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Old 07-15-2022, 08:09 AM   #1
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Jump starting tow vehicle using lithium bank inside Airstream?

Has anyone ever jump started their tow vehicle using the lithium batteries installed inside their Airstream?

If so, how did you plan to make that practical (access to lithium terminals, long thick jumper cables, etc)?

If you tried it, did it work? I'm worried about how much current a large lithium bank could try to dump into a dead lead acid battery in the tow vehicle. I picture the jumper cable melting in my hands, causing the Airstream and the two vehicle to go up in flames

We hope to be boondocking in our Airstream, and knowing my luck.... my tow vehicle battery will decide to go to lead-acid-heaven on the first boondocking excursion miles from no-where with zero cell phone signal

So, I'm trying to think ahead. Since we will be immediately implementing a large lithium/solar/inverter upgrade after we take possession of the Airstream, I'd like to plan for this eventuality during the lithium upgrade installation.

I don't want to carry an extra battery boost/jump starter appliance. That's excess weight and something else that I'll always have to remember to keep charged up.
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Old 07-15-2022, 08:53 AM   #2
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Not sure about jumping from batteries but I carry a Gooloo jumpstart power pack. It's about the size of hardcover book. I've used it in the past on my F150 and now on my Ford Expedition. It works so well I bought one for my daughter and son-in-law .

They used it to jumpstart their F450 based motorhome.

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Old 07-15-2022, 08:53 AM   #3
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I would carry a small battery booster that fits in the glovebox. They are lighter than jumper cables and you have it when the truck is not around the Airstream. I've never rescued myself with mine but I have jumped other peoples cars. They are probably cheaper than a good set of jumper cables also.
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Old 07-15-2022, 09:46 PM   #4
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I’ve never had to jumpstart the tow vehicle from the Airstream lithiums but I have had to jump start the Airstream from the TV!

Storage had the power go out and the Czone drained the batts before I caught it. BB batteries shut off and require a 12V source to turn them back on. The cheesy converter that came with the Airstream couldn’t do it so I used jumper cables to kick it on.
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Old 07-16-2022, 06:04 AM   #5
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Quote:
Originally Posted by foobar View Post
... I'm worried about how much current a large lithium bank could try to dump into a dead lead acid battery in the tow vehicle. I picture the jumper cable melting in my hands, causing the Airstream and the two vehicle to go up in flames ...
Generally speaking, current is pulled by the device needing the power and not pushed (dumped) by the power source. The rate at which current would flow to the dead lead acid battery would be determined by how fast the dead battery can suck it in. Wiring is sized according to the load, not the power source.

For instance, if lithium batteries were able to 'dump' all their potential then how could anything be connected via smaller-gauged wires like a lighting circuit. Lighting circuits use smaller wiring than a truck's starting circuit because the load is smaller, not the power source.

Voltage is what gets "pushed" from the power source, so as long as the voltage of the lithium batteries is within the acceptable charging voltage for the the dead batteries you'd be okay on that side.

All in all, the amount of current your lithium batteries is not higher than available when a tow truck comes and gives you a jump start. Some trucks have alternators which can pump out a few hundred amps as well as high capacity batteries, and I'd guess most can provide much more starting current to a dead battery than a pair of lithium.

A suitably sized battery jumper cable set should not melt in your hands. By suitably sized I'm talking about 4ga or even 2ga, depending on the length of the cable set and the current draw of your starter.

All that said, I'm not making any comments on how good this all is for the lithium batteries. That's something better answered by the manufacturer. Here's a quote from Battleborn's website about starting using their batteries:

Quote:
Our battery is designed as a deep cycle storage battery and doesn’t offer the cold cranking amps most applications require for starting.

Multiple batteries connected in parallel can be used in an emergency situation, but prolonged use in starting applications can result in a diminished capacity or damage to the battery’s management system.

