Yippee! Lipo saved us on the way back home

[markusvt]

Normal charging is what, 13.6?

Hook up a 4S to a 800CCA battery at 10V, (if it was at 11.5+, the car would start), and wait, you will wait a long time for the little 4S to get the car battery to any dangerous levels, (Poor little LIPO will loose the battle).

It will get her good enough to start, but blow anything up, not in this lifetime.

It is supplying a way better signal than 99% of the chargers you can buy, and they don't blow anything up, do they?

Originally Posted by gravityKills

if it's about american cars, remember that most of those are still running on steam power. Don't draw any conclusions about a modern car that contains semiconductor technology

PS
if someone finds out "the hard way" that your advice wasn't that great, the lesson will be very very expensive.

[gravityKills]

well... I'm not that interested to continue this discussion. Do what you like, because you'll do it anyway.
I will continue to jump-start my car from 3s. I got myself a spare 72Ah Pb battery anyway, because one flight with the electric 700-size heli burns about half the battery capacity from my steam-powered Ford.

Points to consider:
1) when a car battery is really discharged, its internal resistance increases dramatically. That means the full LiPo voltage appears across the terminals.

2) when it has at least some charge, the resistance of the car battery is negligible. The difference voltage (16.8 - 12 V = something around 4 V) is only limited by cable and LiPo resistance. It drives a hell of a lot of current, and that's why the wires are getting hot.
With this kind of overcurrent, the LiPo takes irreversible damage and may even form a fire hazard much later.

[Yellowspider]

Normal charging voltage is 13.8 to 14.3 most cars domestic and rice charge at 14.1, But that is alternator output not battery voltage. Dont get the two mixed up. Markusvt is about right on a fresh battery off the shelf arond 13.8 give or take a few. I am NOT telling anyone to go and jump their auto with a lipo at all. If you have too and know what your doing you can do it with a good amount of voltage. Just know what your doing. Best thing is another car battery hooked to a ground and the positive of your current battery with a switch to turn it on and off as needed for charging and emergencey starting. That is what I use now. I am out of this one.
Happy flying guys
Yellowspider

[Old Sloppy]

Originally Posted by gravityKills

It only matters for the 2nd cable - you can't have any current with a single cable.

a really old car jump starting "trick" is to touch the bumpers together.
This is the "second cable" when you have only one available cable and it is across the positive posts.

or if you have really high resistance cables (low grade cheap cables) you put both of them across the positive posts.

can't do this with rubber bumpers.....Ha, Ha, Ha....

Harry

[Old Sloppy]

Originally Posted by antslake

Well I can't agree with you. It happened on my 97 maxima.
Voltage spikes are bad....

this is possible if you exceed 20 volts.
Mostly caused by a loose connection/badly corroded battery cables , factory alternator testing involves 19.5 volts...max.

I have seen a Maxima come into the shop with all lights blown out and it took out the radio too. it had 21+ volts

Harry

[markusvt]

Yup, but put a dead 10V car battery in parallel with a fresh 4S LIPO at 16.8V, you will wait a LONG time to see >20V.

Originally Posted by Old Sloppy

this is possible if you exceed 20 volts.
Mostly caused by a loose connection/badly corroded battery cables , factory alternator testing involves 19.5 volts...max.

I have seen a Maxima come into the shop with all lights blown out and it took out the radio too. it had 21+ volts

Harry

[Old Sloppy]

My Aeromarine Conquest Pro r/c boat has a Flight Power 12s 7,400 mah lipo power (50.4 volts) 148 amp (370 amp burst) rating with a 4 kw (5 kw peak) Plett motor. Lets see, that means 5.3 hp steady and 6.6 hp peak.

Will this jump start my car?

Harry

[Shpook]

Originally Posted by Old Sloppy

this is possible if you exceed 20 volts.
Mostly caused by a loose connection/badly corroded battery cables , factory alternator testing involves 19.5 volts...max.

I have seen a Maxima come into the shop with all lights blown out and it took out the radio too. it had 21+ volts

Harry

Wow, you(err, the customer rather) got lucky that's all that burned up. I've replaced quite a few Ford GEM modules that failed due to an overcharge of just 16V.

And just for kicks for everyone, there's the possibility for quite a catastrophic failure with an alternator. Imagine cruising down the road at 1400rpm. Now imagine the voltage regulator were to fail and allow 100% duty cycle(constant battery voltage) to the field coils, and the rectifier bridge/diode pack failed and let the full 3-phase AC output through. A Wye wound alternator would typically produce 1V per roughly 16rpm. That's almost 90V that could surge through your system!

Even if my logic is faulty, it sure scares the customers.

[antslake]

Originally Posted by Old Sloppy

this is possible if you exceed 20 volts.
Mostly caused by a loose connection/badly corroded battery cables , factory alternator testing involves 19.5 volts...max.

I have seen a Maxima come into the shop with all lights blown out and it took out the radio too. it had 21+ volts

Harry

I think I pointed out that when I jumped the car, the battery was no good. In other words there was a bad connection internally, which was the exact same thing as taking the battery terminal off. I am not sure at what voltage things start to fry. The same thing happened on my Dad's Mariner outboard motor. The wire going to the battery came off in rough water, and almost everything fried int he motor. In the old days, you could take the cable off the battery (BC-before computers) to see if the alternator was working. If the car shut off, the alternator was bad. Now adays, I have learned to be more careful.

Yellowspider, jumping your car a few times doesn't make you an expert on the subject, just like my few experiences haven't made me an expert. I was only sharing with you, cause I don't want to see anything bad happen to my fellow modelers.

I think if you hook up a volt meter while your doing this, you might be surprised. I also feel that not only is the car's electrical system in danger, but the lipo could be in danger as well.

But having said all that, I guess if I was stranded without being able to start my car, I might hook up a 3s or 4s pack, but not turn the key on with it hooked up. I wouldn't care about losing the pack.

[antslake]

Originally Posted by gravityKills

This is why:

If you slip and accidentally touch "something" with the cable you're holding, chances are 99 % that you'll touch ground.

It only matters for the 2nd cable - you can't have any current with a single cable.

Option A)
Connect ground first, then connect plus. While doing so
*slip* and accidentally touch ground with the wire you're holding
result: Short circuit, sparks, burnt fingers etc

Option B:
Connect plus first, then connect ground. While doing so
*slip* and touch ground
Result: Nothing

Option B is safer, that's the only reason. The electrons don't really care where you interrupt or close the circuit.

There is another reason. You should be hooking up the last negative cable to ground, as far from the dead battery as possible. Thereby eliminating a spark igniting a dead battery's hydrogen gas that might possibly be leaking out.

I was also told when I was younger, like 20+ years ago that hooking up can fry an ECU. I have read several instances of this on the internet. I also remember several people caliming it happened to them when I was younger. But that was when ECU's first come out. I heard many explanations for this. Not sure exactly why.

I did fry my motorcycles regulator by trying to start it with a battery chrager hooked up to it.

[Shpook]

That used to be the case, but a lot of modern PCMs have built-in overload protection. Needless to say, it's not 100% failsafe. Hooking up cables can cause an initial voltage spike. The booster pack I use at work has a smaller ground lead that you hook up before the main lead, in order to reduce that spike.

Also, on-car welding and bad ignition wires and/or coils can fry an ECU.

Honestly though, the 2 main causes of computer failure are vibration and incorrectly installed aftermarket accessories.

[ChuckA]

All you kids would have a ball trying to start an old Ford that used a POSITIVE ground.

[Yellowspider]

LOL I have worked on many positive ground cars in my time. They should all be recycled into soup cans by now.
Yellowspider