DJI drone charging

[Vigo]

So as far as figuring out your 'available power', if you happen to get an adjustable DC-DC charger you should be able to find the 'sweet spot' pretty easily just by watching voltage.

General background info:
Alternators do not produce full output at engine idle. It's usually something like 60-80% of max at idle and max power is available anywhere from 1500 rpm and up.
Most car alternators are around 100amp (@1500+ rpm), but some can be upwards of 200 amps. Usually a vehicle with a ton of electrical equipment or a vehicle which is a 'basis for upfitting' (things that turn into police cars/limos/rv/service trucks) will at least have the option of a massive alternator.
Alternators are usually air cooled by an internal fan that spins the same speed as the alt. This means alternators are more prone to 'overheating' at idle than while driving just due to the internal fan spinning faster, plus there is usually a lot of ambient airflow in an engine bay when a vehicle is driving. If you have the rare vehicle with a liquid cooled alternator you simply dont have to worry about overheating it, period. But it's rare.


All you really need to do to figure out 'available power' is adjust your charge rate upwards until your voltage starts to drop close to battery voltage. The battery (depending on type) will only make 12.6-13.0 volts, so any time your voltage is above that, the alternator is meeting the need and the battery is not being drained. So, you can simply load the system until voltage drops to ~13.0, and that is the 'max available power' at that rpm.

Now, that is 100% of available power which means the alternator MAY gradually overheat and 'de-rate', so this is something you probably want to watch for at least 30 minutes before calling your settings 'final'. Some alternators have an onboard temp sensor in their regulator and will reduce their output to prevent from overheating themselves. So your 'initial' max power and what your max power is after 30 minutes of idling, may not be the same.

It's not actually critical to know the exact amps your charging system can sustain. You just need to make sure voltage is not dropping below 13.0, and you can be guaranteed that all that power is coming from the alternator and none from the battery. Knowing how many amps that actually is is just academic.

 

[RV8R]

One more recommendation @Joelfred

Flesh out your idea / design & maybe vet it here, BEFORE buying anything for it.

I have seen ( & even have a Victron 12/3000/120 new & never used collecting dust since 2018 ), DIYers buy items going down a path & then change direction & the stuff they just purchased not really fit the new better idea/design.

Use the knowledge of the forum to your advantage, before you buy.

 

[Joelfred]

Consider adding a receiver hitch trailer, and a portable inverter-gen (your choice of fuels). In the field, fire up the gen and support any array of drone battery chargers (no inverter needed at this stage). These hitch frames hold upwards of 500lbs, and you can build a secure frame around them (or move stuff into the vehicle at night, while at a hotel).

I'd still build a portable "solar generator", as here you can get the battery-bank sized to fit your personal requirements in the field. No need to charge at hotel (or lug stuff back & forth) because the gen can recharge the battery-bank. It always seems that you get more capacity for your money if DIY, whereas with the vendor solar gens, you get more show-features at higher cost & smaller capacity.

Hope this helps ...

Thanks, I used and still have a Honda Generator and love it. However it cant run on the go and the smell and noise just gets to me after a while. been using a lifepo4 Li Time mini 100ah for all my USB-C charging and love it! so its hard to go back and when you need to run equipment all day electric is the way to go as once its a good running system its hands off even people saying the LFP will work are right however I really don't want to cart any more into the hotel so a large DC-DC charger and some solar and a big battery sounds like the way to go.

 

[Joelfred]

So let’s look at it ;

#3) 4000Whr including inverter efficiency is your daily energy need

#2) 1100W / say 80% efficiency would give you a 1375W power ,,, so a 2000W inverter should be plenty ,,, thus for easy math drop a zero & you can expect your typical current from a 12vdc battery to be less than 200 amps.

#1) So this is where you issue will be. The only source that you can get this spec/info from is the vehicle manufacturer. Alternators & available power to charge your system depends upon many variable; temperature, rpm, other vehicle needs ( like charging the starter battery or HVAC or etc ). I have a Promaster van with a 220A alternator & the “van” can use more than 180A itself under the right conditions. It is important for you to “figure this out to the best of your ability”. You could consider a 2nd alternator just to charge your DIY system.

So if You DIY or buy an AIO unit really comes down to #1 & the “available power” that can go to the DIY system.

Now that being said, AIO are getting better, but you would need to look at the specs & understand their operations & limitations. If you have a particular Make / Model in mind you can post it here & it can be reviewed in light of your application. Pros & Cons to all decision.

Some of the Cons to AIO in the past;

1) Very slow alternator charging capability ( anything off a cigarette lighter / power plug by definition is dismal ). Some new AIO are better now, but depends upon which model

2) Self energy consuming ,,, idle energy use ,,, might not matter if the unit is turned off, but this spec & how a unit functions really matters in the equasion.

3) Upgrade or serviceability


If you do not have the “alternator power” available to recharge a DIY or AIO for the timeframe of your driving, then you will need grid power 120vac or solar ( & the Sun’s cooperation ), or a generator.

