Can anyone confirm what the actual minimum input voltage is for the DJI Phantom 4 Car Charger to work?
- The advertising material and manual state 12.3v
- On the back of the actual charger it states 13v

This is a big and critical difference in the purchasing decision and the products operation:
- at 12.3v the car battery would not need to be under charge down to approx 50%-60% state of charge left in a 12v car battery.
- at 13v the car battery would need to be supplied with charge via engine running or solar input etc.

So which one is actually correct... 12.3v or 13v mimimum?

Further conerns are raised as Mavic owners state that the car charger for that kit is rated the same as the P4 one in terms of input voltage and again with different specs listed in the marketing/manual vs on the actual charger, and after real world testing 13v is the actual coltage required in that case. Is this the same for the P4 car charger or not?

I have a third party car charger, and it supplies around 17 volts output to charge the battery. It only does this while the engine is running, because it is a simple voltage-doubler design. I would think the same would apply to the official version, it should only be used while the engine is running, as it charges are near to 4 Ampere. So my guess would be that 13 volts or higher would be required. A car supplies 13.8 volts when the engine is running.

Geebax Posted at 2017-9-14 16:43
I have a third party car charger, and it supplies around 17 volts output to charge the battery. It only does this while the engine is running, because it is a simple voltage-doubler design. I would think the same would apply to the official version, it should only be used while the engine is running, as it charges are near to 4 Ampere. So my guess would be that 13 volts or higher would be required. A car supplies 13.8 volts when the engine is running.

Thanks for your info. Any chance you could link or provide info on which third party one you have (if that's allowed or PM). I understand the OEM and third party ones all output 17.4v-17.5v and up to 5amp but really need to know what the DJI OEM ones real input voltage is.

Various third party ones list their input voltage down as low as 10v (so basically with no low voltage cutoff). In my case I have dual batteries in my car with a dedicated aux battery to supply power even when the car is turned off. It powers various appliances as required that take up to 7amp. I have my own dedicated low voltage relays to protect the main car battery and aux battery. Need to charge battery from aux battery while car is off so need a charger that can actually run with an input voltage of down to 12.3 or less. If the OEM does actually run at 12.3 then no issues but if it kicks in at 13v or higher well that is useless for me (and contradicting the advertised specs for the OEM charger). There is no point of having a low voltage cut-off if the cut-in voltage is 13v and not 12.3v.

Or better phrased perhaps is a 'low voltage cut off' is commonly used to refer to 12v DC products that cut-off leaving a safe enough charge in the car battery to start the car such as 12.3v. If the device cuts off at 13v then its not really a low voltage cutoff feature in the more common sense of the term... it more accurately is a full battery cut ensuring the car battery is not depleted at all when the engine is off (in other words leaving a car battery at 100% full state of charge vs 50% low state of charge but safe to start still).

Anyway I just would like to know before I buy the expensive OEM charger can it operate and cut-in / start charging at 12.3v or is it 13v (2 different specs listed for this device so which one is correct)?

Dingoz Posted at 2017-9-14 16:56
Thanks for your info. Any chance you could link or provide info on which third party one you have (if that's allowed or PM). I understand the OEM and third party ones all output 17.4v-17.5v and up to 5amp but really need to know what the DJI OEM ones real input voltage is.

It was just one on eBay, but I don't recall which. There are plenty of them, but none of them have any specifications. I have noticed that mine charges significantly faster if the car's engine is running. Sorry, but I cannot help you with information on the DJI device.

Dingoz Posted at 2017-9-14 17:17
Or better phrased perhaps is a 'low voltage cut off' is commonly used to refer to 12v DC products that cut-off leaving a safe enough charge in the car battery to start the car such as 12.3v. If the device cuts off at 13v then its not really a low voltage cutoff feature in the more common sense of the term... it more accurately is a full battery cut ensuring the car battery is not depleted at all when the engine is off (in other words leaving a car battery at 100% full state of charge vs 50% low state of charge but safe to start still).

Anyway I just would like to know before I buy the expensive OEM charger can it operate and cut-in / start charging at 12.3v or is it 13v (2 different specs listed for this device so which one is correct)?

Since most of my aerial photography is made in remote wilderness and off the boat, the battery charging issue is of paramount importance. I spent countless hours researching and experimenting with various solutions, ending with DIY devices based on commonly available step-up voltage converters. These work with voltages as low as 10V. I can't tell you what is the actual minimum input voltage for DJI car charger to kick in, didn't bother to measure. But for sure you need to keep car battery in good shape. Avoid charging with engine shut off, even idling motor may not provide enough energy from alternator. Bottom line: only charging during driving is reliable enough and will not leave you with dead car next morning. Been there, did that ...

