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Discussion in 'Pro/Adv Discussion' started by 92lambie, Jul 7, 2015.
Thoughts on this please clever people
Is car charging these batteries to be avoided?
I bought a $20 inverter to charge
Check the link below for a good, reliable brand inverter. I've had two of these for a while.
I've also ordered an inverter. Seems like a car power port will provide more than enough to power the charger fully:
Worst case scenario, the "fast" charger, consumes 100w. Let's also take into about 25% inefficiency within the inverter, and we now have a power consumption of 125w for the whole system. At 12v (the voltage of most car power ports), this equates to a current draw of 125/12 = 10.5 Amps from the car charger port, if my assumptions are correct. Most car power ports are fused at 15A-20A, so this should be absolutely fine. Do at your own risk of course, and be careful not to run it too long with the engine off!
Assuming your car battery is about 50 Ah, that permits a draw of 1 Amp for 50 hours at 12v, if you were to completely discharge the battery from full. That equates to about 5 hours at our required 10 Amps. We also don't want to discharge to completely flat, so allow half that to be safe, giving us 2.5 hours charge time. Also assume the battery wasn't full to begin with, leaving perhaps only 2 hours charge time, about enough to charge 2 batteries in my experience. Then again, I think the draw of the charger tapers off towards the end of the charge cycle, so it's not always drawing the full 10 Amps. If you allowed 30 minute charging cycles, you might be able to get away with 4 charges without having to turn your engine on, assuming my very quick calculations are correct...again, do this at your own risk, you don't want to get stuck out in the middle of nowhere with a flat battery! To be safe, you may wish to invest in a portable car battery booster/charger.
Where did you get it please?
I have an inverter and three small batteries 8ah. I can recharge all my 4 P3 batteries, I will recommend to read the battery manual prior any connection or chargings. Lots of interesting things in that manual - I had no idea that if you put your fully charged battery in water it will explode.
I have 3 batteries and keep them all charged all the time. Typically I will charge any depleted batteries with my inverter while I drive between locations. Charges just as quickly as at home. I can only assume these car chargers can't supply the current (stepped up voltages) to charge very quickly. If you do go with an inverter, a true sine wave inverter will help your batteries last longer.
I've also been looking into getting a good quality power inverter to charge the batteries. Makes more sense than buying over priced proprietary chargers. One concern though is that not all power inverters are going to give a suitably clean power signal. I want a clean steady power source from it to prevent possible damage to the charger and or battery itself. It's critical not to do anything which may harm a battery operating a flying machine as it's one thing if it were an RC car, so what if it stops mid drive, but you don't want your flying machine stopping mid flight do to a damaged battery as result of using a less than great power inverter.
Tripp Lite is a solid name in electronics and here are a couple I may consider.. http://www.tripplite.com/power-inverter-for-car-150w-1-outlet~PV150/
When I only had 1 battery, and then only 2, I charged in car out in field. I bought the Bestek 300watt Inverter and it works a treat! Simply hold battery in front of A/C vent for a few minutes to cool enough for charging.
Interesting, I hadn't considered the effects of a poorly formed output wave - what do you suspect would go wrong?
This person says his AC laptop charger blew up through the use of such a device...:
I'm not an electrical engineer, only work in the electronics and communications industry, so, from the web first...
That said, most newer power supplies and chargers these days are "probably" fine. The DJI stuff is new enough, and built in China, so it may be of better quality and able handle bad/poor power input. From my experience in the past, charging laptop and drill batteries regularly with a modified square inverter has decreased the charge capacity and lifespan of the batteries significantly. That said, those were generally NiCad or Li-ion, not LiPo with balancing so it may be different. But, with the cost and delivery times of these batteries, not to mention what is relying on them, I'll stick with pure sine wave. ;-)
I think you're probably right - the cost of the battery and the charger together are about as much as a pure sine wave inverter...
The most efficient way, of course, would be to use a DC-DC converter, rather than DC-AC-DC as achieved through an inverter... I wonder if I could hack something together that would step the voltage up to the ~17v the charger outputs
You're right, DC-DC is best. stepping up can be a pain. Just keep the current draw in mind - 5-6 A for a very low battery. The LM2577-ADJ will switch up to 3A - just keep a big heat sink on it. ;-)
I totally underestimated the need for heat sinks last time I did something similar. I won't forget the burning smell it produced, and that was only 2A! Live and learn...
I had a look around, and it seems like there might be a safer option than making it totally from scratch:
Seems quite reliable! We'd need to make some adapter from this to the battery terminals, but it's possible
Oooohhh... I like that. At 600W you could potentially charge a few batteries at the same time. Maybe not, looks like you may only get enough for one battery quick charge. Still good with no inverter.
I was thinking along the same lines, however I think the in-car fuse would trip if you tried to draw too much.
I've been thinking about the cheapy inverters again, too. I'm fairly confident that the batteries themselves would be isolated from the nastiness of the inverter, and we'd only be risking the charger itself. I might see if I can get a scope and take a look at the DC output of the charger, see if anything bad is happening. Trouble is, I don't have a scope handy
This is turning out to be much more hassle than I thought haha.
I have a few scopes in our shop. But, you're a little too far away. haha I just ordered one of those DC-Dc converters. I will probably drop it in a small box with a couple of digital meters to monitor DC in, out and current. Should be here by the end of summer.
Are there any facts about simul sine inverters? I have one and wonder if there Abby tell harm to using those one every few months
I think that a DC-DC convertor is less efficient then a good AC convertor coupled to your charger.
With a DC-DC convertor from 12 up to 17,5 V you "loose" almost 6volts by a current of approx 7 amps. It's quite a lot. Thats the reason you need a heavy heatsink.
My jeep has a standard electrical outlet plug in, I would assume its all good.