable extensions. You can make them with previous items but this one is 30cm long.
- 1x Kit of battery connectors (https://www.amazon.f...duct/B09BKPLTP3)
Note: this is only to connect the monitor to the battery M8 equipment... Not required if you can live with the wires directly connected to the M8 screws. I just like things be correctly done so I prefer to have a proper connector and soler the wires onto them.
- 1x Small rechargeable battery with DC 5521 connector (https://www.amazon.f...duct/B07H891KDC)
Note: this is required if you want the batttery monitor to still work when the battery is nearly depleted and enters in protection mode. This one is nice because it can be charged easily with any 12V adapter and has a BMS integrated plus 12V sockets and a power switch.
- 1x 14AWG cable (https://www.amazon.f...duct/B07TT3KP8S)
Note: you don't need it if you take all the wired connectors above. You need it if you want more DIY stuff, more cable length, etc.
- 1x 16AWG cable (https://www.amazon.f...duct/B07TT47CYQ)
- M8 bolts (https://www.amazon.f...t/dp/B08RMV8BRB)
- USB hub car charger with 12-24V input (https://www.amazon.c...duct/B0779D7DFG)
Note: useful if you need to power some USB equipment, charge a phone, etc. Can even be powered on the unregulated socket.
- Heat gun with heat shrink tubes
- Insulating red/black tape
- Soldering equipement
- Gaffer tape
- Optional: More heat shrink tubes
- Optional: quick 12V voltmeter
- Optional: some DC 12V 5521 connectors easy to wire (tighten with screws)
This is an approximate cost of 900 euros to build such power tank. This is a cost of 900 / 100 = 9 euros per Ah.
Compared to that, the BLUETTI EB70 (650 euros for less than 60Ah IN THEORY) has a cost of ~11 euros per Ah.
- Unlimited power!
- The unregulated docket taked power directly from the battery, so the only limit in amps is what the wire can support
- 2 regulated 12V soket, 10A each
- The pack can power at least 3 setups at the same time
- Flexible: thanks to the XT60 wireing, it is really easy to adapt the setup
- Really fun and interesting to build
- Thanks to the optional addition, it is even possible to add USB!
- More bulky compared to having 2 BLUETTI EB55
- No inverters for AC
- Complicated to build and properly wire and choose the right wires
- Needs more attention and care
Here are some photos of the voltage test:
I hope this thread will help some people choose the right product for them!
Edited by mathieucarbou, 23 September 2022 - 07:41 AM.