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iaw4

jump starter to support/boost internal lead-acid battery on ground?

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my hangar does not have electricity.  (heck, it was the only hangar in the LA area under $800/month.)  I can live with it.  I am thinking of a 3W solar trickle charger, but this is an altogether different story.

my real question is as follows.  I want to play with the internal avionics without the airplane running.  roughly speaking, with my dual dynons, ads-b, etc., I lose about 15% of the capacity of the Odyssey battery for every 10 minutes the avionics are switched on.  not good.  I don't want to accidentally end up with running the battery down to 30%.  now, there are many portable "jump starter" on amazon that emit 12V, usually used to jump-start cars.  I am guessing that their voltage is too low to charge up the battery, but I am wondering whether the avionics will draw their power from such an external battery rather than from the internal one when it is connected to the wire/exhaust.

the amazon bestseller in the category is NOCO Genius Boost Plus GB40 1000 Amp 12V UltraSafe Lithium Jump Starter, which has about the same capacity as the built-in odyssey 310 (I think).

will this work?

/iaw

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would it likely draw proportionally?  if so, it could just buy a higher-power genius.  I figure if I can use up 10% of the battery with 30 minutes use, I will be just fine.

 

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IAW,

I'm an ME not EE... but I don't mind making a fool of myself.

Batteries don't "emit" 12 volts. Instead there's 12 volts of potential across the terminals. If you connect the terminals of a battery (hopefully with some resistance) current will flow from one terminal to the other.

If you connect two batteries in parallel (plus to plus and negative to negative) current will flow from the battery with a higher potential, into the one with the lower potential - the battery with higher voltage will discharge into the battery with lower voltage.

If you add a load (the avionics) to this parallel battery configuration, as you have proposed, current will flow from the battery with the higher voltage into both the load and into the battery with lower voltage.

The voltage of the lead-acid Odyssey battery in your plane is nominally 12 volts but it drops at high loads and as the battery loses charge. It charges at something just above 13 volts.

The voltage of the lithium battery in the portable jump starter is listed at 12 volts, but I would guess that its closer to 14 volts and possible even higher. Further, its voltage varies very little as it discharges and I suspect very little with load as well.

So assuming the connections are good (low resistance) the jump starter would discharge into both the load (which is the result you want) and into the Odyssey (which is worrisome).

Since the Odyssey is already charged, you're wasting energy trying to charge it further. Also, I'm concerned that over an extended period of playing with your avionics you may overcharge and damage the Odyssey. I suspect these jump starters are only supposed to be connected to car batteries for a short period. In fact, I think they probably turn themselves off after a minute or two.

Connecting batteries with different chemistries together, for any significant period of time, is a mistake.

Further, the jump starter is designed for high power, not high energy. In other words, it can do a lot of work over a short period of time (seconds). You want something that can do a little work over a long period (minutes or hours).

Instead, I would use another lead acid battery. A convenient choice would be your car battery. You can run jumper cables from the car to the plane to hook the batteries in parallel. Further, you can leave the engine running so its charging both batteries at something just above 13 volts (assuming you have good connections at both ends of the jumpers). Both batteries were designed for this. I don't think it will damage either battery no matter how long you leave it hooked up and neither battery will drain.

Mike Koerner

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thank you, mike (and ed).  this was very helpful.

my car would have been great and it has a ton of battery power...except it is a Tesla :and basically has very little standard 12V available -(.  

I will probably never do this for more than 1-2 hours (and maybe once a month), so this shouldn't be too bad.  I am thinking a not-too-big lithium battery would be ok,, as would be another lead-acid.  I would prefer the latter, but it needs to be maintained a lot more (recharged every 3-4 weeks.)

 

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33 minutes ago, iaw4 said:

 

thank you, mike (and ed).  this was very helpful.

my car would have been great and it has a ton of battery power...except it is a Tesla :and basically has very little standard 12V available -(.  

I will probably never do this for more than 1-2 hours (and maybe once a month), so this shouldn't be too bad.  I am thinking a not-too-big lithium battery would be ok,, as would be another lead-acid.  I would prefer the latter, but it needs to be maintained a lot more (recharged every 3-4 weeks.)

 

I have both a genius charger on my CT as well as a genius jump starter.  If you put the 2 together and use the jump starter 110v output to power the intellegant charger then you would have what you need (I'm pretty sure this time)

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I have used two 15watt solar panels screwed to my Hanger roof, feeding a regulator. Got at Harbor Freight Aviation. For cable I used about 20ft. of 12 ga. Landscaping lighting wire. Connected to planes battery. Never out of power even through a hurricane.

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