Aquire the “specs” of your vehicle & alternator, but if it is a 60 amp alternator I am not sure what the auxiliary power would be ,,, but I highly doubt 50 amps ,,, I’m guessing more like 10A, 20A, maybe 30A if the vehicle loads are light.

So 140W / 280W / 420W ,,, & You need 4000Whrs ,,, Back to the drawing board.

Even @ 50A @ 14V = 700W you would need to drive about 6 hours to replenish 4000Whrs

Unless I misunderstood your scenario, I highly doubt you will achieve alternator charging 4000Whrs ,,, DIY system or AIO and shore power / grid ( or generator ).


Not that Drone Batteries are inexpensive ,,, but another way of looking at it is just double your drone battery quantity ( & chargers ) & go to the field work with more drone batteries. I don’t totally understand your scenario, but more Drone Batteries might be your solution ? When looking at the economics of this ( all batteries ), like tires on a car are a consumable. More drone batteries you have cuts out the middleman or in this case the middle electrical equipment. If you are a commercial operator, time is money & more drone batteries = less waiting to charge, less down time, more redundancy, more grid charging where you are way less limited. I am guessing plugged into a grid 120vac, you have your 4000Whrs charged up in about 4hrs. Double your drone batteries / charger then you have 8000Whrs in 4hrs @ your hotel room.

Again; I do not fully understand your needs, but you are considering a DIY or AIO & alternator to charge drone batteries by having LFP batteries. Maybe just double your drone batteries ?


OR;

Buy what you need for field capacity in LFP batteries & assume recharging them by EV Plug In & Grid, if that is available. At that point, I’m guessing you are looking at 48v battery bank ( maybe 24v ), and an ( Inverter / Charger ) unit ,,, and any alternator / solar input is going to be a drop in the bucket assistance to you.

all good info, I have been balancing whether to buy drone batteries $1500 a pair or buy the system and its definitely close. The main reason for the system is I like to be done with work when I park the truck. I did the run up to the hotel room and monitor batteries and uploads all night and its not ideal and draining. I did the same with my data and I'm just more productive when I park it and walk away. I'm not getting paid to sit in a hotel room and watch batteries charge all night and that's what I did the first year of the business.

 

[justinm001]

The only downside to something like an ecoflow for your use is the alternator charging limitation but couldn't you just use the solar input and connect that to the alternator?

Another option is to just get an inverter for your truck plugged into your engine battery like 800w or 1000w then use the ecoflow's AC charger to charge while driving.

You can add additional batteries for the ecoflows and easily get a foldable solar panel. Can easily pull it out and charge in a hotel room with the drone all separately. I'm not a fan of these things but man is this a perfect usecase.

 

[HarryN]

You are in ID and the temperatures get too cold in the winter to charge Li batteries that get cold soaked if that matters at all. This more or less eliminates the use of Li batteries unless you heavily insulate / heat.

I would not use a cheap battery like that for daily mobile use like you are planning, nor a 12 volt battery pack configuration.

In order to get 4 kW-hrs of charging with just 2 hrs of driving, the only way to get that will be an aux alternator.

The biggest "stable" charging setup that I have seen produces ~ 3.5 kW of charging power from an alternator and will do it at idle or driving, but the price to implement is non trivial.

Added

The way that this would normally be done is to use the AGM (or Li for the right temperature range use ) batteries in either a 24 or 48 volt configuration. The aux alternator would change that pack and the inverter would feed your drone via 120 vac.

Depending on your setup, you could also plug into an EV charger and perhaps 600 watts of solar to deal with the slower finishing stages.

 

[Vigo]

One thing to consider about cold lithium charging is whether it actually gets that cold where the battery is or not. For example, how many people have left a bottle of water in their car overnight when it is below freezing outside, and yet when they get in the car the next morning the water is not frozen? Yes, low temp charging protection is a concern but its more of a concern in an open truck bed (with no cap/tonneau/camper etc) and much less of a concern inside the car where you could simply insulate the battery by throwing a coat over it or wrapping it in some kind of blanket etc. Using an actual 12v heating pad to keep the battery warm would require a control scheme, but insulating the battery would be simple and passive. Depending on the size of battery one option would be to throw it in a cooler (as a way to keep it warm!).

couldn't you just use the solar input and connect that to the alternator?

The solar inputs mostly require the voltage to be higher than the battery voltage, and a lot of solar generators use more than 12v as their internal battery voltage. So generally no you cannot alternator charge through the solar port. If you got something like a 12>24v step up converter or a 12>48, you could feed THAT into it but it's extra complexity/doodads.

 

[Brucey]

The solar inputs mostly require the voltage to be higher than the battery voltage, and a lot of solar generators use more than 12v as their internal battery voltage. So generally no you cannot alternator charge through the solar port. If you got something like a 12>24v step up converter or a 12>48, you could feed THAT into it but it's extra complexity/doodads.

At least with the Ecoflow river 2 and Delta 2 series they'll accept anything from 11V and up. So you can absolutely charge from a 12V system, however current is limited to 15A max per port so the speed of charging wouldn't be super fast (will max out at 8A when using the provided car charge cable to avoid overload on the 12V outlet)