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Charging the Phantom 2 battery from a 12v supply

Discussion in 'General Discussion' started by philipfretwell, Jan 30, 2014.

  1. philipfretwell

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    My experience of charging LiPo batteries has always been in conjunction with an intelligent LiPo charger. These intelligent chargers use connections to the three cells which make up an 11.1v LiPo to ensure that the charge is balanced across the three cells. The charger supplied with the Phantom 2 battery would appear to have only two connections to the battery, from what looks like a simple 12v power supply. I guess that the intelligence is held within the battery itself, which might be why the battery is so expensive. If this is the case, why can't we charge the battery from the twelve volt supply in a car (by cutting the charging cord and making up an adapter so that it could be switched between the mains or 12v source. (Just make sure that you have at least 4 amps available on your connection to the car). I haven't done this yet as I haven't yet needed to charge the batteries away from home.
    I would appreciate anyone thoughts on this...

    BTW, does anyone fly quads near Sheffield in the UK??
     
  2. ElGuano

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    You're right that the charging and balancing circuitry is built into the battery itself. If the p2's power brick outputs 12vdc, you should be able to hook it up to a car (you don't need to cut the spade connectors if you just buy the spare p2 battery connectors that fit in the shell).
     
  3. 1dr1

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    I've also wondered about using a car battery for charging the P2 battery (see this thread: viewtopic.php?f=7&t=6134#p45803 ).

    I would think that you would at least need some current sensing device to cut off the charging once the battery is at capacity.
     
  4. ElGuano

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    Assuming you can hook it up to a car battery, the charge protection circuitry is also on the battery itself, so it should automatically turn off when fully charged even if you leave it plugged into the car (or AC).
     
  5. 1dr1

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    Good point about the smart circuitry in the battery sensing when to shut off the juice. Now, does anyone know where to get a spare set of battery contacts that are inside the P2/P2V?
     
  6. macheung

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  7. Driffill

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    You can do it!

    But if your not careful you will cook a battery and or your car! The voltage of the car battery will likely be 12.8v (or more if the car has just been shut off, or still running) and the max for the lipo is around 12.6v. Also, once the lipo is fully charged, the car battery will still allow current to flow into the lipo because of the voltage difference, and because of the size of the car battery (compared to the lipo) it will over charge it.
     
  8. EMCSQUAR

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    Why don't you shop for a DC powered battery charger that clamps to your car battery. Most of them have protection/limiters to prevent cooking your Lipo
     
  9. 1dr1

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    Thanks, now just need to wait until the Lunar New Year is over before placing an order with HeliPal. Thanks also for the warning about the lipo overcharging. It does look like I'll need a current limiter / shut off to prevent overcharging. This seems like a more efficient route than first converting from DC to AC via an inverter, then converting back to DC via the P2 charger then finally into the lipo.
     
  10. ElGuano

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    That protection circuit resides in the battery's smart logic as well. The battery itself contains a full-fledged charger and cell balancer. The "charger" is just a power supply, it just dumbly delivers power (just like the car battery). The battery itself won't allow the cells to overcharge, and will cut off current from the car battery when it's done. At least, that's how it's supposed to work :)
     
  11. EMCSQUAR

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    Imax makes a pretty good line of 12v chargers for Lipos. The single units are inexpensive. I have an Imax Quattro that chages four Lipos at a time and it ran about $100.
     
  12. 1dr1

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    So how long did it take to charge a P2/P2V battery with the Imax?
     
  13. RemE

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    I agree, this would most likely work. The battery smart chip monitors charge and all of the individual cell voltages and disconnects the battery when full or if a cell is out of spec. You can see this when charging normally with the A/C charger, the battery turns off when full.

    What I don't know is the charge current that you would get from a direct connection to a car battery. I would want to have a meter on it the first time. The A/C charger is rated at 4A. Charging the battery at 1C would be 5.2A so as long as you were in that range it's probably all good.
     
  14. EMCSQUAR

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    I'm finding a little over an hour - It was 11.4 when I put it on, at 4 amps and it took 64 mins to get to 12.8 before auto shut off.
     
  15. Driffill

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    I didn't want to ramble more in my post, but the "smarts" of the vision battery wouldn't be able to handle to amount to current the car battery can provide. The balancing taps and load used to balance the lipo wouldn't be able to use the current that the battery has available, and until the voltage of the lipo and "power supply" (battery or PSU) is matched, current will flow from the one with higher voltage.

    If you put a 5a fuse between the batteries, it will just blow when the batteries are connected. The charger on the battery isn't a charger, it's simply a balancer and stops the cells from overcharging, but like all electronics, it will have a current limit it can handle, given the stock charger is 4a, I'd be surprised if the balancer on the battery could handle any more than 8a.

