Way to solve the 12 volt charger issue

[Kilrah]

The Mavic car charger is a buck-boost device, but DJI have simply decided that to save you from overdischarging your car battery it wouldn't turn on below 12.5V, and once it's on will work down to 12V but no lower (25.4V/24.8V for the 24V range). The top of the 12V range is 16.4V and the top of the 24V range is >32V (limit of my supply).

What's in the plug is probably just an overcurrent proteciton, it does nothing to change or switch the voltage.

I just checked it. If you feed the power supply 10 volts it will output 10 volts, if you feed it 13 volts it will output 13 volts, if you feed it 15 volts, it will output 13 volts.

OK, maybe it doesnt work, or mine is broken, I tested the input and output with meters.

You need an actual dummy load or you'll measure a floating voltage on the output that would just fall down as soon as you try to draw anything.

 

[JustinVV]

I dont thinkDJI care about your battery.. Its just a cost saving measure.

I had a load on it. the DJI charger just regulates the max outputs.Its a cheap way of selling a 12 volt car charger.

In reality the DJI charger stop charging the minute you turn off the engine. Its really a joke in this day and age of cheap switch mode power supplies. the simplest of devices have 12 Volt power supplies worked out.

The idea that DJI are worried about us depleting out car batteries is laughable to say the least.

 

[HFMan]

Little detail, 400-600 amps refers to how much it can deliver at once to cold crank it. No indication of the capacity. I personally have 665 CCA battery.

True- most typical car batteries have less than 80aH of capacity. Taking into consideration that it's best to not drop a starting battery below 50%, that leaves you with 40aH of capacity. At 4 amps, you can charge for approximately 10 hours safely- that's probably more than you can possibly fly.

 

[Cyberpower678]

The Mavic car charger is a buck-boost device, but DJI have simply decided that to save you from overdischarging your car battery it wouldn't turn on below 12.5V, and once it's on will work down to 12V but no lower (25.4V/24.8V for the 24V range). The top of the 12V range is 16.4V and the top of the 24V range is >32V (limit of my supply).

What's in the plug is probably just an overcurrent proteciton, it does nothing to change or switch the voltage.



You need an actual dummy load or you'll measure a floating voltage on the output that would just fall down as soon as you try to draw anything.

A nice 5k resistor should do the trick. It could also be an overcorrect protector, but we assumed voltage because of the dual OpAmp chip it has mounted to it.

 

[Cyberpower678]

True- most typical car batteries have less than 80aH of capacity. Taking into consideration that it's best to not drop a starting battery below 50%, that leaves you with 40aH of capacity. At 4 amps, you can charge for approximately 10 hours safely- that's probably more than you can possibly fly.

True, just thought I'd point it out.

 

[stangman]

Hi from France!
I don't understand your issue regarding the car charger. In fact I am using it with both my cars (small AClass Mercedes and 2017 Mustang GT - not the one in my avatar )and a power bank Booster. It's working with no issue at all.

I even tested to recharge 3 batteries woith the booster and again no issue. There's a voltmeter on the booster to check the charge and it shows usually more than 13V. It's acheap one so I'm pretty sure it's only a 12V motorcycle battery inside.

This is the king of device I am talking about :

Amazon.com: Bay Valley Parts 900Peak Amp 12 Volt Jump Starter Battery Charger Air Compressor Booster Pack Car: Cell Phones & Accessories


Weird...

 

[AlanTheBeast]

@JustinVV 's DC-DC converter is just what I was thinking about recently for outing-and-abouting. Except I'd throw a deep-discharge battery (trawling battery) in the trunk and drive it off of that. Recharge the trawling battery night before.

I'll be looking into getting the P4P car charger as well, so I'll need two of these DC-DC converters or one with higher capacity (current).

I was going to buy a more expensive DC-DC than this. Nice to know there are solutions designed to output "car running" voltage as opposed to the nominal voltage.

 

[AlanTheBeast]

Hi from France!
I don't understand your issue regarding the car charger. In fact I am using it with both my cars (small AClass Mercedes and 2017 Mustang GT - not the one in my avatar )and a power bank Booster. It's working with no issue at all.

I even tested to recharge 3 batteries woith the booster and again no issue. There's a voltmeter on the booster to check the charge and it shows usually more than 13V. It's acheap one so I'm pretty sure it's only a 12V motorcycle battery inside.

This is the king of device I am talking about :

Amazon.com: Bay Valley Parts 900Peak Amp 12 Volt Jump Starter Battery Charger Air Compressor Booster Pack Car: Cell Phones & Accessories


Weird...

An automobile battery quickly falls in voltage below the threshold ('seuil') of the Mavic battery charging requirement. It won't continue charging a couple minutes after shutting off the engine in my car.

 

[stangman]

An automobile battery quickly falls in voltage below the threshold ('seuil') of the Mavic battery charging requirement. It won't continue charging a couple minutes after shutting off the engine in my car.

I see... The tests I made were always with almost fully charged batteries. I'll make a full test since I will need to be able to charge like this in August in Africa...
WIll keep you posted. R

 

[AlanTheBeast]

Little detail, 400-600 amps refers to how much it can deliver at once to cold crank it. No indication of the capacity. I personally have 665 CCA battery.

The car battery makers don't often publish the capacity which is a pain in the butt.

 

[Cyberpower678]

The car battery makers don't often publish the capacity which is a pain in the butt.

You can always test it. By attaching a load to drain at a constant ampage, time how long it takes to drain and voila. Multiply the 2 values together to get your capacity.

 

[Cyberpower678]

You can always test it. By attaching a load to drain at a constant ampage, time how long it takes to drain and voila. Multiply the 2 values together to get your capacity.

