My "lightweight" solution to charging batteries in the field

[LimitedPowers]

I wasn't happy with the "portable" power brick options available for field charging our batteries. They were either too expensive, too inefficient, or too unreliable. I didn't need an AC inverter, since everything I use in the field is DC. Those small inverters only give you 80% conversion efficiencies anyway and would just be more weight.

So I did what all DIYers should do and built my own. Using the skills I learned building my home solar power system I looked for the best possible components that would give me light weight, portability, and scalability. Studying the problem, I found there was a lot of confusion around the USB C power protocols and how those power levels are delivered to devices, so you need a system capable of delivering 20 A to the charger. If you're not getting full wattage to your batteries that is likely your bottleneck.

Here's my build:

(Costs in $USD)
Zeee Lipo Fireproof Safe Bag (Amazon) $21
Anker USB-C Car Charger, 167.5W Max 3-Port Ultra-Compact Type-C Fast Car Charger (Amazon) $36
Victron Energy SmartSolar MPPT Solar Charge Controller (48V) 100 - 20 (Amazon) $88
Power Queen 12.8V 50Ah LiFePO4 20A output BMS (Amazon) $126
2 x 50 Watt monocrystalline flexible 12 V solar panels in series (Already had these)
Anker USB C - C 100 W 6ft cable (Amazon) $9

Test results and notes:

This shoud give me 3-4 full charge cycles for my 3 x Air 3 batteries (12723 mAh total). The Victron controller supports any solar panels up to 100 V @ 20 A with real MPPT to get the most out of your PV. It also has an excellent Bluetooth app for full system monitoring. This lets me use much more efficient house-type 48V framed panels if I want. The controller will support a 20 A load output. The thin flexible panels I have aren't great and only give about 65W at best, but that is enough to keep the battery charging a bit. I can connect two other USB devices to the charger at the same time, a phone and RC2 controller for instance.

The Anker charger does a great job negotiating the load and doesn't overheat. I measured the USB C output to be 20 V and 5 Amps while bulk charging the batteries, so 100 W. I think the next step will be to get the Renogy 200W ($200) portable solar panels, which seem to give about 180W from user reviews.

The total cost of the system was $280 and it weighs around 15 lbs (7 kg) and can be carried in a backpack or on my shoulder. The panels can be disconnected for portability or left off if I am walking or riding offroad.

What solutions have you all found for field charging?

 

[GadgetGuy]

I bought the DJI Power 1000 with the Mavic 4 Pro cable for the charging hub.
Power 1000 was $419 during Amazon Prime and the cable was $50 from China. Problem with the car charger is the charge rate is about 1/3 of the 240W charger, while the Power 1000 with the charge cable takes about 70 minutes to charge two Mavic 4 Pro batteries in the hub from 5% to 100%, and only uses 22% of the Power 1000 capacity, which itself can be fully recharged from 0% to 100% on AC in a little over an hour. Good for all day flying in the field with just 3 batteries and the Power 1000. Recharge the Power 1000 on AC at night and repeat.

 

[Chip]

I wasn't happy with the "portable" power brick options available for field charging our batteries. They were either too expensive, too inefficient, or too unreliable. I didn't need an AC inverter, since everything I use in the field is DC. Those small inverters only give you 80% conversion efficiencies anyway and would just be more weight.

So I did what all DIYers should do and built my own. Using the skills I learned building my home solar power system I looked for the best possible components that would give me light weight, portability, and scalability. Studying the problem, I found there was a lot of confusion around the USB C power protocols and how those power levels are delivered to devices, so you need a system capable of delivering 20 A to the charger. If you're not getting full wattage to your batteries that is likely your bottleneck.

Here's my build:

(Costs in $USD)
Zeee Lipo Fireproof Safe Bag (Amazon) $21
Anker USB-C Car Charger, 167.5W Max 3-Port Ultra-Compact Type-C Fast Car Charger (Amazon) $36
Victron Energy SmartSolar MPPT Solar Charge Controller (48V) 100 - 20 (Amazon) $88
Power Queen 12.8V 50Ah LiFePO4 20A output BMS (Amazon) $126
2 x 50 Watt monocrystalline flexible 12 V solar panels in series (Already had these)
Anker USB C - C 100 W 6ft cable (Amazon) $9

Test results and notes:

This shoud give me 3-4 full charge cycles for my 3 x Air 3 batteries (12723 mAh total). The Victron controller supports any solar panels up to 100 V @ 20 A with real MPPT to get the most out of your PV. It also has an excellent Bluetooth app for full system monitoring. This lets me use much more efficient house-type 48V framed panels if I want. The controller will support a 20 A load output. The thin flexible panels I have aren't great and only give about 65W at best, but that is enough to keep the battery charging a bit. I can connect two other USB devices to the charger at the same time, a phone and RC2 controller for instance.