    Also, the spade pins on the battery are always in connection with the lipo, there is no way for the battery to disconnect the terminals. The dji dumb charger and a car battery are both power supplies, the difference is, the dji PS has a 4a limit, where as a car battery has no external limit on the current it can supply, and the last time I tested my RX8 battery, it spat out 1,008 Cranking Amps (cranking amps is short term/high draw rating).
     
  16. ElGuano

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    I see what you're saying (thanks for the detail), but what do we actually know about the battery and charger? I can connect a 12v 200W PSU or a cara battery to my charger and it will charge a 1S lipo just fine. Do we know that some component of the P2 battery is missing or insufficient to the task to regulate this? Do we know it's a "balancer only?" Also, can we really say the spades are directly connected to the lipo cells? If you turn off the P2 battery, it registers 0v. And we know the circuit board does sit directly between the cells and the spades. Doesn't that imply that the battery is actually not connected directly? I get that caution is warranted, I'm just trying to see what we actually know versus think about the battery.

    This is definitely not my area of expertise so I appreciate your insight.
     
  17. Driffill

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    I don't have a v2 so I don't have one of these batteries, I'm just going off electrical theory. In the lead up the the vision being released I made a post that I doubt the vision will have a switch, the reason I said this was because the main battery supply is rather critical for flight, and putting a switch in the circuit is adding two extra ways to cut the voltage from the naza. 1 by manually pressing the switch, 2 because of high current draw thru the switch, causing it to fail.

    If the output terminals do lose voltage when the battery is "switched off" it would suggest a likely point of failure, a mechanical electronic relay will suffer from vibration and a PCB Fet based system would suffer from high current draw ("burst" current draw) and excessive heat.

    I assume the battery connects to the pcb and either the positive or negative run via a shunt (for measuring current) then back to the output, but even a shunt is fully connected and not switchable. I'm assuming the off switch simply turns off the digital output signal to the naza. This could also explain many of the "dropped like a rock" posts.

    The worst thing about all this is that the smart battery concept is really a "Fu*k you" to anyone who buys a vision or V2 as the phantom v1 did just fine without the smart batteries. It's not needed for flying, it's only there to ensure your $$$'s go to them (DJI) and not some other lipo manufacture. The smart battery only added on faults to an otherwise revised phantom . . .

    . . A V2 that doesn't need a smart battery, I'd buy it! And on the flip side, all smart batteries are locked to the dji built "balancer/charger" attached to the battery, and going by the v1, the quality of dji chargers is still something to be developed upon. Someone at dji had the great idea to add potential failure points on, lock a battery that's capable of self igniting to a low quality charging PCB, supply a <1C power supply, throw on a few LED's and label it smart, and no one would notice! Lmao!
     
  18. BigSky

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    Why go through all that? Just get a small 12Volt inverter and run it off your cigarette lighter socket. At 4 amps and 12v you would only be drawing about 48 Watts, so you could easily get by with a 100 Watt inverter. They are available at all auto stores and most dept stores and fairly inexpensive. I have a black and Decker I carry right in my DJI case. Got it at Wally World under $20.00

    http://www.walmart.com/ip/21804439?wmls ... 36&veh=sem
     
  19. ElGuano

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    I get it about DC switches. I researched that for a potential mod and dropped it like a bad habit! On the P2, I don't know what the mechanism is, but it's confirmed you can use a P2 battery as you would any battery but you do have to turn the battery on first. If you solder an Xt60 to the spades and plug it into your P1, it'll power right up, but you have to turn on the P2 battery first.

    I'm with you there. Currently, the P2-Naza won't arm the motors without a handshake and authentication from the smart battery's data pins. People have swapped out the P2-Naza with a Naza-M V2 and it works and flies just fine (for the most part). Some folks are trying to see if there's a way to bypass the smart battery lockout of the P2 Naza. I'm not sure if the resources are there, but this whole expensive-proprietary-battery deal really leaves a sour taste in a lot of people's mouths!
     
  20. philipfretwell

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    I have a mains powered 12v supply which I used to use to power my mega LiPo charger and this unit will deliver 23 amps at 12v if asked... I connected the DJI charger to my smart battery this morning and measured the current draw at 4.0 amps which is the rating of the charger. I then connected my power supply and the battery started to charge with scrolling lights in the usual way but the charge current went to 13.5 amps. After a couple of seconds the battery resets and stops charging. I repeated this a couple of times but didn't want to damage the battery.
    To sum up, if we were to use a 12v to 12v regulated supply to a maximum of 4.0 amps, we should be fine without fear of damaging either the DJI smart battery or the cars system.