The continuous discharge rate of our batteries is 100 amps, 200 amps for 30 seconds and higher loads for ½ second. Cold cranking applications typically exceed 200 amps which will cause our batteries to shut off.
Seems like they're talking about one of their 100Ah batteries, so you have to do math if you want to know about using more of them in parallel.
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Old 07-16-2022, 09:22 AM   #6
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Quote:
Originally Posted by richard5933 View Post
Generally speaking, current is pulled by the device needing the power and not pushed (dumped) by the power source. The rate at which current would flow to the dead lead acid battery would be determined by how fast the dead battery can suck it in. Wiring is sized according to the load, not the power source.

For instance, if lithium batteries were able to 'dump' all their potential then how could anything be connected via smaller-gauged wires like a lighting circuit. Lighting circuits use smaller wiring than a truck's starting circuit because the load is smaller, not the power source.

Voltage is what gets "pushed" from the power source, so as long as the voltage of the lithium batteries is within the acceptable charging voltage for the the dead batteries you'd be okay on that side.

All in all, the amount of current your lithium batteries is not higher than available when a tow truck comes and gives you a jump start. Some trucks have alternators which can pump out a few hundred amps as well as high capacity batteries, and I'd guess most can provide much more starting current to a dead battery than a pair of lithium.

A suitably sized battery jumper cable set should not melt in your hands. By suitably sized I'm talking about 4ga or even 2ga, depending on the length of the cable set and the current draw of your starter.

All that said, I'm not making any comments on how good this all is for the lithium batteries. That's something better answered by the manufacturer. Here's a quote from Battleborn's website about starting using their batteries:



Seems like they're talking about one of their 100Ah batteries, so you have to do math if you want to know about using more of them in parallel.
FYI, I understand the electrical issues quite well (I'm an electrical engineer). However, I'm aware that real world scenarios often deviate from theoretical behavior so I'm checking with folks here on the forum. I kept things very simple in order to not overload folks with too much detail. But since you brought up the topic, I can't resist the urge to go deeper

Current is driven by voltage difference and is only limited by resistance.

Some facts:

Lithium batteries have very, very low internal resistance and are capable of supplying very high levels of current.

The Lithium batteries I am installing have a maximum recommended continuous discharge limit of 400Amps "per battery". I will have 4 of them in parallel, so the battery bank can easily supply 1600Amps continuously.

That's the recommended safe limit. In real life, the actual discharge rate is only limited by rate at which the chemical energy stored in the battery can be converted to electrical energy. And this can be much higher than 1600Amps in total for these particular batteries that are paralleled. Unlimited current draw will quickly overheat the batteries, likely causing them to self destruct in some probably gruesome manner if the short circuit condition is maintained long enough

Now let's talk about voltages. A discharged car battery with a shorted cell will be sitting at 10v or so without a load on it. You will lose about 2v per shorted cell, so if more than one cell is shorted, the voltage can be even lower (say 8v or so if two cells have shorted out due to sulfation).

If you hook a 1290 ah Lithium battery bank (yes, that is the size of my battery bank) that can in theory easily supply a couple of thousand amps (yes, I really mean 2000+ amps) through a set of jumper cables into a discharged car battery with one or more shorted cells, you can boil off the electrolyte in the flooded lead acid car battery, thus releasing hydrogen gas, which can then ignite and cause the battery to explode (yes, lead acid batteries can and do explode).

What I don't know is what the internal resistance of a deeply discharged car battery is, with or without one or more cells shorted out.

So if the 1290 ah lithium bank is fully charged and sitting at 13.6-14v and the car battery is at 10v or so, how much current will really flow when we close this circuit using jumper cable? I think the car battery is probably the limiting factor here in terms defining the voltage difference that drives the current and it's internal chemistry and internal resistance probably sets the limit on how much current will flow.

Though I'm an electrical engineer, I spent 35 years designing CPU's for Intel, AMD, IBM and TI and I'm not familiar with battery chemistries and real world limitations of large capacity battery based systems beyond the high level concepts I wrote about above.

