Thoughts on this please clever people
Is car charging these batteries to be avoided?View attachment 24123
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.
Thoughts on this please clever people
Is car charging these batteries to be avoided?View attachment 24123
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'm not an electrical engineer, only work in the electronics and communications industry, so, from the web first...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...:
http://electronics.stackexchange.co...er-destroy-damage-the-ac-adapter-for-a-laptop
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. ;-)...the 'effective' voltage of AC sources is the RMS value (Root Mean Square). For sine waves the RMS voltage is 70.7% of the peak voltage. For square waves, it's 100%. For a "modified sine wave", it could be anything. Battery chargers that derive their charge voltage from this RMS input voltage will only work properly with a pure sine wave AC input.
If you give that kind of circuit a square wave instead of a sine wave but at the same peak voltage you can get a 1/.707 = 41% over charge - depending on the exact circuit details.
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. ;-)
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 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. ;-)
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 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.