Of course, I left devices plugged into my battery for a whole week, and it was still delivering, of course my car wouldn't start, but still. They were probably draining 4 amps so if I had to guess the capacity of my battery, it would be about 672 Ah. I would say the average battery has about 400 Ah, considering mine is a high end.

 

[AlanTheBeast]

I found this battery
MotoMaster Nautilus Group 27 Starting & Deep Cycle Battery | Canadian Tire
(Canadian dollars including an environmental deposit of $20.00 here in Quebec).

80 A-h of charge or 960 W-h.

With 10% inefficiency using the DC-DC converters and 20% inefficiency charging on the MP side )converter and battery) you could get up to 16 MP battery charges. (43.6 W-h).

That's 6.5 hours of flight (20 minute flights) assuming you get to the field with 3 MP batteries already charged and the 12 V battery fully charged.

Of course, hard to charge the batteries fast enough ... you'd need about 6 batteries in rotation (meaning you get to the field with 7.5 hours of power!). Seriously - I don't think anyone will fly that much in a day. And you'd need to make sure you have enough storage for video and stills.

I could see mounting the DC-DC converter to the 12 V battery with really short leads and the socket mounted there too. Strap the 12V battery to a slab of plywood so it won't tip over in the trunk of the car. Strap the MP charger to that with tie-wraps.

Sounds like a project I'll do in the very near future.

 

[dwallersv]

The car charger isn't just a cheap dumb device, it is capable of handling up to 30V, but the pack could well be the limiting factor on allowing the charge to take place.

Yes it is. It's a sinfully cheap design for something like this -- LiHV batteries that need 13.05V to fully charge. As @Dragonfly and I have both pointed out, a simple Buck Converter would have solved this problem, and at little expense.

No, this was clearly a rushed, cheap engineering project, as any electrical engineer such as myself can see. For an application like this, using a simple voltage regulator to produce the output voltage is beyond engineering sin.

As far as protecting the car battery from over discharge, that's easy. Monitor the input voltage. Shut down when it reaches a LEAD-ACID critical voltage for still being able to start the car (something like 11-11.5V). The point is, there's plenty of juice to charge several batteries before starting the car is a problem, however it will all be below 13V.

The DJI car charger is a POS, only worth the money to get the connector. I plan to get one, but will be putting a buck converter in-line (in between the cig-lighter plug and the power socket in the car) to present 14V to the DJI charger. I'll share the design and parts here when I do it, though it won't be for a month or so. Can't imagine it will cost more than $20 or so.

 

[AlanTheBeast]

You can always test it. By attaching a load to drain at a constant ampage, time how long it takes to drain and voila. Multiply the 2 values together to get your capacity.

Yeah, standing in the store with a bunch of loads and meters makes you real popular!

I've been able to figure it out when they say so many hours with such and such motor at such and such load and ignoring the "emergency reserve".

But, Lo-and-behold, see my other post. The store actually did post the A-h rating.

 

[dwallersv]

The Mavic car charger is a buck-boost device,

Can you validate this with some actual evidence?

The fact that below an input voltage of 13V the output voltage tracks input down would seem to strongly dispute your claim.

 

[AlanTheBeast]

Yes it is. It's a sinfully cheap design for something like this -- LiHV batteries that need 13.05V to fully charge. As @Dragonfly and I have both pointed out, a simple Buck Converter would have solved this problem, and at little expense.

No, this was clearly a rushed, cheap engineering project, as any electrical engineer such as myself can see. For an application like this, using a simple voltage regulator to produce the output voltage is beyond engineering sin.

As far as protecting the car battery from over discharge, that's easy. Monitor the input voltage. Shut down when it reaches a LEAD-ACID critical voltage for still being able to start the car (something like 11-11.5V). The point is, there's plenty of juice to charge several batteries before starting the car is a problem, however it will all be below 13V.

The DJI car charger is a POS, only worth the money to get the connector. I plan to get one, but will be putting a buck converter in-line (in between the cig-lighter plug and the power socket in the car) to present 14V to the DJI charger. I'll share the design and parts here when I do it, though it won't be for a month or so. Can't imagine it will cost more than $20 or so.

I'd rather a nicely regulated DC-DC converter. A little more expensive. A lot less noise.

 

[dwallersv]

Guys, save yourself some effort and get a smaller deep-cycle battery. Motorcycle size. There are all sorts of them -- go to a place like Batteries Plus or equivalent.

There's no need to haul around a car/boat size battery. Big, heavy, awkward. A much smaller battery will hold more than enough juice to keep you flying for hours and hours.

 

[AlanTheBeast]

Guys, save yourself some effort and get a smaller deep-cycle battery. Motorcycle size. There are all sorts of them -- go to a place like Batteries Plus or equivalent.

There's no need to haul around a car/boat size battery. Big, heavy, awkward. A much smaller battery will hold more than enough juice to keep you flying for hours and hours.

Agree, but a boat deep-cycle isn't all that big and can be semi permanently left in my car trunk. I will look into the motorcycle size too - as long as they are deep-cycle.

 

[dwallersv]

Agree, but a boat deep-cycle isn't all that big and can be semi permanently left in my car trunk. I will look into the motorcycle size too - as long as they are deep-cycle.

Yeah -- the "motorcycle" term is only for familiarity with the size. That size 12V lead-acid is used for all sorts of stuff, including backup power, monitoring systems, etc. Go to a battery specialty store, and they'll have racks of all sorts of different batteries in this, and other compact sizes. Most of this size are at least 50Ah, good for 10 or so MP battery charges.