The Anker charger does a great job negotiating the load and doesn't overheat. I measured the USB C output to be 20 V and 5 Amps while bulk charging the batteries, so 100 W. I think the next step will be to get the Renogy 200W ($200) portable solar panels, which seem to give about 180W from user reviews.

The total cost of the system was $280 and it weighs around 15 lbs (7 kg) and can be carried in a backpack or on my shoulder. The panels can be disconnected for portability or left off if I am walking or riding offroad.

What solutions have you all found for field charging?

Good work and perfect avatar!

 

[LimitedPowers]

@GadgetGuy:

I wonder what the conversion efficiency is on the SDC port. DJI says the SDC provides 9-27V @ 10A which is great. There would have to be some DC buck/boost circuit to give you the range it supports. Hard to easily measure unless the DJI 1000 was able to tell you what the power draw was from the battery side, then you could measure what you were getting at the endpoint. They also claim the USB C PD ports will give you 140 W per port. Can you use them at the same time as the SDC ports? They also seem to not give you much PV in, limiting you to 30 V per panel input and a max of 400 W on their proprietary dongle, which would be a dealbreaker to me.

Perfect if all you need is a few extra charges and then you can throw it back onto AC to charge at the end of the day.

 

[GadgetGuy]

@GadgetGuy:

I wonder what the conversion efficiency is on the SDC port. DJI says the SDC provides 9-27V @ 10A which is great. There would have to be some DC buck/boost circuit to give you the range it supports. Hard to easily measure unless the DJI 1000 was able to tell you what the power draw was from the battery side, then you could measure what you were getting at the endpoint. They also claim the USB C PD ports will give you 140 W per port. Can you use them at the same time as the SDC ports? They also seem to not give you much PV in, limiting you to 30 V per panel input and a max of 400 W on their proprietary dongle, which would be a dealbreaker to me.

Perfect if all you need is a few extra charges and then you can throw it back onto AC to charge at the end of the day.

USB C PD ports can be used simultaneously with the SDC ports. Great for output, but primarily optimized for AC input, rather than car charging or solar charging. The latter both work, but very slowly compared to AC charging of the Power 1000. It will fully charge 10 batteries before it is depleted, so starting with 3 fully charged batteries, you have effectively leveraged them into 13 batteries for a little more than the price of two batteries. Just recharge everything at the end of the day during dinner, and you're ready for another day in the field.

 

[MS Coast]

It will fully charge 10 batteries before it is depleted,

Which drone model(s) are you thinking of?

 

[GadgetGuy]

Which drone model(s) are you thinking of?

Mavic 4 Pro. 2 depleted batteries from 5% to 100% only used 22%. So 15% to 100% should recharge 10 batteries. Having a second charged controller would max the battery recharging, or recharge 8 batteries and recharge the controller every 4 hours of use, while you have lunch.

 

[MS Coast]

Mavic 4 Pro. 2 depleted batteries from 5% to 100% only used 22%. So 15% to 100% should recharge 10 batteries. Having a second charged controller would max the battery recharging, or recharge 8 batteries and recharge the controller every 4 hours of use, while you have lunch.

Thanks. Makes sense. Those batteries hold about 95.3 Wh. So, taking the power station down to near 0 SOC would charge 10 if there's not much loss.

I've been looking at a much smaller and less sophisticated power station someone gave me and I'm seeing only about 50% useful output compared to the claimed capacity.

 

[GadgetGuy]

Thanks. Makes sense. Those batteries hold about 95.3 Wh. So, taking the power station down to near 0 SOC would charge 10 if there's not much loss.

I've been looking at a much smaller and less sophisticated power station someone gave me and I'm seeing only about 50% useful output compared to the claimed capacity.

As long as the power consumption is linear, my estimates should hold true.
This little 27 pound monster will also power an AC unit or a refrigerator during a power outage at home, for a while anyway. Others use them to power their electric tools and gardening equipment without needing a nearby AC outlet. Very versatile.

 

[Rchawks]

I’ve got the power 1000W + 2000W, , they’re heavy though. I purchased a solar panel as well.