So I'm interested if any redneck engineers have tried this and whether or not they survived

Anyway, all fun aside ... I'll probably just buy a small lithium battery boost kit like other folks have recommended.

Side note: the reason why these tiny lithium booster can supply the high current draw needed to start F250/F350 pickup trucks is because they can supply very high currents due to their very low internal resistance without triggering a high voltage drop across their terminals. The small booster packs don't blow up and overheat because the current is only required for a short period of time and also because with the very low resistance inside the battery, the heat dissipated by the internal resistance is also minimal. Lead acid batteries on the other hand, have much higher internal resistance and can have significant voltage drop (and self heating concerns) under short circuit conditions.

Digression #2: I know someone who accidentally dropped a monkey wrench across a 100ah LiFePO4 battery. The wrench literally exploded and sent molten metal fragments everywhere. It wasn't a pretty picture ... the injuries were pretty gruesome.
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Old 07-16-2022, 09:35 AM   #7
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Ok. As you saw, my answer was based on the typical install of a couple of Battleborn 100 amp batteries. Your situation is quite different.

Still, it seems to me that jump starting a dead battery typically is done due to a discharged battery, not one with a dead short. A dead short battery would create a similar problem (to a different degree) when being jumped from a tow truck running a multi-hundred amp alternator combined with one or two 8D batteries with over 1,000 amps available for cranking as it would from a typical lithium install.

And, most lithium installations typically have a catastrophic fuse installed, which would prevent the type of tragedy you're describing. Mine is 225 amos, which might or might not be large enough to crank over an engine. If I was planning to use my house battery bank to jump start the truck I'd install a larger catastrophic fuse and then an Anderson connector to make hooking up the jumper cables.

All that said, it kind of sounds like you already had your answer before you posted the question.
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Old 07-16-2022, 09:47 AM   #8
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Quote:
Originally Posted by richard5933 View Post
Ok. As you saw, my answer was based on the typical install of a couple of Battleborn 100 amp batteries. Your situation is quite different.

Still, it seems to me that jump starting a dead battery typically is done due to a discharged battery, not one with a dead short. A dead short battery would create a similar problem (to a different degree) when being jumped from a tow truck running a multi-hundred amp alternator combined with one or two 8D batteries with over 1,000 amps available for cranking as it would from a typical lithium install.

And, most lithium installations typically have a catastrophic fuse installed, which would prevent the type of tragedy you're describing. Mine is 225 amos, which might or might not be large enough to crank over an engine. If I was planning to use my house battery bank to jump start the truck I'd install a larger catastrophic fuse and then an Anderson connector to make hooking up the jumper cables.

All that said, it kind of sounds like you already had your answer before you posted the question.
Honestly, I don't really know what would happen. It's not all clear how much current would flow.

Good point on the catastrophic fuse protection, but that wouldn't come into play if I clamped the cables directly to one of the lithium batteries. The fuse sits between the bank and the cable that runs to busbar feeding the rest of the trailer stuff.

You are right, most jump start situations are due to a discharged battery, not a shorted battery. However, twice in my lifespan so far, I have had a battery die due to a shorted cell and not because it was fully discharged. I couldn't jump start the vehicle because the most of the current pulled through the crappy jumper cables I had back then (poor college student scenario) was sunk into the car battery whose shorted cell served to clamp the voltage in the car systems well below 12v. The jumper cables got pretty hot too. I could only start the car if I disconnected the positive terminal of the car battery with the shorted cell and hooked the jumper cable to it.

Time to shop for a battery jump start kit ...

Richard, thanks for taking the time to reply. I appreciate it. Like I said before, I really was curious if someone tried this and it worked. It might have served as a method of last resort ... but I'm paranoid that something untoward might occur ...
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Old 07-16-2022, 09:52 AM   #9
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Oh, and Richard, your battery bank of 200+ah is more than adequate to jump start a vehicle. Those small booster kits mentioned in the first couple of replies are lithium batteries with a much lower capacity (probably something like 5 or so amp hours).
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