Neither DJI or any 3rd party Chinese clones couldn't provide enough juice to charge multiple batteries at once and reasonably fast for my needs. If that's not your case, than DJI charger in question will do just fine during drive from one place to another. Here's my 2-channel charger: see the charging current! Two Inspire batteries need up to 25A current ... Takes about 65 min to fully charge 2 batts, with input directly from car battery posts. No cigarette lighter socket will tolerate such abuse, believe me ...

However, if you're in desperate need for field charging energy, than venerable Honda generator and multiple chargers is your best bet.

Truthfully, a 12 volt car battery does charge up to 13v.  Most of them range around 12.6 to 12.8v on a good full charge.  One volt won't make a difference to your charger, as it only allows a safe amount of power through its circuits.  The only difference between 12 and 13 volts is it might take 5 minutes longer to charge a battery, that's about it.

Do DJI ever comment in these forums with answers or does one need to reach out to them somehow else to get a direct answer... after all it's their product so surely they must be able to clarify at what voltage the OEM car charge works/starts to charge at?

Otherwise still hoping someone on here has used one for the P4 and can clairfy if it needs over 12.3v to start charging.

Capt Whitefoot Posted at 2017-9-14 20:05
Truthfully, a 12 volt car battery does charge up to 13v.  Most of them range around 12.6 to 12.8v on a good full charge.  One volt won't make a difference to your charger, as it only allows a safe amount of power through its circuits.  The only difference between 12 and 13 volts is it might take 5 minutes longer to charge a battery, that's about it.

I understand this... but that's not really the info I am seeking. Need to know what is the minimum voltage the OEM charger needs to actually start charging. Is it 12.3  as per manual or is it 13v as per specs on back of the OEM box.

Dingoz Posted at 2017-9-15 23:53
Do DJI ever comment in these forums with answers or does one need to reach out to them somehow else to get a direct answer... after all it's their product so surely they must be able to clarify at what voltage the OEM car charge works/starts to charge at?

Otherwise still hoping someone on here has used one for the P4 and can clairfy if it needs over 12.3v to start charging.

Forum moderators are often tryin' to find answers or help, but this is not their responsibility from within job description. Send e-mail to DJI tech support instead ...

Dingoz Posted at 2017-9-15 23:54
I understand this... but that's not really the info I am seeking. Need to know what is the minimum voltage the OEM charger needs to actually start charging. Is it 12.3  as per manual or is it 13v as per specs on back of the OEM box.

I meant to find this out too - I'm not able to use my P4 charger in my car due to it having a "smart alternator" setup (Euro 5 diesel engine).  Unlike my older cars where the voltage  sat at around 13.8V with the engine running, the voltage often drops away to under 13V and I noticed that my P4 charger would stop charging. In fact, the only time I saw my P4  car charger start to charge a battery was when the car was going down hill or applied the brakes (regenerative braking using the alternator to give additional braking whilst boosting the battery too).

I really must stick the charger on a variable PSU to find out what the cut off voltage is...

Dingoz Posted at 2017-9-15 23:54
I understand this... but that's not really the info I am seeking. Need to know what is the minimum voltage the OEM charger needs to actually start charging. Is it 12.3  as per manual or is it 13v as per specs on back of the OEM box.

I did a test this afternoon - the charger light comes on at 12.2 Volts but the charger does not start delivering full output voltage until the input reaches 12.3V.

If Euro 5/6 vehicles are happy to let the alternator sit at 12.5V across the battery for much of the time, it's quite conceivable that when the P4 charger pulls 9A, the voltage drop between the battery and the charger input terminals is sufficient to bring the input below 12.3V and the charger shuts down.

Hope that helps!

It doesn't really matter which it is since if you try taking 70W out of a fully charged 13v battery without alternator assistance the battery voltage will drop below 12.3v within seconds.  The DJI car charger will not charge without assistance from the car alternator.

I use the mains charger via an inverter when I want to charge from a 12v caravan battery without alternator assistance, I don't try it from my car battery because then it wouldn't start the engine.

G Davidson Posted at 2017-9-16 06:25
I did a test this afternoon - the charger light comes on at 12.2 Volts but the charger does not start delivering full output voltage until the input reaches 12.3V.

If Euro 5/6 vehicles are happy to let the alternator sit at 12.5V across the battery for much of the time, it's quite conceivable that when the P4 charger pulls 9A, the voltage drop between the battery and the charger input terminals is sufficient to bring the input below 12.3V and the charger shuts down.

Thanks. Exactly the info I was looking for. So it looks like it will operate down to 12.3v (engine does not need to be on if battery is fully charged (12.6 for wet cells and 12.8 for AGMs). Once the battery goes down to 12.3 it will stop working. This assumes no voltage drop across any leads/connectors so is a little optimistic depending on the vehicle or setup (perhaps a safer estimation is a 12.5 terminal voltage on the battery allowing for some voltage drop).

Nigel_ Posted at 2017-9-16 06:43
It doesn't really matter which it is since if you try taking 70W out of a fully charged 13v battery without alternator assistance the battery voltage will drop below 12.3v within seconds.  The DJI car charger will not charge without assistance from the car alternator.

I use the mains charger via an inverter when I want to charge from a 12v caravan battery without alternator assistance, I don't try it from my car battery because then it wouldn't start the engine.

This makes no sense to me. I do not think this is accurate at all. To my knowledge:

- For example, let assume we have a fully charged 12v 100 amp hour AGM battery
- The 12v charger is rated at max 90 watt with output of 17.4v equals a max draw of 5.17amps
- A 100 amp hour battery in theory provides 5amps for 20 hours before fully depleted*
- *Yes you would never fully empty your car battery but deep cycling to 50% is fine with AGM
- It takes an estimated 70 minutes approx. to charge the Phantom 4 Battery.
- You should be able to easily charge 1 battery from a full car battery of 12.8v and not drop below 12.3v (12.3v being 50%-70% left in an AGM).

Or to put it simply in the real world, overnight with my car turned off I run a 12v fridge constantly (2-5 amps while compressor cycles) + have some lights on (2amps) + re-charger various batteries (dslr camera + phone + laptop) and its just fine (by morning the battery might be down to 12.5v). 1 phantom battery on its own is not going to bring a full car battery from 12.8 to 12.3 in seconds.  

Dingoz Posted at 2017-9-16 16:13
This makes no sense to me. I do not think this is accurate at all. To my knowledge:

- For example, let assume we have a fully charged 12v 100 amp hour AGM battery

BTW a 100 amp hour car battery = 100,000mah hours vs 5870mah for the phantom 4 high battery.  In rough theory that means a 100 amp hour car battery holds the equivalent power of 17 phantom 4 5870 batteries.

Nigel_ Posted at 2017-9-16 06:43
It doesn't really matter which it is since if you try taking 70W out of a fully charged 13v battery without alternator assistance the battery voltage will drop below 12.3v within seconds.  The DJI car charger will not charge without assistance from the car alternator.

I use the mains charger via an inverter when I want to charge from a 12v caravan battery without alternator assistance, I don't try it from my car battery because then it wouldn't start the engine.

Just to add to this, your caravan theory sounds right. But using an inverter is actually less efficient than a direct DC charger (loss in the conversion from DC-AC-DC vs using DC-DC charger on its own).

My car has 2 batteries so its just like your caravan as such... a spare 100 amp hour AGM battery to use for aux charging (the starting battery is isolated and remains untouched).

Dingoz Posted at 2017-9-16 16:13
This makes no sense to me. I do not think this is accurate at all. To my knowledge:

- For example, let assume we have a fully charged 12v 100 amp hour AGM battery

The problem you have missed is that the battery voltage does not reflect its state of charge unless there is no load on it, put a heavy load on it and the voltage will drop instantly, remove the load and the voltage will rise back up and then indicate the state of charge after 10 minutes or so.  At 70W load it will not stay above 12.3V for long.

Having said that, I have not tried a large AGM battery, my caravan battery is non-AGM and although my car battery is AGM it is only 32ah.  At 70W load I would get a lot less than 32ah, realistically I would only get 2 Phantom battery charges out of it before 50% and that is in the very unlikely event that it started off at 100% full so more likely only 1 full phantom battery charge.

I'm not convinced the inverter route is much less efficient, the amount of heat generated by the inverter and mains charger doesn't appear to be that much but the car charger feels really hot!  Stepping 12V up to 17V at 80A is not an easy task, if it was going the other way then it would be much more efficient.